Globally, millions of persons have contracted the coronavirus disease 2019 (COVID-19) over the past several months, resulting in significant mortality. Health care systems are negatively impacted including the care of individuals with cancers and other chronic diseases such as chronic active hepatitis, cirrhosis and hepatocellular carcinoma. There are various probable pathogenic mechanisms that have been presented to account for liver injury in COVID-19 patients such as hepatotoxicity cause by therapeutic drugs, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection of the bile duct cells and hepatocytes, hypoxia and systemic inflammatory response. Liver biochemistry tests such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT) and alkaline phosphatase (ALP) are deranged in COVID-19 patients with liver injury. Hepatocellular damage results in the elevation of serum AST and ALT levels in early onset disease while a cholestatic pattern that develops as the disease progress causes higher levels of ALP, GGT, direct and total bilirubin. These liver biochemistry tests are prognostic markers of disease severity and should be carefully monitored in COVID-19 patients. We conducted a systematic review of abnormal liver biochemistry tests in COVID-19 and the possible pathogenesis involved. Significant findings regarding the severity, hepatocellular pattern, incidence and related clinical outcomes in COVID-19 patients are highlighted. The novel coronavirus disease 2019 (COVID-19) is caused by the new strain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) . This laSARS-CoV-2 mainly attacks the lungs, but it also causes damage to other organs including the liver, kidneys, intestines, heart as well as the central nervous system . The damThere is increasing evidence in the literature that some individuals presenting with COVID-19 have hepatic injury and atypical liver function test results with increase in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels due to hepatocellular damage . StudiesHistopathological investigations involving liver biopsy specimens (taken during autopsy) from COVID-19 patients demonstrated insignificant portal and lobular activity, mitosis, hepatocellular necrosis as well as modest micro-vesicular steatosis in hepatic tissue with no viral inclusions . The abnGiven the widespread and harmful nature of SARS-CoV-2 and its impacts on human health and clinical systems, there has been an exponential increased in the number of articles published since December 2019. We have conducted a comprehensive systematic review to summarize numerous articles published regarding abnormal liver biochemistry tests in COVID-19 patients and the possible pathogenesis involved. Furthermore, we highlighted significant findings regarding the disease severity, hepatocellular and cholestatic pattern, incidence and ongoing changes in liver function biochemistry tests as well as related clinical outcomes in COVID-19 patients. This will assist healthcare providers to identify liver complications in COVID-19 patients and closely monitor the liver biochemistry tests in the management of acute hepatic injury in COVID-19 patients.A systematic search was conducted by the reviewers to identify all the relevant studies on the different causes of liver impairment in COVID-19 patients published from 1 January 2020 to 30 April 2021. The methodological outline involve taking the following steps: (i) documentation of a defined research objectives and search strategy (ii) identification and selection of peer-reviewed research articles (iii) final selection of peer-reviewed research articles according to defined eligibility criteria and in keeping with review objective (iv) arranging and reporting the data and findings of peer-reviewed research articles in the different sections (v) discussion of the findings and conclusion.We searched electronic databases such as PubMed, Cochrane Library, Google Scholar, Scopus and Web of Science for potentially relevant studies using pertinent words and medical subject headings such as: acute liver injury, liver damage, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), novel coronavirus disease 19 (COVID-19), liver function tests, liver biochemistry tests, severity, morbidity, mortality, liver disease and prognosis.The studies retrieved were prudently examined to omit overlapping data or possible duplication. Those written in other languages, no accessible full data and information on pediatric population were excluded.The studies included in this review were published in the last 16 months in specialized journals, written in English and reported clinical findings. Observational articles that reported the prevalence or incidence of acute hepatic injury in adults and elevated transaminases as well as both randomized and non-randomized interventions performed in different populations were included in this review article. We also included studies that reported on admission and liver function test results in hospitalized patients with confirmed COVID-19. In addition, the pertinent data that were extracted from published articles by review authors comprised: first author, year of publication, study design, study population size, the quantity of hospitalized patients, the proportions that were severe or critically ill with elevated liver biomarkers, mortality of those with liver injury and serum laboratory parameters (aspartate aminotransferase (AST), alanine aminotransferase (ALT), albumin, alkaline phosphatase (ALP), serum and total bilirubin, ferritin and interleukin-6 (IL-6)).There were 411 articles identified through database including PubMed, Google Search and Cochrane Library. We exclude 224 because of duplication and 187 articles reviewed for inclusion. There were 174 full-text articles assessed for eligibility with subsequent 159 of these included in this review .SARS-CoV-2 gains access into the host through the angiotensin-converting enzyme 2 (ACE2) receptor. ACE2 is a zinc-containing type I integral transmembrane protein that exhibits enzymatic activity by cleaving the vasoconstrictor peptide angiotensin II to angiotensin I, a potent vasodilator peptide, thus lowing blood pressure . The ACEThe spike (S) protein of SARS-CoV-2 facilitates entry into target cells including cholangiocytes and hepatocytes of the liver. The process involves the attachment of SARS-CoV-2 to the surface of the target cell via binding of the surface unit (S1) to a receptor . FurtherThe pathology of liver injury may involve the cytopathic effect of SARS-CoV-2 where its spike protein binds to the ACE2 receptor on cholangiocytes with subsequent decreased function and hepatobiliary damage  19]. Zh. Zh19]. 6 copies/g of tissue. In an earlier study that examined biopsies from three COVID-19 patients with presentation of liver impairment, apoptosis was seen in all three patients and a noticeable buildup of cells in mitosis in two patients. In addition, pathological features observed included mild as well as moderate lymphocytic infiltration into the lobular regions with no fibrosis or eosinophilic infiltration . Th. Th25]. Therapeutic agents such as hydroxychloroquine, arbidol, oseltamivir as well as lopinavir and ritonavir have been introduced in the treatment of COVID-19 patients and these may cause varying degrees of hepatotoxicity . In a syThere are other studies that have examined the effectiveness and safety of lopinavir and ritonavir treatment for SARS-CoV-2 infection . A recenRemdesivir an antiviral drug, is a straight-acting nucleotide analogue that inhibits RNA polymerase. It was initially used to treat patients with hepatitis C, Ebola virus disease and Marburg virus infections . This anA retrospective study that examined the efficacy and safety of remdesivir in 76 hospitalized COVID-19 patients with severe illness reported that it was clinically effective in a community hospital setting as the mean length of stay for the patients was 10.09 days and the average duration of oxygen therapy was 9.42 days . MoreoveIn a recent retrospective cohort study by Hundt and colleagues comprising 1827 hospitalized COVID-19 patients, remdesivir and other medications such as tocilizumab, lopinavir, ritonavir, and hydroxychloroquine were concomitant with AST and ALT levels greater than 5 times the upper limit of normal . Addition = 53) [There is a report of two cases of supposedly acute liver failure caused by remdesivir with significant increases in ALT and AST levels on day 3 and 10 of therapy respectively, and rapid clinical improvement with continuous infusion of acetylcysteine with subsequent lowering of the transaminases . There an = 53) , and elen = 53) . Finallyn = 53) .Hydroxychloroquine and chloroquine are commonly prescribed medications for the treatment of malaria as well as systemic lupus erythematosus, porphyria cutanea tarda and rheumatological disease ,44. BothThere are two large observational studies performed in hospitalized COVID-19 patients with moderate to severe illness that examined the clinical efficacy of hydroxychloroquine and possible adverse effects. The studies reported that hydroxychloroquine administration  was not beneficial as there was no significant reduction in hospitalized mortality ,50. PrelOverall, there is limited evidence demonstrating the clinical efficacy of hydroxychloroquine in the treatment of COVID-19 patients ,56. HepaTocilizumab is a humanized recombinant IL-6 receptor monoclonal antibody therapeutic agent that effectively blocks the signal transduction pathway of cytokines and prevent them from exercising their pro-inflammatory actions . HoweverRecent studies have indicated that tocilizumab administered to severe COVID-19 patients with significant elevated IL-6 levels due to cytokine storm may improve their prognosis . TocilizThe data on possible hepatotoxicity of tocilizumab in severe COVID-19 data is limited and sparse as well as on its clinical efficacy. Investigators have examined the use of tocilizumab in COVID-19 patients with severe illness and associated cytokine release syndrome, and also the incidence of drug complications. In a retrospective study of 65 non-intensive care severe COVID-19 patients who exhibited hyper-inflammatory features, there was an observed transitory elevation in transaminases levels in 15% of participants in the tocilizumab-treatment group between 9 and 13 days which was not significantly different from the standard care group . In a moMuhovic et al. described the first case of acute liver injury in a 52-year-old COVID-19 patient with severe illness after tocilizumab administration. The patient experienced cytokine storm and there was an observed 40-fold elevation of ALT and AST levels that reverted to normal after 10 days of treatment. The authors are of the opinion that the hepatotoxicity may have been stimulated by prior use of lopinavir and ritonavir . RecentlFinally, there is a report by Gatti et al. of the analysis of data of serious adverse events subsequent to tocilizumab administration, that indicate hepatic damage after a median of 15 days and the development of drug-induced liver injury in 91 COVID-19 patients. The authors suggested that tocilizumab use should be closely monitored during and after therapy .Azithromycin is an antimicrobial therapeutic drug used to treat several bacterial infections, which has been found to be very effective in reducing severe episodes of lower respiratory tract illness . ResultsAzithromycin is currently used as an antibiotic to treat COVID-19 patients as it inhibits the initial stage of SARS-CoV-2 replication. The results of clinical trials points to its use in supportive care treatment and it is administered alone or in combination with hydroxychloroquine ,74. HoweThere are very few reports that have indicated the impact of azithromycin use on liver function tests. In a case study of seven patients by Serviddio et al. the combination of lopinavir, ritonavir, hydroxychloroquine and azithromycin caused significant increase in transaminases levels up to five times the upper limit of normal in COVID-19 patients with no prior history of liver disease . In a moThere is need for more studies preferably well-controlled, prospective, randomized clinical studies to examine the side effects particularly as it related to liver injury and associated liver function test abnormality of the use of azithromycin alone or in combination with other drugs.Paracetamol and ibuprofen are repurposed and are regarded as supportive therapeutic option for COVID-19 patients ,79. EarlAcetaminophen, a recommended antipyretic medication is a well-documented cause of fulminant liver failure at high dose  and therThere are few studies that examined the clinical efficacy and safety of acetaminophen as a monotherapy in COVID-19 patients. Piano et al. conducted a multi-center, retrospective study comprising 565 in-hospital COVID-19 patients and found that 15.2% developed abnormal liver function tests after tocilizumab, lopinavir, ritonavir, and acetaminophen use . FurtherThe symptoms of COVID-19 vary widely in individuals, from slight respiratory symptoms to clinical syndromes such as pneumonia and acute respiratory distress syndrome with associated multiple-organ failure which may progress to death—particularly in older patients with a number of comorbidities including diabetes mellitus and hypertension . Sepsis,During systemic stress and shock, acute heart failure or respiratory failure may be evident in critically ill COVID-19 patients with a reduction of oxygen saturation levels and a decrease in systemic arterial pressure. This may lead to a decrease in arterial perfusion of the liver with subsequent hepatic ischemia and hypoxia-reperfusion dysfunction with accompanying hepatocellular hypoxia . The priSecondary hypoxic hepatic damage takes place owing to the presence of acute respiratory distress syndrome in COVID-19 patients with pneumonia as well an overactive inflammatory response to SARS CoV-2 infection, and multi-organ failure . The mecThere is supporting evidence that hypoxia may be concomitant with hepatic injury and there is a negative association between the latter and blood oxygen saturation . SymptomIncreasingly, COVID-19 patients with hepatic injury and gastrointestinal symptoms have been observed more frequently and one report found high prevalence of chronic liver disease in SARS-CoV-2 infected patients with gastrointestinal manifestations . COVID-1In a retrospective study of 838 hospitalized COVID-19 patients, 51.2% presented with liver injury and had abnormal liver biochemistry tests that were due to hypoxia, use of antiviral medications and hypoxia. The study found that the pattern of hepatocellular injury was related to hypoxia and the mortality was 25.0% . LikewisHypoxic hepatic injury caused by ischemia and inflammation results in deranged liver biochemistry tests in COVID-19 patients with severe illness. The pathogenesis regarding the mechanism of hypoxia requires further elucidation. However, it is recommended that special care should be given to monitoring inflammatory markers and hypoxia for the prevention and management of hepatic damage in COVID-19 patients with severe illness .SARS-CoV-2 enters the human body and infects cells of the upper and lower respiratory tract resulting in persons being asymptomatic or experiencing mild, moderate or severe COVID-19 . The undThe ongoing cascade of exaggerated and abnormal inflammatory responses due to the stimulation of immune and adaptive immune cells triggers an overwhelming cytokine storm in an advanced and uncontrollable manner, cytokine storm syndrome . It impoThere are a number of studies that have investigated the relationship between liver dysfunction and causative factors such as cytokine storm with the involvement of pro-inflammatory biomarkers in COVID-19. In a group of 150 hospitalized COVID-19 patients, 45.6% of the patients presented with elevated ALT levels that were associated with high AST/ALT ratio as well as raised GGT and ALP levels. The mild hepatitis observed in these patients may be due to immune-mediated hepatic injury caused by the inflammatory response subsequent to the SARS-CoV-2 infection . MoreoveSystematic inflammation and cytokine storm in COVID-19 patients with severe illness may contribute to acute liver injury . In a reStudies have examined the risk factors of hepatic injury in patients with severe COVID-19. In a retrospective of 657 COVID-19 patients of which 46.1% had inflammatory-liver injury, there were increased neutrophils and white blood cells, decreased lymphocytes, elevated inflammatory markers such as TNF-α, hs-CRP, ferritin, IL-2R and procalcitonin . COVID-1Deranged liver function tests due to hepatic injury could arise from underlying chronic liver diseases. Reported prevalence rates of underlying liver diseases present in COVID-19 patients from large observational studies ranged from 3–11% ,120. OyeHowever, there are conflicting findings from a pooled analysis of six studies by Lippi et al. comprising 904 COVID-19 patients where underlying chronic hepatic disease was not significantly related with higher odds of severe illness or mortality . MoreovePatients with cirrhosis have long-lasting and irreparable scarring of the liver and with less functional mass there is impairment in liver function . Generalp = 0.03) but not substantially different from those individuals with only cirrhosis  [There are studies which demonstrated that presence of comorbid conditions such as liver cirrhosis in patients with COVID-19 was associated with worse prognosis ,132. A m = 0.16) .Notably, in The APCOLIS Study that investigated liver patterns in 288 COVID19 patients including 43 with cirrhosis and reviewing data from 13 Asian countries, patients with both conditions and elevated baseline liver function tests had increased risk of mortality. The study also found that patents in the decompensation phase with Child-Pugh class B cirrhosis had a 43% mortality with noted predictors such as increasing AST/ALT ratio and total bilirubin levels . LikewisNon-alcoholic fatty liver disease also called metabolic associated fatty liver disease is characterized by the accumulation of significantly elevated lipids in the liver in the absence of alcohol use . In a prThe mechanism by which non-alcoholic fatty liver disease could cause severe COVID-19 might be due to the presence of mild chronic systemic inflammation, dysregulated and suppressed immune response, involvement of pro-inflammatory markers and stimulation of macrophages in inflammatory reaction and metabolic pathways ,143. AddThe management and wellbeing of patients who are liver transplant recipients are important and can be daunting during the COVID-19 pandemic as these persons receive immunosuppressive drugs that make them more susceptible to SARS-CoV-2 and likely protracted vital shedding . Quin anThe data pertaining to the management of liver transplant recipients with COVID-19, risk and severity of the respiratory illness is sparse and is an area that warrants urgent investigation. The literature reports a retrospective single-center study comprising 37 liver transplant recipients who were diagnosed with COVID-19. The mortality was 18% while 71% were hospitalized, and the study also found that of the hospitalized patients 46% had severe COVID-19 disease, 79% decreased immunosuppression and 54% presented with acute kidney injury . Similarp = 0.003) [There is also evidence that liver transplant recipients who contracted SARS-CoV-2, older and presented with co-morbidities such as obesity may have worse clinical outcomes . In a sm= 0.003) .In summary, most of the studies mentioned above had a small number of patients, which was one of the major limitations. The findings highlight the negative effect of COVID-19 on liver transplant recipients particularly those with co-morbidities. This points to the need for the implementation of preventative strategies and the wearing of personal protective equipment in high-risk situations as these patients are chronically immunosuppressed and are more susceptible to contracting SARS-CoV-2 with probably worse clinical outcomes.COVID-19 patients with severe illness are likely to present with atypical liver biochemistry tests. A number of systematic and meta-analysis studies have examined pooled odds ratios of hepatocellular and hepatobiliary enzymes to differentiate between severe and non-severe COVID-19 illness. In a meta-analysis of 8 studies involving 7467 COVID-19 patients by Xin et al. individuals had pooled odds ratio of 3.21, 2.35 and 1.87 for elevated AST, ALT and total bilirubin levels respectively in severe illness . KaushikAt the time of admission liver function test of COVID-19 patients are usually determined and the prevalence are reported in a number of observational cohort and retrospective studies. The reported prevalence of deranged liver function tests for COVID-19 patients in China was approximately 14.9% on analysis of 14 recent studies comprising of 2595 individuals , compareA number of studies have examined the relationship between liver function tests on admission and prognostic outcome in COVID-19 patients. AST and ALT, biomarkers of hepatocellular damage were significantly increased in a retrospective study including 675 COVID-19 patients, and individuals with AST > 3 times the upper limit of normal had the greatest risk of death . In a meStudies have also investigated the relationship between cholangiocyte-related enzymes and hepatobiliary biomarkers such as ALP, GGT, direct and total bilirubin, and the hepatocellular biochemical markers ALT and AST, and clinical outcomes. In a multi-center retrospective cohort study comprising 5771 adult COVID-19 patients that examine temporal patterns of liver function biomarkers in a longitudinal manner, significant increase in AST than ALT levels were observed followed by mildly elevated total bilirubin and modest increase in ALP levels in hospitalized patients. The study reported that elevated AST levels were related to the highest mortality risks in hospitalized patients  Table 2Table 2. There are studies that assert that in severe hospitalized COVID-19 patients there is significant elevation of GGT, direct and total bilirubin and moderate elevations of ALP. The alterations in the liver biochemistry tests could possibly be due to the dysfunction of cholangiocytes as they possess a significant amount of ACE2 receptors, which can become infected by SARS-CoV-2 . ElevateThis article is a comprehensive systematic review of the literature on abnormal liver biochemistry tests in COVID-19 patients and the possible pathogenesis involved. It also affords robust findings regarding the severity, hepatocellular and cholestatic pattern, incidence and ongoing changes in liver function tests as well as related clinical outcomes in COVID-19 patients.The mechanism involved in acute hepatic injury in COVID-19 patients is equivocal and multifaceted. There is documented in vitro and in vivo evidence of the involvement of ACE2 for cellular entry of SARS-CoV-2 and in terms of the liver, increased ACE2 receptor expression on cholangiocytes. Damage to cholangiocytes due to SARS-CoV-2 infection accounts for cholestatic and mixed hepatocellular/hepatobillary patterns in liver injury with resulting increased GGT, direct bilirubin, total bilirubin and ALP levels. There is also significant data published in the last year on liver injury caused by therapeutic drugs such as lopinavir, ritonavir, remdesivir, hydroxychloroquine and azithromycin. Drugs such as lopinavir are broken down by cytochrome P450 3A4 enzymes in hepatocytes, which may contribute to the elevated ALT and AST levels due to hepatocellular damage . AntipyrNotwithstanding, the increased knowledge of the pathogenesis of liver injury particular by use of these repositioned therapeutic agents, point to the need for more studies preferably well-controlled, prospective, randomized clinical studies to examine the side effects and deranged liver biochemistry tests associated with liver injury due to the use of these drugs singly or in combination. Furthermore, there is no standardized criteria for liver injury due to COVID-19. Therefore, more observational studies are necessary to define the levels of liver biochemistry tests that equate to COVID-19-induced hepatic injury to guide appropriate care and management of these patients.The essential mechanism that is intricately involved in hepatic injury in COVID-19 patients comprise immune reconstitution due to SARS-CoV-2 infection as well as cytokine storm-induced systemic inflammation. This review documents studies that found decreased T-lymphocytes subsets mainly CD4+ T and CD8+ T cells as well as elevated cytokines such as IL-6 in severe and critically ill COVID-19 patients. These inflammatory biological mediators when significantly elevated above their respective upper limit of normal have been found to be associated with worse clinical outcomes in COVID-19 patients. The inflammatory biomarker IL-6 is an indicator of COVID-19 severity and tocilizumab has been employed in clinical trials for treating critically ill persons.The evidence in this analysis indicates that COVID-19 patients with abnormal liver biochemistry tests at admission are likely to progress to severe illness. This means that liver function tests, particularly AST and ALT should be carefully monitored and their levels should be utilized to decide on therapeutic dosages of medications prescribed to COVID-19 patients in the management of their condition. Besides, there are limited studies that have reported low albumin levels in COVID-19 patients with severe illness as well as cholestatic liver biomarkers such as GGT and ALP, which are usually deranged in persons with severe disease. The reduced albumin may be related to the progression of the disease particularly in severe and critically ill COVID-19 patients. The reasons for decreased albumin warrant further investigation, which could be due to the contribution of humoral immunity or modifications in vascular permeability.Patients who are liver transplant recipients treated with immunosuppressant drugs are of particular concern as they are at a greater risk of SARS-CoV-2 infection as reported by studies in this review. Those patients with comorbidities such as hypertension and diabetes mellitus are more immunocompromised and therefore significant complications and higher mortality are observed in this group of patients. Another group of patients that must be carefully monitored are those with nonalcoholic fatty liver disease since there is evidence that those with COVID-19 are more ill as the respiratory disease progress more rapidly and there is extended SARS-CoV-2 shedding time. While it is unclear regarding the severity of COVID-19 in patients with nonalcoholic fatty liver disease, the literatures cite possible causative factors such as low-grade inflammation and modifications in the immune response. This is an area which warrants further research, so that these patients can have better clinical outcomes.The preventative measures against SARS-CoV-2 infection and transmission are critical and patients must be aware of the benefits of such procedures. These measures include regular washing of hands with soap for at least twenty seconds, the use of approved hand sanitizers, correct wearing of masks , and avoiding contacts with persons who are suspected or confirm with COVID-19.In summary, the pathogenesis and mechanism for liver injury in COVID-19 patients are multifactorial and involved hepatotoxicity by repositioned therapeutic agents, liver damage caused by SARS-CoV-2, hepatic ischemia associated with hypoxia and cytokine storm syndrome due to systemic inflammatory response amongst others. The acute hepatic injury is evidenced by deranged liver function tests such as AST and ALT that increased with disease progression. There is also up regulation of hepatobiliary biomarkers such as GGT and to a lesser extent ALP, which are prognostic factors with poor clinical outcomes. Therefore, liver biochemistry tests in COVID-19 patients should be closely monitored particularly in high-risk individuals such as the elderly, patients with underlying liver disease and liver transplant recipients. Larger observational studies are warranted to define the role of liver biochemistry tests in risk stratification and diagnostic algorithms.


We present a description of pediatric pneumology biological medications and other target therapies. The article aims at introducing the importance of a molecular approach to improve treatments. The first item treated was T2-High asthma and its current biological treatment and prescribing indications to propose a flow-chart to guide the clinical choice. Molecular rationales of such treatments are used to introduce a more general description of the biological and molecular approach to target therapies application. We introduce a general interpretation approach to neutrophilic asthma using the molecular plausibility one in order to propose possible future treatments mainly targeting interleukin-1 (IL-1), IL-17, IL-12, and IL-23. Indeed, cytokines can be excellent targets for several biological treatments. Downregulation of specific cytokines can be crucial in treating autoinflammatory and rheumatological diseases with a pulmonary involvement. Such conditions, although rare, should be early recognized as they can involve significant improvement with a properly targeted therapy. We face these conditions in a cherry-picking fashion picturing SAVI (STING-associated vasculopathy with onset in infancy), CANDLE , and COPA  syndrome pulmonary involvement. Such examples are functional to introduce molecular-based approach for patients with rare conditions. Molecular plausibility can be highly valuable in treating patients with not-approved but possibly highly effective therapies. Due to the rarity of these conditions, we stress the concept of basket trials using the example of cytokinin-directed immunosuppressive treatment. Lastly, we provide an example of augmentative therapy using the alpha1 antitrypsin deficiency as a model. In summary, the article presents a collection of the most recent achievements and some possible future developments of target therapies for pediatric pulmonary conditions. The article aims at providing a comprehensive overview, although necessarily incomplete, of current biological treatments for asthma and other pulmonary conditions in children. The main focus will be set on molecular mechanisms, and in doing so, we will also discuss treatments that may be clinically applied in the next future. We searched PubMed and Scholar databases, limiting our consultation to the past 20 years and publications in English.We consider it necessary to provide an adequate definition of biological treatment. Biopharmaceuticals are considered those drugs derived from a biological source, comprising somesthesis as well. This broad definition includes blood components, hormones, cellular therapies, and even gene therapies . In thisApproximately 4–5% of asthmatic children present a severe disease. Severe asthma is defined as the need for high doses of inhaled corticosteroids (ICS) plus a second treatment to achieve symptoms control, or the persistence of symptoms despite such treatments. Therefore, this step-up approach modulated on the symptoms severity and clinical response results sometimes unsatisfactory .ad-hoc therapeutic approach. The endotype is the complex of the molecular and pathobiological mechanisms leading to the disease, while the phenotype is the categorization based on its clinical features  is characterized by a T-helper inflammatory response with IL-4 (interleukin-4) and Il-13 (interleukin-13) release. Such cytokines lead to IgE production (class E immunoglobulin) and IL-5 (interleukin-5), which are proliferative and act as survival factors for eosinophils. T2-High markers commonly considered in the clinical practice are high fractional exhaled nitric oxide (FeNO) values, and elevated eosinophils count in blood, sputum, and airways.T-helper type 2 cell low endotype (T2-Low) is characterized by a neutrophilic or pauci-granulocytic inflammation, with normal levels of eosinophils in blood sputum and airways. IL-1, IL-8, IL-17, and Il-23 are the molecules implied in this endotype . Often eT2-High asthma is characterized by the activation and abundance of T-helper 2 that plays a crucial role in generating and maintaining eosinophilic inflammation through IL-4, IL-5, and IL13 production . Th2 celLike mast cells, basophils liberate histamine and PGD2 (plated derived growth factor 2), but they produce IL-4 as well (ILC2s (innate lymphoid cells of group 2) are those that respond to DAMPs (damage-associated molecular patterns) producing IL-5 and IL-13. Such response leads to eosinophilia without an allergen-specific stimulation . TherefoIL-4, IL-13, PDGF2, histamine, eosinophils degranulation causes smooth cells contraction, hypertrophy, collagen deposition in airway walls leading to airway remodeling  on the eosinophils and basophils surface, inducing apoptosis. Benralizumab can be prescribed in patients older than 12 years, with a peripheral blood eosinophil count ≥ 150/microL. In SIROCCO study benralizumab obtained a 55% reduction of exacerbations and has shown to be more effective in patients with a high number of exacerbations per year. Benralizumab leads to profound eosinophils reduction. Like mepolizumab, benralizumab is administered subcutaneously but every 8 weeks –25.Overall, in adolescents and adults, mepolizumab, reslizumab and benralizumab present a reduction in the number of severe asthma attacks of around 50%. The safety profile is optimal with no excess of severe adverse events and a similar discontinuation rate in the placebo groups, except for reslizumab that presents slightly more discontinuations in the treatment group .Dupilumab is a monoclonal antibody that binds the interleukin-4 receptor (IL-4R), inhibiting the IL-4 and IL-13 molecular pathways that present a pivotal role in the Th-2 differentiation. Dupilumab initially approved for atopic dermatitis, had recently obtained approval for its use in patients older than 12 years, with severe asthma and high FeNO or peripheral blood eosinophil count ≥ 150/microL. This biological treatment showed to reduce the asthmatic exacerbation rates and the dose of oral corticosteroids as opposed to placebo . Dupilumhttps://clinicaltrials.gov/ct2/show/NCT03513458). Canakinumab was demonstrated to be effective in a similarly designed trial  fall hundreds of different conditions leading to interstitial involvement and are often extremely difficult to treat. A tiny minority of chILD present an underlying genetically determined systemic autoinflammatory disease . As we mSTING (stimulator of interferon gene)-associated vasculopathy with onset in infancy (SAVI) is a systemic autoinflammatory disease caused by a mutation in the STING gene, causing its constitutive activation resulting in an autosomal dominant disease in nearly all cases. STING protein is located in the endoplasmic reticulum, and its activation is part of the early innate response to the viral infections  and bactChronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE), formerly known as Nakajo–Nishimura syndrome, is another monogenic condition caused by the PSMB8 gene encoding for a protein of the proteasome. PSMB8 encodes for immunoproteasome subunit β5i and, together with other mutations of the immunoproteasome, are grouped within the proteosome-associated autoinflammatory syndromes (PRAASs). PRAASs determine the ineffectiveness of the immunoproteasome with a consequent increase of old and misfolded waste proteins. Therefore, the cell responds by increasing interferons that usually activate and assemble the immunoproteasome. The lack of immunoproteasome effectiveness leads to a vicious circle in which type I interferon levels rise uncontrolled . CANDLE Coat proteins alpha (COPA) syndrome is an autosomal dominant condition caused by a mutation in a gene encoding for a coatomer protein. More specifically, COPA participates in Coatomer Protein I (COPI) assembly, which is crucial for the backward trafficking of the proteins between the Golgi vesicles and from the Golgi apparatus to the endoplasmic reticule, leading proteins to stuck in the Golgi. An incorrect assembly of coated vesicles impairs the trafficking with a consequent intracellular stress and, therefore, interferon pathway activation, but also IL-1B and IL-6 release with Th-17 proliferation . ClinicaSmall molecules are usually designed to present a key-lock action, with very narrow or no effects on other pathways. Such medicines are generally obtained by full chemical synthesis and therefore are not biologics . Such a This concept of inhibition of a single molecule key for several diseases went so further that recently trials were approved to test the effectiveness of one single target therapy for different diseases at once. Most of such trials are oncological ones, but IL-1inhibition was also tested in this specific study design called basket trial , 58.Augmentation therapy provides a homologous of a defective molecule  to keep its function within a tolerable range to avoid the progression of the disease caused by a molecule deficiency. Such type of therapy is broadly diffused in metabolic medicine but is also used for some immunodeficiencies from hypogammaglobulinemia to the Adenosine DeAminase Severe Combined Immune Deficiency (ADA-SCID). Augmentation therapy is part of the common practice of adults' pneumologists to treat alpha-1 antitrypsin deficiency. This therapy is administered intravenously weekly when serum levels are confirmed under 11 μM (80 ng/mL), and FEV1 is reduced to 35-70% of the predicted value  or in thad-hoc therapy that may be even more challenging. As a result, some of the classical randomized controlled trials designed to treat a disease may be inconclusive due to various underlying biological mechanisms. The obvious risk is the fragmentation of the study population with a consequent extreme difficulty in reaching the sample size for clinical studies exploring therapies for each biological cascade. Obtaining an adequate sample size will be even more challenging in the pediatric population. The concept of basket trial may be a possible partial answer to reach the necessary sample size for such studies.Target therapies are rapidly changing pediatric pulmonology, causing a turning point in the patients' care. Such a shift in the mindset of clinical approach is ongoing and led to the need for a biologically precise diagnosis to administer the correct The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.SG, MM, AD, and FP drafted the manuscript. NU, MC, and RC reviewed the manuscript. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


The Dutch province of Limburg borders the German district of Heinsberg, which had a large cluster of COVID-19 cases linked to local carnival activities before any cases were reported in the Netherlands. However, Heinsberg was not included as an area reporting local or community transmission per the national case definition at the time. In early March, two residents from a long-term care facility (LTCF) in Sittard, a Dutch town located in close vicinity to the district of Heinsberg, tested positive for COVID-19. In this study we aimed to determine whether cross-border introduction of the virus took place by analysing the LTCF outbreak in Sittard, both epidemiologically and microbiologically.Surveys and semi-structured oral interviews were conducted with all present LTCF residents by health care workers during regular points of care for information on new or unusual signs and symptoms of disease. Both throat and nasopharyngeal swabs were taken from residents suspect of COVID-19, based on regional criteria, for the detection of SARS-CoV-2 by Real-time Polymerase Chain Reaction. Additionally, whole genome sequencing was performed using a SARS-CoV-2 specific amplicon-based Nanopore sequencing approach. Moreover, twelve random residents were sampled for possible asymptomatic infections.Out of 99 residents, 46 got tested for COVID-19. Out of the 46 tested residents, nineteen (41%) tested positive for COVID-19, including 3 asymptomatic residents. CT-values for asymptomatic residents seemed higher compared to symptomatic residents. Eleven samples were sequenced, along with three random samples from COVID-19 patients hospitalized in the regional hospital at the time of the LTCF outbreak. All samples were linked to COVID-19 cases from the cross-border region of Heinsberg, Germany.Sequencing combined with epidemiological data was able to virtually prove cross-border transmission at the start of the Dutch COVID-19 epidemic. Our results highlight the need for cross-border collaboration and adjustment of national policy to emerging region-specific needs along borders in order to establish coordinated implementation of infection control measures to limit the spread of COVID-19.The online version contains supplementary material available at 10.1186/s12879-021-06093-9. Rapid global spread of the novel coronavirus SARS-CoV-2 has led to an increasing number of cases of coronavirus disease 2019 (COVID-19) in the Netherlands. Since the first case of COVID-19 in the Netherlands was reported on February 27, 2020 . In the The Dutch province of Limburg borders the German district of Heinsberg in the federal state of North Rhine-Westphalia which had a large cluster of COVID-19 cases linked to local carnival activities, even before the first cases were reported in the Netherlands . An immuOn March 1st 2020, the first long-term care facility (LTCF) resident in Sittard, a Dutch town located in close vicinity to the district of Heinsberg, started experiencing moderate respiratory symptoms, but did not meet the national test criteria for COVID-19. Two LTCF residents were admitted on the 5th and the 6th of March to two different wards of the regional hospital with a suspected respiratory infection, but no  pneumonia. Even though they did not fit the national COVID suspect criteria, they were tested for COVID-19 and tested positive. The Public Health Service South Limburg received first reports of two COVID-19 positively tested residents on March 7th 2020.Introduction of the virus could have occurred following the carnival activities in the surrounding area by LTCF visitors or health care workers (HCWs). This assumption is fuelled by the fact that the border region of Sittard (The Netherlands) and Heinsberg (Germany) is typified for its cross-border travel. Therefore, these densely-packed carnival activities were most likely visited by HCWs, as well as citizens from both sides of the border.Our study group has conducted several studies regarding infectious disease control along the Dutch-German border region , 10, higIn this manuscript, we have determined whether cross-border transmission from the Heinsberg region took place by analysing the first COVID-19 LTCF outbreak in the Netherlands, located in Sittard, both epidemiologically and microbiologically. In particular, we compared SARS-CoV-2 sequences of samples found in this LTCF, as well as three samples from the regional hospital, with sequences from Heinsberg. In doing so, we want to address the challenges of a cross-border region and highlight the importance of specific, regional guidelines and needs in limiting the introduction of pathogens from across the border.We performed a cross-sectional epidemiological and laboratory investigation of an ongoing COVID-19 outbreak that occurred in a LTCF in South Limburg, the Netherlands, in early March 2020. Surveys were conducted with all present residents during regular points of care. On the day of survey, HCWs from the LTCF performed semi-structured oral interviews of all 99 present LTCF residents, divided over five different wards, to collect information on age, sex, new or unusual signs and symptoms of disease, complemented with comorbidity information from their patient records and taking their temperature  in the morning and the evening during regular moments of care. An increase in temperature from 37.5 to 38 degrees Celsius was categorized as subfebrile temperature, whereas 38.0 C and above was classified as fever. Optimal collection of signs and symptoms was hampered by the fact that part of the residents had some stage of impaired cognition.These data were shared with the Public Health Service South Limburg. No HCWs were tested, as HCWs who experienced any symptoms of disease were instructed to stay at home. Twelve random samples of possible asymptomatic residents were taken from residents from all five wards to avoid possible selection bias. Any missing data was coded as missing and was not imputed. All descriptive analyses were done using IBM SPSS Statistics version 26 .Both international and national case definition for suspect cases, at the time, included a sudden onset of either cough, fever, shortness of breath with no other aetiology that fully explains the clinical presentation. Additionally, a suspected case must have met an epidemiological criterium of a history of travel or residence in a country/area reporting local or community transmission, or have had to be in close contact with a confirmed, or probable COVID-19 case . Within n = 10), according to this adjusted case definition for COVID-19, were sampled on March 8th, which resulted in six confirmed COVID-19 cases on March 9th. Subsequent screening of contacts (n = 14) in the same ward as the index patient and on other wards revealed additional COVID-19 cases. Additionally, a random sample of twelve asymptomatic residents were tested on March 11th.Suspect residents of the LTCF  . In addihttps://github.com/rrwick/Porechop) after which a reference-based alignment was performed using minimap2 [Whole genome sequencing was performed using a SARS-CoV-2 specific amplicon-based Nanopore sequencing approach . Sequencminimap2 . The conminimap2 .All available full-length SARS-CoV-2 genomes were retrieved from GISAID (supplementary) on the 17th of March 2020 and aligned with the Dutch SARS-CoV-2 sequences from this study using MUSCLE . UnfortuTable The ages of the residents ranged from 64 to 97 years. Out of the 99 residents, 46 (47%) were tested for COVID-19 of whom nineteen (41%) tested positive. More tests were done on wards three and five, because COVID-19 was first detected here. Out of the twelve randomly tested asymptomatic residents, three (25%) tested positive for COVID-19.Up until 8 weeks after the last infection was determined, five residents have died. All five deceased residents tested positive for COVID-19.Out of the nineteen residents who tested positive for COVID-19, sixteen (84%) reported any signs and symptoms of disease. Out of these sixteen symptomatic residents, we were unable to fully evaluate the symptoms of three (19%) residents, as they were hospitalized and passed away before the interviews took place. The most common signs and symptoms in the remaining thirteen positive residents were fever (54%), subfebrile temperature (47%), and cough (39%). Other, less frequently reported symptoms, were fatigue (15%), malaise (15%), vomiting (8%), loss of appetite (8%), nausea (8%), and dizziness (8%). An overview of these reported symptoms within symptomatic COVID-19 positively tested residents is shown in Table Additionally, another eighteen residents reported an increase in temperature, with seven reporting fever and eleven reporting subfebrility, but tested negative for COVID-19.n = 16) and asymptomatic residents (n = 3) are shown in Fig. The CT values of positively tested symptomatic residents n = 6 and asyComplete genome sequencing of the SARS-CoV-2 virus from eleven residents from the LTCF in South Limburg was performed. In addition, three random samples from the regional hospital were sequenced. All accession numbers for the sequences are shown in Table Figure As of March 8th 2020, additional infection control measures were implemented by the LTCF. Wards three and five, the wards on which the first residents tested positive for COVID-19, were isolated, and visitors were banned from entering these wards. Admission of new residents was temporarily halted. All suspect residents (residents with respiratory complaints with and without fever) and confirmed COVID-19 residents, as well as residents with (at least) subfebrility, were put into isolation. All other residents were closely monitored by taking their temperature twice during regular moments of care, as well as checking for new or unusual signs and symptoms of disease, including coughing, subfebrility, and shortness of breath. Additionally, all planned group activities on all wards were cancelled, and residents were served meals in their own rooms.At first, the number of visitors was limited to two per day for the other wards. However, when residents tested positive for COVID-19 on these remaining wards , a total visitor ban was also introduced for these wards.HCWs worked in set teams and wore gowns, surgical mouth masks, and gloves when they expected to get in close contact (within 1.5 m) with COVID-19 positive residents or their surroundings. Additionally, hand hygiene among HCWs was intensified. HCWs were regularly briefed with updates on a closed online portal, by team meetings with social distancing, and by newsletters shared via internal e-mail.Since the implementation of these infection control measures, only one additional resident tested positive for COVID-19 on the 31st of March, after which no more residents have been infected, hospitalized, or have died due to complications from COVID-19 up to 8 weeks after the last infection. As a result, this LTCF was among the first 37 of 139 LTCFs in our region to allow visitors again.Both international and national case definitions for suspect cases at the start of the COVID pandemic was based on a manifestation of disease like pneumonia rather than diseases with various manifestations ranging from mild to severe. Therefore, the case definition included a sudden onset of COVID symptoms including fever, as well as a history of travel or residence in a country or area reporting local or community transmission, or have had to be in close contact with a confirmed, or probable COVID-19 case . This deFirst, we included travel to or from Gangelt (Heinsberg) as an area reporting local or community transmission. Second, a more sensitive case definition for COVID-19 suspected cases was used for the residents of the LTCF involved, which meant any respiratory symptoms or fever, including subfebrility (defined as temperature between 37.5 en 38 degrees Celsius) was seen as a suspect COVID case.A series of geographical maps of the border region of Sittard and Gangelt is shown in Fig. Complete genome sequencing of the SARS-COV-2 samples of the eleven LTCF residents from Dutch Limburg showed complete clustering with virus strains found in the neighbouring German region of Heinsberg. This is in line with the open-border region of Limburg and Heinsberg characterized by cross-border commuter activity in both directions. Given the mutual carnival festivities on both sides of the border, the initial outbreak of COVID-19 in Heinsberg was accompanied by intensified cross-border movements. Though it has not been possible to identify the actual index case who introduced the SARS-CoV-2 virus into the LTCF, it seems plausible that the index was a (pre-)symptomatic carrier who picked up the virus through direct involvement in  activities across the border, or was a secondary contact, especially since pre-symptomatic cases and pre-symptomatic transmission have been reported , 19 and Furthermore, this cross-border outbreak showed that (inter) national guidelines are not always sufficient or fully applicable in a border-region setting. Because Gangelt (Heinsberg) was not labelled as a COVID-19 endemic area during this outbreak, prior visits to this transmission area would not be categorized as a risk area, which could lead to many missed cases. As such, the (inter)national definition for suspect COVID cases at that moment in time turned out to be inappropriate for this specific region. In response to the cross-border situation in Gangelt, several guidelines were adjusted on a regional level by the public health service, as well as the regional hospital. For example, the physicians in the region were uneasy with the diagnostic testing for SARS-CoV-2 for admitted patients with pneumonia only when these cases were unexplained, as in most cases of community acquired pneumonia a causal agent often goes undetected. Therefore, even when the case definition for admitted cases was not completely met, a test for COVID-19 was immediately requested upon admission in the regional hospital. Nevertheless, deviation from national guidelines and international agreements was limited. Our results highlight the need for cross-border collaboration and adjustment of national policy to emerging region-specific needs along borders in order to establish coordinated implementation of infection control measures to limit the spread of COVID-19.Many studies have examined the effect of travel restrictions such as closing the border or limiting air travel between countries , 20–22. With regards to the LTCF, we observed a number of cases among LTCF residents in a cross-sectional analysis following two hospitalized residents who tested positive for COVID-19. Many of the residents who tested positive did not meet the clinical criteria for suspect cases of COVID-19 at that time . SymptomA study on COVID-19 within LTCFs by Arons et al. reports similar findings . In a COn = 3). Lastly, although it is very likely that the introduction of the SARS-CoV-2 virus was caused by an asymptomatic or pre-symptomatic HCW or visitor, the transmission route into the LTCF could not be identified with certainty. In order to give more support to the likelihood that cross-border transmission took place, we sequenced eleven samples from positive residents, as well as three positive patients from the regional hospital, which showed a strong similarity between sequences from Limburg and Heinsberg.This study extensively describes the first LTCF outbreak in the Netherlands from a cross-border perspective. By sequencing strains from the LTCF as well as the regional hospital, we were able to virtually prove cross-border transmission. Furthermore, this study describes the challenges a cross-border region encounters when dealing with a health crisis such as COVID-19. We were able to highlight the need for cross-border collaboration and adjustment of national policy to emerging needs along borders, which are applicable to other infectious diseases in a cross-border setting. However, we also encountered several limitations in the investigation of the outbreak. Due to a large difference in (mild) types of symptoms, it was difficult to pinpoint the onset of disease for positively tested residents, which hampered us in presenting a trustworthy epicurve. Instead, we have given a detailed description of events surrounding the LTCF. Additionally, although we were able to verify any new infections or deaths up to 8 weeks after the last detected infection, we were not able to acquire any follow-up data on symptoms, which made it impossible to categorize any asymptomatic residents as pre-symptomatic residents. In addition, a sample size of 99 residents is too small to draw any decisive conclusions, and the results presented in the manuscript should be interpreted as such. This is especially the case for the CT-values of the number of asymptomatic  residents found national criteria for suspect cases of COVID-19. Hence, adjusted criteria should be formed with regional- and cross-border partners to limit potential spread of the SARS-CoV-2 virus. Moreover, whole genome sequencing can help to identify and resolve potential transmission clusters. Given the clustering sequences found between the LTCF residents and the Heinsberg samples, introduction of the SARS-CoV-2 virus by a pre-symptomatic visitor or HCW with direct or indirect cross-border contacts, seems highly likely. The cross-border nature of this outbreak underlines the importance of sharing information with cross-border partners, as well as adjustment of national policy to emerging region-specific needs, in order to establish a coordinated implementation of infection control measures in the region to limit the spread of infectious diseases.Additional file 1. The complete phylogenetic tree (.pdf file). The full phylogenetic tree of COVID-19 cases at the time of testing (March 2020), including the sequenced samples from the LTCF.


The relationship holds using county and patient-level data, as well as in hospital and nursing home settings. Results do not appear to be driven by systemic or policy-related factors, instead suggesting an individual-level response to prior influenza pandemic exposure. The findings merit investigation into potential biological and immunological mechanisms that account for these differences—and their implications for future pandemic preparedness.Past pandemic experience can affect health outcomes in future pandemics. This paper focuses on the last major influenza pandemic in 1968 (H3N2), which killed up to 100,000 people in the US. We find that places with high influenza mortality in 1968 experienced 1–4% lower COVID-19 death rates. Our identification strategy isolates variation in COVID-19 rates across people born before and after 1968. In places with high 1968 influenza incidence, older cohorts experience lower COVID-19 death rates  The COVID-19 pandemic resulted in the global implementation of an unprecedented set of public health and economic measures including social distancing and supply chain innovations, along with widespread emergency use of new pharmaceuticals and vaccines. To evaluate pandemic response effectiveness and to better understand how to prepare for and prevent future pandemics, researchers are investigating the epidemiological and pathological nature of the SARS-CoV-2 virus in the hope of fully assessing the disease’s global impact—and, in particular, investigating the susceptibility of populations to illness. This paper presents novel findings associating distant life experiences—and potentially biological factors—with the severity of COVID-19 illness, and contributes to several strands of related research spanning the social and biological sciences.One such research area involves the investigation of heterogeneous COVID-19 outcomes among different populations. Previous work has presented evidence linking demographic, racial, social, and policy factors to the spread and severity of COVID-19 . PandemiA second relevant area of research explores genetic, immunological, and other biological factors linked to the severity and transmissibility of COVID-19 . Such reA third related research thread explores the persistence of past public crises and how they alter human and institutional responses in such a way that mediates the spread, morbidity, and mortality of COVID-19 . These sLooking beyond COVID-19, there is abundant research into the links between pandemics and disease. One representative study connects an HIV-resistant gene to exposure to the plague and smallpox . Anotherrelative to younger ones. The findings are robust to using county-and patient-level data, as well as hospital and nursing home data, and do not appear to be driven by systemic or policy-related factors. Instead, they suggest a potential biological and immunological response to prior influenza pandemic exposure.Our paper applies a similar lens to an underexplored but arguably consequential pandemic, the 1968 influenza pandemic, which killed up to 100,000 people in the US. We find that areas with high influenza mortality in 1968 experienced 1–4% lower COVID-19 death rates. Leveraging variation in COVID-19 rates across people born before and after 1968, we find that in areas with high 1968 influenza incidence, older cohorts experience lower COVID-19 death rates 1 The death toll of the ensuing pandemic was comparable to that of the COVID-19 pandemic given the smaller US population of the time of around 200 million people, with 100,000 deaths in the US . Globally, the 1968 flu pandemic resulted in between 1 to 4 million deaths. Paralleling the present day, the flu reached the White House, with both President Lyndon B. Johnson and Vice President Hubert Humphrey falling ill  in places that experienced high death rates from the 1968 flu, perhaps resulting in the development of a culture favoring extra precaution or social (dis)trust. In such cases, we would expect an equivalent shift for all people living within a geography , as all residents would be more or less equally affected by these social forces.A individual channel, in contrast, involves not a population but rather individuals for whom a difference in outcomes is expressed. The individual channel may be biological2  or behavioral , both of which may lessen the likelihood of infection or death. Along this line, Cheemarla et al. finds that previous exposure to rhinovirus lends resistance to SARS-CoV-2 infection. The individual channel requires heterogeneous effects across a population, with sub-populations demonstrating unique COVID-19 outcomes based on past exposure.An outcomei is a COVID-19 outcome in county i at a given month, β is the coefficient of interest related to flu, which is the excess respiratory death rate attributable to the 1968 flu as described in the controlsi is a vector of county-level covariates, αs is a dummy for fixed effects in state s, and ϵi is the error term. Standard errors are clustered at the state level.Our baseline linear regression model takes the following form:For outcomes of interest, we variously use (1) COVID-19 death rates, (2) hospital admissions, (3) a subset of patient-level data from Healthjump, and (4) nursing home death rates. All values are aggregated to the county level to match our data on 1968 flu intensity. We replicate this cross-sectional analysis at different snapshots in time representing the progression of the pandemic, as categorized by end-of-month outcomes.To address endogeneity and omitted variable bias concerns in the relationship between the 1968 flu and COVID-19 outcomes, we also employ differences in death rates and hospital admissions by age group as the outcome variable. We choose the age cutoff based on whether someone was born before or after 1968 in an attempt to isolate those people likely to have been exposed to the 1968 pandemic.relative to those born after 1968. The identifying assumption relies on the fact that potential confounders are unlikely to shift the relative degree of COVID-19 morbidity or mortality across proximate age groups within a given county. Finally, to address concerns about the coarse categorization of individuals into decadal birth cohorts, we validate the results with patient-level data from Healthjump containing annual year of birth.The bottom panel of First, we explore patterns in the underlying data. 3We next present regression results using the model specified in worse off. A discontinuity appears to occur at the 1968 birth year, indeed suggesting some relationship between a likely individual experience of the 1968 flu pandemic and COVID-19 outcomes.To evaluate the hypothesis of a connection between being alive during the 1968 flu and variance in susceptibility to COVID-19, we next employ patient-level data from Healthjump containing patients’ birth year. This analysis involves 48,000 unique patient records where a COVID-19 diagnosis is explicitly linked to a medical procedure within 30 days of the diagnosis. Such procedures include, but are not limited to, hospitalization. Next, we address concerns that demographic patterns may be driving these results. We test how health outcomes relate to known confounders—both in the present and in 1968.Columns (A) and (B) showcase the difference among all those older and all those younger than 50 and 60 years old, respectively. Columns (C) and (D) limit the span to single decades. For example, column (C) shows the difference in death rates between people in their sixties versus those in their forties, highlighting groups just old enough to have lived through the 1968 pandemic and those not. Column (D) uses people in their fifties as the control, although it is less obvious how to categorize this cohort, considering that many were alive in 1968 although flu transmission tends to increase after age five with the onset of schooling .In addition to examining death rates, we look at hospital admissions driven by COVID-19 as a proxy for case severity. We again test whether there is a differential effect of 1968 flu exposure on hospitalizations between people who lived through the pandemic and those who did not. The top panel of We replicate our analyses using CMS data on nursing homes. The bottom panel of Next, we test a number of potential relationships that would indicate potential policy, social, or individual responses to the 1968 pandemic. One potential explanation is that places with high 1968 flu mortality subsequently invested in hospital capacity to be better prepared for future challenges. Such actions could explain why hard-hit counties saw better outcomes under COVID-19. To test this, less. The relationship holds even after controlling for state-level differences and potential covariates .Another possibility is that individual behavior responds to an event like the 1968 flu. Adoption of risk-averse behaviors  could explain differential COVID-19 outcomes. Finally, we report changes in mobility in response to 1968 flu death rates using Google mobility data. We look at both mobility involving time spent commuting to work as well as engaging in retail and recreational activities. We compute two measures to account for the potential timing of COVID-19 responses. One is a summer average of the baseline change in mobility in a county from June to August. Another is change in county mobility between 28 days before and 28 days after a counties’ first reported death. Our findings suggest there is a persistent link between the 1968 flu pandemic and COVID-19 pandemic outcomes. People in counties among the worst hit by the 1968 flu had COVID-19 death rates 1–4% lower than the average US county. This general relationship is robust to controlling for known confounders and holds across populations , as well as specifications that exploit age-based variation in exposure.Perhaps the most salient finding in support of this conclusion is the discontinuity in better today—mitigates concerns of a lurking omitted variable. In such a case, we would imagine the opposite relationship in which some characteristic of places hit hard by the 1968 flu also makes them susceptible to COVID-19. Such a bias would indicate that the magnitude of our results are in fact understated.The direction of the relationship—that people in locales with adverse outcomes in 1968 fare These results suggest that the primary channel through which COVID-19 outcomes are affected is at the individual level. By contrast, we find no evidence of collective social activity suggesting better mitigation of COVID-19 outcomes. In fact, we find modestly lower levels of mask use and social distancing among the high-flu counties. Moreover, even if behaviors occurred that limited viral spread, the fact that positive outcomes were more pronounced among age cohorts that lived through the 1968 flu pandemic suggests an individual rather than societal-level mechanism.who were infected are dying. Assuming identical distributions of social distancing policy in nursing homes in counties with adverse 1968 flu histories and those without, better outcomes for nursing home residents in the former group are likely to suggest that some non-behavioral and non-policy mechanism is at play. This accumulated evidence lends support to potential biological mechanism(s) driving differential outcomes.Focusing on nursing homes also allows us to isolate a population that—unlike the elderly living outside nursing homes—exercises less agency in their social distancing practices and other risk-mitigating behaviors, instead following nursing home protocols. In addition, epidemiology within nursing homes is in some ways independent of what is found for the general population. Factors such as travel patterns of nursing home staff have a large effect on infection rates in such settings . We findIt is worth noting that our results are generally strongest in the autumn of 2020. The effect of the 1968 flu on COVID-19 outcomes appears to fade into the winter as COVID-19 becomes widespread, a dynamic also seen in , and as While we cannot speak to any specific biologic mechanism, direct immunological cross-reactivity seems unlikely, as SARS-CoV-2 coronavirus is a different type of virus than H3N2 influenza. However, individuals may have general innate, nonspecific, anti-viral immune pathways that are more robust due to factors such as genetics and lifestyle that may have been selected for during the 1968 pandemic and its aftermath. There is also precedent for generalized immune response experience early in life having an impact on susceptibility to future illness and injury, as has been observed in the aforementioned work examining the association between 1918 flu exposure and cardiovascular disease. Thus some sort of selective pressure may have occurred over time in which people who survived the 1968 pandemic were generally better suited to survive the COVID-19 pandemic. This mechanism would not be unlike that identified in research linking tuberculosis outcomes to the 1918 flu pandemic, and is plausible considering that 1968 flu mortality skewed toward younger people .These mechanisms are speculative at this point, and further research would be required to fully understand whether the differential outcomes observed here are truly meaningful and what caused them. Assessing the plausibility of cohort-based resilience to all respiratory diseases or whether this resilience is more specific to some element of COVID-19 that would otherwise cause death is certainly difficult, doing so may be worthwhile as we try to further understand this pandemic in the coming years.County-level mortality estimates of the 1968 influenza pandemic are derived from Centers for Disease Control and Prevention (CDC) Compressed Mortality files, 1968–1978, accessed via CDC’s WONDER database . We estiIndividual-level data are from CDC’s COVID-19 Case Surveillance Restricted Access Detailed Data accessed January 2021. The restricted dataset includes over 12 million records of COVID-19 cases with date, decadal age group, and county identifiers. Deaths are also reported. Note that because of CDC reporting delays and state-level data filing practices, aggregate totals are less than those of other sources and records November 2020 onward contain fewer counties reporting than earlier .4 Patient-level healthcare data with year-of-birth information available from Healthjump via the COVID-19 Research Database consortium . We aggregate weekly-level hospital data for different decadal age groups to the county-month level . Nursingnsortium . The numnsortium . County-nsortium .Covariate data include county-level race, ethnicity and age structure data from the US Census and mean county-level income data from the US Bureau of Economic Analysis . Data on


The COVID-19 pandemic has drastically affected everyone in a hit or miss manner. Since it began, evidence of the neuro-invasive potential of the virus has been intensifying significantly. Several pathways have been hypothesized to elucidate the neurotropic nature of SARS-CoV2. It is the need of the hour to collect vital information.To evaluate and correlate the neuro-radiological and neurological manifestations in patients diagnosed with SARS-CoV2.To identify neuro-invasive pathways of COVID infection.Relevant studies were identified through four databases—the Cochrane Library, PubMed, Science Direct, and Web of Science. These were searched using relevant keywords—“COVID-19,” “SARS-CoV2,” “neurological manifestations,” “neuroimaging,” “CT,” and “MRI.” Relevant articles were screened according to a pre-defined inclusion and exclusion criteria from December 2019 to August 2020.Our review included a total of 63 full text publications with 584 patients, composed mainly of observational studies, case reports, and case series. The most common neurological manifestations associated with COVID-19 were altered mental status, stroke, and paralysis. About 17.85% patients who underwent neuroimaging were found to be having ischemic changes suggestive of a stroke. This was followed by hemorrhagic changes as the second most common finding. The most commonly involved vessel was the Middle Cerebral Artery. Besides stroke, we found that SARS-CoV2 could be the cause for new-onset seizures, Guillain-Barre Syndrome, encephalitis, and many other severe neurological diseases.The information that we have obtained so far will prove dynamic to healthcare providers working against the COVID-19 pandemic. It is necessary to be aware of these atypical neurological findings for the early diagnosis and treatment of COVID-19 infected patients. However, to completely understand the connection between SARS-CoV2 and the nervous system, further research is necessary. The infamous COVID-19 pandemic has drastically involved everyone in a hit or miss manner. The world is currently fighting against a highly infectious novel coronavirus, known as SARS-CoV2. What began as an outbreak of pneumonia in Wuhan, China, has rapidly engulfed the entire world .Though the respiratory symptoms are the most common, there have been studies which highlight the potential neurotropism of the virus. The incubation period of COVID-19 infected patients, whether asymptomatic or possessing wide spread signs and symptoms, varies from 2 to 11 days with an approximate mortality rate of 2-4% . There hThis initial data reflects that the brain seems to be a target organ for various infections and critical diseases, either due to direct insult or through secondary involvement. The peripheral nervous system (PNS) is also particularly susceptible during infection-related immune-mediated diseases .Even though there is extensive data on the respiratory involvement of SARS-CoV2, documentation of its neurological aspect has been limited to observational studies and case reports. There is a further lack of information on the neuroimaging findings of COVID-19. In this rapidly evolving situation, it has become essential for healthcare providers to stay updated on the various atypical presentations of SARS-CoV2 and keep in mind COVID-19 as a potential diagnosis when encountering such cases. Therefore, we performed a comprehensive literature search in this systematic review to ascertain the different neurological manifestations and neuroimaging findings linked with COVID-19 infection.To evaluate and correlate the neuro-radiological and neurological manifestations in patients diagnosed with SARS-CoV2.To identify neuro-invasive pathways of COVID infection.A comprehensive search of the literature was performed from the following databases: PubMed, Web of Science, Cochrane Library, and Science Direct. The following search terms were used in combination with the Boolean operators AND and OR; “COVID-19,” “SARS-CoV2,” “neurological manifestations,” “neuroimaging,” “MRI,” and “CT.” We selected for analysis only articles in which the title and abstract contained the aforementioned search terms. In an initial screen, we excluded articles which were duplicates, and those in which title and abstract were not relevant to our search terminology. Of the remaining studies, screening was done based on the full text of the article under the following inclusion criteria: (1) Studies reporting patients with laboratory confirmation of SARS-CoV2, (2) case reports, case series, cohort studies, and case-control studies, (3) studies in which subjects were above the age of 18, (4) studies containing neuroimaging (CT or MRI) of the brain, (5) studies performed between December 2019 and August 2020. The exclusion criteria were as follows: (1) reviews, editorials, or commentaries. (2) Studies in which subjects were in the pediatric age group, were pregnant, or had prior neurological conditions. (3) Studies with no neurological evaluation, (4) studies published in any language other than English, without available English translations. The articles were screened in their entirety, by two independent readers, in each of the aforementioned scientific databases, to determine eligibility for inclusion. Discrepancies were discussed among all authors, and a collective effort was undertaken to resolve them.The search strategy and article selection process are depicted in the flowchart in Fig. Through the search strategy, we identified 63 articles with neurological and neuroimaging manifestations in patients infected with COVID-19. We included 584 patients who presented with neurological manifestations and underwent different neuroimaging modalities. The age of patients ranged from 24-88 years.In terms of neuroimaging findings Table , among tOut of the 157 distinct neurological manifestations presented in the 63 articles Table , we wereSince the outbreak of the SARS-CoV2 virus in December 2019, the majority of research has been centered around respiratory pathogenesis and manifestations of the virus. However, recent focus has shifted toward its invasive nature and complications in the nervous system. There has been a surge in the number of cases documenting the nervous system involvement in COVID-19 positive patients with minimal respiratory involvement. Some studies reported absence of SARS-CoV-2 RNA in the nasal and throat swabs even though it was found to be present in the cerebrospinal fluid upon further investigations . HoweverCurrently, there are 4 mechanisms of neuro-invasion that have been hypothesized.The body has a traditional angiotensin-converting enzyme (ACE) in lung capillaries which is a part of the renin-angiotensin-aldosterone system (RAAS) and is involved in regulating blood pressure. COVID-19 is known to use ACE2 receptors, present in the endothelium of the heart, kidneys, and alveolar cells, especially alveolar type 2 (AT2), for cell entry. Binding to these receptors, the virus hampers the body’s natural mechanism of decreasing blood pressure thus increasing the likelihood of intracranial hemorrhages and stroke –71. The The anosmia in many cases points toward viral entry via olfactory bulb and across the cribriform plate . This mePrior research of SARS-CoV and MERS has shown that cytokines like tumor necrosis factor (TNF-α) and interleukins (IL-6 and IL-1) led to direct death of neurons in the respiratory center in the medulla , 75. The2 and CO2. These pathways run-up to the respiratory centers in the brainstem and send signals to the pre-synapses there. Porcine hepatitis E virus studies depict a similar pathway of transmission and since HEV is almost homologous to hCoV-OC432, a close relative of SARS-CoV-2, it might be the same case here [The entry of the virus into CNS through the peripheral nerves is another hypothesized secondary pathway. The alveoli in the lungs have sensory innervations that detect changes in Oase here .The neuropathological mechanisms reported to play a role in the development of neurological disorders in COVID-19 are—hypoxic brain injury and immune-mediated damage. The hypoxic brain injury is believed to be due to the alveolar gas exchange disorders caused by proliferation of virus in the alveolar cells . As mentAbout 17.85% patients who underwent neuroimaging were found to be having ischemic changes suggestive of a stroke. Rajan Jain  and collIn this study, we observe that COVID-19 patients presented with a variety of neurological complications. In our review, the most prevalent finding has been altered mental status 52.5%). Among the earliest articles about COVID-19 by Mao 2.5%. Amo, 81. NepStroke has been observed to be the most frequent finding in neuroimaging of patients affected by COVID-19. A peculiar thing about COVID-19 related strokes is that they can be found in younger patients as observed in a case series by Ashrafi  which exAs far as we know, this is the only study with documentation of reports published until August 2020 which is based on the nervous system involvement and neuroradiological findings of COVID-19 patients. The limitations of our study were that a subset of reported neurological or neuroimaging findings in severely ill and elderly patients may be incidental. The radiological findings might have been susceptible to clinical bias hence it is difficult to standardize them. Radiological imaging presumably is performed selectively on those presenting with notable neurological involvement, leaving out the probable findings in those diseases which are milder in nature, as routine imaging may increase the risk of transmission of the virus. Our study only included articles published in the English language.In the past few months of the global pandemic, the connection between COVID-19 and neurological manifestations has been growing substantially. Having strong knowledge about such associations will prove to be instrumental in early detection, isolation, and care of patients who present with unusual neurologic symptoms, especially during the ongoing pandemic. Focus on long-term neurologic sequelae and neuroimaging findings is necessary to further the research on the neurotropic involvement of SARS-CoV-2.


At the same time as microscope observation of the thermal decomposition phenomena, two-step thermal decomposition process of KMnO4 is identified and the thermal decomposition temperatures are obtained. The TG/DTA microinstrument is promising to be applied for study of various materials.Combined use of thermal analysis techniques can realize complementarity of different characterization methods. Comprehensive thermal analysis with both thermogravimetric analysis and differential thermal analysis (TG/DTA) can measure not only mass change of a sample but also its temperature change during programmed heating-induced reaction or phase transition processes, thereby obtaining multiaspect thermal information of the material such as dehydration, structural decomposition, phase change and thermal stability. This study proposes and develops a MEMS chip-based TG/DTA microsystem that integrates both programmed heating and detecting elements into a TG chip and a DTA chip to enable the microinstrument performing TG/DTA joint characterization under microscope observation. The TG chip contains a self-heating resonant microcantilever to measure heating-induced mass change of a sample and the DTA chip is with a microheater and a temperature-detecting thermopile integrated on a suspended thermal-insulating diaphragm. Only nanogram and microgram-level samples are needed for the TG and DTA chips, thereby achieving safe measurement to energetic materials such as strong oxidants. The chip-based microinstrument surpasses the state-of-the-art commercial TG/DTA instruments that have, in the long term, suffered from large sample-amount (milligram level) requirements and have been unable to measure energetic materials. Compared with commercial instruments, the chip-based microinstrument is advantageous given its more accurate analysis, much higher heating rate, much smaller instrument volume and much lower power consumption, etc. The microinstrument has been fabricated by using wafer-level MEMS techniques. Testing results show that the mass-detection sensitivity of the TG-chip is as high as 0.45 Hz/pg in air and the temperature sensitivity of the DTA chip achieves 2.9 mV/K under the high heating rate of 25 °C/s. The strong oxidant of KMnO Material thermal analysis technologies are frequently used to evaluate temperature-dependent properties of substances under programmed heating, which can be applied for the characterization and investigation of structure decomposition, thermal stability and phase transition, food safety assessment and drug evaluation ,2,3,4, eTG is a classic characterization technique for measuring the relationship between mass change of a sample and programmably heated temperature under a certain atmosphere. The technique is often used to study heating-induced dissociation, dehydration, decomposition and oxidation/reduction of substances by measuring the temperature related mass change. The disadvantage lies in that it is difficult to obtain the temperature-related heat-change process such as physical transition temperature of the sample  and the endothermic properties of a chemical reaction, where not only mass but also heat will change.DTA is a technique for measuring the heat release or absorption-induced temperature change of a sample during the programmed temperature-increasing process under a certain atmosphere, which is often used to determine the special temperature of a sample during endothermic or exothermic phase transition or reaction. The disadvantage of DTA lies in that it is difficult to quantitatively obtain mass change during the test, such as chemical composition change and content  of the sample.Therefore, joint characterization by using both TG and DTA has complementary advantages to obtain comprehensive thermal analysis information , therebyIt should be noted that the sample consumption of state-of-the-art commercial TG/DTA dual-function instruments is generally at the milligram level. The needed large amount of sample does cause difficulties in uniformly heating the sample during rapid heating, as well as inevitably leading to uneven temperature distribution and inaccurate measurement . If the To solve the above-mentioned problem, herein a TG/DTA microsystem is proposed with all the core components fully integrated into a specifically designed micromachined resonance-cantilever chip for TGA (named MR-TGA) and a thermopile-embedded suspending diaphragm MEMS chip for DTA. The size of the TG/DTA microsystem based on the two MEMS chips is as small as centimeter level. The chip-based TG/DTA microsystem can be put under a microscope to observe the sample changes during the joint thermal analysis. Moreover, the samples can easily be loaded on the chips under the microscope by using a micromanipulator. The required sample amount is only at the level of 10s of nanograms (ng) and micrograms (μg) for MR-TGA and DTA, respectively. Ultrasensitive microchips loaded with a tiny amount of sample are advantageous in high-speed heating and high-efficiency accurate analysis. More importantly, the required tiny amount of sample makes the TG/DTA microsystem safe to use for thermal analysis of dangerous explosive substances such as strong oxidants. All these advances make the microsystem surpasses the market-available TG/DTA instrument.Compared with the bulky commercial TG/DTA instrument, the proposed TG/DTA chip-based microsystem is only at centimeter scale. The smaller heating size helps to realize a much faster heating rate, where the TG/DTA microsystem can measure and control the temperature change within milliseconds. For maintaining a uniform thermal distribution of the sample, the maximum heating speed can reach 25 °C/s.α is Poisson’s ratio of the cantilever material and β is temperature drift coefficient of Young’s modulus. For the silicon cantilever, the value of α is 2.6 × 10−6/°C and the value of β is −6 × 10−5/°C.The traditional TGA instrument measures changes in gravity of a sample through a precision balance, while the proposed MR-TGA continually measures the mass change of sample during programmed heating by detecting the shift of resonant frequency of the cantilever beam. In the MR-TGA, a metal heating resistor located at the free end of the cantilever is used to heat the sample pool. After precalibration between the temperature and the resistance change of the heater, the heating current inside the resistor wire can be controlled to achieve uniform heating to the sample. At the same time, the cantilever beam is excited into resonance by flowing DC-biased AC current into the silicon electric–thermal exciting resistor  integratAs shown in n-doped polysilicon and p-doped polysilicon are chosen as the two thermocouple materials, since such design achieves quite large difference in Seebeck coefficient for high temperature-detection sensitivity. The DTA chip consists of two diaphragms that have identically designed two heating plates and two thermopiles. On one heating plate, the sample will be loaded. In contrast, the other plate will be kept empty or hold a reference sample that is insensitive to heating. Through a preset linear heating program, the two heating plates are heated at the same rate; therefore, there will be a differential temperature output between the two thermopiles when the tested sample experiences exothermic or endothermic reaction during the programmed heating. The differential signal The thermopile in the DTA chip relies on the Seebeck effect to detect temperature change. The hot-junctions of the thermocouples connected in serial are located at the central heating plate of the suspended diaphragm, and the cold-junctions are connected to the heat sink outside the square diaphragm. When the temperature on the heating plate changes, the thermopile generates a potential essed as U=N, which is a typical hazardous chemical due to its strong oxidizing properties and explosiveness.Explosive, corrosive, or strongly oxidizing samples are difficult to test with market-available TG/DTA instruments due to the risk of contamination or even blast damage of the instrument by heating such samples at the mg level. In contrast, the herein-proposed TG/DTA microsystem requires only ng-level samples for TGA and µg-level samples for DTA, which are too small to pose severe explosion or other dangers. As shown in 4, which indicates the continual heating induced two-step decomposition process of KMnO4 with the number marked in the figure. The differential results of the mass-loss curve (see the dotted green curve) also indicates the two steps. The corresponding decompositions are known as [known as ,21(1)10In step (1), the overall reaction includes the decomposition of 4 thermal decomposition being an endothermic process.The DTA curve confirms the TGA results, which distinguishes that the first decomposition occurs between 100 and 400 °C and the second decomposition occurs between 450 and 630 °C. More importantly, the DTA results clearly judge that the two reaction stages are endothermic by the negative sign of the output waveform. Through the combined test of both MR-TGA and thermopile DTA, the MEMS chip-based TG/DTA microsystem can real-time obtain the characterization results, such as the reaction temperature range, the composition changes and the judgment of KMnOThanks to the small testing system for microscopic observation, the sample morphologic evolution during the two-step decomposition are real-time recorded which can be seen in the insets of The proposed MEMS chip-based thermogravimetric/differential-thermal analysis (TG/DTA) joint-detection microsystem has been developed by using MEMS integration techniques. Compared with commercially available TG/DTA equipment, the microinstrument has advantages in its smaller size, lower manufacturing cost, faster heating rate, etc., thereby enabling rapid heating testing, real-time microscopic observation of the morphologic evolution of the material during programmed heating. Thanks to the required sample amount of nanogram and microgram levels for TGA and DTA, the TG/DTA microinstrument can analyze energetic materials that have historically been difficult to measure in commercially available TG/DTA instruments. The proposed TG/DTA microinstrument is expected to be widely used for the thermal analysis of various advanced materials.


Multilayer reduced graphene oxide (mrGO) was chemically modified by electroless plating of copper on surface to form mrGO-Cu. The scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis revealed that nano-Cu particles were uniformly dispersed on the surface of mrGO. The mrGO-Cu powders were further utilized as reinforcements for aluminum (Al) matrix and the mrGO-Cu/Al composite was successfully fabricated through clad rolling of milled powder. The tribological properties of the mrGO-Cu/Al composites were explored. The tribological results show that the mrGO-Cu could reduce the friction coefficient and wear loss of mrGO-Cu/Al composites, since the mrGO-Cu participated in lubricating processes due to the formation of a transfer layer on the contact surface. Furthermore, it is found that the composition of mrGO-Cu could significantly influence the tribological properties of the mrGO-Cu/Al composites. The composites with 4% of mrGO-Cu for composites exhibited the best tribological behavior, which transformed from adhesive wear to abrasive wear, due to the formation of a graphite lubricating film. Aluminum and aluminum alloys have been widely used as light structural materials in aerospace, automotive and machinery manufacturing engineering as well as in other fields, due to their outstanding properties, such as high specific strength and good ductility . HoweverAs carbon materials can lead to a conformal protective coating on the sliding contact interfaces owing to low shear stress of C-C layer and self-lubricating property, reinforcing aluminum composites with carbon materials is regarded as an effective way to improve its abrasive resistance performance. Various types of carbon materials, such as carbon nanotubes, carbon fiber and graphite, have been applied as the reinforcements in aluminum alloy to improve their wear properties ,6,7.3N4 could be improved through adding graphene. Most of the recent studies on graphene reinforcing tribological properties focused on organic polymer and ceramics [Since graphene was fabricated and observed by UK Geim and Novoselov by micro-mechanical exfoliation method on graphite, its excellent physical and electrical properties have been widely explored in science and industry ,10,11,12ceramics ,25,26, bIn this work, we tried to explore the effect of graphene on enhancing the tribological properties of aluminum. The multilayer reduced graphene oxide was chemically modified by electroless Cu plating, aiming to improve the wettability between aluminum and graphene. Expectedly, the mrGO-Cu/Al composite was successfully fabricated through clad rolling of milled powder. Moreover, the influence of mrGO-Cu on the tribological properties of mrGO-Cu/aluminum composites, as well as its wear behavior and wear mechanism, were investigated in detail.Pure aluminum power (≥99.5%) with an average particle diameter of 20 μm was used as the matrix. Multilayer reduced graphene oxide was prepared by Hummers method, and then modified with copper using an electroless Cu plating method . Figure Pure aluminum powder and the mixed powder were analyzed by scanning electron microscopy  coupled by energy dispersive X-ray spectroscopy (EDS). TEM (Transmission electron microscopy) was using to observe the graphene morphology. The tribological properties of the composites were measured using a MMW-1A configuration control universal wear testing machine  with a pin-on-disc apparatus, and friction pair and the disc are #45 steel and the mrGO-Cu/Al composites disk, respectively. The samples with size of 65 mm × 28 mm × 2.5 mm were polished with # 2000 sandpaper and treated by ultrasonic vibration in alcohol before wear test. The disc with hardness of HRC55 ~ 62, diameter of 30 mm and Ra = 3.2 μm was spun perpendicular to the sample surface, and the schematic diagram is shown in The morphology of the composite powder was observed by SEM and TEM to explore the distribution of mrGO-Cu and the state of copper particles on mrGO surface.2Cu precipitate in Al particles, which means that Cu is either distributed at the boundary or the solute in Al matrix. No aggregation of graphene was observed in The friction factor of the composite with different mrGO-Cu contents is shown in Wear loss of the composites with different contents of mrGO-Cu is presented in 2O3 could easily be produced during the wear process. Therefore, it can be speculated that the white particles, as shown in 2O3. The presence of Fe (SEM results with EDS analysis  were conce of Fe b was cauThe worn surface morphologies of the sample with mrGO-Cu contents of 0 and 3 wt.% under the same conditions of friction are presented in Compared to the morphology of pure aluminum substrate in From Multilayer reduced graphene oxide was chemically modified by electroless plating Cu, and mrGO-Cu/Al composite was successfully fabricated through clad rolling of milled powder. The enhanced tribological properties of composites have been summarized as follows:The graphene lubrication film could change the mode from unlubrication friction to boundary friction. With the increase in graphene content, the friction coefficient of composite materials gradually decreased. The decrement was obvious at a lower content of mrGO-Cu. Friction coefficient of the composite with 4% of mrGo-Cu could reduce by 28.8%, and the wear loss of the composite reduced by 50% compared to pure aluminum.The mrGO-Cu played an important role of dispersion strengthening in the aluminum matrix. As the content of mrGO-Cu increased, the grain size of the composite material was refined and the hardness increased, the wear resistance of the material was improved. The wear loss of mrGO-Cu/Al composites decreased with the addition of mrGO-Cu.Under the action of shear force, the mrGO-Cu was unfolded at the wear interface. The mrGO-Cu can form a graphite lubricating film and thus reduce the adhesive wear. Wear mechanism was also dominated by adhesive wear into abrasive wear with the addition of mrGO-Cu.