Anti-carbamylated protein antibody isotype pattern differs between palindromic rheumatism and rheumatoid arthritis.
Background
A restricted response against citrullinated peptides/proteins, with less isotype usage, has been found in palindromic rheumatism (PR) in comparison with rheumatoid arthritis (RA). We hypothesized that this different antibody response may be observed for other post-translational modified proteins. We compared the prevalence and isotype usage of two specificities of anti-carbamylated peptide/protein antibodies (Anti-CarP) in patients with PR and RA.


Methods
Cross-sectional study including 54 patients with pure PR and 53 patients with RA, matched by sex, age, disease duration and ACPA. Anti-CarP specificities were determined by home-made enzyme-linked immunosorbent assay tests using a synthetic chimeric fibrin/filaggrin homocitrullinated peptide (CFFHP) and fetal calf serum (FCS) homocitrullinated protein as antigens. IgG, IgA and IgM isotypes were measured.


Results
Anti-CarP were positive (CFFHP or FCS) in 24% and 64% of patients with PR and RA, respectively (p < 0.005). All Anti-CarP isotype proportions were significantly lower in PR than in RA: Anti-CarP-IgG (24% versus 51%), Anti-CarP-IgA (7% versus 34%) and Anti-CarP-IgM (7% versus 36%). Mean titers of Anti-CarP isotypes were also lower in PR. In Anti-CarP positive patients, the isotype distribution differed between PR and RA: IgG Anti-CarP was used in all PR patients and in 79% of RA patients. By contrast, a significantly lower isotype usage of both IgA (31% versus 53%) and IgM (31% versus 56%) was observed in PR patients. No significant differences in clinical or demographic characteristics were observed according to Anti-CarP status in PR patients, except for a higher prevalence of ACPA and higher mean titers of ACPA and rheumatoid factor in Anti-CarP positive patients.


Conclusion
Anti-CarP are found in patients with PR but in a lower proportion and with a different isotype usage from in RA, suggesting a distinct B cell response to homocitrullinated antigens in PR.
['Castellanos-Moreira|Raul|R|https://orcid.org/0000-0002-4104-4101', 'Rodriguez-Garcia|Sebastian C|SC|', 'Cabrera-Villalba|Sonia|S|', 'Gomara|María José|MJ|', 'Salvador|Georgina|G|', 'Ruiz-Esquide|Virginia|V|', 'Ramirez|Julio|J|https://orcid.org/0000-0002-7047-8056', 'Inciarte-Mundo|Jose|J|', 'Morla|Rosa|R|', 'Garcia-Moreno|Cristina|C|', 'Cuervo|Andrea|A|', 'Gómez-Puerta|Jose A|JA|', 'Cañete|Juan D|JD|', 'Haro|Isabel|I|', 'Sanmarti|Raimon|R|https://orcid.org/0000-0002-8864-3806']
palindromic rheumatism rheumatoid arthritis Anti-CarP ACPA B cells autoantibodies