XXXX , immunity, and inflammation.

@entity1 @entity1200 @entity904 @entity1968
@entity904 (also called @entity904 ), absorbed in the intestine and stored mainly in the liver and fat, is normally maintained at significant concentrations in the @entity1 blood plasma. @entity904 is constitutively metabolized at high levels in certain tissues such as the small intestine and eyes. @entity1968 (RA) produced at high levels in the intestine plays important roles in @entity1200 and immune tolerance. RA at basal levels is required for immune cell survival and activation. During immune responses, enzymes metabolizing @entity904 are induced in certain types of immune cells such as dendritic cells (DCs) and tissue cells for induced production of RA. As a result, induced gradients of RA are formed during immune responses in the body. RA regulates gene expression, differentiation, and function of diverse immune cells. The cells under the influence of RA in terms of differentiation include myeloid cells such as neutrophils, macrophages, and DCs. Also included are lymphoid cells such as effector T cells, regulatory T cells, and B cells. Our current understanding of the function of RA in regulation of these immune cells is reviewed in this chapter.
