In particular the crucial role of NF-AT detected herein may form the basis of direct action of CsA on IL-22 expression by T cells, which may contribute to therapeutic efficacy of the drug in autoimmunity.
Interleukin 22 (IL-22), a relatively new cytokine has been found to induce significant proliferation of human keratinocytes and fibroblast like synoviocytes (FLS) and thus plays an important role in the pathogenesis of autoimmune diseases like psoriasis and rheumatoid arthritis (RA) which are characterized by hyperproliferation of keratinocytes and FLS respectively.
Using a mouse model for multiple sclerosis, here we show that B10-cell maturation into functional IL-10-secreting effector cells that inhibit in vivo autoimmune disease requires IL-21 and CD40-dependent cognate interactions with T cells.
Taken together, SLV appears to be a Th1-polarized autoimmune disease, whereby IFN-γ expression is strongly associated with parallel increases in IL-10 and IL-21, particularly during early and active stages of SLV.
IL-21 is therefore an autocrine cytokine that regulates human Th17 cells in rheumatoid arthritis, and serves as a good target for treating this autoimmune disease.
Co-expression of IL-22 and IL-17 has been identified and demonstrated to be involved in the immunopathogenesis of some autoimmune diseases as well as the defense against pathogenic infections in animal studies.
We propose that, by driving cycles of T cell expansion and apoptosis to excess, IL-21 increases the stochastic opportunities for T cells to encounter self antigen and, hence, for autoimmunity.
Also, the studies on the production of IL-21 in human autoimmune diseases and its behaviour on human cells in vitro are revealing the potential of IL-21 to exacerbate cellular processes that determine the course of autoimmune diseases.
Finally, BXSB-Yaa mice, which develop a systemic lupus erythematosus-like disease, have greatly elevated IL-21, suggesting a role for IL-21 in the development of autoimmune disease.