IL17A and rheumatoid arthritis: In summary, this study not only corroborates findings in our previous study and those in animal model and fibroblast-like synoviocytes of RA that higher frequencies of IL-22+CD4+T cells and plasma IL-22 level served as bio-markers reflecting the disease activity and might critically promote RA development, but also reveals, for the first time, that targeting these immune components, particularly circulating Th22, Th17 cells and cytokines (IL-22 and IL-17) produced by these cells, may significantly benefit RA therapy.