The characteristic Th subpopulations in RA are Th1, Th17, Th22, and Treg, exhibiting considerable flexibility and plasticity in patients and producing significant amounts of inflammatory cytokines (IL-1, IL-6, IL-12, IL-17, and IFNγ), while Treg cells are responsible for controlling the pathological immune response by producing IL-10 and TGF-β [21,22]. Here, IL17A is linked to rheumatoid arthritis.