We demonstrate the potentiating influence of synovial IL-9 on the IL-17+ CD4 T cells derived from RA affected joints, evidenced by their increased production of IL-17(Fig. 5c), upregulation of Th17 related transcription factor expression RORγt (Fig. 4c) and phosphorylation of STAT3 with nuclear translocation (Fig. 6a, c). Here, STAT3 is linked to rheumatoid arthritis.