IL17A and rheumatoid arthritis: Accumulating scientific evidence shows that interleukin 17 (IL-17) and IL-17-producing T helper (Th17) cells play critical roles during the development and progression of RA.2, 3 Although the exact pathogenesis of RA remains unclear, data from experimental models suggest that IL-17 plays a role in pannus growth,4 structural destruction of rheumatoid joints through receptor activator of nuclear factor κB ligand-independent osteoclastogenesis,5 and synovial neoangiogenesis.6