IL17A and rheumatoid arthritis: For example, Th1 and Th2 cells inhibit osteoclastogenesis through the production of IFN-γ and IL-4, while Th17 cells induce osteoclast formation and osteolysis in rheumatoid arthritis (RA) via the IL-17-mediated induction of RANKL expression on synovial fibroblasts [9, 62].