IL4 and Arthritis: Protective effects on the clinical and immunopathological features of rheumatoid arthritis by reducing serum IL-17 and increasing IFN-r and IL-10. Reduces collagen-induced arthritis by downregulation of the Th1 (IFN-r) response and pro-inflammatory cytokines (TNF-α and IL-17A), and upregulation of the Th2 (IL-4) response and an anti-inflammatory cytokine (IL-10).