EGF and rheumatoid arthritis: STAT3 is activated by many cytokines and growth factors such as the IL-6 family of cytokines (IL-6, IL-11, leukemia inhibitory factor, and oncostatin M), platelet-derived growth factor, and epidermal growth factor, in addition to IL-10 [4], but previous studies have demonstrated that IL-6 is the major factor in RA synovial fluid that induces constitutive activation of STAT3 in mononuclear cells [31].