IL-10 inhibits macrophage activation and proliferation by distinct signaling mechanisms: evidence for Stat3-dependent and -independent pathways

Interleukin-10 (IL-10) limits inflammatory responses by inhibiting macrophage activation, In macrophages, IL-10 activates Stat1 and Stat3. We characterized IL-10 responses of the J774 mouse macrophage cell line, and of J774 cells expressing wild-type hIL-10R, mutant hIL-10R lacking two membrane-distal tyrosines involved in recruitment of Stat3 (hIL-10R-Tyr(FF)), a truncated Stat3 (Delta Stat3) which acts as a dominant negative, or an inducibly active Stat3-gyraseB chimera (Stat3-GyrB). A neutralizing anti-mIL-10R monoclonal antibody was generated to block the function of endogenous mIL-10R, IL-10 inhibited proliferation of J774 cells and of normal bone marrow-derived macrophages, but not J774 cells expressing hIL-10RTyr(FF), Dimerization of Stat3-GyrB by coumermycin mimicked the effect of IL-10, and expression of Delta Stat3 blocked the anti-proliferative activity of IL-10, For macrophage de-activation responses, hIL10R-Tyr(FF) could not mediate inhibition of lipopolysaccharide-induced TNF alpha, IL-1 beta or CD86 expression, while Delta Stat3 did not interfere detectably with these IL-10 responses, Thus signals mediating both anti-proliferative and macrophage de-activation responses to IL-10 require the two membrane-distal tyrosines of IL-10R, but Stat3 appears to function only in the anti-proliferative response.