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 (ΔStat3) 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 ΔStat3 blocked the anti‐proliferative activity of IL‐10. For macrophage de‐activation responses, hIL10R‐Tyr FF could not mediate inhibition of lipopolysaccharide‐induced TNFα, IL‐1β or CD86 expression, while ΔStat3 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.