A role for STAT3 and cathepsin S in IL-10 down-regulation of IFN-γ-induced MHC class II molecule on primary human blood macrophages

IL-10, a potent anti-inflammatory cytokine, activates its primary mediator STAT3 to exert inhibitory effects on activated immune response. It has been reported that IFN-γ signaling can be suppressed by IL-10, which deactivates macrophages and suppresses cell-mediated antigen presentation. Cathepsin S, a cysteine protease, plays a significant role in the antigen processing. We hypothesize that the IL-10-induced and STAT3-mediated signaling pathway interferes with IFN-γ-induced immune responses in primary human blood macrophages. Here, we investigated whether IL-10 perturbs MHC-II levels via its effect on cathepsin S expression in antigen processing. We showed that the expression of cathepsin S and MHC-II, inducible by IFN-γ, was downregulated in the presence of IL-10. Additionally, we revealed that the inhibitory effect of IL-10 was demonstrated to be independent of the classical IFN-γ-induced JAK2/STAT1 signaling cascade or the NF-κB pathway. Following STAT3 suppression with specific siRNA, the expression of IFN-γ-induced surface MHC-II antigens and cathepsin S levels was restored, even in the presence of IL-10. Taken together, our results demonstrated that the immunosuppressive effects of IL-10-STAT3 on MHC-II antigen presentation may occur via the inhibition of cathepsin S expression. © Society for Leukocyte Biology.link_to_OA_fulltex