227: IL-27 affects helper T cell response via regulation of PGE2 production by macrophages
IL-27 is a heterodimeric cytokine that regulates both innate and adaptive immunity. Although IL-27 was initially reported as a Th1 inducer by the induction of IL-12R on naive CD4+T cells, recently it is revealed that IL-27 acts as an immune suppressor by the induction of Tr1 type T cells, which produce IL-10 and inhibit effector T cells. IL-27 also suppresses function of macrophages and dendritic cells by regulation of cytokine secretion. On the other hand, effects of IL-27 on regulation of inflammation via mediators other than cytokines remain poorly understood. To address this issue, we examined immunoregulatory effects of conditional medium of bone marrow-derived macrophages (BMDMs) from WSX-1 (IL-27Ra) KO mice to find enhanced IFN-g and IL-17A secretion by CD4+T cells as compared with that of control BMDMs. This enhancement was abolished by EP2 and EP4 antagonist, suggesting possible involvement of prostaglandins. We then found the PGE2 secretion and COX-2 expression by BMDMs from WSX-1 KO mice was increased compared to control macrophages in response to LPS. To explore how IL-27/WSX-1 signal regulate COX-2/PGE2 production, murine WSX-1-expressing Raw264.7 cells (mWSX-1-Raw264.7) were established. mWSX-1-Raw264.7 showed phosphorylation of both STAT1 and STAT3 in response to IL-27 and produced less amounts of PGE2 and COX-2 compared to parental Raw264.7. Finally, to examine whether STAT1 and STAT3 downstream of IL-27R regulate PGE2 and COX-2 production, siRNA knockdown study was performed and siSTAT1, but not siSTAT3, resulted in increased production of PGE2 and COX-2. In addition, BMDMs from STAT1 KO mice showed higher COX-2 expression than those from control mice. Collectively, our result indicated that IL-27/WSX-1 regulated PGE2 secretion via STAT1-COX-2 pathway in macrophages and affected helper T cells response in a PGE2-mediated indirect fashion.