Pivotal Role of Signal Transducer and Activator of Transcription (Stat)4 and Stat6 in the Innate Immune Response during Sepsis

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Abstract
Signal transducer and activator of transcription (Stat)4 and Stat6 are transcription factors that provide type 1 and type 2 response, respectively. Here, we explored the role of Stat4 and Stat6 in innate immunity during septic peritonitis. Stat4−/− and Stat6−/− mice were resistant to the lethality compared with wild-type (WT) mice. At the mechanistic level, bacterial levels in Stat6−/− mice were much lower than in WT mice, which was associated with increased peritoneal levels of interleukin (IL)-12, tumor necrosis factor (TNF)-α, macrophage-derived chemokine (MDC), and C10, known to enhance bacterial clearance. In Stat4−/− mice, hepatic inflammation and injury during sepsis were significantly ameliorated without affecting local responses. This event was associated with increased hepatic levels of IL-10 and IL-13, while decreasing those of macrophage inflammatory protein (MIP)-2 and KC. Sepsis-induced renal injury was also abrogated in Stat4−/− mice, which was accompanied by decreased renal levels of MIP-2 and KC without altering IL-10 and IL-13 levels. Thus, Stat6−/− and Stat4−/− mice appeared to be resistant to septic peritonitis by enhancing local bacterial clearance and modulating systemic organ damage, respectively, via balancing cytokine responses. These results clearly highlight an important role of local type 1 and systemic type 2 cytokine response in protective immunity during sepsis, which can be regulated by Stat proteins.