Fc γ RIIb protects from reperfusion injury by controlling antibody and type I IFN-mediated tissue injury and death.

Intestinal ischemia and reperfusion (I/R) is accompanied by an exacerbated inflammatory response characterized by deposition of IgG, release of inflammatory mediators, and intense neutrophil influx in the small intestine, resulting in severe tissue injury and death. We hypothesized that Fc _γ RIIb activation by deposited IgG could inhibit tissue damage during I/R. Our results showed that I/R induction led to the deposition of IgG in intestinal tissue during the reperfusion phase. Death upon I/R occurred earlier and was more frequent in Fc _γ RIIb ^-/- than WT mice. The higher lethality rate was associated with greater tissue injury and bacterial translocation to other organs. Fc _γ RIIb ^-/- mice presented changes in the amount and repertoire of circulating IgG, leading to increased IgG deposition in intestinal tissue upon reperfusion in these mice. Depletion of intestinal microbiota prevented antibody deposition and tissue damage in Fc _γ RIIb ^-/- mice submitted to I/R. We also observed increased production of ROS on neutrophils harvested from the intestines of Fc _γ RIIb ^-/- mice submitted to I/R. In contrast, Fc _γ RIII ^-/- mice presented reduced tissue damage and neutrophil influx after reperfusion injury, a phenotype reversed by Fc _γ RIIb blockade. In addition, we observed reduced IFN-β expression in the intestines of Fc _γ RIII ^-/- mice after I/R, a phenotype that was also reverted by blocking Fc _γ RIIb. IFNAR ^-/- mice submitted to I/R presented reduced lethality and TNF release. Altogether our results demonstrate that antibody deposition triggers Fc _γ RIIb to control IFN-β and IFNAR activation and subsequent TNF release, tailoring tissue damage, and death induced by reperfusion injury.
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