The phagosome-mediated anti-bacterial immunity is governed by the proton-activated chloride channel in peritoneal macrophages.

Unlabelled: Phagosome degradation is an evolutionally conserved and highly effective innate immune response against pathogen infections. The success of this process relies on the ability of phagocytes to regulate the maturation of phagosomes. However, the underlying molecular mechanisms and its roles in shaping downstream immune activation remain poorly understood. Here, we identify the proton-activated chloride (PAC) channel as a key negative regulator of phagosome maturation. PAC deletion enhanced phagosomal acidification and protease activities, leading to augmented bacterial killing in large peritoneal macrophages (LPMs) upon peritoneal infection in mice. Surprisingly, phagosome bacterial degradation also stimulated STING-IRF3-interferon responses and inflammasome activation in LPMs, both of which are enhanced upon PAC deletion. The increased inflammasome activation and pyroptosis induced an unexpected release of cleaved gasdermin D, which localized to the surface of bacteria in the peritoneum and further contributed to their killing. Finally, enhanced bacterial clearance by PAC-deficient LPMs reduced proinflammatory immune cell infiltration and overall peritoneal inflammation, resulting in improved survival in mice. Our study thus provides new insights into the molecular mechanism of phagosome maturation and the dynamics of host defense response following phagosome-mediated bacterial degradation in peritoneal macrophages. It also highlights the potential of targeting the PAC channel as a therapeutic strategy for treating bacterial infections.

Summary: PAC channel mediates phagosome maturation during bacterial infection in macrophages. The deletion of PAC promotes phagosome-mediated interferon signaling and inflammasome-mediated gasdermin D secretion during bacterial infection in peritoneal macrophages.