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

Phagosome-mediated degradation is a well-conserved and highly effective innate immune response against pathogen infections. However, its role in shaping immune responses remains underappreciated. The molecular mechanisms underlying how phagosomes mature are also poorly understood. Here, we identify proton-activated chloride (PAC) channel as a key negative regulator of phagosome maturation. PAC deletion facilitates phagosomal acidification and protease activation, leading to augmented bactericidal activity in peritoneal macrophages upon Escherichia coli infection. Moreover, enhanced phagosome bacterial degradation in PAC-deficient macrophages promotes downstream STING-IRF3 activation and type 1 interferon (IFN) responses through the release of bacterial ligands. Such ligand release also activates the inflammasome, leading to gasdermin D (GSDMD) cleavage and secretion. The secreted N-terminus GSDMD directly participates in bacterial killing by forming GSDMD pores on bacterial surfaces. Eventually, this macrophage hyperactivation is terminated by pyroptotic cell death. In mice, PAC deletion in macrophages reduced overall peritoneal inflammation and proinflammatory neutrophil and monocyte infiltrations, as well as improved survival after peritoneal infection. Our study thus provides new insights into mechanisms of phagosome maturation and the dynamics of host defense response following phagosome-mediated bacterial degradation.