Plays a key role in the innate immune response following bacterial infection by inserting into the bacterial surface to form pores (PubMed:26402460). By breaching the surface of phagocytosed bacteria, allows antimicrobial effectors to enter the bacterial periplasmic space and degrade bacterial proteins such as superoxide dismutase sodC which contributes to bacterial virulence (PubMed:30249808). Shows antibacterial activity against a wide spectrum of Gram-positive, Gram-negative and acid-fast bacteria (PubMed:23257510, PubMed:23753625, PubMed:26402460). Reduces the viability of the intracytosolic pathogen L.monocytogenes by inhibiting acidification of the phagocytic vacuole of host cells which restricts bacterial translocation from the vacuole to the cytosol (PubMed:26831467). Required for the antibacterial activity of reactive oxygen species and nitric oxide (PubMed:26402460). Bacterial infection induces translocation of the cytoplasmic vesicles to bacterium-containing phagocytic vesicles and fusing of the vesicles. Expressed constitutively in a variety of cell types including macrophages, microglia, neutrophils, T cells, marginal zone B cells, keratinocytes, splenocytes and intestinal epithelial cells. By CSF1 in fetal liver macrophages (PubMed:7888681). By interferon-alpha, by interferon-beta, by interferon-gamma and by bacterial infection with E.coli and M.smegmatis in embryonic fibroblasts (PubMed:23257510). Monoubiquitinated in response to bacterial infection; ubiquitination is required for vesicular localization and antibacterial activity and can be blocked by bacterial cell cycle inhibiting factor (cif) (PubMed:26418746). Inability of neutrophils and phagocytes to kill pathogenic bacteria including M.smegmatis, M.avium and M.tuberculosis (PubMed:26402460). Decreased survival following epicutaneous infection with methicillin-resistant S.aureus or orogastric infection with S.typhimurium in contrast to wild-type littermates which clear the infections (PubMed:26402460). Rapid development of listeriosis following L.monocytogenes infection with mutants showing increased bacterial burden and increased serum levels of inflammatory cytokines in contrast to wild-type mice which show no signs of the disease (PubMed:26831467). Belongs to the MPEG1 family.