Natural killer lytic-associated molecule is a component of macrophage phagosomes and contributes to bacterial killing (117.23)

Abstract

Abstract Macrophages are a critically important component of the immune system. They are equipped with oxidative and non-oxidative mechanisms to kill pathogens that have been compartmentalized into phagosomes following phagocytosis. Ubiquitin, a small protein modifier that regulates protein degradation, has been found to play a role in macrophage bacterial killing. Natural killer lytic-associated molecule (NKLAM) is an E3 ubiquitin ligase expressed in macrophages and natural killer cells. We have shown that NKLAM expression in macrophages is enhanced by Toll-like receptor agonists and pro-inflammatory cytokines. Using bone marrow-derived macrophages from wild type (WT) and NKLAM-deficient mice we found the levels of phagocytosis and phagosome acidification to be similar; however, killing of E. coli by NKLAM-deficient macrophages is less than by WT macrophages. Using confocal immunofluorescence microscopy, we found that NKLAM is colocalized with ingested bacteria. In assays using IgG-opsonized latex beads as targets, we demonstrated that NKLAM is translocated to the phagosome early in the maturation process. In addition, the presence of NKLAM in the phagosome temporally coincides with increased levels of ubiquitin. Collectively, our data demonstrate that NKLAM is a novel component of macrophage phagosomes and that NKLAM is involved in macrophage bactericidal functions.