Complement receptor type 3 mediates phagocytosis and killing of Listeria monocytogenes by a TNF-α- and IFN-γ-stimulated macrophage precursor hybrid

Previous work demonstrated that engagement of complement receptor type 3 (CR3) was required for inflammatory peritoneal macrophages to phagocytose and kill the facultative intracellular bacterium Listeria monocytogenes. The experiments described here tested the role of CR3 in phagocytosis and killing of Listeria by a clonal population of TNF-α/IFN-γ-stimulated macrophage precursor hybrids. Stimulation with TNF-α and IFN-γ increased CR3 expression 20 fold and induced a big increase in phagocytic activity. Phagocytosis and killing of Listeria by these cells were inhibited when bacteria were opsonized with complement depleted serum or by incubation of the macrophages with anti CR3 mAb, Furthermore, cytokine stimulated macrophages could not kill Listeria opsonized with heat-inactivated anti-Listeria antiserum, indicating that macrophage receptors which mediate phagocytosis do not necessarily promote bactericidal activity. These data suggest that upregulation of CR3 and CR3 mediated phagocytosis are mechanisms by which TNF-α and IFN-γ stimulate nonphagocytic, nonbactericidal macrophage precursors to kill intracellular bacterial pathogens.