Interferon-γ Listericidal Action Is Mediated by Novel Rab5a Functions at the Phagosomal Environment*

Control and clearance of Listeria monocytogenesinfection is an interferon-γ-dependent process. The listericidal mechanism of action involves activation of NADPH oxidase and inducible nitric-oxide synthase to produce reactive oxygen and nitrogen intermediate radicals, respectively. Recently, we have described in a nonpathogenic model of L. monocytogenes(hemolysin negative mutant strain) that the interferon-γ-inducible GTPase Rab5a contributed to Listeriadestruction in resting macrophages. Here, we report in a pathogenic model of L. monocytogenes(hemolysin-positive strain) that Rab5a plays a central role inListeriadestruction induced by interferon-γ and within the phagosomal environment. These findings reveal the importance of Rab5a as the responsible factor mediating the listericidal action of interferon-γ. Active Rab5a causes remodeling of the phagosomal environment, facilitates the translocation of Rac2 to LM phagosomes, and regulates the activity of this GTPase. Rac2 activation and translocation governs the phagocyte NADPH oxidase activity and the consequent reactive oxygen intermediate production that leads to killing of the pathogen.