NF-κB activation controls phagolysosome fusion-mediated killing of mycobacteria by macrophages

Macrophages can potentially kill all mycobacteria by poorly understood mechanisms. In this study, we explore the role of NF-kappa B in the innate immune response of macrophages against Mycobacterium smegmatis, a nonpathogenic mycobacterium efficiently killed by macrophages, and Mycobacterium avium which survives within macrophages. We show that infection of macrophages with M. smegmatis induces an activation of NF-kappa B that is essential for maturation of mycobacterial phagosomes and bacterial killing. In contrast, the pathogenic M. avium partially represses NF-kappa B activation. Using microarray analysis, we identified many lysosomal enzymes and membrane-trafficking regulators, including cathepsins, LAMP-2 and Rab34, were regulated by NF-kappa B during infection. Our results argue that NF-kappa B activation increases the synthesis of membrane trafficking molecules, which may be rate limiting for regulating phagolysosome fusion during infection. The direct consequence of NF-kappa B inhibition is the impaired delivery of lysosomal enzymes to M. smegmatis phagosomes and reduced killing. Thus, the established role of NF-kappa B in the innate immune response can now be expanded to include regulation of membrane trafficking during infection.