CD4 and tuberculosis: Cellular-mediated immunity (CMI), in particular CD4+ T cells, are unequivocally important in restricting tuberculosis progression, and are seen as the primary immunologic axis mediating host immunity to Mtb. Both CD4 knock-out studies in animal models (7–9), as well as epidemiologic data documenting increased rates of active disease among HIV-infected patients with low CD4+ T cell counts (10, 11), clearly demonstrate the lack of bacterial control in the absence of this pivotal immune effector.