Mechanisms of reactivation of latent tuberculosis infection due to SIV co-infection.

HIV is a major driver of tuberculosis (TB) reactivation. Depletion of CD4(+) T cells is assumed to be the basis behind TB reactivation in individuals with latent tuberculosis infection (LTBI) coinfected with HIV. Nonhuman primates (NHPs) coinfected with a mutant simian immunodeficiency virus (SIV Delta GY) that does not cause depletion of tissue CD4(+) T cells during infection failed to reactivate TB. To investigate the contribution of CD4(+) T cell depletion relative to other mechanisms of SIV-induced reactivation of LTBI, we used CD4R1 antibody to deplete CD4(+) T cells in animals with LTBI without lentiviral infection. The mere depletion of CD4(+) T cells during LTBI was insufficient in generating reactivation of LTBI. Instead, direct cytopathic effects of SIV resulting in chronic immune activation, along with the altered effector T cell phenotypes and dysregulated T cell homeostasis, were likely mediators of reactivation of LTBI. These results revealed important implications for TB control in HIV-coinfected individuals.