HIV-1/mycobacterium tuberculosis coinfection immunology: how does HIV-1 exacerbate tuberculosis?

Abstract

Human immunodeficiency virus type 1 (HIV) and Mycobacterium tuberculosis have become intertwined over the past few decades in a "syndemic" that exacerbates the morbidity and mortality associated with each pathogen alone. The severity of the coinfection has been extensively examined in clinical studies. The extrapolation of peripheral evidence from clinical studies has increased our basic understanding of how HIV increases susceptibility to TB. These studies have resulted in multiple hypotheses of how HIV exacerbates TB pathology through the manipulation of granulomas. Granulomas can be located in many tissues, most prominently the lungs and associated lymph nodes, and are made up of multiple immune cells that can actively contain M. tuberculosis. Granuloma-based research involving both animal models and clinical studies is needed to confirm these hypotheses, which will further our understanding of this coinfection and may lead to better treatment options. This review examines the data that support each hypothesis of how HIV manipulates TB pathology while emphasizing a need for more tissue-based experiments.

FIG. 1.

Proposed mechanism of HIV-induced reactivation of latent TB. (Stage 1) Necrotic granuloma functioning “normally” in an individual with latent TB. (Stage 2) HIV enters the granuloma and induces functional changes within T cells and macrophages. HIV also kills activated T cells. (Stage 3) The decrease in T cell number and increase in cellular dysfunction lead to a functional disruption of the granuloma. This may lead to increased dissemination. (Stage 4a) Granulomas functionally disrupted shortly after HIV infection leads to continued M. tuberculosis dissemination and early TB reactivation. (Stage 4b) Fibrotic granulomas temporarily reestablish granuloma containment, which prevents reactivation.