Mycobacterium tuberculosis and HIV co-infection in the lung: synergic immune dysregulation leading to disease progression.

There is evidence that Mycobacterium tuberculosis (Mtb) impacts on human immunodeficiency virus (HIV) infection and that HIV promotes mycobacterial diseases. Epidemiological and clinical studies demonstrate the detrimental effect of tuberculosis (TB) on the progression of HIV infection, that is an increased risk of death among Mtb-HIV co-infected patients. Pulmonary TB may occur very early during HIV infection, whereas extrapulmonary or atypical manifestations are associated with more profound immunodeficiency, showing features like mycobacteraemia and multi-drug resistance, much more severe than in immunocompetent hosts. During the last decade, many efforts have been focused on the immunological aspects of Mtb-HIV co-infection. The host protective response to TB is mediated by cell immunity, which, mainly supported by interleukin (IL)-12 and interferon (IFN)-gamma production, leads to granuloma formation. Perturbations in the cytokine expression, that is a reduced type-1-like response, have been suggested in HIV-infected patients to contribute to their susceptibility to TB. Indeed, an impaired balance between pro-inflammatory and anti-inflammatory cytokines and apoptosis-induced depletion of immune effector cells account for the dissemination of both the pathogens and for a poor granulomatous reaction in Mtb-HIV co-infected patients. However, the recently elucidated role of chemokines and their receptors in immune regulation opens new questions on the pathogenesis of Mtb-HIV co-infection.