Alveolar macrophages as a cell source of cytokine hyperproduction in HIV-related interstitial lung disease

Pulmonary macrophages play an important role in the pathogenesis of the acquired immunodeficiency syndrome (AIDS). They are known to be discrete target cells for human immunodeficiency virus (HIV), and compelling evidence is accumulating that alveolar macrophages (AMs) from HIV-infected patients behave as versatile secretory cells that, acting as antigen-presenting cells, release a great variety of cytokines. The secretory products of AMs, pivotal to their immune effects, may contribute to localized immune dysregulation as well as to primary lung damage and clinical disease. Pulmonary macrophages are also thought to facilitate retroviral spread by their direct infection, by presenting HIV antigens to uninfected T cells, and by secreting cytokines that transactivate HIV expression. This review briefly considers the events underlying the role of AMs in the pulmonary defense mechanisms against HIV and AIDS-related opportunistic infections. Following a brief overview of immune mechanisms taking place in the lungs of HIV-infected subjects, we describe the specific role of AMs in the immune mechanisms devoted to recognizing and removing HIV-infected cells and controlling the local growth of opportunists. The pathogenetic role envisaged for macrophages in lung damage are also reviewed in the context of the known biology of these cells. Finally, this review examines the relevance of the retroviral infection of AMs in terms of pathogenesis of the HIV-related interstitial lung disease.