Potential role of alveolar macrophages in HIV persistence and lung disease

Abstract

While antiretroviral therapy (ART) has revolutionized the management of human immunodeficiency virus (HIV) and has enabled people living with HIV (PLWH) to achieve near-normal life expectancies, an HIV cure remains elusive due to the presence of HIV reservoirs. Furthermore, compared with individuals in the general population, PLWH support a higher burden of multimorbidity, including pulmonary diseases of both an infectious and non-infection nature, which may be a consequence of the formation of HIV reservoirs. Their gut, lymph nodes, brain, testes and lungs constitute important anatomic sites for the reservoirs. While CD4+ T-cells, and particularly memory CD4+ T-cells, are the best characterized cellular HIV reservoirs, tissue resident macrophages (TRM) and alveolar macrophages (AM) also harbor HIV infection. AM are the most abundant cells in bronchoalveolar (BAL) fluid in healthy conditions, and act as sentinels in the alveolar space by patrolling and clearing debris, microbes and surfactant recycling. Long-lived tissue-resident AM of embryonic origin have the capacity of self-renewal without replenishment from peripheral monocytes. As in other tissues, close cell-cell contacts in lungs also provide a milieu conducive for cell-to-cell spread of HIV infection and establishment of reservoirs. As lungs are in constant exposure to antigens from the external environment, this situation contributes to pro-inflammatory phenotype rendering pulmonary immune cells exhausted and senescent-an environment facilitating HIV persistence. Factors such as tobacco and e-cigarette smoking, lung microbiome dysbiosis and respiratory co-infections further drive antigenic stimulation and HIV replication. HIV replication, in turn, contributes to ongoing inflammation and clonal expansion. Herein, the potential role of AM in HIV persistence is discussed. Furthermore, their contribution towards pulmonary inflammation and immune dysregulation, which may in turn render PLWH susceptible to chronic lung disease, despite ART, is explored. Finally, strategies to eliminate HIV-infected AM are discussed.