A Quantitative Approach to SIV Functional Latency in Brain Macrophages

Abstract

Lentiviruses are retroviruses that primarily infect myeloid cells, leading to acute inflammatory infections in many tissues particularly, lung, joints and the central nervous system (CNS). Acute infection by lentiviruses is followed by persistent/latent infections that are not cleared by the host immune system. HIV and SIV are lentiviruses that also infect CD4+ lymphocytes as well as myeloid cells in blood and multiple tissues. HIV infection of myeloid cells in brain, lung and heart cause tissue specific diseases as well as infect cells in gut, lymph nodes and spleen. AIDS dementia and other tissue specific disease are observed when infected individuals are immunosuppressed and the number of circulating CD4+ T cells declines to low levels. Antiretroviral therapy (ART) controls viral spread and dramatically changes the course of immunodeficiency and AIDS dementia. However, ART does not eliminate virus-infected cells. Brain macrophages contain HIV DNA and may represent a latent reservoir that persists. HIV latency in CD4+ lymphocytes is the main focus of current research and concern in efforts to eradicate HIV. However, a number of studies have demonstrated that myeloid cells in blood and tissues of ART suppressed individuals harbor HIV DNA. The resident macrophages in tissues such as brain (microglia), spleen (red pulp macrophages) and alveolar macrophages in lung are derived from the yolk sac and can self renew. The question of the latent myeloid reservoir in HIV has not been rigorously examined and its potential as a barrier to eradication been considered. Using a well characterized SIV ART suppressed, non-human primate (NHP) model, our laboratory developed the first quantitative viral outgrowth assay (QVOA) designed to evaluate latently infected CD4+ lymphocytes and more recently developed a similar protocol for the assessment of latently infected myeloid cells in blood and brain. Using an SIV ART model, it was demonstrated that myeloid cells in blood and brain harbor latent SIV that can be reactivated and produce infectious virus in vitro. These studies demonstrate for the first time that myeloid cells have the potential to be a latent reservoir of HIV that produces infectious virus that can be reactivated in the absence of ART and during HIV eradication strategies. Graphical Abstract.

Keywords: ART; HIV; Latent reservoir; QVOA; SIV.

Figure 1.

MΦ-QVOA. Monocytes from blood and macrophages from brain were collected from SIV-infected animals and purified by CD11b-specific bead selection. Macrophages expressing CD11b were plated in serial dilutions in triplicate wells. Cells were cultured with zidovudine (AZT) and darunavir (DRV). Nonadherent cells and the antiretrovirals were removed prior to activation with TNF and co-culture with CEMx174 cells (85, 94).

Figure 2.

Quantitation of latently infected brain macrophages in ART-treated macaques by MΦ-QVOA. Quantitation of infected brain macrophages from ART-treated macaques (85). Comparison between the numbers of SIV-infected brain macrophages isolated from animals that were not given ART (-ART) and the numbers isolated from animals that were treated with ART and with viral suppression <10 copies SIV RNA/ml plasma. The horizontal black line represents the median IUPM values. The MΦ QVOA results from SIV-infected animals with and without ART have been reported (85, 94). Significance was determined by Mann-Whitney nonparametric t test; a P of <0.05 was considered significant.