Introduction: HIV-infected macrophages form reservoirs in tissues of people living with HIV on antiretroviral therapy. The use of natural killer (NK) cell-mediated antibody-dependent cellular cytotoxicity (ADCC) is a promising approach to eliminating HIV-infected cells. ADCC requires antibody opsonisation of HIV envelope (Env) expressed on infected cells and is influenced by the interaction between ligands on the target cells with activating and inhibitory receptors expressed on NK cells. The nature and kinetics of HIV infection in macrophages is different to that in T cells, which may influence the expression of both HIV proteins and cellular HLAs, and subsequently NK cell recognition. However, it is unknown how expression of Env, or ligands that can modulate NK recognition (e.g. HLAs), changes during HIV infection in macrophages.
Methods: Monocyte-derived macrophages from HIV- blood donors were infected in vitro with HIV (BaL and AD8 strains) and synchronised using an HIV fusion inhibitor on day 3 post-infection. Productive infection (indicated by intracellular HIVp24 protein expression) and surface expression of Env/CD4/HLA-ABC/HLA-E on MDM were quantified using flow cytometry at various stages post-infection.
Results: Env was detected on the surface of HIV+ macrophages using the antibodies PGT151/NIH45-46 as early as 3 days post-infection and peaked at 7-10 days (mean=42%/26%, p=0.03 compared to p24 which did not plateau during this period). HIV+ MDM downregulated surface expression of CD4 and HLA-ABC relative to bystander (p24-) cells (p<0.02, days 3/7/10) but upregulated expression of HLA-C (p<0.05, days 3/7/10) and HLA-E. HIV-induced upregulation of HLA-C and HLA-E was specific to HIV+ macrophages and was not seen on T cells.
Discussion and Conclusions: Increased Env expression on HIV+ macrophages over time suggests higher susceptibility to antibody opsonisation and thus ADCC at later stages of infection. HLA downregulation on HIV+ MDM suggests susceptibility to NK cell recognition. However, specific upregulation of HLA-C/E in HIV+ macrophages may impair this response. Furthermore, increased HLA-C/E expression on macrophages could affect which types of NK cells recognise HIV-infected macrophages compared to T cells. Together these data indicate that HIV-infected macrophages are a dynamic reservoir that modulates ligands which may influence their ability to be targeted by NK cells.