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Published online before print July 6, 2005

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(Journal of Leukocyte Biology. 2005;78:675-685.)
© 2005 by Society for Leukocyte Biology

HLA-A2 down-regulation on primary human macrophages infected with an M-tropic EGFP-tagged HIV-1 reporter virus

Amanda Brown^*,,1, Suzanne Gartner^*, Thomas Kawano, Nicole Benoit^* and Cecilia Cheng-Mayer

^* Johns Hopkins University School of Medicine, Department of Neurology, Baltimore, Maryland; and
Aaron Diamond AIDS Research Center, The Rockefeller University, New York, New York

¹Correspondence: Johns Hopkins University School of Medicine, Department of Neurology, Meyer 6-181, 600 North Wolfe Street, Baltimore, MD 21287. E-mail: abrown76{at}jhmi.edu

Multiple mechanisms are used by the human immunodeficiency virus type 1 (HIV-1) to interfere with host-cell immune effector functions. The 27-kD Nef protein has been shown to down-modulate specific genes of the major histocompatibility complex class I (MHC-I) on the surface of infected primary T cells, facilitating their escape from lysis by cytolytic T lymphocytes. Macrophages, as the other major immune cell type targeted by the virus, also contribute to the transmission, persistence, and pathogenesis of HIV-1. Yet, whether Nef modulates MHC-I expression on HIV-infected primary macrophages remains unclear. Currently available infectious HIV-1 molecular clones, which express a reporter gene, only infect T cells and/or do not express Nef. To overcome these limitations, we generated macrophage-tropic green fluorescent protein (GFP)-tagged HIV-1 viruses, which express the complete viral genome, and used these to assess the expression of human leukocyte antigen (HLA)-A2 on the surface of productively infected macrophages. The reporter viral genomes were replication-competent and stable, as Nef, p24 antigen, and GFP expression could be detected by immunostaining of infected, monocyte-derived macrophages (MDM) after more than 2 months postinfection. Fluorescence-activated cell sorter analyses of infected macrophages and T cells revealed that although wild-type reporter virus infection induced a statistically significant decrease in the density of surface HLA-A2, down-regulation of HLA-A2 was not seen in cells infected with reporter viruses encoding a frameshift or a single point mutation in Nef at prolines ⁷⁴P and P⁸⁰. The impact of Nef on HLA-A2 surface expression in MDM was also confirmed by confocal microscopy. These results suggest that the mechanisms of HLA-A2 down-modulation are similar in primary T cells and macrophages.

Key Words: Nef • MHC • confocal microscopy • immunofluorescence

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