Simian Immunodeficiency Virus (SIV)/Immunoglobulin G Immune Complexes in SIV-Infected Macaques Block Detection of CD16 but Not Cytolytic Activity of Natural Killer Cells

Abstract

Natural killer cells are components of the innate immune system that play an important role in eliminating viruses and malignant cells. Using simian immunodeficiency virus (SIV) infection of macaques as a model, flow cytometry revealed a gradual loss of CD16؉ NK cell numbers that was associated with disease progression. Of note, the apparent loss of NK cells was detected in whole-blood samples but not in isolated peripheral blood mononuclear cells (PBMC), suggesting that an inhibitor(s) of the antibody used to detect CD16, the low-affinity immunoglobulin G (IgG) receptor, was present in blood but was removed during PBMC isolation. (Actual decreases in CD16؉ cell numbers in PBMC generally were not detected until animals became lymphopenic.) The putative decrease in CD16 ؉ cell numbers in whole blood correlated with increasing SIV-specific antibody titers and levels of plasma virion RNA. With the addition of increasing amounts of plasma from progressor, but not nonprogressor, macaques to PBMC from an uninfected animal, the apparent percentage of CD16

Robust NK Cell-Mediated Human Immunodeficiency Virus (HIV)-Specific Antibody-Dependent Responses in HIV-Infected Subjects

“…5D). This may be a result of the receptor's being occupied by IgG and preventing antibody binding, for example, by immune complexes (31). We confirmed that the CD56 downregulation was specific for HIV-positive donor cells by incubating serum of a separate HIV-positive subject with either autologous cells or cells from another HIV-positive donor and a HIV-negative donor.…”

IL-17-producing innate lymphoid cells are restricted to mucosal tissues and are depleted in SIV-infected macaques

“…It was previously reported that detection of CD16 on NK cells in whole blood preparations can be “masked” by non-covalent binding of SIV/IgG immune complexes when using the anti-CD16 antibody clone 3G8, which is not observed in fractionated (washed) peripheral blood mononuclear cells 21 . To identify a better antibody for detecting CD16, we compared 4 different anti-human CD16 antibody clones, which target different CD16 epitopes, which were reported to cross-react with rhesus macaques, and compared percentages of CD16+ ILCs (CD3 − CD8 high ) cells of whole blood and isolated (washed) PBMCs from chronically SIV-infected macaques.…”

“…Another NK marker, CD16, also known as FcγRIII, is important in antibody-dependent cell-mediated cytotoxicity, and is among the first of activating receptors expressed on NK cells. However, detection of CD16 with the widely used 3G8 monoclonal antibody clone has been shown to be “masked” by anti-SIV immunoglobulin G immune complexes in SIV-infected rhesus macaques, at least when using whole blood staining techniques 21 . Therefore, some prior studies may reflect misleading or incomplete definitions of NK cells in SIV-infected macaques.…”

CD16− natural killer cells: enrichment in mucosal and secondary lymphoid tissues and altered function during chronic SIV infection

“…[6][7][8] The definition of macaque NK cells as CD3 Ϫ CD16 ϩ cells in unprocessed whole blood has also been further complicated by "CD16 masking" by SIV/immunoglobulin G immune complexes, a phenomenon not observed in fractionated peripheral blood mononuclear cells (PBMCs). 9 We have previously identified macaque NK cells as CD3 Ϫ CD8␣␣ ϩ CD20 Ϫ/dim NKG2A ϩ cells, and determined that whereas the major NK-cell subpopulation is indeed CD16 ϩ CD56 Ϫ/dim , 2 minor populations, CD16 Ϫ/dim CD56 hi and CD16 Ϫ CD56 Ϫ NK cells also exist in peripheral blood of rhesus macaques. 10 This phenotypic definition of nonhuman primate NK cells has been verified in rhesus macaques by another group and also shown to apply to sooty mangabeys.…”