Effect of NKG2C absence on natural killer cell phenotype and function in human immunodeficiency virus/cytomegalovirus co-infection

Abstract

Natural killer (NK) cells expressing NKG2C and CD57 expand following human cytomegalovirus (CMV) infection. This NK cell subset downregulates FcεR1γ and acquires enhanced capacity to mediate antibody-dependent cellular cytotoxicity (ADCC). Expansion of these differentiated NK cells is exaggerated in human immunodeficiency virus (HIV) infection. Individuals lacking the gene encoding NKG2C have diminished resistance to HIV, but it remains unclear whether differentiation into NK cells with superior ADCC is impaired in NKG2Cnull individuals. Therefore, our objective was to investigate if CMV-driven NK cell differentiation into enhanced killers is impaired in NKG2Cnull HIV-infected individuals. Phenotypic (CD57⁺, FcεR1γ⁻) and functional (IFN-γ, TNF-α induction and cytotoxicity) NK cell responses were compared between NKG2Cnull and matched NKG2C-expressing individuals by flow cytometry following stimulation through natural cytotoxicity receptors (using K562 cells) or CD16 (using monoclonal antibody, 3G8). Cytotoxicity was measured in ⁵¹Chromium release assays against anti-CD16-coated P815 cells (redirected lysis) and anti-human leukocyte antigen (HLA) class I antibody-coated C1R cells (classical ADCC). Antibodies were titrated to determine concentrations producing half maximal responses (EC₅₀) to compare sensitivity. Our data indicate highly similar CMV-driven NK cell differentiation in terms of both general phenotype and function, regardless of NKG2C genotype. The observed equivalency between groups suggests alternate routes of CMV-driven NK cell differentiation, which are independent of NKG2C.