NKG2C Sequence Polymorphism Modulates the Expansion of Adaptive NK Cells in Response to Human CMV

A subpopulation of NK cells with distinctive phenotype and function differentiates and expands specifically in response to infection by human cytomegalovirus (HCMV). A hallmark of these adaptive NK cells is their increased expression levels of the activating CD94/NKG2C receptor for HLA-E, and lack of expression of its inhibitory homologue CD94/NKG2A. Their frequency is highly variable in HCMV⁺ individuals, and the basis for such differences is only partially understood. Here, we explore the possible influence of sequence polymorphism of the NKG2C (or KLRC2) gene on the expansion of NKG2C⁺NKG2A^- NK cells in healthy HCMV-seropositive donors. Our results show a significant association of greater proportions of adaptive NK cells with allele NKG2C*02. This is defined by two amino acid substitutions in comparison with the most prevalent allele, NKG2C*01, and associates with additional sequence polymorphisms in noncoding regions. Furthermore, we demonstrate consistently higher mRNA levels of NKG2C*02 in heterozygous individuals co-expressing this allele in combination with NKG2C*01 or *03. This predominance is independent of polymorphisms in the promoter and 3' UTRs and is appreciated also in HCMV-seronegative donors. In summary, although additional factors are most likely implicated in the variable expansion of NKG2C⁺NKG2A^- NK cells in response to HCMV, our results demonstrate that host immunogenetics, in particular NKG2C diversity, influences the magnitude of such response.