Importantly, age-related and infection-induced differentiation of human NK cells results in progressive loss of cytokine-responsive cells and concomitant accumulation of cells that are highly adapted to activation by immune complexes (termed “adaptive” CD57+NKG2C+ or CD57+FcεRγ− NK cells), suggesting that the response to vaccination may vary with age and environmental exposures to infection, in particular human cytomegalovirus19,20. This evidence concerns the gene KLRC2 and infection.