The Ly49G2 inhibitory receptor is essential to MHC I-dependent NK cell control of murine cytomegalovirus infection

Abstract

Abstract Licensed Ly49G2+NK cells mediate H-2Dk-dependent control of murine cytomegalovirus (MCMV) in NK gene complex (NKC)C57L mice. However, a precise role for the Ly49G2 inhibitory receptor in Dk-dependent MCMV control is not defined. Thus, we generated Ly49g2C57L mutant mice via CRISPR/Cas9 gene-editing. A single cytosine insertion resulted in Ly49G2 truncation and undetectable NK cell surface expression. Ly49G2null mice exhibited increased mortality due to abrogated MCMV control by NK cells, despite an otherwise unmodified Ly49 repertoire and normal NK cell development. We further found Dk-dependent MCMV control requires Ly49R signaling, as blocking the activation receptor prior to infection resulted in rapid MCMV spread. Coincident with MCMV control, Ly49R+Ly49G2+ (R+G2+) NK cells were more frequently Klrg1hi, CD27−CD11b+, and CD62Llo than their Ly49R+ (R+) counterparts, and this effect was Dk-dependent. R+G2+ NK cells likewise out proliferated R+ NK cells in infected Ly49G2wt mice. NK cell subset activation and proliferation differences suggested impaired virus control in Ly49G2null mice might result from inept target cell sensing or poor NK cell expansion. To verify a role for Dk-licensed NK cells, we examined donor NK cells after adoptive transfer to NK cell-deficient hosts. Licensed R+G2+ NK cells in peripheral blood and spleen robustly expanded and mediated MCMV control in contrast to R+ NK cells. Both Ly49G2 and Ly49R receptors expressed together in NK cells thus are essential to Dk-dependent MCMV control. Our data and novel mouse model suggest licensed NK cells may be better equipped to sense infected targets, which aligns with human genetics studies implicating a role for licensed NK cells in control of chronic infection.