Distinct Surface Expression of Activating Receptor Ly49H Drives Differential Expansion of NK Cell Clones upon Murine Cytomegalovirus Infection

Natural killer (NK) cells show some features of adaptive immunity but have not been studied at the clonal level. Here, we used retrogenic color-barcoding and single-cell adoptive transfers to track clonal immune responses to murine cytomegalovirus (MCMV) infection, derived from individual NK cells expressing activating receptor Ly49H. Clonal expansion of single NK cells varied substantially, and this variation could not be attributed to the additional presence or absence of inhibitory Ly49 receptors. Instead, single-cell-derived variability correlated with distinct surface expression levels of Ly49H itself. Ly49H(hi) NK cell clones maintained higher Ly49H expression and expanded more than their Ly49H(lo) counterparts in response to MCMV. Thus, akin to adaptive processes shaping an antigen-specific T cell receptor (TCR) repertoire, the Ly49H(+) NK cell population adapts to MCMV infection. This process relies on the clonal maintenance of distinct Ly49H expression levels, generating a repertoire of individual NK cells outfitted with distinct reactivity to MCMV.