Effect of Ly49 Haplotype Variance on NK Cell Function and Education

The class I MHC-specific receptors expressed by murine NK cells exhibit remarkable variation. Specific activating killer Ig-related receptor/Ly49 have major effects on autoimmune and infectious disease induction and outcome in humans and mice. However, these studies are greatly affected by individual background genetics. Furthermore, the educational impact of variable inhibitory KIR/Ly49 gene numbers on NK cell development and the subsequent ability to survey for MHC class I (MHC-I) expression remain unknown. To address these questions, Ly49 congenic mice were generated that maintain a 129-derived Ly49 gene cluster on a C57BL/6 genetic background (B6.Ly49(129) mice), and the in vitro and in vivo NK cell function of these mice was compared with their inbred parental 129S1 and C57BL/6 counterparts. Notably, target cell recognition directed by activating Ly49 receptors was profoundly affected by allelic variation in B6.Ly49(129) congenic cells versus C57BL/6 NK cells. Furthermore, when assessing NK cell function based on education and subsequent recognition of the C57BL/6 MHC-I haplotype by inhibitory Ly49 receptors, B6.Ly49(129) congenic mice exhibited robust NK cell activity, demonstrating efficient NK cell education by the 129S1 Ly49 cluster during development. The responsiveness of NK cells expressing 129S1 Ly49 was shown to be mediated by subsets expressing one or more self-MHC receptors, including Ly49I, Ly49O, Ly49V, and NKG2A. These findings demonstrate that the genetically segregating and diverse MHC-I and Ly49 loci in mice exhibit independent and epistatic effects on NK cell education that can be uncoupled during the intercrossing of inbred strains.