NK cell-mediated murine cytomegalovirus (MCMV) resistance ( Cmv r ) is under H-2 k control in MA/My mice, but the underlying gene(s) is unclear. Prior genetic analysis mapped Cmv r to the MHC class I (MHC-I) D k gene interval. Because NK cell receptors are licensed by and responsive to MHC class I molecules, D k itself is a candidate gene. A 10-kb genomic D k fragment was subcloned and microinjected into MCMV-susceptible ( Cmv s ) (MA/My.L- H2 b × C57L)F 1 or (B6 × DBA/2)F 2 embryos. Transgenic founders, which are competent for D k expression and germline transgene transmission, were identified and further backcrossed to MA/My.L- H2 b or C57L mice. Remarkably, D k expression delivered NK-mediated resistance in either genetic background. Further, NK cells with cognate inhibitory Ly49G receptors for self-MHC-I D k were licensed and critical in protection against MCMV infection. In radiation bone marrow chimeras, NK resistance was significantly diminished when MHC-I D k expression was restricted to only hematopoietic or nonhematopoietic cells. Thus, MHC-I D k is the H-2 k -linked Cmv r locus; these findings suggest a role for NK cell interaction with D k -bearing hematopoietic and nonhematopoietic cells to shape NK-mediated virus immunity.

MHC I Dk and Ly49G2 inhibitory receptor-expressing NK cells are essential to murine (M)CMV5 resistance in MA/My mice. Without Dk, Ly49G2+ NK cells in C57L mice fail to protect against MCMV infection. As a cognate ligand of Ly49G2, Dk licenses Ly49G2+ NK cells for effector activity. These data suggested that Dk-licensed Ly49G2+ NK cells might recognize and control MCMV infection. However, a role for licensed NK cells in viral immunity is uncertain. We combined classical genetics with flow cytometry to visualize the host response to MCMV. Immune cells collected from individuals of a diverse cohort of MA/MyxC57L offspring segregating Dk were examined before and after infection, including Ly49+ NK subsets, receptor expression features and other phenotypic traits. To identify critical NK cell features, automated analysis of 110 traits was performed in R using Pearson’s correlation followed with a Bonferroni correction for multiple tests. Hierarchical clustering of trait-associations and principal component analyses were used to discern shared immune response and genetic relationships. The results demonstrate that Ly49G2 expression on naïve blood NK cells was predictive of MCMV resistance. However, rapid Ly49G2+ NK cell expansion following viral exposure selectively occurred in Dk offspring; this response was more highly correlated to MCMV control than all other immune cell features. We infer that Dk-licensed Ly49G2+ NK cells efficiently detected missing-self MHC cues on viral targets, which elicited cellular expansion and target cell killing. MHC polymorphism therefore regulates licensing and detection of viral targets by distinct subsets of NK cells required in innate viral control.

The transmission of herpesviruses depends on viral shedding at mucosal surfaces. The salivary gland represents a major site of persistent viral replication for many viruses, including cytomegalovirus. We established a mouse model of salivary gland dysfunction after acute viral infection and investigated the cellular requirements for the loss of secretion. Murine cytomegalovirus (MCMV) infection severely impaired saliva secretion independently of salivary gland virus levels. Lymphocytes or circulating monocytes/macrophages were not required for secretory dysfunction. Dysfunction occurred before glandular inflammation, suggesting that a soluble mediator initiated the disruption of acinar cell function. Despite genetic differences in innate resistance to MCMV, NK cells protected the host against acinar atrophy and the loss of secretions under conditions of an exceedingly low virus inoculum. NK cells also modulated the type of glandular inflammation after infection, as they prevented an influx of Siglec-F ؉ polymorphonuclear leukocytes (PMNs). Therefore, beyond their recognized role in controlling MCMV replication, NK cells preserve organ integrity and function and regulate the innate inflammatory response within the gland.