Murine Cytomegalovirus Is Regulated by a Discrete Subset of Natural Killer Cells Reactive with Monoclonal Antibody to Ly49h

Daniels, Keith A.; Devora, Gene; Lai, Wayne C.; O'Donnell, Carey L.; Bennett, Michael; Welsh, Raymond M.

NK cell populations, we also routinely monitored the NK1.1 ϩ CD3 ϩ NK/T populations. During MCMV infection, the proportions of these NK/T cell populations dropped dramatically in the liver, where they were relatively high before infection (Fig. 9 , bottom). Similar drops in percents and total cell numbers of liver NK/T cells were seen with MHV and VV, though less so with LCMV ( Fig. 9 , top). Thus, while prototypical NK cell numbers were rising dramatically in infection (Fig. 1) , NK/T cells were declining dramatically. Few NK/T cells were found in the peritoneal cavity either before or after infection. Although some of this apparent decline could be an artifact due to downmodulation of NK1.1 and CD3, our data, and those of others (R. Brutkiewitz, University of Indiana, personal communication), to be published elsewhere, indicate that this NK/T cell population undergoes apoptosis and declines in number at early stages of infection and under conditions of strong IFN-inducing stimuli. NK1.1 ϩ CD3 ϩ (NK/T) lymphocytes were analyzed for coexpression of Ly49 molecules before and after infection. Monitoring Ly49 expression on these populations was sometimes difficult during infection because of high background staining with isotype-control Abs, perhaps due to the fact that many of these cells were undergoing apoptosis. Nevertheless, it was clear that a substantial proportion of the NK/T cells reacted with mAb 5E6 (Ly49 C/I) and mAb 1F8 (Ly49 C/I/H), but very few NK/T cells displayed the Ly49H phenotype of 1F8 ϩ 5E6 Ϫ . This pattern was seen in spleen, PECs, and liver from both uninfected and infected mice. Displayed in Fig. 10 are data for NK1.1 ϩ CD3 Ϫ NK cells from uninfected spleens, where there is very little contamination from NK/T cells, and data for NK1.1 ϩ CD3 ϩ NK/T cells from uninfected liver, where the highest numbers of NK/T cells are found, making them easier to unambiguously discriminate from prototypical NK cells. This shows that few if any of the NK/T cells have a characteristic Ly49H phenotype and are likely not to express this positively signaling ligand. In general we have noted that some T cells, even those not expressing NK1.1, occasionally stain with Abs to the negatively signaling Ly49 molecules (Ly49 A, C/I, G2) but not to the positively signaling molecules (Ly49 D and H; reference 37). These experiments mean that any viral enhancement effects due to administration of the 1F8 mAb in vivo are likely a consequence of its action on true NK cells, not NK/T cells, as the 5E6 mAb, which has no affect on MCMV replication, should deplete virtually all of the 1F8 ϩ NK/T cells in vivo.