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 cells represent up to 15% of peripheral blood lymphocytes and can reach high concentrations at sites of inflammation, but despite their discovery 25 yr ago, convincing evidence for their importance has only been established in a limited number of systems (1) . Although proposed to mediate immunoregulatory and tumor surveillance functions, their primary role, like that of the rest of the immune system, is most likely to combat infectious agents. To do so, they may need the capacity to selectively recognize and attack infected host cells or else to nonselectively respond to stimuli and mediate effector function by the nonspecific release of cytokines. An understanding of the molecular mechanisms of NK cell recognition of target cells has been developed after the identification of a series of families of NK cell receptor (NKR) * molecules that can deliver either negative or positive signals to NK cells on encounter with a target (2) (3) (4) . Many of these receptor molecules recognize MHC class I antigens, but the possibility remains that some might also recognize other cell surface structures.