ABSTRACT
Natural killer (NK) cells were originally described in 1975 as effector cells capable of in vitro lysis of certain tumor targets.1,2 Uniquely different than elements of adaptive immunity, i.e., T and B cell functions, NK cells were found in nonsensitized hosts and were postulated to have a role as the first line of defense against arising neoplasia. The interaction of an invading virus with the defense systems of the host is complex and elements of both natural resistance and adaptive immunity are required to provide protection from the pathogen. NK cells have been shown to be capable of lysing a number of virus-infected target cells in vitro and, in general, virus-infected cells are lysed more efficiently than the uninfected targets. Considerable evidence has been developed demonstrating that murine NK cells are heterogeneous and can be differentiated on the basis of sensitivity to Sr, cell surface markers, ontogeny, and sensitivity to lymphokines.
