Vital involvement of a natural killer cell activation receptor in resistance to viral infection

Natural killer (NK) cells are lymphocytes that can be distinguished from T and B cells through their involvement in innate immunity and their lack of rearranged antigen receptors. Although NK cells and their receptors were in itially characterized in terms of tumor killing in vitro, we have determine d that the NK cell activation receptor, Ly-49H, is critically involved in r esistance to murine cytomegalovirus in vivo. Ly-49H requires an immunorecep tor tyrosine-based activation motif (ITAM)-containing transmembrane molecul e for expression and signal transduction. Thus, NK cells use receptors func tionally resembling ITAM-coupled T and B cell antigen receptors to provide vital innate host defense.