Cytomegalovirus-specific cytotoxicity mediated by non-T lymphocytes from peripheral blood of normal volunteers

The cytotoxicity of circulating mononuclear cells from normal volunteers was determined using human leukocyte antigen (HLA)-typed, low-passaged human skin fibroblasts infected with cytomegalovirus as target cells. Peripheral blood lymphocytes from both seropositive and seronegative individuals possessed virus specific cytotoxicity. Although all target cells used were susceptible to virus specific lysis, lymphocytes from some individuals were more active against some target cells than others. This differential cytotoxicity did not follow a consistent pattern of HLA restriction. Some variations in cytotoxic activity were noted on sequential studies of individual volunteers. Studies of fractionated lymphocytes from selected immune and nonimmune individuals demonstrated that cytotoxicity of lymphocytes from both groups was mediated by nonadherent, Fc receptor bearing cells which did not form rosettes with sheep erythrocytes. Repeated washing sometimes decreased cytotoxicity of lymphocytes from immune individuals, and addition of serum containing antibody to cytomegalovirus enhanced cytotoxicity, suggesting antibody dependence. It is concluded that cytotoxic lymphocytes from nonimmune volunteers possessed characteristics of natural killer cells, whereas those from immune volunteers probably consisted of both natural killer cells and antibody-dependent killer cells.