In vitro cytotoxicity by human lymphocytes from individuals immunized against histocompatibility antigens. II. Relation to HL-A incompatibility between effector and target cells.

Lymphocytes from humans immunized by allogeneic skin grafts destroyed fibroblast monolayer cultures derived from the skin donor. Cytotoxicity also developed on several allogeneic fibroblast monolayers from unrelated persons. HL-A typing showed that all of these allogeneic fibroblasts shared one or more HL-A antigens with the skin donor. The intensity of the cytotoxic reaction increased with the number of these antigens present on the fibroblast targets, whereas no reaction occurred on allogeneic targets lacking these antigens or on the autochthonous fibroblasts. It is suggested, therefore, that the cytotoxic reaction reflects immunization against antigens within the HL-A system. An analogous correlation between the response of immunized lymphocytes and the number of immunizing HL-A antigens present was demonstrated in mixed lymphocyte cultures. Lymphocytes from kidney grafted patients were not cytotoxic to any fibroblasts tested, including those from the kidney donor, not even during periods of clinical rejection. Humoral antibodies directed against the donor cells were demonstrated in one patient, but still no cytotoxicity occurred on the donor fibroblasts. Similarly negative results were obtained with lymphocytes from bone grafted patients.