Spontaneous cytotoxicity of human peripheral mononuclear cells toward red blood cell targets in vitro. I. characterization of the killer cell.

Abstract

Human peripheral blood mononuclear cells become spontaneously cytotoxic toward a broad range of erythrocyte targets after 6 to 7 days in culture. The presence of high concentrations of fetal calf serum (20%) inhibits the development of spontaneous cytotoxicity, whereas low concentrations (1 to 2%) markedly enhance cytotoxicity. Allogeneic, xenogeneic, and even syngeneic RBC are suitable targets, suggesting little, if any, target cell specificity. The addition of excess unlabeled RBC inhibits 51 Cr release from both identical and totally unrelated RBC targets; further arguing that the cytotoxic effector cell is not directed toward one and only one antigenic specificity on the target. Cell separation techniques employed at the beginning of culture demonstrate that cytotoxicity is markedly enhanced by T cell depletion by using a SRBC rosetting technique. Removal of phagocytic cells by incubation with iron particles and a magnet substantially depletes subsequent cytotoxic potential. EA rosette depletion of cells also markedly reduces subsequent cytotoxic potential. Interestingly, EA rosette depletion at the end of 7 days in culture has almost no effect on cytotoxicity, whereas E rosette depletion after 7 days continues to enhance cytotoxicity. Depletion of the cultured effector cell populations over a nylon wool column or with iron and a magnet abolished cytotoxicity. These results suggest that the cell responsible for spontaneous RBC cytotoxicity is a non-T cell which initially expresses an easily detectable Fc receptor and exhibits surface adherence properties. However, after 7 days in culture the cytotoxic cell either no longer expresses an Fc receptor, or its affinity, density, or availability are somehow altered in vitro .