Relationship between expression of Fcγ receptors or la antigens and cytolytic activities of alloactivated human T cells

The relationship between expression of Ia antigens or Fcγreceptors (FcγR) and different cytolytic activities of mixed leukocyte culture (MLC)-activated T-cell populations was studied. Lymphocytes mediating specific lysis of target cells bearing the stimulating alloantigens (CTL) could clearly be distinguished from cells mediating antibody-dependent cellular cytotoxicity (ADCC) in that CTL were FcγR^- while cells mediating ADCC were FcγR⁺. In contrast, MLC-generated natural killer (NK) cells were distributed in both the FcγR^- and FcγR⁺ cell fractions. The presence or absence of Ia antigens did not correlate with any of the cytolytic activities studied. In addition, FcγR^- and not FcγR⁺ cells responded in the secondary MLC. Thus, although FcγR⁺ cells are generated in large numbers in MLC, they do not appear to play a direct role in specific cytotoxicity nor do they proliferate in response to secondary stimulation. However, their ability, following MLC generation, to mediate NK activity and ADCC, both of which may contribute to in vitro and in vivo lysis of allogeneic cells, might explain their appearance following allogeneic stimulation.