The role of the Fc receptor (FcR) of thymus‐derived lymphocytes I. Presence of FcR on cytotoxic lymphocytes and absence of direct role in cytotoxicity

Abstract

Abstract Cytotoxic T lymphocytes (CTL) were prepared by injecting C3H/He (H‐2 k ) thymocytes into host‐irradiated BALB/b (H‐2 b ) mice. Specific cytolysis was measured on MBL2 lymphoma cells from C57BL/6 (H‐2 b ) mice. Alloantigen‐activated T cells (ATC) were taken from the spleens of the recipients at day 5 and separated according to size and/or to the presence of membrane Fc receptors (FcR) by the use of velocity sedimentation techniques. The data showed that CTL were found in populations of lymphocytes heterogeneous in cell size and were always present in the FcR‐positive population. Depletion of FcR‐positive ATC, after rosetting with IgG‐sensitized sheep erythrocytes led to an abolishment of cytolytic activity while enrichment in FcR‐positive ATC led to a parallel increase of cytolytic activity. Taking advantage of the rapid release of FcR at 37°C by ATC, we investigated the direct involvement of the FcR molecule in cytolysis. We found that ATC which had released their FcR after pre‐in‐cubation for 2 h at 37°C exerted the same level of cytotoxicity as control ATC incubated at 4 °C. The data lead us, therefore, to conclude that FcR may be a marker of differentiation of cytotoxic T cells found in the spleen, but does not itself play a role in the cytolytic reaction.