Phenotypic Discrimination Of Rat Splenic Effector Cells Mediating Suppression And Cytotoxicity In Vitro

BALB/c mice were immunized with an OX8-positive (T(,c/s), NK) cell enriched subpopulation of rat splenic lymphocytes in an attempt to generate monoclonal antibodies specific for rat suppressor cells. Three of the resulting antibodies, all of the IgG2a isotype, recognized determinants expressed on normal rat T lymphocytes and on OX8-positive thymic lymphoma cells demonstrating suppressor function, but not on splenic B lymphocytes, splenic red blood cells, or non-lymphoid pancreatic or fibroblastoid cells. These antibodies were employed in the negative selection of effector cells mediating NK, cytotoxic, and suppressor function in vitro, using complement-mediated cytolysis, and were found to be capable of lysing only the suppressor cells. Parallel indirect immunofluorescence analysis of depleted effector cell populations revealed that one of these antibodies was incapable of lysing a significant percentage of marker-positive cells, however, suggesting expression of the determinant to a lesser degree on other spleen cell subpopulations. A fourth antibody was found to recognize normal splenic T lymphocytes from some rat strains, but not rat thymic lymphoma cells. Additionally, because this antibody was incapable of lysing the cells it recognized, it could not be employed in effector cell depletion studies, although it may be relevant to suppressor cell analysis. The availability of monoclonal antibodies capable of discriminating between suppressor and cytotoxic rat lymphocytes should provide answers to a number of key questions regarding the role of suppressor cells in transplantation tolerance and in protection against autoimmunity, using the rat model system