Specificity and immunosuppressive potency of a rabbit antimouse T cell-specific antiserum

An attempt was made to prepare a specific heterologous rabbit antimouse T cell antiserum (anti-MTLA) by absorbing rabbit antimouse thymocyte globulin (ATG) with spleen cells from BALB/c TXBM mice. Cytotoxicity data showed that whereas ATG was cytotoxic to both T and B cells, anti-MTLA was highly cytotoxic to only T cells. Whereas spleen cells treated with ATG and complement (C) failed to respond in all assays studied, spleen cells treated with anti-MTLA and C: (1) responded to the B cell mitogens but failed to respond to the T cell mitogens; (2) were able to stimulate allogeneic spleen cells but failed to respond to mixed lymphocyte culture (3) failed to act as T killer cells in the CML reaction but retained their ability to kill antibody-coated target cells; and (4) did not cause a graft-versus-host reaction when injected in allogeneic mice and increased their survival significantly. Furthermore, anti-MTLA was just as immunosuppressive in vivo as ATG in its ability to suppress the immune response to sheep red blood cells and prolong skin allograft survival. Anti-MTLA was found to be different in specificities from anti-theta serum by several points: (1) it was cytotoxic for T cells from both theta-C3H and theta-AKR mice; (2) it was highly immunosuppressive in vivo when compared to anti-theta serum; (3) absorption of anti-MTLA with mouse brain did not decrease the immunosuppressive activity; and (4) rabbit antimouse brain antiserum failed to show any immunosuppressive activity. These data indicate that anti-MTLA is a specific antiserum against a unique marker on T cells distinct from the theta marker.