Membrane phenotype of the rat cytotoxic T lymphocyte.

We have examined rat cytotoxic T lymphocytes for expression of W3/25, OX8, Ia, Thy-1 antigens, and Fc gamma receptors using an effector cell-target cell conjugate formation assay in conjunction with immunofluorescence techniques. Lymph node, spleen, and peritoneal exudate T cells from Lewis rats immunized with allogeneic BN tumor cells specifically bound to and lysed BN tumor targets and BN blast cells, but did not bind or lyse syngeneic Lewis sarcoma cells, Lewis blast cells, or Lou/M blast cells. The numbers of binding and cytotoxic T lymphocytes were greatest in peritoneal exudate cells of immunized rats, less in spleens, and least in lymph nodes. Seventy to 80% of the lymphocytes bound to tumor targets were OX8+ T lymphocytes; less than 12% expressed W3/25, Ia, Thy-1, or Fc gamma R. Moreover, only OX8+ T cells efficiently lysed the target cells to which they were bound. The membrane phenotype of rat cytotoxic T lymphocytes was: OX8+, W3/25-, Ia-, Thy-1, and Fc gamma R-. Monoclonal OX8 antibody did not inhibit target cell binding or subsequent lysis by effector T cells, and there was no diminution of target cell binding or cytotoxic activity when the OX8 antigen was shed from the cell surface before interaction with target cells. There was no preferential association of OX8 antigen at the interface between the effector and target cell. Thus, OX8 antigen marks a subset of rat T lymphocytes that are cytotoxic but the molecule appears not to play a functional role in the cytotoxic process.