Thymus‐dependent cytotoxic lymphocytes in the rat

The nature of effector cells mediating cytotoxicity in vitro in a rat tumor allograft model using 51Cr release assays has been investigated. On the basis of a series of in vitro cell depletion techniques including glass absorption, removal of Fc receptor‐bearing cells and lysis of thymus‐dependent lymphocytes with a cytotoxic rabbit anti‐thymus cell sera, the predominant effector cell in this situation appears to be a thymus‐dependent lymphocyte. The main difference from previous published studies in mice appears to be the more rapid evolution of cytotoxic activity in the rat and the difficulty in detecting marked cytotoxic activity in the thoracic duct cells. Determination of the antigenic specificity of these cytotoxic cells by an inhibition assay suggests that their specificity is directed solely to transplantation antigens on the tumor cell.