Prolonged lymphocytopenia in the rat

Summary The intrasplenic infection of colloidal 185 W tungsten trioxide is followed by a deficit of small lymphocytes in blood and thoracic duct lymph which persists for many weeks. Recirculating small lymphocytes are the only cells affected and the rats remain in good general condition. The immonological performance of such rats was compared to that of splenectomised controls. The scrum haemolysin response to sheep erythrocytes was depressed by 3 log 2 units. The primary agglutinin response to S. adelaide flagella was more depressed (by 5 log 2 units) but the secondary response to flagella, in rats primed before lymphocytopenia was induced, was barely affected. The effect of lymphocytopenia on skin allograft survival depended on whether a "weak" or "strong" antigenic difference was involved. Skin allograft survival in a weak strain combination (Ag‐B identical) was prolonged From 10 days to a mean of 22 days. By contrast, skin allograft survival in strong strain combinations (Ag‐B different) was only very marginally affected and thymectomy prior to the induction of lymphocytopenia had no additional effect. Although no explanation is provided for the discriminatory effect of lymphocytopenia on reactions to weak and strong histocompatibility antigens, it is probably associated with the much higher proportion of lymphocytes reactive to strong antigens.