Cellular Rejection*

Delayed or cellular hypersensitivity is the primary immunologic mechanism in the rejection of organ homografts. Mounting evidence implicates the small lymphocyte as the cell responsible for implementing this reaction. The immunologic role of the lymphocyte in the graft-versus-host reaction was first recognized by Simonsen (1957). He showed that if newborn or heavily irradiated mice are injected with foreign adult lymphoid cells, the animals will waste and die. He further demonstrated that the cells causing the graftversus-host reaction are present in the peripheral blood of the mouse. Other investigators have since demonstrated that this cell is the small lymphocyte. Strober and Gowans (1965) have demonstrated that there is interaction between small lymphocytes and a foreign organ graft. In this study, lymphocytes were first perfused through isolated allogenic kidneys and then injected back into the animal from which the lymphocytes were derived. It could then be demonstrated that these animals reacted to a skin graft from the kidney donor with a secondary response, indicating prior sensitization. This study seemed to indicate that the small lymphocyte is involved in the af-