This project continues to investigate the immune response, particularly the kinds of lymphocytes involved. We are investigating the mechanisms of activation of thymus-derived cells (T cells) in contact hypersensitivity and the mechanisms of producing immunologic unresponsiveness (tolerance) in vivo and in vitro. We are exploring T cell subpopulations and the rates of cell cycling and involvement in various aspects of cell-mediated immunity as measured by such variables as mixed leukocyte reaction, graft-versus-host reactions and response to mitogens. BIBLIOGRAPHIC REFERENCES: Phanuphak, P., Moorhead, J.W., and Claman, H.N.: Tolerance and Contact Sensitivity. III Transfer of Tolerance with "Suppressor T Cells." J. Immunology, 113:1230, 1974. Phanuphak, P., Moorhead, J.W., Claman, H.N.: Tolerance and Contact Sensitivity to DNFB in Mice. IV. Desensitization as a Manifestation of Increased Proliferation of Sensitized Cells. J. Immunology 114:4 1147-1152. 1975.