The thymic peptides FTS (serum thymic factor), thymosin alpha 1 and thymopoietin induce the differentiation of prothymocytes into T lymphocyte. Synthetic peptide-protein conjugates will be used for the production of hybridomas that secrete monoclonal antibodies specific for each of these three thymic hormones. The specific antigenic sites recognized by these antibodies will be defined using batteries of synthetic peptide analogues. Radioimmunoassays for the thymic hormones will be developed using synthetic radiolabeled thymic peptides. These assays will be used to identify the presence of these thymic hormones in peripheral blood, thymic and peripheral lymphoid tissues, and skin. The radioimmunoassays will also be used to quantitate the circulating levels of these thymic hormones in the plasma of normal individuals of various ages and patients with primary and secondary innumodeficiency diseases, with cutaneous T-cell lymphoma and others with cancer, or those undergoing bone marrow transplantation for the treatment of aplastic anemia or certain leukemias. The availability of radioimmunoassays using specific monoclonalal antibodies whose detailed antigenic specificity is precisely know will minimize misinterpretation of these results. Fluorescent and radiolabeled derivatives of the synthetic thymic peptides will be used to show the presence of thymic hormone receptor(s) on certain precursor and differentiated lymphocytes and to sort selected lymphocyte populations bearing receptor(s). Photoliabile derivatives of the thymic hormones will be used for photoaffinity labeling of membrane proteins at or near the thymic hormone receptors. These studies will combine the techniques of peptide synthesis, monoclonal antibody production, radioimmunoassay, and receptor study to advance our knowledge of the role of FTS, thymosin alpha 1 and thymopoietin in the normal state and a variety of immunodeficienty diseases or cancer.