Immunoassay for bovine serum thymopoietin: discrimination from splenin by monoclonal antibodies

A polyclonal rabbit anti-bovine thymopoietin antiserum was used to develop a radioimmunoassay and sandwich enzyme-linked immunosorbent (ELISA) assay for the thymic hormone thymopoietin. Both assays showed slightly less sensitivity for the closely related splenic hormone splenin (SP) than thymopoietin (TP) and markedly less sensitivity for the human as compared with the bovine polypeptides. A number of murine monoclonal antibodies specific for bovine thymopoietin were generated; they were unreactive with bovine splenin and were also unreactive with human thymopoietin and splenin. A sandwich ELISA using these monoclonal anti-TP antibodies together with polyclonal rabbit anti-TP was specific for bovine thymopoietin and measured 300-500 ng/ml thymopoietin in bovine serum. Similar approaches are being pursued to develop an immunoassay for thymopoietin in human serum.