[Immunochemical identification and study of an interspecific thymus antigen (AgT-1)].

A new interspecific human and animal thymic antigen (AgT-1) was identified immunochemically. It was shown that AgT-1 is a protein with a molecular mass about 40000 dalton, electrophoretic mobility of alpha 1-globulins and isoelectric points 4.0 and 4.5. Heating of the protein to 80 degrees C led to the loss of its immunochemical activity. Antisera to AgT-1 were obtained by immunization of rabbits by conjugated extract of bovine thymus in complete Freund's adjuvant. AgT-1 was identified immunochemically in bovine embryonal thymus, spleen and liver. In addition to these organs, AgT-1 was discovered in lung extracts of adult animals. Identical antigen was identified in the embryonal thymus and extracts of human small intestine. AgT-1 antibodies inhibited the biological activity of the active thymic fraction (AFT-6) in recovering the sensitivity of spleen fRFC from thymectomized mice to the inhibitory action of azathioprin. The data indicate that the biological activity of AFT-6 is partly due to the molecules having antigenic determinants of AgT-1.