Termination of tolerance to HSA in chickens.

A major part of chickens made tolerant to HSA at hatching formed anti-HSA antibodies when immunized with cross-reacting antigen, the BSA, at 4 weeks of age, although tolerant birds immunized with HSA produced no detectable antibody levels. Immunization with HSA + BSA did not prevent anti-HSA antibody formation in tolerant chickens, but it seems that the escape from tolerance is more rapid in birds immunized with BSA only than in those immunized with HSA + BSA and/or HSA only.