Specific suppression of antibody production in young rabbit kits after maternal ingestion of bovine serum albumin

Passive transfer of antibody across the placenta or in milk has been thought to have a regulatory effect on the immune reponsiveness of young animals. Since most natural immune responses are initiated by exposure to antigen at mucosal surfaces, the regulatory effect of maternal antibody on the systemic immune responses of rabbit kits was studied after ingestion and injection of bovine serum albumin (BSA). Serum and milk obtained during the 30-day nursing period from female rabbits fed 0.1% BSA either before or during pregnancy contained varying amounts of anti-BSA, primarily of the IgG isotype. Kits born to BSA-fed dams were fed BSA (p.o. immunized) for 10 or 52 days beginning at 20 days of age. Control kits from unimmunized dams and from a dam immunized i.v. were similarly fed BSA. The concentrations of circulating anti-BSA during p.o. immunization in 20 kits born to unimmunized dams approximated those in p.o. immunized adult rabbits. In contrast, 55 kits from dams fed BSA, including 20 kits of mothers with no detectable anti-BSA in either serum or milk, synthesized little or no circulating anti-BSA during or after p.o. immunization. Kits born to an i.v.-immunized dam had high circulating concentrations of passively acquired anti-BSA, but they responded to p.o. immunization as well as the kits of the unimmunized dams. Similarly, anti-BSA passively acquired from p.o.-immunized mothers did not alter the suppressed responses of kits to BSA ingestion.