Systemic antibody responses of different species following ingestion of soluble protein antigens.

Following ingestion of bovine serum albumin (BSA), human infants and rabbits synthesize circulating anti-BSA. Using a similar protocol, the serum antibody response was examined in C3H mice offered 0.1, 1.0 or 6.0% BSA for 10 or 56 days. Sera from these animals contained similar amounts of antigen, but anti-BSA was undetectable. Half the animals in each group were subsequently injected i.v. with 50.0 mg BSA. Mice fed 1.0 or 6.0% BSA were unresponsive to this challenge, but animals fed 0.1% BSA responded comparably to i.v. immunized, non-fed controls. The remaining animals in each group were injected s.c. with 1.0 mg BSA in adjuvant. Most of these mice produced circulating anti-BSA. However, these responses were significantly reduced relative to s.c. immunized, non-fed controls. Hyporesponsiveness again was least after 0.1% BSA ingestion. CF1 mice and BN, HCR and HCS rats fed 0.1% BSA for 56 days also did not produce circulating antibodies during ingestion, and almost all were hyporesponsive after parenteral challenge. Suppression of specific antibody responses also was observed in C3H mice fed and challenged with diphtheria toxoid. The data suggest that under identical experimental conditions, ingestion of soluble protein antigens induces a state of systemic hyporesponsiveness in mice and rats in contrast to the systemic immunity demonstrated in human neonates and adult rabbits.