Serum and salivary antibody responses and the development of oral tolerance after oral and intragastric antigen administration.

Repeated administration of human serum albumin to female Wistar rats via stomach tube or dropwise into the oral cavity resulted in simultaneous induction of serum and salivary antibody together with a state of specific systemic hyporesponsiveness. The induction of the hyporesponsive state was found to be related to the level and class of serum antibody elicited by ingested antigen. Rats dosed intragastrically produced low levels of serum antibody, predominantly of the IgM class; some of the rats dosed orally responded similarly, and both groups were hyporesponsive on subsequent parenteral immunisation with human serum albumin. However, other rats dosed orally produced IgG serum antibody and were not hyporesponsive, except when assayed for cross-reacting antibodies to bovine serum albumin. The kinetics of the immune response after parenteral challenge was similar in experimental and control rats over the 5-week test period.