Feeding of antigen reduces antigen-binding activity and blunts the secondary response of actively immunized rats

Enteric administration of soluble or particulate antigens to unprimed animals has been repeatedly demonstrated to blunt or abrogate the cellular and humoral immune response to parenteral immunization. We tested the effect of administering bovine serum albumin by gavage or in the drinking water on the serum antigen-binding activity of rats primed by previous immunization with bovine serum albumin and alum. In some animals, this treatment served initially to boost the systemic humoral response; prolonged treatment led to a reduction in antigen-binding activity at a faster rate than was observed in sham-fed controls. In all rats treated with enteric antigen, the booster response to a second parenteral immunization was reduced or absent. Example of the use of enteric antigen in treatment of patients are cited. On the basis of our findings in rats and those of other investigators who studied mice, as well as the results obtained in patients, it is suggested that further exploration of the enteric approach to treating actively immunized subjects appears warranted.