Systemic tolerance and secretory immunity after oral immunization

Diminished systemic immune reaction after ingestion of antigen has been reported in several animal models. Conversely, it has been reported recently that oral immunization may lead to the production of secretory antibodies. To determine whether these events could occur concurrently, CBA/J mice were immunized intragastrically with varying doses of ovalbumin (OVA) and Streptococcus mutans. After 7 d, the animals were challenged systemically with antigen in complete adjuvant and 8 d later serum and saliva taken, and the draining lymph nodes assayed for a proliferative response. Intragastric doses of 1 mg OVA or 10(9) S. mutans led to significant suppression of the proliferative response, and intragastric doses of 10 mg OVA or 2.5 X 10(9) S. mutans led to the production of detectable salivary antibodies using hemagglutination. Serum antibodies were not detected after intragastric administration of OVA or S. mutans. Suppression of the proliferative response could be detected from 2-60 d after intragastric administration of OVA, and 2-21 d after S. mutans. Prior intragastric immunization with heterologous antigens did not suppress the response to OVA or S. mutans. Transfer of 40 X 10(6) mesenteric lymph node cells from mice given 20 mg OVA or 10(9) S. mutans led to suppression of the proliferative response in syngeneic recipients. Salivary antibodies wer removed by absorption with anti-IgA, but not anti-IgG or IgM, indicating that they were of the IgA class. It appears that intragastric administration of soluble or particulate antigens in mice may lead to the concurrent induction of salivary antibodies and systemic suppression.