Local IgA-memory response to bacterial antigens.

For over 100 years, it has been known that oral immunization can protect against challenge by certain enteropathogenic ba~teria. ' .~ The mechanism of this protection was unclear as most individuals did not demonstrate strong serum agglutinins to the orally administered vaccine. Work by Davies in 1922 provided evidence that agglutinating antibodies in stool specimens from patients with dysentery correlated better with the disease activity than serum antibody levels.' Following the demonstration by Tomasi et al. in 1965 that IgA was the main antibody on mucosal surfaces, a new area of investigation was opened that led to the elucidation of the mechanism of protection by oral vaccination.' In order to follow the development of the local IgA-immune response, we developed a chronically isolated ileal loop model in rabbits.' This model allowed us to sample ileal loop secretions daily. In other studies, we immunized the isolated segment directly with bacteria, toxins, or other macromolecules. In the present study, we have used this model to demonstrate that a mucosal IgA-memory response can be elicited following oral immunization with Shigella flexneri antigen.