Abstract
Most traditional methods of immunization involve parenteral vaccines. Using a chronically isolated ileal loop model as the probe, we examined the effect of a primary parenteral immunization on the local immune response of the intestine. Secretions from isolated ileal loops of rabbits given a primary parenteral immunization with Shigella flexneri without adjuvant showed a small, but definite, specific immunoglobulin A (IgA) response locally, whereas a vigorous serum antigen-specific IgG response was elicited. Also, stronger antigen-specific IgG activity was detected in secretions of parenterally immunized animals than from animals given shigella only by oral immunization. No local IgA or IgG memory response could be elicited by prior parenteral priming with S. flexneri antigens. Lastly, no increase in the primary local IgA response was found in secretions from animals given an oral dosage regimen previously shown to prime for mucosal memory and then challenged with a single parenteral dose of the same antigen. These studies demonstrate that without adjuvant, parenteral doses of S. flexneri antigens elicit both specific serum and local immune responses, but they are not able to prime for a mucosal memory response upon subsequent mucosal challenge. The implications of these findings for programs that use parenteral vaccination to protect against mucosal diseases are discussed.