Parenteral immunization with Shigella ribosomal vaccine elicits local IgA response and primes for mucosal memory

The parenteral Shigella ribosomal vaccine (SRV), which previously was shown to protect guinea pigs and monkeys, has been compared with lypopolysaccharide (LPS) for its ability to induce a systemic and a local immune response. Injection of SRV caused a significant rise of the serum O antibodies of different classes and the appearance of IgA O antibodies in tears of guinea pigs and saliva and bile of monkeys. In guinea pigs, the local IgA response to parenteral SRV was much more intensive than that to feeding of high doses of LPS, while in monkeys it was nearly as high as that to challenge with a high dose of live pathogen. These data provide an immunological basis for the protective effect of SRV and are in disagreement with the widely accepted view of the inefficiency of parenteral antigens in stimulating mucosal immunity. The results are interpreted from the viewpoint of the role of ribosomes as a delivery system for the Shigella O antigen which provides high potency of SRV in stimulating local lymphoid tissue and makes it a good vaccine candidate.