Potential Shigella flexneri 2a and Shigella sonnei I live vaccinal strains. Characterization of immunogenicity in animal models.

Rats and rabbits were immunized intraintestinally with different doses of virulent and nonvirulent live Shigella flexneri 2a and Shigella sonnei I strains. The nonvirulent strains had one or two attenuating markers. The period of excretion with the faeces of the bacteria and of their polysaccharide antigens, the proliferation of antigen-binding and antibody-producing cells in the spleens and gut-associated lymphoid tissues and the levels of antibodies in sera and faeces were studied. Attenuated strains S. flexneri 2a 77 and S. sonnei I 3359 induced the most potent and long lasting local immune response.