Local and systemic immune response in rabbits after intraintestinal immunization with a double-marker attenuated strain of Salmonella typhimurium

Local and systemic immune response was studied in 3 groups of rabbits immunized and reimmunized 190 days later with S. typhimurium double-marker attenuated strain 1,771 and doses ranged from 20.10(9) to 0.2.10(9) cells. Another group of rabbits was immunized with extract (hydroxylammine) vaccine. It was found that the attenuated strain persisted for considerable time in the gut, and induced pronounced and continuous immune response as measured by the passive hemagglutination test. The serum antibody response had the character of a secondary one with switching on the synthesis of IgM to IgG already after basic immunisation. By the Coombs' technique it was shown that specific immunoglobulins demonstrated in feces were secretory antibodies of the class IgA (SIgA). The immune response developed after reimmunization was still more vigorous and prolonged pointing to an immune memory existance. It was possible to obtain well manifested immunity with the lowest dose. The extract vaccine revealed only weak and transitory serum and intestinal antibody levels without SIgA appearance. The results obtained in this setup make S. typhimurium 1771 a perspective candidate for a live vaccine.