[Systemic immunological memory in enteral immunization with the O antigen from S. sonnei]

Mice received S. sonnei O-antigen at various concentrations (0.01-20,000 micrograms/ml) in drinking water. Systemic immunological memory, induced by feeding with O-antigen, was manifested by secondary immune response to parenteral boosting with homologous O-antigen or ribosomal vaccine. A pronounced priming effect was also produced by O-antigen at concentrations as low as 0.01 micrograms/ml after courses of feeding as short as 1-3 days. Even high doses of the antigen had no tolerogenic activity. The state of immunological memory was formed at least 12 days after the first feeding and lasted for a long period (at least 4 months after the last feeding). The specificity of immunological memory was proved in experiments with heterologous O-antigen (Salmonella typhimurium): the insignificant stimulating action of this antigen was revealed only when high concentrations of the antigen (1000 micrograms/ml) were used for feeding.