Neutralization of heterologous toxicities in mice immunized with proteins from S. typhimurium and from a human pathogen (S. emek).

Groups of mice immunized with proteins from S. typhimurium and from a non-pathogenic Salmonella for mice (S. emek) were infected with S. tymphimurium, S. emek, S. blockley and S. paratyphi A. The mice immunized with the S. typhimurium proteins were, as always protected against infection with the pathogen and resisted the toxicities, which killed the controls, of S. paratyphi A and S. emek but not of S. blockley. The mice immunized with S. emek proteins resisted the toxicity of S. paratyphi A and, to a lesser degree, that of the homologous S. emek. The animals did not resist the toxicity of a similar concentration of S. blockley and the immunized mice died, like the controls, within 20-40 hours. Mice in this group infected with S. typhimurium had a much longer delay before dying, than the controls. Antiprotein antibodies present in the sera of the immunized mice are, apparently, responsible for the neutralization of the toxicities of the heterologous strains and for the eventual protection against infection.