Behaviour of Salmonellae non-pathogenic for mice. I. Neutralization of their toxicities by induced antiprotein antibodies.

Groups of mice hyperimmunized with proteins from Salmonella strains which are not pathogens for mice (S. typhi o901, S. typhi Ty2, S. blockley, S. newport) resisted inoculation with concentrations of homologous and related heterologous liver bacteria, which killed all the controls in 20-48 hrs. The toxicity of the Salmonella tested was about 100-1000 times lower than that of the pathogenic S. typhimurium and concentrations of 10(8) or 10(9) bacteria (according to the strains used) were necessary to kill all the controls. In contrast to the period of incubation (2-12 days) required for S. typhimurium to kill all the controls and eventually some of the immunized mice, too, the killing with the human pathogenic Salmonella took place within 20-48 hrs. The toxicity of the big concentrations of bacteria needed to kill the controls was apparently neutralized by the antiprotein antibodies induced in the immunized mice. In no group of mice resisting inoculations with 1 x 10(8) or 1 x 10(9) of the homologous or heterologous tested Salmonellae protection could be obtained against infection with 1LD100 (1 x 10(6) of S. typhimurium. These results underline the specificity of host-parasite relations in infection and minimize the role attributed to the cellular mechanism, which is insufficient for protection against an infection if the pathogen tested is not specific for the host in experiment. In contrast to events in mice protected against the infection with S. typhimurium, and its related "in vivo", S. paratyphi B and S. paratyphi C, the antibodies initially present in the sera of the mice immunized with proteins from the human pathogens were no longer found 25 days after the infections. Reinfections of some of the groups of the surviving mice did not result in protections.