The pathogenic and immunogenic activities ofSalmonella typhiin relation to its antigenic constituents

Abstract

1. The most virulent strains ofSalmonella typhiare those that develop both the Vi and O antigens in maximum quantities.2. The Vi antigen is not a particularly toxic substance; it is less toxic for the mouse than the O antigen.3. The main biological function of the Vi antigen is to protect the O antigen against the action of the natural or immune O antibody, thereby protecting the bacterial cell against phagocytosis and the bactericidal action of the serum.4. The relative virulence for mice of freshly isolated strains ofSalmonella typhireflects their virulence for man.