Why are the killed S. typhi vaccines ineffective.

The mosaic of proteins synthesized by S. typhi, S. enteritidis and E. coli, induced in immunized rabbits corresponding antibodies that precipitated almost indiscriminately numerous heterologous antigens. Antibodies induced against eventual specific antigens could not be identified unless the sera were absorbed with heterologous proteins. The comparative immunochemical analysis of the total and absorbed sera proved that the proteins from E. coli are mixed with proteins sharing Salmonella specificities while E. coli proteins are present in the mixtures of proteins isolated from S. enteritidis and S. typhi. The absorption of anti S. typhi sera with proteins from different E. coli serotypes, removed a large amount of antibodies, leaving free for reaction those induced against Salmonellae common proteins. The absorption of the anti S. typhi sera with proteins from S. enteritidis eliminated the totality of preciptating antibodies meaning that no specific antibody was induced in the sera of animals immunized with S. typhi proteins. In contrast, the S. enteritidis proteins induced antibodies against a specific S. enteritidis protein, in addition to numerous heterologous determinants; the existence of the specific antibody was evident in all the absorbed sera, notwithstanding the eventual relationship with the heterologous absorbing proteins. Absorptions of the antisera to proteins from E. coli with proteins from either S. typhi or S. enteritidis removed the antibodies induced against the absorbing proteins leaving free for reactions antibodies for the specific E. coli proteins. As the behaviour in vivo of the human pathogen is quite different form that of E. coli or S. enteritidis, the absence of a specific antigen in the material synthesized by S. typhi grown on artificial media provides an explanation for the inefficacy of vaccinations with killed S. typhi.