Immunogenic and antigenic characteristics of Salmonella heat-labile enterotoxin

The intramuscular immunization of rabbits with enterotoxin of S. weltevreden failed to provide protection against challenges with homologous Salmonella enterotoxin as well as heterologous enterotoxins (cholera toxin or E. coli LT). Similar results were obtained in rabbits immunized with cholera toxin, choleragenoid and E. coli LT. However, Salmonella antitoxin contained neutralizing antibodies against Salmonella enterotoxin (but not against cholera toxin) and thus was capable of neutralizing Salmonella enterotoxin when tested for skin permeability reaction. Immunodiffusion experiments showed that antitoxin prepared against the enterotoxin of one of the strains of S. weltevreden formed precipitin bands with enterotoxin preparations of 5 strains of S. weltevreden and 2 strains of S. anatum. However, Salmonella antitoxin failed to form precipitin bands with enterotoxins of other heterologous Salmonella species (S. dublin, S. enteritidis, S. hindmarsh and S. newport), cholera toxin and E. coli LT. The immunoelectrophoretic studies corroborated the results obtained by double immunodiffusion experiments. However, both Salmonella and cholera toxins migrated electrophoretically toward the cathode and resembled globulin in this respect. Salmonella enterotoxin, though immunogenic, yet proved unprotective through the parenteral route and appears to be antigenically distinct from cholera and E. coli enterotoxins.