Immunological responses to Salmonella R antigens. The bacterial cell and the protein edestin as carriers for R oligosaccharide determinants.

Abstract

Responses in rabbits to heat-killed Salmonella minnesota R mutants (chemotypes Ra, Rc and Re) were heterogeneous with respect to the amounts and specific haemagglutinin activities (SHAA) of IgM and IgG antibodies produced to each mutant. Amounts of antibodies in IgM and IgG fractions of sera were determined by quantitative precipitation. For comparison, antibodies were also isolated using an R oligosaccharide-specific immunoadsorbent and quantitated spectrophotometrically. SHAA (haemagglutinating units/mg antibody) of IgG antibodies were similar for all three mutants. In contrast, the Ra mutant induced IgM antibodies with the highest SHAA, while the Re mutant induced IgM antibodies 10-fold lower in activity. The ratio of the amount of IgM/IgG produced was approximately 1/1 for both the Ra and the Rc mutants, while the ratio for the Re mutant was about 1/2. Salmonella R oligosaccharide-protein conjugates (chemotypes Rb2, Rc and Re) were prepared, and the responses to these antigens were compared with those to the heat-killed mutants. The conjugates were specific for the given chemotype, and they were strongly immunogenic when incorporated into Freund's complete adjuvant and administered intramuscularly. Haemagglutinin titres were relatively high, but amounts of antibodies were considerably reduced when the conjugates were administered intravenously without adjuvant. Rabbits immunized with the conjugates in the same manner as with heat-killed R mutants produced predominantly IgM responses in all three cases.