Antibody response to various single-factor o antigens of salmonella

The relative agglutinin responses to various single O-antigenic (Kauffmann-White) factors were measured after immunization of rabbits with several strains of heat-killed salmonella organisms. As expected, the relative strength of the responses to the various O factors was quite varied and in some cases depended on the presence or absence of other single factors. For example, antibodies to factor 12₂ were formed rapidly and to extremely high levels in rabbits immunized with either Salmonella typhi (O 9,12₁,12₂,12₃) or S. paratyphi B (O 1,4,5,12₁,12₂), whereas factor 12₃ in S. typhi and factor 1 in S. paratyphi B induced only minimal responses. However, rabbits immunized with S. paratyphi A var. durazzo (O 2,12₁,12₃), which lacks factor 12₂, produced high levels of agglutinins to the 12₃ antigenic determinant. In general, most of the agglutinin responses to the various single factors measured were formed in parallel, but there were several exceptions. For instance, the responses to factors 4 and 5 were relatively strong in rabbits receiving three graded doses of S. paratyphi B. However, agglutinins to factor 4 did not appear until after the second injection, and not at all in rabbits given the full amount of antigen in one injection. In contrast, antibodies to factor 4 were formed rapidly in rabbits receiving three graded doses of a strain of S. typhimurium (O 1,4,12) lacking factor 5. Good overall agreement was obtained between agglutination and hemagglutination assays of antibodies, as demonstrated by the responses to the various O factors of S. friedenau. It was concluded that measurement of the antibody responses to the various single-factor O antigens throughout the immunization program was necessary for effective evaluation of the relative significance of these factors in antibody formation against intact bacteria.