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 12(2) were formed rapidly and to extremely high levels in rabbits immunized with either Salmonella typhi (O 9,12(1),12(2),12(3)) or S. paratyphi B (O 1,4,5,12(1),12(2)), whereas factor 12(3) in S. typhi and factor 1 in S. paratyphi B induced only minimal responses. However, rabbits immunized with S. paratyphi A var. durazzo (O 2,12(1),12(3)), which lacks factor 12(2), produced high levels of agglutinins to the 12(3) 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.