Contributions to the study of Salmonella. Immunological specificity of proteins separated from Salmonella typhi.

Rabbits were immunized with live organisms and with proteins separated by various methods from (acetone-treated cells); anti-extract and antibacterial sera were investigated in agglutination and gel diffusion tests with various antigens. The results show that the determinant groups of polysaccharides are not the sole factors involved in O agglutination of the bacteria. Apart from large amounts of H agglutinins and precipitins, anti-extract sera, containing no antibodies to polysaccharides, have been found to contain O agglutinating and precipitating antibodies. In tests performed with extracts containing the whole bacterial antigen complex, the antibodies precipitated from antibacterial sera by polysaccharides were found to account for about one-third to one-half of the total antibody content of these sera. Antibacterial sera absorbed with polysaccharide still contain O agglutinins which may be removed by subsequent saturation with protein. Gel diffusion tests illustrate the results obtained. The proteins separated from veronal buffer extracts by precipitation with trichloracetic acid are immunologically identical with the protein separated from the bacteria by means of dilute hydrochloric acid. From the serological and physicochemical points of view they behave like the flagellins isolated by Ada, Nossal, Pye and Abbot (1964) from flagella. As in the case of flagellins, attempts to purify the proteins isolated from the bacterial organisms did not result in separation of the factors involved in O and H agglutination. The peptide determinants involved in both types of agglutination may well coexist on the same molecule.