Immunity to Experimental Salmonella Infection: Studies on the Protective Capacity and Immunogenicity of Lipopolysaccharide, Acetone-Killed Cells, and Ribosome-Rich Extracts of Salmonella Typhimurium in C3H/HeJ and CD-1 Mice

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Abstract
Phenol-water-extracted lipopolysaccharide of Salmonella typhimurium, strain W118-2, was tested for protective capacity and immunogenicity in C3H/HeJ and CD-1 mice 21 days post vaccination. It was found that in C3H/HeJ mice the LPS was not protective and gave no anti-O titer, as measured by passive hemagglutination, whereas in CD-1 mice it was protective and immunogenic. In contrast, acetone-killed cells and a ribosomal vaccine prepared from the same strain of Salmonella were protective and resulted in an anti-O titer in both the C3H/HeJ and the CD-1 mice. It was shown, therefore, that LPS co-extracted with ribosomes, or present in whole cells, is more immunogenic for C3H/HeJ mice than phenol-water purified LPS. These observations imply that ribosome-rich extracts and acetone-killed cells contain substances, in addition to LPS, that modulate the immune response in C3H/HeJ mice. It was also observed that ribosomal vaccine prepared from a rough strain of S. typhimurium, strain TA1659, that lacks O antigens and makes LPS of the Rc type, did not protect C3H/HeJ or CD-1 mice against Salmonella infection. Mixtures of LPS with ribosomal vaccine derived from this mutant were also tested for their protective capacity. The results are discussed with regard to the antigens involved in immunity to Salmonella infection.