Ribonucleic acid-protein purified from Salmonella typhi involved in experimental immunity

An immunogenic complex was obtained from Salmonella typhi by the bacterial acetone powder method. This complex induced in mice a high degree of protection against a challenge with the virulent Salmonella. This immunogenic complex was fractionated at least into 19 fractions when chromatographied on a DEAE-cellulose column. By SDS-polyacrylamide gel electrophoresis, 25 protein bands were observed. Eleven DEAE-cellulose fractions were tested in order to know their immunogenicity. Mice were inoculated with 10 micrograms of protein of each fraction. Seven days after, the mice received a booster. Thirty days after the first inoculation, the animals were challenged with S. typhi resuspended in chondroitin-sulphate at 13%, by the intraperitoneal route. Appropriate control mice were included; 30 min before the challenge, mice had been inoculated with 850 microgram of lead acetate by the intravenous route. The immunogenic complex protected 100% of mice; six of its fractions were good immunogens; one of them, the fraction 4, was shown to contain at least 3 proteins by electrophoresis assay. This fraction induced in mice a high degree of protection against the challenge by the virulent Salmonella. Finally, a ribonucleoprotein purified from this fraction was highly immunogenic to mice against the challenge by 10 LD50 of S. typhi (1 LD50 was equivalent to 2 X 10(6) CFU).