The immunogenic activity of ribosomal fractions derived from Brucella abortus.

The immunizing activity of ribosome preparations derived from Brucella abortus strain 19 cells was examined in guinea-pigs and mice. After subcutaneous injections of Br. abortus ribosomes in Freund's incomplete adjuvant, both mice and guinea-pigs developed immunity to challenge by virulent Br. abortus 544 organisms which was at least as effective as the protection conferred by live strain 19 vaccine. Both mice and guinea-pigs also developed agglutinating and complement-fixing antibodies and delayed hypersensitivity to Br. Abortus antigens. Conversely, ribosome preparations elicited delayed hypersensitivity reactions on intracutaneous injection into guinea-pigs chronically infected with Br. abortus or Br. melitensis. On injection into rabbits, Br. abortus ribosomes incorporated in incomplete adjuvant induced high titres of agglutinins, complement fxing antibodies and precipitins for Br. abortus antigens. On immunochemical examination, the ribosome preparations were not grossly contaminated with antigens derived from the cell surface. They were chemically complex, however, and in addition to RNA contained numerous protein components identified by disk electrophoresis. The nature of the components responsible for conferring protection against Br. abortus was not determined.