Studies on the immune protection to murine experimental brucellosis conferred by Brucella fractions. I. Positive role of immune serum.

Mouse inoculation with three different phenol-insoluble fractions extracted from Brucella melitensis (fractions 'PI', '4A' and '5') induces an acceleration of the blood clearance of i.v. inoculated live Brucella and a diminution of the rate of multiplication of the injected bacteria in the spleen. Preincubation of the challenge inoculum in immune serum or i.p. injections of immune serum confer a good specific protection to non-immunized hosts. The results observed with fractionated sera suggest that, not only antibodies, but also other serum constituents may participate in the protective activity of immune sera. This discussed in terms of the respective importance of humoral and cellular immunity to Brucella and of the choice of the best preparations for human or animal vaccination.