VACCINATION WITH BRUCELLA-ABORTUS ROUGH MUTANT RB51 PROTECTS BALB C MICE AGAINST VIRULENT-STRAINS OF BRUCELLA-ABORTUS, BRUCELLA-MELITENSIS,AND BRUCELLA-OVIS/

Vaccination of BALB/c mice with live Brucella abortus RB51, a stable r ough mutant, produced protection against challenge with virulent strai ns of Brucella abortus, Brucella melitensis, and Brucella ovis. Passiv e-transfer experiments indicated that vaccinated mice were protected a gainst B. abortus 2308 through cell-mediated immunity, against B. ovis PA through humoral immunity, and against B. melitensis 16M through bo th forms of immunity. Live bacteria were required for the induction of protective cell-mediated immunity; vaccination with whole killed cell s of strain RB51 failed to protect mice against B. abortus 2308 despit e development of good delayed-type hypersensitivity reactions, Protect ive antibodies against the heterologous species were generated in vacc inated mice primarily through anamnestic responses following challenge infections. Growth of the antigenically unrelated bacterium Listeria monocytogenes in the spleens of vaccinated mice indicated that nonspec ific killing by residual activated macrophages contributed minimally t o protection. These results encourage the continued investigation of s train RB51 as an alternative vaccine against heterologous Brucella spe cies. However, its usefulness against B. ovis would be limited if, as suggested here, epitopes critical for protective cell-mediated immunit y are not shared between B. abortus and B. ovis.