VARIATION IN BRUCELLA-ABORTUS-2308 INFECTION IN BALB C MICE INDUCED BY PRIOR VACCINATION WITH SALT-EXTRACTABLE PERIPLASMIC PROTEINS FROM BRUCELLA-ABORTUS-19/

The study compared the immune and protective responses induced in BALB /c mice vaccinated with six salt-extractable periplasmic protein fract ions (Brucella cell surface proteins [BCSP]) of Brucella abortus 19 an d later challenge exposed with B. abortus 2308. BCSP70 was precipitate d with ammonium sulfate at 70% saturation, and BCSP100 was precipitate d with ammonium sulfate at 100% saturation by use of supernatant fluid of BCSP70 that had been precipitated with 70% ammonium sulfate. Four subfractions were separated from BCSP100 by anion-exchange high-perfor mance liquid chromatography (HPLC). Monophosphoryl lipid A (MPL) from Salmonella typhimurium Re mutant strain was used as a potential immune response modifier in some vaccines. Reduced or increased numbers of C FU and increased spleen size in the principal groups of mice relative to that of the nonvaccinated control group were considered protectiven ess or virulence (survival) criteria. Results indicated that vaccines prepared from BCSP70 and BCSP100 were moderately protective and immuno genic. The subfractions designated BCSP100-A through BCSP100-D purifie d by anion-exchange HPLC were not protective when MPL was not used as an immune response modifier. However, two subfractions were associated with significant (P < 0.05) increases in CFU per spleen and splenomeg aly in vaccinated mice compared with those in nonvaccinated challenge- exposed mice. MPL enhanced protection or was neutral when used with BC SP70, BCSP100, BCSP100-C, and BCSP100-D. Serologic results of an enzym e-linked immunosorbent assay indicated that MPL modulated the immunogl obulin G responses induced by BCSP70, BCSP100, and subfraction BCSP100 -B vaccines only. The overall results suggest that certain proteinaceo us periplasmic fractions might serve as virulence or survival factors in B. abortus infections.