In this study, the immunogenicity and protective efficacy of recombinant proteins Omp19 (rO) and P39 (rP) from Brucella abortus were evaluated individually and compared with the cocktail protein (rO+rP) against B. abortus 544 and Brucella melitensis 16M infection in BALB/c mouse model. Intra-peritoneal (I.P.) immunization with rO+rP cocktail developed substantially higher antibody titers predominant with Th1 mediated isotypes (IgG2a/2b). Western blot analysis using anti-rO+rP antibodies showed specific reactivity with native Omp19 (19 kDa) and P39 (39 kDa) among whole cell proteins of B. abortus and B. melitensis. Splenocytes extracted from rO+rP immunized mice induced significantly (P<0.001) higher proliferative responses at 30 μg/ml with considerable expression of pro-inflammatory cytokines (IFN-γ, IL-2 and IL-12) than rO and rP. Macrophage cell (RAW 264.7) monolayer supplemented with anti-rO+rP polysera exhibited enhanced viability against challenge with B. abortus 544 (72.27%) and B. melitensis 16M (68.57%). On the other hand, individual anti-rO and anti-rP polysera resulted in relatively lesser protection against the pathogens (64.79%, 54.45% and 47.13%, 45.11%, respectively). Immunized group of mice when I.P. challenged with 5 × 10(4) CFU of B. abortus 544 and B. melitensis 16M were found significantly (P<0.001) protected in the rO+rP group (log units of protection, spleen: 2.38, 2.12; liver: 1.04, 0.81, respectively) than in rO (spleen: 1.43, 1.21; liver: 0.7, 0.47) and rP (spleen: 1.24, 1.17; liver: 0.65, 0.34). Findings from this study depicted that rO+rP cocktail is highly immunogenic with the Th1 predominant serum antibody titers and T-cell mediated immune protection, would be a valuable intervention in the development of a safer and improved Brucella vaccine.
Keywords: B. abortus; B. melitensis; Omp19; P39; Protein cocktail (rO+rP).
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