Expression of recombinant DnaK of Brucella abortus and its evaluation as immuno-modulator

Heat shock proteins are molecular chaperones that are immunogens as well as potent inducers of an antigen-specific immunological response. In this study, we aimed to evaluate if co-immunization of Brucella rOmp22 and rDnaK proteins had boosted immunogenic activity as compared to rOmp22 immunization alone in mice. For this, gene-encoding DnaK of B. abortus was cloned, expressed in E. coli and purified using Ni-NTA agarose. Immuno-modulatory effect of rDnaK protein was evaluated in mice when co-immunized with Brucella rOmp22. Four groups of mice (n = 6 per group) were used in the study. The control group was immunized with rOmp22 alone, while rOmp22 emulsified with conventional adjuvants (Freund's complete and incomplete adjuvants) and rOmp22 mixed with rDnaK were injected to group I and group II in mice, respectively. Group III mice were immunized with rDnaK alone. IgG class switching (IgG1 and IgG2a) response to immunization was assessed by enzyme-linked immunosorbent assay and expression of IL-4 and IL-12 mRNA was assessed by real-time PCR to evaluate the immune response in mice. The ratio of IgG1-IgG2a was less than 1 in mice co-immunized with rOmp22 and rDnaK, indicating that the immune response was directed towards CMI arm in this group of mice. Moreover, IL-12 mRNA expression was also up-regulated to a greater extent in mice co-immunized with rOmp22 and rDnaK as compared to those immunized with rOmp22 along with the conventional adjuvants, or rOmp22 alone. Our data suggest that rDnaK could be responsible for modulating the immune response, specifically the CMI response.