Immunogenicity and protective efficacy of Recombinase A from Wolbachia endosymbiont of filarial nematode Brugia malayi (wBmRecA).

ABSTRACT

Lymphatic filariasis causes global morbidity. Wolbachia, an endo-symbiotic intracellular bacterium of the filarial nematode helps in their growth and development, regulates fecundity in female worms and contributes to the immunopathogenesis of the disease. However, genes and proteins of Wolbachia that may act as putative vaccine candidates are not known. In this study, we cloned recombinase-A protein of Wolbachia from Brugia malayi (wBmRecA) and carried out its detailed biochemical and immunological characterization. Bioinformatics analysis, circular dichroism and fluorescence spectral studies showed significant sequence and structural similarities between wBmRecA and RecA of other alpha-proteo- bacterial species. wBmRecA was ubiquitously expressed in all the three major life stages of B. malayi, including excretory-secretory products of the adult worm. In silico studies suggested immunogenic potential of wBmRecA, and mice immunized with wBmRecA exhibited elevated levels of immunoglobulins IgG1, IgG2a, IgG2b and IgG3 in their serum along with increased percentages of CD4+, CD8+ T cells and CD19+ B cells in their spleens. Notably, splenocytes from immunized mice showed increased m-RNA expression of T-bet, elevated proinflammatory cytokines IFN-γ and IL-12, while peritoneal MФs exhibited increased levels of iNOS, downregulated Arg-1 and secreted copious amounts of nitric oxide which contributed to severely impaired development of the infective larvae (Bm-L3). Interestingly, sera from immunized mice promoted significant cellular adherence and cytotoxicity against microfilariae and Bm-L3. Importantly, wBmRecA demonstrated strong immuno-reactivity with bancroftian sera from endemic normal individuals. These results suggest that wBmRecA is highly immunogenic, and should be explored further as a putative vaccine candidate against lymphatic filariasis.