Abstract
We earlier demonstrated the immunoprophylactic efficacy of recombinant heavy chain myosin (Bm-Myo) of Brugia malayi (B. malayi) in rodent models. In the current study, further attempts have been made to improve this efficacy by employing alternate approaches such as homologous DNA (pcD-Myo) and heterologous DNA/protein prime boost (pcD-Myo+Bm-Myo) in BALB/c mouse model. The gene bm-myo was cloned in a mammalian expression vector pcDNA 3.1(+) and protein expression was confirmed in mammalian Vero cell line. A significant degree of protection (79.2%±2.32) against L3 challenge in pcD-Myo+Bm-Myo immunized group was observed which was much higher than that exerted by Bm-Myo (66.6%±2.23) and pcD-Myo (41.6%±2.45). In the heterologous immunized group, the percentage of peritoneal leukocytes such as macrophages, neutrophils, B cells and T cells marginally increased and their population augmented further significantly following L3 challenge. pcD-Myo+Bm-Myo immunization elicited robust cellular and humoral immune responses as compared to pcD-Myo and Bm-Myo groups as evidenced by an increased accumulation of CD4+, CD8+ T cells and CD19+ B cells in the mouse spleen and activation of peritoneal macrophages. Though immunized animals produced antigen-specific IgG antibodies and isotypes, sera of mice receiving pcD-Myo+Bm-Myo or Bm-Myo developed much higher antibody levels than other groups and there was profound antibody-dependent cellular adhesion and cytotoxicity (ADCC) to B. malayi infective larvae (L3). pcD-Myo+Bm-Myo as well as Bm-Myo mice generated a mixed T helper cell phenotype as evidenced by the production of both pro-inflammatory (IL-2, IFN-γ) and anti-inflammatory (IL-4, IL-10) cytokines. Mice receiving pcD-Myo on contrary displayed a polarized pro-inflammatory immune response. The findings suggest that the priming of animals with DNA followed by protein booster generates heightened and mixed pro- and anti-inflammatory immune responses that are capable of providing high degree of protection against filarial larval invasion.
Highlights
Lymphatic filariasis (LF), a neglected tropical disease caused by Wuchereria bancrofti, Brugia malayi (B. malayi) and B. timori affects ~1.4 billion people globally
We earlier picked up Bm-Myo cDNA clone by immunoscreening of adult female B. malayi cDNA λuniZap expression library and demonstrated its potential as an immunoprophylactic candidate antigen in single [13] as well as cocktail immunization with two other B. malayi recombinant proteins; independent phosphoglycerate mutase (Bm-iPGM) and trehalose6-phosphate phosphatase (Bm-TPP) in rodent model [17]
The DNA vaccines remain poorly immunogenic compared to protein vaccines [39], new findings suggest that the prime-boost can be more immunogenic than the homologous vaccination and may elicit unique immune responses allowing for improved immunogenicity and protection against viral, bacterial, and parasitic infections [40,41,42,43,44]
Summary
Lymphatic filariasis (LF), a neglected tropical disease caused by Wuchereria bancrofti, Brugia malayi (B. malayi) and B. timori affects ~1.4 billion people globally. Irradiated L3, recombinant proteins [6,7,8] and subunit vaccines [9,10,11] have been employed in the past to discover safe and effective vaccine against human filariids. Several efforts have been employed to improve the efficacy of DNA vaccine such as codon/promoter optimization [24,25,26], use of adjuvants [27,28], formulations [29,30] and heterologous prime-boost regimes [31,32]. Attempts have been made in the current investigation to generate protective immune response employing Bm-Myo as DNA, DNA prime/protein-boost in BALB/c mice and their immunoprophylactic efficacies have been compared with the purified recombinant myosin
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