Evaluation of recombinant leukocidin domain of VvhA exotoxin of Vibrio vulnificus as an effective toxoid in mouse model

• Mouse immunized with rL/VvhA demonstrated substantial degree of serum antibodies.
• Anti-rL/VvhA antibodies neutralized cytotoxicity in vitro.
• The rL/VvhA induced co-expression of Th1 and Th2 immune response.
• Active immunization demonstrated protection in mouse model.
• Protected intestinal tissue damage against native VvhA toxin challenge.

Vibrio vulnificus hemolysin A (VvhA) is a pore forming toxin and plays an important role in the pathogenesis. The hemolytic and cytotytic property of VvhA toxin is associated with N-terminal leukocidin domain which triggers apoptotic signaling cascade in epithelial cells. The present study was undertaken to assess the protective efficacy of recombinant VvhA leukocidin domain (rL/VvhA) against VvhA toxin challenge using in vitro and in vivo assays. The rL/VvhA protein was found to be non-toxic with no significant hemolytic or cytotoxic effects. Intraperitoneal (I.P.) immunization of BALB/c mice with rL/VvhA protein elicited significantly higher specific serum antibody titer with mixed Th1/Th2 mediated immune responses. HeLa cell monolayer supplemented with anti-rL/VvhA antibodies were effectively protected (viability 86.69%) against lethal 5 LD50 toxin challenge. An effective in vitro proliferation of lymphocyte was observed upon re-stimulation of rL/VvhA primed splenocytes with formalin inactivated VvhA toxin (fVvhA). Co-expression of Th1/Th2 polarized cytokines (IFN-γ, IL-12 and IL-4), were seen in the cell culture supernatant. In contrast to sham immunized mice, rL/VvhA immunized mice demonstrated significant protection (90% survival) against native toxin challenge in vitro and in vivo infection models. These results suggested leukocidin domain of the VvhA toxin as protective immunogen for possible protection against V. vulnificus VvhA.