Long-term antibody response and protective effect induced by attenuated scorpion toxins: Involvement of memory plasma cells.

In Algeria, Androctonus australis hector scorpion envenomation remains a major problem of public health because of non-efficient therapy. The development of safe vaccine against scorpion venom could be one key strategy for the envenomation prevention. The irradiation of venom by γ-rays develops suitable immunogens which produced effective antivenom and safe vaccine. In this study, we investigated the ability of the irradiated toxic fraction (γ-FtoxG50) to induce long-term memory humoral response in immunized animals (mice and rabbits), by involving the long-lived plasma cells to prevent efficiently the lethality of scorpion envenomation. For this purpose, an appropriate immunization schedule was established in mice and rabbits using three (3) similar doses of γ-FtoxG50 associated with Alum adjuvant. Obtained results indicate that the long-term immunogenicity of γ-FtoxG50 is able to induce the long-term memory humoral response with a high level of specific antibodies. The long-term persistence of antibody levels could depend on bone marrow memory plasma cells. These cells produce continuously antibodies without antigen stimulus. Furthermore, an enhanced memory response was obtained post-repeated envenomation with toxic native venom that leads to improved protection of animals. Together, pre-existing protective antibodies and the activation of memory B-cells could induce a rapid neutralization of scorpion toxins and long-term protection against scorpion envenomation.

Safety and efficiency of active immunization with detoxified antigen against scorpion venom: side effect evaluation.

OBJECTIVE: The efficiency and safety of vaccine are the most important properties, however, as any medication, it can induce side effects. This prophylactic therapy could be used to prevent the lethal and pathophysiological effects induced after scorpion envenomation. METHODS: In this study, detoxified venom associated to alum adjuvant (V*alum) is used as a vaccine against scorpion venom for immunization of mice. We evaluate the safety and the inflammatory response of this vaccine. We also investigated the protective effect of this formulation against the toxicity of native Androctonus australis hector venom. RESULTS: Results showed no adverse events occurred after immunization of animals. This active immunization of animals did not cause change in vascular permeability, no edema formation in the studied organs. Furthermore, there are no IgE production in sera, nor change in the morphology of the mast cells in skin tissues. However, low inflammatory response triggered by activating the recruitment of eosinophils associated to IL-4 and IL-5 release was observed. All immunized animals are protected from the toxic effects of native venom until 6 LD50 and to 7 LD50 after the second challenge. CONCLUSION: This safe vaccine preparation seems to induce a long-term protection without any risk of deleterious inflammatory response.