Scorpion venom exhibits adjuvant effect by eliciting HBsAg-specific Th1 immunity through neuro-endocrine interactions

The Hottentotta rugiscutis scorpion venom (Hrv) contains neurotoxins, which elicit a strong innate immune response through the activation of the Hypothalamus-pituitary-adrenal axis, which could improve the quality of adaptive immunity. Hence, the Hrv was used as an adjuvant for the Hepatitis-B virus surface antigen (HBsAg) and assessed its ability in the activation of innate (NGF, CORT, cellularity, NO) and adaptive (IgM, IgG, IgG1/IgG2a/IgG2b/IgG3, Th1/Th2 cytokines, avidity) immunity. Here, the Hrv and HBsAg were given in the mixed form (HBsAg-Hrv) as well as in a separate form (HBsAg+Hrv). The NGF levels in plasma/spleen and CORT in plasma were found to be elevated optimally at 5 h and 6 h post-Hrv injection, respectively. Further studies showed that CORT and NGF levels were also highly upregulated in the HBsAg-Hrv group. The HBsAg-specific IgM titer was found to be increased in the HBsAg+Hrv group and total IgG was relatively similar among alum and Hrv-test groups, but IgG2a/IgG2b/IgG3 levels were higher along with IL-1β in HBsAg-Hrv groups. The study showed that the venom from H. rugiscutis acts as a vaccine adjuvant for HBsAg to develop strong antigen-specific Th1 immunity. The Hrv also enhances the antibody-avidity which may improve the neutralizing ability of antibodies with systemic infectious agents. The study also elucidated that the venom acts by neuroendocrine-immune mechanism and majorly impacts splenocytes through NGF and corticosterone.