Ginsenoside Re as an adjuvant to enhance the immune response to the inactivated rabies virus vaccine in mice

• The adjuvant effect of Ginsenoside Re to improve the immune response was evaluated.
• Ginsenoside Re enhanced the antibody titers in mice immunized with rabies vaccine.
• Similar protection was achieved by low-dose of vaccine with Re as did of high-dose.
• Ginsenoside Re activated both cellular and humoral immune responses in this model.

The inactivated rabies virus vaccine (RV) is a relatively expensive vaccine, prone to failure in some cases. Ginsenoside Re (Re) is a saponin isolated from Panax ginseng, and has an adjuvant property. Here the adjuvant effect of Re to improve the immune response to the RV is evaluated in mice. ICR mice were immunized with saline, 2.50 mg/kg Re, 20 μl RV, 100 μl RV, or 20 μl of RV adjuvanted with Re (1.25, 2.50 or 5.00 mg/kg). Different time points after boosting, we measured serum antibodies in blood samples and separated splenocytes to detect lymphocyte proliferation and the production of IL-4, IL-10, IL-12, and IFN-γ in vitro. We also compared immunizations containing 20 μl RV and 20 μl RV adjuvanted with Re (5.00 mg/kg) for the expression of CD4+ and CD8+ T-cell subsets at different time points. Results indicated that co-administration of Re significantly enhanced serum antibody titers, increased the CD4+:CD8+ ratio, and enhanced both proliferation responses and IL-4, IL-10, IL-12 and IFN-γ secretions. Both Th1 and Th2 immune responses were activated. The supplementation of the Re (5.00 mg/kg) to 20 μl of RV significantly amplified serum antibody responses and Th1/Th2 responses inducing similar protection as did 100 μl of RV. This suggests that Re could be used to reduce the dose, and therefore the cost, of the RV to achieve the same effective protection. Re merits further studies for use with vaccines of mixed Th1/Th2 immune responses.