Preliminary assessment of adjuvant activities of Glycine Max (L.) Merr saponin extract in BALB/c mice immunized with hepatitis B virus vaccine [version 1; peer review: awaiting peer review]

Background: Vaccine adjuvants are used to increase the immunogenicity of weak antigens. Some saponins have adjuvant effects that are exerted via their immune-stimulatory effects and production of cytokines. Soybean ( Glycine max (L.) Merr.) contains saponins that could provide affordable vaccine adjuvants. This study aimed to assess the effect of the saponin extracts of soybean on the immune system in BALB/c mice immunized with the hepatitis B virus (HBV) vaccine and hepatitis B surface antigen (HBsAg). Methods: Saponins were extracted from soybean meal and their presence confirmed by foam generation and Fourier-transform infrared methods. A total of 51 mice were immunized in triplicate with 50 µL of various regimens of concentrations of the extracts and either HBV vaccine or HBsAg. The plasma anti-HBsAg antibody titre was determined using an enzyme immunosorbent assay (ELISA) 14 days post-immunization. Gene expression levels of interleukin-6 (IL-6) and tumour necrosis factor alpha (TNF-α), and haematological profile of the blood samples were determined. Results: When the two immunogens were co-administered with the soybean extract, immune response was slightly higher (0.799 + 0.013 for HBsAg and 0.758 + 0.012 for vaccine) than with the Revac B vaccine used alone. However, this difference was not statistically significant (p-value > 0.467, and 0.416 respectively) . Unexpectedly, mice immunized with the vaccine expressed less IL-6 levels than the untreated mice (0.603- and 1.469-fold change in transcription (FCT), respectively). Mice treated with the vaccine expressed higher TNF-α levels than the untreated group (28.84 –and 1.00 FCT respectively) while adding the extract significantly reduced the expression of TNF-α (p < 0.063 ). Administration of immunogens and extract reduced neutrophil ( P-value = 0.027) and platelet ( p-value > 0.592) counts. Conclusions: The study demonstrated that soybean extract lacked marked adjuvant activity for HBV vaccine, that HBV vaccine suppressed expression of IL-6 and promoted expression of TNF-α.