Haemolytic activity and adjuvant effect of soyasaponins and some of their derivatives on the immune responses to ovalbumin in mice.

Immunological adjuvants are agents that enhance specific immune responses to vaccines. At present more studies are needed to identify a suitable adjuvant for a particular vaccine with maximum safety and efficacy. In this study, six soyasaponins (Aa, Ab, Af, Ba, Bb, and Bb') and three soyasaponin Ab-derivatives (AbDs) were selected to evaluate their toxicities and adjuvant activities. The haemolytic activity assay was performed to evaluate the toxicity of the tested soyasaponins and AbDs. Immunoadjuvant activity was investigated in vivo and in vitro using a splenocyte proliferation assay and sera indirect ELISA. Our results demonstrated that soyasaponins and AbDs showed a slight haemolytic effect to 0.5% red blood cell. Except for the Af and Ba groups, other soyasaponins and AbDs groups stimulated by concanavalin A (ConA) and lipopolysaccharide (LPS) showed a greater proliferative response at appropriate doses (0.01-10 μg/ml) compared with the control and Alum groups. Anti-OVA IgG, IgG1, IgG2a, and IgG2b were significantly enhanced by the soyasaponins (Ab, Ba, Bb, and Bb'), QS and AbDs groups (p < 0.05 or p < 0.01). In addition, three AbDs indicated a tendency of immunoadjuvant potential improvement after structural modification. Moreover, Ab-D2 showed adjuvant activity at the lowest injection dose among the three AbDs. In conclusion, these results suggested that soyasaponins together with their derivatives may represent viable candidates for effective vaccine adjuvants due to their higher immune response and lower or non-haemolytic effects.