Stereospecificity of ginsenoside Rg3 in promotion of the immune response to ovalbumin in mice.

Our previous investigation demonstrated that ginsenoside Rg3 was active in promotion of the immune response. In this study, two epimers, 20(R)-Rg3 and 20(S)-Rg3, were compared for their adjuvant effects on the immune response against ovalbumin (OVA). BALB/c mice were immunized subcutaneously with 10 μg of OVA alone or with 10 μg of OVA mixed in 20(R)-Rg3 (50 μg) or 20(S)-Rg3 (50 μg) on days 1 and 15. Two weeks after the last immunization, blood was sampled to test IgG and the IgG subclasses as well as IFN-γ and IL-5; splenocytes were prepared to measure proliferative responses to stimulations with Con A, LPS and OVA and mRNA expressions of cytokines and transcription factors by reverse transcription-PCR. Results indicated that both 20(R)-Rg3 and 20(S)-Rg3 exhibited the adjuvant effect on OVA-induced immune responses. 20(R)-Rg3 promoted significantly higher serum-specific IgG and the IgG isotype responses in association with highly up-regulated serum IFN-γ and IL-5 than 20(S)-Rg3. In addition, 20(R)-Rg3 significantly enhanced splenocyte proliferative responses to Con A, LPS and OVA as well as mRNA expression of IFN-γ, IL-12, IL-4 and IL-10 and transcription factors T-bet and GATA-3 by splenocytes when compared with the 20(S)-Rg3. Therefore, ginsenoside Rg3 is stereospecific in stimulation of the immune response, and 20(R)-Rg3 has more potent adjuvant activity than 20(S)-Rg3.