Adjuvant effects of protopanaxadiol and protopanaxatriol saponins from ginseng roots on the immune responses to ovalbumin in mice

Protopanaxadiol saponins (Rg3, Rd, Rc, Rb1 and Rb2) and protopanaxatriol saponins (Rg1, Re and Rg2) isolated from the root of Panax ginseng C.A. Meyer were evaluated for their adjuvant effects on the immune responses to ovalbumin (OVA) in mice. BALB/c mice were subcutaneously injected twice at a 3-week interval with 10 μg of ovalbumin or 10 μg of OVA plus 50 μg of ginsenosides Rg3, Rd, Rc, Rb1, Rb2, Rg1, Re or Rg2 or Quil A (n = 5). Blood samples were collected for measuring specific total-IgG, IgG1 and IgG2a, and splenocytes were harvested for determining lymphocyte proliferation as well as IFN-γ and IL-5 production 2 weeks after the boosting. The results indicated that OVA-specific antibody responses were significantly higher in mice immunized with OVA co-administered with Rg1, Re, Rg2, Rg3 and Rb1 but not with Rd, Rc and Rb2 when compared with the control (immunized with OVA only). Significantly enhanced splenocyte proliferative responses to Con A, LPS and OVA as well as the production of both IL-5 and IFN-γ stimulated by OVA were also detected in mice immunized with OVA co-administered with Rg1 but not with Rb1, Re and Rg3. Of the ginsenosides studied, Rg1, Re, Rg2, Rg3 and Rb1 have more potent adjuvant properties than the others, indicating that they are the major constituents contributing to the adjuvant activities of total ginseng saponins. Varieties of ginsenosides in adjuvant activity might be attributed to the varieties of molecular conformations determined by the side sugar chains attaching to their dammarane skeleton.