Platycodin D2 is a potential less hemolytic saponin adjuvant eliciting Th1 and Th2 immune responses

Platycodin D2 (PD2), a saponin isolated from the root of Platycodon grandiflorum, was evaluated for its haemolytic activity and adjuvant potential on the cellular and humoral immune responses to ovalbumin (OVA) in ICR mice. The HD(50) values of PD2 and Quit A were 18.57 +/- 1.37 and 5.76 +/- 0.23 mu g/ml against 0.5% rabbit red blood cell, respectively, implicating the less haemolytic activity for PD2 than Quit A. ICR mice were immunized subcutaneously with OVA 100 mu g alone or with OVA 100 mu g dissolved in saline containing Alum (200 mu g), or PD2 (25, 50, 75 or 100 mu g) on Day 1 and 15. Two weeks later (Day 28), concanavalin A (Con A)-, lipopolysaccharide (LPS-) and OVA-stimulated splenocyte proliferation and OVA-specific antibodies in serum were measured. PD2 significantly enhanced the Con A-, LPS-, and OVA-induced splenocyte proliferation in the OVA-immunized mice (P<0.05, P<0.01 or P<0.001). OVA-specific IgG, IgG1, IgG2a, and IgG2b antibody titers in serum were also significantly enhanced by PD2 compared with OVA control group (P<0.05, P<0.01 or P<0.001). Further, the effects of PD2 on mRNA expression of cytokines and transcription factors in Con A-stimulated mice splenocytes were evaluated by RT-PCR analysis. PD2 significantly promoted the mRNA expression of cytokines IL-2, IFN-gamma, IL-4, and IL-10 and transcription factors T-bet and GATA-3 (P<0.05, P<0.01 or P<0.001). In conclusion, the results suggest that PD2 could be safety used as adjuvant eliciting Th1 and Th2 immune responses. (C) 2008 Elsevier B.V. All rights reserved.