Screening and appraisal for immunological adjuvant-active fractions from Platycodon grandiflorum total saponins

In this study, the total saponins from the root of Platycodon grandiflorum (PGS(t)) was subjected to D101 macroreticular resin column chromatography to afford four fractions (PGS₃₀, PGS₅₀, PGS₇₅ and PGS₉₅). PGS(t) and its four fractions were evaluated and compared for the haemolytic activities and adjuvant potentials on the specific cellular and humoral immune responses of ICR mice against recombinant hepatitis B surface antigen (HBsAg). PGS(t), PGS₃₀, PGS₅₀, PGS₇₅, and PGS₇₅ showed a slight haemolytic effect, with their concentration inducing 50% of the maximum haemolysis (HD₅₀) being 16.13 ± 0.81, >200, 17.53 ± 0.24, 20.16 ± 0.76, 76.31 ± 2.20 μg/mL against 0.5% rabbit red blood cell, respectively. PGS(t), PGS₅₀, and PGS₇₅ significantly not only enhanced the Con A-, lipopolysaccharide-, and HBsAg-induced splenocyte proliferation, but promoted the killing activities of natural killer (NK) cells from splenocytes in HBsAg-immunized mice (P < 0.01 or P < 0.001). HBsAg-specific IgG, IgG1, IgG2a, and IgG2b antibody levels in serum were also significantly enhanced by PGS(t), PGS₅₀, and PGS₇₅ compared with HBsAg control group (P < 0.05, P < 0.01, or P < 0.001). Moreover, the adjuvant effects of PGS₅₀ and PGS₇₅ on the cellular immune responses and HBsAg-specific IgG2a and IgG2b antibody responses were more significant than those of Alum, PGS₃₀, and PGS₉₅. The results indicated that PGS₅₀ and PGS₇₅ could improve both cellular and humoral immune responses, and elicit a balanced Th1/Th2 response to HBsAg in mice, and that PGS₇₅ may be developed as an ideal candidate adjuvant for hepatitis B vaccine.