A promising balanced Th1 and Th2 directing immunological adjuvant, saponins from the root of Platycodon grandiflorum

The haemolytic activities and adjuvant potentials of Platycodon grandiflorum saponin (PGS) and its fractions on the cellular and humoral immune responses of ICR mice against ovalbumin (OVA) were evaluated. PGS was subjected to silica gel column chromatography to afford four fractions, and two fractions PGSC and PGSD selected for testing for activities because of containing dominant saponin peaks. PGS, PGSC, and PGSD showed a slight haemolytic effect, with their HD50 value being 37.91 ± 2.24, 21.30 ± 1.22, 37.58 ± 1.86 μg/ml against 0.5% rabbit red blood cell, respectively. ICR mice were immunized subcutaneously with OVA 100 μg alone or with OVA 100 μg dissolved in saline containing Alum (200 μg), Quil A (10 μg), PGS (50, 100 or 200 μg), PGSC, or PGSD (25, 50 or 100 μg) on days 1 and 15. Two weeks later (day 28), concanavalin A (Con A)-, pokeweed (PWM)-, and OVA-stimulated splenocyte proliferation and OVA-specific antibodies in serum were measured. PGS and PGSC significantly enhanced the Con A-, PWM-, and OVA-induced splenocyte proliferation in OVA-immunized mice at three doses (P < 0.01 or P < 0.001). However, no significant differences (P > 0.05) were observed among the OVA group, OVA/Alum group and OVA/PGSD group. OVA-specific IgG, IgG1, and IgG2b antibody levels in serum were significantly enhanced by PGS, PGSC, and PGSD compared with OVA control group (P < 0.05, P < 0.01, or P < 0.001). Moreover, the adjuvant effects of PGSC (50 or 100 μg) on the OVA-specific IgG, IgG1, and IgG2b antibody responses to OVA in mice were more significant than those of Alum. In conclusion, PGS seem to be a promising balanced Th1 and Th2 directing immunological adjuvants which can enhance the immunogenicity of vaccine.