Adjuvant effect of water-soluble polysaccharide (PAP) from the mycelium of Polyporus albicans on the immune responses to ovalbumin in mice

In our previous work, a new water-soluble polysaccharide (PAP) from the mycelium of Polyporus albicans was identified for the first time. Preliminary tests in vitro showed PAP have potent stimulating effects on murine lymphocyte proliferation induced by mitogen. So in this study, the immunomodulatory effect and the adjuvant potential of PAP on the cellular and humoral immune response of ICR mice against ovalbumin were investigated. In vivo toxicity assays of PAP showed not to be lethal for mice in doses ranging from 0.5 to 4 mg. ICR mice were immunized subcutaneously with OVA 0.1 mg alone or with OVA 0.1 mg dissolved in saline containing alum (0.2 mg) or PAP (0.5, 1 and 2 mg) on days 1 and 15. Two weeks later (day 28), concanavalin A (Con A)-, lipopolysaccharide (LPS)- and OVA-stimulated splenocyte proliferation and OVA-specific serum antibodies were measured. PAP (0.5, 1 and 2 mg) other than alum significantly enhanced the Con A-, LPS- or OVA-induced splenocyte proliferation in the OVA-immunized mice (P < 0.05 or <0.01). The OVA-specific IgG, IgG1 and IgG2b antibody levels in serum were also significantly enhanced by PAP (0.5, 1 and 2 mg) compared with OVA control group (P < 0.05 or <0.01). Moreover, alum (0.2 mg) only induces IgG and IgG1 antibody responses to OVA in mice. In conclusion, the results suggest that PAP could be a safe efficacious adjuvant capable of boosting cellular and humoral immunity without unacceptable toxicity. Thus adjuvants based on PAP have enormous potential for use in vaccines against both pathogens and cancer.