Adjuvant-active fraction from Albizia julibrissin saponins improves immune responses by inducing cytokine and chemokine at the site of injection.

The total saponin from the stem bark of Albizia julibrissin (AJSt) has previously showed the adjuvant potentials in mice. In this study, AJSt was subjected to resin column chromatography to afford four fractions (AJS30, AJS50, AJS75 and AJS95), and these fractions were further compared for the hemolytic activities and adjuvant potentials on the immune response to ovalbumin (OVA) and recombinant fowl pox virus vector-based avian influenza vaccine (rFPV). AJSt, AJS50, AJS75 and AJS95 showed a slight hemolytic effect. AJSt, AJS50 and AJS75 significantly enhanced not only the concanavalin A (Con A)-, lipopolysaccharide (LPS)- and antigen-stimulated splenocyte proliferation, but also serum antigen-specific IgG, IgG1, IgG2a and IgG2b antibody titers in the mice immunized with OVA and rFPV. AJSt, AJS50 and AJS75 also significantly promoted the NK cell activity and delayed-type hypersensitivity (DTH) in the OVA-immunized mice. Furthermore, the mechanisms of adjuvant action were explored by determining the effects of AJS75 on cytokines and chemokines at the site of injection using antibody array. AJS75 induced or up-regulated the protein expression of 12 cytokines (IL-12p40, IL-12p40/p70, IFN-γ, IL-13, IL-1β, IL-6, IL-10, TNF-α, sTNFR I, sTNFR III, IL-3 and IL-9) and 10 chemokines (Eotaxin, I-TAC, MIG, MIP-1α, RANTES, TECK, Fracatlkine, FasL, M-CSF and GM-CSF) in the injected muscles. The results suggested that AJS75, the most adjuvant-active fraction of AJSt, could improve antigen-specific both cellular and humoral immune responses and simultaneously elicit a Th1/Th2 response by inducing cytokine and chemokine at the site of injection.