Characterization of adjuvant properties of microparticulate beta-glucan

A novel preparation of microparticulate beta-glucan (MG) derived from Saccharomyces cerevisiae has been characterized with respect to adjuvanticity. Previous studies demonstrated that MG particles are avidly phagocytized by murine peritoneal macrophages and induce proinflammatory cytokine secretion and upregulation of B7 costimulatory molecule expression, leading to the hypothesis that MG can serve as a vaccine adjuvant. A test vaccine antigen, FITC-BSA, was conjugated to MG via carbodiimide linkage and injected intradermally into Swiss-Webster mice. MG:FITC-BSA conjugates induced serum titers of anti-BSA IgG that were significantly higher than those induced by FITC-BSA alone, and performed comparably to animals given FITC-BSA in complete Freund's adjuvant. MG:FITC-BSA vaccine was orally administered via food pellet to BALB/c mice; primary immunization induced no increase in antibody titers, but upon booster immunization mice treated with MG:FITC-BSA showed a significant anti-BSA antibody response. Mice given MG appeared normal and healthy throughout both studies, indicating that MG may serve as an effective yet safe adjuvant.; In vitro studies were performed to examine the effect of MG on antigen-presenting cells (APC). MG significantly upregulated MHC class II on peritoneal macrophages; this effect was entirely dependent on endogenous IFN-gamma production, as demonstrated by studies with IFN-gamma -/- macrophages. MG treatment also increased the expression of MHC class II on bone marrow-derived dendritic cells (BMDC) from BALE/c mice. IFN-gamma was not required for the MG-induced increase in MHC class II in BMDC, indicating that MG may act through different pathways in macrophages and dendritic cells. MG also increased surface expression of costimulatory molecules B7.1, B7.2, B7-DC, CD40 and CD83 on BMDC.; To determine if APC treated with MG:vaccine conjugates can augment antigen-specific T cell immunity, BMDC were treated with ovalbumin (OVA) or MG:OVA. Splenocytes from DO11.10 transgenic mice were incubated with BMDC and analyzed for activation of CD4+ T cells, which was verified by positive expression of surface markers CD25 and CD69. BMDC treated with MG:OVA induced significantly higher numbers of activated OVA-specific CD4+T cells than BMDC treated with OVA alone or beads conjugated to OVA, demonstrating that MG enhances activation of naive antigen-specific T cells.