F-036. Cytokine Release Stimulated by Particulate β1,3-D-Glucans in the Presence and Absence of Ligands for Toll-Like Receptors

H. Huang, G. R. Ostroff, S. M. Levitz;
Univ. of Massachusetts Med. Sch., Worcester, MA.

The fungal cell wall component, β1,3-D-glucan (BG), can influence the immune response to fungal pathogens during infection and also has potential uses as an immunomodulating agent and vaccine adjuvant. Yeast glucan particles (YGPs) are Saccharomyces cerevisiae cell walls which have been treated so they are >80% BG and free of mannan. YGPs are being studied as an antigen delivery system because of their high capacity for antigen loading and targeting to macrophages and dendritic cells (DCs) via the BG receptor, dectin-1. YGPs stimulated secretion of the proinflammatory cytokine TNF-α in murine bone marrow-derived myeloid DCs, but did not stimulate IL-12p70 production. As IL-12p70 is a key cytokine driving Th1 differentiation, this inability to stimulate IL-12p70 could impact the use of YGPs in vaccine delivery systems. We therefore next studied cytokine responses in DCs dually stimulated by YGPs and Toll-like receptor (TLRs) ligands. TNF-α production was enhanced when DCs were stimulated with YGPs together with Pam3CSK4 (TLR1/6 ligand), poly I:C (TLR3 ligand), LPS (TLR4 ligand), or CpG (TLR9 ligand). Administration of CpG with YGPs overcame the inability of YGPs to stimulate IL-12p70 production whereas YGPs inhibited IL-12 production stimulated by LPS. The other TLR ligands did not significantly stimulate DC IL-12p70 secretion at the concentrations tested. Thus, the capacity of YGPs to stimulate DC cytokine release can be profoundly enhanced by the addition of TLR ligands. However, the specific cytokine effects seen depend upon the TLR ligand utilized. These results have implications for how BG influences the immune response to fungi and suggest that adding CpG to antigen-loaded YGPs could improve their capacity to stimulate Th1-type immune responses.