TLR2- and Dectin 1-associated Innate Immune Response Modulates T-cell Response to Pancreatic β-cell Antigen and Prevents Type 1 Diabetes

The progression of autoimmune diseases is dictated by deviations in the fine balance between proinflammatory versus regulatory responses, and pathogen recognition receptors (PRRs) play a key role in maintaining this balance. Previously, we have reported that ligation of Toll-like receptor 2 (TLR2) and Dectin 1 on antigen-presenting cells by zymosan results in a regulatory immune response that prevents type 1 diabetes (T1D). Here, we show that TLR2 and Dectin 1 engagement by zymosan promotes regulatory T-cell (Treg) responses against the pancreatic β-cell-specific antigen (Ag). Unlike the TLR4 ligand, bacterial lipopolysaccharide, which induced proinflammatory cytokines and pathogenic T cells, zymosan induced a mixture of pro- and anti-inflammatory factors and Tregs, both in vitro and in vivo. Ag-specific T cells that are activated using zymosan-exposed dendritic cells (DCs) expressed Foxp3 and produced large amounts of IL-10, TGF-β1, and IL-17. NOD mice that received β-cell-Ag-loaded, zymosan-exposed DCs showed delayed hyperglycemia. Injection of NOD mice at the prediabetic age and early hyperglycemic stage with β-cell-Ag, along with zymosan, results in a superior protection of the NOD mice from diabetes as compared with mice that received zymosan alone. This therapeutic effect was associated with increased frequencies of IL-10-, IL-17-, IL-4-, and Foxp3-positive T cells, especially in the pancreatic lymph nodes. These results show that zymosan can be used as an immune regulatory adjuvant for modulating the T-cell response to pancreatic β-cell-Ag and reversing early-stage hyperglycemia in T1D.