IL-4 Triggers Autoimmune Diabetes by Increasing Self-Antigen Presentation within the Pancreatic Islets

Several findings have recently questioned the long held hypothesis that cytokines belonging to the Th2 pathway are protective in T-cell-mediated autoimmunity. Among them, there is our previous report that pancreatic expression of IL-4 activated islet antigen-specific BDC2.5 T cells and rendered them able to trigger insulin-dependent diabetes mellitus in ins-IL-4/BDC2.5 mice (Mueller et al., Immunity, 7, 1997). Here we analyze the mechanisms underlying IL-4-mediated activation of the self-reactive BDC2.5 T cells. IL-4 is mainly known as the Th2-driving cytokine. However, IL-4 is also critical for DC maturation and upregulation of antigen uptake and presentation by macrophages. In our model, we found that pancreatic expression of IL-4 activated self-reactive BDC2.5 T cells by increasing islet antigen presentation by macrophages and dendritic cells. IL-4 could have triggered self-antigen presentation within the pancreatic islets both by driving maturation of DC from a tolerizing to a priming state and by increasing self-antigen uptake by macrophages.