Functional specialization of islet dendritic cell subsets

Dendritic cells (DC) play important roles in both tolerance and immunity to β cells in type 1 diabetes. How and why DC can have diverse and opposing functions in islets remains elusive. To answer these questions, islet DC subsets and their specialized functions were characterized. Under both homeostatic and inflammatory conditions, there were two main tissue-resident DC subsets in islets, defined as CD11b ^lo/-CD103 ⁺CX3CR1 ^- (CD103 ⁺ DC), the majority of which were derived from fms-like tyrosine kinase 3-dependent pre-DC, and CD11b ⁺CD103 ^-CX3CR1 ⁺ (CD11b ⁺ DC), the majority of which were derived from monocytes. CD103 ⁺DC were the major migratory DC and cross-presented islet-derived Ag in the pancreatic draining lymph node, although this DC subset displayed limited phagocytic activity. CD11b ⁺ DC were numerically the predominant subset (60-80%) but poorly migrated to the draining lymph node. Although CD11b ⁺ DC had greater phagocytic activity, they poorly presented Ag to T cells. CD11b ⁺DC increased in numbers and percentage during T cell-mediated insulitis, suggesting that this subset might be involved in the pathogenesis of diabetes. These data elucidate the phenotype and function of homeostatic and inflammatory islet DC, suggesting differential roles in islet immunity.