Reduced frequency of peripheral plasmacytoid dendritic cells in type 1 diabetes

Dendritic cells (DCs) as antigen presenting cells play an important role in the initiation of an autoimmune disease like type 1 diabetes. Although there is evidence from the NOD mouse model that the function and frequency of DCs is altered in type 1 diabetes, there is little data on dendritic cells in human type 1 diabetes. We investigated peripheral blood myeloid (mDC1 and mDC2) and plasmacytoid dendritic cells (pDCs) in 15 type 1 diabetes patients with recent onset (within the last 3 months) of type 1 diabetes as well as in 15 patients with long standing (more than 5 years) type 1 diabetes by flow cytometry. Both groups were compared to age matched controls. We observed a significantly reduced percentage of pDCs of peripheral blood mononuclear cells (PBMCs) in both recent onset (0.13 vs. 0.25%, p=0.01) and long standing type 1 diabetes patients (0.13 vs. 0.24%, p=0.01). The absolute counts of pDCs per ml of blood were also significantly lower in both recent onset (mean 9560 vs. 13524, p=0.048) and long-standing diabetes (mean 7869 vs. 12202; p=0.05). The percentage of mDC1 was significantly diminished in recent onset (0.21% vs. 0.30%, p=0.034), but not in long standing type 1 diabetes. Our study demonstrates a persisting reduction of peripheral plasmacytoid DCs in type 1 diabetes patients. Since pDCs are involved in the control of immune responses and inducing regulatory cells, a reduced number of pDCs may predispose to an autoimmune reaction in the pancreatic islets.