Circulating plasmacytoid dendritic cells in patients with primary and Helicobacter pylori-associated immune thrombocytopenia

Objectives: Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by the production of autoreactive antibodies against platelet antigens. Although dysfunction of multiple aspects of cellular immunity is considered to be important in the pathogenesis of ITP, it has not been clarified which cell types play a principal role. Methods: We enrolled 46 untreated patients with chronic ITP and 47 healthy adult volunteers, and investigated by flow cytometry the percentage and absolute number of cells in their peripheral blood that participate in the regulation of cellular immunity. These included plasmacytoid dendritic cells (pDCs), myeloid dendritic cells (mDCs), natural killer (NK) cells, natural killer T (NKT) cells, regulatory T (Treg) cells, and Th17 cells. Results: We found a significant reduction in the absolute number of pDCs, but not of mDCs, in patients with ITP when compared with healthy controls (P < 0.001). Reduced numbers of circulating pDCs were observed in both Helicobacter pylori (H. pylori)-positive and Helicobacter pylori (H. pylori)-negative patients with ITP. In contrast, there were no significant differences in the numbers of circulating Treg cells, Th17 cells, NK cells, or NKT cells. Interestingly, we observed increases in the number of pDCs after H. pylori eradication by antibiotics in responders but not in non-responders, while pDCs and mDCs decreased markedly after prednisolone therapy in both responders and nonresponders. In patients without treatment, low pDC numbers persisted during the observational period. Conclusions: We demonstrated that the number of circulating pDCs is low in patients with primary and H. pylori-associated ITP and that it changes depending on treatment modality. Further investigation is warranted with regard to the role of pDCs in the immunopathogenesis of ITP.