Significantly Reduced Circulating Plasmacytoid Dendritic Cells In Patients with Primary and Helicobacter Pylori-Associated Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder caused by production of autoreactive antibodies against platelet antigens. The association between Helicobacter pylori infection and a subgroup of ITP is now widely recognized. Although multiple dysfunctions in cellular immunity are considered to be important in the pathogenesis of ITP, little is known about the role of innate immune cells. Dendritic cells (DCs) play an essential role in innate and adaptive immune response by regulating the differentiation of naïve T cells and interacting with NK or NKT cells. DCs are composed of two subsets: myeloid DCs (mDCs) and plasmacytoid DCs (pDCs) in human peripheral blood. PDCs play an important role in several autoimmune diseases such as systemic lupus erythematosus through their ability to produce large amounts of type I interferon. In the present study, we analyzed the number of circulating DCs, regulatory T (Treg) cells, Th17 cells, NK cells and NKT cells in untreated patients with primary and H. pylori-associated ITP and assessed the changes of DC subsets after treatment in order to elucidate the role of these cells in the pathogenesis of ITP.

This study was approved by the local institutional review board. After obtaining written informed consent, we enrolled 46 untreated patients with chronic ITP (38 females and 8 males; median age: 52.5 years) and 47 healthy adult volunteers (43 females and 4 males; median age: 50.5 years). We investigated the percentage and the absolute number of circulating pDCs (Lineage marker (Lin)⁻ CD123⁺ HLA-DR⁺) and mDCs (Lin⁻ CD11c⁺ HLA-DR⁺) in whole blood, and NK cells (CD3⁻ CD56⁺), invariant NKT (iNKT) cells (Vα24⁺ Vβ11⁺), Treg cells (CD4⁺ CD25⁺ Foxp3⁺) and Th17 cells (CD4⁺ Interleukin (IL)-17A⁺) among peripheral blood mononuclear cells (PBMCs) by flow cytometry. Intracellular IL-17A production in CD4⁺ T cells activated by phorbol 12-myristate 13-acetate (PMA) and ionomycin was assessed in order to detect Th17 cells. In addition, we consecutively analyzed the number of DC subsets in ITP patients before and after H. pylori eradication or the administration of prednisolone (PSL).

H. pylori was detected in 15 of 38 patients (39.5%), and 7 of 15 H. pylori-positive patients (46.7%) probably had secondary ITP (H. pylori-associated), as platelet count elevation was observed only after H. pylori eradication in these cases. Thirteen patients underwent H. pylori eradication and 9 patients underwent PSL. We found a significant reduction in the percentage and absolute number of pDCs in untreated ITP patients when compared with controls (p < 0.001), while the percentage and absolute number of mDCs tended to decrease in ITP patients; however, the differences were not significant. In addition, the frequency of circulating pDCs was significantly lower in H. pylori-positive patients when compared with controls (p < 0.05) and was equal to that in H. pylori-negative patients. The frequency of circulating Treg cells, Th17 cells, NK cells and iNKT cells in ITP patients was similar to that in controls. Interestingly, we observed increases in the frequency of pDCs after H. pylori eradication only in responders, while there were no changes or slight reductions after this treatment in non-responders. On the other hand, we were unable to elucidate the relationship between changes in the frequency of mDCs and H. pylori eradication. To investigate the differences with treatment type, we performed serial measurement of DC numbers in cases treated by oral administration of PSL, which is standard therapy in primary ITP patients. The frequency of both pDCs and mDCs in all cases treated with PSL was markedly reduced in 1–2 months after treatment and tended to increase with dose reduction for 3–8 months after treatment. Because there were no differences in this trend between responders and non-responders to PSL, and because the frequency of DC subsets appeared to be inversely correlated with PSL dose, we considered that these results were caused by PSL, in contrast to cases undergoing H. pylori eradication.

We found for the first time that circulating pDCs were significantly reduced in untreated patients with both primary and H. pylori-associated ITP. In addition, the reduced number of pDCs was restored after eradication in H. pylori-associated ITP patients. This suggests that pDCs play an important role in the pathogenesis of ITP.

No relevant conflicts of interest to declare.