Innate Immunity in Idiopathic Thrombocytopenic Purpura (ITP)

Background: Dendritic cells (DCs), natural killer (NK) cells, and invariant NKT (iNKT) cells play important roles in innate immune systems. These cells have recently been shown to be involved in immunoregulation, and some studies have suggested associations with various kinds of autoimmune disease. Conversely, regulatory T cells (Tregs) that are important for peripheral tolerance and Th17 cells that play a central role in maintenance of chronic inflammation are also associated with the pathogenesis of several autoimmune diseases. Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disease mediated by anti-platelet autoantibodies, but relationships to innate immunity are unclear. In addition, the pathogenesis of ITP associated with Helicobacter pylori remains obscure. In particular, the regulation of immune responses by these cells in patients infected with H. pylori has not been investigated. This study analyzed DCs, NK cells, iNKT cells, Tregs and Th17 cells in patients with ITP.

Methods: Subjects comprised 31 patients with ITP and 22 healthy donors. Study protocols were approved by the Institutional Review Board of Gunma University Hospital, and written informed consent was obtained from all subjects. Flow cytometry was used to investigate amounts of circulating plasmacytoid DCs (pDCs) (CD123+ HLA−DR+) and myeloid DCs (mDCs) (CD11c+ HLA−DR+) from whole white blood cells, and NK cells (CD3− CD56+), iNKT cells (Vα24+ Vβ11+), Tregs (CD4+ CD25+ Foxp3+) and Th17 cells (CD4+ IL−17A+) from mononuclear cells. The intracellular interleukin (IL)-17A production in CD4+ T-cells activated by phorbol 12-myristate 13-acetate (PMA) and ionomycin was assessed to detect Th17 cells.

Results: Both the percentage and numbers of pDCs were significantly reduced in patients compared to healthy controls (p<0.001), while those of mDCs tended to be lower in patients than in controls, but with no significant differences. NK cell counts tended to be higher in patients than in controls and counts of iNKT cells tended to be lower in patients than in controls, but again no significant differences were demonstrated. Notably, Treg levels were comparable between patients and controls, while Th17 cells were significantly increased in patients compared with controls (p<0.002). In all cases, no significant differences were demonstrated between patients with H. pylori-positive and -negative results.

Conclusion: These results suggest that alterations in innate immunity as a reduction of pDCs could be associated with the pathogenesis of ITP. Furthermore, as in some autoimmune diseases that have been considered as Th1 diseases, Th17 cells may play an important role in ITP.