Elevated Interleukin-21 Correlated to Th17 and Th1 Cells in Patients with Immune Thrombocytopenia

Interleukin-21 (IL-21) is critical in the development of autoimmune diseases. The role of IL-21 in the pathogenesis of immune thrombocytopenia (ITP) remains unknown. We examined the expression of IL-21, IL-17, and interferon (IFN)-gamma in ITP patients and controls by enzyme-linked immunosorbent assay and flow cytometry. Detection of specific anti-platelet GPIIb/IIIa and/or GPIb/IX autoantibodies was measured by modified monoclonal antibody specific immobilization of platelet antigens. IL-21 was expressed on both CD3(+)CD8(-) T cells and CD3(+)CD8(+) T cells by flow cytometry. Plasma IL-21 level and the percentage of CD3(+)CD8(-)IL-21(+) T cells and CD3(+)CD8(+)IL-21(+) T cells were significantly elevated in ITP patients compared to controls. The percentage of CD3(+)CD8(-)IL-17(+) T (Th17), CD3(+)CD8(-)IFN-gamma(+) T (Th1), and CD3(+)CD8(+)IFN-gamma(+) T (Tc1) cells also significantly increased in ITP patients. Moreover, we found a significant positive correlation between CD3(+)CD8(-)IL-21(+) T cells and Th17 cells. In addition, a positive correlation between CD3(+)CD8(-)IL-21(+) T cells and Th1 cells was also found. Together, our results indicated a possible role of IL-21 in ITP patients correlated to Th17 and Th1 cells, and blockade of IL-21 may be a reasonable therapeutic strategy for ITP especially those with active disease.