Figure 2. Tc17 and Th17 cells, and the Th17:Tc17 ratio in ITP patients and controls. (a) Significantly elevated percentage of Tc17 was found in newly-diagnosed ITP patients (median, 0.79%; range, 0.25–3.58%) compared to controls (median, 0.30%; range, 0.04–1.80%; ***P,0.0001) and CR patients (median, 0.39%; range, 0.10–1.54%; **P = 0.0017). (b) Statistically elevated percentage of Th17 cells was found in newly-diagnosed ITP patients (median, 2.24%; range, 0.72– 8.18%) compared to controls (median, 1.19%; range, 0.04–4.53%; **P = 0.0016; [similar to our previous study]). (c) The Th17:Tc17 ratio in newly-diagnosed patients (median, 2.5850; range, 1.4221–3.0714) was 0.76-fold lower than controls (median, 3.3852; range, 1.0000– Tc17 in ITP 5.8571; ***P,0.0001) and 0.70-fold lower than CR cases (median, 3.6771; range, 2.3896–5.5000; ***P,0.0001). doi:10.1371/journal.pone.0026522.g002 patients and healthy controls. The ratio of CD4:CD8 was decreased in ITP patients (median, 1.42; range, 0.26–4.18) compared to healthy controls (median, 1.90; range, 0.93–3.95; P = 0.029), and the percentage of CD8+ T cells was increased in ITP patients (median, 29.34%; range, 9.78–68.97%) compared with healthy controls (median, 22.35%; range, 12.89–32.3%; P = 0.025). In the study we determined the correlation of Tc17 with the CD8:CD4 ratio, as well as CD8+ cells in ITP patients. As shown in Figs. 5a and 5b, Tc17 and CD8:CD4 ratios were positively related (r = 0.6256, P = 0.001), while Tc17 and CD8+ cells were also positively related in ITP patients (r = 0.5562, P = 0.006). Marginally elevated Tc17 in autoantibody-negative ITP patients Circulating anti-platelet autoantibodies are frequently detected in ITP patients. The most common targets of anti-platelet antibodies are the GPIIb/IIIa complex and GPIb/IX. We determined the correlation of anti-platelet GPIIb/IIIa and/or GPIb/IX autoantibodies with Tc17 in ITP patients. The number of Tc17 was marginally elevated in patients who had a negative MAIPA test (median, 1.00; range, 0.18–3.58) compared to patients with a positive MAIPA test (median, 0.50; range, 0.23–0.96; P = 0.07). Tc17 and Th17 cells are decreased in the presence of DEX in PBMCs of ITP patients in vitro To determine the response of Tc17 and Th17 cells to DEX, we measured the changes in the percentages of Tc17 and Th17 cells from PBMCs of ITP patients in the presence of DEX in vitro. As shown in Fig. 6, the percentage of Tc17 and Th17 cells decreased with the increase in the concentration of DEX in culture media. Clinical relevance of Tc17 in ITP patients Because insufficient platelet production by megakaryocytes is a main cause of ITP, we analyzed the association between Tc17 and megakaryocytes or platelet counts in ITP patients. There was no significant correlation between Tc17 and the megakaryocyte count (r = 0.0319, P = 0.867). In addition, no significant correlation existed between the number of Tc17 and the platelet count (r = 20.1749, P = 0.301). Discussion ITP is an autoimmune disease in which abnormalities in cellular immunity have been clearly demonstrated [18]. Apart from a shift in the Th1/Th2 balance, a new T cell subset (Th17 cells), the primary CD4+ cells producing IL-17, is often regarded as the principal instigator of autoimmune disorders. Th17 cells are increased in patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) [19] and psoriasis [20]. The Tc17 subset is a new unique cell lineage in terms of function and differentiation [21]. There are considerable data showing that Th17 cells are increased in ITP patients [9]. However, only a few studies have focused on Tc17 in autoimmune diseases. More recently, it has been shown that the percentages of Tc17 were increased in psoriatic skin lesions or the peripheral blood of SLE patients, which indicates that this type of CD8+ T cell plays a significant role in the pathogenesis of autoimmune diseases PLoS ONE | www.plosone.org 4 October 2011 | Volume 6 | Issue 10 | e26522