ICOS and autoimmune thrombocytopenic purpura: We found that BM CD4+CXCR5+ and CD4+CXCR5+ICOS+ Tfh levels from ITP patients were considerably increased than from HCs (CD4+CXCR5+: 21.43 ± 3.94 % vs. 10.71 ± 2.21 %, P < 0.001; CD4+CXCR5+ICOS+: 5.42 ± 2.56 % vs. 1.26 ± 0.24 %, P < 0.001; Figure 5E and F).