In the culturing of PBMCs from ITP patients, we found the expression of CD25 in CD4+ T cells (Figure 2A,B), CD4+CD45RA+ T cells (Figure 2C) and CD4+CD45RO+ T cells (Figure 2D) were significantly reduced after treated with indirubin in a dose‐dependent manner, indicating that indirubin could decrease the activation of effector T cells in ITP. This evidence concerns the gene CD4 and autoimmune thrombocytopenic purpura.