Dexamethasone was used as a positive control for it was reported to enhance Tregs in the treatment of ITP.24 To explore whether indirubin could enhance the suppressive function of Tregs aside from increasing the number of Tregs, we co‐cultured CFSE‐labelled effector T cells with CD4+CD25+ Tregs isolated from ITP PBMCs in presence of either 1 μmol/L indirubin or 1‰ DMSO. Here, CD4 is linked to autoimmune thrombocytopenic purpura.