CD4 and autoimmune thrombocytopenic purpura: To further assess whether indirubin alters the suppressive function of CD4+CD25+Foxp3+Treg cells in ITP mice, we thus compared the immunosuppressive effects of CD4+CD25+Treg cells sorted by bead separation from ITP mice treated with or without indirubin using an in vitro immunosuppressive assay [18].