Indirubin was found to significantly increase the PD1 expression on CD4+ T cells and Tregs in PBMCs from ITP patients (Figure 3J,K) with a concomitant increase in PD1, PTEN mRNA expression levels, though the increasing of PD1 mRNA expression was not significant (Figure 3H,I), thus indicating that indirubin's therapeutic action on Tregs and effector T cells might be through the induction of PD1 and PTEN expression and signalling in ITP. Here, CD4 is linked to autoimmune thrombocytopenic purpura.