Low-dose decitabine ameliorated thrombocytopenia in active ITP murine models via Treg cells. ITP models were established in irradiated SCID mice with engraftment of 2 × 10⁴ splenocytes from CD61 knockout mice immunized against wild-type C57 mice platelets; platelet counts were then monitored every week for 4 weeks (mean ± standard error of the mean). (A) From day 7, decitabine (0, 0.01 mg/kg, 0.03 mg/kg) was administered. The horizontally dotted lines represent the baseline platelet counts of SCID mice (mean ± standard error of the mean). On days 21 and 28, significantly higher platelet counts were observed in the group administered the 0.03-mg/kg dose of decitabine compared with control group. (B) Decitabine-treated ITP mice had a significantly higher percentage of splenic Treg cells in CD4⁺ T cells compared with control mice (n = 11 in the control group and n = 13 in the decitabine group, respectively). The percentage of Th1 (C) and Th17 (D) in CD4⁺ T cells were decreased in decitabine-treated spleens compared with controls. No significance was found in Th22 cells (E) in splenic CD4⁺ T cells (n = 9 in the control group and n = 10 in the decitabine group). Treg deletion (F) by magnetic beads and depletion (K) by anti-CD25 antibody partly offset the effect of decitabine on increasing platelet counts of ITP mice (n = 6). Treg-deleted splenocyte-transferred mice (G) and anti-CD25 antibody-treated mice (L) were significantly depleted of Treg cells in the spleens on day 28 (n = 6). (H-J) After Treg deletion, decitabine had no significant effect on splenic Th1, Th17, or Th22 cells on day 28 in ITP mice (n = 6). (M-O) With Treg depletion by anti-CD25 antibody, decitabine had no significant effect on splenic Th1, Th17, or Th22 cells on day 28 in ITP mice (n = 6). *P < .05, **P < .01, ***P < .001. Dec, decitabine; ns, not significant.