Absence of GARP:TGF-β1 complexes on Tregs, but not on MKs, reduces fibrosis and tumor burden in PMF mouse models. (A) BM cells were isolated from 5-FU-treated Foxp3^Cre × Garp^wt/wt mice or Foxp3^Cre × Garp^fl/fl mice, transduced with a retrovirus encoding MPL^W508A, and transplanted into irradiated recipient mice of the same genotype as the donor mice (n = 8-9 mice per group). C57BL/6 mice that did not undergo transplantation were used as controls. Blood was taken on day 28 and mice were euthanized on day 34 to collect femurs and spleens. Blood cell counts, GFP expression, and spleen fibrosis were measured as indicated in Figure 2. Data points: values in individual mice; horizontal lines: mean ± SEM per group; stacked bars: mean + SEM. P values were calculated using a two-tailed Student t test. (B) Same as in (A), except that BM cells were isolated from Garp^fl/fl or Tg(Pf4^Cre) × Garp^fl/fl mice and transplanted into irradiated Garp^fl/fl recipients (n = 4-6 mice per group).