Stat5-deficient bone marrow fails to repopulate mast cells in W/W-v mice. (A) Wild-type or Stat5-deficient bone marrow cells were transplanted to W/W-v mice. At 12 weeks after transplantation, peritoneal cells were harvested and stained with toluidine blue. Arrow indicates mast cell morphology, present in wild-type, but not Stat5-deficient, recipients. Final magnification is × 200. (B) Representative flow cytometry profiles of peritoneal cells from W/W-v mice (control) or W/W-v mice that received transplants of wild-type or Stat5-deficient bone marrow cells. Samples were stained for IgE receptor and Kit expression. Background staining with control antibodies averaged 0.05%.