In vitro megakaryocytopoiesis in children with acute idiopathic thrombocytopenic purpura.

Idiopathic thrombocytopenic purpura (ITP) of childhood is a disorder characterized by a history of previous viral illness followed by acute onset of low circulating platelet count with present or increased megakaryocytes in the bone marrow. The majority of children recover a normal platelet count within 6 months to 1 year after onset of the disease. To better understand the regulation of megakaryocytopoiesis in this disorder, we studied nine patients with childhood ITP with the plasma clot colony assay in vitro for megakaryocyte colony forming units (CFU-Mk). Mononuclear bone marrow cells from some of the patients with ITP contained greater numbers of CFU-Mk and greater numbers of cells per colony than mononuclear bone marrow cells from healthy adult volunteers (p less than 0.026) when the cultures contained no added megakaryocyte colony-stimulating activity (Mk-CSA). The serum from patients with ITP did not stimulate in vitro megakaryocytopoiesis from healthy adult volunteers' bone marrow mononuclear cells above baseline values. These findings are consistent with the hypothesis that a decrease in bone marrow megakaryocytes is needed for Mk-CSA production. Alternatively, Mk-CSA is consumed by active megakaryocytopoiesis in the bone marrow.