RESUMO
Persistent or chronic immune thrombocytopenias (P/C-ITP) are acquired blood disorders lasting more than 3 months or 1 year, respectively. The pathogenesis of these disorders is thought to be immunological. We hypothesized that some patients with P/C-ITP might have an intrinsic megakaryopoiesis defect. We identified a group of P/C-ITP patients with acquired isolated mild thrombocytopenia (30-100 × 10(9) /l), undetectable anti-platelet antibodies, negative autoimmune investigations and no need for treatment. We examined in vitro megakaryocyte differentiation and compared these patients' results with those of acute-ITP patients and healthy controls. No difference in proliferation, ploidy or expression of surface markers was found. In contrast, P/C-ITP patients had significantly fewer proplatelet-forming megakaryocytes. This novel observation demonstrated that some patients diagnosed with P/C-ITP have an intrinsic megakaryopoiesis defect independent of the bone-marrow environment. Further investigations are needed to dissect mechanisms underlying this impaired proplatelet formation in these patients.