Idiopathic myelofibrosis (IF) is due to an acquired somatic mutation(s) of a single hematopoietic multipotent progenitor and thus circulating myeloid, erythroid, megakaryocyte, B and T cells (

Reeder et al Blood. 2003;101: 1981–1983
) are clonal. It has been suggested that fibrosis may occur secondary to cytokines secreted by the malignant clone. Although marked elevation of circulating CD34 cells occurs in patients with IF, it is not known whether it is a consequence of the primary defect of the hematopoietic stem cell, or secondary to fibrosis and impaired marrow microenvironment. To answer this question, we studied CD34 count in peripheral blood of patients with IF and secondary myelofibrosis due to pulmonary hypertension. Nineteen patients with either primary or secondary pulmonary hypertension due to connective tissue disease and 11 patients with IF were studied. Bone marrow biopsy revealed fibrosis in all 19 patients with PH: 11 severe, 3 moderate, and 5 mild. All eleven patients with IF had severe fibrosis. Clonality studies in 13/14 informative patients with PH showed polyclonal platelets and granulocytes in contrast to monoclonal platelets and granulocytes in patients with IF. Peripheral blood was assayed for CD34+ cells using a three-color direct immunofluorescent staining method. Mean absolute CD34 count was significantly (P=0.02) lower - 6/ul (range: 1–18/ul) in patients with PH compared to 142 /ul (range 4–833/ul) in patients with IF. We therefore conclude that high CD34 count is not seen in patients with PH with secondary myelofibrosis; furthermore, elevated CD34 in patients with IF is not due to marrow fibrosis and altered microenvironment.

Topics:
cd34 antigens, fibrosis, myelofibrosis, idiopathic, chronic, secondary myelofibrosis, bone marrow biopsy, clonality (genetic analysis), connective tissue diseases, cytokine, pulmonary hypertension, secondary pulmonary hypertension

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2005, The American Society of Hematology
2004
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