Mapping of the Lung Megakaryocytes: A Role in Pathogenesis of Idiopathic Pulmonary Arterial Hypertension?

It has been postulated that platelets are produced by fragmentation of the megakaryocytes within the pulmonary circulation rather than budding of their cytoplasm within the bone marrow. Although literature is scarce depicting the levels of the megakaryocytes within the lungs from previously healthy individuals, there are several studies describing the presence of these cells in human necropsy specimens, and it has been hypothesized that their rearrangements could contribute to the pathogenesis of chronic pulmonary vascular disorders. The objective of this study was to describe the characteristics, distribution and total count of megakaryocytes in explants from lung transplant (LTx) recipients based on the final clinicopathological diagnosis, as well as in samples from LTx donors without previously known pulmonary disease. Using the immunohistochemical marker CD61 we quantified and characterized such cells in 20 biopsy samples from LTx donors and in 30 biopsy samples from LTx recipients with different pathologic conditions: vascular disorders of the lungs, obstructive pulmonary disorders and fibrotic lung diseases. Patients suffering from idiopathic pulmonary arterial hypertension (IPAH) showed morphological differences and strikingly higher numbers of the lungs megakaryocytes (264.5 cells/cm2) compared to all the other groups (the average count among donors was 33.55 megakaryocytes/cm2). Such finding could contribute to the understanding of the origin of vasoconstriction, thrombosis and vascular remodeling of the pulmonary circulation - all the basic mechanisms leading to the development of IPAH, as for there is an increasing evidence of several products of platelets and megakaryocytes to be capable of triggering such processes.