In vitro studies of megakaryocytopoiesis in thrombocytotic disorders of man

Abstract

Increased numbers of bone marrow megakaryocytes and thrombocytosis are frequently observed in patients with myeloproliferative disorders (MPD). Increased marrow megakaryocytes and thrombocytosis are also noted in a variety of inflammatory and neoplastic disease leading to the phenomenon of reactive thrombocytosis (RT). The pathogenesis of this finding remains incompletely understood. Using methodology developed in our laboratory, we investigated the causative role of megakaryocyte colony-stimulating activity (Meg-CSA) in generating this phenomenon. We also examined the cloning efficiency of colony-forming units-megakaryocyte (CFU-M) and their responsiveness to an exogenous source of Meg-CSA in patients with these diseases. The results of our investigations suggest that: (1) increased production of Meg-CSA is not responsible for the megakaryocyte hyperplasia and thrombocytosis noted in these patients; (2) the intrinsic stem cell defect described in MPD appears to affect the CFU-M of these patients as well, resulting in an effective expansion of the CFU-M pool with consequent megakaryocyte hyperplasia and thrombocytosis; (3) the CFU-M of patients with MPD remain responsive to an exogenous source of Meg-CSA, suggesting that this megakaryocyte hyperplasia may not be entirely autonomous of its effects; and (4) the CFU-M pool in RT is normal both in size and responsiveness to Meg-CSA, suggesting that in these disorders, the stimulus leading to megakaryocyte hyperplasia and thrombocytosis is active at the post-CFU-M level of megakaryocyte differentiation.

Serum from patients with various thrombopoietic disorders alters terminal cytoplasmic maturation of human megakaryocytes in vitro

“…The number of MK populating the bone marrow must ultimately be determined by the committed progenitors (CFU-MK), since recognizable MK lack the capacity to proliferate. Regulation of CFU-MK appears more closely related to MK numbers than platelet numbers, because serum from thrombocytopenic patients with normal or elevated marrow MK does not promote colony formation (4,21). Changes in recognizable MK are more directly related to platelet counts (22)(23)(24).…”

“…MK-CSA was not elevated, and CFU-MK were not more sensitive to growth factors. CFU-MK were increased in number, which eventually resulted in more MK and higher platelet counts (21,(26)(27)(28)(29)(30).…”

Human megakaryocytic progenitors (CFU‐M) assayed in methylcellulose: Physical characteristics and requirements for growth

“…In this study we describe the requirements for growth and several physical characteristics of normal human marrow CFU-M employing the methylcellulose system introduced by Messner et al (1982). Previously published assays for human CFU-M used the plasma clot technique (Vainchenker et al, 1979, 198213;Hoffman et al, 1981Hoffman et al, , 1982Mazur et al, 1981a,b;Ash et al, 1982;Gewirtz et al, 1983). Our initial experience with this technique was unsatisfactory, however.…”

“…Such differences may he important to the interpretation of recently described assays for Meg-CSA (Hoffman et al, 1981; Gewirtz et al, 1983). If serum from thrombocytopenic patients is used, it may contain less plateletderived inhibitory activity than serum from patients with elevated platelet counts.…”

Circulating erythroid and megakaryocytic progenitors in polycythaemia vera and essential thrombocythaemia

“…erative syndromes is less well-known and scant information is available about their endogenous growth in essential thrombocythaemia (4, 6,7) and even less about polycythaemia Vera (8).…”