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Characterization of human megakaryocytic colony formation in human plasma
Abstract:
We have analysed the contribution to megakaryocyte colony formation in methylcellulose made by human plasma, serum, media conditioned by phytohemagglutinin (PHA) stimulated leukocytes (PHA-LCM), erythropoietin (EPO) preparations, and platelets. The culture system was used as a bioassay for megakaryocyte colony stimulating activity (Meg-CSA) in plasma samples of patients with perturbed megakaryocytopoiesis. Preparations of heparinized platelet-poor plasma yielded the most consistent results. Platelet-poor plasma of normal subjects will at best facilitate the occasional growth of small megakaryocyte colonies. Colony frequency and size are reproducibly enhanced in the presence of PHA-LCM as a source of exogenous Meg-CSA. Commercially available EPO preparations may vary in their content of activities that influence megakaryocyte colony formation. Addition of these preparations to cultures that contain plasma and PHA-LCM usually does not enhance colony formation. In contrast to platelet-poor plasma, platelet rich plasma and serum are less supportive of megakaryocyte colony growth. It is suggested that this loss of activity may be related to the release of inhibitors by activated platelets or alternatively caused by absorption of activities by platelets. Plasma samples from patients with megakaryocytopoietic dysfunction may contain components that promote colony formation without addition of PHA-LCM or EPO. This phenomenon is consistently observed for patients with severe aplastic anemia and bone marrow transplant recipients after completion of their ablative preparative regimen.
Insights
Human plasma and leukocyte-conditioned media support megakaryocyte colony formation. Platelet-rich plasma and serum are less supportive, suggesting platelet-derived inhibitors may impact megakaryocyte colony stimulating activity (Meg-CSA).
Area of Science:
- Hematology
- Cell Biology
- Stem Cell Research
Background:
- Megakaryocyte colony formation is crucial for platelet production.
- Understanding factors influencing megakaryopoiesis is vital for treating blood disorders.
Purpose of the Study:
- To investigate the role of various human biological components in supporting megakaryocyte colony formation.
- To utilize a methylcellulose culture system as a bioassay for megakaryocyte colony stimulating activity (Meg-CSA).
Main Methods:
- Analysis of human plasma, serum, phytohemagglutinin (PHA)-stimulated leukocyte-conditioned media (PHA-LCM), erythropoietin (EPO) preparations, and platelets in methylcellulose cultures.
- Assay of Meg-CSA in plasma from patients with abnormal megakaryocytopoiesis.
Main Results:
- Heparinized platelet-poor plasma provided consistent results.
- Platelet-poor plasma from normal subjects minimally supported colony growth.
- PHA-LCM reproducibly enhanced colony frequency and size.
- Commercial EPO preparations showed variable effects on colony formation.
- Platelet-rich plasma and serum were less supportive, potentially due to platelet-derived inhibitors.
Conclusions:
- PHA-LCM is a significant source of exogenous Meg-CSA.
- Platelets may release inhibitors or absorb factors that reduce megakaryocyte colony growth.
- Plasma from patients with severe aplastic anemia or post-bone marrow transplant may contain endogenous factors promoting megakaryopoiesis.