title: Paracrine regulation of megakaryo/thrombopoiesis by macrophages.
abstract: OBJECTIVE
  Megakaryo/thrombopoiesis is a complex process regulated by multiple signals provided by the bone marrow microenvironment. Because macrophages are relevant components of the bone marrow stroma and their activation induces an upregulation of molecules that can regulate hematopoiesis, we analyzed the impact of these cells on the control of megakaryocyte development and platelet biogenesis.
  
  
  METHODS
  The different stages of megakaryo/thrombopoiesis were analyzed by flow cytometry using an in vitro model of human cord blood CD34(+) cells stimulated with thrombopoietin in either a transwell system or conditioned media from monocyte-derived macrophages isolated from peripheral blood. Cytokines secreted from macrophages were characterized by protein array and enzyme-linked immunosorbent assay.
  
  
  RESULTS
  Resting macrophages released soluble factors that promoted megakaryocyte growth, cell ploidy, a size increase, proplatelet production, and platelet release. Lipopolysaccharide stimulation triggered the secretion of cytokines that exerted opposite effects together with a dramatic switch of CD34(+) commitment to the megakaryocytic lineage toward the myeloid lineage. Neutralization of interleukin-8 released by stimulated macrophages partially reversed the inhibition of megakaryocyte growth. Activation of nuclear factor κB had a major role in the synthesis of molecules involved in the megakaryocyte inhibition mediated by lipopolysaccharide-stimulated macrophages.
  
  
  CONCLUSIONS
  Our study extends our understanding about the role of the bone marrow microenvironment in the regulation of megakaryo/thrombopoiesis by showing that soluble factors derived from macrophages positively or negatively control megakaryocyte growth, differentiation, maturation, and their ability to produce platelets.
authors.affiliation: Thrombosis I Laboratory, Hematological Research Institute Mariano R Castex, National Academy of Medicine, CONICET, Buenos Aires, Argentina.
authors.forename: Lina Paola
authors.initials: LP
authors.lastname: D'Atri
authors.forename: Roberto Gabriel
authors.initials: RG
authors.lastname: Pozner
authors.forename: Karen Amelia
authors.initials: KA
authors.lastname: Nahmod
authors.forename: Verónica Inés
authors.initials: VI
authors.lastname: Landoni
authors.forename: Martín
authors.initials: M
authors.lastname: Isturiz
authors.forename: Soledad
authors.initials: S
authors.lastname: Negrotto
authors.forename: Mirta
authors.initials: M
authors.lastname: Schattner
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D018925:Chemokines / Q000494:pharmacology; D018920:Coculture Techniques; D017077:Culture Media, Conditioned / Q000378:metabolism / Q000494:pharmacology; D016207:Cytokines / Q000494:pharmacology*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005312:Fetal Blood / Q000166:cytology; D005434:Flow Cytometry; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D008533:Megakaryocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D019899:Paracrine Communication; D034061:Thrombopoiesis / Q000187:drug effects*; D013926:Thrombopoietin / Q000494:pharmacology
chemical_list: D018952:Antigens, CD34; D018925:Chemokines; D017077:Culture Media, Conditioned; D016207:Cytokines; D008070:Lipopolysaccharides; D016328:NF-kappa B; D013926:Thrombopoietin