title: The influence of T lymphocyte subsets and humoral factors on colony formation by human bone marrow and blood megakaryocyte progenitor cells in vitro.
abstract: Cellular and humoral influences of T lymphocytes on human megakaryocyte colony formation in vitro were assessed by using a microagar system. Megakaryocyte colony formation from nonadherent low density T lymphocyte-depleted (NALDT-) bone marrow cells was increased significantly after the addition of aplastic anemia serum (AAS) or purified megakaryocyte colony-stimulating factor (Meg-CSF). The addition of conditioned medium obtained from phytohemagglutinin-stimulated T lymphocytes replaced, at least partially, the requirement for AAS or purified Meg-CSF for the growth of megakaryocyte colonies. The cellular influence of T lymphocytes and T lymphocyte subsets on megakaryocyte colony formation was assessed by removing either T cells from nonadherent peripheral blood mononuclear cells with monoclonal OKT4, OKT8, or OKT3 antibodies plus complement, or by adding back populations of bone marrow or blood T4+ or T8+ lymphocytes, isolated by means of fluorescence-activated cell sorting, respectively, to NALDT--bone marrow or -blood cells. When sorted T cell subpopulations were added to a fixed number of NALDT--bone marrow or -peripheral blood cells in the presence of AAS or Meg-CSF, T4+ cells enhanced megakaryocyte colony formation and T8+ cells decreased it. These studies demonstrate that although the stimulation of megakaryocytic progenitor cells by Meg-CSF may not require the presence of monocytes or T lymphocytes, T4+ lymphocytes enhance and T8+ lymphocytes down-regulate megakaryocyte colony formation induced by Meg-CSF. These observations suggest that the immune system is capable of modulating the proliferative response of human megakaryocytic progenitor cells to Meg-CSF.
mesh_terms: D000917:Antibody Formation; D002478:Cells, Cultured; D003165:Complement System Proteins / Q000276:immunology; D003602:Cytotoxicity, Immunologic; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000276:immunology; D006801:Humans; D007111:Immunity, Cellular; D008213:Lymphocyte Activation; D008533:Megakaryocytes / Q000166:cytology* / Q000276:immunology; D013601:T-Lymphocytes / Q000145:classification* / Q000276:immunology
chemical_list: D003165:Complement System Proteins