title: A regulatory role of activated T-lymphocytes on human megakaryocytopoiesis in vitro.
abstract: Cellular interactions responsible for regulating in vitro megakaryocytopoiesis were studied using a microagar culture system which permits the simultaneous proliferation of human megakaryocytic progenitor cells (CFU-M) and T-lymphocytic colonies (CFU-TL). The proliferation of these colony types depends mainly on two factors: phytohaemagglutinin (PHA) and erythropoietin (EP). The direct addition of increasing PHA concentrations to the liquid overlayer resulted in a parallel increase of CFU-M and CFU-TL. If the T-lymphocytes were removed by an E-rosetting technique a marked diminution of CFU-M and CFU-TL numbers was observed. However, monocyte depletion resulted in a marked augmentation of CFU-M proliferation compared to unfractionated mononuclear cells. In order to confirm that the reduction of CFU-M proliferation observed after T-depletion was primarily mediated by the absence of T-lymphocytes, we have co-cultured different concentrations of previously removed autologous T-lymphocytes with a constant number of T-depleted bone marrow cells. A parallel increase of CFU-TL and CFU-M was found if 0.75 - 7.5 X 10(4) T-lymphocytes were added to the culture. In conclusion, our results indicate that activated T-lymphocytes augment proliferation of human bone marrow CFU-M and that monocytes are less important for the growth of megakaryocytic colonies.
mesh_terms: D001854:Bone Marrow Cells; D002478:Cells, Cultured; D004921:Erythropoietin / Q000494:pharmacology; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008213:Lymphocyte Activation / Q000187:drug effects; D008533:Megakaryocytes / Q000502:physiology*; D009000:Monocytes / Q000502:physiology; D010835:Phytohemagglutinins / Q000494:pharmacology; D013601:T-Lymphocytes / Q000502:physiology*
chemical_list: D010835:Phytohemagglutinins; D004921:Erythropoietin