A regulatory role of activated T‐lymphocytes on human megakaryocytopoiesis in vitro

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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 2 factors: phytohemagglutinin (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. 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, different concentrations of previously removed autologous T-lymphocytes were cocultured 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 .times. 104 T-lymphocytes were added to the culture. Apparently, activated T-lymphocytes augment proliferation of human bone marrow CFU-M and monocytes are less important for the growth of megakaryocytic colonies.