Cell - Mediated Suppression of Megakaryocytopoiesis in Acquired

Acquired amegakaryocytic thrombocytopenic purpura (AATP) is a disorder of hematopoiesis characterized by severe thrombocytopenia due to a selective reduction or total absence of megakaryocytes in an otherwise normalappearing bone marrow. Although the development of autoantibodies directed against cells in the megakaryocyte progenitor cell pool has been implicated in the pathogenesis of this disorder. cell-mediated suppression of megakaryocytopolesis has not been described. Accordingly. we report two casesof AATP in which in vitro suppression of megakaryocyte colony formation by autologous ancillary marrow cells was demonstrable. Light-density bone marrow mononuclear cells (MNCs) obtained from both patients were either plated directly into plasma clot cultures. or after first being depleted by adherent monocytes (MO) or T lymphocytes using standard methodologies. In some experiments. the depleted ancillary marrow cells were recovered for autologous co-culture studies with the MNCs from which they had been depleted. Megakaryocyte colony formation was detected in the cultures using an indirect immunofluorescence assay with a rabbit anti-human platelet glycoprotein antiserum. Removal of MO (n = 6). or T lymphocytes (n = 4) from normal marrow MNCs had no apparent effect on colony formation. In contrast. depleting T lymphocytes from the MNCs of patient 1 significantly