Cell-mediated suppression of megakaryocytopoiesis in acquired amegakaryocytic thrombocytopenic purpura

Abstract

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 normal-appearing 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 megakaryocytopoiesis has not been described. Accordingly, we report two cases of 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 (M phi) 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 M phi (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 augmented megakaryocyte colony formation; a similar effect was observed after depleting M phi from the MNCs of patient 2. This observed augmentation in colony formation could be abrogated by autologous co-culture with the putative suppressor cell at effector cell/target cell ratios of 1:10 in the case of T lymphocytes or 1:5 in the case of M phi. Neither suppression nor stimulation of megakaryocyte colony formation was observed after culturing normal MNCs with autologous T cells (n = 4) or M phi (n = 3) at similar or greater ratios. We also observed inhibition of megakaryocyte colony formation after culturing normal MNCs in the presence of tissue culture medium conditioned by the M phi of patient 2. This effect was shown to be specific for megakaryocytes since this same conditioned medium had no significant effect on BFU-E and CFU-E-derived colony formation by autologous marrow mononuclear cells. These results suggest that: both T cells and M phi are capable of exerting a regulatory effect on the proliferation of human megakaryocyte progenitor cells (CFU-Meg); in the case of M phi, a soluble factor elaborated by these cells may be responsible for suppressing CFU-Meg growth; and aberrant ancillary cell- megakaryocyte progenitor cell interactions may lead to clinically significant disease.

CD8+ T cells suppress autologous megakaryocyte apoptosis in idiopathic thrombocytopenic purpura

“…However, the role of cellular regulation on megakaryocytopoiesis in ITP is largely unclear. Some studies suggested that CD8 + T cells may be involved in the pathogenesis of acquired amegakaryocytic thrombocytopenic purpura by exerting suppression on megakaryocyte differentiation (Gewirtz et al, 1986;Benedetti et al, 1994). In the present study, we performed a similar culture system to the methods of Benedetti et al (1994) to preliminarily measure the quantity and quality of megakaryocytes.…”

Acquired amegakaryocytic thrombocytopenic purpura

“…Gewirtz et al in 1986 proposed cell-mediated suppression of megakaryocytopoiesis by demonstrating in vitro suppression of megakaryocyte colony formation by autologous ancillary marrow cells in two cases of AATP. Depletion of T lymphocytes from the mononuclear cells of both these patients significantly augmented megakaryocyte colony formation [4]. In 1994, Benedetti et al showed cell-mediated immunosuppression of megakaryocytes by demonstrating a marked increase of T-activated suppressor cells (CD8 + / DR + ) in association with AATP [5].…”

Relationship between megakaryocyte mass and serum thrombopoietin levels as revealed by a case of cyclic amegakaryocytic thrombocytopenic purpura

“…Cyclic megakaryocytopenia is a variant of acquired amegakaryocytic thrombocytopenic purpura (AATP) which is characterized by an isolated failure of megakaryocyte development and platelet production. AATP may be idiopathic or due to either humoral (Hoffman et al , 1985, 1982; Katai et al , 1994) or cell‐mediated (Gewirtz et al , 1986b) inhibition of megakaryocytopoiesis. Cyclic AATP has also been described and may be due to either humoral (Hoffman et al , 1989; Balduini et al , 1993) or cell mediated (Dan et al , 1991) immune mechanisms.…”