Suppression of in vitro megakaryocyte production by antiplatelet autoantibodies from adult patients with chronic ITP

Abstract

Chronic immune thrombocytopenic purpura (ITP) is manifested by autoantibodyinduced platelet destruction. Platelet turnover studies suggest that autoantibody may also affect platelet production. To evaluate this, we studied the effect of plasma from adult patients with chronic ITP on in vitro megakaryocyte production. CD34 ؉ cells, obtained from healthy donors, were cultured in medium containing PEG-rHuMGDF and 10% plasma from either ITP patients or healthy subjects. Cultures containing plasma from 12 of 18 ITP patients showed a significant decrease (26%-95%) in megakaryocyte production when compared with control cultures. Positive ITP plasmas not only reduced the total number of megakaryocytes produced during the culture period but also inhibited megakaryocyte maturation, resulting in fewer 4N, 8N, and 16N cells. The role of antibody in this suppression is supported by 2 factors: (1) immunoglobulin G (IgG) from ITP patients inhibited megakaryocyte production when compared with control IgG; and (2) adsorption of autoantibody, using immobilized antigen, resulted in significantly less inhibition of megakaryocyte production when compared with unadsorbed plasma. These results show that plasma autoantibody from some adult patients with ITP inhibits in vitro megakaryocyte production, suggesting that a similar effect may occur in vivo. IntroductionIn 1950, Dr William Harrington was infused with blood from a patient with chronic immune thrombocytopenic purpura (ITP), resulting in the rapid onset of severe thrombocytopenia. He recovered within the next few days. Further studies by Harrington et al 1 and Shulman et al 2 showed clearly that patients with chronic ITP have a circulating factor capable of destroying homologous and autologous platelets. The severity of the thrombocytopenia was dose dependent, and the plasma factor could be adsorbed by platelets and was present in the immunoglobulin G (IgG)-rich fraction after ion-exchange chromatography. For the next several years, it was concluded that thrombocytopenia in patients with chronic ITP was caused solely by autoantibody-induced platelet destruction.However, in the early 1980s, autologous platelet survival studies from several laboratories showed that in approximately two thirds of ITP patients, platelet turnover is either reduced or normal, not increased, as would be expected if platelet destruction were the only mechanism causing thrombocytpenia. [3][4][5][6] Because megakaryocytes express GPIIb-IIIa and GPIb-IX on their surfaces during maturation 7 and because most ITP autoantibodies react with one or both of these glycoprotein complexes, 8,9 it follows that autoantibody binding to megakaryocytes could interfere with platelet production and release from the bone marrow either by causing intramedullary megakaryocyte or platelet destruction or by interfering with megakaryocyte maturation.Recently, Chang et al 10 evaluated the effect of plasma, from patients with childhood ITP (44 with acute ITP and 9 with chronic ITP), on thrombopoietin-induced production of megaka...

Platelet production rate predicts the response to prednisone therapy in patients with idiopathic thrombocytopenic purpura

“…The variability in PPR among different individuals is therefore likely to be related to the degree of autoantibody binding to megakaryocyte antigens. Other mechanisms, including capacity and function of the reticuloendothelial system, the degree of autoantibody-induced activation of complement, and T-lymphocyte-mediated cytotoxity may also play a role [1]. We did not observe a difference in response rates to prednisone between patients with normal and increased PPRs.…”

“…Previous studies have shown that, in the majority of ITP patients, the PPR is either reduced or normal [28,30,[32][33][34][35][36]. Additional support for a suppressed platelet production in ITP comes from in vitro studies showing that megakaryocyte production and maturation can be inhibited by antiplatelet antibodies [1,2,37]. Similar in vitro cultured megakaryocytes in the presence of ITP plasma show features compatible with premature cell death [3].…”

“…Thrombocytopenia in idiopathic thrombocytopenic purpura (ITP) is predominantly caused by autoantibodies that recognize antigens on platelets and megakaryocytes resulting in accelerated platelet destruction and decreased platelet production rate (PPR) [1,2]. Premature cell death of megakaryocytes plays an important role in the reduced platelet production [3].…”

Helicobacter pylori infection and chronic immune thrombocytopenic purpura: long-term results of bacterium eradication and association with bacterium virulence profiles

“…45 The disease has also been associated with impaired megakaryocyte production. 46 Several hypotheses have been raised to explain the possible interaction between H pylori and thrombocytopenia. 10,41,[46][47][48][49] Some H pylori strains bind von Willebrand factor and interact with glycoprotein Ib to induce platelet aggregation, but its contribution to immune thrombocytopenia remains to be demonstrated.…”

“…46 Several hypotheses have been raised to explain the possible interaction between H pylori and thrombocytopenia. 10,41,[46][47][48][49] Some H pylori strains bind von Willebrand factor and interact with glycoprotein Ib to induce platelet aggregation, but its contribution to immune thrombocytopenia remains to be demonstrated. 50 Nevertheless, these hypotheses have yet to be confirmed and cannot be easily reconciled with the observation that improvement in the platelet count was generally seen 2 weeks after completion of eradication therapy, as reported also by others.…”