To characterize the nature of thyroid peroxidase (TPO) autoantibodies present in the sera of patients with autoimmune thyroid disease, we cloned three IgG1/kappa Fab fragments which bind 125I-TPO. This was accomplished by the molecular cloning and expression in bacteria of IgG gene fragments from B cells infiltrating the thyroid of a patient with Graves' disease. The three Fab fragments (SP2, S...

The activity of the c-Mpl ligand hematopoietic progenitors meets criteria expected for thrombopoietin (TPO). Bio-assays have shown that blood TPO levels are inversely related to platelet mass. We sought to identify the molecular basis for this regulation. To determine if TPO mRNA levels respond to platelet demand, RNA from selected organs of mice with high, normal or low platelet counts was sub...

Thrombocytopenia in liver diseases is considered to be due to splenic platelet pooling and accelerated destruction. Since thrombopoietin (TPO), a regulator of thrombopoiesis, is produced mainly in the liver, decreased production of TPO may account for thrombocytopenia in liver diseases. To address this issue, we measured serum TPO, using a sensitive sandwich ELISA, in 108 patients with chronic ...

Thrombopoietin (TPO), the primary regulator of platelet production, also plays an important role in hematopoietic stem cell (HSC) biology. In previous studies we demonstrated that the self-renewal and expansion of HSCs is 10 to 20 times less robust in tpo-/- mice than in controls. To explore the molecular basis of this effect, we postulated that Hoxb4 might mediate at least part of the TPO effe...

The pathophysiology of thrombocytopenia in the syndrome of thrombocytopenia with absent radii (TAR) is not yet understood. We examined thrombopoietin (TPO) serum levels and the in vitro reactivity of platelets to TPO in five patients affected with TAR syndrome. We found elevated TPO serum levels in all patients tested, excluding a TPO production defect as cause for thrombocytopenia in TAR syndr...

Thrombopoietin (TPO) is a hematopoietic growth factor that regulates megakaryocytopoiesis and platelet production through binding to its receptor, Mpl, encoded by the c-mpl proto-oncogene. Circulating levels of TPO are regulated by receptor-mediated uptake and degradation. To better understand this mode of TPO regulation, we examined whether expression of Mpl was regulated by its ligand. Using ...

Thrombopoietin (Tpo) is the primary cytokine regulating megakaryocyte development and platelet production. Tpo signaling through its receptor, c-mpl, activates multiple pathways including signal transducer and activator of transcription (STAT)3, STAT5, phosphoinositide 3-kinase-Akt, and p42/44 mitogen-activated protein kinase (MAPK). The adaptor protein Lnk is implicated in cytokine receptor an...

We have studied the effects of recombinant human thrombopoietin (TPO, Mpl ligand) on human hematopoiesis in vitro. TPO alone did not support erythroid burst formation but, in the presence of erythropoietin, it enhanced erythroid burst formation from CD34+ bone marrow and cord blood cells. The burst-promoting activity (BPA) was stronger under 5% serum than 30% serum conditions. The direct nature...

The relationship between thrombopoietin (TPO) and its receptor cMpl in thrombocytopenic conditions has not been entirely clarified. To elucidate this interplay may expand the spectrum of indications of TPO mimetics. In this study we have explored the relationship between TPO and cMpl in platelets and megakaryocytes of 43 patients with thrombocytopenia due to idiopathic thrombocytopenic purpura ...

Thrombopoietin (Tpo) is a major regulator of megakaryopoiesis both in vivo and in vitro. Tpo initiates its biologic effects by binding to the Mpl receptor, which is a member of the hematopoietin receptor family. To define the Tpo binding characteristics of the Mpl receptor, we iodinated purified 70-kD recombinant human Tpo using the Bolton-Hunter reagent. Autoradiographic analysis of (125)I-Tpo...