Platelets are required for enhanced activation of the endothelium and fibrinogen in a mouse thrombosis model of APS

Antiphospholipid syndrome (APS) is defined by thrombosis, fetal loss, and the presence of antiphospholipid antibodies, including anti-beta 2-glycoprotein-1 autoantibodies (anti-beta 2GP1) that have a direct role in the pathogenesis of thrombosis in vivo. The cellular targets of the anti-beta 2GP1autoantibody/beta 2GP1complex in vivo were studied using a laser-induced thrombosis model of APS in a live mouse and human anti-beta 2GP1 autoantibodies affinity-purified from APS patients. Cell binding of fluorescently labeled beta 2GP1 and anti-beta 2GP1 autoantibodies revealed their colocalization on the platelet thrombus but not the endothelium. Anti-beta 2GP1 autoantibodies enhanced platelet activation, monitored by calcium mobilization, and endothelial activation, monitored by intercellular adhesion molecule-1 expression. When eptifibatide was infused to block platelet thrombus formation, enhanced fibrin generation and endothelial cell activation were eliminated. Thus, the anti-beta 2GP1 autoantibody/beta 2GP1 complex binds to the thrombus, enhancing platelet activation, and platelet secretion leads to enhanced endothelium activation and fibrin generation. These results lead to a paradigm shift away from the concept that binding of the anti-beta 2GP1 autoantibody/beta 2GP1 complex activates both endothelial cells and platelets toward one in which activation of platelets in response to anti-beta 2GP1 autoantibody/beta 2GP1 complex binding leads to subsequent enhanced endothelium activation and fibrin generation

Histidine phosphorylation of P-selectin upon stimulation of human platelets: A novel pathway for activation-dependent signal transduction

AbstractTransient phosphorylation of histidine characterizes the two-component systems in prokaryotes that control important physiological functions, but analogous events have not been implicated in signal transduction in mammalian cells. To explore histidine phosphorylation during activation of human cells, stimulated platelets were analyzed for the formation of protein phosphohistidine in a model system employing P-selectin. P-selectin, a leukocyte adhesion molecule, undergoes rapid phosphorylation and selective dephosphorylation of tyrosine, serine, and threonine. We now establish that phosphorylation following platelet activation with thrombin or collagen generates phosphohistidine at histidines on the cytoplasmic tail of P-selectin. With thrombin stimulation, the kinetics of phosphohistidine appearance and disappearance on P-selectin are very rapid. Platelets exhibit a novel ligand-induced signaling pathway to generate phosphohistidine. These results provide direct biochemical evidence for the induction of rapid and reversible histidine phosphorylation in mammalian cells upon cell activation and represent a novel paradigm for mammalian cell signaling

Peritoneal macrophages express both P-selectin and PSGL-1

Macrophages, phagocytic cells involved in an early phase of host defense, are known to express the P-selectin ligand, PSGL-1. Heretofore, P-selectin has only been found on platelets and endothelial cells. Here, we demonstrate that peritoneal macrophages isolated by peritoneal lavage of unchallenged mice express P-selectin on the plasma membrane. The peritoneal macrophages synthesize P-selectin, as indicated by metabolic labeling experiments. P-Selectin is constitutively expressed on the extracellular surface of macrophages but is only partially colocalized with PSGL-1. P-Selectin is rapidly translocated from the macrophage plasma membrane to intracellular vesicles and to lysosomes. Peritoneal macrophages assemble into cell strings under flow conditions based upon macrophage–macrophage interactions mediated by P-selectin and PSGL-1. This is the first description of a leukocyte shown to express both P-selectin and PSGL-1

Hartwig Wessely (1725-1805); a study in Jewish educational reform

Thesis (Ed.M.)--Boston University, 1936. This item was digitized by the Internet Archive

A history of Jewish education in Poland before 1765

Thesis (Ph.D.)--Boston University, 193

Studies on the Structure of Human Fibronectin

Plasma fibronectin is a glycoprotein that consists of two polypeptide chains of approximately 250,000 and 245,000 daltons, joined by disulfide bonds located near one end of the molecule. Fibronectin was isolated from human plasma by gelatin-agarose affinity chromatography and DEAE-cellulose ion exchange chromatography. The two subunit chains were found to be similar or identical with respect to primary structure, using a one-dimensional peptide mapping technique