The platelet function defect of paroxysmal nocturnal haemoglobinuria

• Published in: Platelets (Edinburgh) 2004-05, Vol.15 (3), p.145-154
• Main Authors: Grünewald, Martin, Grünewald, Anja, Schmid, Anke, Schöpflin, Christine, Schauer, Stefanie, Griesshammer, Martin, Koksch, Mario
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Aged; Aged, 80 and over; Biomarkers - analysis; Blood Platelets - physiology; Case-Control Studies; Female; Humans; Immunophenotyping; Membrane Proteins - blood; Middle Aged; Pancytopenia; Platelet Activation; Platelet Function Tests; Receptors, Cell Surface - analysis
• ISSN: 0953-7104; 1369-1635
• DOI: 10.1080/09537105310001657110

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare, acquired stem cell disorder, characterised by an abnormal susceptibility of red blood cells to complement induced lysis, resulting in repeated episodes of intravascular haemolysis and haemoglobinuria, thromboembolic events at atypical locations and, to a much lesser extent, bleeding complications. Platelet function is assumed to be abnormal, however, a defect has not yet been characterised and underlying mechanisms remain elusive. To explore these issues, we investigated platelet function in PNH patients using assays for clot formation under low and high shear force (thrombelastography and PFA100® device), adhesion to glass beads in native whole blood (Hellem method), aggregometry using various agonists (Born method), and flow cytometric assays for baseline and agonist-induced surface expression density of α-granule (CD62P) and lysosomal granule proteins (CD63), ligand binding to surface receptors (thrombospondin), and expression density of activation-induced neoepitopes of the fibrinogen receptor complex (PAC-1). Platelet PNH clone size determined by CD55 and CD59 labelling was compared to the clone sizes of granulocytes, monocytes, erythrocytes, and reticulocytes. A profound reduction of platelet reactivity was observed in PNH patients for all 'global function' assays (clot formation, adhesion, aggregation). Platelet hyporeactivity was confirmed using flow cytometric assays. Whereas baseline levels of flow cytometrically determined platelet activation markers did not differ significantly between controls and PNH patients, agonist-induced values of all markers were distinctly reduced in the PNH group. Moreover, significantly reduced white blood cell counts (3.1 nl vs. 5.9 nl), haemoglobin values (9.5 vs. 14.3 g per dl), and platelet counts (136 vs. 219 nl) delineate profound tricytopenia in PNH patients. The fraction of particular cell types lacking the surface expression of GPI-anchored glycoproteins is referred to as the respective PNH clone; median PNH clone sizes of cells with short life spans (reticulocytes, platelets, granulocytes) was 50-80% of total cell populations compared to 20% of red blood cells. The results of our laboratory investigations show, that in PNH, reduced platelet counts coincide with reduced platelet reactivity. The foremost clinical complication in PNH, however, is venous thromboembolism, very probably induced by an activated and dysregulated plasmatic coagulation system. Fro