Antibody response to this new panel of serological markers was associated with complicated disease phenotype, NOD2/CARD15 genotype, and a need for surgery in this eastern European IBD cohort.

Soluble von Willebrand factor (VWF) has a low affinity for platelet glycoprotein (GP) Ib␣ and needs immobilization and/or high shear stress to enable binding of its A1 domain to the receptor. The previously described anti-VWF monoclonal antibody 1C1E7 enhances VWF/GPIb␣ binding and recognizes an epitope in the amino acids 764 -1035 region in the N-terminal DD3 domains. In this study we demonstrated that the DD3 region negatively modulates the VWF/GPIb-IX-V interaction; (i) deletion of the DD3 region in VWF augmented binding to GPIb␣, suggesting an inhibitory role for this region, (ii) the isolated DD3 region inhibited the GPIb␣ interaction of a VWF deletion mutant lacking this region, indicating that intramolecular interactions limit the accessibility of the A1 domain, (iii) using a panel of anti-VWF monoclonal antibodies, we next showed that the DD3 region is in close proximity with the A1 domain in soluble VWF but not when VWF was immobilized; (iv) destroying the epitope of 1C1E7 resulted in a mutant VWF with an increased affinity for GPIb␣. Our results support a model of domain translocation in VWF that allows interaction with GPIb␣. The suggested shielding interaction of the A1 domain by the DD3 region then becomes disrupted by VWF immobilization. The plasma protein von Willebrand factor (VWF)4 has a central role in normal primary hemostasis (1). The interaction of VWF with its platelet receptor glycoprotein (GP) Ib␣ in the GPIb-IX-V complex mediates platelet adhesion to extracellular matrices exposed at sites of vascular injury. This interaction is essential for thrombus formation at sites of high shear stress, as in microarterioles or in stenosed arteries.Mature VWF comprises a series of multimers that are composed of homodimers interlinked through disulfide bridges. The mature VWF subunit consists of four distinct types of internal homology present in two to three copies in the following order from the N terminus:

To cite this article: Ré ti M, Farkas P, Csuka D, Rá zsó K, Schlammadinger Á , Udvardy ML, Madá ch K, Domjá n G, Bereczki C, Reusz GS, Szabó AJ, Prohá szka Z. Complement activation in thrombotic thrombocytopenic purpura. J Thromb Haemost 2012; 10: 791-8.Summary. Background: Ultra-large von Willebrand factor and deficiency of its cleaving protease are important factors in the events leading to thrombotic microangiopathy; however, the mechanisms involved are only partly understood. Whereas pathological activation of the alternative complement pathway is linked to atypical hemolytic uremic syndrome, the role of complement activation in thrombotic thrombocytopenic purpura (TTP) is unknown. The aim of this study was to investigate whether signs of complement activation are characteristic of TTP. Patients and methods: Twenty-three patients with TTP (18 women, median age 38 years) and 17 healthy controls (13 women, median age 38 years) were included. Complement parameters (C3, Factors H, I, B and total alternative pathway activity) together with complement activation fragments (C3a) or complexes (C1rs-INH, C3bBbP, sC5b9) were measured by ELISA or RID. ADAMTS13 activity and anti-ADAMTS13 inhibitory antibodies were measured by the VWF-FRET73 assay. Results: Increased levels of C3a, and SC5b9 were observed in TTP during acute episodes, as compared with healthy controls. Decreased complement C3 levels indicative of complement consumption occurred in 15% of acute TTP patients. Significant decrease of complement activation products C3a and SC5b9 was observed during plasma exchange (PEX). The sustained presence of anti-ADAMTS13 inhibitory antibodies in complete remission was associated with increased complement activation. Conclusion: These data document in an observational study the presence of complement activation in TTP. Further investigation is needed to determine its potential pathogenetic significance.