Concentration and Subclass Distribution of Anti-ADAMTS13 IgG Autoantibodies in Different Stages of Acquired Idiopathic Thrombotic Thrombocytopenic Purpura.

György Sinkovits,György Sinkovits,Zoltán Prohászka,Zoltán Prohászka,Péter Farkas,Anikó Szilvási,Ágnes Szilágyi,Ágnes Szilágyi,Attila Tordai,Dóra Inotai,Katalin Rázsó,Marienn Réti

doi:10.3389/fimmu.2018.01646

Abstract

The acquired form of idiopathic thrombotic thrombocytopenic purpura (TTP) is an autoimmune disease, in which the underlying deficiency of the ADAMTS13 protease is caused by autoantibodies, predominantly of the IgG isotype. Certain HLA-DR-DQ haplotypes were associated with the risk of developing TTP. To investigate the development of the ADAMTS13-specific antibody response during the course of the disease, we analyzed the concentration, subclass distribution, and inhibitory potential of anti-ADAMTS13 IgG autoantibodies in samples of TTP patients drawn during the first acute phase, in remission, and during relapse. Additionally, we compared the anti-ADAMTS13 IgG levels between patients carrying and not carrying risk and protective HLA-DR-DQ haplotypes. We determined the anti-ADAMTS13 IgG concentration and subclass distribution in 101 antibody-positive samples of 81 acquired TTP patients by ELISA methods. The presence and semi-quantitative amount of anti-ADAMTS13 inhibitors were determined in 97 of 100 deficient samples, and the specific inhibitory potential of anti-ADAMTS13 autoantibodies was determined in 49 selected samples, by mixing ADAMTS13-activity assays. HLA-DR-DQ typing and haplotype prediction were performed in 70 of the above patients. We found that IgG1 and IgG4 were the predominant subclasses, present in almost all samples. While IgG1 was the dominant subclass in almost half of the samples taken during the first acute episode, IgG4 was dominant in all samples taken during or following a relapse. The inhibitory potential of the samples correlated with levels of the IgG4 subclass. Anti-ADAMTS13 antibodies of IgG4-dominant samples had higher specific inhibitory potentials than IgG1-dominant samples, independently of disease stage. Interestingly, we found that patients carrying the protective DR7-DQ2 and DR13-DQ6 haplotypes had higher anti-ADAMTS13 IgG levels. Our results indicate that IgG4 becomes the dominant subtype at some point of the disease course, apparently before the first relapse, parallel to the increase in inhibitory potential of the anti-ADAMTS13 autoantibodies. Furthermore, we found an association between the genetic background and the antibody response in TTP.

Highlights

Idiopathic thrombotic thrombocytopenic purpura (TTP) is a rare but life-threatening disease, which belongs to the group of thrombotic microangiopathies, and presents with episodes of severe thrombocytopenia, microangiopathic hemolytic anemia (MAHA) with fragmentation of erythrocytes, and end-organ dysfunction caused by microvascular thrombosis [1]
From the 113 patients in our registry who fulfilled the criteria of acquired idiopathic TTP during the inclusion period, 81 patients had anti-ADAMTS13 IgG-positive samples appropriate for the determination of IgG subclasses
Comparing samples from the first acute episode, we found that the anti-ADAMTS13 IgG levels were higher in patients carrying protective haplotypes than in those not carrying protective haplotypes [240.2 (122.9–533.1) vs. 67.1 (43.6–152.0) U/mL, p = 0.0025] (Figure 7C)

Summary

Introduction

Idiopathic thrombotic thrombocytopenic purpura (TTP) is a rare but life-threatening disease, which belongs to the group of thrombotic microangiopathies, and presents with episodes of severe thrombocytopenia, microangiopathic hemolytic anemia (MAHA) with fragmentation of erythrocytes, and end-organ dysfunction caused by microvascular thrombosis [1]. The underlying ADAMTS13 deficiency is caused by ADAMTS13 mutations in the rare, congenital form of TTP [7], whereas the more common, acquired form of TTP is an autoimmune disease, in which autoantibodies against the ADAMTS13 enzyme are responsible for its deficiency [8, 9]. Some of these antibodies are inhibitory, directly blocking the enzymatic activity of the protease [8, 9], while some are non-inhibitory [10]. Certain HLADR-DQ haplotypes were associated with the risk of developing TTP

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Conclusion