The IgA Isotype of Anti-β2 Glycoprotein I Antibodies Recognizes Epitopes in Domains 3, 4, and 5 That Are Located in a Lateral Zone of the Molecule (L-Shaped).

Manuel Serrano,Gary L Norman,Antonio Serrano,Jose Angel Martinez-Flores,Laura Naranjo,Jose Maria Morales

doi:10.3389/fimmu.2019.01031

Manuel Serrano, Gary L Norman + Show 4 more

Open Access

https://doi.org/10.3389/fimmu.2019.01031

Copy DOI

Abstract

Background: Antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy morbidity with presence of anti-phospholipid antibodies (aPL). The APS classification criteria only consider the aPL of IgG/IgM isotype, however testing of aPL of IgA isotype is recommended when APS is suspected and consensus aPL are negative. IgA anti-βeta-2 glycoprotein-I (B2GP1) has been clearly related with occurrence of thrombotic events. Antibodies anti-B2GP1 of IgG/M isotypes recognize an epitope in Domain 1 (R39-G43), the epitopes that recognize IgA anti-B2GP1 antibodies are not well-identified.Aim: To determine the zones of B2GP1 recognized by antibodies of IgA isotype from patients with APS symptomatology and positive for IgA anti-B2GP1.Methods: IgA antibodies to Domain-1(D1) and Domain-4/5(D4/5) of B2GP1 (ELISA) and epitope mapping on oligopeptide arrays of B2GP1 were evaluated in sera from a group of 93 patients with at least one thrombotic and with isolated positivity for IgA anti-B2GP1 antibodies (negative for other aPL).Results: A total of 47 patients (50.5%) were positive for anti-D4/5 and 23(25%) were positive for anti-D1. When peptide arrays were analyzed, three zones of B2GP1 reactivity were identified for more than 50% of patients. The center of these zones corresponds to amino acids 140(D3), 204(D4), and 264(D5). The peptides recognized on D3 and D4 contain amino acid sequences sharing high homology with proteins of microorganism that were previously related with a possible APS infectious etiology. In the three-dimensional structure of B2GP1, the three peptides, as the R39-G43 epitope, are located on the right side of the molecule (L-shape). The left side (J-shape) does not bind the antibodies.Conclusions: Patients with thrombotic APS clinical-criteria, and isolated IgA anti-B2GP1 positivity appear to preferentially bind, not to the D1 or D4/5 domains of B2GP1, but rather to three sites in D3, D4, and D5. The sites on D3 and D4 were previously described as the target identified by human monoclonal antibodies derived from patients that were capable of inducing APS in animal models. The localization of these epitopes opens a new route to explore to increase understanding of the patholophysiology of the APS and to propose new alternatives and therapeutic targets.

Highlights

Antiphospholipid syndrome (APS) is an autoimmune vascular disorder characterized by recurrent thrombosis and gestational morbidity in carriers of antiphospholipid autoantibodies [1].The most common form of the disease is the Primary antiphospholipid syndrome (P-APS) [2]
The selection criteria for patient group were that they had at least one thrombotic event consistent with clinical APS classification criteria and that they were only positive for IgA anti-β2GP1
We have demonstrated for the first time that the antibodies of isotype IgA from patients with thrombotic clinical signs consistent with APS who are only positive for the IgA against B2GP1 have affinity to specific zones of the B2GP1 molecule

Summary

Introduction

Antiphospholipid syndrome (APS) is an autoimmune vascular disorder characterized by recurrent thrombosis and gestational morbidity in carriers of antiphospholipid autoantibodies (aPL) [1].The most common form of the disease is the Primary antiphospholipid syndrome (P-APS) [2]. The classification criteria of APS established by an International consensus statement in 2006 are based on the simultaneous presence of at least one clinical and one laboratory criterion. The laboratory criteria include positivity of any lupus anticoagulant, anticardiolipin antibodies (aCL) and/or of anti-B2GP1, persistently positive and at medium to high titer. Antibodies of IgM and IgG Isotypes were included in classification criteria. Antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy morbidity with presence of anti-phospholipid antibodies (aPL). The APS classification criteria only consider the aPL of IgG/IgM isotype, testing of aPL of IgA isotype is recommended when APS is suspected and consensus aPL are negative. Antibodies anti-B2GP1 of IgG/M isotypes recognize an epitope in Domain 1 (R39-G43), the epitopes that recognize IgA anti-B2GP1 antibodies are not well-identified

Objectives

Methods

Results

Discussion

Conclusion