PF794 DETECTION OF ANTIBODIES DIRECTED AGAINST DOMAIN 1 OF BETA 2 GLYCOPROTEIN I IN PATIENTS WITH ANTIPHOSPHOLIPID SYNDROME

Abstract

Background:Antiphospholipid syndrome (APS) is an acquired thrombophilia caused by antiphospholipid autoantibodies (aPL). Diagnosis of APS is based on laboratory and clinical criteria (thrombosis or pregnancy‐related complications). The detection of lupus anticoagulant (LA), IgG and/or IgM isotype anti‐cardiolipin (ACA) and anti‐β2 glycoprotein I antibodies (aβ2GPI) constitutes the laboratory tests of APS. The β2GPI protein consists of 5 domains and an association of thrombosis with the presence of antibodies directed against domain 1 (aD1β2GPI) was suggested in the literature.Aims:The aim of this study was to investigate the presence of IgG isotype aD1β2GPI and its association with thrombosis in our patient cohort.Methods:Using a chemiluminescence immunoassay (INOVA QUANTA Flash β2GPI‐Domain I, ACL Acustar) we have measured aD1β2GPI titer in 51 patients having IgG isotype aβ2GPI (APS with thrombosis: n = 21; APS with pregnancy loss: n = 7; other autoimmune disease: n = 18; aPL positive asymptomatic patients, n = 5).Results:In patient samples the concordance between the presence of IgG isotype aD1β2GPI and aβ2GPI was 67% and the correlation between these antibody titers was high (r = 0.71). We have found that the level of IgG isotype anti‐β2GPI was significantly higher in thrombotic APS patients compared to all other patient groups. The aD1β2GPI titer was the highest in thrombotic patients however, there was no significant difference in the antibody titer among the patient groups. The IgG isotype aβ2GPI and aD1β2GPI titers were significantly higher in triple positive patients (LA, ACA and aβ2GPI positive) than in double positive patients (ACA and aβ2GPI positive). In the aD1β2GPI positive group 47% of patients had thrombosis, while in the aD1β2GPI negative group this figure was only 29%, however, the association of aD1β2GPI positivity with thrombosis was non‐significant.Summary/Conclusion:This study provides further evidence that the large majority of IgG isotype aβ2GPI is directed against domain 1. Since the concordance between the two antibody positivity was not 100% and aD1β2GPI negative patients can present with thrombosis, we conclude that monitoring aD1β2GPI cannot replace detection of aβ2GPI in the laboratory diagnosis of APS.