Background/Purpose:   Domain(D)I is the immunodominant epitope of antiβ2-glycoproteinI(aβ2GPI) and in several studies antibodies to DI were shown to be associated with clinical manifestations of APS. Herein, we aimed to describe the prevalence, correlations and clinical associations of IgG/IgA/IgM aβ2GPI and aDI in an APS cohort of patients from Turkey.

Methods:   Serum was obtained from 75 patients with: primary APS, n=31; systemic lupus erythematosus (SLE) and APS, n=44. IgG/IgA/IgM aβ2GPI, aDI and IgG anticardiolipin (aCL) were measured by ELISA. Positivity was defined as titres > 99th percentile of the mean activity of healthy control cohort. Cut-offs for positivity were: 17GPLU; 9GBU; 14GDIU for IgG aCL/aβ2GPI and aDI, 18MBU; 21MDIU for IgM aβ2 GPI and aDI, and 9ABU; 8ADIU for IgA aβ2 GPI and aDI respectively. Lupus anticoagulant (LA) was measured in the clinical laboratory of Istanbul Faculty of Medicine. Triple positivity was defined as IgG aβ2GPI/aCL and LA; double positivity as LA/IgG aCL, LA/IgG aβ2GPI or IgG aCL/aβ2GPI and single positivity as LA or IgG aCL or IgG β2GPI.

Results:   76% of the patients were female. The mean age and duration of disease were 40±11 years and 114±92 months respectively. 17 patients suffered arterial thrombosis (AT) only, 23 venous thrombosis (VT) only, 5 AT + VT, 15 pregnancy morbidity (PM) only, 13 thrombosis and PM and 2 catastrophic antiphospholipid syndrome. The prevalence and the titers of the tested antiphospholipid antibodies(aPL) are shown in tables 1 and 2. There were patients with single positivity for IgA aDI (n=2) and aβ2GP1 (n=1) and they all suffered vascular thrombosis. Comparison of the vascular thrombosis only and PM only groups revealed a significantly higher IgM aDI positivity (table1) and titer in the PM only group (mean, interquartile range; 14, 8 vs 22,15 respectively; p=0.04) There were 10 triple positives, 19 double and 49 single positives. 80% of patients with triple positivity had vascular thrombosis and all had IgG aDI antibodies. There was a positive correlation between IgG aβ2GP1 and DI (p<0.05). 58 % of double and 27 % of single positives had IgG aDI antibodies.

Conclusion:   We found a high prevalence of IgA aβ2GP1 and aDI in this cohort. Given that some patients with thrombosis had single positivity for IgA aβ2GP1 and aDI, these tests may help to recognize a small group of patients with APS. Significantly more patients with PM only were positive for IgM aDI. Whether testing IgM aDI may be of value in relation to PM needs to be validated. Despite lacking significance, the positivity for IgG aDI was higher in the vascular thrombosis group. IgG aDI was more frequent in triple-positives most of whom had thrombotic events. There was a positive correlation between IgG aDI and aβ2GPI which may show that DI is the major antigenic target in β2GPI and that IgG aDI antibodies can be used to identify APS patients with a high thrombotic risk. TABLE THE PREVALENCE OF THE TESTED aPL

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-prevalence-and-associations-of-iggam-anti-%ce%b22gpi-and-anti-domain-i-antibodies-in-an-antiphospholipid-syndrome-aps-cohort-of-patients-from-turkey/