Background Studies on antiphospholipid antibodies (aPL) have mainly focused on the IgG and IgM isotypes, with only a few on the pathogenic significance of IgA aPL. Positive IgA anticardiolipin (aCL) and IgA anti-β2glycoprotein I (anti-β2GPI) were reported to be predominantly associated with other aPL, making it difficult to understand the role of IgA alone . Recently, antibodies against phosphatidylserin/prothrombin (aPS/PT) IgG and IgM have been indicated as a potential marker for antiphospholipid syndrome (APS) [2, 3]. Our previous study reported that IgG and IgM aPS/PT showed highest association with lupus anticoagulant (LA) activity of all tested aPL , while no studies to date have investigated possible clinical benefits of IgA aPS/PT.
Objectives To determine the prevalence of IgA aPS/PT in patients with systemic autoimmune diseases and evaluate their association to thrombosis and obstetric complications.
Methods We examined 254 patients with systemic autoimmune diseases: 91 APS, 40 APS secondary to systemic lupus erythematosus (SLE), 47 SLE, 57 rheumatoid arthritis (RA) and 19 Sjögren's syndrome (SS) patients for LA, aCL, anti-β2GPI and aPS/PT (for IgG, IgM, IgA isotypes) . 55 subjects experienced arterial thrombosis (AT), 60 venous thrombosis (VT) and 54 obstetric complications (OC).
Results An overall prevalence of 63/254 (25%) was found for IgA aPS/PT in our cohort of patients. IgA aPS/PT were statistically significantly associated to both AT and VT (p=0.026 and p=0.002, respectively), however no association was found to OC (p=0.534). 19/63 (30%) patients were solely positive for IgA aPS/PT and negative for IgG or IgM aPS/PT. Five of these patients (3 SLE, 1 RA and 1 SS) were concomitantly negative also for LA, aCL and anti-β2GPI. One of the solely positive IgA aPS/PT patients experienced AT, while the other four showed no clinical manifestations significant for APS. IgA aPS/PT showed significant association with LA activity (p<0.001; OR 4.7), comparable to IgG anti-β2GPI (OR 5.1) and higher than IgG/IgM aCL (OR<3.4) or IgM/IgA anti-β2GPI (OR<2.9).
Conclusions IgA aPS/PT presented an independent risk factor for thrombosis, and highly correlated to LA activity. Larger studies are needed to confirm whether IgA aPS/PT testing could contribute to the assessment of thrombotic risk, especially in “seronegative” APS patients.
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Disclosure of Interest None declared
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