The Prevalence and Clinical Significance of Iga Anti-Phosphatidylserine/ Prothrombin Antibodies in Systemic Autoimmune Diseases

Objective: Studies on antiphospholipid antibodies have mainly focused on the IgG and IgM isotypes, with only a few investigating the pathogenic significance of IgA antiphospholipid antibodies. Positive IgA anticardiolipin (aCL) and IgA anti-β2 glycoprotein I (anti-β2GPI) were reported to be predominantly associated with other antiphospholipid antibodies, making it difficult to understand the role of IgA alone. Recently, antibodies against phosphatidylserine/ prothrombin (aPS/PT) IgG and IgM have been indicated as a potential marker for antiphospholipid syndrome (APS). Our previous study reported that IgG and IgM aPS/PT showed highest association with lupus anticoagulant (LA) activity of all tested antiphospholipid antibodies, while no studies to date have investigated possible clinical benefits of IgA aPS/PT. In this study, we determined the prevalence of IgA aPS/PT in patients with systemic autoimmune diseases and evaluated their clinical association to thrombosis and obstetric complications. Methods: 254 patients with systemic autoimmune diseases were screened for LA, aCL, anti-β2GPI and aPS/PT (for IgG, IgM, IgA isotypes). 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 LA activity and to both arterial and venous thrombosis, however no association was found to obstetric complications. Median levels of IgA aPS/PT were significantly higher in APS patients than in the non-APS patient control group comprising systemic lupus erythematosus, rheumatoid arthritis and Sjogren’s syndrome patients. Conclusion: Although IgA aPS/PT were predominantly associated with other antiphospholipid antibodies this study first confirmed their presence in APS patient samples and also showed a clear association of IgA aPS/PT to thrombosis and LA activity.