Background Anti-phospholipid antibodies (aPLs) are frequently associated with arterial and/or venous thromboembolic complications and recurrent fetal loss in patients with systemic lupus erythematosus (SLE). We recently reported that the clinical picture of SLE apparently depends on subclasses of aPLs in the patient's sera, but the contribution of each subclass remains uncertain. Methods We newly developed an ELISA system for simultaneous detection of six specific categories of aPLs: anti-cardiolipin (aCL), anti-β2- glycoprotein I (aβ2GPI), anti-cardiolipin/β2- glycoprotein I (aCL/β2GPI), anti-phosphatidylserine (aPS), anti-prothrombin (aPT), and anti-phosphatidylserine/prothrombin (aPS/PT). They were measured in 331 patients with SLE including 63 patients with arterial thromboembolic complications, 64 with venous thromboembolic complications, and 43 with recurrent fetal loss. Lupus anticoagulant (LA) activity in their plasma was measured according to the guidelines recommended by the Subcommittee on Lupus Anticoagulant/Phospholipid-Dependent Antibodies. Results Multivariate logistic analysis revealed that the concentration of aPS/PT was most closely associated with arterial thrombosis. In contrast, the concentration of aβ2GPI was most closely related to venous thrombosis. Furthermore, both aCL/β2GPI and aPS/PT were independently associated with episodes of recurrent fetal loss. Regarding the relation between APLs and LA activity, aPS/PT, followed by aβ2GPI and aPT, showed the closest association with the presence of LA activity. Conclusions Anti-phospholipid syndrome in patients with SLE can be classified by antigenic specificities of their aPLs as to their susceptibility to arterial and/or venous thromboembolic complications or obstetric complications.
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