Clinical utility of anti-phosphatidylinositol ELISA in antiphospholipid syndrome

Abstract

Antiphospholipid syndrome (APS) is currently diagnosed on the basis of both clinical findings and laboratory evidence of persistent aPLs. At present, the detection of IgG/IgM classes of anti-cardiolipin (aCL) and anti-β₂-glycoprotein I (aβ₂GPI) antibodies measured by standardized enzyme-linked immunosorbent assay (ELISA) has been adopted as the diagnostic criterion for APS. The major problem with APS diagnosis is that even if all current commercially available ELISA techniques are performed, only about 75% of all APS cases can be diagnosed. Therefore, it is necessary to establish an ELISA technique that can detect new anti-phospholipid antibodies useful for diagnosing APS. The objective of this study was to evaluate the prevalence of autoantibodies against phosphatidylethanolamine (PE) or phosphatidylinositol (PI) in patients with APS and various autoimmune diseases. We have established a new ELISA technique with solid-phased PE or PI and examined the prevalence of anti-PE and anti-PI autoantibodies in 20 patients with primary APS (PAPS), 30 SLE patients with APS (SLE/APS), 10 SLE patients without APS, 40 other collagen disease patients (Others), and 73 healthy subjects. The present study showed that both antibody titers and positivity rates of aPI-ELISA were significantly higher in the PAPS and SLE/APS patients than in the SLE patients, Others, and healthy persons. Furthermore, aPI-ELISA showed positive results in 4 of 13 non-criteria APS patients who were negative for aCL and aβ₂GPI but had thrombotic complications peculiar to APS. These results suggest that aPI-ELISA detects autoantibodies specific to APS patients, and positive results of aPI-ELISA may be useful in diagnosing APS in addition to conventional aPLs.