Abstract

OBJECTIVE--To investigate whether beta 2-glycoprotein I antibody (aGPI) exists in sera that are positive for antiphospholipid antibodies (aPL). METHODS--Thirty six patients with systemic lupus erythematosus (SLE) and 20 healthy volunteers were recruited. GPI independent and dependent aPL (anticardiolipin (aCL), antiphosphatidylserine, antiphosphatidylinositol, antiphosphatidic acid) were measured using a conventional enzyme linked immunosorbent assay (ELISA). aGPI was measured by an ELISA using a gamma irradiated plate coated with purified GPI. RESULTS--Twenty of 36 SLE patients were positive for at least one of the GPI-dependent aPL. Five of these 20 were also positive for aGPI. Another five of the 20 showed low GPI dependency aCL antibodies; however, three of these patients required GPI for binding to phosphatidylserine, phosphatidylinositol, or both. CONCLUSION--We confirmed the existence of aGPI in patients with true GPI dependent aPL. From these results, we recommend the use of a gamma irradiated plate with GPI as antigen for the detection of true GPI dependent aPL or aGPI.