To investigate whether beta 2-glycoprotein I antibody (aGPI) exists in sera that are positive for antiphospholipid antibodies (aPL).
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.
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.
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.