British Journal of Rheumatology 1996;35:523-528 ANTIBODIES TO ENDOTHELIAL CELLS AND TO /J2-GLYCOPROTEIN I IN THE ANTIPHOSPHOLIPID SYNDROME: PREVALENCE AND ISOTYPE DISTRIBUTION

The aim of this study was to analyse the prevalence and isotype distribution of antibodies to endothelial cells (aEQ and to /?2-glycoprotein I (a/?2GPI) in the antiphospholipid syndrome (APS). Fifteen patients with an APS [nine associated with systemic lupus erythematosus (SLE) and six 'primary'] and 15 with SLE without an APS were prospectiyely studied. The aEC were determined by an enzyme-linked immunosorbent assay (ELISA) using endothelial cells derived from human umbih'cal vein and the a/J2GPI by ELISA using highly purified 02GPI. A positive titre of aEC was detected in 20 out of 30 patients (67%), but in none of the control group. Ten patients had both IgG and IgM isotypes, five had IgG only and five had only IgM. Thirteen patients with the APS (87%) were found to have a positive titre of aEC, while only seven with SLE but without a history of APS (47%) had aEC {P < 0.05). Nine patients with the APS (60%) had a positive titre of a/?2GPI (four had both IgG and IgM isotypes, one had IgG only and four had only IgM), while none of the patients without an APS (0%) had these antibodies (P < 0.001). A significant association was also found between the presence of aPL and aEC (P < 0.05), as well as between aPL and a/?2GPI (P < 0.001). Both aEC and a/?2GPI can be found in the APS. This reinforces the theory that APS represents a complex autoimmune disorder in which several autoantibodies co-exist with aPL