2 POPULATIONS OF ENDOTHELIAL-CELL ANTIBODIES CROSS-REACT WITH HEPARIN

As endothelial cells (EC) express heparin-like glycosaminoglycans, suc h as heparan sulfate, it was essential to investigate the relation of anti-EC antibody (AECA) to heparin reactivity. AECA were detected in 4 3 of 131 autoimmune sera and anti-heparin antibodies (AHA) in 25. Thes e autoimmune reactivities were significantly associated (P corrected < 0.0005). Seven AECA-positive/AHA-positive and three AECA-negative/AHA- positive sera were affinity-purified using protein G column followed b y a heparin-Sepharose column. Two populations of AECA were recovered f rom the second column. One was eluted with 0.4 M NaCl which bound to E C and to solid-phase heparin with low affinity, but not to soluble hep arin. The second population of AECA, which was eluted with 4 M guanidi ne HCl/2 M NaCl, recognized EC and solid-phase heparin with high affin ity, but also soluble heparin. The latter population of AECA might thu s be an important cause of autoimmune vascular thrombosis in systemic diseases.