Characterization of the endothelial surface proteins recognized by anti-endothelial antibodies in primary and secondary autoimmune vasculitis.

The antigenic structures recognized by anti-endothelial cell antibodies (AECA) in sera from 10 Wegener's granulomatosis (WG) and 12 systemic lupus erythematosus (SLE) patients with signs of vasculitis were characterized by immunoprecipitation of selectively radiolabeled surface membrane proteins from human umbilical vein endothelial cells. Electrophoretic analysis of the immunoprecipitated proteins revealed reactivities against endothelial antigens ranging in size from 200 to 25 kDa. AECA antigens were not cell specific, since the same sera also reacted, at least in part, with radiolabeled human fibroblast surface proteins. The majority of WG patients displayed a constant precipitation pattern of five proteins (180, 155, 125, 68, and 25 kDa). On the contrary, AECA from SLE sera reacted with a more heterogeneous series of endothelial proteins. A group of four proteins, however, was also found in the majority of SLE sera: 200, 180, 155, and 25 kDa. In addition, some endothelial antigens were immunoprecipitated only by WG (125 kDa) or by SLE sera (200 kDa), suggesting a different endothelial reactivity in different vasculitic processes. The reaction did not involve intracellular proteins as demonstrated by the lack of reactivity of SLE sera negative for AECA but positive for anti-cytoplasmic or anti-nuclear antibodies. These data confirming that AECA recognize surface endothelial determinants further support a potential pathogenetic role for these antibodies in autoimmune vasculitis.