Scl-95/100: doublet of endothelial marker autoantigens in progressive systemic sclerosis

Thirteen out of 60 sera (22%) from patients with progressive systemic sclerosis reacted by immunoblotting with a doublet of 95 kD and 100 kD proteins in endothelial cells of human and bovine origin. Reactivity with the doublet was not seen in any of 125 control sera. The endothelial doublet was localized to the nucleus by immunoblot reactivity with nuclear subcellular fractions but not with mitochondrial, microsomal or soluble subcellular fractions. In HEp-2 cells and in HeLa cells, positive sera reacted with the 100 kD antigen, but not with the 95 kD antigen. Identical immunoblot reactivity was obtained with a standard reference serum containing anti-scl-70 activity by immunodiffusion. All positive sera also reacted with cell nuclei by indirect immunofluorescence and 10 gave anti-scl-70 reactivity by immunodiffusion. These observations suggest that the 95 kD/100 kD doublet may be a larger form of the Scl-70 autoantigen.