Autoantibody to gp50, a glycoprotein shared in common between fibroblasts and lymphocytes, in progressive systemic sclerosis.

Five out of 51 sera (10%) from patients with progressive systemic sclerosis reacted by immunoblotting with tissue concanavalin A binding glycoproteins of 50 kD and 45 kD Mr, whereas only one out of 133 control sera gave the same reaction (P less than 0.001). The antigens were localized to the microsomal fractions of tissues and were eluted from concanavalin A affinity columns by the competing sugar alpha-D-methymannoside but not by lactose, fucose or N-acetylglucosamine. Serum reactivity with these antigens was seen with a variety of human and porcine tissues and with human, porcine, bovine and canine spleens. Immunoblotting with cultured human fibroblasts and with human lymphocytes showed reactivity with the 50-kD component (gp50) only. No reactivity was seen with bovine or human endothelial cells or with HeLa, Hep-2 or mouse 3T3 cells. The gp50 antigen in human fibroblasts and lymphocytes and in human spleen had identical isoelectric points by two-dimensional immunoblotting, suggesting that they are the same molecule. These observations suggest that circulating autoantibodies to a 50-kD glycoprotein of fibroblasts and lymphocytes are present in some patients with progressive systemic sclerosis. The microsomal localization of the molecule suggests that it may have a role in the pathogenesis of progressive systemic sclerosis.