Identification of surface antigens of endothelial cells.

A monolayer of a clone of endothelial cells derived from rat lung cells (RLE) was overlaid with 1 M urea to extract the surface proteins. Hydrolysis and SDS-gel electrophoresis of the urea extracted cell surface proteins (UCSP) yielded four peptides of 350,000, 84,000, 66,000 and 18,500 molecular weight. Of these only the 66,000 and 18,500 molecular weight peptides reacted with antibodies raised in rabbit against rat lung endothelial cells (RLE). The 18,500 mol. wt. antigenic peptide was a serum protein associated with the cell surface, whereas the 66,000 mol. wt. peptide was the surface antigen synthesized and released into the medium by the rat lung endothelial cells. On rocket immunoelectrophoresis, the 66,000 mol. wt. rat kidney fibroblast surface peptide produced only a single rocket whereas peptides of RLE produced two rockets, suggesting the presence of an additional antigenic peptide which could serve as a marker for endothelial cells.