Abstract
Radiolabeled amino acids were incorporated into nondialyzable protein by cultures of endothelial cells derived from calf aorta. Antibody prepared against purified bovine plasma cold-insoluble globulin (CIG) formed a strong precipitin line upon immunodiffusion against 3H-labeled proteins from endothelial cell culture media. This precipitin line formed a line of identity with the precipitin line formed by anti-CIG and purified CIG. Double-antibody immunoprecipitation of 3H-labeled protein showed that 36.3% of the radioactivity was specifically precipitated by the anti-CIG antibody. Gel filtration and polyacrylamide gel electrophoresis of the immunoprecipitate indicated that it contained a single protein species whose molecular weight was consistent with that of CIG isolated from plasma. When cultured cells were examined by indirect immunofluorescence microscopy, the endothelial cells stained specifically with anti-CIG antibody. These data indicate that cultured endothelial cells derived from calf aorta synthesize and secrete a protein antigenically similar to CIG.