A novel, 85 kDa endothelial antigen differentiates plasma membrane macrodomains in lung alveolar capillaries

A monoclonal antibody raised against purified rat lung endothelial plasma membranes was found to recognize an apparently novel, 85 kD, integral endothelial plasma membrane glycoprotein. By immunofluorescence and electron microscope immunocytochemistry, this endothelial antigen was detected at the luminal and tissue fronts of all rat endothelia, except those of discontinuous type (liver and spleen sinusoids). In lung alveolar capillaries the antigen appeared to be uniquely associated with the very attenuated endothelial processes forming the blood-air barrier, and virtually absent on the surface of the rest of the cell, where the nucleus and the organelles are located. No other cells, except fibroblasts, appeared to be labeled by this monoclonal antibody.