A monoclonal antibody that induces T cell aggregation reacts with vascular endothelial cells and placental trophoblasts

We have found that a mouse monoclonal antibody (αLeu-13) to a 16 kilodalton human lymphocyte surface antigen reacts with vascular endothelial cells as determined by immunoperoxidase staining of frozen tissue sections. In earlier studies, αLeu-13 was found to induce purified T cells to aggregate when added to cultures in nanogram concentrations. In the studies reported here, αLeu-13 stained vascular endothelial cells of arteries, capilaries, and veins in all organs examined from adults. It also reacted weakly with epithelial cells of proximal tubules of the kidney and with nonkeratinized basal epithelial cells of the cervix and esophagus. When a panel of tissues from a 14-wk-old fetus was examined, αLeu-13 was not found to react with endothelial cells of any specimen. However, it did stain medullary thymocytes and placental trophoblasts of this fetus. The implications of these findings to the possible function of the Leu-13 antigen in immune ontogeny are discussed.