MONOCLONAL-ANTIBODIES SPECIFIC FOR ENDOTHELIAL-CELLS OF MOUSE-BLOOD VESSELS - THEIR APPLICATION IN THE IDENTIFICATION OF ADULT AND EMBRYONIC ENDOTHELIUM

Two monoclonal antibodies (mAb), MEC 7.46 (IgG1) and MEC 13.3 (IgG2a) that specifically recognize mouse endothelial cells (EC) of blood vess els, were produced immunizing a Lewis rat with a polyoma middle T tran sformed EC line. Antibodies were screened by enzyme-linked immunosorbe nt assay (ELISA) and by immunofluorescence on different cultured cell lines and by immunoperoxidase staining on frozen sections of various m ouse normal and inflammatory tissues. Both mAbs reacted with eight tra nsformed endothelial lines tested in vitro, but were consistently nega tive on various cell lines of different histological origin. Reactivit y was not altered by preexposure of the cell lines to IL-1. Microscopi c immunofluorescence analysis showed that the MEC mAbs localized at th e cell-cell contacts in EC. Immunohistochemical staining of various mo use tissue was always restricted to the EC of all blood vessels of the organ considered. Staining of the endothelial lining of blood vessels was greater at cell-to-cell contacts. Weak reactivity was detected in bone marrow and spleen megakaryocytes. This picture was not altered i n inflamed and tumor tissues. In the developing mouse embryo, MEC 13.3 specifically stained proliferating and sprouting endothelium in all o rgans and tissues examined. Both MEC 7.46 and MEC 13.3 mAbs were able to precipiate a molecule with an apparent molecular mass of 130 kDa fr om endothelioma lysates. The protein was synthesized by the cells and exposed on the cell surface. Immunodepletion analysis indicated that M EC 13.3 recognized a molecule related to the murine from of PECAM or C D31. We believe that these mAbs are promising tools for the identifica tion of murine EC and for studying their ontogenesis and functions.