CD73 IS INVOLVED IN LYMPHOCYTE BINDING TO THE ENDOTHELIUM - CHARACTERIZATION OF LYMPHOCYTE VASCULAR ADHESION PROTEIN-2 IDENTIFIES IT AS CD73

We have recently described a monoclonal antibody (mAb) 4G4 recognizing a 70-kD molecule constitutively expressed on human endothelial cells and on subpopulations of lymphocytes. We showed that this molecule, wh ich we named lymphocyte-vascular adhesion protein 2 (L-VAP-2), mediate s lymphocyte adhesion to cultured endothelial cells. Protein sequencin g of tryptic peptides from immunoaffinity-purified L-VAP-2 revealed se quence identity between L-VAP-2 and CD73 (ecto-5'-nucleotidase, E.C.3. 1.3.5), and COS cells transfected with a CD73 cDNA were positively sta ined with the mAb 4G4, which recognizes L-VAP-2. mAb 4G4 was also able to partially inhibit the ecto-5'-nucleotidase activity of peripheral blood lymphocytes. Moreover, cross-precipitation studies performed wit h mAb 4G4 and a CD73 workshop mAb 1E9 showed that these two antibodies recognize the same molecule. Since the tissue distribution and bioche mical characteristics of the two molecules are also similar, we conclu de that L-VAP-2 and CD73 are the same glycoprotein. Adhesion experimen ts showed significantly increased binding of freshly isolated lymphocy tes to COS cells transfected with a CD73 cDNA, as compared to mock-tra nsfected COS cells, and binding of lymphocytes to CD73-expressing COS cells was inhibited by the presence of mAb 4G4 in the adhesion assay. CD73 is a glycosyl phosphatidylinositol-linked molecule previously sho wn to have a cosignalling role in T lymphocyte proliferation. Our data suggest that it also has a function in mediating lymphocyte adhesion to the endothelium.