LIGAND FOR HUMAN CD48 ON EPITHELIAL-CELLS

CD48 is a member of the Ig superfamily with a high degree of sequence homology to CD58 (LFA-3), in rodents, CD48 is the ligand for CD2 where as in humans, CD58 if the ligand for CD2. Despite intensive efforts, n o ligand for human CD48 has been convincingly demonstrated. We now sho w that a ligand for human CD48 is present on epithelial cells, The lig and was detected based on the ability of epithelial cells to bind both a decameric, soluble CD48 IgM fusion protein and monomeric CD48 immob ilized on plastic dishes, mAbs raised to the ligand completely block b inding of CD48 to all epithelial cells tested, We further show that th e cell surface proteoglycan CD44 plays an auxiliary role in the bindin g of epithelial cells to CD48 and that this interaction involves the g lycosaminoglycan binding site of CD44. No interaction of human CD48 wi th CD2 was detected, This is the first clear demonstration that human CD48 can function as an adhesion molecule and suggests a role for CD48 in lymphocyte epithelial cell interactions.