CD18 represents the common beta2 integrin subunit that associates non-covalently with the alpha beta chains of CD11a/LFA-1a, CD11b/Mac-1, and CD11c to form various integrin heterodimers. It is expressed strongly on lymphocytes and monocytes, and weakly on granulocytes, CD18 mediates a variety of heterotypic and homotypic intercellular adhesion reactions, and it regulates the ligand-binding activities of the various CD11/CD18 complexes. MAb C71/16 has not been reported to inhibit cell adhesion.1-4