Department of Surgery, University of Hong Kong, Pokfulam, Hong Kong

The organization of mammalian cells in differentiated organs and tissues depends on cell-cell and cell-extracellular matrix interactions, which are mediated by specialized cell adhesion molecules (CAMs). Four CAMs families have been identified: integrin, immunogloblin superfamily CAM, selectin, and cadherin. Integrins are heterodimeric surface glycoproteins, which play pivotal roles in cell traffic and inter-cellular communication in the immune system. Mac-1 (CD11b/CD18) is a major integrin receptor expressed essentially on phagocytic cells, and its adhesive activity is highly regulated. In this study, monoclonal antibodies against the ligand recognition sites of Mac-1 were characterized using CD11b x CD11c chimeric transfectants. Based on the epitope mapping and functional inhibition data, the "I" domain of Mac-1 integrin chain was found to be the binding sites for ICAM-1, complement iC3b, and extracellular matrix fibrinogen. Studies from this laboratory and others have indicated that Mac-1 may serve as receptor for foreign molecules (say, bacterial toxins) as well. A better understanding on how the Mac-1 integrin is involved in cell function can facilitate development of strategic therapies to ameliorate certain inflammatory and immunologic diseases.