virus type 1 co-receptor on lymphoid and monocytoid cells o

The CD4 molecule serves as the principal cell surface receptor common to both the human and simian immunodeficiency viruses (HIV-1, HIV-2 and SIV). Since binding to CD4 is not sufficient o permit virus entry, HIV 'co-receptors ' have been implicated in mediating the fusion of viral and cellular membranes necessary for completing the entry process. In order to identify candidate co-receptor molecules, a panel of monoclonal antibodies (MAbs) directed against ad-hesion molecules was tested for the ability of the MAbs to inhibit HIV-l-induced cell fusion (syncytium forma-tion) and HIV-1 entry. Certain antibodies directed against CD18, CDl lb and CDl lc inhibited HIV-1-induced syncytium formation but not entry, in agreement with previous reports. Interestingly, certain antibodies to ICAM-3 (intercellular adhesion molecule 3) (CD50) significantly inhibited HIV-l-specific entry but not syncytium formation using human SupT1 cells. Only one antibody directed against ICAM-3 significantly inhibited HIV-l-induced syncytium formation, entry and infec-tivity. Our results suggest that certain epitopes of ICAM-3 may be involved in mediating HIV-l-specific entry into lymphoid and monocytoid cells