IS CD4 SUFFICIENT FOR HIV ENTRY - CELL-SURFACE MOLECULES INVOLVED IN HIV-INFECTION

HIV-1, HIV-2 and SIV each bind to CD4 as the first step in virus entry . However, alternative receptors may also be used. HIV-1 binds to glyc olipids with terminal galactosylceramide residues on neural cells; ops onized virus binds to Fc receptors; HIV-2 can infect certain CD4-negat ive cells. Further receptors may also play a role in CD4-mediated infe ction, including cell adhesion molecules and possibly cell surface pro teinases. After binding to CD4, immunodeficiency viruses require secon dary molecules to effect fusion between the virus envelope and the cel l membrane; these accessory requirements differ between HIV-1, HIV-2 a nd SIV.