CD4 and HIV-1 infection: Among drugs that interfere with the first steps of HIV-1 infection, we may identify i) CCR5 antagonists that imped the interaction between co-receptor and gp120, ii) gp120 antagonists that bind to the virus, preventing the association with the host CD4 receptor, iii) gp41 antagonists that inhibit the fusion with the host cell membrane, and iv) CD4 antagonists, monoclonal antibodies that block HIV-1 entry into target cells (6).