ITIH4 and AIDS: The authors are indebted to those providing monoclonal antibodies to NIH AIDS Research and Reference Reagent Program, Division of AIDS, NIAID, NIH: HIV-1 gp120 MAb IgG1b12 from Dr. Dennis Burton and Carlos Barbas; HIV-1 gp41 MAb 2F5 and gp120 MAb 2G12 from Dr. Hermann Katinger.