title: A CD4 domain important for HIV-mediated syncytium formation lies outside the virus binding site.
abstract: HIV infection of chimpanzees results in a chronic viremia unaccompanied by the ultimately fatal immunodeficiency that marks HIV infection in man. We show here that expression of HIV envelope proteins allows syncytium formation between cells expressing human but not chimpanzee or macaque CD4. We find that the CD4 sequences regulating cell fusion lie outside the recognized virus binding site; in the simplest exchange, chimpanzee CD4 bearing human residue 87 supports syncytium formation, while human CD4 bearing chimpanzee residue 87 does not. Neither the equilibrium nor the forward rate constants for HIV-CD4 association are affected by substitution at position 87. Infection of human cells expressing chimpanzee CD4 is insensitive to lysosomotropic agents, suggesting that viral penetration under these circumstances does not require endocytosis. The benign course of HIV infection in chimpanzees may reflect the failure of the host to support direct cell to cell transmission of the virus.
authors.affiliation: Department of Genetics, Harvard Medical School, Boston, Massachusetts.
authors.forename: D
authors.initials: D
authors.lastname: Camerini
authors.forename: B
authors.initials: B
authors.lastname: Seed
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015704:CD4 Antigens / Q000235:genetics* / Q000276:immunology; D002460:Cell Line; D005434:Flow Cytometry; D006678:HIV / Q000276:immunology*; D015699:HIV Envelope Protein gp120 / Q000276:immunology; D015658:HIV Infections / Q000276:immunology; D006367:HeLa Cells / Q000276:immunology; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000235:genetics; D007135:Immunoglobulin Variable Region / Q000235:genetics; D007145:Immunoglobulin kappa-Chains / Q000235:genetics; D008253:Macaca mulatta; D008969:Molecular Sequence Data; D002679:Pan troglodytes; D011485:Protein Binding; D011487:Protein Conformation; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D014162:Transfection
chemical_list: D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D007147:Immunoglobulin Light Chains; D007135:Immunoglobulin Variable Region; D007145:Immunoglobulin kappa-Chains