title: A human recombinant Fab identifies a human immunodeficiency virus type 1-induced conformational change in cell surface-expressed CD4.
abstract: To explore the role of the CD4 molecule in human immunodeficiency virus (HIV) infection following initial virus-CD4 binding, we have characterized CD4-specific antibodies raised by immunizing an HIV-1-infected human with human recombinant soluble CD4 (rsCD4). Fabs were selected from a human recombinant Fab library constructed from the bone marrow of this immunized individual. Here, we describe a human rsCD4-specific recombinant Fab clone selected by panning the library over complexes of human rsCD4 and recombinant HIV-1 envelope protein. While this Fab does not bind to CD4-positive T-cell lines or to human T lymphocytes, it recognizes cell surface-expressed CD4 following the incubation of these cells with a recombinant form of HIV-1 gp120 or with HIV-1 virions. The Fab is not HIV-1 envelope specific, since it does not bind to recombinant gp120 or to native cell surface-expressed HIV-1 envelope proteins. As confirmation of its CD4 specificity, we show that this Fab immunoprecipitates a 55-kDa protein, corresponding to the molecular mass of cellular CD4, from an H9 cell lysate. The specificity of this human Fab provides evidence for a virus-induced conformational change in cell surface-expressed on CD4. The characterization of this altered CD4 conformation and its effects on the host cell will be important in defining postbinding events in HIV infection.
authors.affiliation: Harvard Medical School, Beth Israel Hospital, Boston, Massachusetts 02215, USA.
authors.forename: R E
authors.initials: RE
authors.lastname: Bachelder
authors.forename: J
authors.initials: J
authors.lastname: Bilancieri
authors.forename: W
authors.initials: W
authors.lastname: Lin
authors.forename: N L
authors.initials: NL
authors.lastname: Letvin
mesh_terms: D000163:Acquired Immunodeficiency Syndrome / Q000276:immunology*; D000818:Animals; D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D001483:Base Sequence; D001853:Bone Marrow / Q000276:immunology / Q000473:pathology; D015704:CD4 Antigens / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D002460:Cell Line; D002522:Chlorocebus aethiops; D017931:DNA Primers; D005434:Flow Cytometry; D015699:HIV Envelope Protein gp120 / Q000378:metabolism*; D015497:HIV-1 / Q000502:physiology*; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000096:biosynthesis; D007145:Immunoglobulin kappa-Chains / Q000096:biosynthesis; D007146:Immunoglobulin lambda-Chains / Q000096:biosynthesis; D007668:Kidney; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D012333:RNA, Messenger / Q000096:biosynthesis; D011991:Receptors, Virus / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D015704:CD4 Antigens; D017931:DNA Primers; D015699:HIV Envelope Protein gp120; D007140:Immunoglobulin Fab Fragments; D007145:Immunoglobulin kappa-Chains; D007146:Immunoglobulin lambda-Chains; D012333:RNA, Messenger; D011991:Receptors, Virus; D011994:Recombinant Proteins