Human recombinant CD4 and CD4-derived synthetic peptides agglutinate immunoglobulin-coated latex particles. Evidence that residues 25-28 and 35-38 of human CD4 form two separate immunoglobulin binding sites.
It has been shown previously that amino acid residues 21-49 of the first extracellular domain of human CD4 form the core of an immunoglobulin (Ig) binding site. Synthetic peptides of human CD4 that encompass this region also bind Ig and, with higher affinity, antigen/antibody complexes. Synthetic peptides also enhance binding of both monomeric and aggregated Ig to monocytic U937 cells and Staphylococcus aureus Protein A. To better characterize the nature of the Ig binding site on CD4, we tested the ability of human recombinant CD4 (rCD4) to agglutinate polystyrene particles coated with Ig. Evidence is presented that soluble rCD4 and CD4 peptide p21-49 were capable of specific agglutination of polystyrene particles coated with polyclonal Ig of either human or sheep origin. Agglutination could be blocked by soluble human polyclonal IgG or F(ab')2 fragments. Both heparin and sulfated dextrans also inhibit agglutination, suggesting that charged residues on rCD4 played an important role in agglutination mediated by rCD4 or CD4 peptide. Similarly, aurintricarboxylic acid (ATA) also blocked agglutination of Ig-coated particles by rCD4. Agglutination mapping studies performed using truncated peptides revealed the existence of two discrete, closely related Ig binding sites (residues 25-28 and 35-38).
Lenert
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Research Center, Notre-Dame Hospital, University of Montréal, Québec, Canada.
Lenert
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Zanetti
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D000595:Amino Acid Sequence; D000818:Animals; D001312:Aurintricarboxylic Acid / Q000494:pharmacology; D001666:Binding Sites, Antibody / Q000235:genetics*; D015704:CD4 Antigens / Q000737:chemistry* / Q000235:genetics*; D003432:Cross-Linking Reagents; D016264:Dextran Sulfate / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007841:Latex Fixation Tests; D008863:Microspheres; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry / Q000235:genetics*; D011137:Polystyrenes / Q000737:chemistry; D011947:Receptors, Antigen, B-Cell / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry / Q000276:immunology; D012756:Sheep
D015704:CD4 Antigens; D003432:Cross-Linking Reagents; D010446:Peptide Fragments; D011137:Polystyrenes; D011947:Receptors, Antigen, B-Cell; D011994:Recombinant Proteins; D001312:Aurintricarboxylic Acid; D006493:Heparin; D016264:Dextran Sulfate