title: Effects of pH and polysaccharides on peptide binding to class II major histocompatibility complex molecules.
abstract: The binding of immunogenic peptides to class II major histocompatibility molecules was examined at various pH values. We studied binding of peptides containing residues 52-61 from hen egg lysozyme (HEL) to I-Ak on fixed peritoneal macrophages or to solubilized affinity-purified I-Ak. Optimum binding occurred at pH 5.5-6.0 with accelerated kinetics relative to pH 7.4; equilibrium binding was also higher at pH 5.5-6.0 than at 7.4. Similar enhancement at pH 5-6 was observed for the binding of hemoglobin-(64-76) to I-Ek and of ribonuclease-(41-61) to I-Ak. In contrast, the binding of HEL-(34-45) to I-Ak was minimally enhanced at acid pH. Dissociation of cell-associated or purified peptide-I-Ak complexes was minimal between pH 5.5 and 7.4, with increased dissociation only at or below pH 4.0 [HEL-(46-61)] or pH 5.0 [HEL-(34-45)]. Thus, optimum peptide binding occurs at pH values similar to the endosomal environment, where the complexes appear to be formed during antigen processing. In addition, we examined the effect of a number of polysaccharides on the binding of peptide to I-Ak. None of these competed with the HEL peptide 125I-labeled YE52-61 for binding to I-Ak. [3H]Dextran also failed to bind purified I-Ak. Polysaccharides do not appear to bind to class II major histocompatibility complex molecules, which explains the T-cell independence of polysaccharide antigens.
authors.affiliation: Washington University School of Medicine, Department of Pathology, St. Louis, MO 63110.
authors.forename: C V
authors.initials: CV
authors.lastname: Harding
authors.forename: R W
authors.initials: RW
authors.lastname: Roof
authors.forename: P M
authors.initials: PM
authors.lastname: Allen
authors.forename: E R
authors.initials: ER
authors.lastname: Unanue
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology*; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008264:Macrophages / Q000276:immunology*; D051379:Mice; D008808:Mice, Inbred CBA; D009113:Muramidase / Q000276:immunology* / Q000378:metabolism; D011134:Polysaccharides / Q000494:pharmacology*; D011485:Protein Binding
chemical_list: D000949:Histocompatibility Antigens Class II; D011134:Polysaccharides; D009113:Muramidase