title: Processing of exogenous antigens for presentation by class I MHC molecules involves post-Golgi peptide exchange influenced by peptide-MHC complex stability and acidic pH.
abstract: Vacuolar alternate class I MHC (MHC-I) Ag processing allows presentation of exogenous Ag by MHC-I molecules with binding of antigenic peptides to post-Golgi MHC-I molecules. We investigated the role of previously bound peptides and their dissociation in generating peptide-receptive MHC-I molecules. TAP1-knockout macrophages were incubated overnight with an initial exogenous peptide, producing a large cohort of peptide-K(b) complexes that could influence subsequent peptide dissociation/exchange. Initial incubation with FAPGNYPAL, KVVRFDKL, or RGYVYQGL enhanced rather than reduced subsequent binding and presentation of a readout peptide (SIINFEKL or FAPGNYPAL) to T cells. Thus, K(b) molecules may be stabilized by an initial (stabilizing) peptide, enhancing their ability to bind readout peptide and implicating peptide dissociation/exchange. In contrast, incubation with SIINFEKL as stabilizing peptide reduced presentation of readout peptide. SIINFEKL-K(b) complexes were more stable than other peptide-K(b) complexes, which may limit their contribution to peptide exchange. Stabilizing peptides (FAPGNYPAL, KVVRFDKL, or RGYVYQGL) enhanced alternate MHC-I processing of HB101.Crl-OVA (Escherichia coli expressing an OVA fusion protein), indicating that alternate MHC-I Ag processing involves peptide dissociation/exchange. Stabilizing peptide enhanced processing of HB101.Crl-OVA more than presentation of exogenous OVA peptide (SIINFEKL), suggesting that peptide dissociation/exchange may be enhanced in the acidic phagosomal processing environment. Furthermore, exposure of cells to acidic pH increased subsequent binding and presentation of readout peptide. Thus, peptide dissociation/exchange contributes to alternate MHC-I Ag processing and may be influenced by both stability of peptide-MHC-I complexes and pH.
authors.affiliation: Department of Pathology, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Chefalo
authors.forename: C V
authors.initials: CV
authors.lastname: Harding
mesh_terms: D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D002461:Cell Line, Transformed; D004527:Egg Proteins / Q000096:biosynthesis / Q000276:immunology; D005434:Flow Cytometry; D006056:Golgi Apparatus / Q000276:immunology / Q000378:metabolism*; D006183:H-2 Antigens / Q000096:biosynthesis / Q000378:metabolism*; D006825:Hybridomas; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010047:Ovalbumin / Q000096:biosynthesis / Q000276:immunology; D010446:Peptide Fragments / Q000096:biosynthesis / Q000276:immunology* / Q000378:metabolism*; D011485:Protein Binding / Q000276:immunology; D011499:Protein Processing, Post-Translational / Q000276:immunology*; D021381:Protein Transport / Q000276:immunology; D012995:Solubility; D014407:Tumor Cells, Cultured
chemical_list: D004527:Egg Proteins; D006183:H-2 Antigens; C032876:H-2Kb protein, mouse; C110366:OVA-8; D010446:Peptide Fragments; D010047:Ovalbumin