title: Peptide-receptive class I major histocompatibility complex molecules on TAP-deficient and wild-type cells and their roles in the processing of exogenous antigens.
abstract: These studies addressed the nature and origin of peptide-receptive class I major histocompatibility complex (MHC-I) molecules used to present exogenous antigens. Peptide-receptive Kb molecules in transporter for antigen presentation (TAP)1-/- and TAP1+/+ macrophages were quantitated by exposing cells to exogenous ovalbumin (OVA)(257-264) peptide and then measuring OVA(257-264):Kb complexes with a T hybridoma assay or flow cytometry (using a complex-specific antibody). Relative to TAP1+/+ cells, TAP1-/- cells had decreased levels of pre-existing cell-surface peptide-receptive MHC-I molecules at 37 degrees. With continued exposure of viable cells to peptide, however, TAP1-/- and TAP1+/+ cells formed similar levels of OVA(257-264):Kb complexes, suggesting that nascent labile MHC-I molecules were captured and stabilized by exogenous peptide. Brefeldin A inhibited generation of OVA(257-264):Kb complexes on TAP1-/- (but not TAP1+/+) cells at 37 degrees, confirming the importance of a flux of unstable nascent MHC-I molecules in TAP1-/- cells at 37 degrees. In contrast, at 26 degrees both TAP1-/- and TAP1+/+ cells expressed brefeldin A-resistant, peptide-receptive MHC-I molecules at similar levels. Alternate MHC-I processing of exogenous particulate antigen correlated with ability to present exogenous peptide. Thus, processing was brefeldin A-sensitive with TAP1-/- macrophages at 37 degrees, but brefeldin A-resistant with TAP1+/+ cells at 37 degrees, as well as with TAP1+/+ or TAP1-/- cells at 26 degrees. We conclude that alternate MHC-I antigen processing normally utilizes pre-existing MHC-I molecules, but TAP1-/- cells at 37 degrees mainly use nascent MHC-I molecules, because of a lack of pre-existing, stable, peptide-receptive MHC-I molecules. The results support a vacuolar processing mechanism with binding of peptides to MHC-I molecules in post-Golgi compartments or on the cell surface.
authors.affiliation: Institute of Pathology, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: R
authors.initials: R
authors.lastname: Song
authors.forename: A
authors.initials: A
authors.lastname: Porgador
authors.forename: C V
authors.initials: CV
authors.lastname: Harding
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000276:immunology*; D000818:Animals; D017951:Antigen Presentation / Q000187:drug effects / Q000276:immunology*; D020126:Brefeldin A / Q000494:pharmacology; D018929:Cell Culture Techniques; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D017737:Macrophages, Peritoneal / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010047:Ovalbumin / Q000276:immunology; D010446:Peptide Fragments / Q000276:immunology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D013696:Temperature
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D015395:Histocompatibility Antigens Class I; D010446:Peptide Fragments; D011500:Protein Synthesis Inhibitors; C073119:TAP1 protein, human; C486171:Tap1 protein, mouse; D020126:Brefeldin A; D010047:Ovalbumin