title: Peptide-dependent expression of HLA-B7 on antigen processing-deficient T2 cells.
abstract: Class I MHC Ag presentation and cell surface expression largely depend on peptide transport into the ER/cis-Golgi by TAP, the transporter associated with Ag processing. Despite this dependency, class I MHC molecules are expressed at low levels on the surface of TAP-deficient T2 cells. We studied the peptide dependency of HLA-B7 expression in transfected T2 cells. HLA-B7 expression was affected by mutations at 19 out of 23 peptide-binding groove residues, but not by nine mutations outside of the peptide-binding groove. T2 cell surface HLA-A2, -B7, and -B51 had similar stabilities, and approximately half of these class I molecules had a long t1/2 consistent with tight peptide binding. Using metabolically labeled T2 cells, HLA-A2-bound peptide eluted as five prominent peaks, but HLA-B7-bound peptide was not detected. In contrast, HLA-B7-eluted peptides were detected spectrophotometrically. These data suggest that HLA-A2 and HLA-B7 molecules utilize distinct TAP-independent peptide supply mechanisms to different degrees. Equivalent amounts of HLA-B7 from TAP- and TAP+ cells yielded similar amounts of peptide, which had the characteristic HLA-B7 peptide-binding motif. The dependency of HLA-B7 cell surface expression on peptide-binding groove residues, the stability of cell surface class I molecules, and the ability to detect HLA-B7-bound peptide indicate that the low level expression on T2 cells is largely peptide dependent. TAP-independent peptide Ag presentation may allow immune recognition of intracellular pathogens that interfere with TAP-dependent peptide transport.
authors.affiliation: Department of Pathology, University of Iowa College of Medicine, Iowa City 52242,USA.
authors.forename: K D
authors.initials: KD
authors.lastname: Smith
authors.forename: C T
authors.initials: CT
authors.lastname: Lutz
mesh_terms: D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000276:immunology; D017951:Antigen Presentation / Q000235:genetics*; D000938:Antigen-Presenting Cells / Q000276:immunology* / Q000378:metabolism*; D002460:Cell Line; D015789:HLA-A2 Antigen / Q000378:metabolism; D015793:HLA-B7 Antigen / Q000235:genetics / Q000378:metabolism*; D015395:Histocompatibility Antigens Class I / Q000145:classification; D006801:Humans; D009154:Mutation / Q000276:immunology; D011485:Protein Binding / Q000276:immunology
chemical_list: D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D015789:HLA-A2 Antigen; D015793:HLA-B7 Antigen; D015395:Histocompatibility Antigens Class I; C071692:TAP2 protein, human