title: HLA-B7 beta-pleated sheet-derived synthetic peptides are immunodominant T-cell epitopes regulating alloresponses.
abstract: Chronic rejection of transplanted allografts is the major cause of graft loss after clinical solid organ transplantation. Recent data link the indirect presentation of allopeptides to chronic graft loss; thus, identification of immunodominant epitopes on major histocompatibility complex (MHC) antigens could significantly contribute to establishing novel ways for monitoring and managing chronic rejection. Here, we show that synthetic allo-MHC-derived peptides covering the polymorphic region 56 to 120 of HLA-B7 modulate alloresponses. In particular, the 2 beta-pleated sheet-derived peptides covering residues 91 to 105 and 96 to 120, respectively, but not sequences from the alpha1 helix, were presented by autologous peripheral blood lymphocytes to induce T-cell proliferation. In addition, the 2 beta-pleated sheet-derived peptides and the alpha1-derived peptide residues 60 to 75 abrogated lysis of HLA-B7 target cells by anti-HLA-B7 cytotoxic T lymphocytes (CTLs). Although most residues between 91 and 120 are normally not directly accessible to T cells, our results indicate that peptides derived from the lower surface of the peptide-binding groove of HLA-B7 are immunodominant in HLA-B7 alloresponses. To characterize the binding and stability of allopeptides to T cells, the 62-70 peptide-derived from the 60-75 allopeptide that blocked cytotoxicity of anti-HLA-B7 CTL-was synthesized and coupled with fluorescein isothiocyanate. The peptide specifically labeled anti-B7 CTL, but not anti-HLA-A2 CTL as measured by flow cytometry. Peptide binding to CTL was specific at 4 degrees C and remained stable for 12 hours, whereas it remained stable for less than 2 hours at 37 degrees C. These studies allow the identification of HLA-B7 T-cell epitopes and reveal for the first time a novel, previously unrecognized application of synthetic HLA-derived allopeptides to visualize alloreactive T cells.
authors.affiliation: Department of Internal Medicine, University of Iowa Hospitals and Clinics and VA Medical Center, Iowa City 52242, USA.
authors.forename: Anja
authors.initials: A
authors.lastname: Freese
authors.forename: Nicholas
authors.initials: N
authors.lastname: Zavazava
mesh_terms: D000595:Amino Acid Sequence; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D005434:Flow Cytometry; D016650:Fluorescein-5-isothiocyanate; D015793:HLA-B7 Antigen / Q000737:chemistry / Q000276:immunology*; D006801:Humans; D016056:Immunodominant Epitopes; D008285:Major Histocompatibility Complex / Q000276:immunology; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000276:immunology* / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D013696:Temperature
chemical_list: D018984:Epitopes, T-Lymphocyte; D015793:HLA-B7 Antigen; D016056:Immunodominant Epitopes; D010446:Peptide Fragments; D016650:Fluorescein-5-isothiocyanate