title: Peptide binding affinity and pH variation establish functional thresholds for activation of HLA-DQ-restricted T cell recognition.
abstract: Peptides derived from the HSV-2 VP16 protein were utilized for studies of peptide binding to DQ0302 molecules and T cell activation at both neutral and acidic pH. The native peptide VP16 430-444 contains an Asp at position 442, binds to DQ0302 strongly, with a Kd value of 50nM at acidic pH and very weakly, with a Kd value of greater than 10 microM at neutral pH. A truncated version of 430-444, i.e., VP16 433-442, binds with an affinity 10-fold lower compared to 430-444 at acidic pH, and binding at neutral pH was barely detectable. The homologous peptide 430-444,442A has an Asp to Ala substitution at position 442 and binds to DQ0302 with a Kd similar to 433-442. The short truncated analog 433-442A binds very poorly at both acidic and neutral pH. Both the wild type 430-444 and 433-442 peptides stimulated a HSV-specific T cell clone after a brief incubation with antigen presenting cells (APC) expressing DQ0302 at acidic pH. Much higher concentrations of wild type peptides were needed to activate T cells at neutral pH. In contrast, APC pulsed with Ala-substituted peptides 430-444,442A or 433-442A at neutral pH failed to stimulate the T cell clone, while APC pulsed at acidic pH and subsequently washed led to successful T cell activation. The Ala-substituted peptide was recognized by the T cell clone at neutral pH only when it was present in the APC culture throughout the stimulation process. While the MHC-peptide complexes formed with the native peptide are stable, complexes formed with the Ala-substituted peptide had a functional t1/2 of less than 4 hr at neutral pH.
authors.affiliation: Virginia Mason Research Center and the Department of Immunology, University of Washington School of Medicine, Seattle 98101, USA.
authors.forename: W W
authors.initials: WW
authors.lastname: Kwok
authors.forename: H
authors.initials: H
authors.lastname: Reijonen
authors.forename: B A
authors.initials: BA
authors.lastname: Falk
authors.forename: D M
authors.initials: DM
authors.lastname: Koelle
authors.forename: G T
authors.initials: GT
authors.lastname: Nepom
mesh_terms: D000595:Amino Acid Sequence; D000938:Antigen-Presenting Cells / Q000276:immunology; D002461:Cell Line, Transformed; D002478:Cells, Cultured; D006683:HLA-DQ Antigens / Q000276:immunology*; D017405:Herpes Simplex Virus Protein Vmw65 / Q000276:immunology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008213:Lymphocyte Activation / Q000276:immunology; D008969:Molecular Sequence Data; D010455:Peptides / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D006683:HLA-DQ Antigens; C051569:HLA-DQ3 antigen; D017405:Herpes Simplex Virus Protein Vmw65; D010455:Peptides