title: Major histocompatibility complex class II molecules function as a template for the processing of a partially processed insulin peptide into a T-cell epitope.
abstract: Our understanding of how an autoantigen is processed and presented during the development of a major histocompatibility complex (MHC) class II-dependent and T-cell-mediated autoimmune disease, such as IDDM, is incompletely understood. We have used insulin as a model autoantigen in IDDM to address the question of whether MHC class II molecules play a role in the generation and/or preservation of an autoantigen peptide that stimulates T-cell activation. Analyses of the requirement of I-Ad class II molecules in the processing of the partially processed porcine insulin peptide A1-A14/B1-B16 demonstrate that the binding of this peptide to I-Ad is essential for it to be further processed and tailored into a T-cell epitope. Based on our observations, we propose a two-step model for insulin processing in which insulin is first processed by an enzyme(s) into an intermediate peptide that binds to class II and then class II functions as a template to guide the processing of this partially processed peptide by cathepsin D into a T-cell epitope. Our data further underscore the important realization that MHC class II-directed processing of an autoantigen (e.g., insulin) may regulate 1) the relative immunodominance of T-cell determinants in an autoantigen, 2) the self-reactivity to cryptic T-cell epitopes in autoantigens, and 3) the susceptibility to autoimmune disease.
authors.affiliation: The John P. Robarts Research Institute, Department of Microbiology and Immunology, University of Western Ontario, London, Canada.
authors.forename: Y
authors.initials: Y
authors.lastname: Lang
authors.forename: F
authors.initials: F
authors.lastname: Forquet
authors.forename: E
authors.initials: E
authors.lastname: Speck
authors.forename: J
authors.initials: J
authors.lastname: Blum
authors.forename: T L
authors.initials: TL
authors.lastname: Delovitch
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D001324:Autoantigens / Q000276:immunology*; D002402:Cathepsin D / Q000378:metabolism; D003922:Diabetes Mellitus, Type 1 / Q000276:immunology*; D010450:Endopeptidases / Q000378:metabolism; D000939:Epitopes / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000276:immunology*; D007328:Insulin / Q000276:immunology*; D051379:Mice; D011480:Protease Inhibitors / Q000494:pharmacology; D013601:T-Lymphocytes / Q000276:immunology*; D013698:Templates, Genetic
chemical_list: D001324:Autoantigens; D000939:Epitopes; D000949:Histocompatibility Antigens Class II; D007328:Insulin; D011480:Protease Inhibitors; D010450:Endopeptidases; D002402:Cathepsin D