T cell epitopes of insulin defined in HLA-DR4 transgenic mice are derived from preproinsulin and proinsulin.
Approximately one-half of Caucasians with newly diagnosed insulin-dependent diabetes mellitus (IDDM) have autoantibodies to insulin, and the majority of those express the HLA-DR4 genotype [Ziegler, R., Alper, C. A., Awdeh, Z. L., Castano, L., Brink, S. J., Soeldner, J. S., Jackson, R. A. & Eisenbarth, G. S. (1991) Diabetes 40, 709-714]. However, it has been difficult to demonstrate T cell proliferative responses to human insulin in IDDM patients [Durinovic-Bello, I., Hummel, M. & Ziegler, A. G. (1996) Diabetes 45, 795-800]. We have immunized transgenic mice expressing the susceptible HLA-DR (alpha1*0101,beta1*0401) (hereafter called DRB1*0401) and human CD4 molecules on a murine major histocompatibility complex class II null background, with human preproinsulin (PPI), proinsulin (PI), and insulin and derived large panels of T cell hybridomas to determine the immunogenic epitopes of these proteins. These results show that the prohormones PI or PPI carry the major immunogenic T cell epitope in the DRB1*0401 transgenic mice. The PPI/PI immunodominant epitope LALEGSLQK was localized at the C-peptide/A-chain junction. This T cell epitope PPI/PI LALEGSLQK is unusual because, normally, it is proteolytically destroyed during the maturation of the insulin molecule. Additionally, this T cell epitope is both processed and presented by human DRB1*0401-positive Epstein-Barr virus transformed B cells, and it can also stimulate T cells from the peripheral blood of HLA-DR4-positive patients with type 1 diabetes. These findings may partly explain why susceptibility to type 1 diabetes is associated with HLA-DR4-positive individuals and why T cell responses to the mature insulin protein are rarely detected in IDDM patients.
Congia
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Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Patel
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Cope
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AP
De Virgiliis
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Sønderstrup
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D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation; D001323:Autoantibodies / Q000276:immunology*; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics / Q000276:immunology*; D000939:Epitopes / Q000235:genetics / Q000276:immunology; D015804:HLA-DR4 Antigen / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007328:Insulin / Q000276:immunology*; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000276:immunology; D011384:Proinsulin / Q000235:genetics / Q000276:immunology*; D011498:Protein Precursors / Q000235:genetics / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*
D001323:Autoantibodies; D000939:Epitopes; D015804:HLA-DR4 Antigen; D007328:Insulin; D010455:Peptides; D011498:Protein Precursors; C013737:preproinsulin; D011384:Proinsulin