Aims/hypothesis: Our aim was to define the molecular specificity of glutamic acid decarboxylase-specific T-cells isolated from a patient (patient 40) with recent onset Type I (insulin-depent) diabetes mellitus.
Methods: The peptide epitope was defined using synthetic peptides to identify the minimal sequence required for T-cell activation and to determine the amino acids that contribute either to MHC binding or T-cell receptor signaling. The MHC class II-restricted peptide presentation was determined using a panel of allogeneic antigen-presenting cells and murine fibroblast-cell lines transfected to express individual human class II alleles and by blocking studies with monoclonal antibodies. The T-cell receptor was also molecularly characterized.
Results: Despite that patient 40 carries high-risk alleles of the DRB1 and DQB1 loci, his T-cells recognize a glutamic acid decarboxylase-derived peptide in association with class II, DR53, molecules. Although anchor residues for DR53 molecules have not yet been determined, it was possible to model epitope binding based on sequence comparisons with other class II molecules associated with susceptibility or protection for Type I diabetes.
Conclusion/interpretation: The complete molecular specification of the MHC-peptide ligand and the T-cell receptor complex of glutamic acid decarboxylase-specific T-cells will enable analysis of strategies designed to alter T-cell function. For example, the role of altered peptide ligands or T-cell receptor-specific peptides can be studied using a model whose components reflect the natural affinities of MHC-peptide and T-cell receptor-ligand interactions selected in response to this important autoantigen.