Ex Vivo Analysis of Thymic CD4 T Cells in Nonobese Diabetic Mice with Tetramers Generated from I-Ag7/Class II-Associated Invariant Chain Peptide Precursors

Abstract

The MHC determines susceptibility and resistance to type 1 diabetes in humans and nonobese diabetic (NOD) mice. To investigate how a disease-associated MHC molecule shapes the T cell repertoire in NOD mice, we generated a series of tetramers from I-Ag7/class II-associated invariant chain peptide precursors by peptide exchange. No CD4 T cell populations could be identified for two glutamic acid decarboxylase 65 peptides, but tetramers with a peptide mimetic recognized by the BDC-2.5 and other islet-specific T cell clones labeled a distinct population in the thymus of young NOD mice. Tetramer-positive cells were identified in the immature CD4+CD8low population that arises during positive selection, and in larger numbers in the more mature CD4+CD8− population. Tetramer labeling was specific based on the use of multiple control tetramers, including one with a single amino acid analog peptide in which a critical TCR contact residue was substituted. The T cell population was already present in the thymus of 2-wk-old NOD mice before the typical onset of insulitis and was detected in B10 mice congenic for the NOD MHC locus, but not B10 control mice. These results demonstrate that a T cell population can expand in the thymus of NOD mice to levels that are at least two to three orders of magnitude higher than estimated for a given specificity in the naive T cell pool. Based on these data, we propose a model in which I-Ag7 confers susceptibility to type 1 diabetes by biasing positive selection in the thymus and later presenting peptides from islet autoantigens to such T cells in the periphery.