A study of pathogenic CD8+ T cells in autoimmune diabetes

Nonobese diabetic (NOD) mice develop an autoimmune disease that models human type 1 diabetes. CD8+ T cells are required for the development of the β cell destruction characteristic of autoimmune diabetes, yet their specific antigenic targets are largely unknown. We have studied two diabetogenic CD8+ T cell clones, 8.3 and AI4, representing CD8+ T cell clonotypes present within the earliest islet infiltrates of NOD mice and whose antigenic targets are unknown. We screened peptides eluted from immunoaffinity purified MHC molecules from an NOD-derived β cell line (NIT-1) and identified islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) as the antigenic target of the prevalent and pathogenic 8.3-like T cell population. To characterize AI4-like T cells, we screened a combinatorial peptide library and identified a mimotope peptide recognized by AI4. We used mimotope peptide/MHC tetramers to demonstrate that AI4-like T cells are detectable in islet infiltrates of NOD mice. We then identified a mimotope-like peptide, contained within a ubiquitously expressed protein (dystrophia myotonica kinase; DMK), that is recognized by AI4. We cloned DMK from NIT-1 β cells and demonstrated AI4 recognition of DMK-transfected target cells. Identification of target autoantigens is a key step in understanding the mechanisms responsible for the defect in establishing and/or maintaining tolerance to certain self proteins. Knowledge of the antigenic targets of the pathogenic 8.3- and AI4-like T cells will allow for studies into the development of these autoreactive T cell populations in NOD mice as well as the importance of these autoantigens in human type 1 diabetes.