The nature of autoantigens that trigger autoimmune diseases has been much discussed, but direct biochemical identification is lacking for most. Addressing this question demands unbiased examination of the self-peptides displayed by a defined autoimmune major histocompatibility complex class II (MHC-II) molecule. Here, we examined the immunopeptidome of the pancreatic islets in non-obese diabetic mice, which spontaneously develop autoimmune diabetes based on the I-Ag7 variant of MHC-II. The relevant peptides that induced pathogenic CD4+ T cells at the initiation of diabetes derived from proinsulin. These peptides were also found in the MHC-II peptidome of the pancreatic lymph nodes and spleen. The proinsulin-derived peptides followed a trajectory from their generation and exocytosis in β cells to uptake and presentation in islets and peripheral sites. Such a pathway generated conventional epitopes but also resulted in the presentation of post-translationally modified peptides, including deamidated sequences. These analyses reveal the key features of a restricted component in the self-MHC-II peptidome that caused autoreactivity.
|Number of pages||9|
|State||Published - Apr 1 2020|