Diabetes and other autoimmune endocrine diseases
T cell clones isolated from the pancreatic infiltrates of nonobese diabetic (NOD) mice have been shown to recognize epitopes formed by covalent cross-linking of proinsulin peptides to other peptides present in secretory granules. Formation of such hybrid insulin peptides (HIPs) has been confirmed through mass spectrometry. In addition, responses to HIPs were recently observed among CD4+ T cells isolated from the pancreatic islets of two organ donors who had T1D. However, unanswered questions remain about the prevalence of HIP-specific T cells in human subjects, the diversity of hybrid sequences they recognize, and their role in human disease. Here we demonstrate that HIP-specific CD4+ T cells can be readily detected in the peripheral blood of patients with T1D through direct ex vivo analysis with HLA class II tetramers. T cell clones isolated from these subjects typically recognized HIP peptide with high affinity. Relevant HIPs discovered in the NOD are restricted by I-Ag7, implying that in human subjects HIPs might be recognized primarily in the context of DQ8. However, we identified six novel HIP sequences that are recognized in the context of DRB1*04:01. Interestingly, these diverse HIPs are derived from the insulin A chain, B chain, and C peptide covalently linked to one another (intra-antigen HIPs) or to other secretory granule proteins (inter-antigen HIPs). These results support the relevance of HIPs in human disease and may help to establish a new mechanism that contributes to the loss of peripheral tolerance in T1D.