Frontline: Self-peptides that bind with low affinity to the diabetes-associated I-Ag7 molecule readily induce T cell tolerance in non-obese diabetic mice

Abstract

Although non-obese diabetic (NOD) mice spontaneously develop T cell autoimmunity, it is not clear whether this phenomenon results from a defect in tolerance to self-Ag. Furthermore, as autoimmunity has been postulated to result from T cell responses directed toward self-peptides that bind with low affinity to NOD I-A^g7 MHC class II molecules, it is important to determine whether the expression of such peptides induces tolerance. We have constructed NOD transgenic (Tg) mice expressing the Leishmania antigen receptor for C kinase (LACK) Ag in either the thymus or pancreatic β cells. We identified LACK peptides that were the targets of T cells in LACK-immunized NOD mice while binding to I-A^g7 with low affinity. While CD4⁺ T cells from NOD mice secreted IFN-γ, IL-4, IL-5 and IL-10 in response to LACK, those from LACK-expressing Tg mice secreted reduced levels of cytokines. Experiments using peptide/MHC multimers showed that LACK-expressing Tg mice exhibited self-reactive CD4⁺ T cells with impaired proliferation capabilities. Hence, even self-peptides that bind to I-A^g7 with low affinity can induce tolerance in NOD mice. This result is important in light of the commonly held hypothesis that T cells reacting to peptides that bind to MHC with low affinity escape tolerance induction and cause autoimmunity.