Interference with MHC class I epitope trimming provides paradoxical protection from autoimmune diabetes

Polymorphism in endoplasmic reticulum antigen processing peptidases (ERAAP) that trim MHC class I ligands is associated with autoimmune diseases, but the mechanism is unknown. We analyzed the effect of Eraap deficiency in the non-obese diabetic (NOD) mouse model of type 1 diabetes. Eraap -/- NOD mice displayed reduced and delayed diabetes, harbored splenic effector T cells unable to transfer diabetes, and exhibited a strong shift from effector to central memory T cells in attenuated islet infiltrates. Eraap deficiency increased presentation of the immunodominant epitope insulin B 15-23 by beta cells but at the same time provided complete protection from diabetes to chimeras reconstituted with bone marrow encoding a CD8 + T cell recognizing this epitope. These results underline the strong impact of self-antigen presentation to CD8 + T cells in diabetes. At the same time, they highlight the complex consequences of interfering with MHC-I antigen presentation in autoimmunity and advise caution in therapeutic modulation of ERAP activity in this context.