Link between Organ-specific Antigen Processing by 20S Proteasomes and CD8+ T Cell–mediated Autoimmunity

Abstract

Adoptive transfer of cross-reactive HSP60-specific CD8⁺ T cells into immunodeficient mice causes autoimmune intestinal pathology restricted to the small intestine. We wondered whether local immunopathology induced by CD8⁺ T cells can be explained by tissue-specific differences in proteasome-mediated processing of major histocompatibility complex class I T cell epitopes. Our experiments demonstrate that 20S proteasomes of different organs display a characteristic composition of α and β chain subunits and produce distinct peptide fragments with respect to both quality and quantity. Digests of HSP60 polypeptides by 20S proteasomes show most efficient generation of the pathology related CD8⁺ T cell epitope in the small intestine. Further, we demonstrate that the organ-specific potential to produce defined T cell epitopes reflects quantities that are relevant for cytotoxic T lymphocyte recognition. We propose tissue-specific antigen processing by 20S proteasomes as a potential mechanism to control organ-specific immune responses.