Unconventional recognition of peptides by T cells and the implications for autoimmunity.

The interaction of antigen-presenting cells with free peptides or a denatured protein can give rise to peptide-MHC class II complexes that are distinct from those generated after the processing of the whole protein. Such atypical peptide-MHC complexes can be recognized by unconventional 'type B' T cells that are not a component of the normal immune response to proteins. Importantly, these unconventional T cells can be found in the setting of autoimmunity. Here, we discuss unconventional peptide recognition by type B T cells and consider the implications for type 1 diabetes and other autoimmune diseases.