Selective interaction of Ni with an MHC-bound peptide.

T cells generally recognize foreign antigens as peptides associated with self-molecules encoded by genes of the major histocompatibility complex (MHC). However, T cells which are specific for non-peptidic haptens have been described, in particular in patients with contact sensitivity reactions to metals such as nickel (Ni). Previously, we isolated MHC class II-restricted Ni-specific T cell clones from patients with Ni allergy. The experiments reported here examine the molecular basis for the interaction between Ni and peptide-MHC complexes. We find that Ni alters a T cell response to a peptide and show that Ni interacts with this peptide to alter its antigenicity rather than its ability to bind to MHC molecules. These findings hold implications for a model of hapten recognition by T cells.