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.