The molecular basis of metal recognition by T cells.

T lymphocytes play critical roles in a series of important immune responses, including delayed-type hypersensitivity and contact sensitivity. Metal haptens such as nickel are among the most common sensitizers. In general, T cells recognize fragments of proteins complexed to MHC molecules. Haptens, however, are too small to be antigenic by themselves. Recent experiments have suggested that hapten-specific T cells recognize hapten-modified MHC-peptide complexes. Here I review the data supporting this hypothesis and speculate on the relevance of these findings for the understanding of chemical-induced hypersensitivities.