The structure of T-cell epitopes.

We have reviewed here studies using synthetic peptides to analyze some of the properties of T-cell epitopes. Several general conclusions can be drawn. First, T-cell epitopes can usually be defined by linear sequences of about seven amino acids. However, the observation that increasing peptide length often results in increased antigenic potency has suggested that antigenicity may crucially depend upon the ability of peptides to adopt appropriate secondary structures. Two models for the prediction of T-cell epitopes on the basis of primary sequence data alone were discussed. Biophysical studies on the association of peptides with Ia molecules have shown that antigenic peptides bind directly to Ia; the evidence suggests that a binary association between Ia and peptide occurs in the absence of specific T-cells. Finally, a hypothesis to explain the observation that B-cells and T-cells generally recognize distinct epitopes on multideterminant antigens has been examined.