DO11.10 and OT-II T cells recognize a C-terminal ovalbumin 323-339 epitope

The OVB323-339 epitope recognized by DO11.10 (H-2(d)) and OT-II (H-2(b)) T cells was investigated using amino- and carboxy-terminal truncations to locate the approximate ends of the epitopes and single amino acid substitutions of OVA(323-339) to identify critical TCR contact residues of the OVA(323-339) peptide. DO11.10 and OT-II T cells are both specific for a C-terminal epitope whose tore encompasses amino acids 329-337. Amino acid 333 was identified as the primary TCR contact residue for both cells, and amino acid 331 was found to be an important secondary TCR contact residue; however, the importance of other secondary TCR contact residues and peptide banking residues differ between the cells. Additional OVA(323-339)-specific clones were generated that recognized epitopes found in the N-terminal end or in the center of the peptide. These findings indicate that OVA(323-339) can be presented by I-A(d) in at least three binding registers. This study highlights some of the complexities of peptide Ags such as OVA(323-330), which contain a nested set of overlapping T cell epitopes and MHC binding registers.