We have previously shown that the T cell response to the synthetic
peptide cI12-26:NP365-380 (covalently linked
epitopes of
lambda repressor (cI) and
influenza A
nucleoprotein (NP)
polypeptides) requires amino acid sequences located in the junctional region between the cI12-26 and NP365-380
epitopes in the H-2d and H-2k haplotypes. In this study, we show that the dominant
epitope of cI12-26:NP365-380 in H-2b mice is also located within the junctional region of the
peptide, indicating that the same amino acid sequence is immunodominant in three different H-2 haplotypes. Based on results using fixed APC, there was no qualitative difference in
epitope recognition due to antigen processing. In addition, antigen presentation by APC expressing mutant I-A molecules constructed by hemiexon shuffling of regions of the molecule containing primarily beta sheet or alpha helix showed that many different substitutions were permissive for at least one of the T hybridomas. More importantly, however, when the junctional sequences are covalently linked in composite synthetic
peptides containing additional previously defined
T cell epitopes, antigenicity of the immunodominant junctional region was silenced and a new
epitope assumed immunodominance. Thus, immunodominance does not correlate with the primary amino acid sequence of the potential
epitope. Instead, the
immunodominant epitope is determined by complex interactions among the
epitopes, which most likely depend on the structural conformation of the composite
peptide.