Methods: We cultured PBMCs from grass allergic patients with Phl p extract and tested for cytokine production after restimulation with 15-mer peptide epitopes. We systematically lengthened these 15-mers to 20-mers and compared the cytokine responses they elicited as a function of the position of the 15-mer within the 20-mer and the composition of the added flanking residues which either matched the pollen sequence or were completely mismatched.
Results: We found that the lengthened 20-mers elicited higher responses in allergic patients than the 15-mers they were derived from, and that a greater number of allergic patients mounted significant responses to them. This effect was especially pronounced when the epitope was flanked on both sides by amino acids and therefore “protected”. We also found that lengthened peptides with mismatched flanking residues did not elicit as high responses as peptides that were sequence matched.
Conclusions: Our findings suggest that longer peptides maximize allergic T-cell responses, by two effects: First, the flanking residues on either side of the epitope seem to protect it from proteolysis. Second, addition of residues that match the pollen sequence may generate additional epitope registers in the peptide thereby increasing the likelihood of MHC binding and T-cell recognition. These results can be utilized for choosing peptides to include in AIT.