Amino acid characteristics of immunogenic peptides presented on HLA class I molecules.

Sets of amino acids were counted in immunogenic and non-immunogenic peptides based on size, aromaticity, acidity and charge, and enrichments were determined (see Methods). The association of these characteristics (e.g. size) with immunogenicity was tested by comparing the distributions in one extreme of a characteristic with the distribution in the other extreme of that characteristic (e.g. large versus small) using Fisher's exact test. This way, one test is performed per characteristic.