Quantitative determination of TCR cross-reactivity using peptide librariesand protein databases

A single T cell clone can be activated by many different peptides in the co ntext of a particular HLA molecule. To quantify the number of peptides that can be recognized by a CD4(+) T cell clone, we screened a one-bead-one-pep tide synthetic peptide library and a protein database for peptides that sti mulate an HLA-DR3-restricted, human glutamic acid decarboxylase (GAD65)-rea ctive CD4(+) T cell clone. Both the library screening and the database anal ysis indicated that this T cell clone is able to recognize approximately 10 (6) 11-mer peptides at low nanomolar concentration. Furthermore, we determi ned that the frequency of cross-reactivity increased only 1.5-3 times when the peptide concentration increased 10 times, in the range of 0.01-1 mu M. These data imply that there is a considerable potential for T cell crossrea ctivity and are useful for studies on the role of molecular mimicry in the etiology of T cell-mediated disease.