Direct binding of gluten-derived peptides and the mycobacterial heat shock protein peptide MT3-13, used as a positive control, to HLA-DR3-expressing L-cell transfectants, measured by FACS analysis. Net binding is expressed in arbitrary units, the calculation of which is described in Materials and Methods. ▴, Peptide MT3-13; ▵, peptide A; ○, peptide B; □, peptide C.