A method of selecting a test molecule that binds to HLA-DP4 by (i) incubating HLA-DP4 with the test molecule and a labeled peptide of formula (I) Z1X1X2X3X4X5X6X7X8X9Z2 thereby forming respective complexes, wherein Z1 and Z2, which may be identical or different, are each either zero or from 1 to 100 amino acids; X1 is an aromatic or hydrophobic amino acid, or S; X6 is an aromatic or hydrophobic amino acid, or C; X9 is an aromatic or hydrophobic amino acid, or C, D, Q, S, T, or E; and X2, X3, X4, X5, X7and X8 are each an amino acid; (ii) separating the respective complexes formed; (iii) detecting the HLA-DP4/labeled peptide complexes; and (iv) selecting the test molecule that exhibits a binding activity of IC50