Evaluation of peptide-HLA binding by an enzyme-linked assay and its application to the detailed peptide motifs for HLA-DR9 (DRB1*0901)

In our recent studies, we identified HLA-DRB1*0901-binding peptides by affinity-based selection of a phage random peptide library and showed that two major anchors (WxxS, where x is any amino acid) play an essential role in binding to DR9, determined using a radioactive peptide in combination with column chromatography. In the current study, we established an ELISA-based peptide-HLA binding assay system, with a new index (relative binding affinity; r.b.a.) for quantitation of peptide-HLA binding, using standard curves of competitive inhibition, an approach which enabled handling of a larger number of samples simultaneously. Quantitation of binding between HLA-DR9 molecules and 39 synthetic peptides showed that: (a) this system yields results which correlate with those obtained using the previous assay system (Spearman's rank correlation coefficient; the p value of the putative first anchor <0.001, and the putative second anchor <0.001); and (b) substituting the putative first (the most N-terminal) anchor Trp to Y, M, F, I, L, V, or C, and the putative second anchor Ser to T, G, A, V, F, or H, allow high-affinity binding to DR9.