ENHANCEMENT OF PEPTIDE ANTIGEN PRESENTATION BY A 2ND PEPTIDE

The influence of nonstimulatory ''competitor'' peptides on the binding of an antigenic peptide to a major histocompatibility complex (MHC) class II molecule was investigated. Using high-performance size-exclusion chromatography and fluorescein-labeled peptides, we show that the presence of the peptides dynorphin A-(1-13) and poly(L-lysine) results in enhancement rather than inhibition of the binding of hen egg lysozyme peptide-(107-116) [HEL-(107-116)] to the detergent-solubilized mouse class II molecule IE(d). In parallel, dynorphin A-(1-13) and poly(L-lysine) were found to enhance the specific activation of an IE(d)-restricted T-cell hybridoma by HEL-(107-116). A molecular mechanism involving an intermediate two peptide-MHC class II protein complex is proposed to explain the enhancement of peptide binding to class II molecules by an irrelevant second peptide.