Quantitation of lysozyme peptides bound to class II MHC molecules indicates very large differences in levels of presentation

Knowing the abundance of peptides presented by MHC molecules is a crucial aspect for understanding T cell activation and tolerance. In this report we determined the relative abundance of four distinct peptide families after the processing of the model Ag hen egg-white lysozyme. The development of a sensitive immunochemical approach reported here made it possible to directly quantitate the abundance of these four epitopes presented by APCs, both in vitro and in vivo. We observed a wide range of presentation among these four different epitopes presented on the surface of APCs, with 250-fold differences or more between the most abundant epitope (48-63) and the least abundant epitopes. Importantly, we observe similar ratios of presentation from APCs in vitro as well as from APCs from the spleens and thymi of hen egg-white lysozyme transgenic mice. We discuss the relationship between the amount of peptide presented and their binding to I-A^k molecules, immunogenicity, and tolerogenicity.