Toward a definition of self: proteomic evaluation of the class I peptide repertoire.

MHC class I molecules present host- and pathogen-derived peptides for immune surveillance. Much attention is given to the search for viral and tumor nonself peptide epitopes, yet the question remains, "What is self?" Analyses of Edman motifs and of small sets of individual peptides suggest that the class I self repertoire consists of thousands of different peptides. However, there exists no systematic characterization of this self-peptide backdrop, causing the definition of class I-presented self to remain largely hypothetical.