Variation in H‐2K k peptide motif revealed by sequencing naturally processed peptides from T‐cell hybridoma class I molecules

Class I major histocompatibility complex (MHC) molecules interact with a diverse array of self and foreign peptides, displaying them on the cell surface and providing an extracellular indication of intracellular invasion. The most clearly defined role for these class I/peptide complexes is to cause effector responses upon binding to antigen‐specific receptors of cytotoxic T cells. We have characterized the mouse thymoma/rat Vβ8.2+ T‐cell hybridoma C14/BW12‐12A1 by fluorescence‐activated cell sorting analysis and have used immunoaffinity chromatography to purify class I molecules from these cells. The peptides bound to the class I molecules were fractionated by high‐performance liquid chromatography and sequenced. Self‐peptide mixtures eluted from the mouse H‐2K k class I allele revealed a dominant primary sequence motif, with a carboxyl‐terminal residue that appeared to be invariantly valine and a secondary or auxiliary anchor residue at position 2 that could be either glutamate or proline. The majority of naturally processed peptide ligands appeared to be octamers. Although peptides eluted off H‐2K k molecules from tissue derived from a number of different inbred mouse strains also appeared to be octamers, others have reported that isoleucine is the dominant carboxyl‐terminal residue. Thus, different cell types displayed distinct differences in naturally processed peptides bound by the same class I alleles. The variation in naturally processed peptides loaded onto the same class I allele most likely reflects the nature of the pool of peptides within the cell available for loading class I molecules. © 1996 Wiley‐Liss, Inc.