Identification of peptides associated with chicken major histocompatibility complex class II molecules of B21 and B19 haplotypes.

Chicken major histocompatibility complex (MHC) molecules present peptides to T cells to initiate immune response. Some variants of the chicken MHC, such as B19 and B21 haplotypes, are strongly associated with susceptibility and resistance to Marek's disease, respectively. The objective of the present study was to characterize the repertoire and origin of self-peptides presented by chicken MHC class II (B-L) molecules of B19 and B21 haplotypes. Following immunoaffinity purification of B21 and B19 B-L molecules from transformed B cell lines, their associated peptides were eluted, high performance liquid chromatography-fractionated, and sequenced by tandem mass spectrometry. Four peptides were identified associated with B21 B-L molecules. These ranged from 16 to 21 residues in length and had originated from membrane-bound, cytosolic, and mitochondrial proteins. Two of these peptides were present in form of an overlapping set, which is a common characteristic of MHC II-associated peptides. The single B19-associated peptide was 17 residues long and had originated from a cytosolic source. Presentation of endogenous peptides, such as those derived from cytosolic and mitochondrial proteins, by B-L molecules is indicative of cross-sampling between MHC class I and II antigen presentation pathways. These findings facilitate future studies aimed at elucidating mechanisms of chicken MHC association with disease resistance.