The myriad of peptides presented at the cell surface by class I and class II major histocompatibility complex (MHC) molecules are referred to as the immunopeptidome and are of great importance for basic and translational science. For basic science, the immunopeptidome is a critical component for understanding the immune system; for translational science, exact knowledge of the immunopeptidome can directly fuel and guide the development of next-generation vaccines and immunotherapies against autoimmunity, infectious diseases, and cancers. In this mini-review, we summarize established isolation techniques as well as emerging mass spectrometry-based platforms (i.e. SWATH-MS) to identify and quantify MHC-associated peptides. We also highlight selected biological applications and discuss important current technical limitations that need to be solved to accelerate the development of this field. Molecular & Cellular

We present a novel mass spectrometry-based high-throughput workflow and an open-source computational and data resource to reproducibly identify and quantify HLA-associated peptides. Collectively, the resources support the generation of HLA allele-specific peptide assay libraries consisting of consensus fragment ion spectra, and the analysis of quantitative digital maps of HLA peptidomes generated from a range of biological sources by SWATH mass spectrometry (MS). This study represents the first community-based effort to develop a robust platform for the reproducible and quantitative measurement of the entire repertoire of peptides presented by HLA molecules, an essential step towards the design of efficient immunotherapies.DOI: http://dx.doi.org/10.7554/eLife.07661.001

The myriad of peptides presented at the cell surface by class I and class II major histocompatibility complex (MHC) molecules are referred to as the immunopeptidome and are of great importance for basic and translational science. For basic science, the immunopeptidome is a critical component for understanding the immune system; for translational science, exact knowledge of the immunopeptidome can directly fuel and guide the development of next-generation vaccines and immunotherapies against autoimmunity, infectious diseases, and cancers. In this mini-review, we summarize established isolation techniques as well as emerging mass spectrometry-based platforms (i.e. SWATH-MS) to identify and quantify MHC-associated peptides. We also highlight selected biological applications and discuss important current technical limitations that need to be solved to accelerate the development of this field.

Selected groups of peptides, including those that are presented by major histocompatibility complex (MHC) proteins, have been proposed to transmit information to the olfactory system of vertebrates via their ability to stimulate chemosensory neurons. However, the lack of knowledge about such peptides in natural sources accessible for nasal recognition has been a major barrier for this hypothesis. Here we analyse urinary peptides from selected mouse strains with respect to genotype-related individual differences. We discover many abundant peptides with single amino-acid variations corresponding to genomic differences. The polymorphism of major urinary proteins is reflected by variations in prominent urinary peptides. We also demonstrate an MHC-dependent peptide (SIINFEKL) occurring at very low concentrations in mouse urine. Chemoreceptive neurons in the vomeronasal organ detect and discriminate single amino-acid variation peptides as well as SIINFEKL. Hence, urinary peptides represent a real-time sampling of the expressed genome available for chemosensory assessment by other individuals.

Genes of the major histocompatibility complex (MHC), which play a critical role in immune recognition, are considered to influence social behaviors in mice, fish, humans, and other vertebrates via olfactory cues. As studied most extensively in mice, the polymorphism of MHC class I genes is considered to bring about a specific scent signature, which is decoded by the olfactory system resulting in an individual-specific reaction such as mating. On the assumption that this signature resides in volatiles, extensive attempts to identify these MHC-specific components in urine failed. Alternatively, it has been suggested that peptide ligands of MHC class I molecules are released into urine and can elicit an MHC-haplotype-specific behavioral response after uptake into the nose by sniffing. Analysis of the urinary peptide composition of mice shows that MHC-derived peptides are present, albeit in extremely low concentrations. In contrast, urine contains abundant peptides which differ between mouse strains due to genomic variations such as single-nucleotide variations or complex polymorphisms in multigene families as well as in their concentration. Thus, urinary peptides represent a real-time sampling of the expressed genome available for sensory evaluation. It is suggested that peptide variation caused by genomic differences contains sufficient information for individual recognition beyond or instead of an influence of the MHC in mice and other vertebrates.