Contribution of mass spectrometry to contemporary immunology.

Mass spectrometry has become an increasingly important tool in the characterization of histocompatibility complex molecule (MHC) bound antigen peptides. It is one of the few technologies capable of identifying minute amounts of peptides in complex (5,000-10,000 constituents) MHC elution mixtures. Currently, the combination of tandem mass spectrometry with electrospray ionization (ESI) and microcapillary liquid chromatography (microLC) has proven to be the more versatile and effective technology. Post-source decay (PSD) and on-slide digestion combined with matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) may be valuable as well in certain circumstances. Recent refinements in the technology, such as the development of the quadrupole ion trap (QIT), Fourier transform ion cyclotron resonance (FTICR), and orthogonal quadrupole-time-of-flight (qToF) mass spectrometers equipped with nanoscale electrospray ionization sources and combined with microscale LC or capillary zone electrophoresis (CZE) yield attomole-range sensitivity in peptide sequencing, a level approaching the immuno-relevant level to a significant extent. In this review, past and ongoing developments in mass spectrometry and analytical separation techniques and their application to contemporary immunology are discussed.