A single naturally processed measles virus peptide fully dominates the HLA-A*0201-associated peptide display and is mutated at its anchor position in persistent viral strains

Abstract

We studied the natural MHC class I display of measles virus (MV) epitopes. Peptide ligands associated with HLA‐A*0201 were purified from a B lymphoblastoid cell line prior to and after infection with MV. Infection‐induced peptides were revealed using microcapillary reversed phase high performance liquid chromatography electrospray ionization / mass spectrometry (μLC‐ESI / MS) by subtraction of the "infected" and "uninfected" ion traces. Three naturally processed viral epitopes derived from different MV proteins were identified through tandem MS sequencing. These peptides were expressed at widely divergent levels of HLA‐peptide complexes, but had similar binding capacities to HLA‐A*0201. The most abundant viral peptide species, identified as residues 84 – 92 (KLWESPQEI) of the MV nonstructural C protein, was expressed at an unprecedented high density (> 105 copies per cell) and was immunogenic in HLA‐A2 / Kb‐transgenic mice. Furthermore, natural mutants of this epitope, occurring in persistent lethal MV strains, were shown to have lost their HLA‐A*0201 binding capacity. Thus, here we report for the first time the direct discovery through μLC‐ESI / MS of a uniquely dominant viral HLA class I ligand, KLWESPQEI, with features eligible for immune selection pressure.

Immunodominance Among EBV-Derived Epitopes Restricted by HLA-B27 Does Not Correlate with Epitope Abundance in EBV-Transformed B-Lymphoblastoid Cell Lines

“…In another viral system, attempts to reactivate in vitro HLA-A*0201-restricted CTL specific for a measles virus epitope have not been successful although this peptide is highly abundant on the surface of measlesinfected cells (37). Additionally, immunization of HLA-A2/K b transgenic mice with high doses of this peptide failed to elicit a CTL response, whereas the administration of a 100-fold lower dose of the peptide proved immunogenic in vivo, suggesting that high doses of Ag inhibit the development of a CTL response to this peptide (37). Furthermore, in a study with the melanoma tumor Ags, immunization of HLA-A2 transgenic mice with large concentrations of tyrosinase elicited only a small population of CD8 ϩ T cell responses, suggesting that the optimal dose of this tumor Ag for activating T cells is not necessarily the largest dose (38).…”

“…Here we report an inverse relationship between the immunogenicity of multiple EBV-derived epitopes and their density on the surface of HLA-B27 ϩ B-LCL. In another viral system, attempts to reactivate in vitro HLA-A*0201-restricted CTL specific for a measles virus epitope have not been successful although this peptide is highly abundant on the surface of measlesinfected cells (37). Additionally, immunization of HLA-A2/K b transgenic mice with high doses of this peptide failed to elicit a CTL response, whereas the administration of a 100-fold lower dose of the peptide proved immunogenic in vivo, suggesting that high doses of Ag inhibit the development of a CTL response to this peptide (37).…”

The contributions of mass spectrometry to understanding of immune recognition by T lymphocytes

“…The number of peptide-MHC complexes required for T lymphocyte recognition varies from several thousand per target cell to as few as one [25,[28][29][30][31][32][33], although weak recognition of other peptides may contribute to the T cell activation process [34]. Some studies have shown a direct correlation between cell surface densities of individual peptide antigens and the magnitude of the immune response against them [35][36][37][38][39], but other studies have shown exactly the opposite [25,27,40]. Higher doses of peptide antigen can actually reduce the magnitude of an immune response in vivo [27,41].…”

“…By standardizing against the ion current of known amounts of model peptides doped into extracts, many MHC-associated peptides are present at 1 copy or less per cell [14,25]. More typically, peptides are present at 10-400 complexes per cell [14,15,26], but a single viral peptide from cells infected with measles virus has been found at the 100,000 copies per cell [27]. How does this wide variation affect their ability to be recognized by the immune system?…”

“…Some studies have shown a direct correlation between cell surface densities of individual peptide antigens and the magnitude of the immune response against them [35][36][37][38][39], but other studies have shown exactly the opposite [25,27,40]. Higher doses of peptide antigen can actually reduce the magnitude of an immune response in vivo [27,41]. Finally, there are examples of self-peptides that become antigens on cancer cells [42,43], suggesting that the immune response may be initiated because their level of presentation is altered.…”