Conversion of Tyrosine to the Inflammation-Associated Analog 3′-Nitrotyrosine at Either TCR- or MHC-Contact Positions Can Profoundly Affect Recognition of the MHC Class I-Restricted Epitope of Lymphocytic Choriomeningitis Virus Glycoprotein 33 by CD8 T Cells

Abstract

Immunohistochemical detection of increased levels of protein-associated nitrotyrosine has become widely used as a surrogate marker of in situ inflammation. However, the potential consequences of protein-associated nitrotyrosine formation in terms of cellular immune recognition has received surprisingly little attention. Using a well-defined I-E^K-restricted epitope of pigeon cytochrome c, we previously demonstrated that conversion of a single tyrosine residue to nitrotyrosine can have a profound effect on recognition by CD4 T cells. In this study, we used the MHC class I-restricted epitope of lymphocytic choriomeningitis virus glycoprotein (gp33) to demonstrate that conversion of tyrosine to nitrotyrosine can also profoundly affect recognition of MHC class I-restricted epitopes. Conversion of the Y4 residue of the gp33 epitope to nitrotyrosine completely abrogated recognition by gp33-specific T cells from P14 TCR-transgenic mice. In contrast, CD8⁺ T cells specific for “nitrated gp33” (NY-gp33) can be readily elicited in C57BL/6 mice after immunization with NY-gp33 peptide. Interestingly, T-T hybridomas specific for NY-gp33 peptide were found to fall into two distinct subsets, being specific for NY-gp33 presented in the context of either H-2D^b or H-2K^b. This latter result is surprising in light of previous structural studies showing that Y4 comprises a critical TCR-contact residue when presented by H-2D^b but that the same residue points downward into the peptide-binding groove of the MHC when presented by H-2K^b. Together, these results indicate that nitrotyrosine formation can impact T cell recognition both directly, through alteration of TCR-contact residues, or indirectly, through alterations in MHC-contact positions.