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Abstract

Previous studies that used peptide-MHC (pMHC) tetramers to identify self-specific T cells have questioned the effectiveness of thymic-negative selection. Here, we used pMHCI tetramers (tet) to enumerate CD8 T cells specific for the immunodominant gp33 epitope of lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP) in mice transgenically engineered to express high levels of GP as a self-antigen in the thymus. In GP-transgenic mice (GP⁺), monoclonal P14 TCR⁺ CD8 T cells that express a GP-specific TCR could not be detected by gp33/D^b -tet staining, indicative of their complete intrathymic deletion. By contrast, in the same GP⁺ mice, substantial numbers of polyclonal CD8 T cells identifiable by gp33/D^b -tet were present. The gp33-tet staining profiles of polyclonal T cells from GP⁺ and GP-negative (GP^-) mice were overlapping but mean fluorescence intensities were ∼15% lower in cells from GP⁺ mice. Remarkably, the gp33-tet⁺ T cells in GP⁺ mice failed to clonally expand after LCMV infection, whereas those of GP^- mice did so. In Nur77^GFP -reporter mice, dose-dependent responses to gp33 peptide-induced TCR stimulation revealed that gp33-tet⁺ T cells with high ligand sensitivity are lacking in GP⁺ mice. Hence, pMHCI tetramer staining identifies self-specific CD8 T cells but tends to overestimate the number of truly self-reactive cells.