Abstract

Multimeric soluble peptide-MHC class I complexes bind to T cell receptors (TCR) on the surface of CD8 cytotoxic T lymphocytes (CTL) with sufficient avidity to enable the labelling of CTL according to their antigen specificity [1]. Visualization of antigen-specific CD8+T lymphocytes with fluorogen-conjugated peptide-MHC class I multimers enables both the physical quantification and the phenotypic characterization of CTL responses directly ex vivo, and these properties have led to the widespread adoption of this technique throughout the field of experimental immunology. However, it is well documented that TCR can exhibit a degree of promiscuity in terms of ligand recognition [2]. We recently demonstrated that the multimerization of peptide-MHC class I can allow binding to TCR with affinities that are too low to generate ligand-induced physiological responses, and result in crossreactive staining of HIV-specific CTL lines and clones by unrecognized natural variant antigens [3]. These results suggest that crossreactivity between peptide-MHC class I multimers and low avidity CTL could be relevant to the interpretation of direct ex-vivo staining. The possibility of such cross-staining is likely to be considerably greater when using peptide-MHC class I multimers to stain CTL specific for epitopes derived from antigenically variable pathogens such as HIV-1 [4]. Here we extend our previous study with the demonstration that the cross-staining of CTL populations with peptide-MHC class I multimers can complicate analyses performed directly ex vivo.

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