Antigen-specific T lymphocytes can be enumerated by peptide/MHC tetramers.

By linking four peptide/MHC monomers to a fluorochrome-conjugated streptavidin molecule, so-called peptide/MHC tetramers canb e used to label T lymphocytes that have T cell receptors (TCR) that are specific for the given peptide/MHC combination ligand. The spatial configuration of the tetramers allows for the required increase in binding avidity to stain the cells for analysis by flow cytometry. Sensitivity of this technique is often in the range of 0.01% to 0.1% of all CD8 cells.