Tetramers and monomers

TCRs recognize and bind to complexes composed of MHC molecules and specific peptides expressed on the surface of antigen-presenting cells. While it was believed that antigen-specific T cells could be detected using soluble MHC/peptide complexes, monomeric MHC/peptide complexes proved to be impractical due to their instability and low affinity yo TCRs. To overcome this difficulty, MHC/peptide monomers are biotinylated and tetramerized with streptavidin to maintain stable binding to multiple TCRs, enabling MHC/peptide tetramers to be used as detection tools. MHC tetramers are labeled with fluorescent molecules such as phycoerythrin (PE), allophycocyanin (APC) or Brilliant Violet 421 (BV421) and thus allow detection of antigen specific T cells by flow cytometry or fluorescence microscopy.