Tetramer assay

A tetramer assay is used to detect the presence of antigen specific T-cells. In order for a T-cell to detect the peptide to which it is specific, it must both recognize the peptide AND the MHC complex at the surface of a cell it comes into contact with. Because the binding affinity of a T-cell receptor to MHC complexed with a peptide is so low, this has historically been a challenging problem. A solution was realized by creating a tetramer of MHC molecules each presenting an identical peptide. This increases the avidity of the binding. The main component of the assay is an MHC tetramer. This reagent has to be custom made for each antigen specific t-cell that one desires to detect. The MHC tetramer consists of four units of the MHC molecule each of which is tagged with a biotin molecule. A peptide from the antigen is attached to the MHC molecules. The MHC/peptides are made into a complex by the addition (typically fluorescently labeled) streptavidin, which has an extremely high affinity to biotin. The MHC with its bound peptide will only bind the specific T-cells that respond to that peptide. The tetramer can be detected by flow cytometry via the fluorescent label.

References

*cite journal |title=Phenotypic Analysis of Antigen-Specific T Lymphocytes |author=John D. Altman, Paul A. H. Moss, Philip J. R. Goulder, Dan H. Barouch, Michael G. McHeyzer-Williams, John I. Bell, Andrew J. McMichael, Mark M. Davis |journal=Science |date=1996-10-04 |volume=274 |number=5284 |pages=94–96 |url=http://www.sciencemag.org/cgi/content/full/274/5284/94?ijkey=a1ae599b2eec8e0197cb29f5477a32b2a6a5bdbb |doi=10.1126/science.274.5284.94