Why is tetramer only used to test the interaction between T cell and peptide-MHC complex and not to test binding affinity between peptide and MHC?
Hello Quyên Tú Nguyễn
Major histocompatibility complex (MHC) antigens bind peptides of diverse sequences with high affinity. Both MHC class I and MHC class II molecules contain peptide-binding grooves formed by two α-helices and eight β-strands. In the peptide-binding groove, specific amino acids compose pockets that accommodate the corresponding side chains of the anchor residues of the presented peptides. Peptide-binding preferences exist among different alleles of both of MHC I and MHC II molecules, which are mainly dependent on amino acid polymorphisms in the peptide-binding grooves of MHC chains. They do this in order to generate maximal immunological protection by covering the spectrum of peptides that may be seen by a host over the course of its lifetime.
On the other hand, TCR (T cell receptor) has a low avidity and fast off-rates for MHC-peptide complexes. So, MHC-peptide tetrameric complexes (so-called MHC tetramers) have been introduced for the detection of antigen-specific T cells. MHC tetramers have increased avidity for their cognate TCRs and are successfully used to directly visualize antigen-specific T cells ex vivo. MHC tetramer technology is based on the ability of MHC-peptide complexes to recognize the antigen-specific T cells at a single cell level.
Hope this information is helpful!
Best.
