Antigen-specific cytotoxic T lymphocytes (CTL) kill target cells by recognizing the antigen peptides bound to major histocompatibility antigen (MHC)-I molecules on the cell surface.\u00a0It is one of the body’s important immune defense responses for anti-tumor, anti-graft and effective control of various infections. The MHC peptide tetramer<\/u><\/a>\u00a0composed of human leukocyte antigen (HLA) heavy chain and \u03b22 microglobulin light chain, antigen peptide and dye-labeled connexin, has the characteristics of high sensitivity, specificity and efficiency.\u00a0By using MHC-peptide tetramers, we can not only directly count antigen-specific T cells, but also analyze their phenotype and function, which greatly improves our understanding of the role of antigen-specific CTL in diseases.<\/p>\n MHC-Peptide Tetramer<\/b><\/strong><\/p>\n As early as 1937, Peter discovered the first histocompatibility antigen and led to the discovery of the H-2 histocompatibility antigen complex in mice. Later, a similar complex was found in the human body and named it human leukocyte antigen (HLA). These complexes in other animals are called major histocompatibility complexes (MHC). T cells recognize short peptides presented by MHC molecules through specific TCRs, so fluorescently labeled MHC-peptide complexes can be used to detect antigen-specific T cells. However, the affinity between TCR and MHC-peptide complex is very low, extremely unstable, and the dissociation time is less than 1 min[1]<\/sup>. The use of MHC-peptide complex multimer can increase the affinity with T cells to solve this problem. The MHC-peptide complex multimer can bind multiple TCRs at the same time, which greatly slows down the dissociation speed, thereby increasing the positive rate of detection. Altman et al. prepared MHC peptide tetramers based on this principle[2]<\/sup>. The light and heavy chains of MHC are produced by Escherichia coli, and they are recombined with antigen peptides by mole in vitro to form MHC-peptide complexes. After purification, a biotin molecule is connected to the C-terminus of the heavy chain of the MHC-peptide complex,\u00a0then a fluorescein labeled streptavidin with four biotinylated MHC-peptide complex binds to form a tetramer (as shown Fig.1).<\/p>\n Figure 1: Diagram of MHC peptide tetramer: biotinylated MHC I-antigen peptide complex is mixed with fluorescently labeled avidin to form a tetramer<\/p>\n MHC-peptide tetramer action principle<\/b><\/strong><\/p>\n Major histocompatibility antigens are glycoproteins located on the surface of cells. They are highly polymorphic and are antigen-presenting molecules that play a key role in immune response. The antigens that antigen-specific CTLs can recognize are mainly peptides derived from endogenous proteins and bound to MHC-I molecules. MHC-I<\/u><\/a>\u00a0molecules are heterodimers composed of a highly polymorphic heavy chain and a conservative light chain, \u03b22 microglobulin [3]<\/sup>, which are expressed in all nucleated cells. Antigen short peptides that are usually combined with MHC-I molecules are synthesized in antigen presenting cells (APC) (endogenous antigen) and binds in the peptide binding groove formed by the \u03b11 and \u03b12 functional regions of the heavy chain of MHC-I molecules in the endoplasmic reticulum of the cell. Subsequently, due to the non-covalent binding of \u03b22 microglobulin to the heavy chain, MHC-I peptide complexes are more stable, and they are finally located on the cell surface. By interacting with the \u03b1\u03b2 T cell receptor (TCR) on the surface of CD8+ antigen-specific CTLs, CTLs are activated to kill infected cells.<\/p>\n![\"\"](\"https:\/\/www.creative-peptides.com\/blog\/wp-content\/uploads\/2021\/02\/Diagram-of-MHC-peptide-tetramer-300x238.png\")
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