The selection process results in developed T cells with specific TCRs that might only respond to certain MHC molecules but not others.The biological reason of MHC restriction is to prevent supernumerary wandering lymphocytes generation, hence energy saving and economy of cell-building materials.[4] Only the thymocytes (developing T cells in the thymus) that are capable of binding, with an appropriate affinity, with the MHC molecules can receive a survival signal and go on to the next level of selection.[10] The interaction between TCRs and peptide-MHC complex is significant in maintaining the immune system against foreign antigens.MHC restriction allows TCRs to detect host cells that are infected by pathogens, contains non-self proteins or bears foreign DNA.Therefore, it is proposed that evolutionary pressure would lead to conserved amino acid sequences at regions of contact with MHCs on TCRs.[17] According to this model, T cells are capable of recognizing a variety of peptide epitopes independent of MHC molecules before undergoing thymic selection.[19] This involves the recruitment of Lck, a tyrosine kinase essential for T cell maturation that is associated with the cytoplasmic tail of the CD4 or CD8 co-receptors.
HLA-A projected away from the cell surface and presenting a peptide sequence.
Interaction of TCR and co-receptors CD4 and CD8 with MHC molecules.
