Explain Major Histocornpatability Complex (MHC)

Major histocompatability complex is also known as the Human Leukocyte Antigen (HLA). MHC molecules are important components of the immune response. They permit cells that have been invaded by an infectious organism to be detected by the cells of the immune system called T-lymphocytes or T-cells. The MHC molecules do this by offering fragments of proteins (peptides) belonging to the invader on the surface of the cell. The T-cell recognizes the foreign peptide attached to the MHC molecule and binds to it, an action which stimulates the T-cell to either destroy or cure the infected cell. The MHC, therefore, is a set of genes that code for cell surface glycoproteins. These glycoproteins mark the body cells as 'self' and are divided into two main classes - class I MHC molecules are found on the surface of almost every cell of the body.

Class ll MHC molecules are confined to a few specialized cell types, such as macrophages, B-cells and activated T-cells. Each MHC antigen combination forms a unique complex that is recognized by specific antigen receptors on T-cells as 'self'. T-cell surface proteins CD4 and CD8 greatly enhance the interaction between an antigen presenting cell (APC) and killer T-cell and between AF'C and helper T-cell, respectively. The primary immunological function of MHC molecules, therefore, is to bind and "present" antigenic peptides on the surfaces of cells for recognition (binding) by the antigen- specific T-cell receptors (TCRs) of lymphocytes. The other specific defence mechanism in our body is the antibodies. Let us learn about their role in the immune system and their interaction with antigens.