The major histocompatibility complex (MHC) is a large gene complex present in all jawed vertebrates with an integral role in the immune system. The antigen-presenting molecules encoded by the MHC class I and class II genes are cell-surface glycoproteins that bind intracellular and extracellular peptides, respectively. The human MHC is located chromosome 6 and contains more than 200 genes. The MHC-encoded glycoproteins are known as human leukocyte antigen (HLA) and are specialized in presentation of short peptides to T cells and play a key role in the body’s immune defence.
MHC name is derived from its role in graft rejection and tissue compatibility between donor-recipient pair. MHC compatibility between individuals is responsible for successful graft transplant. MHC is characterized by extensive polymorphism which is one hand is obstacle for finding matched pairs and in the other hand enables the immune system to recognized any invading pathogen.