Histocompatibility complex

Major histocompatibility complex refers to a clusterof genes responsible for immune response, transplantation antigens and proteins of the complement system. It is abbreviated as MHC. It was discovered by Gorer in 1930. The major histocompatibility complex produces a set of proteins called histocompatible molecules. These molecules are located on the cell membranes of nucleated cells of the body as well as in the blood serum. These molecules are responsible for graft rejection in transplantation, immune recognition, complement levels, etc.

MHC : The gene segment is named as major histocompatibility complex because its orginial discovery was based on transplantation experiments. Transplantation means the implantation of a tissue from one individual to another. The implanted tissue is called graft. The individual who donates the tissue is called the donor and the individual who receives the tissue is called recipient. When the donor and recipient are identical in their genotype and antigenic pattern , the graft remains alive and healthy. Now the graft is said to be accepted. But when the donor and recipient are dissimilar in their genotype and phenotype the graft dies and it is said to be graft rejection.

The rejection of graft is due to an immunological reaction. The graft tissue releases antigen into the recipient. The immune system of the recipient recognizes the antigen as non self and elicits immune response which rejects the graft.

The antigen which is responsible for graft rejection is called transplantation antigens or histocompatibility antigens.

Formerly it was thought that the major histocompatibility complex is involved in the production of histocompatibility antigens alone. But now it is proved that these genes are also involved in the production of antigens associated with the regulaton of immune response, certain components of the complement and certain abnormal or primitive proteins. Hence the term major histocompatibility complex is a misnomer.

The MHC is present in all mammals. The MHC of mouse and man has been extensively studied.