Definition web: Major Histocompatibility Complex (MHC)

These are gene clusters which are present on the surface of a cell, and which identify that cell as being either "native" or "foreign." They help the organism distinguish invading cells from its own body cells. MHC differences can cause a host organism to reject and attack an organ graft.

MHC molecules also bind foreign antigens and present them to the immune system. In humans, MHCs are also known as HLA (human leukocyte antigen) molecules.