MAJOR HISTOCOMPATIBILITY COMPLEX

a group of genes that control the expression of cell surface protein markers (also known as human leukocyte antigen or HLA markers) that determine receptor shape and allow immune cells to recognize components of the body (i.e., to distinguish "self" from "non-self"). MHC molecules are necessary for antigen presentation and for recognition of antigens by immune system cells. Each individual has one of a variety of genetically-determined MHC/HLA patterns. There are two classes of MHC molecules, MHC-I and MHC-II.