Structure and function of the HLA system
HLA antigen are controlled by a series of highly polymorphic genes on the short arm of chromosome 6, referred to as the human major histocompatibility complex (MHC). Two classess of MHC molecules are important in transplantation. Genes in the HLA-A, HLA-B and HLA-C regions encode for class I molecules, and genes in the HLA-DR, HLA-DQ and HLA-DP regions encode for class II molecules.
These HLA class I and class II alloantigens can induce transplant immunity at both humoral (antibody) and cellular (T lymphocyte) immune levels. The human MHC contains other class I and class II genes (eg, HLA-G and HLA-DM, respectively) whose product do not seem important as transplantation antigens. A third set, so-called class III genes