The major function of the MHC antigens is to present antigens as fragments of foreign proteins, forming complexes that can be recognised by T lymphocytes through special receptors.
The MHC genes in humans are mainly on 6p, the short arm of chromosome 6. Separate genes on other chromosomes also play a role. For instance the gene encoding the beta-2 microglobulin component of human leucocyte antigen A2 (HLA-A2) is on chromosome 15. 1
Daussett working in Paris discovered the first human histocompatibility antigen in 1958. He was searching for a system akin to the ABO system discovered for red blood cell transfusion. He found an ntigen on leucocytes, and termed it Human Leucocyte Antigen (HLA). Daussett acutally discovered what is now termed HLA-A2. The molecular structure of HLA-A2 was described in 1987. [BSS$^+$87]
The HLA-B system was discovered in 1968. [KNSH68] In 1970 further refinements are made and the HLA-A,B and C genes are grouped together to comprise the MHC-1 complex. In 1973 Van Leeuwan et al discover the HLA-D system, which is termed MHC-2. [VLSVR73] By 1984 there was enough information available to organise the MHC-2 system in the DR, DP and DQ series, this was accomplished at a workshop in Munich.
The MHC genes are subdivided into classes based upon their cellular distribution, chemical and crystallographic structure and their immunological function.