[Gene structure of the human MHC region]

The human major histocompatibility complex (MHC) encodes the highly polymorphic human leukocyte antigens (HLA) responsible for antigen presentation to T cells. The HLA gene complex is located on the short arm of chromosome 6 within 6p21.3 and covers a distance of about 4,000 kb that has arisen through repeated gene duplication and conversion during evolution. The HLA class I region is about 2,000 kb in size, while the class II region is about 1,000 kb. The remainder comprises the HLA class III region. There are presently 19 HLA or HLA-like expressed genes and about 80 non-HLA expressed genes as well as 27 pseudogenes or gene fragments localized within the HLA region, although the function of most of these genes is still uncertain. This paper provides a comprehensive overview of non-HLA genes as well as HLA genes which are so far identified in this region.