Human Leukocyte Antigen - Classification

Classification

MHC class I proteins form a functional receptor on most nucleated cells of the body.

There are 3 major and 3 minor MHC class I genes in HLA:

• HLA-A
• HLA-B
• HLA-C
• minor genes are HLA-E, HLA-F and HLA-G
• β₂-microglobulin binds with major and minor gene subunits to produce a heterodimer

There are 3 major and 2 minor MHC class II proteins encoded by the HLA. The genes of the class II combine to form heterodimeric (αβ) protein receptors that are typically expressed on the surface of antigen-presenting cells.

Major MHC class II

• HLA-DP
  • α-chain encoded by HLA-DPA1 locus
  • β-chain encoded by HLA-DPB1 locus
• HLA-DQ
  • α-chain encoded by HLA-DQA1 locus
  • β-chain encoded by HLA-DQB1 locus
• HLA-DR
  • α-chain encoded by HLA-DRA locus
  • 4 β-chains (only 3 possible per person), encoded by HLA-DRB1, DRB3, DRB4, DRB5 loci

The other MHC class II proteins, DM and DO, are used in the internal processing of antigens, loading the antigenic peptides generated from pathogens onto the HLA molecules of antigen-presenting cell.