Human leukocyte antigen (HLA)

The human leukocyte antigen (HLA) is a family of genes found on chromosome 6 which provide the instructions to make a group of proteins known as the HLA complex. The HLA proteins are present on the surface of cells, and they help the immune system to distinguish foreign invaders such as viruses and bacteria from the body's own cells and tissues. HLA is the human version of a gene family that occurs in many animals, where it's known as the major histocompatibility complex (MHC).

The HLA genes determine an individual's tissue type, which varies from person to person as HLA genes have many possible variants. The HLA complex is probably best known for its major role in organ transplantation. If you require a transplantation, tests are carried out to try and get a perfect match, or as close as possible match, between the HLA genes of the donor and those of the recipient to reduce the risk of the transplanted organ being rejected.

However, the primary role of the HLA complex is in the regulation of the immune system to defend against disease. Your individual HLA type is inherited from your parents, half from your mother and half from your father, this is why there's a wide variation seen from person to person. This variation in the HLA genes allows the immune system to be fine-tuned to react to a wide range of invaders. Differences in the HLA genes influence how well you as an individual respond to specific viruses or bacteria and explains why some people may be affected more severely by a particular infection or condition than others.

Variants in the HLA genes are associated with more than 100 diseases, including infectious diseases like HIV, and some cancers. Some autoimmune conditions, including diabetes and multiple sclerosis, are also linked to specific variations in the HLA. In MS, the immune system fails to distinguish between the body's tissues and foreign proteins resulting in it attacking myelin as if it were foreign. Several HLA genes have been found to influence the risk of developing MS. Some variants make an individual more likely to develop MS, whereas others may have a protective effect and decrease the risk.

Although the precise genes involved in the development of multiple sclerosis are still not fully understood, research has identified one HLA gene that is more prevalent in women with MS and may be part of the explanation why more women than men get the condition.

Find out more

Ramagopalan SV, et al.
Multiple sclerosis and the major histocompatibility complex.
Current Opinion in Neurology 2009;22(3):219-225.
Summary (link is external)
Chao MJ, et al.
MHC transmission: insights into gender bias in MS susceptibility.
Neurology 2011;76(3):242-246.
Full article (link is external)