Human Leukocyte Antigen (HLA)
About ||
Types ||
Importance in Disease ||
Overview ||
Related Articles
References and Resources ||
Leave a Comment ||
Search
About
The human leukocyte antigen (HLA) is a set of genes located on chromosome 6. They encode protein molecules known as "major histocompatibility complexes" (MHC) that play a pivotal role in proper immune function.
Each human being inherits half of their HLA genes from their mother on one chromosome 6, and half from their father on their other chromosome 6. Because of this random mixing of HLA genes a greater diversity of immune responses is possible amongst the population, which ensures survival of the species.
Major histocompatibility complex proteins get embedded in the membranes of nearly every cell in the human body. From there the MHC proteins "display" various antigens to other cells in the body. The antigens can be protein fragments of viral, bacterial, or self origin depending on the type of MHC protein.
The combination of the MHC protein plus its antigen is able to bind to specific receptors on T-cells (another important immune related cell). The T-cell may then "rev" up the immune system to fight any detected abnormalities. In essence, the MHC proteins allow cells in the body to "talk" with the immune system, which allows them to tell the immune system what infections may be brewing.
Types
There are two categories of human leukocyte antigen genes. Those that encode for MHC-1 proteins, and those that encode for MHC-2 proteins. The genes that encode for MHC-1 are given single letter names such as HLA-A, HLA-B, etc. The genes that encode for MHC-2 get two letter names such as HLA-DR, HLA-DQ, etc.
type 1 and type 2
MHC proteins
MHC-2 proteins show antigen that originates from outside the cell. For example, some cells are able to gobble up bacteria and chew up its proteins. These cells are known as antigen presenting cells (APCs). They take that gobbled up bacterial protein and show it to T-cells on MHC-2 proteins embedded in their cellular membranes.
HLA Genes and Disease
For complicated reasons specific HLA genes are linked to various autoimmune disorders. For example, the HLA-B8 gene (which encodes an MHC-1 protein) is associated with an increased risk of Grave's disease. HLA-DR4 is seen in higher frequencies in patient's with rheumatoid arthritis and diabetes mellitus type 1. See the table below for a more complete list of diseases associated with specific HLA genes.
| HLA Gene | Associated Disease |
|---|---|
| DR2 | - Multiple sclerosis |
| DR3 | |
| DR4 | - Rheumatoid arthritis |
| DR5 | - Pernicious anemia |
| DQ3 | - Alopecia areata |
| B8 | - Grave's disease - Systemic lupus erythematosus |
| B27 | - Psoriasis |
| A3 | - Hemochromatosis |
Overview
The human leukocyte antigens are a set of genes located on chromosome 6 that encode for major histocompatibility complex proteins. MHC proteins play a vital role in cellular immunity. For unclear reasons, certain HLA genes are associated with specific autoimmune disorders.
Related Articles
- Systemic lupus erythematosus
References and Resources
(2) Le T, Bhushan V, Grimm L. First Aid for the USMLE Step 1
(3) Harvey RA, Champe PC. Lippincott's Illustrated Reviews: Immunology (Lippincott's Illustrated Reviews Series)
(4) Hansen TH, Connolly JM, Gould KG, et al. Basic and translational applications of engineered MHC class I proteins. Trends Immunol. 2010 Oct;31(10):363-9. Epub 2010 Sep 9.
(5) Li XC, Raghavan M. Structure and function of major histocompatibility complex class I antigens. Curr Opin Organ Transplant. 2010 Aug;15(4):499-504.