Human Leukocyte Antigen B27 (HLA-B27) is a specific protein found on the surface of immune cells, playing a role in the body’s defense system. Its presence has been observed to correlate with certain health considerations. Understanding this protein can provide insights into how the immune system functions and how genetic factors can influence health.
Understanding HLA-B27
HLA-B27 is a type of human leukocyte antigen (HLA) protein. These proteins are located on the surface of various cells, particularly white blood cells, and are part of the major histocompatibility complex (MHC class I proteins). Their primary function is to help the immune system identify and distinguish between the body’s own healthy cells and foreign invaders, such as viruses or bacteria. They achieve this by presenting small pieces of proteins, called peptides, to T-cells. The presence of the HLA-B27 protein is determined by a specific gene located on chromosome 6.
The Inheritance Pattern of HLA-B27
The HLA-B27 gene is inherited in an autosomal dominant manner. This means an individual needs to inherit only one copy of the gene from either parent to test positive for the protein. If one parent carries the HLA-B27 gene, each child has approximately a 50% chance of inheriting it.
HLA-B27 and Associated Conditions
While HLA-B27 is a naturally occurring human protein, its presence is strongly associated with a group of autoimmune diseases known as spondyloarthropathies. The most prominent association is with ankylosing spondylitis, a condition characterized by chronic inflammation primarily affecting the spine and other joints, which can lead to spinal stiffness and reduced flexibility. Other conditions linked to HLA-B27 include reactive arthritis, which often develops after an infection and causes inflammation in joints, the urethra, and eyes; psoriatic arthritis, affecting individuals with psoriasis; and acute anterior uveitis, an inflammation of the eye’s middle layer. HLA-B27 functions as a genetic predisposition or a risk factor, rather than a direct cause of these conditions. The precise mechanisms through which HLA-B27 contributes to the development of these diseases remain an active area of research.
Having HLA-B27 Does Not Mean You Will Get Sick
Possessing the HLA-B27 gene does not guarantee that an individual will develop an associated disease. This concept, known as “incomplete penetrance,” means that a significant number of people who carry the HLA-B27 gene never experience related health conditions. For example, while the gene increases the risk for ankylosing spondylitis, only about 5% to 10% of children who inherit HLA-B27 will develop the condition. The development of these conditions is likely influenced by a combination of factors, including other genetic components, environmental triggers, and lifestyle choices.