Human leukocyte antigens (HLA) are proteins that help the body's immune system differentiate between its own cells and foreign, harmful substances. The HLA-B27 protein, located on the surface of white blood cells, has been linked to the development of spondyloarthropathies, a group of inflammatory diseases including ankylosing spondylitis.
The major histocompatibility complex (MHC) present in all vertebrates is known as the human leukocyte antigen system or HLA. The molecules that make up the MHC are found on the surface of the cells that make up our tissues and are encoded by genes located on chromosome 6. MHCs are the most polymorphic proteins and are involved in antigen presentation to a type of immune cell known as cytotoxic T cells. MHC binds to fragments of pathogen-derived proteins and displays these peptides on its surface to cytotoxic T cells and activates the immune system response.
We have more than 200 genes coding for MHC proteins (HLA in humans) that can be divided into two groups: class I and class II. There are three main types of MHC class I molecules called A, B and C that are expressed in most cells in the body. B27 is one of the most common B alleles in Europeans. The rs4349859 single nucleotide polymorphism (SNP) genotype is considered a genetic marker of HLA-B27-positive individuals of Caucasian ancestry; it is not correlated in African or Asian populations.
The HLA-B27 test is a serological test to detect the HLA-B27 protein located on the surface of white blood cells. The presence of the HLA-B27 antigen is associated with the development of spondyloarthropathies, a group of inflammatory diseases that typically affect the axial skeleton and include, among others, ankylosing spondylitis (AS). Together with rheumatoid arthritis, they are the two most common rheumatic-type diseases in the general population, with a prevalence of AS for the European population of 0.23%.
In addition, the presence of HLA-B27 is related to the appearance of other pathologies, mainly autoimmune disorders such as reactive arthritis, psoriatic arthropathy, juvenile rheumatoid arthritis and enteropathic arthritis.
Therefore, early detection of HLA-B27-positive patients is of paramount importance, as this will make it possible to take precautions aimed at prevention and/or to apply more effective and earlier treatments.
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