[The role of HLA-B27 in the pathogenesis and diagnosis of axial spondyloarthritis : 50 years after discovery of the strong genetic association].
BackgroundThe association of the human lymphocyte antigen B27 (HLA-B27) with ankylosing spondylitis (AS), also now called axial spondylarthritis (axSpA), was first described 50 years ago.ObjectiveThis article gives an overview of the available knowledge on the topic.Material and methodsThis is a narrative review based on the experience of the authors.ResultsThe HLA-B27 is a member of the HLA class I family of genes of the major histocompatibility complex (MHC). The prevalence of HLA-B27 in the central European population is approximately 8 %, i.e., the vast majority of carriers of HLA-B27+ remain healthy. The frequency of HLA-B27 shows a decline from north to south. The HLA-B27 explains only 30 % of the genetic burden of axSpA. The prevalence of the disease correlates with the frequency of HLA-B27 in the population, i.e., there are geographic differences. Approximately 60-90 % of patients with axSpA worldwide are HLA-B27+. Some 200 subtypes of HLA-B27 can be differentiated using the polymerase chain reaction (PCR). In Thailand and Sardinia two subtypes were found that are not associated with axSpA. The physiological function of HLA class I molecules is the defence of the organism against microbes. Microbial peptides are presented to the immune system, which can be specifically attacked by CD8+ T‑cells. Genetic polymorphisms of the enzyme endoplasmic reticulum aminopeptidase 1 (ERAP1), which breaks down peptides in the endoplasmic reticulum, are associated only with HLA-B27+ diseases.DiscussionThe pathogenesis of axSpA is unclear but a major hypothesis is that of the arthritogenic peptides. In this it is assumed that potentially pathogenic foreign or autologous peptides can be presented by HLA- B27. If nothing else, HLA-B27 plays an important role in the diagnosis, classification and determination of the severity of axSpA.