What is the relationship between HLA-B27 and ankylosing spondylitis?

HLA-B27 is a subtype of human leukocyte antigen (HLA), a genetically inherited marker primarily used in the evaluation and diagnosis of ankylosing spondylitis. The following provides a detailed analysis:

HLA-B27 is a specific allele located at the HLA-B locus on the surface of human leukocytes and belongs to the class I major histocompatibility complex (MHC) antigens. As a genetically inherited component involved in immune regulation, HLA-B27 testing detects the presence of this specific gene sequence on chromosomes. It is primarily employed to assess and diagnose spondyloarthritis—particularly ankylosing spondylitis.

In patients with ankylosing spondylitis, the prevalence of HLA-B27 positivity is significantly higher than in the general population. HLA-B27 testing is one of the most commonly used diagnostic markers for ankylosing spondylitis and serves as a highly specific indicator for this condition. However, a positive HLA-B27 result alone is insufficient for definitive diagnosis of ankylosing spondylitis; it should be interpreted as a supportive, rather than conclusive, diagnostic reference.

Although HLA-B27 exhibits a strong association with ankylosing spondylitis, not all individuals who test positive for HLA-B27 will develop the disease. The pathogenesis of ankylosing spondylitis involves multiple factors—including genetic predisposition (beyond HLA-B27), infections, environmental influences, and immune dysregulation. Therefore, diagnosis requires comprehensive integration of clinical manifestations, HLA-B27 test results, and additional diagnostic evaluations. Characteristic clinical features include morning stiffness in the lower back, heel pain, enthesitis (inflammation at sites of tendon or ligament insertion into bone), uveitis, and iridocyclitis.