Introduction
HLA-B27 is a genetic marker that plays a pivotal role in the immune system. Its presence is strongly associated with several autoimmune diseases, particularly those affecting the spine and joints. Understanding HLA-B27 can help patients and clinicians navigate complex diagnoses and treatment plans.
What Is HLA-B27?
HLA-B27 (Human Leukocyte Antigen B27) is a protein found on the surface of white blood cells. It belongs to the MHC class I family and is responsible for presenting antigens to T cells. This process helps the immune system identify and respond to pathogens — but in some cases, it may trigger autoimmune reactions.
Diseases Associated with HLA-B27
HLA-B27 is linked to a group of inflammatory conditions known as seronegative spondyloarthropathies:
| Disease | HLA-B27 Positivity Rate |
| HLA-B27 Positivity Rate | ~90% |
| Reactive Arthritis | 60–80% |
| Psoriatic Arthritis (Axial) | 20–50% |
| Enteropathic Arthritis | 50–70% |
These conditions often involve chronic inflammation of the spine, sacroiliac joints, and entheses (where tendons attach to bone).
HLA-B27 Testing: What You Need to Know
- Purpose: Supports diagnosis when symptoms suggest autoimmune inflammation
- Result Interpretation:
- Positive: Indicates increased risk for certain autoimmune diseases
- Negative: Does not rule out disease
Important: Many people with HLA-B27 never develop autoimmune conditions. Its presence should be interpreted alongside clinical symptoms and imaging.
Pathophysiology: Why HLA-B27 Matters
Researchers propose several mechanisms for HLA-B27’s role in autoimmunity:
- Misfolding Hypothesis: Misfolded HLA-B27 proteins may trigger cellular stress and inflammation.
- Molecular Mimicry: Pathogens may resemble HLA-B27, leading to immune cross-reactivity.
- Altered Peptide Presentation: HLA-B27 may present self-peptides that activate autoreactive T cells.
These mechanisms are under active investigation and may guide future therapies.
Clinical Use and Limitations
- Prognostic Tool: May predict disease severity or progression
- Treatment Decisions: Does not directly influence therapy but supports comprehensive evaluation
Conclusion
HLA-B27 is a powerful genetic clue in the diagnosis of autoimmune diseases. While not a standalone diagnostic tool, its presence can guide clinicians toward more accurate assessments and personalized care. As research evolves, HLA-B27 continues to unlock new insights into immune system behavior.
Sources: NIH, American College of Rheumatology