Ankylosing spondylitis
Reactive arthritis
Psoriatic arthropathy
Enteropathic arthropathy
Juvenile spondarthritis
Undifferentiated spondarthritis
Isolated peripheral enthesitis
Table 23.2
Extra-articular disease and HLA-B27
Definite or probable association | Possible association | |
|---|---|---|
Ocular Aural Pulmonary Cardiovascular Haematological Renal Endocrine Gastrointestinal Bone Skin Immune system | • Acute anterior uveitis (AAU) • Scieritis (anterior and posterior) • Upper lobe fibrosis • Aortic regurgitation • Cardiac conduction abnormalities • Aortitis, aortic aneurism, aortic dissection • Acute leukemia • IgA nephropathy • Inflammatory bowel disease • Ulcerative colitis • Type II psoriasis • Palmoplantar pustulosis • Attenuation of viral infections – HIV, HCV, influenza, EBV, HSV-2 | • HSV recurrence after corneal graft • Sensorineural hearing loss • Asbestosis, pleurisy, pleural abscess, bronchitis, pneumonia, pneumothorax, sarcoidosis • Myelodysplastic syndrome • Agranulocytosis • Childhood nephritic syndrome • Autoimmune thyroiditis • Cushing’s disease • Osteoporosis • Vitiligo • Increased susceptibility to – Malaria – Tuberculosis |
Table 23.3
Proposed pathogenic mechanisms of action of HLA-B27
1. Thymic selection – Selection of arthritogenic T cells |
2. Arthritogenic peptide – Cytotoxic T cell response to a peptide in joint |
3. Antigen cross reactivity – HLA class II restricted T cells stimulated by bacteria may cross react with HLA-B27 derived peptide presented by host cells |
4. Unique biological properties – May predispose to disease development |
5. Altered self – Unpaired cysteine residue at position 67 |
6. Interaction with microbial superantigens – Although not usual for HLA class I antigens |
7. Molecular mimicry (antibody cross reactivity) – Cross-reactive antibody response between portion of HLA-B27 and bacterial epitope |
8. Receptor hypothesis – Bacteria use HLA-B27 to enter the cell |
9. HLA-B27 misfolding – Leads to pro-inflammatory cytokine production |
Epidemiology
The prevalence of HLA-B27 gene varies geographically by race and by ethnicity. The prevalence of the gene is relatively low around the equator and rises with increase in latitude. It varies from as high as 50 % in Haida Indians in the Pacific Northwest of the United States to 25 % in Eskimos, 20 % in Sardinians, 8 % in UK population, and 3 % in Southern Italy to as low as 0 % in Australian Aborigines [2]. In a 2009 study in the US, HLA-B27 was found in 7.5 % of non-Hispanic whites and 3.5 % among all other US races/ethnicities combined [3].
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