HLA B27 is seen associated with aEUR’
HLA B27 is a human leukocyte antigen class I molecule. It's strongly associated with several autoimmune and inflammatory diseases. The most common one is ankylosing spondylitis. Other conditions include reactive arthritis, psoriatic arthritis, and Behçet's disease. But the primary association is AS.
So the options probably included ankylosing spondylitis. The correct answer would be that. The other options might be other HLA types like B51 for Behçet's, or HLA DR4 for rheumatoid arthritis. Let's structure the explanation. Core concept is the HLA association with AS. Then why correct is right: HLA B27 in AS, pathogenesis involves immune response. Wrong options: other HLA types for other diseases. Clinical pearl: HLA B27 testing in AS. Correct answer is ankylosing spondylitis.
**Core Concept**
HLA-B27 is a class I major histocompatibility complex (MHC) antigen strongly associated with ankylosing spondylitis (AS) and other spondyloarthritides. Its presence increases genetic susceptibility by modulating immune responses via antigen presentation and innate immune pathways.
**Why the Correct Answer is Right**
HLA-B27 is present in **90% of ankylosing spondylitis patients** of European descent. The exact mechanism is unclear, but it likely involves molecular mimicry, misfolding-induced immune activation, and dysregulated T-cell responses. HLA-B27 also links to reactive arthritis, psoriatic arthritis, and Behçet’s disease, but its **strongest association is with AS**.
**Why Each Wrong Option is Incorrect**
**Option A:** *Rheumatoid arthritis* is primarily associated with **HLA-DR4/DR1** (shared epitope hypothesis), not HLA-B27.
**Option B:** *Systemic lupus erythematosus* is linked to **HLA-DR2/DR3**, not HLA-B27.
**Option C:** *IgA nephropathy* has weak HLA associations (e.g., HLA-B8), but **no strong HLA-B27 connection**.
**Clinical Pearl / High-Yield Fact**
Ankylosing spondylitis is a **HLA-B27–associated seronegative spondyloarthropathy**. Remember: **B27 = back pain + bamboo spine**. Always test for HLA-B27 in patients with chronic axial inflammation and family history.
**Correct Answer: D. Ankylosing spondylitis**