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Human Leucocyte Antigen B27 (HLA-B27), Interpretations

May 3, 2026Immune systemLab Tests

Human Leucocyte Antigen B27 (HLA-B27), Interpretations

What sample is needed for Human Leucocyte Antigen B27 (HLA-B27)?

  1. The patient’s serum is needed.
  2. A random sample can be taken; no special preparation is needed.

What are the Indications for Human Leucocyte Antigen B27 (HLA-B27)?

  1. To diagnose Ankylosing spondylitis.
  2. HLA B27 is also advised when the patient has:
    1. Joint pain and swelling.
    2. The stiffness of the joints.
  3. HLA Antigen typing may be done in Bone marrow or kidney transplantation.
  4. It is advised for Rheumatoid arthritis variants.
  5. Reiter’s syndrome.
  6. Yersinia enetrocolitis arthritis.

How will you define Human Leucocyte Antigen B27 (HLA-B27)?

  1. White blood cells possess a complex antigen substance, also found in other nucleated cells. It is called the human leukocyte antigen-A  (HLA) system.
  2. HLA-B27 is a specific type of protein found on various body cells.
    1. HLA-B27 presents to T-lymphocytes (CD8+).
  3. It is found on chromosome number 6. Each locus consists of four subloci. Each of these 4 loci contains one gene.
  4. The four major loci are A, B, C, and D. There is a possibility of a fifth, called DR (D-related).
  5. HLA-B27 is quite common. It is associated with ankylosing spondylitis in 90% to 95% of Europeans and 50% of African Americans.
    1. 50% of African Americans have this antigen.
  6. Reiter’s syndrome is positive in 80% to 90% of Europeans and 35% of African Americans.

How will you describe the pathophysiology of Human Leucocyte Antigen B27 (HLA-B27)?

  1. HLA B27 was discovered in 1972 and is associated with ankylosing spondylitis.
  2. The major histocompatibility antigen in humans is a class of surface antigens on white cells known and HLA (human leukocyte antigen).
  3. These are present in nucleated cells and platelets and are most commonly detected in lymphocytes.
  4. HLA-Ag is present in minimal concentration due to the absence of expression on the RBCs.
  5. These antigens are labeled HLA-A, HLA-B, HLA-C, and HLA-D.
    1. The presence or absence of these genes is present on chromosome 6.
  6. HLA-B27 is found in 90% of patients with ankylosing spondylitis.
    1. HLA-B27 is also present in the normal population in 5% to 7%.
    2. HLA-B27 is also found in other diseases like Reiter’s syndrome, Anterior uveitis, and Graves’ disease.

What is the distribution of HLA-B27 in various diseases?

HLA antigen B27 positive  Risk of developing the disease
  • Ankylosing spondylitis
  • 90 times (80% to 90%)
  • Anterior uveitis
  • 15 times (19% to 88%)
  • Reiter’s syndrome
  • 40 times (80%)
  • Septic arthritis (Yersinia enterocolitica  arthritis)
  • 20 times
  • Normal population
  • 5% to 7%

What is the structure of the HAL-Antigen Class-1 molecule (HLA-Ag)?

  1. Class-1 molecules (antigens) are composed of a single polypeptide chain with 3 domains very similar to the domain of the immunoglobulin heavy chain, and there is one transmembrane domain.
  2. Class-1 molecules are embedded as transmembrane proteins in the cell membrane; each is non-covalently associated with a single molecule of β2-microglobulin.
  3. HLA-antigen is distributed on:
    1. All nucleated cells.
    2. Platelets.
    3. Minimal to absent amount on RBCs.
HLA-B27 structure

HLA-B27 structure

What is the importance of HLA-B27?

  1. HLA-B27 is associated with autoimmune diseases.
  2. It is associated with ankylosing spondylitis, reactive arthritis, and psoriatic arthritis, Enetropathic arthritis, and acute anterior uveitis.

What is the mechanism of the diseases caused by HLA-B27?

  1. It is not understood, but there are a few hypotheses, such as:
    1. Molecular mimicry occurs when the immune system is confused after infection.
    2. Abnormal immune system activation after chronic infection.
    3. Misfolding of HLA-B27 triggers the inflammation.

What is the presentation of Ankylosing Spondylitis (AS)?

  1. The prominent features of the AS are:
    1. It primarily involves the spine and sacroiliac joints.
    2. Peripheral joint arthritis is present in about 30% of cases.
    3. You can see iritis in 30% to 40% of the cases.
    4. The incidence of AS is less in African Americans than in Europeans.
  2. Males are more affected than females.
  3. ESR is typically raised in 80% to 90% of cases in active disease.
  4. There may be mild anemia.
  5. HLA-B27 is positive in about 90% of cases.
Ankylosing spondylitis presentation

Ankylosing spondylitis presentation

What is the normal Human Leucocyte Antigen B27?

  • HLA-B27 is negative.

Where will you see Positive Human Leucocyte Antigen B27?

  1. Ankylosing spondylitis.
    1. In close relatives of the patients, it is found with increased frequency.
  2. Reiter syndrome.
  3. Grave’s disease.
  4. Anterior uveitis.
  5. Chronic active hepatitis.
  6. Multiple sclerosis.
  7. Myasthenia gravis.
  8. Psoriasis.
  9. Rheumatoid arthritis.
  10. Celiac disease.
  11. Juvenile diabetes.
  12. Hemochromatosis.

How will you diagnose Ankylosing spondylitis?

  1. HLA-B27 may be advised as supportive, not diagnostic.
  2. ESR/CRP indicates active inflammation.
  3. Rheumatoid arthritis is negative.
  4. MRI detects sacroillitis.

Questions and answers:

Question 1: HLA B-27 to which class of HLA system belong to?

Question 2: What is the distribution of HLA class 1 molecule?
Possible References Used
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