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Human Leucocyte Antigen B27, Histocompatibility Antigen (HLA B-27)

December 18, 2022Immune systemLab Tests

Table of Contents

  • Human Leucocyte Antigen B27
      • Sample for Human Leucocyte Antigen B27
      • Purpose of the test (Indications) for Human Leucocyte Antigen B27
      • Definition of Human Leucocyte Antigen B27
      • Pathophysiology of Human Leucocyte Antigen B27
      • Structure of the HAL-Antigen Class-1 molecule (HLA-Ag):
        • Normal of Human Leucocyte Antigen B27
        • Positive Human Leucocyte Antigen B27 seen in:
      • Questions and answers:

Human Leucocyte Antigen B27

Sample for Human Leucocyte Antigen B27

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

Purpose of the test (Indications) for Human Leucocyte Antigen 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.

Definition of Human Leucocyte Antigen B27

  1. White blood cells possess a complex antigen substance and are also found in other nucleated cells. It is called the human leukocyte antigen-A  (HLA) system.
  2. It is found on chromosome number 6. Each locus consists of four subloci. Each of these 4 loci contains one gene.
  3. The four major loci are labeled as A, B, C, and D. There is the possibility of the fifth one called DR (D-related).
  4. HLA-B27 is quite common. It is associated with ankylosing spondylitis in 90% to 95%.
    1. 50% of African-Americans have this antigen.

Pathophysiology of Human Leucocyte Antigen B27

  1. The major histocompatibility antigen in humans belongs to the presence of these antigens on the surface of white cells and the so-called HLA (human leukocyte antigen).
    1. These are present in the nucleated cells and platelets and are mostly detected in lymphocytes.
    2. HLA-Ag is present in minimal concentration to the absent expression on the RBCs.
  2. These antigens are labeled at HLA- A, B, C, and D.
    1. The presence or absence of these genes is present on chromosome 6.
  3. HLA-B27 is found in 90 % of patients with ankylosing spondylitis.
  4. HLA-B27 is also present in the normal population in 5% to 7 %.
  5. HLA-B27 is also found in other diseases like Reiter’s syndrome, Anterior uveitis, and Grave disease.
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 20 times
Normal people 5% to 7%

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 immunoglobulins 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. Distributed on:
    1. All nucleated cells.
    2. Platelets.
    3. Minimal to the absent amount on RBCs.
Human leucocyte antigen (HLA B-27)

Human leukocyte antigen (HLA B-27)

Normal of Human Leucocyte Antigen B27

  • HLA-B27 is negative.

Positive Human Leucocyte Antigen B27 seen in:

  1. Ankylosing spondylitis.
    1. In close relatives of the patients, it is found in 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.

Questions and answers:

Question 1: HLA B-27 to which class of HLA system belong to?
Show answer
HLA B-27 belongs to HLA class 1 molecule.
Question 2: What is the distribution of HLA class 1 molecule?
Show answer
HLA class 1 molecule is found on nucleated cells like White cells and platelets .

Possible References Used
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