Human Leucocyte Antigen B27, Histocompatibility Antigen (HLA B-27)
Human Leucocyte Antigen B27
Sample for HLA-B27
- The patient serum is needed.
- The random sample can be taken, no special preparation is needed.
Purpose of the test (Indications)
- To diagnose Ankylosing spondylitis.
- HLA B27 is also advised when the patient has:
- Joint pain and swelling.
- The stiffness of the joints.
- HLA Antigen typing may be done in Bone marrow or kidney transplantation.
Definition of HLA-B27
- White blood cells possess a complex antigen substance and it is also found in other nucleated cells. It is called the human leukocyte antigen-A (HLA) system.
- It is found on chromosome number 6. Each locus consists of four subloci. Each of these 4 loci contains one gene.
- The four major loci are labeled as A, B, C, and D. There is the possibility of the fifth one called DR (D-related).
- HLA-B27 is quite common. It is associated with ankylosing spondylitis in 90% to 95%.
- 50% of African-Americans have this antigen.
Pathophysiology of Human Leucocyte Antigen B27
- 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).
- These are present in the nucleated cells, platelets and mostly detected on lymphocytes.
- HLA-Ag is present in minimal concentration to the absent expression on the RBCs.
- These antigens are labeled at HLA- A, B, C, and D.
- The presence or absence of these genes is present on chromosome 6.
- HLA-B27 is found in 90 % of patients with ankylosing spondylitis.
- HLA-B27 is present in the normal population as well in 5% to 7 %.
- 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):
- Class-1 molecules (antigens) are composed of a single polypeptide chain that has 3 domains very similar to the domain of the immunoglobulins heavy chain, and there is one transmembrane domain.
- Class-1 molecules are embedded as transmembrane proteins in the cell membrane, and each is noncovalently associated with a single molecule of β2-microglobulin.
- Distributed on:
- All nucleated cells.
- Minimal to the absent amount on RBCs.
- HLA-B27 is negative.
Positive HLA-B27 seen in:
- Ankylosing spondylitis.
- In close relatives of the patients, it is found in increased frequency.
- Reiter syndrome.
- Grave’s disease.
- Anterior uveitis.
- Chronic active hepatitis.
- Multiple sclerosis.
- Myasthenia gravis.
- Rheumatoid arthritis.
- Celiac disease.
- Juvenile diabetes.