Human Leucocyte Antigen B27 (HLA B27), Interpretations

Table of Contents

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

White blood cells possess a complex antigen substance 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 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% of Europeans and 50% of African Americans.
1. 50% of African Americans have this antigen.
Reiter’s syndrome is positive in 80% to 90% of Europe and 35% of African Americans.

HLA B27 was discovered in 1972 and is associated with ankylosing spondylitis.
The major histocompatibility antigen in humans belongs to 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 due to the absence of expression on the RBCs.
These antigens are labeled at HLA- A, B, C, and D.
1. 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 also present in the normal population in 5% to 7%.
HLA-B27 is also found in other diseases like Reiter’s syndrome, Anterior uveitis, and Grave 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%

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.
Class-1 molecules are embedded as transmembrane proteins in the cell membrane; each is non-covalently associated with a single molecule of β2-microglobulin.
HLA-antigen is distributed on:
1. All nucleated cells.
2. Platelets.
3. Minimal to the absent amount on RBCs.

Human Leucocyte Antigen B27: HLA-B27 structure

The prominent features of the AS are:
1. It primarily involves the spine and sacroiliac joints.
2. There is peripheral joint arthritis present in about 30% of the 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 Europe.
Males are more affected than females.
ESR is typically raised in 80% to 90% of the cases in active disease.
There may be mild anemia.
HLA B27 is positive in about 90% of the cases.

Ankylosing spondylitis presentation

Ankylosing spondylitis.
1. 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.
Psoriasis.
Rheumatoid arthritis.
Celiac disease.
Juvenile diabetes.
Hemochromatosis.

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

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