Our immune system does an awesome job (most of the time) of fighting off pathogenic bacteria and viruses. But to fight off these pathogens, the body needs to know that they are the bad guys. This is where the HLA system comes in.
This article covers background information on HLA-B27 and the genetic variants available in 23andMe or AncestryDNA data.
What is the HLA system?
Human leukocyte antigens (HLA) belong to part of our immune system known as the major histocompatibility complex (MHC). The HLA genes code for the proteins that help our body determine what is a foreign invader that needs to be attacked and what is ‘self’.
There are many different HLA serotypes that people can have, giving us all slightly different strengths and weaknesses against microbial diseases. But along with attacking foreign invaders, a handful of HLA types also increase the susceptibility to autoimmune diseases, where the body attacks its own cells.
HLA-B27 links to the susceptibility to inflammatory-related autoimmune diseases include:
- ankylosing spondylitis[ref]
- reactive arthritis
- inflammatory bowel disease[ref]
- acute anterior uveitis (inflammation of the eye)[ref]
Post-infectious syndrome for shigellosis, salmonella, and chlamydia is more common in HLA-B27 positive.
What is ankylosing spondylitis (AS)?
Ankylosing spondylitis is a chronic inflammatory disease that mainly affects the spine. It causes back pain and spinal stiffness, and the vertebrae can fuse together. This often occurs in young adults. More info can be found on the Spondylitis Association of America site. Carriers of HLA-B27 are at a 20-fold risk for the disease.
Why is HLA-B27 linked to autoimmune diseases?
There are multiple subtypes of HLA-B27, and the specific types associated with ankylosing spondylitis include HLA-B*2701, HLA-B*2702, HLA-B*2704, HLA-B*2705, and HLA-B*2707.
Not everyone who carries the HLA-B27 serotype will have ankylosing spondylitis, but over 95% of people with AS carry HLA-B27. Similarly, over 80% of people with reactive arthritis are HLA-B27 positive.[ref] Therefore, the HLA-B27 serotype is a big risk factor for these autoimmune diseases, but it doesn’t cause the autoimmune disease by itself. Instead, there must be other factors involved – environmental, pathogens, gut microbiome, diet?[ref]
Proteins in the body, including the HLA proteins, are made up of amino acids that join together and then fold up in a particular way. Researchers have found that HLA-B27 has a tendency to misfold. The specific subtypes of HLA-B27 associated with autoimmune diseases are the ones likely to be misfolded or unfolded, causing problems when formed in the endoplasmic reticulum (ER). The misfolded or unfolded proteins in the ER cause stress in that organelle, possibly causing inflammation due to an unfolded protein response mechanism.[ref]
HLA-B27 and immune system:
At one point, researchers advanced a theory that HLA-B27 seemed similar to an infecting bacterial pathogen and thus caused autoimmune diseases. The idea is called ‘molecular mimicry’ and the idea reasons the immune system attacks ‘self’ thinking it is a bacteria. (Some nice YouTube videos explaining ankylosing spondylosis state that this is the reason for it…) The problem is newer research shows that you can create AS in an animal model without the T-cells needed for attacking a pathogen, so there is a lot of uncertainty as to whether this is actually a cause of AS.[ref][ref]
Genetic variants included in 23andMe data coding for HLA-B27 are listed below. These variants show if you are likely to carry an HLA-B27 type. There are several subtypes of HLA-B27 and not all of them cause a higher risk of inflammatory autoimmune diseases. A blood test is still needed to be 100% certain that you carry the HLA-B27 type associated with autoimmune diseases.
Check your genetic data for rs4349859(23andMe v5 only; AncestryDNA):
- A/A: high likelihood of carrying 2 copies of HLA-B27[ref][ref][ref]
- A/G: high likelihood of carrying 1 copy of HLA-B27
- G/G: typical
Members: Your genotype for rs4349859 is —.
Check your genetic data for rs13202464 (23andMe v4,v5; AncestryDNA):
- G/G: high likelihood of carrying 2 copies of HLA-B27[ref][ref][ref]
- A/G: high likelihood of carrying 1 copy of HLA-B27
- A/A: typical
Members: Your genotype for rs13202464 is —.
Keep it in perspective:
Don’t freak out if you are a carrier of HLA-B27.
In Caucasians, about 10% of people carry one copy, whereas only ~1% of African populations carry HLA-B27.[ref]
If you want to get the blood test for HLA-B27 and you can’t get it through your doctor, you can order it on your own in the US. UltaLab Tests is one place that I use. There are other websites as well, so shop around for the best price.
Although HLA-B27 increases the risk of ankylosing spondylosis by 20-fold, it is still a rare disease with about 1 in 2000 people having it.[ref] If you have the HLA-B27 serotype, the lifetime absolute risk is about 6%.[ref] There are other genetic variants thought to be involved in the risk for ankylosing spondylosis, as well as environmental factors.[ref]
There is also a connection between HLA-B27 and changes to the gut microbiome.[ref] Interestingly, spondylitis patients also showed changes in the gut microbiome with decreased F. prausnitzii and increased Bacteroides fragilis.[ref] You may want to consider getting a gut microbiome test to see if everything is in order down there.
Animal studies show that Lactobacillus G/G probiotics may help with preventing recurrence of inflammatory bowel problems associated with HLA-B27.[ref] Although I couldn’t find a human clinical trial on it, if you are wanting to try a Lactobacillus G/G probiotic, Culturelle contains that strain.
Autoimmune Paleo (AIP) diet:
The link between diet and symptoms of reactive arthritis or ankylosing spondylitis isn’t clear. A meta-study looked at a bunch of studies on the subject and found no statistical links with diet. On the contrary, individuals report that diet can make a difference in their joint pain with certain foods making it worse. So trying an elimination diet or the autoimmune protocol diet may be worthwhile.
Related Genes and Topics:
CTLA-4 – General Autoimmune Risk Factor
The CTLA4 gene codes for a protein that is important in the immune system. It acts as a checkpoint that can downregulate your immune system response. Genetic variants in the CTLA4 gene can increase your risk for several different autoimmune diseases.
Psoriasis is an autoimmune condition that causes dry, sometimes itchy patches of skin. It is caused by the immune system attacking your skin cells, speeding up the turnover of the cells. Genetics plays a role in your susceptibility
Originally published 07/2018. Updated 1/2020.