New data on the relationship between autoimmune diseases and an intestinal bacterium
Can the bacteria of our gastrointestinal tract send the wrong "messages" to the body? Researchers at Queen's University in Belfast present new evidence.
Researchers discovered for the first time that a specific bacterium in the gastrointestinal tract produces protein molecules that mimic a human protein, causing the immune system to accidentally attack its own cells. The culpable in this case is called Bacteroides fragilis, a bacterium that lives normally in the human intestine. The research team showed that this bacterium produces a human-like protein that may trigger autoimmune diseases such as rheumatoid arthritis. This protein is called "ubiquitin" and it is essential for the normal cellular processes in our body.
The study, published in the journal Clinical and Experimental Immunology of the British Society of Immunology, is a breakthrough. Protein mimetics confuse our immune system, leading to autoimmune diseases. As it is well known, there are more than 80 different types of autoimmune diseases: rheumatoid arthritis, multiple sclerosis, lupus, etc. Millions of people around the world are suffering from these debilitating and painful conditions, which currently have no cure.
In an autoimmune disease, the immune system mistakenly attacks the body. Antibodies that are part of the immune system usually target bacteria or viruses, but they are poorly oriented in people with autoimmune diseases. Autoantibodies can attack various healthy parts, e.g. in the joints in the case of rheumatoid arthritis.
Sheila Patrick, a professor at Queen's University, explained: "When we mapped the Bacteroides fragilis genome a few years ago, we were surprised by the discovery of a human gene in it, not found in any other bacterium. This gene produces a protein that is almost identical in shape to a human protein that is produced in almost every human cell. When we discovered that Bacteroides fragilis produces large amounts of this protein, we were very excited. It is the unique bacterium that produces a mimic of human ubiquitin in our gut. We immediately wondered if it could be linked to autoimmune diseases such as lupus. It has been known since the 1990s that some people with autoimmune diseases produce antibodies that target their own human ubiquitin, but we do not know why this happens. So, we decided to see if humans have antibodies that target the ubiquitin version of Bacteroides fragilis".
Linda Stewart, a lecturer in the School of Biological Sciences who participated in the study, said: "We have found that some people with autoimmune diseases produce high levels of antibodies against the bacterial ubiquitin. "Now we should investigate if the bacterial ubiquitin triggers the wrong immune response. That way we can detect some autoimmune diseases in time and prevent some of them before they happen".
The next step for the research team is to find out the relationship between the stage of autoimmune disease and the levels of antibodies to the mimetic bacterium in each patient. This could help develop a rapid test that would detect antibodies to bacterial ubiquitin and provide evidence for a person's predisposition to autoimmunity.
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