Rheumatoid arthritis is a long-term autoimmune disease in which the immune system mistakenly attacks healthy tissue around the joints.
It can cause pain, swelling and stiffness, and over time it may damage cartilage and bone and make everyday movement more difficult.
Scientists still do not know exactly why rheumatoid arthritis begins. Genes can increase a person’s risk, but environmental factors also appear to matter, and growing evidence suggests that some of those triggers may come from microbes living in the mouth or gut.
Researchers led by the University of Colorado Anschutz Medical Campus have identified a strain of gut bacteria that may help start rheumatoid arthritis in some people who are already at risk. The study was published in 2022 in the journal Science Translational Medicine and involved researchers from several institutions.
The team studied people who had certain antibodies in their blood that are strongly linked to rheumatoid arthritis, even though some had not yet developed the disease. These antibodies can appear years before the joint pain and swelling that normally lead to a diagnosis.
Researchers used antibodies taken from these participants to find out which gut bacteria the immune system was recognizing. Their work led them to a strain of bacteria from the genus Subdoligranulum, later called Subdoligranulum didolesgii.
The discovery was important because the immune response did not appear to be random. Immune cells from people with rheumatoid arthritis reacted more strongly to one particular strain of the bacterium than cells from people without the disease.
The scientists then tested the bacterium in mice to investigate whether it could actually contribute to arthritis rather than simply being present alongside the disease. Mice exposed to one strain developed immune changes associated with rheumatoid arthritis, and some developed inflammation in their joints.
The experiments suggested that both B cells and T cells, two important parts of the immune system, were involved. The bacterium appeared to stimulate immune activity in the gut that eventually affected the joints, providing a possible explanation for how a disease of the joints could begin somewhere else in the body.
The finding fits with a broader idea known as the gut-joint connection. The human intestine contains trillions of microorganisms, most of which are harmless or helpful, but changes in this community may sometimes disturb the immune system and contribute to autoimmune disease.
This does not mean that rheumatoid arthritis is simply an infection or that everyone carrying this bacterium will develop the disease. The researchers believe it may be one trigger among many, and its effects may be important only in people with the right combination of genetic and immune risk factors.
If future studies confirm the connection, the discovery could eventually lead to new ways of preventing rheumatoid arthritis. Doctors might one day be able to identify high-risk people and target harmful bacteria or the immune responses they produce before permanent joint damage begins.
However, that possibility is still being investigated. There is currently no proven antibiotic, probiotic, special diet or other gut treatment that can prevent rheumatoid arthritis by eliminating this bacterium, so people should not try to treat themselves based on these findings.
Some established steps can still reduce overall risk or support health. Smoking is one of the strongest preventable risk factors for rheumatoid arthritis, so avoiding tobacco is particularly important, while regular exercise, healthy food and maintaining a suitable weight can support joint and general health.
People who develop persistent swelling, pain or morning stiffness in several joints should seek medical advice. Early diagnosis matters because modern rheumatoid arthritis medicines can control inflammation, reduce symptoms and greatly lower the risk of lasting joint damage.
The study adds an important piece to the puzzle of how rheumatoid arthritis may begin. By understanding the conversation between gut bacteria and the immune system, researchers hope they can eventually stop that harmful process before arthritis takes hold.
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