Rheumatoid arthritis is a long-lasting autoimmune disease that mainly attacks the joints.
It happens when the immune system, which normally protects the body from infections, mistakenly attacks healthy tissue and causes pain, swelling and stiffness.
Scientists have long wondered why this immune attack begins. Research from the University of Colorado and other institutions suggests that certain bacteria living in the gut may help trigger rheumatoid arthritis in some people who are already at higher risk.
The human gut contains trillions of bacteria and other tiny organisms. Most are harmless or helpful, but changes in this community can affect the immune system because the gut and immune system constantly communicate with each other.
To investigate this possible connection, researchers studied people who were considered at risk of developing rheumatoid arthritis. These participants had certain antibodies in their blood that can appear years before the first obvious symptoms of the disease.
The scientists used these antibodies together with stool samples from the participants. This allowed them to search for gut bacteria that were being recognized and attacked by the immune system.
The team eventually identified bacteria that appeared to attract an unusually strong immune response. They then tested whether these bacteria could actually contribute to arthritis rather than simply being present in people who were already at risk.
In experiments using animals, the researchers introduced the bacteria and watched what happened. The animals developed some of the same blood markers seen in people with rheumatoid arthritis, and some also developed arthritis-like disease.
This result provided important evidence that the bacteria might help start the disease process. It does not mean that a single type of gut bacteria causes every case of rheumatoid arthritis, because genetics, smoking, environmental exposures and other factors can also influence a person’s risk.
The researchers found another clue when they examined T cells, important immune cells that help the body decide what to attack. T cells from people with rheumatoid arthritis reacted strongly to the identified bacteria, while cells from healthy people did not show the same response.
This suggests that in susceptible people, the immune system may mistake certain gut bacteria for a threat and launch a powerful response. That reaction could possibly spread beyond the gut and eventually contribute to the immune attack on the joints.
If future studies confirm this process, it could lead to new ways of preventing rheumatoid arthritis before permanent joint damage begins. Scientists might eventually be able to reduce or change the troublesome bacteria, or block the specific immune response they produce.
Such treatments are still a future possibility, however. Researchers need to learn why these bacteria cause problems in some people but not others, whether removing them actually prevents disease, and how treatments could target harmful bacteria without disturbing beneficial microbes in the gut.
People can already reduce some known risks for rheumatoid arthritis, especially by avoiding smoking and maintaining good general health. Regular physical activity, a balanced diet, healthy body weight, adequate sleep and stress management can support overall health, but they cannot guarantee that rheumatoid arthritis will be prevented.
People who have persistent joint swelling, pain or morning stiffness should speak with a health professional. Early diagnosis is important because modern rheumatoid arthritis treatments can reduce inflammation, protect joints from permanent damage and help people maintain normal daily activities.
The study took about five years and depended on volunteers who knew they were at increased risk of rheumatoid arthritis. Their participation allowed researchers to examine biological changes that can happen before the disease becomes fully established.
The research was led by Dr. Kristine Kuhn and was published in Science Translational Medicine. The findings add to growing evidence that the gut and immune system are closely connected and may eventually help scientists find ways to stop rheumatoid arthritis before painful joint disease develops.
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