Rheumatoid arthritis, or RA, is an autoimmune disease that affects one in 100 people worldwide with symptoms such as inflamed, painful, and swollen joints, primarily in the hands and wrists. RA can lead to loss of joint function, joint damage, joint deformities, and chronic pain. While the cause of RA is still unknown, a recently published study found that bacteria in the human gut may play an important role.

Unlike degenerative joint conditions like osteoarthritis, RA develops when the body’s antibodies, the cells that protect against bacteria and virus, attacks the joints instead. Scientists have struggled for years to find the origins of these RA antibodies. The fact that some of them start to form around the mouth, lungs, and intestines years before a patient experiences RS symptoms provided a clue for the new study.

Researchers in the study, published in Science Translational Medecine, hypothesized that bacteria found in the microbiome, microorganisms that live in the intestines, could be responsible for the RA antibodies found in areas of the body commonly associated with the gut. They believed that these antibodies were formed to attack bacteria in the digestive system but instead managed to bypass the intestinal “firewall” and spread to the joints.

The team exposed bacteria in the feces of people at risk for developing rheumatoid arthritis to these antibodies and the results were in line with their hypothesis. A new species of gut bacteria (which they named Subdoligranulum didolesgii) was found in approximately 20% of the study’s subjects. The study also found that Subdoligranulum didolesgii can activate T cells, specialized immune cells associated with inflammation and linked to other autoimmune disorders, in RA patients.

The new bacteria species has not been detected in healthy people, and it’s currently unknown how widespread it is within the general population or why RA patients develop an intestinal immune response to it. Researchers tested and confirmed their theory that the immune response itself was allowing RA antibodies to escape the gut and attack the joints.

Next, the research team wants to find how prevalent this new species is in the general population, how we can stop it from spreading, and hopefully, reduce the number of people suffering from rheumatoid arthritis.