Gut-Residing Bacteria and Arthritis: What's the Link?

What causes rheumatoid arthritis? As with other autoimmune disorders, it likely has a strong genetic component. But not everyone with the genes for arthritis develops. Clearly, there needs to be a trigger of some kind. Now researchers believe they've discovered one of the triggers of arthritis after completing a study using mice.

The scientists, from Harvard Medical School and New York University, bred two groups of mice that are known to develop a severe form of arthritis. One group was kept in a sterile environment free of any germs, and the other was put into an environment with a variety of naturally occurring bacteria. During the study the mice's blood was tested, and the mice in the sterile environment were found to have much lower levels of the antibodies that cause arthritis.

When the mice were three weeks old, some were transferred from the sterile environment into one laden with naturally occurring germs. Those mice also were injected with a single type of bacteria that normally occurs in the gut. The transplanted mice not only produced more antibodies than the mice that had been in the bacteria-laden environment all along, they also rapidly developed rheumatoid arthritis. In fact, it took just four days for the disease to manifest itself. The researchers explained that the bacteria itself isn't what causes the mice to develop the disease; rather, the presence of the bacteria triggers a sequence of events that ultimately triggers the antibody production in susceptible mice.

One of the most surprising findings of the study was that even a single species of bacteria in the gut can affect the autoimmune disease process in bodily tissues far away from the gut. While autoimmune diseases affecting the gastrointestinal tract have been linked to gut bacteria, the researchers in this study were pioneers in demonstrating that gut bacteria can have a major impact on various other parts of the body. The study team plans to further its knowledge by looking at the connection between bacteria in the gut and other autoimmune diseases such as type 1 diabetes.



Harvard Medical School,

Cleveland Clinic,