Every hundredth person in Germany suffers from rheumatoid arthritis, women much more often than men. The disease attacks the immune system of the joints. Cause: so far unclear. Now US researchers are finding a connection with periodontal disease – the inflammation of the gums can even trigger arthritis.
Periodontal disease can contribute to rheumatoid arthritis (RA) and may even trigger the autoimmune disease in susceptible people. A US research team has now determined the mechanisms of this long-suspected connection in detail. “The work establishes an immunological connection at a very high and modern level,” says Ulf Wagner, Vice President of the German Society for Rheumatology (DGRh), who was not involved in the study. It is unclear whether better oral hygiene can improve existing joint inflammation.
In Germany, about one percent of adults have rheumatoid arthritis. Women are affected much more often than men. Usually the joint problems – often in fingers, toes, elbows or knees – develop after the age of 50. In the disease, the immune system attacks the joints for reasons that have not yet been clarified.
It has long been suspected that such autoimmune reactions can be caused by infections. Periodontosis, an inflammation of the periodontium, affects almost half of the population and is noticeably common in people with rheumatoid arthritis, writes the team led by immunologist William Robinson from Stanford University in California in the journal Science Translational Medicine.
This means that bacteria from the oral cavity can enter the bloodstream as a result of this permanent inflammation. The fact that arthritis patients with acute gum problems often experience aggravation of the symptoms also speaks in favor of periodontal disease being involved in joint inflammation.
A central involvement of certain antibodies has already been suspected. These so-called ACPAs (Anti-Citrullinated Protein Antibodies) are directed against certain proteins that are altered by enzymes as a result of inflammation – in technical jargon: citrullinated. Such ACPAs often precede the onset of symptoms by years and are associated with a particularly severe course of RA.
In order to clarify a possible connection, Robinson’s team examined blood samples from five RA patients over a period of one to four years – on average, each participant gave 67 samples. After a whole series of analyzes and laboratory tests, the following picture emerges: In people with periodontal disease, oral bacteria – in the women examined it was predominantly streptococci – get into the bloodstream. These bacteria activate different groups of immune cells in the blood. As part of this immune reaction, antibodies can develop that are actually directed against citrullinated proteins in the oral bacteria. However, these ACPAs cross-react with citrullinated proteins in human tissues, causing inflammatory joint disease.
The presence of bacteria from the mouth can trigger immune responses that likely contribute to the development of rheumatoid arthritis over time in susceptible people, the group writes. Since periodontal disease affects 47 percent of the population, but rheumatoid arthritis only 1 percent, additional factors must be involved in the development of the disease.
These factors included certain genetic traits, explains German expert Wagner. The study provides new target structures for the development of drugs through the precise characterization of immune cells involved in the disease.
In addition, according to the Head of Rheumatology at Leipzig University Hospital, oral hygiene in patients with rheumatoid arthritis should now be a greater focus of research. “The study reinforces the need for good oral hygiene, although demonstrating a benefit in rheumatoid arthritis will not be easy to come by.” It is questionable whether oral hygiene can help those patients in whom the autoimmune disease has already broken out.
