Brushing your teeth, flossing, and rinsing regularly helps you maintain a healthy smile, and ward off gum disease. The accumulation of mouth bacteria not only affects your oral health, but also your joint health. A recent study in Science Translational Medicine found bacteria that causes gum disease may also trigger the onset of inflammation in rheumatoid arthritis (RA).

“This research may be the closest we’ve come to uncovering the root cause of RA,” said Maximilian Konig, lead author, and a former Johns Hopkins scientist now at Massachusetts General Hospital, in a statement.

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RA is an autoimmune condition where the body's immune cells attack the joints, which typically starts with the small joints of the hands and feet, causing inflammation, swelling, pain and stiffness. Researchers have noted a biological connection between RA and gum disease, a bacterial inflammatory disease. Previous research has found tooth loss, a marker for gum disease, may predict RA and its severity. The researchers noted the more teeth lost, the greater their risk for joint inflammation.

However, little is known about the specific bacteria in gum disease that may trigger the autoimmune inflammation.

An international team of researchers sought to examine whether RA had a possible bacterial cause, and whether these bacteria could come from the mouth. Blood samples were collected from over 100 people with gum disease and 100 healthy people. In addition, the samples of fluid from the space between the gums and teeth were obtained from nine of the people with periodontitis, and eight healthy people. The researchers also obtained blood and joint fluid samples from another sample of approximately 200 people who met standard disease criteria for RA.

The composition of the gum fluid was analyzed to see how it differed between healthy people and those with gum disease. Similarities between blood and joint fluid samples of people with RA were also observed.

The findings revealed the gum fluid of people with gum disease contained high levels of citrullinated proteins. Citrullination is a natural protein regulatory process in everyone. However, in patients with RA, the process is overactive, resulting in abnormal levels of citrullinated proteins. They're known to trigger an immune response in people with RA. There were extensive citrullinated proteins in the fluid, and people with RA are often found to produce antibodies against these proteins, known as anti-cyclic citrullinated peptides (anti-CCP).

Researchers also found Aggregatibacter actinomycetemcomitans, a strain of bacteria, seemed to be raising the high levels of citrullinated proteins. A. actinomycetemcomitans   causes high production of citrullinated proteins within a particular type of white blood cell (neutrophil). The bacteria does this by producing a toxin called leukotoxin A (LtxA). This toxin splits open neutrophil cells which releases citrullinated proteins.  

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In people with rheumatoid arthritis, antibodies specifically targeting LtxA were found to be associated with the presence of anti-CCP antibodies.

This suggests the bacteria could trigger the autoimmunity of RA, but this isn't definitive. Not everyone with RA has these antibodies, and not everyone with these antibodies has RA. Moreover, there could be other infective and inflammatory processes that may contribute to the raised levels of citrullinated proteins, other than A. actinomycetemcomitans .

The truth is the onset and evolution of the disease can take decades. Not everyone with gum disease develops rheumatoid arthritis, and not everyone with rheumatoid arthritis has had previous gum disease, or poor dental hygiene.

However, the findings do provide a better understanding of causes of autoimmune disease, like RA, which currently have no definitive cause.

In the meantime, brushing your teeth could help prevent tooth decay, and gum diseases, and potentially RA.

Source: Konig MF,  Abusleme L, Reinholdt J et al. Aggregatibacteractinomycetemcomitans–induced hypercitrullination links periodontal infection to autoimmunity in rheumatoid arthritis. Science Translational Medicine . 2016.

See Also:

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Rheumatoid Arthritis Patients Have Better Chance To ‘Live Valued Life’ Than Two Decades Ago