High levels of certain bacteria in the mouth have been associated with features of immune activity that can affect joints in a small study.

Health

February 22, 2023

by clara wilson

Oral bacteria can enter the blood and trigger features of the immune activity involved in rheumatoid arthritis, reinforcing the idea that gum disease may contribute to the painful joint condition.

The study is one of the first to show that the same antibodies that target the joints in rheumatoid arthritis also attack bacteria that live in the gums and reinforces advice that people with the condition should maintain good dental hygiene. , says dana orange at Rockefeller University in New York.

Rheumatoid arthritis is an autoimmune disease, which means that the immune system attacks the body’s tissues. Previous research has found that people with the condition are more likely to have gum disease when the gums are inflamed and sometimes bleed, but it’s not clear why.

In the latest study, Orange and his colleagues followed five people with rheumatoid arthritis, two of whom also had gum disease, asking them to provide weekly blood samples for up to four years. These samples were analyzed for bacterial genetic material, as well as various markers of immune system activity.

Unlike the three people without gum disease, those with the condition had frequent traces of genes from oral bacteria, such as Streptococcus species, in their blood, usually seen every few weeks.

This is likely due to bouts of bleeding gums, Orange says. “As the blood goes out, the bacteria comes in.”

When the bacteria in the mouth peaked, there were also signs of activity from a type of immune cell called monocytes, which are known to be involved in the immune response against joints in arthritis.

Sometimes the researchers also found traces of bacteria that normally live on the skin in the blood samples, but these were not accompanied by immunological activity. This suggests that skin bacteria contaminated the sample while it was being drawn from a participant, Orange says. “We know [the immune system] does not ignore bacteria in the blood; they are usually removed very quickly.”

A second part of the study looked at single blood samples from 73 people, about half of whom had rheumatoid arthritis. A blood test for rheumatoid arthritis looks for antibodies that target a group of proteins with a chemical modification called citrullination. This alteration can happen to any protein, but certain citrullinated proteins are found at elevated levels in the joints of people with rheumatoid arthritis.

In the study, antibodies against citrullinated proteins from those with rheumatoid arthritis also worked against citrullinated proteins produced by mouth bacteria that enter the blood. This suggests that bacteria from the mouth find their way into the blood, triggering immune cells to produce antibodies against the citrullinated proteins, leading to an immune attack on the joints, Orange says.

Although the study was small, paul emery at the University of Leeds, UK, says that taking blood samples from participants every week increases the validity of their results. It is the first to show a correlation between [markers of] flare-ups of rheumatoid arthritis and bacteria in the blood.

Immune activity caused by gum disease has been linked to a growing number of various medical conditions, from heart attacks to Alzheimer’s disease, although different mechanisms and bacteria may be involved. In Alzheimer’s disease, for example, bacteria in the mouth called Porphyromonas gingivalis have been implicated in the condition.

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