Gum-disease bacteria may also give cancer a boost

A bacterium that lives in our mouths, sometimes causing gum disease, can also help cancer develop by inhibiting the immune system, scientists have found.
Fusobacterium nucleatum is a common bacterium that lives in our mouths, often without causing any ill effects, although it is also frequently the culprit in gum disease.
Gilad Bachrach at the Hebrew University of Jerusalem, Israel, and his colleagues incubated F nucleatum together with a variety of human tumour cells and natural killer cells, and found that the bacterium inhibited the killer cells' ability to attack cancer.
Researchers also found that a bacterial protein called Fap2 binds to a receptor on the natural killer cells called TIGIT, 'New Scientist' reported.

"By activating this receptor, F nucleatum prevents the killing of cancer cells by the natural killer cells," Bachrach said.
Whether this interaction is a coincidence or a deliberate strategy on the part of the bacterium remains unclear, but the relationship between it and cancer is probably a mutually beneficial one, researchers said.

F nucleatum prefers anaerobic - low-oxygen - environments, and tumours are often precisely that.
"The purpose of this pathogen is not to kill the host; it is to survive. Maybe by preventing these tumours from being killed, the bacterium creates a sheltered niche in which to proliferate," said Yiping Han of Columbia University in New York.

She recently published data suggesting that F nucleatum can also stimulate the growth of colon cancer cells via a different mechanism.