Microbes that live in the lungs can spur tumour growth by triggering inflammation, studies in mice have shown.

Lung cancer has been linked to inflammation, but the details of that association have remained unclear. To investigate this, Tyler Jacks at the Massachusetts Institute of Technology in Cambridge and his colleagues studied mice that were genetically engineered to grow tumours similar to lung adenocarcinoma, a common form of human lung cancer. The researchers found that the types of lung microbes, as well as their abundance, differed between tumour-ridden mice and mice that were cancer free.

The microbes in the cancerous mice boosted the animals’ levels of gamma delta T cells — a type of immune cell — that produce the inflammatory protein IL-17. This increase was not seen in ‘germ-free’ mice that had been raised in sterile environments, further suggesting that microbes caused the spike in inflammatory T cells. Inhibition of the IL-17-producing T cells slowed tumour growth.