Flu infection has long-ranging effects

Gastrointestinal symptoms are often seen with flu infection, but because the virus only grows in lung cells, it's unclear how intestinal symptoms develop. Researchers in China now show that flu infection in mice prompts responding immune cells in the lung to alter their homing receptors, causing them to migrate to the gut.

Once there, they produce the antiviral mediator IFN-γ, which alters the natural composition of gut bacteria. In turn, the bacterial changes lead to inflammation that promotes tissue injury and diarrhea. Blocking inflammatory molecules in the intestine or treating mice with antibiotics to deplete bacteria attenuated flu-induced intestinal injury without affecting immune responses in the lung.

Why some flu infected patients develop gastrointestinal symptoms while others do not remains unknown. However, these findings suggest ways to directly relieve intestinal symptoms like diarrhea during flu infection without interfering with the body's ability to fight the virus in the lung.