From lung to gut

Respiratory infection with influenza virus induces gastroenteritis-like symptoms, such as nausea, vomiting and diarrhea, especially in young children. In The Journal of Experimental Medicine, Wang et al. show that during infection of mice with influenza virus, CCR9⁺CD4⁺ T cells from the respiratory mucosa migrate to the intestinal mucosa, where they cause changes in the intestinal microbiota and induce immunological injury. Influenza virus is not detected in the small intestine during intranasal infection, but lung-derived interferon-γ-producing CD4⁺ cells are recruited to the intestine in a manner dependent on the chemokine CCL25 and its receptor CCR9; there, they induce changes in the composition of intestinal microbiota. In turn, the imbalance of the microbiota causes intestinal injury through a process dependent on polarization to the T_H17 subset of helper T cells and production of interleukin 17A (IL-17A). Intragastric infection with influenza virus does not cause intestinal injury, which demonstrates that these effects are truly secondary to the lung pathology.

J. Exp. Med. 211, 2397–2410 (2014)