Type 3 innate lymphoid cells (ILC3 cells) have been linked to driving colitis. In eLife, Powrie and colleagues offer insight into how the otherwise small population of gut-resident ILC3 cells can exert a disproportionate influence on the immunopathology of colitis. Using two different experimental models of colitis, as well as data from patients with colitis, the authors show that ILC3 cells are important producers of the proinflammatory cytokine GM-CSF. This cytokine serves to recruit inflammatory monocytes, which are critical to the immunopathology of colitis. Under steady-state conditions, ILC3 cells dynamically enter and exit cryptopatches (lymphoid structures within the gut), but during colitis there is net movement of ILC3 cells into adjacent tissues. These findings suggest how ILC3 cells can disseminate potent proinflammatory effects throughout the colon.

eLife (18 January 2016) doi:10.7554/eLife.10066.001