The cellular sources of IL-9 in lung inflammation remain unknown. Stockinger and colleagues use an IL-9 reporter to show IL-9 production is restricted to innate lymphoid cells during papain-induced lung inflammation. Interleukin 9 (IL-9) is a cytokine linked to lung inflammation, but its cellular origin and function remain unclear. Here we describe a reporter mouse strain designed to map the fate of cells that have activated IL-9. We found that during papain-induced lung inflammation, IL-9 production was largely restricted to innate lymphoid cells (ILCs). IL-9 production by ILCs depended on IL-2 from adaptive immune cells and was rapidly lost in favor of other cytokines, such as IL-13 and IL-5. Blockade of IL-9 production via neutralizing antibodies resulted in much lower expression of IL-13 and IL-5, which suggested that ILCs provide the missing link between the well-established functions of IL-9 in the regulation of type 2 helper T cell cytokines and responses.

IL-9 fate reporter mice established type 2 innate lymphoid cells (ILC2s) as major producers of this cytokine in vivo. Here we focus on the role of IL-9 and ILC2s during the lung stage of infection with Nippostrongylus brasiliensis, which results in substantial tissue damage. IL-9 receptor (IL-9R)–deficient mice displayed reduced numbers of ILC2s in the lung after infection, resulting in impaired IL-5, IL-13, and amphiregulin levels, despite undiminished numbers of Th2 cells. As a consequence, the restoration of tissue integrity and lung function was strongly impaired in the absence of IL-9 signaling. ILC2s, in contrast to Th2 cells, expressed high levels of the IL-9R, and IL-9 signaling was crucial for the survival of activated ILC2s in vitro. Furthermore, ILC2s in the lungs of infected mice required the IL-9R to up-regulate the antiapoptotic protein BCL-3 in vivo. This highlights a unique role for IL-9 as an autocrine amplifier of ILC2 function, promoting tissue repair in the recovery phase after helminth-induced lung inflammation.

Type 2 immune responses are essential in protection against intestinal helminth infections. In this study we show that IL-22, a cytokine important in defence against bacterial infections in the intestinal tract, is also a critical mediator of anti-helminth immunity. After infection with Nippostrongylus brasiliensis, a rodent hookworm, IL-22-deficient mice showed impaired worm expulsion despite normal levels of type 2 cytokine production. The impaired worm expulsion correlated with reduced goblet cell hyperplasia and reduced expression of goblet cell markers. We further confirmed our findings in a second nematode model, the murine whipworm Trichuris muris. T.muris infected IL-22-deficient mice had a similar phenotype to that seen in N.brasiliensis infection, with impaired worm expulsion and reduced goblet cell hyperplasia. Ex vivo and in vitro analysis demonstrated that IL-22 is able to directly induce the expression of several goblet cell markers, including mucins. Taken together, our findings reveal that IL-22 plays an important role in goblet cell activation, and thus, a key role in anti-helminth immunity. Intestinal helminth (worm) infections are some of the most common parasite infections in the world. Immunity to worm infection is dependent on the production of Type 2 cytokines, such as IL-4 and IL-13, and the induction of mucosal defence mechanisms including production of mucus by intestinal goblet cells. Here we show that the cytokine IL-22, which was previously known to be involved in the defence against bacterial infections in the gut, is also involved in the defence against intestinal worms. IL-22 deficient mice are unable to expel the rodent parasites Nippostrongylus brasiliensis and Trichuris muris from their intestines despite the fact that they make strong Type 2 cytokine responses. This inability to expel the worms correlates with a reduction in the number of goblet cells as well as a reduction in intestinal mucins and other goblet cell products. We also demonstrate that IL-22 is able to act directly on goblet cells to stimulate the secretion of mediators such as mucins. Taken together, our data show that IL-22 is a key mediator of anti-helminth immunity in the gut. Furthermore, our data provide additional insight into the pivotal role played by IL-22 in protection against various types of intestinal pathogens.

Parasitic helminths have evolved together with the mammalian immune system over many millennia and as such they have become remarkably efficient modulators in order to promote their own survival. Their ability to alter and/or suppress immune responses could be beneficial to the host by helping control excessive inflammatory responses and animal models and pre-clinical trials have all suggested a beneficial effect of helminth infections on inflammatory bowel conditions, MS, asthma and atopy. Thus, helminth therapy has been suggested as a possible treatment method for autoimmune and other inflammatory disorders in humans.