Katherine J. Guild

Epithelial-cell-intrinsic IKK-β expression regulates intestinal immune homeostasis

Intestinal epithelial cells (IECs) provide a primary physical barrier against commensal and pathogenic microorganisms in the gastrointestinal (GI) tract, but the influence of IECs on the development and regulation of immunity to infection is unknown. Here we show that IEC-intrinsic IκB kinase (IKK)-β-dependent gene expression is a critical regulator of responses of dendritic cells and CD4+ T cells in the GI tract. Mice with an IEC-specific deletion of IKK-β show a reduced expression of the epithelial-cell-restricted cytokine thymic stromal lymphopoietin in the intestine and, after infection with the gut-dwelling parasite Trichuris, fail to develop a pathogen-specific CD4+ T helper type 2 (TH2) response and are unable to eradicate infection. Further, these animals show exacerbated production of dendritic-cell-derived interleukin-12/23p40 and tumour necrosis factor-α, increased levels of CD4+ T-cell-derived interferon-γ and interleukin-17, and develop severe intestinal inflammation. Blockade of proinflammatory cytokines during Trichuris infection ablates the requirement for IKK-β in IECs to promote CD4+ TH2 cell-dependent immunity, identifying an essential function for IECs in tissue-specific conditioning of dendritic cells and limiting type 1 cytokine production in the GI tract. These results indicate that the balance of IKK-β-dependent gene expression in the intestinal epithelium is crucial in intestinal immune homeostasis by promoting mucosal immunity and limiting chronic inflammation.

Interleukin 25 regulates type 2 cytokine-dependent immunity and limits chronic inflammation in the gastrointestinal tract

The cytokine interleukin (IL) 25 has been implicated in the initiation of type 2 immunity by driving the expression of type 2 cytokines such as IL-5 and IL-13, although its role in the regulation of immunity and infection-induced inflammation is unknown. Here, we identify a dual function for IL-25: first, in promoting type 2 cytokine-dependent immunity to gastrointestinal helminth infection and, second, in limiting proinflammatory cytokine production and chronic intestinal inflammation. Treatment of genetically susceptible mice with exogenous IL-25 promoted type 2 cytokine responses and immunity to Trichuris. IL-25 was constitutively expressed by CD4+ and CD8+ T cells in the gut of mouse strains that are resistant to Trichuris, and IL-25–deficient mice on a genetically resistant background failed to develop a type 2 immune response or eradicate infection. Furthermore, chronically infected IL-25−/− mice developed severe infection-induced intestinal inflammation associated with heightened expression of interferon-γ and IL-17, identifying a role for IL-25 in limiting pathologic inflammation at mucosal sites. Therefore, IL-25 is not only a critical mediator of type 2 immunity, but is also required for the regulation of inflammation in the gastrointestinal tract.

TSLP regulates intestinal immunity and inflammation in mouse models of helminth infection and colitis

Intestinal epithelial cells (IECs) produce thymic stromal lymphopoietin (TSLP); however, the in vivo influence of TSLP–TSLP receptor (TSLPR) interactions on immunity and inflammation in the intestine remains unclear. We show that TSLP–TSLPR interactions are critical for immunity to the intestinal pathogen Trichuris. Monoclonal antibody–mediated neutralization of TSLP or deletion of the TSLPR in normally resistant mice resulted in defective expression of Th2 cytokines and persistent infection. Susceptibility was accompanied by elevated expression of interleukin (IL) 12/23p40, interferon (IFN) γ, and IL-17A, and development of severe intestinal inflammation. Critically, neutralization of IFN-γ in Trichuris-infected TSLPR−/− mice restored Th2 cytokine responses and resulted in worm expulsion, providing the first demonstration of TSLPR-independent pathways for Th2 cytokine production. Additionally, TSLPR−/− mice displayed elevated production of IL-12/23p40 and IFN-γ, and developed heightened intestinal inflammation upon exposure to dextran sodium sulfate, demonstrating a previously unrecognized immunoregulatory role for TSLP in a mouse model of inflammatory bowel disease.

Novel effector molecules in type 2 inflammation: lessons drawn from helminth infection and allergy.

Type 2 cytokine-induced inflammatory responses are critical components of the mucosal immune response required for host defense against helminth infection and are also responsible for the pathogenesis of many debilitating diseases including asthma, allergy, and forms of inflammatory bowel disease.

Goblet Cell-Derived Resistin-Like Molecule β Augments CD4+ T Cell Production of IFN-γ and Infection-Induced Intestinal Inflammation

The secreted goblet cell-derived protein resistin-like molecule β (RELMβ) has been implicated in divergent functions, including a direct effector function against parasitic helminths and a pathogenic function in promoting inflammation in models of colitis and ileitis. However, whether RELMβ influences CD4+ T cell responses in the intestine is unknown. Using a natural model of intestinal inflammation induced by chronic infection with gastrointestinal helminth Trichuris muris, we identify dual functions for RELMβ in augmenting CD4+ Th1 cell responses and promoting infection-induced intestinal inflammation. Following exposure to low-dose Trichuris, wild-type C57BL/6 mice exhibit persistent infection associated with robust IFN-γ production and intestinal inflammation. In contrast, infected RELMβ−/− mice exhibited a significantly reduced expression of parasite-specific CD4+ T cell-derived IFN-γ and TNF-α and failed to develop Trichuris-induced intestinal inflammation. In in vitro T cell differentiation assays, recombinant RELMβ activated macrophages to express MHC class II and secrete IL-12/23p40 and enhanced their ability to mediate Ag-specific IFN-γ expression in CD4+ T cells. Taken together, these data suggest that goblet cell-macrophage cross-talk, mediated in part by RELMβ, can promote adaptive CD4+ T cell responses and chronic inflammation following intestinal helminth infection.

IL-27 Regulates Homeostasis of the Intestinal CD4+ Effector T Cell Pool and Limits Intestinal Inflammation in a Murine Model of Colitis

IL-27 limits CD4+ TH17 cell development in vitro and during inflammatory responses in the CNS. However, whether IL-27-IL-27R interactions regulate the homeostasis or function of CD4+ T cell populations in the intestine is unknown. To test this, we examined CD4+ T cell populations in the intestine of wild-type and IL-27R−/− mice. Naive IL-27R−/− mice exhibited a selective decrease in the frequency of IFN-γ producing CD4+ TH1 cells and an increase in the frequency of TH17 cells in gut-associated lymphoid tissues. Associated with elevated expression of IL-17A, IL-27R−/− mice exhibited earlier onset and significantly increased severity of clinical disease compared with wild-type controls in a murine model of intestinal inflammation. Rag−/−/IL-27R−/− mice were also more susceptible than Rag−/− mice to development of dextran sodium sulfate-induced intestinal inflammation, indicating an additional role for IL-27-IL-27R in the regulation of innate immune cell function. Consistent with this, IL-27 inhibited proinflammatory cytokine production by activated neutrophils. Collectively, these data identify a role for IL-27-IL-27R interaction in controlling the homeostasis of the intestinal T cell pool and in limiting intestinal inflammation through regulation of innate and adaptive immune cell function.

IL-31-IL-31R Interactions Limit the Magnitude of Th2 Cytokine-Dependent Immunity and Inflammation following Intestinal Helminth Infection

IL-31 is a recently identified cytokine made predominantly by CD4+ Th2 cells and its receptor, IL-31R, is expressed by a number of cell types including monocytes, epithelial cells, and T cells. Originally identified as a potential mediator of inflammation in the skin, we recently reported a novel function for endogenous IL-31R interactions in limiting type 2 inflammation in the lung. However, whether IL-31-IL-31R interactions regulate immunity or inflammation at other mucosal sites, such as the gut, is unknown. In this study, we report a regulatory role for IL-31-IL-31R interactions in the intestine following infection with the gastrointestinal helminth Trichuris muris, immunity to which is critically dependent on CD4+ Th2 cells that produce IL-4 and IL-13. IL-31Rα was constitutively expressed in the colon and exposure to Trichuris induced the expression of IL-31 in CD4+ T cells. In response to Trichuris infection, IL-31Rα−/− mice exhibited increased Th2 cytokine responses in the mesenteric lymph nodes and elevated serum IgE and IgG1 levels compared with wild type mice. IL-31Rα−/− mice also displayed enhanced goblet cell hyperplasia and a marked increase in secretion of goblet cell-derived resistin-like molecule β into the intestinal lumen. Consistent with their exacerbated type 2 inflammatory responses, IL-31Rα−/− mice exhibited accelerated expulsion of Trichuris with significantly decreased worm burdens compared with their wild type counterparts early following infection. Collectively, these data provide the first evidence of a function for IL-31-IL-31R interactions in limiting the magnitude of type 2 inflammatory responses within the intestine.