Intravenous immunoglobulin (IVIg) or IVIg‐treated macrophages reduce DSS‐induced colitis by inducing macrophage IL‐10 production

Intravenous immunoglobulin (IVIg) is used to treat immune‐mediated diseases but its mechanism of action is poorly understood. We have reported that co‐treatment with IVIg and lipopolysaccharide activates macrophages to produce large amounts of anti‐inflammatory IL‐10 in vitro. Thus, we asked whether IVIg‐treated macrophages or IVIg could reduce intestinal inflammation in mice during dextran sulfate sodium (DSS)‐induced colitis by inducing macrophage IL‐10 production in vivo. Adoptive transfer of IVIg‐treated macrophages reduces intestinal inflammation in mice and collagen accumulation post‐DSS. IVIg treatment also reduces DSS‐induced intestinal inflammation and its activity is dependent on the Fc portion of the antibody. Ex vivo, IVIg induces IL‐10 production and reduces IL‐12/23p40 and IL‐1β production in colon explant cultures. Co‐staining tissues for mRNA, we demonstrate that macrophages are the source of IL‐10 in IVIg‐treated mice; and using IL‐10‐GFP reporter mice, we demonstrate that IVIg induces IL‐10 production by intestinal macrophages. Finally, IVIg‐mediated protection is lost in mice deficient in macrophage IL‐10 production (LysMcre^+/?IL‐10^fl/fl mice). Together, our data demonstrate a novel, in vivo mechanism of action for IVIg. IVIg‐treated macrophages or IVIg could be used to treat people with intestinal inflammation and may be particularly useful for people with inflammatory bowel disease, who are refractory to therapy.     

Regulatory effects of IFN‐β on production of osteopontin and IL‐17 by CD4+ T Cells in MS

IFN‐β currently serves as one of the major treatments for MS. Its anti‐inflammatory mechanism has been reported as involving a shift in cytokine balance from Th1 to Th2 in the T‐cell response against elements of the myelin sheath. In addition to the Th1 and Th2 groups, two other important pro‐inflammatory cytokines, IL‐17 and osteopontin (OPN), are believed to play important roles in CNS inflammation in the pathogenesis of MS. In this study, we examined the potential effects of IFN‐β on the regulation of OPN and IL‐17 in MS patients. We found that IFN‐β used in vitro at 0.5–3 ng/mL significantly inhibited the production of OPN in primary T cells derived from PBMC. The inhibition of OPN was determined to occur at the CD4⁺ T‐cell level. In addition, IFN‐β inhibited the production of IL‐17 and IL‐21 in CD4⁺ T cells. It has been described that IFN‐β suppresses IL‐17 production through the inhibition of a monocytic cytokine, the intracellular translational isoform of OPN. Our further investigation demonstrated that IFN‐β also acted directly on the CD4⁺ T cells to regulate OPN and IL‐17 expression through the type I IFN receptor‐mediated activation of STAT1 and suppression of STAT3 activity. Administration of IFN‐β to EAE mice ameliorated the disease severity. Furthermore, spinal cord infiltration of OPN⁺ and IL‐17⁺ cells decreased in IFN‐β‐treated EAE mice along with decreases in serum levels of OPN and IL‐21. Importantly, decreased OPN production by IFN‐β treatment contributes to the reduced migratory activity of T cells. Taken together, the results from both in vitro and in vivo experiments indicate that IFN‐β treatment can down‐regulate the OPN and IL‐17 production in MS. This study provides new insights into the mechanism of action of IFN‐β in the treatment of MS.     

Human gingiva‐derived mesenchymal stem cells alleviate inflammatory bowel disease via IL‐10 signalling‐dependent modulation of immune cells

Current evidence indicates that inflammatory bowel disease (IBD) is caused primarily by impaired mucosal immunity, resulting in an imbalance between epithelial barrier function and tissue inflammation. Human gingiva‐derived mesenchymal stem cells (GMSCs) exhibit immunomodulatory and anti‐inflammatory effects in a variety of immunity‐ and inflammation‐associated diseases. However, the role of GMSCs in treating IBD has not been elucidated. Our study, therefore, examined the therapeutic effect and mechanism of GMSCs in a murine colitis model of IBD. Our results indicate that the infusion of GMSCs significantly prolonged survival and relieved symptoms. Phenotype analyses showed that the frequencies of NK1.1⁺ and CD11b⁺ cells, as well as CD4 T cells in the spleen, were suppressed in GMSC‐treated mice compared with the PBS‐ or fibroblast‐treated control groups. Additionally, GMSC treatment markedly increased the numbers of interleukin (IL)‐10⁺ regulatory T cells, reduced the secretion of pro‐inflammatory cytokines, and increased production of anti‐inflammatory cytokines. A mechanistic study revealed that anti‐IL‐10R antibody abolished the protective effect of GMSCs compared with mice treated with anti‐IgG antibody. Thus, our results indicate that GMSCs play a critical role in alleviating colitis by modulating inflammatory immune cells via IL‐10 signalling.     

Interleukin‐33 exacerbates acute colitis via interleukin‐4 in mice

Interleukin‐33 (IL‐33) and its receptor ST2 are over‐expressed in clinical colitis tissue. However, the significance of these observations is at present unknown. Significantly, we demonstrate here that IL33 and ST2 are the primary early genes induced in the inflamed colon of BALB/c mice following dextran sulphate sodium (DSS)‐induced experimental ulcerative colitis. Accordingly diarrhoea and DSS‐induced colon inflammation were impaired in ST2^?/? BALB/c mice and exacerbated in wild‐type mice by treatment with exogenous recombinant IL‐33, associated respectively with reduced and enhanced expression of chemokines (CXCL9 and CXCL10), and inflammatory (IL‐4, IL‐13, IL‐1, IL‐6, IL‐17) and angiogenic (vascular endothelial growth factor) cytokines in vivo. The exacerbation effect of treatment with recombinant IL‐33 on DSS‐induced acute colitis was abolished in IL‐4^?/? BALB/c mice. Hence, IL‐33 signalling via ST2, by inducing an IL‐4‐dependent immune response, may be a major pathogenic factor in the exacerbation of ulcerative colitis.     

Rectal administration of tranilast ameliorated acute colitis in mice through increased expression of heme oxygenase‐1

Mast cells play a key role in the pathophysiology of inflammatory bowel disease (IBD). Tranilast, a mast cell stabilizer, has been empirically used for IBD in Japan, but its precise role in the treatment of IBD is largely unknown. To investigate the role of tranilast for the treatment of IBD, tranilast was administered intrarectally to mice with dextran sulfate sodium (DSS)‐induced colitis. Tranilast ameliorated DSS colitis clinically and pathologically, as demonstrated by decreased number and degranulation of mast cells in the colon. mRNA expression was increased for tumor necrosis factor‐α, interferon‐γ and interleukin (IL)‐6, and decreased for IL‐10 in the colon of DSS colitis mice. In contrast, tranilast markedly decreased expression of mRNAs for the pro‐inflammatory cytokines, and increased that of the anti‐inflammatory cytokines. Moreover, tranilast increased heme oxygenase (HO)‐1 expression on colonic epithelial cells as well as on colon‐infiltrating cells of DSS colitis. In conclusion, tranilast ameliorated DSS colitis by regulating mast cell degranulation, decreasing inflammatory cytokines and increasing anti‐inflammatory cytokines. Tranilast might exert these effects partly through enhanced HO‐1 expression in the colon, suggesting a potential adjunctive therapy for IBD.     

Hypoxia inducible factor‐1α‐induced interleukin‐33 expression in intestinal epithelia contributes to mucosal homeostasis in inflammatory bowel disease

Intestinal epithelial cells (IECs), an important barrier to gut microbiota, are subject to low oxygen tension, particularly during intestinal inflammation. Hypoxia inducible factor‐1α (HIF‐1α) is expressed highly in the inflamed mucosa of inflammatory bowel disease (IBD) and functions as a key regulator in maintenance of intestinal homeostasis. However, how IEC‐derived HIF‐1α regulates intestinal immune responses in IBD is still not understood completely. We report here that the expression of HIF‐1α and IL‐33 was increased significantly in the inflamed mucosa of IBD patients as well as mice with colitis induced by dextran sulphate sodium (DSS). The levels of interleukin (IL)?33 were correlated positively with that of HIF‐1α. A HIF‐1α‐interacting element was identified in the promoter region of IL‐33, indicating that HIF‐1α activity regulates IL‐33 expression. Furthermore, tumour necrosis factor (TNF) facilitated the HIF‐1α‐dependent IL‐33 expression in IEC. Our data thus demonstrate that HIF‐1α‐dependent IL‐33 in IEC functions as a regulatory cytokine in inflamed mucosa of IBD, thereby regulating the intestinal inflammation and maintaining mucosal homeostasis.     

Arginase activity in alternatively activated macrophages protects PI3Kp110δ deficient mice from dextran sodium sulfate induced intestinal inflammation

Alternatively activated or M2 macrophages have been reported to protect mice from intestinal inflammation, but the mechanism of protection has not been elucidated. In this study, we demonstrate that mice deficient in the p110δ catalytic subunit activity of class I phosphatidylinositol 3‐kinase (PI3Kp110δ) have increased clinical disease activity and histological damage during dextran sodium sulfate (DSS) induced colitis. Increased disease severity in PI3Kp110δ‐deficient mice is dependent on professional phagocytes and correlates with reduced numbers of arginase I⁺ M2 macrophages in the colon and increased production of inflammatory nitric oxide. We further demonstrate that PI3Kp110δ‐deficient macrophages are defective in their ability to induce arginase I when skewed to an M2 phenotype with IL‐4. Importantly, adoptive transfer of IL‐4‐treated macrophages derived from WT mice, but not those from PI3Kp110δ‐deficient mice, protects mice during DSS‐induced colitis. Moreover, M2 macrophages mediated protection is lost when mice are cotreated with inhibitors that block arginase activity or during adoptive transfer of arginase I deficient M2 macrophages. Taken together, our data demonstrate that arginase I activity is required for M2 macrophages mediated protection during DSS‐induced colitis in PI3Kp110δ‐deficient mice.     

High-fat diet modulates non-CD1d-restricted natural killer T cells and regulatory T cells in mouse colon and exacerbates experimental colitis

Environmental factors such as diet are known to play important roles in inflammatory bowel disease (IBD). Epidemiological studies have indicated that a high-fat diet is a risk factor for IBD. In addition, the balance between effector T cells (T(eff)) and regulatory T cells (T(reg)) contributes to the pathogenesis of mucosal inflammation. The aim of this study was to understand the mechanisms by which a high-fat diet can regulate susceptibility to intestinal inflammation. Wild-type C57BL/6 mice were fed either a commercial high-fat diet or a normal diet, then exposed to dextran sulphate sodium (DSS) to induce colonic inflammation. Intraepithelial lymphocytes (IEL) were isolated from the colon, and their phenotype and cytokine profile were analysed by flow cytometry. Mice receiving the high-fat diet were more susceptible to DSS-induced colitis. They had higher numbers of non-CD1d-restricted natural killer (NK) T cells in the colonic IEL, when compared to mice fed a normal diet. These cells expressed tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma, which are up-regulated by high-fat diets. Mice fed the high-fat diet also had decreased levels of colonic T(reg). Depletion of colonic NK T cells or adoptive transfer of T(reg) reduced the DSS colitis in these mice, and reduced the colonic expression of TNF-alpha and IFN-gamma. We conclude that a high-fat diet can increase non-CD1d-restricted NK T cells and decrease T(reg) in the colonic IEL population. This altered colonic IEL population leads to increased susceptibility to DSS-induced colitis. This effect may help to explain how environmental factors can increase the susceptibility to IBD.     

Enhanced protection from fibrosis and inflammation in the combined absence of IL‐13 and IFN‐γ

Persistent or dysregulated IL‐13 responses are key drivers of fibrosis in multiple organ systems, and this identifies this cytokine as an important therapeutic target. Nevertheless, the mechanisms by which IL‐13 blockade leads to the amelioration of fibrosis remain unclear. Because IFN‐γ exhibits potent anti‐fibrotic activity, and IL‐4Rα signalling antagonizes IFN‐γ effector function, compensatory increases in IFN‐γ activity following IL‐13/IL‐4Rα blockade might contribute to the reduction in fibrosis. To investigate the role of IFN‐γ, we developed novel IL‐13^?/?/IFN‐γ^?/? double cytokine‐deficient mice and examined disease progression in models of type 2‐driven fibrosis. As predicted, we showed that fibrosis in the lung and liver are both highly dependent on IL‐13. We also observed increased IFN‐γ production and inflammatory activity in the tissues of IL‐13‐deficient mice. Surprisingly, however, an even greater reduction in fibrosis was observed in IL‐13/IFN‐γ double deficient mice, most notably in the livers of mice chronically infected with Schistosoma mansoni. The increased protection was associated with marked decreases in Tgfb1, Mmp12, and Timp1 mRNA expression in the tissues; reduced inflammation; and decreased expression of important pro‐inflammatory mediators such as TNF‐α. Experiments conducted with neutralizing monoclonal antibodies to IL‐13 and IFN‐γ validated the findings with the genetically deficient mice. Together, these studies demonstrate that the reduction in fibrosis observed when IL‐13 signalling is suppressed is not dependent on increased IFN‐γ activity. Instead, by reducing compensatory increases in type 1‐associated inflammation, therapeutic strategies that block IFN‐γ and IL‐13 activity simultaneously can confer greater protection from progressive fibrosis than IL‐13 blockade alone. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.     

Card9‐dependent IL‐1β regulates IL‐22 production from group 3 innate lymphoid cells and promotes colitis‐associated cancer

Inflammatory bowel diseases (IBD) are key risk factors for the development of colorectal cancer, but the mechanisms that link intestinal inflammation with carcinogenesis are insufficiently understood. Card9 is a myeloid cell‐specific signaling protein that regulates inflammatory responses downstream of various pattern recognition receptors and which cooperates with the inflammasomes for IL‐1β production. Because polymorphisms in Card9 were recurrently associated with human IBD, we investigated the function of Card9 in a colitis‐associated cancer (CAC) model. Card9^?/? mice develop smaller, less proliferative and less dysplastic tumors compared to their littermates and in the regenerating mucosa we detected dramatically impaired IL‐1β generation and defective IL‐1β controlled IL‐22 production from group 3 innate lymphoid cells. Consistent with the key role of immune‐derived IL‐22 in activating STAT3 signaling during normal and pathological intestinal epithelial cell (IEC) proliferation, Card9^?/? mice also exhibit impaired tumor cell intrinsic STAT3 activation. Our results imply a Card9‐controlled, ILC3‐mediated mechanism regulating healthy and malignant IEC proliferation and demonstrates a role of Card9‐mediated innate immunity in inflammation‐associated carcinogenesis.     

NUR77 exerts a protective effect against inflammatory bowel disease by negatively regulating the TRAF6/TLR–IL‐1R signalling axis

Nur77, an immediate‐early response gene, participates in a wide range of biological functions. Its human homologue, NUR77, is known by several names and has the HGNC‐approved gene symbol NR4A1. However, the role of Nur77 in inflammatory bowel disease (IBD) and its underlying mechanisms remain elusive. Here, using public data from the International Inflammatory Bowel Disease Genetics Consortium (IIBDGC) on the most recent genome‐wide association studies (GWAS) for ulcerative colitis (UC) and Crohn's disease (CD), we found that genetic variants of the NUR77 gene are associated with increased risk for both UC and CD. Accordingly, Nur77 expression was significantly reduced in colon tissues from patients with UC or CD and mice treated with DSS. Nur77 deficiency increased the susceptibility of mice to DSS‐induced experimental colitis and prevented intestinal recovery, whereas treatment with cytosporone B (Csn‐B), an agonist for Nur77, significantly attenuated excessive inflammatory response in the DSS‐induced colitis mouse model. Mechanistically, NUR77 acts as a negative regulator of TLR–IL‐1R signalling by interacting with TRAF6. This interaction prevented auto‐ubiquitination and oligomerization of TRAF6 and subsequently inhibited NF‐κB activation and pro‐inflammatory cytokine production. Taken together, our GWAS‐based analysis and in vitro and in vivo studies have demonstrated that Nur77 is an important regulator of TRAF6/TLR–IL‐1R‐initiated inflammatory signalling, and loss of Nur77 may contribute to the development of IBD, suggesting Nur77 as a potential target for the prevention and treatment of IBD. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

A bone‐protective role for IL‐17 receptor signaling in ovariectomy‐induced bone loss

Post‐menopausal osteoporosis is considered to be an inflammatory process, in which numerous pro‐inflammatory and T‐cell‐derived cytokines play a bone‐destructive role. IL‐17A is the signature cytokine of the pro‐inflammatory Th17 population and plays dichotomous roles in diseases that affect bone turnover. Although IL‐17A promotes bone loss in rheumatoid arthritis, it is protective against pathogen‐induced bone destruction in a periodontal disease model. We used a model of ovariectomy‐induced osteoporosis (OVX) in IL‐17 receptor (IL‐17RA)^?/? mice to evaluate the role of the IL‐17A in bone loss caused by estrogen deficiency. Unexpectedly, IL‐17RA^?/? mice were consistently and markedly more susceptible to OVX‐induced bone loss than controls. There were no changes in prototypical Th1, Th2 or Th17 cytokines in serum that could account for increased bone loss. However, IL‐17RA^?/? mice exhibited constitutively elevated leptin, which further increased following OVX. Consistently, IL‐17A and IL‐17F treatment of 3T3‐L1 pre‐adipocytes inhibited adipogenesis, leading to reduced production of leptin. In addition to its role in regulating metabolism and satiety, leptin can regulate bone turnover. Accordingly, these data show that IL‐17A negatively regulates adipogenesis and subsequent leptin expression, which correlates with increased bone destruction during OVX.     

Interleukin (IL)-21-independent pathogen-specific CD8+ T-cell expansion, and IL-21-dependent suppression of CD4+ T-cell IL-17 production

Although interleukin‐21 (IL‐21) potently activates and controls the differentiation of immune cells after stimulation in vitro, the role for this pleiotropic cytokine during in vivo infection remains poorly defined. Herein, the requirement for IL‐21 in innate and adaptive host defence after Listeria monocytogenes infection was examined. In the innate phase, IL‐21 deficiency did not cause significant defects in infection susceptibility, or in the early activation of natural killer and T cells. In the adaptive phase, L. monocytogenes‐specific CD8⁺ T cells expand to a similar magnitude in IL‐21‐deficient mice compared with control mice. Interestingly, the IL‐21‐independent expansion of L. monocytogenes‐specific CD8⁺ T cells was maintained even in the combined absence of IL‐12 and type I interferon (IFN) receptor. Similarly, L. monocytogenes‐specific CD4⁺ T cells expanded and produced similar levels of IFN‐γ regardless of IL‐21 deficiency. Unexpectedly however, IL‐21 deficiency caused significantly increased CD4⁺ T‐cell IL‐17 production, and this effect became even more pronounced after L. monocytogenes infection in mice with combined defects in both IL‐12 and type I IFN receptor that develop a T helper type 17‐dominated CD4⁺ T‐cell response. Despite increased CD4⁺ T‐cell IL‐17 production, L. monocytogenes‐specific T cells re‐expanded and conferred protection against secondary challenge with virulent L. monocytogenes regardless of IL‐21 deficiency, or combined defects in IL‐21, IL‐12, and type I IFN receptor. Together, these results demonstrate non‐essential individual and combined roles for IL‐21, IL‐12 and type I IFNs in priming pathogen‐specific CD8⁺ T cells, and reveal IL‐21‐dependent suppression of IL‐17 production by CD4⁺ T cells during in vivo infection.     

The RAGE signaling pathway is involved in intestinal inflammation and represents a promising therapeutic target for Inflammatory Bowel Diseases

Inflammatory Bowel Diseases (IBD) are chronic inflammatory conditions of the intestinal tract. IBD are believed to result from an inappropriate immune response against the intestinal flora in genetically predisposed patients. The precise etiology of these diseases is not fully understood, therefore treatments rely on the dampening of symptoms, essentially inflammation, rather than on the cure of the disease. Despite the availability of biologics, such as anti-TNF antibodies, some patients remain in therapeutic failure and new treatments are thus needed. The multiligand receptor for advanced glycation end-products (RAGE) is a pattern recognition receptor implicated in inflammatory reactions and immune system activation. Here, we investigated the role of RAGE in intestinal inflammation and its potential as a therapeutic target in IBD. We showed that RAGE was upregulated in inflamed tissues from IBD patients compared to controls. Rage^−/− mice were less susceptible to intestinal and colonic inflammation development than WT mice. WT mice treated with the RAGE-specific inhibitor FPS-ZM1 experienced less severe enteritis and colitis. We demonstrated that RAGE could induce intestinal inflammation by promoting oxidative stress and endothelial activation which were diminished by FPS-ZM1 treatment. Our results revealed the RAGE signaling pathway as a promising therapeutic target for IBD patients.     

MD-1 deficiency attenuates dextran sodium sulfate (DSS)-induced colitis through modulating the function of colonic lamina propria dendritic cells

Available evidence suggests that both dysregulated innate and adaptive immune pathways contribute to the aberrant intestinal inflammatory response in patients with inflammatory bowel disease (IBD). Myeloid Differentiation 1 (MD-1), also known as Lymphocyte Antigen 86 (Ly86), a secreted protein interacting with radioprotective 105 (RP105), plays an important role in Toll-like receptor 4 (TLR4) signaling pathway. Previous studies showed that MD-1 may be involved in the (patho) physiological regulation of the innate immune system and inflammation. In this study, we reported for the first time that MD-1 mRNA expression was up-regulated in both human IBD patients and DSS-treated WT mice. We showed that MD-1^−/− mice were less susceptible to the development of colitis than WT controls as demonstrated by significantly reduced weight loss, disease activity index, colon histological scores, cellular infiltration and expression of inflammatory mediators. In addition, mucosal barrier function seemed to be intact in response to the loss of MD-1. Finally, lamina propria dendritic cells (LPDCs) from the colon of MD-1^−/− mice after DSS exposure not only decreased in number but also significantly down-regulated the expression of surface maturation co-stimulatory molecules MHC-II, CD40 and CD86 compared with those from WT mice. Taken together, our results reveal that MD-1 deficiency is of critical importance in down-regulating induction and progression of DSS colitis, thereby suggesting that MD-1 might be a target for future interventional therapies of IBD.     

An imbalance in mucosal cytokine profile causes transient intestinal inflammation following an animal's first exposure to faecal bacteria and antigens

Intestinal microflora play a critical role in the initiation and perpetuation of chronic inflammatory bowel diseases. In genetically susceptible hosts, bacterial colonization results in rapid‐onset chronic intestinal inflammation. Nevertheless, the intestinal and systemic immune response to faecal bacteria and antigen exposure into a sterile intestinal lumen of a post‐weaned animal with a mature immune system are not understood clearly. This study examined the effects of faecal bacteria and antigen exposure on the intestinal mucosal and systemic immune system in healthy axenic mice. Axenic wild‐type mice were inoculated orally with a crude faecal slurry solution derived from conventionally raised mice and were analysed prior to and then at days 3, 7, 14 and 28 post‐treatment. Ingestion of faecal slurry resulted in a transient, early onset of proinflammatory interferon (IFN)‐γ, tumour necrosis factor (TNF)‐α and interleukin (IL)‐17 response that was maximal at day 3. In contrast, the transient release of the anti‐inflammatory cytokines IL‐10 and IL‐4 occurred later and was maximal at day 7. Both responses subsided by day 14. This early cytokine imbalance was associated with a brief rise in colonic and caecal histopathological injury score at day 7. The bacterial antigen‐specific systemic response was found to follow the intestinal immune response with a maximal release of both pro‐ and anti‐inflammatory cytokines at day 7. Thus, first exposure of healthy axenic wild‐type mice to normal faecal flora and antigens results in an early proinflammatory cytokine response and transient colonic inflammation that then resolves in conjunction with a subsequent anti‐inflammatory cytokine profile.     

IL‐18Rα‐deficient CD4+ T cells induce intestinal inflammation in the CD45RBhi transfer model of colitis despite impaired innate responsiveness

IL‐18 has been implicated in inflammatory bowel disease (IBD), however its role in the regulation of intestinal CD4⁺ T‐cell function remains unclear. Here we show that murine intestinal CD4⁺ T cells express high levels of IL‐18Rα and provide evidence that IL‐18Rα expression is induced on these cells subsequent to their entry into the intestinal mucosa. Using the CD45RB^hi T‐cell transfer colitis model, we show that IL‐18Rα is expressed on IFN‐γ⁺, IL‐17⁺, and IL‐17⁺IFN‐γ⁺ effector CD4⁺ T cells in the inflamed colonic lamina propria (cLP) and mesenteric lymph node (MLN) and is required for the optimal generation and/or maintenance of IFN‐γ‐producing cells in the cLP. In the steady state and during colitis, TCR‐independent cytokine‐induced IFN‐γ and IL‐17 production by intestinal CD4⁺ T cells was largely IL‐18Rα?dependent. Despite these findings however, IL‐18Rα?deficient CD4⁺ T cells induced comparable intestinal pathology to WT CD4⁺ T cells. These findings suggest that IL‐18‐dependent cytokine induced activation of CD4⁺ T cells is not critical for the development of T‐cell‐mediated colitis.