Dextran sulfate sodium (DSS) induced experimental colitis in immunodeficient mice: effects in CD4(+) -cell depleted, athymic and NK-cell depleted SCID mice

Methods of inducing inflammatory bowel disease in mice

Animal models of experimentally induced inflammatory bowel disease (IBD) are useful for understanding more about the mechanistic basis of disease, identifying new targets for therapeutic intervention, and testing novel therapeutic agents. This unit provides detailed protocols for four of the most commonly used mouse models of experimentally induced intestinal inflammation: chemical induction of colitis by dextran sodium sulfate (DSS), hapten-induced colitis via 2,4,6-trinitrobenzene sulfonic acid (TNBS), Helicobacter-induced colitis in mdr1a(-/-) mice, and the CD4(+) CD45RB(hi) SCID transfer colitis model.

Berberine promotes recovery of colitis and inhibits inflammatory responses in colonic macrophages and epithelial cells in DSS-treated mice

Inflammatory bowel disease (IBD) results from dysregulation of intestinal mucosal immune responses to microflora in genetically susceptible hosts. A major challenge for IBD research is to develop new strategies for treating this disease. Berberine, an alkaloid derived from plants, is an alternative medicine for treating bacterial diarrhea and intestinal parasite infections. Recent studies suggest that berberine exerts several other beneficial effects, including inducing anti-inflammatory responses. This study determined the effect of berberine on treating dextran sulfate sodium (DSS)-induced intestinal injury and colitis in mice. Berberine was administered through gavage to mice with established DSS-induced intestinal injury and colitis. Clinical parameters, intestinal integrity, proinflammatory cytokine production, and signaling pathways in colonic macrophages and epithelial cells were determined. Berberine ameliorated DSS-induced body weight loss, myeloperoxidase activity, shortening of the colon, injury, and inflammation scores. DSS-upregulated proinflammatory cytokine levels in the colon, including TNF, IFN-γ, KC, and IL-17 were reduced by berberine. Berberine decreased DSS-induced disruption of barrier function and apoptosis in the colon epithelium. Furthermore, berberine inhibited proinflammatory cytokine production in colonic macrophages and epithelial cells in DSS-treated mice and promoted apoptosis of colonic macrophages. Activation of signaling pathways involved in stimulation of proinflammatory cytokine production, including MAPK and NF-κB, in colonic macrophages and epithelial cells from DSS-treated mice was decreased by berberine. In summary, berberine promotes recovery of DSS-induced colitis and exerts inhibitory effects on proinflammatory responses in colonic macrophages and epithelial cells. Thus berberine may represent a new therapeutic approach for treating gastrointestinal inflammatory disorders.

Genetic and pharmacological targeting of TPL-2 kinase ameliorates experimental colitis: a potential target for the treatment of Crohn's disease?

Inflammatory bowel disease is characterized by dysregulated immune responses against intestinal microflora leading to marked activation of nuclear factor-κB (NF-κB) with subsequent production of pro-inflammatory cytokines. Besides NF-κB, the tumor progression locus 2 (TPL-2)/extracellular signal-regulated kinase (ERK) pathway also regulates inflammatory cytokines such as interleukin-1β and tumor necrosis factor-α, but its role during intestinal inflammation is incompletely understood. We analyzed the impact of TPL-2 in the dextran sulfate sodium-induced experimental colitis model. Despite normal activation of NF-κB, animals lacking TPL-2 developed only mild colitis with reduced synthesis of inflammatory cytokines. Further, pharmacological inhibition of the TPL-2 kinase was similarly effective in ameliorating colitis as TPL-2 deficiency without obvious side effects. Because increased TPL-2/ERK activation was seen in patients with Crohn's disease (CD) but not ulcerative colitis, our findings encourage further investigation of TPL-2 kinase as potential target for the treatment of CD patients.

Investigating intestinal inflammation in DSS-induced model of IBD

Inflammatory bowel disease (IBD) encompasses a range of intestinal pathologies, the most common of which are ulcerative colitis (UC) and Crohn's Disease (CD). Both UC and CD, when present in the colon, generate a similar symptom profile which can include diarrhea, rectal bleeding, abdominal pain, and weight loss.(1) Although the pathogenesis of IBD remains unknown, it is described as a multifactorial disease that involves both genetic and environmental components.(2) There are numerous and variable animal models of colonic inflammation that resemble several features of IBD. Animal models of colitis range from those arising spontaneously in susceptible strains of certain species to those requiring administration of specific concentrations of colitis-inducing chemicals, such as dextran sulphate sodium (DSS). Chemical-induced models of gut inflammation are the most commonly used and best described models of IBD. Administration of DSS in drinking water produces acute or chronic colitis depending on the administration protocol.(3) Animals given DSS exhibit weight loss and signs of loose stool or diarrhea, sometimes with evidence of rectal bleeding.(4,5) Here, we describe the methods by which colitis development and the resulting inflammatory response can be characterized following administration of DSS. These methods include histological analysis of hematoxylin/eosin stained colon sections, measurement of pro-inflammatory cytokines, and determination of myeloperoxidase (MPO) activity, which can be used as a surrogate marker of inflammation.(6) The extent of the inflammatory response in disease state can be assessed by the presence of clinical symptoms or by alteration in histology in mucosal tissue. Colonic histological damage is assessed by using a scoring system that considers loss of crypt architecture, inflammatory cell infiltration, muscle thickening, goblet cell depletion, and crypt abscess.(7) Quantitatively, levels of pro-inflammatory cytokines with acute inflammatory properties, such as interleukin (IL)-1β, IL-6 and tumour necrosis factor (TNF)-α,can be determined using conventional ELISA methods. In addition, MPO activity can be measured using a colorimetric assay and used as an index of inflammation.(8) In experimental colitis, disease severity is often correlated with an increase in MPO activity and higher levels of pro-inflammatory cytokines. Colitis severity and inflammation-associated damage can be assessed by examining stool consistency and bleeding, in addition to assessing the histopathological state of the intestine using hematoxylin/eosin stained colonic tissue sections. Colonic tissue fragments can be used to determine MPO activity and cytokine production. Taken together, these measures can be used to evaluate the intestinal inflammatory response in animal models of experimental colitis.

The severity of dextran sodium sulfate-induced colitis can differ between dextran sodium sulfate preparations of the same molecular weight range

BACKGROUND

We hypothesized that the severity of dextran sodium sulfate (DSS)-induced colitis could differ between DSS preparations of the same molecular weight, and that this difference may be affected by the sulfur content. To test this, we used three DSS preparations of similar molecular weights but with different sulfur contents.

METHODS

Three DSS preparations with molecular weights of 40,000 to 50,000 were tested: MP Biomedicals (MP Bio), USB (USB), and The Lab Depot (The Lab). Epithelial cell lines were used to assess the levels of poly (ADP-ribose) polymerase (PARP) in the presence of 2.0% DSS in vitro. Eight-week-old female C57/B6 mice were fed 2.0% DSS in water for 1 week, and then sacrificed to investigate the effects of the DSS preparations in vivo.

RESULTS

In vitro experiments using CaCo-2 and CMT-93 cells revealed decreased PARP levels from all DSS preparations. Notably, the PARP level was significantly decreased in CaCo-2 cells treated with DSS from USB as compared to The Lab Mice treated with The Lab DSS had significantly decreased body weight losses on day 7 as compared to mice receiving DSS from MP Bio and USB. This result was supported by their DAI score, colon weight/length ratio, and histological scores.

CONCLUSION

The severity of colitis can differ between similar DSS preparations of the same molecular weight range. This difference in colitogenic properties may be affected by the total sulfur content of each DSS preparation.

Allergen-induced IgE-dependent gut inflammation in a human PBMC-engrafted murine model of allergy

BACKGROUND

Humanized murine models comprise a new tool to analyze novel therapeutic strategies for allergic diseases of the intestine.

OBJECTIVE

In this study we developed a human PBMC-engrafted murine model of allergen-driven gut inflammation and analyzed the underlying immunologic mechanisms.

METHODS

Nonobese diabetic (NOD)-scid-γc(-/-) mice were injected intraperitoneally with human PBMCs from allergic donors together with the respective allergen or not. Three weeks later, mice were challenged with the allergen orally or rectally, and gut inflammation was monitored with a high-resolution video miniendoscopic system, as well as histologically.

RESULTS

Using the aeroallergens birch or grass pollen as model allergens and, for some donors, also hazelnut allergen, we show that allergen-specific human IgE in murine sera and allergen-specific proliferation and cytokine production of human CD4(+) T cells recovered from spleens after 3 weeks could only be measured in mice treated with PBMCs plus allergen. Importantly, these mice had the highest endoscopic scores evaluating translucent structure, granularity, fibrin, vascularity, and stool after oral or rectal allergen challenge and a strong histologic inflammation of the colon. Analyzing the underlying mechanisms, we demonstrate that allergen-associated colitis was dependent on IgE, human IgE receptor-expressing effector cells, and the mediators histamine and platelet-activating factor.

CONCLUSION

These results demonstrate that allergic gut inflammation can be induced in human PBMC-engrafted mice, allowing the investigation of pathophysiologic mechanisms of allergic diseases of the intestine and evaluation of therapeutic interventions.

Opposing consequences of IL-23 signaling mediated by innate and adaptive cells in chemically induced colitis in mice

The interleukin-23 (IL-23) pathway has emerged as a promising therapeutic target for inflammatory bowel disease. Although the pathogenic role of IL-23 receptor (IL-23R) on T lymphocytes is well established, its function on innate immune cells has not been thoroughly examined. Here we investigate the consequence of IL-23R deletion in dextran sulfate sodium (DSS)-induced colitis. In IL23R(-/-) and IL23p19(-/-) mice, we observed decreased weight loss and reduced leukocyte infiltrate following DSS exposure. Surprisingly, when the IL-23R(-/-) allele was crossed into Rag2(-/-) mice, we observed exacerbated disease, increased epithelial damage, reduced pSTAT3 in the epithelium, and delayed recovery of IL23R(-/-)Rag2(-/-) mice. This phenotype was rescued with exogenous IL22-Fc, and epithelial pSTAT3 was restored. Depletion of Thy1(+) innate lymphoid cells eliminated the majority of IL-22 production in the colon lamina propria of DSS-treated Rag2(-/-) mice, suggesting that these are the major IL-23 responsive innate cells in this context. In summary, we provide evidence for opposing consequences of IL-23R on innate and adaptive lymphoid cells in murine colitis.

Inflammasomes in intestinal inflammation and cancer

Inflammasomes are multi-protein complexes that mediate activation of caspase-1, which promotes secretion of the proinflammatory cytokines interleukin-1β and interleukin-18 and pyroptosis, a form of phagocyte cell death induced by bacterial pathogens. Members of the Nod-like receptor family (including Nlrp1, Nlrp3, and Nlrc4), the DNA sensor Aim2, the adaptor apoptosis-associated speck-like protein (ASC), and pro-caspase-1 are important components of inflammasomes. Stimulation with specific microbial and endogenous molecules leads to inflammasome assembly and caspase-1 activation. Inflammasomes are believed to mediate host defense against microbial pathogens and tissue homeostasis within the intestine, and their dysregulation might contribute to inflammatory diseases and intestinal cancer. Improving our understanding of inflammasome signaling pathways could provide insights into the pathogenesis of many gastrointestinal disorders and the development of therapeutic targets and approaches to treat diseases such as inflammatory bowel diseases and gastrointestinal cancers.

Commensal gut flora reduces susceptibility to experimentally induced colitis via T-cell-derived interleukin-10

BACKGROUND

Regulatory cytokines are well known to modify experimental colitis in mice. The aim of this study was to elucidate the effect of interleukin (IL)-10 derived from different cellular sources and the effect of commensal gut flora in dextran sulfate sodium (DSS)-induced colitis in mice.

METHODS

Wildtype (WT) and IL-10 deficient (IL-10(-/-) ) mice either harboring a characterized specific pathogen-free (SPF) gut flora or germfree were exposed to 2% DSS. Moreover, cell type-specific IL-10, IL-4, and IL-12 knockout mice and animals combining the T-cell-specific IL-10 knockout with a deficiency in IL-12 or IL-4 were exposed to DSS.

RESULTS

SPF IL-10(-/-) mice showed an increased susceptibility to DSS-induced colitis compared to WT mice determined by histopathology and proinflammatory cytokine and chemokine responses. Under germfree conditions, both WT and IL-10(-/-) mice were highly susceptible to DSS. IL-10 mRNA was increased upon DSS exposure in WT SPF but not in germfree mice. Mice carrying a specific deletion of IL-10 in T-cells exhibited a tendency towards an enhanced susceptibility to DSS. The lack of T-cell-derived IL-10 in combination with the lack of IL-4 increased the susceptibility to DSS colitis, as did the lack of IL-12 alone.

CONCLUSIONS

IL-10 is a crucial factor inhibiting the innate proinflammatory immune response induced by DSS. Intestinal bacteria are necessary for the induction of protective IL-10, which is mainly T-cell-derived. T-cell-derived IL-10 can only mediate its protective effect in a Th1-dominated milieu. If the balance is shifted towards a Th2 response, IL-10 is not protective.

An experimental mouse model to establish Tropheryma whipplei as a diarrheal agent

Tropheryma whipplei has long been considered as a rare bacterium causing a rare disease, Whipple's disease. However, recent advances now suggest that T. whipplei is a ubiquitous environmental bacterium that may cause gastroenteritis, commonly associated with viral pathogens. We developed an animal model to support this hypothesis. We found that orally given T. whipplei induced diarrhea in mice, without spreading into the intestines. Aggravating factors, such as damage to the intestinal mucosa, favored bacterial spreading. Indeed, bacterial presence was prolonged in stools of dextran sulfate-treated mice, and bacteria were detected in the colon. This resulted in an immune response, with T. whipplei-specific serum IgM and IgG and fecal IgA, as measured by newly introduced immuno-polymerase chain reaction technique. Our results confirm that T. whipplei is an agent causing gastroenteritis and suggest that existing mucosal damage may favor bacterial invasion of tissues.

Enteric neuronal density contributes to the severity of intestinal inflammation

BACKGROUND & AIMS

Enteric neurons have been reported to be increased in inflamed regions of the bowel in patients with inflammatory bowel disease or intestinal neurogangliomatosis. It is impossible to determine whether this hyperinnervation predates intestinal inflammation, results from it, or contributes to its severity in humans, so we studied this process in mice.

METHODS

To determine whether the density of enteric neurons determines the severity of inflammation, we studied transgenic mice that have greater than normal (NSE-noggin mice, which overexpress noggin under the control of the neuron-specific enolase promoter) or fewer than normal (Hand2(+/-) mice) numbers of neurons in the enteric nervous system. Colitis was induced with trinitrobenzene sulfonic acid or dextran sulfate sodium, and the intensity of the resulting inflammation in Hand2(+/-) and NSE-noggin mice was compared with that of wild-type littermates.

RESULTS

Severity of each form of colitis (based on survival, symptom, and histologic scores; intestinal expression of genes that encode proinflammatory molecules; and levels of neutrophil elastase and p50 nuclear factor κB) were significantly reduced in Hand2(+/-) mice and significantly increased in NSE-noggin animals. Neither mouse differed from wild-type in the severity of delayed-type hypersensitivity (edema, T-cell and neutrophil infiltration, or expression of interleukin-1β, interferon-γ, or tumor necrosis factor-α) induced in the ears using 2,4-dinitro-1-fluorobenzene. Transgene effects on inflammation were therefore restricted to the gastrointestinal tract.

CONCLUSIONS

The severity of intestinal inflammation is associated with the density of the enteric innervation in mice. Abnormalities in development of the enteric nervous system might therefore contribute to the pathogenesis of inflammatory bowel disease.

Involvement of tyrosine kinase-2 in both the IL-12/Th1 and IL-23/Th17 axes in vivo

Tyrosine kinase-2 (Tyk2), a member of the Jak family of kinases, mediates the signals triggered by various cytokines, including type I IFNs, IL-12, and IL-23. In the current study, we investigated the in vivo involvement of Tyk2 in several IL-12/Th1- and IL-23/Th17-mediated models of experimental diseases, including methylated BSA injection-induced footpad thickness, imiquimod-induced psoriasis-like skin inflammation, and dextran sulfate sodium- or 2,4,6-trinitrobenzene sulfonic acid-induced colitis. In these disease models, Tyk2 deficiency influenced the phenotypes in immunity and/or inflammation. Our findings demonstrate a somewhat broader contribution of Tyk2 to immune systems than previously expected and suggest that Tyk2 may represent an important candidate for drug development by targeting both the IL-12/Th1 and IL-23/Th17 axes.

HVEM signalling promotes colitis

BACKGROUND

Tumor necrosis factor super family (TNFSF) members regulate important processes involved in cell proliferation, survival and differentiation and are therefore crucial for the balance between homeostasis and inflammatory responses. Several members of the TNFSF are closely associated with inflammatory bowel disease (IBD). Thus, they represent interesting new targets for therapeutic treatment of IBD.

METHODOLOGY/PRINCIPAL FINDINGS

We have used mice deficient in TNFSF member HVEM in experimental models of IBD to investigate its role in the disease process. Two models of IBD were employed: i) chemical-induced colitis primarily mediated by innate immune cells; and ii) colitis initiated by CD4(+)CD45RB(high) T cells following their transfer into immuno-deficient RAG1(-/-) hosts. In both models of disease the absence of HVEM resulted in a significant reduction in colitis and inflammatory cytokine production.

CONCLUSIONS

These data show that HVEM stimulatory signals promote experimental colitis driven by innate or adaptive immune cells.

Role of TNFR-related 2 mediated immune responses in dextran sulfate sodium-induced inflammatory bowel disease

Previous work has suggested that the LIGHT-TR2 costimulatory pathway plays a role in the acute and chronic stages of dextran sulfate sodium (DSS)-induced colitis [Steinberg et al. (2008); Wang et al. (2005)]. To clarify the role of TNFR-related 2 (TR2) signaling in the maintenance of intestinal homeostasis, we generated a TR2 knock-out (KO) mouse. Using DSS to induce colitis, we compared the colitic symptoms and pathological changes in wild type (WT) and TR2 KO mice, and the production of cytokines by the diseased colons. We also studied the role of TR2 in suppressing innate and adaptive immunity in the DSS model. TR2 deficient mice were characterized by reduced symptoms of intestinal inflammation compared with wild-type mice, and reduced production of cytokines. We therefore generated a monoclonal antibody against mouse TR2 which was specific to TR2 and capable of blocking TR2 signals. With this antibody, we demonstrated that antagonizing TR2 during the development of DSS-induced colitis reduced the symptoms of inflammation. Our findings suggest that TR2 is an important mediator in colitis, and may serve as a therapeutic target in inflammatory bowel disease.

IL-33 is a crucial amplifier of innate rather than acquired immunity

IL-33, a member of the IL-1-related cytokines, is considered to be a proallergic cytokine that is especially involved in Th2-type immune responses. Moreover, like IL-1α, IL-33 has been suggested to act as an "alarmin" that amplifies immune responses during tissue injury. In contrast to IL-1, however, the precise roles of IL-33 in those settings are poorly understood. Using IL-1- and IL-33-deficient mice, we found that IL-1, but not IL-33, played a substantial role in induction of T cell-mediated type IV hypersensitivity such as contact and delayed-type hypersensitivity and autoimmune diseases such as experimental autoimmune encephalomyelitis. Most notably, however, IL-33 was important for innate-type mucosal immunity in the lungs and gut. That is, IL-33 was essential for manifestation of T cell-independent protease allergen-induced airway inflammation as well as OVA-induced allergic topical airway inflammation, without affecting acquisition of antigen-specific memory T cells. IL-33 was significantly involved in the development of dextran-induced colitis accompanied by T cell-independent epithelial cell damage, but not in streptozocin-induced diabetes or Con A-induced hepatitis characterized by T cell-mediated apoptotic tissue destruction. In addition, IL-33-deficient mice showed a substantially diminished LPS-induced systemic inflammatory response. These observations indicate that IL-33 is a crucial amplifier of mucosal and systemic innate, rather than acquired, immune responses.

Bacteria penetrate the inner mucus layer before inflammation in the dextran sulfate colitis model

Background

Protection of the large intestine with its enormous amount of commensal bacteria is a challenge that became easier to understand when we recently could describe that colon has an inner attached mucus layer devoid of bacteria (Johansson et al. (2008) Proc. Natl. Acad. Sci. USA 105, 15064–15069). The bacteria are thus kept at a distance from the epithelial cells and lack of this layer, as in Muc2-null mice, allow bacteria to contact the epithelium. This causes colitis and later on colon cancer, similar to the human disease Ulcerative Colitis, a disease that still lacks a pathogenetic explanation. Dextran Sulfate (DSS) in the drinking water is the most widely used animal model for experimental colitis. In this model, the inflammation is observed after 3–5 days, but early events explaining why DSS causes this has not been described.

Principal Findings

When mucus formed on top of colon explant cultures were exposed to 3% DSS, the thickness of the inner mucus layer decreased and became permeable to 2 µm fluorescent beads after 15 min. Both DSS and Dextran readily penetrated the mucus, but Dextran had no effect on thickness or permeability. When DSS was given in the drinking water to mice and the colon was stained for bacteria and the Muc2 mucin, bacteria were shown to penetrate the inner mucus layer and reach the epithelial cells already within 12 hours, long before any infiltration of inflammatory cells.

Conclusion

DSS thus causes quick alterations in the inner colon mucus layer that makes it permeable to bacteria. The bacteria that reach the epithelial cells probably trigger an inflammatory reaction. These observations suggest that altered properties or lack of the inner colon mucus layer may be an initial event in the development of colitis.

PPARα contributes to colonic protection in mice with DSS-induced colitis

Inflammatory bowel disease (IBD) is characterized by repeated chronic inflammation of the gastrointestinal tract. We have used the complementary model of colonic inflammation to examine the roles of peroxisome proliferator-activated receptor α (PPARα) in colonic inflammation and thus its possible role in IBD. We characterized an innate immune-mediated model of colitis induced by dextran sulfate sodium (DSS). Mice with DSS-induced colitis were injected with Wy-14643 (2 mg/kg) as a PPARα agonist every day from day 0 to day 5. We show that mice given Wy-14643 were less susceptible to experimental acute colitis induced by DSS, and this decreased susceptibility was correlated with decreased production of IFNγ, IL-1β, IL-6, and TNF-α. Our findings suggest that PPARα has a role in controlling colonic inflammation and mucosal tissue homeostasis.

IL-33 and IL-33 receptors in host defense and diseases

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family, which includes IL-1 and IL-18. IL-33 is considered to be crucial for induction of Th2-type cytokine-associated immune responses such as host defense against nematodes and allergic diseases by inducing production of such Th2-type cytokines as IL-5 and IL-13 by Th2 cells, mast cells, basophils and eosinophils. In addition, IL-33 is involved in the induction of non-Th2-type acute and chronic inflammation as a proinflammatory cytokine, similar to IL-1 and IL-18. In this review, we summarize and discuss the current knowledge regarding the roles of IL-33 and IL-33 receptors in host defense and disease development.

Abscisic acid ameliorates experimental IBD by downregulating cellular adhesion molecule expression and suppressing immune cell infiltration

BACKGROUND & AIMS

Abscisic acid (ABA) has shown effectiveness in ameliorating inflammation in obesity, diabetes and cardiovascular disease models. The objective of this study was to determine whether ABA prevents or ameliorates experimental inflammatory bowel disease (IBD).

METHODS

C57BL/6J mice were fed diets with or without ABA (100mg/kg) for 35 days prior to challenge with 2.5% dextran sodium sulfate (DSS). The severity of clinical disease was assessed daily. Colonic mucosal lesions were evaluated by histopathology, and cellular adhesion molecular and inflammatory markers were assayed by real-time quantitative PCR. Flow cytometry was used to quantify leukocyte populations in the blood, spleen, and mesenteric lymph nodes (MLN). The effect of ABA on cytotoxic T-lymphocyte antigen 4 (CTLA-4) expression in splenocytes was also investigated.

RESULTS

ABA significantly ameliorated disease activity, colitis and reduced colonic leukocyte infiltration and inflammation. These improvements were associated with downregulation in vascular cell adhesion marker-1 (VCAM-1), E-selectin, and mucosal addressin adhesion marker-1 (MAdCAM-1) expression. ABA also increased CD4(+) and CD8(+) T-lymphocytes in blood and MLN and regulatory T cells in blood. In vitro, ABA increased CTLA-4 expression through a PPAR γ-dependent mechanism.

CONCLUSIONS

We conclude that ABA ameliorates gut inflammation by modulating T cell distribution and adhesion molecule expression.

TLR5 is not required for flagellin-mediated exacerbation of DSS colitis

BACKGROUND

The two forms of human inflammatory bowel disease, Crohn's disease (CD) and ulcerative colitis (UC), are both associated with loss of tolerance to gut microbial antigens. The dominant antigen recognized by antibody and T-cell responses in patients with CD is bacterial flagellin. Flagellin is also the only known ligand for Toll-like receptor 5 (TLR5), a key protein in innate immunity. Although flagellin activates TLR5 to produce inflammatory responses in many cell types in the gut, there is conflicting evidence as to whether TLR5 is harmful or protective in CD and murine colitis models. A recent study found that administration of flagellin enemas to mice along with dextran sodium sulfate (DSS) made their colitis worse.

METHODS

We sought to determine whether this exacerbation was due to TLR5 ligation, or to TLR5-independent adaptive immune responses to flagellin as an antigen, by using a transposon insertional mutant of the Escherichia coli H18 flagellin, 2H3, which lacks TLR5 stimulatory activity.

RESULTS

We found that flagellin enemas produced only a mild exacerbation of DSS colitis, and that 2H3 was equivalent to or worse than wildtype flagellin. Moreover, we found that DSS colitis was more severe in TLR5(-/-) mice than wildtype C57BL/6 mice.

CONCLUSIONS

Together, these results suggest that flagellin-mediated exacerbation of colitis is independent of TLR5.

Inhibition of HDAC9 increases T regulatory cell function and prevents colitis in mice

BACKGROUND & AIMS

Foxp3+ T regulatory cells (Tregs) help prevent autoimmunity, and increases in their numbers of functions could decrease the development of inflammatory bowel disease. Like other cells, Foxp3+ Tregs express histone/protein deacetylases (HDACs), which regulate chromatin remodeling and gene expression. We investigated whether disruption of a specific class IIa HDAC, HDAC9, activity in Tregs affects the pathogenesis of colitis in mice.

METHODS

We tested the effects of various HDAC inhibitors (HDACi) in models of colitis using wild-type mice. We also transferred Tregs and non-Treg cells from HDAC9-/- or wild-type mice to immunodeficient mice. HDAC9 contributions to the functions of Tregs were determined during development and progression of colitis.

RESULTS

Pan-HDACi, but not class I-specific HDACi, increased the functions of Foxp3+ Tregs, prevented colitis, and reduced established colitis in mice, indicating the role of class II HDACs in controlling Treg function. The abilities of pan-HDACi to prevent/reduce colitis were associated with increased numbers of Foxp3+ Tregs and their suppressive functions. Colitis was associated with increased local expression of HDAC9; HDAC9-/- mice resistant to development of colitis. HDAC9-/- Tregs expressed increased levels of the heat shock protein (HSP) 70, compared with controls. Immunoprecipitation experiments indicated an interaction between HSP70 and Foxp3. Inhibition of HSP70 reduced the suppressive functions of HDAC9-/- Tregs; Tregs that overexpressed HSP70 had increased suppressive functions.

CONCLUSIONS

Strategies to decrease HDAC9 expression or function in Tregs or to increase expression of HSP70 might be used to treat colitis and other autoimmune disorders.

Degraded carrageenan causing colitis in rats induces TNF secretion and ICAM-1 upregulation in monocytes through NF-kappaB activation

Carrageenan (CGN) is a high molecular weight sulphated polysaccharide derived from red seaweeds. In rodents, its degraded forms (dCGN) can induce intestinal inflammation associated with macrophage recruitment and activation. The aim of this study was: 1) to analyze the size-dependent effects of dCGN on colon inflammation in vivo, and 2) to correlate these effects with monocyte/macrophage proliferation, cytokine production and expression of various cell surface antigens including ICAM-1 adhesion molecule. Peripheral blood monocytes (PBM) and THP-1 monocytic cells were cultured in the presence of either 10 or 40 kDa, dCGN. The 40 kDa, but not the 10 kDa dCGN, induced colitis in in vivo. Degraded CGN inhibited THP-1 cell proliferation in vitro, arresting the cells in G1 phase. In addition, dCGN increased ICAM-1 expression in both PBM and THP-1 cells with a major effect seen after 40 kDa dCGN exposure. Also, dCGN stimulated monocyte aggregation in vitro that was prevented by incubation with anti-ICAM-1 antibody. Finally, dCGN stimulated TNF-α expression and secretion by both PBM and THP-1 cells. All these effects were linked to NF-κB activation. These data strongly suggest that the degraded forms of CGN have a pronounced effect on monocytes, characteristic of an inflammatory phenotype.

Adrenomedullin treatment reduces intestinal inflammation and maintains epithelial barrier function in mice administered dextran sulphate sodium

Hyperactivation and hyperpermeability of the intestinal epithelium is a hallmark of IBD. AM has been shown to reduce the severity of colitis in the acetic acid and TNBS-induced colitis model, however the mechanism of the therapeutic effect of AM against the colitis has not been clarified. Here, we show that the protective capability of AM is associated with suppression of inflammation and maintenance of the intestinal epithelial barrier function. In the DSS-induced colitis model, intra-rectal AM-treated mice showed a reduction in loss of body weight and severity of colitis. AM-treatment suppressed phosphorylation of STAT1 and STAT3 in the colonic epithelium, and altered the cytokine balance in the intestinal T cells, with lower levels of IFN-gamma and TNF-alpha but higher levels of TGF-beta. Expression of the epithelial intercellular junctions such as tight and adherence junctions were sustained in the AM-treated mice. In contrast, the epithelial junctions were down-regulated in the control mice, leading to loss of epithelial barrier integrity and enhanced permeability. Collectively, these data indicate a broad spectrum of AM-induced effects with respect to protection against DSS-induced colitis, and suggest a potential therapeutic value of this treatment for IBD.

An FcRn-dependent role for anti-flagellin immunoglobulin G in pathogenesis of colitis in mice

BACKGROUND & AIMS

The neonatal Fc receptor for immunoglobulin (Ig)G (FcRn) protects monomeric IgG from catabolism in parenchymal and hematopoietic cells during adult life. In dendritic cells, FcRn also promotes presentation of antigens in association with IgG. Because IgGs with anti-bacterial specificity are a hallmark of inflammatory bowel disease, we sought to determine their significance and relationship to FcRn expression in antigen-presenting cells, focusing on IgGs specific for flagellin.

METHODS

Levels of circulating anti-flagellin IgG were induced in wild-type and FcRn(-/-) mice, followed by induction of colitis with dextran sodium sulfate (DSS). Bone marrow chimera models were used to localize the site of FcRn action.

RESULTS

Wild-type mice that received anti-flagellin IgG exhibited more severe colitis following administration of DSS, compared with mice that received control IgG. Wild-type mice immunized with flagellin exhibited significantly more severe colitis in response to DSS administration than that observed in similarly treated FcRn(-/-) mice. In chimera studies, FcRn(-/-) mice given wild-type bone marrow and immunized with flagellin exhibited significantly more colitis than wild-type mice given FcRn(-/-) bone marrow and immunized with flagellin. Serum anti-flagellin IgG levels were similar in both sets of chimeric mice, consistent with the equal participation of hematopoietic and nonhematopoeitic cells in FcRn-mediated IgG protection.

CONCLUSIONS

Anti-bacterial IgG antibodies are involved in the pathogenesis of colitis; this pathway requires FcRn in antigen presenting cells, the major subset of hematopoietic cells that express FcRn.

Induction and cellular expression of tartrate resistant acid phosphatase during dextran sodium sulphate induced colitis in rats

The aim of this study was to investigate the cellular and molecular expression of tartrate resistant acid phosphatase (TRAP) as a marker of activated macrophages in macrophage dependent dextran sulphate sodium (DSS)-induced colitis in rats. In normal colon, TRAP+/CX(3)CR(1)+ macrophages were located in the upper part of the lamina propria. In the early stage (day 1-3) of acute colitis prior to histopathological changes, induction of the cytokines TNFalpha, IL-12 and IFN gamma occurred concomitant with increased mRNA and enzyme activity of TRAP along with a slight increase of TRAP immunolabelling in macrophages of the upper lamina propria, suggesting induction of TRAP in resident macrophages. Among these cytokines, TNFalpha up-regulated TRAP expression in the RAW 264.7 monocyte/macrophage cell line. In a later phase (day 7) with fulminant colitis, a massive infiltration of macrophages including recruited TRAP+/CCR2+ cells was observed also in the lower part of the lamina propria as well as in the submuscular layer. Additionally, differentiated cellular expression of pro- and mature TRAP also suggest that mucosal macrophages in the lower part of lamina propria bordering the sub-mucosa provide a source of replenishment of macrophages situated in the upper lamina propria. In conclusion, induction of TRAP provides an early sign of macrophage responsiveness in DSS induced colitis.

Suppression of experimental colitis in mice by CD11c+ dendritic cells

BACKGROUND

The innate immune system serves a critical role in homeostasis of the gastrointestinal (GI) tract. Both macrophages (MØs) and dendritic cells (DCs) have been shown to have pathogenic roles in animal models of inflammatory bowel disease. However, studies by several labs have established that resident MØs and DCs within the normal GI tract maintain an immunosuppressive phenotype compared to that seen in other peripheral sites. Recent studies by our lab demonstrated that the depletion of both MØs and DCs before the initiation of dextran sodium sulfate (DSS)-induced colitis resulted in exacerbation of disease, partly caused by increased neutrophil influx.

METHODS/RESULTS

In this current report, DSS-induced colitis was shown to be significantly more severe when DCs were selectively depleted in mice as indicated by changes in weight loss, stool consistency, rectal bleeding, and histopathology. In contrast to enhanced colitis in MØ/DC-depleted mice, which was associated with increased neutrophil influx, increased colitis in DC-depleted mice was not associated with an increase in neutrophils in the colon, as shown by CXCL1 chemokine levels and myeloperoxidase (MPO) activity. However, increased IL-6 gene and protein expression in colon tissues correlated positively with increased colitis severity in DC-depleted mice compared to colitis in DC-intact mice.

CONCLUSIONS

This study demonstrates that resident DCs can suppress the severity of acute DSS colitis and that regulation of IL-6 production may contribute to DC-mediated control of intestinal inflammation.

Innate and adaptive interleukin-22 protects mice from inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disease thought to be mediated by dysfunctional innate and/or adaptive immunity. This aberrant immune response leads to the secretion of harmful cytokines that destroy the epithelium of the gastrointestinal tract and thus cause further inflammation. Interleukin-22 (IL-22) is a T helper 17 (Th17) T cell-associated cytokine that is bifunctional in that it has both proinflammatory and protective effects on tissues depending on the inflammatory context. We show herein that IL-22 protected mice from IBD. Interestingly, not only was this protection mediated by CD4+ T cells, but IL-22-expressing natural killer (NK) cells also conferred protection. In addition, IL-22 expression was differentially regulated between NK cell subsets. Thus, both the innate and adaptive immune responses have developed protective mechanisms to counteract the damaging effects of inflammation on tissues.

Innate and adaptive interleukin-22 protects mice from inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disease thought to be mediated by dysfunctional innate and/or adaptive immunity. This aberrant immune response leads to the secretion of harmful cytokines that destroy the epithelium of the gastrointestinal tract and thus cause further inflammation. Interleukin-22 (IL-22) is a T helper 17 (Th17) T cell-associated cytokine that is bifunctional in that it has both proinflammatory and protective effects on tissues depending on the inflammatory context. We show herein that IL-22 protected mice from IBD. Interestingly, not only was this protection mediated by CD4+ T cells, but IL-22-expressing natural killer (NK) cells also conferred protection. In addition, IL-22 expression was differentially regulated between NK cell subsets. Thus, both the innate and adaptive immune responses have developed protective mechanisms to counteract the damaging effects of inflammation on tissues.

Leukocyte adhesion molecules in animal models of inflammatory bowel disease

The dysregulated recruitment of leukocytes into the intestine is required for the initiation and maintenance of inflammatory bowel disease (IBD). Several families of molecules regulate the influx of these cells into sites of inflammation. Interference with some of these molecules has already shown efficacy in the clinics and antibodies that target the molecules involved have been approved by the FDA for use in Crohn's disease (CD), multiple sclerosis (i.e., natalizumab), and psoriasis (i.e., efalizumab). Here, we discuss basic aspects of the different families of relevant molecules and compile a large body of preclinical studies that supported the targeting of specific steps of the leukocyte adhesion cascade for therapeutic purposes in colitis and in novel models of CD-like ileitis.

CD5 plays an inhibitory role in the suppressive function of murine CD4(+) CD25(+) T(reg) cells

A subset of CD4(+) T cells, the CD4(+) CD25(+) regulatory T (T(reg)) cells in the lymphoid organs and peripheral blood are known to possess suppressive function. Previous in vitro and in vivo studies have indicated that T cell receptor (TCR) signal is required for development of such 'natural regulatory (T(reg)) cells' and for activation of the effector function of CD4(+) CD25(+) regulatory T cells. CD5 is a cell surface molecule present on all T cells and a subtype of B lymphocytes, the B-1 cells, primarily localized to coelomic cavities, Peyer's patches, tonsils and spleen. CD5 acts as a negative regulator of T cell and B cell signaling via recruitment of SHP-1. Here, we demonstrate that T(reg) cells obtained from CD5(-/-) mice are more potent than those from wild type mice in suppressing the in vitro cell proliferation of anti-CD3 stimulated CD4(+) CD25(-) responder T cells. This phenomenon was cell contact and GITR dependent. Lack of CD5 expression on T(reg) cells (from spleen, lymph node and thymus) did not affect the intracellular levels of Foxp3. However, CD5(-/-) T(reg) thymocytes were able to elicit a higher Ca(2+) response to TCR + co-stimulatory signals than the wild type cells. CD5(-/-) mice expressed more Foxp3 mRNA in the colon than wild type mice, and additionally, the severity of the dextran sulfate sodium (DSS)-induced colitis in CD5(-/-) mice was less than the wild type strain. We suggest that manipulation of CD5 expression or the downstream signaling components of CD4(+) CD25(+) T(reg) cells as a potential strategy for therapeutic intervention in cases of auto-immune disorders.

Mucosal macrophages and the regulation of immune responses in the intestine

The healthy intestinal mucosa is home to one of the largest populations of macrophages (mvarphi) in the body [Lee SH, Starkey PM, Gordon S. Quantitative analysis of total macrophage content in adult mouse tissues. Immunochemical studies with monoclonal antibody F4/80. J Exp Med 1985;161:475-89], yet little is known about their function. Resident mvarphi in the large and small intestine are distinct from other mvarphi populations in the body, with regards to both their functional properties and surface phenotype. They respond in an unconventional manner to inflammatory stimuli, with little upregulation of proteins involved in antigen presentation and T cell co-stimulation, and no production of pro-inflammatory cytokines. This suggests that under resting conditions, intestinal mvarphi may be conditioned to be anti-inflammatory in response to local stimuli such as commensal bacteria. In contrast, during inflammation, intestinal mvarphi exhibit increased bactericidal and inflammatory abilities, promote protective immunity and/or mediate pathology. Thus the status of this cell may be the key to understanding how the intestine maintains a balance between being able to generate protective immunity against pathogens, but still prevent pathological inflammation under normal conditions. In this review, we discuss the current knowledge of intestinal mvarphi biology, and highlight the different levels of immunoregulation which influence these cells, with particular focus on innate pathogen recognition receptor (PRR) function and responsiveness to microbial stimuli.

The ICE inhibitor pralnacasan prevents DSS-induced colitis in C57BL/6 mice and suppresses IP-10 mRNA but not TNF-alpha mRNA expression

Previously we demonstrated an ameliorating effect of the interleukin-1beta converting enzyme (ICE) inhibitor pralnacasan on dextran sulfate sodium (DSS)-induced colitis. This study investigates the effects of pralnacasan on cytokine expression in DSS-induced colitis. Colitis was induced by oral administration of DSS. Mice were treated intraperitoneally with the ICE inhibitor pralnacasan (50 mg/kg body weight twice daily). Body weight as well as the presence of occult blood or diarrhea was monitored daily. Subgroups were sacrificed at days 4, 8, and 11 after the beginning of DSS application. Cytokine profiles in colonic tissue were analyzed on the protein level by ELISA and on the mRNA level by real time RT-PCR. Administration of DSS led to an increase in IL-18, IL-12, TNF-alpha, and IFN-gamma protein as well as IP-10 and TNF-alpha mRNA. The increase in IL-18 and IFN-gamma was reduced by ICE inhibition. Pralnacasan prevented DSS-induced colitis in C57BL/6 mice. In C57BL/6 mice, the DSS-induced increase in IP-10 mRNA, but not TNF-alpha mRNA, was completely prevented by ICE inhibition. In conclusion, prevention of colitis in C57BL/6 mice was associated with a suppresion of IP-10 mRNA, but not TNF-alpha mRNA expression, indicating that IL-18-mediated cytokine production is a key element in the pathogenesis of DSS-induced colitis.

Dextran sulfate sodium-induced colitis generates a transient thymic involution--impact on thymocyte subsets

One of the most widely used animal models for inflammatory bowel disease (IBD) is the dextran sulfate sodium (DSS)-induced colitis. We have previously reported that 5 days administration of DSS in C57Bl/6J mice induces a colonic inflammation that progresses into chronicity after DSS removal, whereas in BALB/cJ mice the inflammation resolves within 4 weeks post-DSS. Here we show that both thymic size and thymocyte numbers dramatically decreased in the acute phase of inflammation in C57Bl/6 mice, 7 days after DSS withdrawal. Mature, CD4(+) and CD8(+) single positive (SP) CD69(lo) CD62L(hi) thymocytes were enriched in these mice, accompanied by a major decrease in the number of immature double positive (DP) thymocytes. However, the different maturation stages within the DP thymocyte subset were unchanged between healthy and inflamed C57Bl/6J mice. Interestingly, as the inflammation progressed into the chronic phase, the thymus recovered and 2 weeks after the acute inflammatory phase all the thymic parameters investigated in this study were restored to normal. In contrast, BALB/cJ mice only develop mild thymic alterations. Nevertheless, we found that within the double negative (DN) thymocytes an increased frequency and also total numbers of CD44(+) CD25(-) (DN1) cells correlated with the severity of colitis, and that the frequency of CD44(-) CD25(-) (DN4) thymocytes decreased proportionally in the acute phase in BALB/cJ mice. Our observations suggest that the thymic effects are intimately connected to the intestinal inflammatory response in colitis regardless of the inflammatory stimuli.

Vitamin D and the vitamin D receptor are critical for control of the innate immune response to colonic injury

Background

The active form of vitamin D (1,25(OH)₂D₃) has been shown to inhibit development of inflammatory bowel disease (IBD) in IL-10 KO mice. Here, the role of the vitamin D receptor (VDR) and 1,25(OH)₂D₃ in acute experimental IBD was probed.

Results

VDR KO mice were extremely sensitive to dextran sodium sulfate (DSS) and there was increased mortality of the VDR KO mice at doses of DSS that only caused a mild form of colitis in wildtype (WT) mice. DSS colitis in the VDR KO mice was accompanied by high colonic expression of TNF-α, IL-1 α, IL-1β, IL-12, IFN-γ, IL-10, MIP-1α and KC. DSS concentrations as low as 0.5% were enough to induce bleeding, ulceration and weight loss in VDR KO mice. VDR KO mice failed to recover following the removal of DSS, while WT mice showed signs of recovery within 5 days of DSS removal. The early mortality of DSS treated VDR KO mice was likely due to perforation of the bowel and resulting endotoxemia. VDR KO mice were hyper-responsive to exogenously injected LPS and cultures of the peritoneal exudates of moribund DSS treated VDR KO mice were positive for bacterial growth. 1,25(OH)₂D₃ in the diet or rectally decreased the severity and extent of DSS-induced inflammation in WT mice.

Conclusion

The data point to a critical role for the VDR and 1,25(OH)₂D₃ in control of innate immunity and the response of the colon to chemical injury.

Triggering endogenous immunosuppressive mechanisms by combined targeting of Dipeptidyl peptidase IV (DPIV/CD26) and Aminopeptidase N (APN/ CD13)--a novel approach for the treatment of inflammatory bowel disease

The ectopeptidases Dipeptidylpeptidase IV and Alanyl-Aminopeptidase N, strongly expressed by both, activated and regulatory T cells were shown to co-operate in T cell regulation. Based on the findings that DPIV and APN inhibitors induce the TGF-beta1 and IL-10 production and a suppression of T helper cell proliferation in parallel, and that particularly APN inhibitors amplify the suppressing activity of regulatory T cells, both peptidases represent a promising target complex for treatment of diseases associated with an imbalanced T cell response, such as inflammatory bowel diseases (IBD). The aim of the present study was to analyze the therapeutic potential of DPIV and APN inhibitors in vivo in a mouse model of colitis. Balb/c mice received 3% (w/v) dextran sulphate sodium with the drinking water for 7 days. After onset of colitis symptoms, inhibitor treatment started at day 3. Disease activity index (DAI) was assessed daily, supplemented by histological and immunological analysis. While the DPIV inhibitor Lys-[Z(NO])(2)]-pyrrolidide or the APN-inhibitor Actinonin alone had marked but no significant therapeutic effects, the simultaneous administration of both inhibitors reduced colitis activity in comparison to placebo treated mice, significantly (DAI 4.8 vs. 7.7, p<0.005). A newly developed compound IP12.C6 with inhibitory capacity toward both enzymes significantly attenuated the clinical manifestation of colitis (DAI 3.2 vs. 7.6, p<0.0001). TGF-beta mRNA was found to be up-regulated in colon tissue of inhibitor-treated animals. In summary our results strongly suggest that combined DPIV and APN inhibition by synthetic inhibitors represents a novel and efficient approach for the pharmacological therapy of IBD by triggering endogenous immunosuppressive mechanisms.

Contribution of polymeric immunoglobulin receptor to regulation of intestinal inflammation in dextran sulfate sodium-induced colitis

BACKGROUND

Inflammatory bowel disease (IBD) affects approximately 4 million people worldwide and can be caused by dysregulated mucosal immune responses to the intestinal commensal microflora. Immunoglobulin A (IgA) is considered to be the principal antibody in intestinal secretions and functions to prevent commensals and pathogenic organisms from gaining access to epithelial cell surfaces. Immunoglobulin A deficiency in humans has been associated with celiac disease and ulcerative colitis. However, the precise role of IgA in the pathogenesis of these disorders is yet to be fully understood.

METHODS

Mice with a targeted disruption in IgA production (IgA(-/-) mice) and polymeric immunoglobulin receptor (pIgR(-/-) mice) were analyzed for the contribution of secretory immunity in the pathogenesis of dextran sulfate sodium (2.5%)-induced colitis.

RESULTS

It was found that dextran sulfate sodium-treated pIgR(-/-) mice displayed greater loss of bodyweight and had severe clinical illness compared to similarly treated IgA(-/-) mice and wild-type animals. Additionally, colonic tissues from the pIgR(-/-) mice exhibited progressively and significantly greater degrees of mucosal edema, ulceration, crypt abscesses and macrophage infiltration when compared to similarly treated IgA(-/-) mice and wild-type animals.

CONCLUSIONS

The results indicate that secretory immunoglobulins contribute to protection of the colonic mucosa against dextran sulfate sodium-induced epithelial injury, although the isotype of the secretory immunoglobulin (IgA or IgM) may not be a decisive factor in such protection. Collectively, the pIgR and/or the secretory component are important for the maintenance of epithelial integrity and mucosal homeostasis in the colonic epithelium.

Suppression of experimental colitis by intestinal mononuclear phagocytes

The contribution of innate immunity to inflammatory bowel disease (IBD) remains an area of intense interest. Macrophages (MØ) and dendritic cells (DC) are considered important factors in regulating the onset of IBD. The goal of this study was to determine if intestinal mononuclear phagocytes (iMNP) serve a pathological or protective role in dextran sulfate sodium (DSS)-induced colitis in mice. Using a conditional MØ/DC depletion transgenic mouse line--MØ Fas-induced apoptosis--to systemically deplete iMNP, DSS colitis histopathology was shown to be more severe in MØ/DC-depleted compared with MØ/DC-intact mice. Similarly, localized iMNP depletion by clodronate-encapsulated liposomes into C57BL/6, BALB/c, and CB.17/SCID mice also increased DSS colitis severity, as indicated by increased histopathology, weight loss, rectal bleeding, decreased stool consistency, and colon length compared with MØ/DC-intact, DSS-treated mice. Histology revealed that iMNP depletion during DSS treatment led to increased neutrophilic inflammation, increased epithelial injury, and enhanced mucin depletion from Goblet cells. iMNP depletion did not further elevate DSS-induced expression of TNF-alpha and IFN-gamma mRNA but significantly increased expression of CXCL1 chemokine mRNA. Myeloperoxidase activity was increased in colons of MØ/DC-depleted, DSS-treated mice, compared with DSS alone, coincident with increased neutrophil infiltration in diseased colons. Neutrophil depletion combined with MØ/DC depletion prevented the increase in DSS colitis severity compared with MØ/DC depletion alone. This study demonstrates that iMNP can serve a protective role during development of acute colitis and that protection is associated with MØ/DC-mediated down-regulation of neutrophil infiltration.

Involvement of lymphocytes in dextran sulfate sodium-induced experimental colitis

AIM: To investigate the roles of lymphocytes in the development of dextran sulfate sodium-induced colitis.

METHODS: Using various doses of dextran sulfate sodium (DSS), we induced colitis in wild-type B6 control and Rag-1 knockout (H-2^b haplotype) mice, and evaluated the colitis in terms of symptomatic and histologic parameters, such as weight loss, survival, severity of diarrhea, shortage of colon length and histological changes. Symptomatic parameters were checked daily and histological changes were scored.

RESULTS: Although development of colitis in Rag-1 knockout mice treated with high dose (5%) of DSS was comparable to that in B6 control mice, colitis progression was much more tolerable in Rag-1 knockout mice compared to than in B6 mice treated with low dose (1.5%) DSS. Symptomatic parameters as well as histopathologic changes were improved in Rag-1 knockout mice.

CONCLUSION: These results indicate that the presence of lymphocytes contributes to colitis progression at low dose of DSS stimulation. Lymphocytes may play roles as an aggravating factor in DSS-induced colitis.

Short-term treatment with anti-CD44v7 antibody, but not CD44v4, restores the gut mucosa in established chronic dextran sulphate sodium (DSS)-induced colitis in mice

Increased expression of CD44 variant isoforms have been shown on the inflammatory infiltrates in human and mouse colitis and blockade or deletion of CD44 isoforms inhibit experimental colitis. The objective of this study was to find out if short-term treatment of CD44 antibodies specific to CD44v7, but not to other variant isoforms, suppresses leucocyte-endothelial interaction in chronic dextran sodium sulphate (DSS)-induced colitis in mice. Chronic colitis was induced by oral administration of four cycles of 5% DSS in BALB/c mice. Expression of CD44 was investigated on isolated mononuclear cells of the gut immune system. In established colitis, mice were treated with antibodies against CD44v7 or CD44v4 three times in 7 days. Intravital microscopy was used to study leucocyte-endothelial interactions and leucocyte extravasation. As a marker of inflammatory infiltrates myeloperoxidase was quantified in gut tissue. CD44-induced apoptosis was determined by fluorescence staining of hypodiploidic cell nuclei. In chronic DSS-induced colitis both CD44 variant isoforms, v4 and v7 were significantly up-regulated on mononuclear cells. However, whereas anti-CD44v7 antibody treatment induced a marked restoration of the gut mucosa and significantly reduced endothelial sticking and extravasation of circulating leucocyte in vivo (P < 0.01), application of anti-CD44v4 or an isotype control antibody had no anti-inflammatory effect. A significant reduction of myeloperoxidase activity was detected after blockade of CD44v7, but not v4. Short-term treatment with anti-CD44v7 antibody blocks T cell extravasation and recruitment to the intestinal mucosa and cures established experimental colitis.

T helper 1-inducing property of IL-27/WSX-1 signaling is required for the induction of experimental colitis

BACKGROUND

WSX-1, a component of the interleukin (IL)-27 receptor, is a novel class I cytokine receptor with homology to the IL-12 receptor beta2 chain. Initially, WSX-1 signaling was reported to play an important role in the promotion of T helper-1 responses, but recent reports have revealed an anti-inflammatory property in WSX-1 signaling. In the present study, we investigated the role of IL-27/WSX-1 signaling in a murine colitis model, dextran sulfate sodium (DSS) colitis, by using WSX-1 knockout (KO) mice.

METHODS

First, we observed whether WSX-1 KO mice developed colitis spontaneously. Second, we induced DSS colitis in WSX-1 KO and wild-type (WT) mice.

RESULTS

WSX-1 KO mice were observed not to develop colitis spontaneously. The severity of DSS colitis was decreased in WSX-1 KO mice in comparison with WT mice in association with a reduced production of interferon-gamma, IL-6, and tumor necrosis factor-alpha by lamina propria mononuclear cells from WSX-1 KO mice and the absence of T-bet expression in the colon from WSX-1 KO mice.

CONCLUSIONS

This study revealed the inflammatory property of IL-27/WSX-1 signaling in intestinal inflammation. As a result, IL-27/WSX-1 signal pathway may thus be a promising candidate for the therapeutic intervention of human inflammatory bowel diseases such as Crohn's disease and ulcerative colitis.

Partially hydrolyzed guar gum down-regulates colonic inflammatory response in dextran sulfate sodium-induced colitis in mice

Partially hydrolyzed guar gum (PHGG), a water-soluble dietary fiber produced by a controlled partial enzymatic hydrolysis of guar gum beans, has various physiological actions. The aim of the present study was to elucidate the beneficial effects of PHGG on colonic mucosal damage and on the inflammatory response in a dextran sulfate sodium (DSS) colitis model. After 2 weeks of prefeeding of PHGG, acute colitis was induced with 8% DSS in female BALB/c mice. Colonic mucosal inflammation was evaluated clinically, biochemically and histologically. Mucosal protein contents and mRNA levels of tumor necrosis factor-alpha (TNF-alpha) were determined by immunoassay and reverse transcription polymerase chain reaction. Disease activity scores determined by weight loss, stool consistency and blood in stool in DSS-treated mice were significantly lower in the PHGG-treated mice compared with the control mice. Shortening of the colon was significantly reversed by PHGG. Histological study also showed a reduced infiltration of inflammatory cells, especially neutrophils, and mucosal cell disruption in PHGG-treated mice compared with the control mice. The increases in tissue-associated myeloperoxidase activity and thiobarbituric acid-reactive substances after DSS administration were both significantly inhibited by pretreatment with PHGG. Partially hydrolyzed guar gum also inhibited increases in intestinal TNF-alpha protein and mRNA expression after DSS administration, respectively. These results suggest that chronic ingestion of PHGG prevents the development of DSS-induced colitis in mice via the inhibition of mucosal inflammatory response.

Activation of epithelial CD98 glycoprotein perpetuates colonic inflammation

Anomalies in the regulation and function of integrins have been implicated in the etiology of various pathologic conditions, including inflammatory disorders such as irritable bowel disease. Several classes of cell surface glycoproteins such as CD98 have been shown to play roles in integrins-mediated events. Here, we investigated the role of CD98 in intestinal inflammation using both in vivo and in vitro approaches. We found that in Caco2-BBE monolayers and colonic tissues, expression of CD98 was upregulated by the proinflammatory cytokine, interferon gamma (INF gamma). Furthermore, CD98 was highly upregulated in colonic tissues from mice with active colitis induced by dextran sodium sulfate (DSS), but not in DSS-treated INF gamma -/- mice. Administration of an anti-CD98 antibody worsened DSS-induced colitis in mice but had no effect on untreated control mice. Finally, we used Caco2-BBE cell monolayers to model intestinal epithelial wound healing, and found that activation of epithelial CD98 in DSS-treated monolayers inhibited monolayer reconstitution, but had no affect on untreated control monolayers. Our data collectively indicate that (i) CD98 upregulation is mediated by INF gamma during intestinal inflammation and (ii) activation of epithelial CD98 protein aggravates intestinal inflammation by reducing intestinal epithelial reconstitution. Overall, our data suggest that epithelial CD98 plays an important role in the perpetuation of intestinal inflammation.

Selective expression of detoxifying glutathione transferases in mouse colon: effect of experimental colitis and the presence of bacteria

Glutathione transferases (GSTs) play a central role in the cellular defense against harmful endogenous compounds and xenobiotics in mouse and man. The gastrointestinal channel is constantly exposed to bacteria, bacterial products, and xenobiotics. In the present study the distribution of alpha, mu, and pi class GSTs was examined immunohistologically in the colon of conventional and germ-free (GF) mice subjected to experimental colitis. The tissues samples were from conventional mice with and without colitis induced by dextran sulfate sodium (DSS); GF mice treated with DSS or carrageenan; and GF mice inoculated with normal mouse bacterial flora as well as with Lactobacillus GG. In conventional as well as in GF mice the mu and pi class GSTs showed reduced intestinal expression when colitis was induced. In con-rast, the level of GSTs reacting with antibodies directed against the alpha class, in particular mGST A4-4, was elevated after induction of inflammation. Of special interest is mGST A4-4 because of its high catalytic activity with toxic products of lipid peroxidation. In the colon of conventionalized GF mice that were given mouse intestinal flora, the mGST A4-4 expression was increased with time for several weeks, but then showed a decrease to a normal level. Additionally, the inoculation of GF mice with Lactobacillus GG induced all the intestinal GSTs studied.

Recognition of commensal microflora by toll-like receptors is required for intestinal homeostasis

Toll-like receptors (TLRs) play a crucial role in host defense against microbial infection. The microbial ligands recognized by TLRs are not unique to pathogens, however, and are produced by both pathogenic and commensal microorganisms. It is thought that an inflammatory response to commensal bacteria is avoided due to sequestration of microflora by surface epithelia. Here, we show that commensal bacteria are recognized by TLRs under normal steady-state conditions, and this interaction plays a crucial role in the maintenance of intestinal epithelial homeostasis. Furthermore, we find that activation of TLRs by commensal microflora is critical for the protection against gut injury and associated mortality. These findings reveal a novel function of TLRs-control of intestinal epithelial homeostasis and protection from injury-and provide a new perspective on the evolution of host-microbial interactions.

Inhibition of p38 MAP kinase- and RICK/NF-kappaB-signaling suppresses inflammatory bowel disease

Ulcerative colitis and Crohn's disease are the two entities of chronic inflammatory bowel diseases (IBD). One of the main pathogenic mechanisms is probably a dysregulated immune response triggered by products of the enteric bacterial flora. The goal of this study was to evaluate the effects of the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 on inflammatory responses using the DSS-induced experimental colitis model in mice reflecting human IBD. We found that SB203580 improved the clinical score, ameliorates the histological alterations, and reduces the mRNA levels of proinflammatory cytokines. In addition to p38 kinase activity, the "classical" and the "alternative" NF-kappaB pathways were also strongly activated during colitis induction. All three pathways were drastically down-regulated by SB203580 treatment. An analysis of the molecular basis of NF-kappaB activation revealed that Rip-like interacting caspase-like apoptosis-regulatory protein kinase (RICK), a key component of a pathway leading to NF-kappaB induction, is also strongly inhibited by SB203580. Since RICK is an effector kinase of NOD2, an intracellular receptor of bacterial peptidoglycan, these results support the notion that NOD signaling could play a pivotal role in the IBD pathogenesis. Thus, RICK could represent a novel target for future therapies in human IBD.