CD4+ T cells reactive to enteric bacterial antigens in spontaneously colitic C3H/HeJBir mice: increased T helper cell type 1 response and ability to transfer disease

Influence of intestinal bacteria on induction of regulatory T cells: lessons from a transfer model of colitis

BACKGROUND

The resident flora plays a critical role in initiation and perpetuation of intestinal inflammation, as demonstrated in experimental models of colitis where animals fail to develop disease under germ free conditions. However, the importance of exposure to commensal bacteria before the onset of colitis is unclear. Our aim was to investigate the influence of previous exposure of donor animals to bacterial antigens on colitis development using a transfer model.

METHODS

Clinical course and histology were evaluated after transfer of CD4(+)CD62L(+) lymphocytes from germ free and conventionally housed donor mice into SCID recipients. Cotransfer of CD4(+)CD62L(+) cells with CD4(+)CD62L(- )lymphocytes from both groups of mice was initiated. Lymphocytes were analysed by FACS, polarisation potential of cells determined, and cytokines measured within the supernatant by enzyme linked immunosorbent assay.

RESULTS

Animals that received cells from germ free donors developed an earlier onset of colitis compared with mice reconstituted with lymphocytes from conventionally housed animals. Additionally, CD4(+)CD62L(- )cells from germ free mice were not able to abrogate colitis induced by cotransfer with CD4(+)CD62L(+) lymphocytes whereas CD4(+)CD62L(- )T cells from normal mice ameliorated disease. The higher percentage of CD4(+)GITR(+) expressing lymphocytes and the production of interleukin 10 after priming by dendritic cells suggests the presence of T(reg) cells within the CD4(+)CD62L(+) lymphocyte subset derived from conventional housed mice and assumes a lack of T(reg) cells within germ free mice.

CONCLUSION

The results indicate that bacterial antigens are crucial for the generation and/or expansion of T(reg) cells in a healthy individual. Therefore, bacterial colonisation is of great importance in maintaining the immunological balance.

Cdcs1, a major colitogenic locus in mice, regulates innate and adaptive immune response to enteric bacterial antigens

BACKGROUND & AIMS

The absence of interleukin 10, a key cytokine in gut homeostasis, causes severe colitis in C3H/HeJBir but not C57BL/6J mice. The major modifier for colitis was mapped on chromosome 3 and designated cytokine deficiency-induced colitis susceptibility 1 (Cdcs1). We developed reciprocal Cdcs1 congenic stocks on both interleukin 10-deficient backgrounds to identify the susceptibility gene and its function.

METHODS

C3H/HeJBir congenic for the C57BL/6J-derived Cdcs1 allele and reciprocal C57BL/6J congenic for the C3H/HeJBir allele were analyzed for colitis development. Parental strains were compared by electrophoretic mobility shift assay to assess the candidacy of nuclear factor-kappaB p50 in the Cdcs1 interval. Functional differences were observed in innate and adaptive immune responses of parental and congenic stocks after bacterial ligand exposure in vitro (cytokine release from bone marrow-derived macrophage and dendritic cells) and in vivo (serum cytokines and primed CD4+ T cell proliferation).

RESULTS

Cdcs1 was positioned within a minimum 7-megabase interval containing nuclear factor-kappaB p50. C3H/HeJBir colitis was significantly diminished by the C57BL/6J genome in this interval. Conversely, colitis in C57BL/6J was significantly exacerbated by the reciprocal C3H/HeJBir genome. C3H/HeJBir macrophages constitutively expressed higher nuclear factor-kappaB p50. Functional assays showed that C3H/HeJBir showed reduced innate responsiveness both in vivo and in vitro to bacterial ligands but showed increased CD4 T-cell responses compared with C57BL/6J. This differential responsiveness was controlled by the respective allele at Cdcs1.

CONCLUSIONS

The colitogenic Cdcs1 allele impairs innate immunity to bacterial products and in turn skews the adaptive immune response toward compensatory hyperresponsiveness and chronic intestinal inflammation.

Experimental models of inflammatory bowel disease reveal innate, adaptive, and regulatory mechanisms of host dialogue with the microbiota

There are now many experimental models of inflammatory bowel disease (IBD), most of which are due to induced mutations in mice that result in an impaired homeostasis with the intestinal microbiota. These models can be clustered into several broad categories that, in turn, define the crucial cellular and molecular mechanisms of host microbial interactions in the intestine. The first of these components is innate immunity defined broadly to include both myeloid and epithelial cell mechanisms. A second component is the effector response of the adaptive immune system, which, in most instances, comprises the CD4+ T cell and its relevant cytokines. The third component is regulation, which can involve multiple cell types, but again particularly involves CD4+ T cells. Severe impairment of a single component can result in disease, but many models demonstrate milder defects in more than one component. The same is true for both spontaneous models of IBD, C3H/HeJBir and SAMPI/Yit mice. The thesis is advanced that 'multiple hits' or defects in these interacting components is required for IBD to occur in both mouse and human.

Rhinosinusitis derived Staphylococcal enterotoxin B possibly associates with pathogenesis of ulcerative colitis

Background

During clinical practice, we noticed that some patients with both ulcerative colitis (UC) and chronic rhinosinusitis (CRS) showed amelioration of UC after treatment of CRS. This study was designed to identify a possible association between CRS and UC.

Methods

Thirty-two patients with both CRS and UC received treatment with functional endoscopic sinus surgery (FESS) for CRS. Clinical symptom scores for CRS and UC, as well as serum levels of anti-Staphylococcal enterotoxin B (SEB) were evaluated at week 0 and week 12. Sinus wash fluid SEB content was measured with enzyme-linked immunosorbent assay (ELISA). The surgically removed tissues were cultured to identify growth of Staphylococcus. aureus (S. aureus). Immunohistochemistry was employed to identify anti-SEB positive cells in the colonic mucosa. Colonic biopsies were obtained and incubated with SEB. Mast cell activation in the colonic mucosa in response to incubation with SEB was observed with electron microscopy and immunoassay.

Results

The clinical symptom scores of CRS and UC severe scores (UCSS) were significantly reduced in the UC-CRS patients after FESS. The number of cultured S. aureus colonies from the surgically removed sinus mucosa significantly correlated with the decrease in UCSS. High levels of SEB were detected in the sinus wash fluids of the patients with UC-CRS. Histamine and tryptase release was significantly higher in the culture supernate in the patients with UC-CRS than the patients with UC-only and normal controls. Anti-SEB positive cells were located in the colonic mucosa.

Conclusion

The pathogenesis of UC in some patients may be associated with their pre-existing CRS by a mechanism of swallowing sinusitis-derived SEB. We speculate that SEB initiates inappropriate immune reactions and inflammation in the colonic mucosa that further progresses to UC.

Animal models of intestinal inflammation: ineffective communication between coalition members

The microbiota, epithelial cells, and mucosal immune cells in the intestine comprise an important gastrointestinal coalition. The intestinal microbiota can exert both beneficial as well as deleterious effects on their animal hosts. They interact with the innate defenses provided by epithelial cells through microbial recognition receptors. This communication, under normal conditions, results in a state of controlled inflammation. This article will focus on several animal models of intestinal inflammation, in which spontaneous or induced mutations or other genetic manipulations result in severe alterations in one of the members of the gastrointestinal coalition. These animal models of colitis have shown that alterations in communication between members of this coalition ultimately lead to gastrointestinal disease.

Antibodies to CBir1 flagellin define a unique response that is associated independently with complicated Crohn's disease

BACKGROUND & AIMS

Antibody responses to certain microbial antigens define heterogeneous groups of Crohn's patients; multiple and high-level responses to these antigens are associated with aggressive clinical phenotypes. The flagellin, CBir1, identified by investigations in the C3H/HeJBir mouse model, has been identified as a dominant antigen capable of inducing colitis in mice and eliciting antibody responses in a subpopulation of patients with Crohn's disease (CD). The aim of this study was to evaluate serum response to CBir1 flagellin in CD patients and to compare this response to responses defined previously to oligomannan (anti-Saccharomyces cerevisiae antibody), I2, OmpC, and neutrophil nuclear autoantigens (pANCA), and to determine anti-CBir1-associated phenotypes.

METHODS

A total of 484 sera from the Cedars Sinai Medical Center repository, previously typed for anti-Saccharomyces cerevisiae antibody, anti-I2, anti-OmpC, and pANCA were tested for anti-CBir1 by enzyme-linked immunosorbent assay, and results were assessed for clinical phenotype associations.

RESULTS

The presence and level of immunoglobulin G anti-CBir1 were associated with CD independently. Anti-CBir1 was present in all antibody subgroups and expression increased in parallel with increases in the number of antibody responses. pANCA+ CD patients were more reactive to CBir1 than were pANCA+ ulcerative colitis patients. Anti-CBir1 expression is associated independently with small-bowel, internal-penetrating, and fibrostenosing disease features.

CONCLUSIONS

Serum responses to CBir1 independently identify a unique subset of patients with complicated CD. This bacterial antigen was identified in a murine model and has a similar pattern of aberrant reactivity in a subset of CD patients.

Generation of antigen-specific, Foxp3-expressing CD4+ regulatory T cells by inhibition of APC proteosome function

We tested the hypothesis that immature APC, whose NF-kappaB-signaling pathway and thus maturation was blocked by the proteosome inhibitor benzyloxycarbonyl-isoleucyl-glutamyl(O-tert-butyl)-alanyl-leucinal (PSI), could be a source of Ag-specific regulatory T (Treg) cells. DO11.10 CD4(+) T cells that were incubated with Ag- and PSI-pulsed APC proliferated poorly, produced less IL-2, IFN-gamma, and IL-10 in secondary cultures, and inhibited the response of both naive and memory CD4(+) T cells stimulated by Ag-pulsed APC. The generation of PSI-APC Treg cells required IL-10 production by APC. PSI-APC Treg cell inhibition required cell-cell contact but not IL-10 or TGF-beta. Addition of IL-2 did not reverse, but Ab to CTLA-4 did reverse partially the inhibitory effect. Depletion of CD25(+) T cells before initial culture with PSI-APC did not affect Treg generation. PSI-APC Treg cells expressed high levels of Foxp3, inhibited proliferation of naive DO11.10 T cells in vivo, and abrogated colitis driven by a memory Th1 response to bacterial-associated Ag. We conclude that NF-kappaB-blocked, immature APC are able to induce the differentiation of Treg cells that can function in vitro and in vivo in an Ag-specific manner.

Immunity, inflammation, and allergy in the gut

The gut immune system has the challenge of responding to pathogens while remaining relatively unresponsive to food antigens and the commensal microflora. In the developed world, this ability appears to be breaking down, with chronic inflammatory diseases of the gut commonplace in the apparent absence of overt infections. In both mouse and man, mutations in genes that control innate immune recognition, adaptive immunity, and epithelial permeability are all associated with gut inflammation. This suggests that perturbing homeostasis between gut antigens and host immunity represents a critical determinant in the development of gut inflammation and allergy.

Variable phenotypes of enterocolitis in interleukin 10-deficient mice monoassociated with two different commensal bacteria

BACKGROUND & AIMS

To explore the hypothesis that selective immune responses to distinct components of the intestinal microflora induce intestinal inflammation, we characterized disease kinetics and bacterial antigen-specific T-cell responses in ex germ-free interleukin 10 -/- and wild-type control mice monoassociated with Enterococcus faecalis , Escherichia coli , or Pseudomonas fluorescens .

METHODS

Colitis was measured by using blinded histological scores and spontaneous interleukin 12 secretion from colonic strip culture supernatants. Interferon gamma secretion was measured from mesenteric or caudal lymph node CD4 + T cells stimulated with bacterial lysate-pulsed antigen-presenting cells. Luminal bacterial concentrations were measured by culture and quantitative polymerase chain reaction.

RESULTS

Escherichia coli induced mild cecal inflammation after 3 weeks of monoassociation in interleukin 10 -/- mice. In contrast, Enterococcus faecalis-monoassociated interleukin 10 -/- mice developed distal colitis at 10-12 weeks that was progressively more severe and associated with duodenal inflammation and obstruction by 30 weeks. Neither bacterial strain induced inflammation in wild-type mice, and germ-free and Pseudomonas fluorescens-monoassociated interleukin 10 -/- mice remained disease free. CD4 + T cells from Enterococcus faecalis- or Escherichia coli-monoassociated interleukin 10 -/- mice selectively produced higher levels of interferon gamma and interleukin 4 when stimulated with antigen-presenting cells pulsed with the bacterial species that induced disease; these immune responses preceded the onset of histological inflammation in Enterococcus faecalis -monoassociated mice. Luminal bacterial concentrations did not explain regional differences in inflammation.

CONCLUSIONS

Different commensal bacterial species selectively initiate immune-mediated intestinal inflammation with distinctly different kinetics and anatomic distribution in the same host.

Regulatory CD4+CD25+ cells reverse imbalances in the T cell pool of bone marrow transplanted TGepsilon26 mice leading to the prevention of colitis

BACKGROUND AND AIMS

Erroneous thymic selection of developing T lymphocytes may be responsible for the expansion of self reactive T cells or may contribute to the absence of regulatory T cells important in controlling peripheral inflammatory processes. Colitis in bone marrow (BM) transplanted Tgepsilon26 mice is induced by abnormally activated T cells developing in an aberrant thymic microenvironment. We investigated the protective role of regulatory CD4+CD25+ T cells in this model.

METHODS

BM from (C57BL/6 x CBA/J) F1 mice was transplanted into specific pathogen free Tgepsilon26 mice (BM-->Tgepsilon26). Transplanted mice received no cells (control), sorted CD4+CD25+, or CD4+CD25- cells from mesenteric lymph nodes (MLN) of normal mice. MLN cell subsets were analysed using membrane markers. Cytokine secretion of MLN cells was measured using intracellular cytokine staining and cytokine secretion in anti-CD3 stimulated cell cultures. Colitis was measured by histological scores.

RESULTS

CD4+CD25+ cells were reduced in the MLNs of BM-->Tgepsilon26 mice. Transfer of regulatory CD4CD4+CD25+ but not of CD4+CD25- cells reduced the number of MLN CD4+ T cells in BM-->Tgepsilon26 recipients and increased the number of MLN CD8+ cells, thereby normalising the CD4+/CD8+ ratio. CD4+CD25+ but not CD4+CD25- cell transfer into BM-->Tgepsilon26 mice reduced the number of tumour necrosis factor alpha+ CD4+ cells and increased the secretion of transforming growth factor beta by MLN cells. Transfer of 3 x 10(5) CD4+CD25+ cells after BM transplantation into Tgepsilon26 mice prevented colitis whereas CD4+CD25- cells had no protective effect.

CONCLUSIONS

These results suggest that defective selection or induction of regulatory T cells in the abnormal thymus is responsible for the development of colitis in BM-->Tgepsilon26 mice. Transfer of CD4+CD25+ cells can control intestinal inflammation in BM-->Tgepsilon26 mice by normalising the number and function of the MLN T cell pool.

Characterization of T-regulatory cells, induced by immature dendritic cells, which inhibit enteroantigen-reactive colitis-inducing T-cell responses in vitro and in vivo

Regulatory T (Treg) cells, derived from co-cultures of unfractionated CD4(+) T cells and immature dendritic cells (DC), suppress enteroantigen-induced proliferation of CD4(+) CD25(-) T cells. The DC-induced Treg cells are a mixture of CD25(+) (10-20%) and CD25(-) (80-90%) T cells. However, all the suppressor activity in vitro and in vivo resides in the CD25(+) T-cell subset. The CD25(+) DC-induced Treg cells can inhibit enteroantigen-induced proliferation in vitro through a transwell membrane, and their function does not appear to depend on previous activation. DC-induced CD25(+) Treg cells display a naive phenotype, expressing high levels of CD45RB and l-selectin (CD62L). In addition, the DC-induced Treg cells mediate a stronger suppressive activity than prototype CD25(+) regulatory T cells. The DC-induced Treg cells, and hereof purified CD25(+) and CD25(-) T-cell fractions, were co-injected into severe combined immunodeficiency (SCID) mice with colitis-inducing CD4(+) CD25(-) T cells. Both unfractionated CD4(+) and purified CD25(+) Treg cells fully protected the recipients against the development of colitis. In contrast, co-transfer of fractionated CD25(-) T cells offered no protection against disease development. Enterobacterial antigen-exposed CD4(+) T cells of the protected mice secreted higher levels of interleukin-10 and lower levels of interferon-gamma than the unprotected mice. The present data demonstrate DC-induced CD4(+) CD25(+) Treg cells, which phenotypically and functionally differ from the generally accepted prototype of CD25(+) Treg cells. These data may initiate new procedures for the expansion of Treg cells for clinical use.

LIGHT Is Constitutively Expressed on T and NK Cells in the Human Gut and Can Be Induced by CD2-Mediated Signaling

The TNF superfamily cytokine, lymphotoxin-like inducible protein that competes with glycoprotein D for binding herpesvirus entry mediator on T cells (LIGHT; TNFSF14), can augment T cell responses inducing IFN-gamma production and can drive pathological gut inflammation when expressed as a transgene in mouse T cells. LIGHT expression by human intestinal T cells suggests the possibility that LIGHT may play a key role in regulation of the mucosal immune system. A nonenzymatic method was developed for the isolation of T cells from the human lamina propria, permitting analysis of native cell surface protein expression. Cell surface LIGHT was constitutively expressed on mucosal T and NK cells and a subpopulation of gut-homing CD4(+) T cells in the periphery. In addition, CD2-mediated stimulation induced efficient LIGHT expression on intestinal CD4(+) T cells, but not on peripheral blood T cells, suggesting a gut-specific, Ag-independent mechanism for LIGHT induction. By contrast, herpesvirus entry mediator expression on gut T cells was unperturbed, implicating the transcriptional regulation of LIGHT as a mechanism modulating signaling activity in the gut. Quantitative analysis of LIGHT mRNA in a cohort of inflammatory bowel disease patients indicated elevated expression in biopsies from small bowel and from inflamed sites, implicating LIGHT as a mediator of mucosal inflammation.

T-cell-induced mucosal damage in the intestine

PURPOSE OF REVIEW

T cells are central to most inflammatory disorders of the intestine, particularly Celiac disease, graft vs. host disease, Crohn disease, and ulcerative colitis. The mechanisms by which T cells contribute to mucosal damage in these disorders have been explored using both in vitro and in vivo models. This review will highlight recent studies directed at understanding the mechanisms by which T cells are involved in the induction of mucosal damage.

RECENT FINDINGS

The recent studies of in vivo T-cell activation using monoclonal anti-CD3 antibody have shown that a number of cytotoxic T-cell pathways are required and involved in the induction of mucosal damage and in particular in the induction of epithelial cell apoptosis. These include the Fas/FasL and perforin pathways. Other mediators of T-cell-induced cytotoxicity, such as TNFalpha and IFNgamma may contribute to mucosal damage but are not required for the induction of mucosal damage in vivo. In addition, several studies have tried to identify the role of regulatory mucosal T cells and the physiologically relevant triggers for T-cell-induced mucosal damage.

SUMMARY

It is now clear that there are significant redundancies in the mechanisms that lead to immune-mediated mucosal damage and that the mechanisms that operate in vivo may not be predicted by in vitro experiments. These investigations are improving our understanding of the pathogenesis of immune-mediated enteropathies and will hopefully lead to new approaches to the management of these disorders.

Review article: gut flora and inflammatory bowel disease

The pathogenesis of inflammatory bowel disease involves interactions between the host susceptibility, mucosal immunity and intestinal microflora. There is therefore great interest in the changes in the endogenous flora in inflammatory bowel disease patients and in the establishment of potential genetic variations in host responses to endogenous bacteria. In this review, we summarize the modifications in the various regional ecosystems in the gastrointestinal tract during inflammatory bowel disease (luminal bacteria in faeces or inside the gastrointestinal tract, bacteria in mucus and bacteria directly attached to the mucosa). Results were obtained following a 'candidate microorganism strategy' and, as is occurring increasingly frequently, following a 'full description strategy', which has progressed largely due to the development of culture-independent techniques. The possibility of modifying the ecosystem using prebiotics or probiotics offers hope for new treatment developments, particularly in the prevention of relapse.

Animal models of inflammatory bowel disease

In inflammatory bowel disease (IBD), experimental models have proven to be important tools for detecting potential therapeutic agents and for investigating the mechanisms of pathogenesis. This review is intended to cover recent advances in basic IBD model applications. The use of more than 20 animal models has allowed the detection of numerous protective pharmacological agents, including a number of immunomodulatory agents that have entered the therapeutic armamentarium. The models have been classified into five main categories based on the methods of induction: gene knockout (KO), transgenic, chemical, adoptive transfer, and spontaneous (each with subcategories).

High-level serum antibodies to bacterial antigens are associated with antibiotic-induced clinical remission in Crohn's disease: a pilot study

In Crohn's disease, antibiotics are used with variable efficacy, suggesting that some patients are more likely to respond. The aim of this study was to determine whether Crohn's patients with predominant serum antibody reactivity toward bacterial antigens OmpC and/or I2 were more likely to achieve remission with antibiotics. Patients with ileal or ileal with right-sided colonic Crohn's disease were studied in a double-blind trial of budesonide alone or budesonide plus metronidazole and ciprofloxacin. In the budesonide plus metronidazole and ciprofloxacin group, patients with OmpC/I2 predominant profiles had the highest remission rate, whereas the group with no antibody predominant profiles had the lowest rate. In the budesonide group, patients with the OmpC/I2 predominant profile had the lowest remission rate, and the no-antibody group rate was higher. Although not statistically significant, these results support further testing to determine whether predominant serum reactivity to certain bacterial antigens may be a marker for efficacious use of antibiotics.

Mechanisms of natural tolerance in the intestine: implications for inflammatory bowel disease

Tolerance, the regulated inability to respond to a specific immunologic stimulant, is a physiological event important to normal immune function. Just as loss of tolerance to self-proteins results in autoimmune diseases, we assert that loss of tolerance to commensal flora in the intestinal lumen leads to inflammatory bowel disease (IBD). Mechanisms through which the mucosal immune system establishes and remains hyporesponsive toward the presence of food proteins and commensal flora, which we define as natural tolerance, are discussed. In addition to the contributions by commensal flora, the innate host defense and the adaptive immune systems promote natural tolerance to sustain normal mucosal homeostasis. Understanding the molecular and cellular events that mediate natural tolerance will lead to more advanced insights into IBD pathogenesis and improved therapeutic options.

Deficient host-bacteria interactions in inflammatory bowel disease? The toll-like receptor (TLR)-4 Asp299gly polymorphism is associated with Crohn's disease and ulcerative colitis

BACKGROUND AND AIMS

Elicitation of an innate immune response to bacterial products is mediated through pattern recognition receptors (PRRs) such as the toll-like receptors (TLRs) and the NODs. The recently characterised Asp299Gly polymorphism in the lipopolysaccharide (LPS) receptor TLR4 is associated with impaired LPS signalling and increased susceptibility to Gram negative infections. We sought to determine whether this polymorphism was associated with Crohn's disease (CD) and/or ulcerative colitis (UC).

METHODS

Allele frequencies of the TLR4 Asp299Gly polymorphism and the three NOD2/CARD15 polymorphisms (Arg702Trp, Gly908Arg, and Leu1007fsinsC) were assessed in two independent cohorts of CD patients (cohort 1, n = 334; cohort 2, n = 114), in 163 UC patients, and in 140 controls. A transmission disequilibrium test (TDT) was then performed on 318 inflammatory bowel disease (IBD) trios.

RESULTS

The allele frequency of the TLR4 Asp299Gly polymorphism was significantly higher in CD (cohort 1: 11% v 5%, odds ratio (OR) 2.31 (95% confidence interval (CI) 1.28-4.17), p = 0.004; and cohort 2: 12% v 5%, OR 2.45 (95% CI 1.24-4.81), p = 0.007) and UC patients (10% v 5%, OR 2.05 (95% CI 1.07-3.93), p = 0.027) compared with the control population. A TDT on 318 IBD trios demonstrated preferential transmission of the TLR4 Asp299Gly polymorphism from heterozygous parents to affected children (T/U: 68/34, p = 0.01). Carrying polymorphisms in both TLR4 and NOD2 was associated with a genotype relative risk (RR) of 4.7 compared with a RR of 2.6 and 2.5 for TLR4 and NOD2 variants separately.

CONCLUSION

We have reported on a novel association of the TLR4 Asp299Gly polymorphism with both CD and UC. This finding further supports the genetic influence of PRRs in triggering IBD.

LIGHT Expression by Mucosal T Cells May Regulate IFN-γ Expression in the Intestine

The TNF superfamily of cytokines play an important role in T cell activation and inflammation. Sustained expression of lymphotoxin-like inducible protein that competes with glycoprotein D for binding herpesvirus entry mediator on T cells (LIGHT) (TNFSF14) causes a pathological intestinal inflammation when constitutively expressed by mouse T cells. In this study, we characterized LIGHT expression on activated human T cell subsets in vitro and demonstrated a direct proinflammatory effect on regulation of IFN-gamma. LIGHT was induced in memory CD45RO CD4+ T cells and by IFN-gamma-producing CD4+ T cells. Kinetic analysis indicated rapid induction of LIGHT by human lamina propria T cells, reaching maximal levels by 2-6 h, whereas peripheral blood or lymph node-derived T cells required 24 h. Further analysis of intestinal specimens from a 41 patient cohort by flow cytometry indicated membrane LIGHT induction to higher peak levels in lamina propria T cells from the small bowel or rectum but not colon, when compared with lymph node or peripheral blood. Independent stimulation of the LIGHT receptor, herpesvirus entry mediator, induced IFN-gamma production in lamina propria T cells, while blocking LIGHT inhibited CD2-dependent induction of IFN-gamma synthesis, indicating a role for LIGHT in the regulation of IFN-gamma and as a putative mediator of proinflammatory T-T interactions in the intestinal mucosa. Taken together, these findings suggest LIGHT-herpesvirus entry mediator mediated signaling as an important immune regulatory mechanism in mucosal inflammatory responses.

Reduced ratio of protective versus proinflammatory cytokine responses to commensal bacteria in HLA-B27 transgenic rats

Germ-free HLA-B27 transgenic (TG) rats do not develop colitis, but colonization with specific pathogen-free (SPF) bacteria induces colitis accompanied by immune activation. To study host-dependent immune responses to commensal caecal bacteria we investigated cytokine profiles in mesenteric lymph node (MLN) cells from HLA-B27 TG versus nontransgenic (non-TG) littermates after in vitro stimulation with caecal bacterial lysates (CBL). Supernatants from CBL-stimulated unseparated T- or B- cell-depleted MLN cells from HLA-B27 TG and non-TG littermates were analysed for IFN-gamma, IL-12, TNF, IL-10 and TGF-beta production. Our results show that unfractionated TG MLN cells stimulated with CBL produced more IFN-gamma, IL-12 and TNF than did non-TG MLN cells. In contrast, CBL-stimulated non-TG MLN cells produced more IL-10 and TGF-beta. T cell depletion abolished IFN-gamma and decreased IL-12 production, but did not affect IL-10 and TGF-beta production. Conversely, neither IL-10 nor TGF-beta was produced in cultures of B cell-depleted MLN. In addition, CD4(+) T cells enriched from MLN of HLA-B27 TG but not from non-TG rats produced IFN-gamma when cocultured with CBL-pulsed antigen presenting cells from non-TG rats. Interestingly, IL-10 and TGF-beta, but not IFN-gamma, IL-12 and TNF were produced by MLN cells from germ-free TG rats. These results indicate that the colitis that develops in SPF HLA-B27 TG rats is accompanied by activation of IFN-gamma-producing CD4(+) T cells that respond to commensal bacteria. However, B cell cytokine production in response to components of commensal intestinal microorganisms occurs in the absence of intestinal inflammation.

Bacterial flagellin is a dominant antigen in Crohn disease

Chronic intestinal inflammation, as seen in inflammatory bowel disease (IBD), results from an aberrant and poorly understood mucosal immune response to the microbiota of the gastrointestinal tract in genetically susceptible individuals. Here we used serological expression cloning to identify commensal bacterial proteins that could contribute to the pathogenesis of IBD. The dominant antigens identified were flagellins, molecules known to activate innate immunity via Toll-like receptor 5 (TLR5), and critical targets of the acquired immune system in host defense. Multiple strains of colitic mice had elevated serum anti-flagellin IgG2a responses and Th1 T cell responses to flagellin. In addition, flagellin-specific CD4(+) T cells induced severe colitis when adoptively transferred into naive SCID mice. Serum IgG to these flagellins, but not to the dissimilar Salmonella muenchen flagellin, was elevated in patients with Crohn disease, but not in patients with ulcerative colitis or in controls. These results identify flagellins as a class of immunodominant antigens that stimulate pathogenic intestinal immune reactions in genetically diverse hosts and suggest new avenues for the diagnosis and antigen-directed therapy of patients with IBD.

Expression of dual TCR on DO11.10 T cells allows for ovalbumin-induced oral tolerance to prevent T cell-mediated colitis directed against unrelated enteric bacterial antigens

The triggering Ag for inflammatory bowel disease and animal models of colitis is not known, but may include gut flora. Feeding OVA to DO11.10 mice with OVA-specific transgenic (Tg) TCR generates Ag-specific immunoregulatory CD4(+) T cells (Treg) cells. We examined the ability of oral Ag-induced Treg cells to suppress T cell-mediated colitis in mice. SCID-bg mice given DO11.10 CD4(+)CD45RB(high) T cells developed colitis, and cotransferring DO11.10 CD45RB(low)CD4(+) T cells prevented CD4(+)CD45RB(high) T cell-induced colitis in the absence of OVA. The induction and prevention of disease by DO11.10 CD4(+) T cell subsets were associated with an increase in endogenous TCRalpha chain expression on Tg T cells. Feeding OVA to SCID-bg mice reconstituted with DO11.10 CD4(+)CD45RB(high) attenuated the colitis in association with increased TGF-beta and IL-10 secretion, and decreased proliferative responses to both OVA and cecal bacteria Ag. OVA feeding also attenuated colitis in SCID-bg mice reconstituted with a mix of BALB/c and DO11.10 CD45RB(high) T cells, suggesting that OVA-induced Treg cells suppressed BALB/c effector cells. The expression of endogenous non-Tg TCR allowed for DO11.10-derived T cells to respond to enteric flora Ag. Furthermore, feeding OVA-induced Treg cells prevented colitis by inducing tolerance in both OVA-reactive and non-OVA-reactive T cells and by inducing Ag-nonspecific Treg cells. Such a mechanism might allow for Ag-nonspecific modulation of intestinal inflammation in inflammatory bowel disease.

CD4+ T cells mediate murine syngeneic graft-versus-host disease-associated colitis

Syngeneic graft-vs-host disease (SGVHD) develops following lethal irradiation, reconstitution with syngeneic bone marrow, and treatment with a 21-day course of the immunosuppressive agent cyclosporin A (CsA). Following cessation of CsA, this inducible disease is characterized by weight loss, diarrhea, and development of inflammation in the colon and liver. Although nonspecific effector cells and Th1 cytokines have been shown to participate in disease induction, the role of T cells has not been fully elucidated. Initial studies demonstrated significant increases in CD4+ T cells, but not other T cell populations in the colons of diseased animals relative to transplant control animals. To demonstrate a functional linkage between increases in colonic CD4+ T cells and disease induction, in vivo T cell depletion studies were performed. Beginning on the day of bone marrow transplantation, groups of control and CsA-treated animals were treated with mAb against either CD4 or CD8 for 21 days. Treatment with anti-CD4, but not anti-CD8, eliminated clinical symptoms and colon pathology. Interestingly, neither anti-CD4 nor anti-CD8 therapy affected the development of liver pathology associated with SGVHD. These findings demonstrated that CD4+ T cells initiate development of the intestinal inflammation associated with murine SGVHD.

Quantitative and functional characteristics of intestinal-homing memory T cells: analysis of Crohn's disease patients and healthy controls

Circulating memory T cells can be subdivided on the basis of beta7 integrin expression. The beta7+ population contains cells primed in the intestine capable of homing back to the gut. We hypothesized that cytokine production by beta7+ memory T cells reflects the specialized mucosal compartment in which they were primed. Flow cytometry of whole blood was used to assess numbers of beta7+ (beta7hi and beta7int) and beta7- memory T cells and their production of Th1 and regulatory cytokines in healthy controls and Crohn's disease patients. In controls, beta7+ and beta7- memory T cells displayed a similar qualitative profile of cytokine production but the beta7+ population was enriched for cytokine-producing effector cells. In addition, the beta7hi population contained more cytokine-producing cells than the beta7int population, suggesting a gradient of cytokine production based on beta7 integrin expression. In active Crohn's disease, there was altered expression of beta7 integrin with a decrease in intestinal-homing memory T cells and an increase in systemic memory T cells. Furthermore, there was a selective loss of IL-10 and increase in TGF-beta in both beta7+ and beta7- memory T cell subsets which may contribute to the pathogenesis of the inflammatory process in Crohn's disease.

Demonstration of strong enterobacterial reactivity of CD4+CD25-T cells from conventional and germ-free mice which is counter-regulated by CD4+CD25+T cells

Unfractionated CD4+ T cells from the gut-associated lymphoid tissue (GALT) and peripheral lymph nodes are unresponsive when exposed to enterobacterial antigens in vitro. Under similar conditions, CD4+ T cells depleted in vivo or in vitro of CD4+CD25+ T cells proliferate extensively. The CD4+CD25- T cell reactivity depends on MHC class II presentation, specific TCR stimulation, CD4 ligation, and antigen processing by antigen-presenting cells. The CD4+CD25- T cells respond to autologous and heterologous enterobacterial antigens, but not to antigens from the feces of germ-free mice. Surprisingly, CD4+CD25- T cells obtained from the GALT of germ-free mice also proliferate when exposed to enterobacterial antigens, and adding back the conventional or germ-free CD4+CD25+ T cells to the enteroantigen-stimulated CD4+CD25- T cells abolishes proliferation. As judged from carboxyfluorescein diacetate succinimidyl ester-labeling experiments, 4-5% of the CD4+CD25- T cells respond to enteroantigen. The data show for the first time that CD4+CD25- T cells with reactivity towards the enterobacterial flora and regulatory CD4+CD25- T cells are present in both conventional and germ-free mice. The data suggest that a significant proportion of the peripheral pool of CD4+CD25- T cells express anti-enterobacterial reactivity, which, due to the presence of regulatory CD4+CD25+ T cells, is kept in a quiescent state.

Association of antibody responses to microbial antigens and complications of small bowel Crohn's disease

BACKGROUND & AIMS

Crohn's disease patients can be characterized by antibody responses against Crohn's disease-related bacterial sequence, Escherichia coli outer membrane porin C, Saccharomyces cerevisiae (oligomannan), and neutrophil nuclear antigens. Our aim was to determine whether expression of antibodies against Crohn's disease-related bacterial sequence and Escherichia coli outer membrane porin C is associated with distinct phenotypic manifestations.

METHODS

Sera from 303 patients were tested for antibodies to the Crohn's disease-related bacterial sequence (I2), anti-Escherichia coli outer membrane porin C, anti-Saccharomyces cerevisiae, and perinuclear antineutrophil cytoplasmic antibodies and for 3 Crohn's disease-associated variants of the NOD2 gene (R702W, G908R, and 1007fs) and compared with clinical data.

RESULTS

Patients expressing I2 were more likely to have fibrostenosing Crohn's disease (64.4% vs. 40.7%; P < 0.001) and to require small bowel surgery (62.2% vs. 37.4%; P < 0.001). Patients with anti-Escherichia coli outer membrane porin C were more likely to have internal perforating disease (50.0% vs. 30.7%; P = 0.001) and to require small bowel surgery (61.4% vs. 44.2%; P = 0.003). Anti-Crohn's disease-related bacterial sequence was independently associated with fibrostenosis (P = 0.027) and small bowel surgery (P = 0.01), whereas anti-Escherichia coli outer membrane porin C was independently associated with internal perforations (P < 0.006). Patients positive for I2, anti-Escherichia coli outer membrane porin C, and anti-Saccharomyces cerevisiae were the most likely to have undergone small bowel surgery (72.0%; odds ratio, 8.6; P < 0.001) compared with patients without reactivity (23.0%). When the presence and magnitude of antibody responses were considered, 90% of patients with small bowel disease who required surgery had high levels of I2, Escherichia coli outer membrane porin C, and oligomannan antibodies, compared with only 18.2% with low-titer responses (P < 0.001).

CONCLUSIONS

I2 and anti-Escherichia coli outer membrane porin C are associated with Crohn's disease phenotypes, and patients with the highest level of serum reactivity toward an increasing number of microbiota have the greatest frequency of strictures, internal perforations, and small bowel surgery.

Induction of colitis by a CD4+ T cell clone specific for a bacterial epitope

It is now well established that the intestinal flora plays an important role in the pathogenesis of inflammatory bowel disease (IBD). However, whether bacteria serve as the sole target of the immune response in this process or whether they act indirectly by triggering an anti-self response is still unclear. We have previously shown that specific pathogen-free IL-10-deficient (IL-10 KO) mice develop a T helper (Th1)-cytokine associated colitis after experimental infection with Helicobacter hepaticus. We here show that H. hepaticus Ag (SHelAg)-specific CD4+ Th1 clones transfer disease to H. hepaticus-infected T cell-deficient RAG KO hosts. Importantly, uninfected recipients of the SHelAg-specific clones did not develop intestinal inflammation, and a control Schistosoma mansoni-specific Th1 clone did not induce colitis upon transfer to infected RAG KO mice. The disease-inducing T cell clones recognized antigen(s) (Ag) specifically expressed by certain Helicobacter species as they responded when stimulated in vitro with H. hepaticus and Helicobacter typhlonius Ag, but not when cultured with Ag preparations from Helicobacter pylori, various non-helicobacter bacteria, or with cecal bacterial lysate from uninfected mice. Characterization of the Ag specificity of one of the clones showed that it reacts uniquely with a 15-mer peptide epitope on the flagellar hook protein (FlgE) of H. hepaticus presented by I-Ab. Together, our results demonstrate that colitis can be induced by clonal T cell populations that are highly specific for target Ag on intestinal bacteria, suggesting that an aberrant T cell response directed against gut flora is sufficient to trigger IBD.

Effects of Rheum tanguticum polysaccharide on TNBS -induced colitis and CD4+ T cells in rats

AIM: To study the effects of Rheum tanguticum polysaccharide_-1 (RTP_-1) on ulcerative colitis in rats induced by 2, 4, 6-trinitrophene sulphonic acid (TNBS) and their possible mechanism.

METHODS: RTP₁ (200 mg·kg^-1, ig) extracted from Rheum tanguticum Maxim. ex Regel was administrated to rats with colitis induced by TNBS for 5 d, 7 d, 10 d and 14 d, respectively. The effects of RTP₁ and dexamethasone (DX, 0.2 mg·kg^-1, ig) were contrastively investigated. The MPO level and SOD activity were determined by chromatometry. The expansion and protein expression of CD4⁺ T lymphocytes isolated from colon mucosae and mesenteric lymph nodes of colitis rats were performed by immunohistochemical analysis and Western-blot methods.

RESULTS: Treatments of RTP₁ (200 mg·kg^-1, ig) significantly reduced diarrhea, mortality, colon mass, ulcer areas and MPO level in colon mucosae on days 5, 7, 10 and 14 (5.2 ± 1.4, 5.4 ± 0.7, 5.2 ± 1.8, P < 0.05. 3.4 ± 0.8, P < 0.01. 16.1 ± 12.1, P < 0.01. 31.8 ± 8.6, 17.7 ± 5.3, 12.7 ± 4.1, P < 0.05). The effects of RTP₁ were similar to those noted above in DX group, but there were no immunosupressive effects of DX in RTP_-1 group, such as body mass loss, thymus and spleen atrophy. The decreased number and down-regulated protein levels of CD4⁺ T cells isolated from the colon of colitis rats treated with RTP₁ were found.

CONCLUSION: RTP₁ shows significantly protective effects but lower side effects on rats with colitis induced by TNBS. The mechanism may be due to the resistance to over expansion of CD4.

Early events in the pathogenesis of a murine transfer colitis

Inflammatory bowel disease (IBD) is a chronic, disabling disease. A dysregulated immune response seems to play a pivotal role in the pathogenesis of this disorder. Here we will review current concepts of the adoptive transfer model of IBD with particular emphasis on early events in disease development. In the adoptive transfer model, the reconstitution of immunoincompetent mice with CD4+ T cells from congenic donor animals leads to severe colitis. We will address the question as to which CD4+ T cell subsets might be involved in the induction, suppression, or regulation of disease, and review data concerning the specificity of their T cell receptor and its putative MHC restriction elements. We will also discuss whether and at what anatomical sites donor T cells could be primed in the recipient.

Animal models of inflammatory bowel disease: an overview

Inflammatory bowel disease (IBD) research has been performed in human in vitro studies and in in vivo studies using appropriate animal models. Such animal models allow both the examination of inflammatory processes (both early and late events) as well as the evaluation of new therapeutic modalities. Since the first description of the immune complex colitis in rabbits in 1961, overall 63 models have been described, most of which within the last decade. These IBD animal models can be divided into 5 different categories: (1) antigen-induced colitis and colitis induced by microbials; (2) other inducible forms of colitis (chemical, immunological, and physical); (3) genetic colitis models (transgenic and knock-out models); (4) adoptive transfer models, and (5) spontaneous colitis models. In spite of the high overall number of models, none of them is the 'perfect' model and therefore numerous aspects need to be considered when choosing one model for a particular study. Importantly, most clinical aspects (e.g. extraintestinal manifestations or fistula) have recently been described in one or the other model allowing further studies with relevance for almost all aspects of IBD. So far, IBD animal models have taught us important lessons, e.g. the requirement of T-helper cells in most models, the need of a particular genetic background, and the role of the flora in the initiation of IBD. It is expected that our understanding of IBD will further increase in a number of additional areas using animal models, e.g. exploring the role of the innate immune system in IBD.

Colitogenic Th1 cells are present in the antigen-experienced T cell pool in normal mice: control by CD4+ regulatory T cells and IL-10

CD4(+) regulatory T cells have been shown to prevent intestinal inflammation; however, it is not known whether they act to prevent the priming of colitogenic T cells or actively control these cells as part of the memory T cell pool. In this study, we describe the presence of colitogenic Th1 cells within the CD4(+)CD45RB(low) population. These pathogenic cells enrich within the CD25(-) subset and are not recent thymic emigrants. CD4(+)CD45RB(low) cells from germfree mice were significantly reduced in their ability to transfer colitis to immune deficient recipients, suggesting the presence of commensal bacteria in the donor mice drives colitogenic T cells into the Ag-experienced/memory T cell pool. This potentially pathogenic population of Ag-experienced T cells is subject to T cell-mediated regulation in vivo by both CD4(+)CD25(+) and CD4(+)CD25(-) cells in an IL-10-dependent manner. Furthermore, administration of an anti-IL-10R mAb to unmanipulated adult mice was sufficient to induce the development of colitis. Taken together, these data indicate that colitogenic Th1 cells enter into the Ag-experienced pool in normal mice, but that their function is controlled by regulatory T cells and IL-10. Interestingly, IL-10 was not absolutely required for CD4(+)CD25(+) T cell-mediated inhibition of colitis induced by transfer of naive CD4(+)CD45RB(high) cells, suggesting a differential requirement for IL-10 in the regulation of naive and Ag-experienced T cells.

Modulation of cytokine release from colonic explants by bacterial antigens in inflammatory bowel disease

The intestinal flora play an important role in experimental colitis and inflammatory bowel disease (IBD). Using colonic explant cultures from 132 IBD and control subjects, we examined tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-1 and interleukin-1 receptor antagonist (IL-1RA) production in vitro in response to bacterial activators. Unstimulated TNF-alpha release was increased significantly in rectal biopsies from involved IBD tissue, correlating with inflammation severity. Whereas lipopolysaccharide (LPS) only moderately stimulated TNF-alpha production from inflamed tissue, pokeweed mitogen (PWM) induced its release in all groups, with a stronger response in involved IBD tissue. Superantigen staphylococcal enterotoxin A (SEA) had a similar, but weaker effect. SEB was observed to be the strongest inducer of TNF-alpha for all groups, again with a more marked response in inflamed tissue. Stimulated release of IL-1 was considerably less than for TNF-alpha. The superantigens' superior potency over LPS was not as marked for IL-1 as it was for TNF-alpha. In addition to IL-1, IL-1RA release was also triggered by the bacterial products. The net effect of activation on the IL-1RA/IL-1 ratio was relatively modest. Release of the proinflammatory cytokines TNF-alpha and IL-1, as well as that of the anti-inflammatory cytokine IL-1RA was increased by incubation of colonic tissue with bacterial factors. TNF-alpha production and release was increased significantly in involved colonic explants from IBD. SEB was even capable of inducing TNF-alpha release from uninvolved colonic tissue.

The immunological and genetic basis of inflammatory bowel disease

The inflammatory bowel diseases (IBDs), Crohn's disease and ulcerative colitis, are chronic inflammatory disorders of the gastrointestinal tract. Enormous progress has been made recently in understanding the pathogenesis of these diseases. Through the study of patients and mouse models, it has emerged that Crohn's disease is driven by the production of interleukin-12 (IL-12) and interferon-gamma (IFN-gamma), whereas ulcerative colitis is probably driven by the production of IL-13. A second area of progress is in the identification of specific genetic abnormalities that are responsible for disease. The most important finding is the identification of mutations in the gene that encodes NOD2 (nucleotide-binding oligomerization domain 2) protein in a subgroup of patients with Crohn's disease. Here, we discuss these recent findings and the implications for therapy.

Immune networks in animal models of inflammatory bowel disease

The animal models of inflammatory bowel disease provide a framework to define the immunopathogenesis of intestinal inflammation. Studies in these models support the hypothesis that exaggerated immune responses to normal enteric microflora are involved in the initiation and perpetuation of chronic intestinal inflammation. A major pathway involves development of acquired immune responses by the interactions of CD4+ T-cell receptor alphabeta T cells with antigen-presenting cells (dendritic cells). Immunoregulatory cells, including Tr1 cells, Th3 cells, and CD4+ CD25+ T cells and B cells, directly or indirectly affect the T-cell receptor alphabeta T cell-induced immune responses and bridge innate and acquired immunity. The study of these complicated immune networks provides the rationale for the development of new therapeutic interventions in inflammatory bowel disease.

Bacteroides vulgatus protects against Escherichia coli-induced colitis in gnotobiotic interleukin-2-deficient mice

BACKGROUND & AIMS

The microflora plays a crucial role in inflammatory bowel diseases (IBDs). Specific pathogen-free (SPF), but not germ-free, interleukin (IL)-2-deficient (IL-2-/-) mice develop colitis. The colitogenicity of commensal bacteria was determined.

METHODS

Gnotobiotic IL-2-/- and IL-2+/+ mice were colonized with Escherichia coli mpk, Bacteroides vulgatus mpk, or both bacterial strains, or with E. coli strain Nissle 1917. DNA arrays were used to characterize E. coli mpk. Colitis was analyzed by histology and real-time reverse-transcription polymerase chain reaction (RT-PCR) for interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, IL-10, and CD14 messenger RNA (mRNA) expression. Bacterial numbers in feces and bacterial localization in the colon was determined by culture and fluorescence in situ hybridization (FISH).

RESULTS

IL-2-/- but not IL-2+/+ mice monocolonized with E. coli mpk developed colitis, whereas mono-association with B. vulgatus mpk, or E. coli Nissle, or co-colonization with E. coli mpk and B. vulgatus mpk, did not induce colitis. DNA array experiments and cellular studies revealed that E. coli mpk is a nonpathogenic strain. FISH and culture methods revealed that the anticolitogenic effect of B. vulgatus mpk on E. coli mpk cannot be explained by a significant reduction in numbers of E. coli in the colon. E. coli mpk-induced colitis was associated with increased IFN-gamma, TNF-alpha, CD14, and IL-10 mRNA expression in the colon.

CONCLUSIONS

In IL-2-/- mice, B. vulgatus mpk protects against E. coli mpk-triggered colitis by an unknown mechanism. E. coli Nissle does not induce colitis. Various bacterial species common to the microflora differ in their ability to trigger IBD.

Murine models of ulcerative colitis

Ulcerative colitis (UC) is an inflammatory bowel disease of unknown etiology limited to the large intestine. The disease is prevalent in industrial societies and is associated with specific ethnic populations. A number of murine models, each focused on distinct aspects of the disease process, were developed over the past 20 years to further our understanding of the pathogenesis of UC. These models have been and remain our best resource for the study of the disorder as a result of their homology to human UC and the ease in which they can be manipulated and examined. This review examines and distills what has been leamed from these models and how this information is related back to human UC.

Gamma interferon augments the intracellular pathway for lipopolysaccharide (LPS) recognition in human intestinal epithelial cells through coordinated up-regulation of LPS uptake and expression of the intracellular Toll-like receptor 4-MD-2 complex

Although some intestinal epithelial cell lines are known to respond to lipopolysaccharide (LPS), understanding of the relationship between LPS responsiveness and the expression of LPS receptors or factors regulating LPS responsiveness of intestinal epithelial cell lines is incomplete. In this study, we demonstrate that commonly studied human intestinal epithelial cell lines can be classified into at least three different types on the basis of LPS responsiveness, Toll-like receptor-4 (TLR4) expression, and the effects of gamma interferon (IFN-gamma) on LPS responsiveness. The first phenotype, which includes the HCT-116 and Caco-2 cell lines, is characterized by relative hyporesponsiveness to LPS and diminished expression of TLR4 protein. In these cells, IFN-gamma does not induce LPS responsiveness. The second phenotype, which includes cell line SW480, exhibits a highly LPS-responsive phenotype and surface expression of TLR4 protein even in unprimed conditions. These lines are functionally similar to cells of monocytic lineage. In the third phenotype, which includes the HT-29 and Colo205 cell lines, TLR4 protein is largely present in the cytoplasmic fraction and the cells are hyporesponsive to LPS in an unprimed condition. However, priming of these cells with IFN-gamma can induce LPS responsiveness through augmentation of LPS uptake and expression of MD-2 mRNA and intracellular TLR4 proteins. Finally, these findings suggest that the Th1 cytokine IFN-gamma modulates LPS responsiveness through several mechanisms in intestinal epithelial cells and that these cells may comprise different subpopulations with distinct roles in innate immune responses.

Inhibition of intestinal bacterial translocation with rifaximin modulates lamina propria monocytic cells reactivity and protects against inflammation in a rodent model of colitis

BACKGROUND

A modification of the intestinal flora and an increased bacterial translocation is a common finding in patients with inflammatory bowel disease as well as in animal model of colitis. Rifaximin, a non-absorbable derivative of rifamycin, is an effective antibiotic that acts by inhibiting bacterial ribonucleic acid synthesis.

AIMS

In the present study, we investigated the effect of the administration of rifaximin (10, 30 and 50 mg/kg/day) or prednisolone (10 mg/kg/day) in 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in mice.

METHODS

Colitis was induced in mice by intrarectal administration of TNBS (1.5 mg/mouse in 50% ethanol) and disease severity assessed clinically and by histologic scoring of colon damage, determination of interleukin (IL)-2, IL-12, interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha (protein and mRNA and myeloperoxidase (MPO) activity in the colon. Cytokines production by the lamina propria mononuclear cells (LPMC) and luminal bacteria were also measured.

RESULTS

Rifaximin administration (30 or 50 mg/kg/day) increased survival rates of colitic mice and reduced colitis severity as demonstrated by improvement of wasting syndrome, histologic scores, decrease in colon IL-2, IL-12, IFN-gamma and TNF-alpha (protein and mRNA) levels, and diminished colon MPO activity. Rifaximin administration caused a significant reduction of colon bacterial translocation towards mesenteric lymph nodes. LPMC obtained from rifaximin-treated mice released significantly lower amount of IFN-gamma in response to ex vivo stimulation with agonistic anti-CD3 and anti-CD28 antibodies. Rifaximin (50 mg/kg/day) significantly accelerates recovery in mice with established colitis.

CONCLUSIONS

Luminal bacterial microflora plays a role in the pathogenesis of TNBS-induced colitis in mice. Rifaximin administration reduces the development of colitis and accelerates healing of established disease by preventing bacterial translocation.

Understanding immune-microbial homeostasis in intestine

The mechanisms concerning how the immune system is able to deal with the massive antigen challenge represented by the commensal bacterial flora have been a mystery. Recently a number of animal models with impairment of these mechanisms have been identified. One of these is the C3H/HeJBir mouse, which, under certain environmental conditions, can spontaneously develop colitis, which later remits. These mice show increased B cell and T cell reactivity to antigens of the enteric bacterial flora. CD4+ T cells from this strain cause colitis, when activated by enteric bacterial antigens and transferred to histocompatible severe combined immunodeficiency recipients. This colitis is mediated by CD4+ Th1 cells and requires a sustained mucosal production of interleukin-12, which, in turn, is dependent on CD40L-CD40 interactions in the gut. Regulatory T cells that appear to limit the colitis have been identified and have the properties of the T-regulatory-1 subset. Functional Tr1 activity for bacterial antigens is present in the lamina propria CD4+ T cells. These Tr1 cells may exert their effects by inhibition of dendritic cell function in the mucosa, rather than by direct effects on Th 1 cells. Manyquestions remain to be answered, including, How do the enteric bacterial-host interactions shape the immune system for abnormal responses such as inflammatory bowel disease, autoimmunity, and allergy?

Intestinal flora and mucosal immune responses

The normal intestinal flora and the mucosal immune system exist in close spatial proximity. A normal structure and function of both very complex systems is required for health and develops in a constant and interactive process. An abnormal host response to the normal intestinal flora leads to chronic intestinal inflammation. Probiotic bacteria may modulate the intestinal flora and the mucosal immune response and are an effective therapy for remission maintenance of ulcerative colitis and pouchitis.

B cell developmental requirement for the G alpha i2 gene

Null mutation of the Galphai2 trimeric G protein results in a discrete and profound mucosal disorder, including inflammatory bowel disease (IBD), attenuation of IL-10 expression, and immune function polarized to Th1 activity. Genetic and adoptive transfer experiments have established a role for B cells and IL-10 in mucosal immunologic homeostasis and IBD resistance. In this study, we addressed the hypothesis that Galphai2 is required for the development of IL-10-producing B cells. Galphai2(-/-) mice were reduced in the relative abundance of marginal zone (MZ), transitional type 2 (T2), and B-1a B cells and significantly increased in follicular mature and B-1b B cells. Reconstitution of RAG2(-/-) mice with Galphai2(-/-) bone marrow induced an IBD-like colitis and a deficiency in absolute numbers of MZ, T2, and B-1 B cells. Thus, the Galphai2(-/-) genotype in colitis susceptibility and B cell development involved a cis effect within the hemopoietic compartment. In vitro, the B cell population of Galphai2(-/-) mice was functionally deficient in LPS-induced proliferation and IL-10 production, consistent with the exclusive capacity of T2 and MZ cell subpopulations for LPS responsiveness. In vivo, Galphai2(-/-) mice were selectively impaired for the IgM response to T-independent type II, consistent with the relative depletion of MZ and peritoneal B-1 subpopulations. Collectively, these results reveal a selective role for Galphai2 in MZ and B-1 B cell development. Disorders of this Galphai2-dependent process in B cell development may represent a mechanism for IBD susceptibility.

Human intestinal epithelial cells are broadly unresponsive to Toll-like receptor 2-dependent bacterial ligands: implications for host-microbial interactions in the gut

Intestinal epithelial cells (IEC) interact with a high density of Gram-positive bacteria and are active participants in mucosal immune responses. Recognition of Gram-positive organisms by Toll-like receptor (TLR)2 induces proinflammatory gene expression by diverse cells. We hypothesized that IEC are unresponsive to Gram-positive pathogen-associated molecular patterns and sought to characterize the functional responses of IEC to TLR2-specific ligands. Human colonic epithelial cells isolated by laser capture microscopy and IEC lines (Caco-2, T84, HT-29) were analyzed for expression of TLR2, TLR6, TLR1, and Toll inhibitory protein (Tollip) mRNA by RT-PCR and quantitative real-time PCR. Response to Gram-positive bacterial ligands was measured by NF-kappa B reporter gene activation and IL-8 secretion. TLR2 protein expression was analyzed by immunofluorescence and flow cytometry. Colonic epithelial cells and lamina propria cells from both uninflamed and inflamed tissue demonstrate low expression of TLR2 mRNA compared with THP-1 monocytes. IECs were unresponsive to TLR2 ligands including the staphylococcal-derived Ags phenol soluble modulin, peptidoglycan, and lipotechoic acid and the mycobacterial-derived Ag soluble tuberculosis factor. Transgenic expression of TLR2 and TLR6 restored responsiveness to phenol soluble modulin and peptidoglycan in IEC. In addition to low levels of TLR2 protein expression, IEC also express high levels of the inhibitory molecule Tollip. We conclude that IEC are broadly unresponsive to TLR2 ligands secondary to deficient expression of TLR2 and TLR6. The relative absence of TLR2 protein expression by IEC and high level of Tollip expression may be important in preventing chronic proinflammatory cytokine secretion in response to commensal Gram-positive bacteria in the gut.

Manipulation of the bacterial flora in inflammatory bowel disease

In this chapter we summarize the clinical and experimental data which indicate that bacteria, especially from the endogenous microflora, play a role in the pathogenesis of Crohn's disease, ulcerative colitis and pouchitis. We review the clinical trials, focusing on randomized controlled trials which used antibiotics or probiotics to treat situations of IBD or prevent recurrence, and we discuss the future of this approach.