Breakdown of tolerance to the intestinal bacterial flora in inflammatory bowel disease (IBD)

Recent Updates on the Therapeutics Benefits, Clinical Trials, and Novel Delivery Systems of Chlorogenic Acid for the Management of Diseases with a Special Emphasis on Ulcerative Colitis

Ulcerative colitis (UC) is a multifactorial disorder of the large intestine, especially the colon, and has become a challenge globally. Allopathic medicines are primarily available for the treatment and prevention of UC. However, their uses are limited due to several side effects. Hence, an alternative therapy is of utmost importance in this regard. Herbal medicines are considered safe and effective for managing human health problems. Chlorogenic acid (CGA), the herbal-derived bioactive, has been reported for pharmacological effects like antiinflammatory, immunomodulatory, antimicrobial, hepatoprotective, antioxidant, anticancer, etc. This review aims to understand the antiinflammatory and chemopreventive potential of CGA against UC. Apart from its excellent therapeutic potential, it has been associated with low absorption and poor oral bioavailability. In this context, colon-specific novel drug delivery systems (NDDS)are pioneering to overcome these problems. The pertinent literature was compiled from a thorough search on various databases such as ScienceDirect, PubMed, Google Scholar, etc., utilizing numerous keywords, including ulcerative colitis, herbal drugs, CGA, pharmacological activities, mechanism of actions, nanoformulations, clinical updates, and many others. Relevant publications accessed till now were chosen, whereas non-relevant papers, unpublished data, and non-original articles were excluded. The present review comprises recent studies on pharmacological activities and novel drug delivery systems of CGA for managing UC. In addition, the clinical trials of CGA against UC have been discussed.

Adiponectin Alleviates Intestinal Fibrosis by Enhancing AMP-Activated Protein Kinase Phosphorylation

BACKGROUND

Intestinal fibrosis is a common complication of Crohn's disease (CD). Adiponectin reportedly exerts anti-inflammatory effects in various disease models, including colitis models.

AIMS

In this study, we aimed to determine the effects of adiponectin on intestinal fibrosis and the underlying mechanisms.

METHODS

A murine model of intestinal fibrosis was established by administering increasing doses of 2,4,6-trinitrobenzene sulfonic acid to Balb/c mice via enema for 7 weeks. Primary human fibroblasts were isolated from the colon tissues of patients with CD. The fibroblasts were incubated with transforming growth factor (TGF)-β1 to establish a fibrosis model in vitro. Pathway inhibitors were used to verify the potential signaling pathways involved in the anti-fibrogenic effect of adiponectin.

RESULTS

Compared with the normal mesentery, adiponectin expression was significantly increased in the hypertrophic mesentery of patients with CD. Intraperitoneal injection of adiponectin significantly decreased the activity of myeloperoxidase and the expression of pro-inflammatory cytokines (tumor necrosis factor α and interleukin 6) in the colon of fibrosis model mice, whereas the expression of the anti-inflammatory cytokine interleukin 10 was substantially increased. Moreover, adiponectin treatment inhibited colon shortening, decreased colon weight, and reduced fibrotic protein deposition in the model mice. Adiponectin reduced the phosphorylation of Smad2 and collagen deposition induced by TGF-β1 in primary human intestinal fibroblasts, with an increase in AMP-activated protein kinase (AMPK) phosphorylation. Furthermore, this phenomenon was reversed by the AMPK inhibitor.

CONCLUSIONS

Adiponectin can protect against intestinal fibrosis by enhancing the phosphorylation of AMPK and inhibiting the activity of the TGF-β1/Smad signaling pathway.

Salvianolic acid B decreases interleukin-1β-induced colitis recurrence in mice

BACKGROUND

Degree of mucosal recovery is an important indicator for evaluating the therapeutic effects of drugs in treatment of inflammatory bowel disease (IBD). Increasing evidences has proved that tight junction (TJ) barrier dysfunction is one of the pathological mechanisms of IBD. The aim of this study was to observe whether enhancement of TJ can decrease colitis recurrence.

METHODS

Eighty C57BL/6 mice were randomly divided into four groups including normal group, colitis group, sulfasalazine (SASP) treated group, and traditional Chinese drug salvianolic acid B (Sal B) treated group. Colitis was established in mice by free drinking water containing dextran sulfate sodium, after treatments by SASP and Sal B, recombinant human interleukin-1β (IL-1β) was injected intraperitoneally to induce colitis recurrence.

RESULTS

Compared with sham control, cell apoptosis in colitis group was increased from 100.85 ± 3.46% to 162.89 ± 11.45% (P = 0.0038), and TJ dysfunction marker myosin light chain kinase (MLCK) was also significantly increased from 99.70 ± 9.29% to 296.23 ± 30.78% (P = 0.0025). The increased cell apoptosis was reversed by both SASP (125.99 ± 8.45% vs. 162.89 ± 11.45%, P = 0.0059) and Sal B (104.27 ± 6.09% vs. 162.89 ± 11.45%, P = 0.0044). High MLCK expression in colitis group was reversed by Sal B (182.44 ± 89.42% vs. 296.23 ± 30.78%, P = 0.0028) but not influenced by SASP (285.23 ± 41.04% vs. 296.23 ± 30.78%, P > 0.05). The recurrence rate induced by recombinant human IL-1β in Sal B-treated group was significantly lower than that in SASP-treated group.

CONCLUSIONS

These results suggested a link between intestinal mucosal barrier dysfunction, especially TJ barrier dysfunction, and colitis recurrence. The TJ barrier dysfunction in remission stage of colitis increased the colitis recurrence. This study might provide potential treatment strategies for IBD recurrence.

Lactococcus lactis As a Versatile Vehicle for Tolerogenic Immunotherapy

Genetically modified Lactococcus lactis bacteria have been engineered as a tool to deliver bioactive proteins to mucosal tissues as a means to exert both local and systemic effects. They have an excellent safety profile, the result of years of human consumption in the food industry, as well as a lack of toxicity and immunogenicity. Also, containment strategies have been developed to promote further application as clinical protein-based therapeutics. Here, we review technological advancements made to enhanced the potential of L. lactis as live biofactories and discuss some examples of tolerogenic immunotherapies mediated by mucosal drug delivery via L. lactis. Additionally, we highlight their use to induce mucosal tolerance by targeted autoantigen delivery to the intestine as an approach to reverse autoimmune type 1 diabetes.

Hsp65-Producing Lactococcus lactis Prevents Inflammatory Intestinal Disease in Mice by IL-10- and TLR2-Dependent Pathways

Heat shock proteins (Hsps) are highly expressed at all sites of inflammation. As they are ubiquitous and immunodominant antigens, these molecules represent good candidates for the therapeutic use of oral tolerance in autoimmune and chronic inflammatory diseases. Evidences from human and animal studies indicate that inflammatory bowel disease (IBD) results from uncontrolled inflammatory responses to intestinal microbiota. Hsps are immunodominant proteins expressed by several immune cells and by commensal bacteria. Using an IBD mouse model, we showed that oral pretreatment with genetically modified Lactococcus lactis that produces and releases Mycobacterium Hsp65, completely prevented DSS-induced colitis in C57BL/6 mice. Protection was associated with reduced pro-inflammatory cytokines, such as IFN-γ, IL-6, and TNF-α; increased IL-10 production in colonic tissue; and expansion of CD4⁺Foxp3⁺ and CD4⁺LAP⁺ regulatory T cells in spleen and mesenteric lymph nodes. This effect was dependent on IL-10 and toll-like receptor 2. Thus, this approach may open alternative options for long-term management of IBD.

Oats and bowel disease: a systematic literature review

Whole-grain foods such as oats may protect against colorectal cancer and have benefits on inflammatory bowel disease and coeliac disease. The present study aimed to systematically review the literature describing intervention studies that investigated the effects of oats or oat bran on risk factors for bowel disease. A literature search was conducted using Embase, Medline and the Cochrane library, which identified 654 potential articles. Thirty-eight articles describing twenty-nine studies met the inclusion criteria. Two studies carried out in participants with a history of colorectal adenomas found no effects of increased oat-bran intake on indirect risk makers for colorectal cancer. One of two interventions with oat bran in patients with ulcerative colitis showed small improvements in the patients' conditions. Most of the eleven studies carried out in adults with coeliac disease showed no negative effects of uncontaminated oat consumption. The fourteen studies carried out in volunteers with no history of bowel disease suggest that oats or oat bran can significantly increase stool weight and decrease constipation, but there is a lack of evidence to support a specific effect of oats on bowel function compared with other cereals. A long-term dietary intake of oats or oat bran could benefit inflammatory bowel disorders, but this remains to be proven. A protective effect on colorectal adenoma and cancer incidence has not yet been convincingly shown. The majority of patients with coeliac disease could consume up to 100 g/d of uncontaminated oats, which would increase the acceptability of, and adherence to, a gluten-free diet.

The role of antibiotics and probiotics in pouchitis

Pouchitis is a non-specific inflammation of the ileal reservoir and the most common complication of proctocolectomy with ileal pouch-anal anastomosis (IPAA) in patients with ulcerative colitis. Its frequency is related to the duration of the follow up, occurring in up to 50% of patients 10 years after IPAA in large series from major referral centers. Treatment of pouchitis is largely empirical and only small placebo-controlled trials have been conducted. The rationale for using probiotics and antibiotics in pouchitis is based on convincing evidence that implicates intestinal bacteria in the pathogenesis of this disease. Probiotics are living organisms, which, upon ingestion in certain numbers, exert health benefits beyond inherent basic nutrition. VSL#3, a highly concentrated cocktail of probiotics has been shown to be effective in the prevention of pouchitis onset and relapses. Antibiotics are the mainstay of treatment of pouchitis, and metronidazole and ciprofloxacin are the most common initial approaches, often with a rapid response. The use of antibiotics in pouchitis is largely justified although proper controlled trials have not been conducted.

Environmental factors in the development of chronic inflammation: a case-control study on risk factors for Crohn's disease within New Zealand

The role of environmental factors in the risk for Crohn's disease (CD), an inflammatory bowel disease (IBD), was investigated in a North Island-based New Zealand case-control cohort. A total of 315 CD patients and 536 controls were recruited through various sources to the Auckland CD Risk Factor Study. As well as demographic characteristics, the self-reported questionnaire included (1) smoking and drinking alcohol, (2) breastfeeding in infancy, (3) early life exposures to allergens and microbes, (4) health conditions lasting 6 months or longer and (5) taking antibiotics and any medications. There was strong evidence for familial associations of the disease, and minor effects of birth order and number of siblings. Being a smoker, especially over a long time period, and exposure to smoking during childhood and adolescence periods increased risk, whereas drinking alcohol at least once per week showed a slight protective effect. Long term use of the oral contraceptive pill increased the risk of developing CD, but breastfeeding and immunisation during infancy showed no significant association. Long term and debilitating illness (lasting 6 months or more), taking antibiotics prior to developing CD, or taking four or more antibiotics or any regular medication in a year during adolescence substantially increased the CD risk. Having a pet during childhood was a protective factor, but regularly feeding an animal was not sufficient to protect. Many of these significant factors are likely to impact on the colonic microflora and/or immune system. We conclude that, in addition to strong evidence for genetic associations, factors likely to impact on immune response or reduce early exposure to microbes provide a main risk factor for CD in this New Zealand population.

Deficiency of invariant NK T cells in Crohn's disease and ulcerative colitis

The aim of this study was to investigate whether immunoregulatory invariant NK T cells are deficient in Crohn's disease or ulcerative colitis. Blood was collected for flow cytometry from 106 Crohn's disease, 91 ulcerative colitis, and 155 control subjects. Invariant NK T cells were assessed by Valpha24 and (alpha-galactosylceramide/CD1d tetramer markers. Intracellular cytokine was measured after in vitro anti-CD3 antibody stimulation. Valpha24+ T cells were quantified in ileocolonic biopsies as mRNA by real-time PCR and by immunofluorescence. Circulating invariant NK T cells were 5.3% of the control levels in Crohn's (P < 0.001) and 7.9% of the control levels in ulcerative colitis (P < 0.001). Interleukin-4 production was impaired in Crohn's disease and ulcerative colitis. Intestinal Valpha24 mRNA expression was 7% in Crohn's disease (P < 0.05) and 9% in ulcerative colitis (P < 0.05). Intestinal Valpha24+ T cells were 23% in Crohn's disease but not reduced in ulcerative colitis. We conclude that invariant NK T cells are deficient in Crohn's disease and in ulcerative colitis.

Kawasaki disease may be a hyperimmune reaction of genetically susceptible children to variants of normal environmental flora

Kawasaki disease (KD) is an acute febrile systemic vasculitis of unknown etiology that occurs predominantly in children <5 years of age. For the etiopathogenesis of KD, there is no agreement even as to whether KD is an infectious disease or an immune-mediated disease. The epidemiologic characteristics of KD, including the strict predilection of age in all ethnic groups and the gradually increased incidence after the KD emergence, suggest that KD is affected by the immune maturation in early childhood that may be determined by genetic factors, and KD is also affected by the changed environmental circumstances such as improved public hygiene.

We postulated that the pathogenesis of KD is a hyperimmune reaction in genetically susceptible children to the variants of normal flora, which are induced by the environmental factors. Using this hypothesis, we might partly explain the clinical and epidemiological characteristics of KD. We expect that this hypothesis may help to determine the causative agents for KD in the near future.

A population-based ecologic study of inflammatory bowel disease: searching for etiologic clues

The authors' objective in this study was to determine geographic variations in the incidence of inflammatory bowel disease (IBD), specifically Crohn's disease and ulcerative colitis, in the Canadian province of Manitoba and its association with the sociodemographic, geographic, and disease-related characteristics of the study population. Using the University of Manitoba IBD Epidemiology Database, the authors applied spatial and ecologic techniques to visualize, explore, and model the incidence of Crohn's disease and ulcerative colitis for the period 1990-2001. The study demonstrated marked, statistically significant geographic variability in rates of both Crohn's disease and ulcerative colitis associated with the characteristics of the study population. Incidences of Crohn's disease and ulcerative colitis were observed to be highest among non-Aboriginal persons, persons of high socioeconomic status, persons with the lowest rates of enteric infection, and persons with the highest rates of multiple sclerosis. The observation of an inverse association between IBD incidence and rates of reportable enteric infection at the population level is consistent with the "hygiene hypothesis," which suggests that early exposure to enteric agents affords protection against eventual development of IBD. The positive association between IBD incidence rates and multiple sclerosis suggests that these two chronic, immunologically mediated diseases may have a common environmental etiology. This study underscores the importance of environment in IBD causation.

A population-based case control study of potential risk factors for IBD

BACKGROUND

We aimed to pursue potential etiological clues to Crohn's disease (CD) and ulcerative colitis (UC) through a population-based case control survey study.

METHODS

Cases with CD (n = 364) and UC (n = 217), ages 18-50 yr were drawn from the population-based University of Manitoba IBD Research Registry. Potential control subjects were drawn from the population-based Manitoba Health Registry by age, gender, and geographic residence matching to the cases (n = 433). Subjects were administered a multiitem questionnaire.

RESULTS

By univariate analysis, some of the variables predictive of CD included lower likelihood of living on a farm, of having drunk unpasteurized milk or having eaten pork, and UC patients were less likely to have drunk unpasteurized milk and to have eaten pork. On multivariate analysis, variables significantly associated with CD were being Jewish (OR = 4.32, 95% CI 1.10-16.9), having a first degree relative with IBD (OR = 3.07, 95% CI 1.73-5.46), ever having smoked (OR = 1.54, 95% CI, 1.06-2.25), living longer with a smoker (OR = 1.03, 95% CI, 1.01-1.04). Being a first generation Canadian (OR = 0.33, 95% CI, 0.17-0.62), having pet cats before age 5 (OR = 0.66, 95% CI, 0.46-0.96) and having larger families (OR = 0.87, 95% CI, 0.79-0.96) were protective against CD. For UC being Jewish (OR = 7.46, 95% CI, 2.33-23.89), having a relative with IBD (OR = 2.23, 95% CI, 1.27-3.9), and ever smoking (OR = 1.62, 95% CI, 1.14-2.32) were predictive.

CONCLUSION

This study reinforced the increased risk associated with family history, being Jewish, and smoking history, however, a number of significant associations with CD and UC on univariate and multivariate analysis may support the "hygiene hypothesis" and warrant further exploration in prospective studies.

True or false? The hygiene hypothesis for Crohn's disease

The "hygiene hypothesis" for Crohn's disease postulates that multiple childhood exposures to enteric pathogens protect an individual from developing Crohn's disease later in life, while individuals raised in a more sanitary environment are more likely to develop Crohn's disease. In this issue of the American Journal of Gastroenterology, two Canadian case-control studies come to diametrically opposed conclusions regarding the hygiene hypothesis for Crohn's disease. This difference may be partially related to differences in study population (population based vs hospital based), age of onset, different genetic determinants, urban/rural residence (40% rural vs principally urban), or different exposures from the putative causative agent. As of now, the veracity of the hygiene hypothesis for Crohn's disease is not confirmed.

The B-cell system in inflammatory bowel disease

Secretory immunity is the best-defined part ot the mucosal immune system. This adaptive humoral defense mechanism depends on a fine-tuned cooperation between secretory epithelia and local plasma cells. Such mucosal immunocytes produce preferentially dimers and larger polymers of immunoglobulin A (collectively called pIgA), which contain J chain and therefore can bind to the epithelial secretory component (SC). This transmembrane glycoprotein functions as pIg receptor (pIgR) that also translocates pentameric IgM to the epithelial surface. B cells with a high level of J-chain expression and pIg-pIgR interactions at mucosal effector sites are thus necessary for the generation of secretory antibodies (SIgA and SIgM). Secretory antibodies perform immune exclusion in a first-line defense, thereby counteracting microbial colonization and mucosal penetration of soluble antigens. However, local production of pIgA is significantly down-regulated in inflammatory bowel disease (IBD), as revealed by strikingly decreased J-chain expression. Although the total increase of the immunocyte population in IBD lesions probably compensates for the relatively reduced pIgA production, decreased pIgR/SC expression in regenerating and dysplastic epithelium signifies that the SIgA system is topically deficient. There is, moreover, a significant shift from IgA2 to IgA1 production, the latter subclass being less resistant to proteolytic degradation. These changes--together with activation of mucosal macrophages and a dramatic increase of IgG-producing cells--may reflect local establishment of a second defense line which, however, is unsuccessful in its attempt to eliminate antigens derived from the indigenous microbial flora. Such a 'frustrated' local humoral immune system results in altered immunological homeostasis and jeopardized mucosal integrity. Complement activation observed in relation to epithelium-bound IgG1 in ulcerative colitis indicates, moreover, that the surface epithelium is subjected to immunological attack by an autoimmune reaction. These luminal deposits regularly contain terminal cytotoxic complement, and often also C3b as a sign of persistent activation. Comparison of identical twins, discordant with regard to ulcerative colitis, suggests that the markedly skewed local IgG1 response seen in this IBD entity may be genetically determined. The initial event(s) eliciting B-cell driven immunopathology in IBD remains unknown. Abrogation of oral tolerance to certain antigens from commensal bacteria has been suggested as a putative early mechanism, and lymphoid neogenesis and hyperplasia in the lesions most likely signify massive microbial overstimulation of the local B-cell system. Such ectopic lymphoid microcompartments may contribute substantially to the proinflammatory systemic-type of B-cell responses occurring in established IBD lesions.

Inflammatory bowel disease pathogenesis: therapeutic implications

The pathogenesis of inflammatory bowel disease (IBD) is complex, involving environmental, genetic, microbial, and immune factors. Therefore, treatment should target components that either predispose to or mediate the chronic inflammatory response of IBD. At the moment it is assumed that all components are necessary to have the typical manifestations of IBD but, in reality, it is unclear to what extent each factor contributes to the disease process, and whether some are more important than others. In addition, some factors are not practical targets; for example, environmental factors are poorly defined, too numerous, and require changes that cannot be implemented by the physician or the patient alone. The same is true for genetic factors that are still not amenable to therapeutic manipulations for technical and ethical reasons. This leaves microbial and immune factors as the two categories that can be selected for therapeutic intervention and where all current treatments are focused. The commensal gut flora can be qualitatively or quantitatively modified with antibiotics, probiotics, or diet, and a better characterization of enteric bacteria strains should help greatly in developing more effective therapies. Most current drugs are focused on inhibiting pro-inflammatory molecules produced by immune cells, including biological agents that block specific cytokines such as tumor necrosis factor-alpha. It is anticipated that combination therapies targeting multiple pathogenic components will prove more effective than those blocking single components of IBD pathogenesis.

The therapeutic potential of anti-cytokine antibodies in the treatment of chronic inflammatory disease

The outcome of inflammatory diseases is likely to be dependent upon the relative balance of pro- versus anti-inflammatory cytokines. Control of this balance through the use of anti-cytokine monoclonal antibodies (mAbs) promises to be an effective means of disease therapy. The treatment of rheumatoid arthritis (RA) or inflammatory bowel disease (IBD) with anti- tumour necrosis factor alpha (TNF-alpha) mAb has dramatically ameliorated disease symptoms, indicating that such a treatment approach can be highly successful. Similarly, based on animal studies, the use of neutralising anti-interleukin (IL)-12 mAb may prove efficacious in a number of inflammatory disorders, particularly for IBD.

Aetiology of inflammatory bowel disease (IBD): role of intestinal microbiota and gut-associated lymphoid tissue immune response

The aetiology of inflammatory bowel disease (IBD) probably involves a combination of genetic predisposition and environmental factors that may be channelled through an abnormality in gut-barrier function, with a loss of antigen tolerance. Some genetic markers that predispose to inflammatory disease have been identified (alleles DR2, DRB1*0103, DRB1*12 and mutations in the NOD2/CARD15 gene on chromosome 16). Alterations in the pattern of cytokine production by T cell subclasses leading to loss of tolerance to oral antigens have been documented. Moreover, a number of environmental factors (cigarette smoking, use of non-steroid anti-inflammatory drugs, psychological stress and the presence of the caecal appendix) have been postulated as a trigger of IBD. It has also been suggested that the gut microbiota plays a major role in the development and persistence of IBD, and numerous modifications of intestinal microbiota composition have been identified. As a result, manipulation of the microbiota with antibiotics is a current therapeutic strategy; more recently, however, a number of studies have reported promising results when using probiotic organisms to manipulate gut microbiota composition in order to restore tolerance to microbial antigens of the host's own microbiota.

Patients with active inflammatory bowel disease lack immature peripheral blood plasmacytoid and myeloid dendritic cells

BACKGROUND

Breakdown of tolerance against the commensal microflora is believed to be a major factor in the pathogenesis of inflammatory bowel disease (IBD). Dendritic cells (DC) have been implicated in this process in various animal models, but data on human DC in IBD are very limited.

AIM

To characterise plasmacytoid DC (PDC) and myeloid DC (MDC) in patients with active versus inactive IBD and healthy controls.

PATIENTS AND METHODS

Peripheral blood was obtained from 106 patients (Crohn's disease (CD) n=49, ulcerative colitis (UC) n=57) and healthy controls (n=19). Disease activity was scored using the modified Truelove Witts (MTWSI) for UC and the Harvey Bradshaw severity indices (HBSI) for CD. Four colour flow cytometric analysis was used to identify, enumerate, and phenotype DC. DC from patients with acute flare ups and healthy controls were cultured and stimulated with CpG ODN 2006 or lipopolysaccharide (LPS).

RESULTS

IBD patients in remission (PDC UC, 0.39%; CD, 0.35%; MDC-1 UC, 0.23%; CD, 0.22% of PBMC) have slightly lower numbers of circulating DC compared with healthy controls (PDC 0.41%, MDC-1 0.25% of PBMC). In acute flare ups IBD patients experience a significant drop of DC (PDC UC, 0.04%; CD, 0.11%; MDC-1 UC, 0.11%; CD, 0.14% of PBMC) that correlates with disease activity (correlation coefficients: PDC MTWSI, 0.93; HBSI, 0.79; MDC-1 MTWSI, 0.75; HBSI, 0.81). Moreover, both express alpha4beta7 integrin and display an immature phenotype. Freshly isolated PDC and MDC-1 from untreated flaring IBD patients express higher baseline levels of CD86 which increases further in culture and upon stimulation compared with healthy controls.

CONCLUSION

IBD patients lack immature blood DC during flare ups which possibly migrate to the gut. An aberrant response to microbial surrogate stimuli suggests a disturbed interaction with commensals.

War and peace at mucosal surfaces

That we live with numerous bacteria in our gut without any adverse effects is a remarkable feat by the body's immune system, particularly considering the wealth of sensing and effector systems that are available to trigger inflammatory or innate immune responses to microbial intrusion. So, a fine line seems to exist between the homeostatic balance maintained in the presence of commensal gut flora and the necessarily destructive response to bacterial pathogens that invade the gut mucosa. This review discusses the mechanisms for establishing and controlling the 'dialogue' between unresponsiveness and initiation of active immune defences in the gut. Si vis pacem, para bellum. (If you wish for peace, prepare for war.).

Ribosomal DNA sequence analysis of mucosa-associated bacteria in Crohn's disease

BACKGROUND

Enteric bacteria are implicated in the pathogenesis of Crohn's disease (CD); however, no specific causative organisms have been identified.

AIMS

This study was undertaken to correlate disease activity with changes in intestinal biota in patients with CD.

SUBJECTS

Ribosomal DNA analysis was used to explore the composition of the intestinal biota in patients with (1) CD undergoing colonoscopy, (2) CD undergoing surgical resection, and (3) no inflammatory bowel disease.

METHODS

Primers targeting bacterial 16S ribosomal DNA (rDNA) were used to amplify bacterial DNA associated with active CD lesions, comparable normal tissue from patients with CD, and normal control tissue. Each amplicon was cloned. Seven hundred thirty-nine rDNA clones were sequenced from 16 biopsies from CD patients, 15 surgical samples, and 10 biopsies from normal control patients.

RESULTS

Known extracellular or intracellular pathogens were not found. No rDNA sequence, phylogenetic group, or subgroup was consistently associated with CD lesions compared with normal tissues from the same patients. Colonic biopsies from CD-afflicted patients compared with biopsies from normal control subjects had an increase in facultative bacteria; in small bowel, CD patients had an increase in the Ruminococcus gnavus subgroup with a decrease in the Clostridium leptum and Prevotella nigrescens subgroups. However, differences in small bowel may have reflected individual variation rather than disease association. Surgical samples showed differences when compared with biopsy-derived samples.

CONCLUSIONS

These findings suggest that CD is not caused by invasive pathogens associated specifically with the sites of lesions but that dysbiosis exists in this condition.

Macroscopic, microscopic and biochemical characterisation of spontaneous colitis in a transgenic mouse, deficient in the multiple drug resistance 1a gene

1 A novel animal model of spontaneous colonic inflammation, the multiple drug-resistant (mdr1) a(-/-) mouse, was identified by Panwala and colleagues in 1998. The aim of our study was to further characterise this model, specifically by measuring cytokines that have been implicated in inflammatory bowel disease (IBD) (IL-8 and IFN-gamma) in the colon/rectum of mdr1a(-/-) mice, and by determining the sensitivity of these, together with the macroscopic, microscopic and disease signs of colitis, to dexamethasone (0.05, 0.3 and 2 mg kg(-1) subcutaneously (s.c.) daily for 7 days). 2 All mdr1a(-/-) mice had microscopic evidence of inflammation in the caecum and colon/rectum, while control mice with the same genetic background did not. Significant increases in colon/rectum and caecal weights and also in cytokine levels (both IFN-gamma and IL-8) in homogenised colon/rectum were observed in mdr1a(-/-) mice compared to mdr1a(+/+) mice. 3 Dexamethasone reduced the increases in tissue weights and also microscopic grading of colitis severity, but had no effect on IFN-gamma or IL-8. 4 This study supports the similarity of the gastrointestinal inflammation present in mdr1a(-/-) mice to that of human IBD, in particular Crohn's disease. This has been demonstrated at the macroscopic and microscopic levels, and was supported further by elevations in colonic levels of IFN-gamma and IL-8 and the disease signs observed. The incidence of colitis was much higher than previously reported, with all mice having microscopic evidence of colitis. The limited variance between animals in the parameters measured suggests that this model is reproducible.

Immunoglobulin coating of faecal bacteria in inflammatory bowel disease

OBJECTIVE

An inappropriate mucosal immune response to the commensal bacterial flora may play a role in the pathogenesis of inflammatory bowel disease (IBD). In this study we determined the percentage of immunoglobulin-coated bacteria in the stools of patients and controls.

METHODS

Faecal samples were obtained from 18 patients with IBD (one sample during exacerbation and one shortly after remission was achieved), 15 healthy volunteers, eight infectious colitis patients, and 13 IBD patients in long-term remission. Bacterial immunoglobulin coating was determined by flow-cytometry analysis. Faecal alpha-1-antitrypsin concentrations were determined by radial immune diffusion.

RESULTS

IBD patients had 69 +/- 19% immunoglobulin A (IgA)-, 56 +/- 32% immunoglobulin G (IgG)- and 56 +/- 29% immunoglobulin M (IgM)-coated bacteria in their faeces. Healthy controls had less immunoglobulin coating, respectively 36 +/- 12%, 11 +/- 4% and 11 +/- 7%. Infectious colitis patients had 57 +/- 14% IgA, 31 +/- 13% IgG, and 42 +/-16% IgM; however, they had higher faecal alpha-1-antitrypsin concentrations than IBD patients. Shortly after remission, IBD patients had 65 +/- 20% IgA, 32 +/- 18% IgG and 40 +/- 21% IgM. Long-term-remission IBD patients had normal IgG and IgM but increased IgA (50 +/- 16%) coating.

CONCLUSIONS

Compared with healthy controls, patients with IBD had an increased percentage of immunoglobulin-coated faecal anaerobic bacteria, both in active disease and shortly after remission. These results support the concept that there may be a breakdown of mucosal tolerance to the commensal gut flora in IBD.

Bugs and the gut: an unstable marriage

There is a symbiotic relationship between the gastrointestinal microflora and the human host. Commensal bacteria provide essential nutrients to the epithelium and promote healthy immune responses in the gut. Commensal bacteria such as Escherichia coli can, however, transform into pathogens when they acquire genetic material encoding virulence factors such as adhesins, enterotoxins, invasins and cytotoxins. Enterovirulent organisms 'communicate' with the host by a variety of diverse mechanisms; these underpin the pathogenic processes that are essential for the expression of diarrhoeal disease. Many of these mechanisms involve the activation of signal transduction pathways in epithelial cells. Classical pathways include activation of adenylate or guanylate cyclases to produce chloride secretion, and subversion of cytoskeletal functions to effect intimate attachment with or without invasion of epithelial cells. Other systems are also involved, including inflammatory cells and local neuroendocrine networks. Understanding the complex interactions between the human gastrointestinal tract and the commensals and pathogens which it encounters will hopefully help us to exploit further the beneficial effects of the 'marriage' and to find new ways of preventing and treating microbial disease of the intestine which occurs when the symbiotic arrangement breaks down.

The effect of etanercept and infliximab on the production of tumour necrosis factor alpha, interferon-gamma and GM-CSF in in vivo activated intestinal T lymphocyte cultures

BACKGROUND/AIMS

Infliximab (Ifx) is effective in the treatment of Crohn's disease (CD) and rheumatoid arthritis (RA), etanercept (Eta) in RA but not in CD. The mechanisms underlying these clinical differences are not fully understood, but this knowledge could be valuable to identify responders and develop new treatments. This study compares Eta and Ifx in vitro regarding transmembrane tumour necrosis factor alpha (tmb-TNF-alpha) expression and interferon-gamma (IFN-gamma), TNF-alpha and granulocyte macrophage colony stimulating factor (GM-CSF) production in intestinal T lymphocytes.

METHODS

T lymphocyte cultures were established from biopsies from 10 CD patients and three healthy controls. The cytokine production and the expression of tmb-TNF-alpha were measured in the presence of Ifx/Eta.

RESULTS

Eta and Ifx downregulated the production of IFN-gamma and GM-CSF in colonic T lymphocytes from CD patients and healthy controls. Both drugs bound tmb-TNF-alpha on activated T lymphocytes besides neutralising TNF-alpha, Eta less efficiently than Ifx (406 pg/ml (337-475); 133 pg/ml (119-147); p=0.004). TNF-alpha was detectable with the present assay in cell lines cultured in the presence of excess Eta.

CONCLUSIONS

We have established that Eta is just as efficient as Ifx in downregulating IFN-gamma and GM-CSF production in vitro and Eta bound to tmb-TNF-alpha. However, Eta bound the TNF-alpha molecule, important in CD, less efficiently than Ifx.

Selected loss of tolerance evidenced by Crohn's disease-associated immune responses to auto- and microbial antigens

BACKGROUND & AIMS

Previous studies in Crohn's disease suggest global loss of tolerance with sonicated bacteria preparations containing hundreds of antigens. Monoassociation studies show that a solitary bacterium can induce colitis in one animal model, whereas another is responsible in other models. Among patients with Crohn's disease, serum responses have been documented to microbial and autoantigens (antibodies to the Escherichia coli outer-membrane porin C and the Pseudomonas fluorescens-associated sequence I2, antisaccharomyces cerevisiae antibody (ASCA), and perinuclear antineutrophil cytoplasmic antibodies). Our aim was to determine whether there are heterogeneous responses to these specific antigens.

METHODS

Sera from 330 Crohn's patients were analyzed. Immunoglobulin A enzyme-linked immunosorbent assays to ASCA, outer-membrane porin C, or I2 and immunoglobulin G enzyme-linked immunosorbent assay to ASCA and ANCA determined the presence and level of antibodies. Perinuclear antineutrophil cytoplasmic antibodies were determined by immunofluorescence.

RESULTS

ASCA was detected in 56% of patients; 55% were seroreactive to outer-membrane porin C, 50% were seroreactive to I2, and 23% were perinuclear antineutrophil cytoplasmic antibody positive. Eighty-five percent responded to at least 1 antigen; only 4% responded to all 4. Among microbial antigens, 78% responded to at least 1, and 57% were double positive, but only 26% responded to all 3. The level of response was stable over time and with change in disease activity. Among patients with the same qualitative antigen-response profiles, quantitative response differed. Cluster analysis of these antibody responses yielded 4 groups: ASCA, outer-membrane porin C/I2, perinuclear antineutrophil cytoplasmic antibodies, or no/low response.

CONCLUSIONS

Rather than global loss of tolerance, there seem to be patient subsets with differing responses to selected microbial and autoantigens.

The influence of a colonic microbiota on HPMA copolymer lectin conjugates binding in rodent intestine

Germ-free (GF) animals lack a colonic microflora like that seen in conventional (CV) animals. Bacterial presence plays a role in the development of glycoproteins in the gastrointestinal (GI) tract; the absence of a microbiota has been seen to suppress the production of certain glycoproteins and glycolipids. Binding patterns of lectins are modified when glycoprotein structures are altered (e.g., during development or disease). Little information on lectin binding patterns in mature GF animals is available. We examined the binding of free and N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-conjugated fluorescein isothiocyanate (FITC)-labeled wheat germ agglutinin (WGA) [P(HPMA)-(WGA-FITC)] and FITC-labeled peanut agglutinin (PNA) [P(HPMA)-(PNA-FITC)] in CV and GF mouse colon with and without neuraminidase pretreatment. Anti-Thomsen-Friedenreich (TF) antigen (a development and disease-related glycoprotein) antibody binding was also examined in these tissues. Subtle differences were seen in the binding patterns between CV and GF animals. CV animals showed strong P(HPMA)-(WGA-FITC) binding in goblet cells, but minimal P(HPMA)-(PNA-FITC) binding was visible. In GF animals, luminal surface binding of P(HPMA)-(WGA-FITC) was visible, and goblet cell binding of P(HPMA)-(PNA-FITC) was seen. These subtle changes suggest that altered glycoprotein expression occurred under GF conditions.

Monocyte/macrophage activation by normal bacteria and bacterial products: implications for altered epithelial function in Crohn's disease

Intestinal immune cells are less reactive than those in the peripheral blood; however, such cells from patients with Crohn's disease may be more responsive to bacterial products. Our study examined if nonpathogenic bacteria or lipopolysaccharide (LPS), can affect epithelial function in the presence of monocytes/macrophages. Lamina propria mononuclear cells (LPMCs) and peripheral blood monocytes (PBMs) were obtained from patients with Crohn's disease and control patients. Filter-grown T84 epithelial monolayers were co-cultured with nonactivated or LPS-activated LPMCs or PBMs for 48 hours. Epithelial secretory [baseline short-circuit current (Isc) and DeltaIsc to forskolin] and barrier (transepithelial electrical resistance) parameters were measured in Ussing chambers. LPS-activated PBMs from both controls and patients with Crohn's disease significantly increased Isc ( approximately 300%) and reduced transepithelial electrical resistance ( approximately 40%). Epithelial function was not altered after co-culture with control LPMCs +/- LPS. However, LPMCs from patients with Crohn's disease spontaneously secreted tumor necrosis factor-alpha, and induced epithelial changes similar to those produced by LPS-activated PBMs. Co-culture with control Escherichia coli and PBMs induced comparable changes in epithelial physiology, which were abrogated by anti-tumor necrosis factor-alpha antibody. We conclude that LPMCs of patients with Crohn's disease are spontaneously activated, possibly by gram-negative luminal bacteria, and can directly cause significant alterations in epithelial ion transport and barrier functions.

Bifidobacterium adolescentis modulates the specific immune response to another human gut bacterium, Bacteroides thetaiotaomicron, in gnotobiotic rats

In order to investigate the capability of an autochthonous bacterium to modulate the host's immune response against the indigenous microfiora, the immunogenicity of two selected bacterial species of the human gut was investigated in a gnotobiotic rat model. Germ-free (GF) rats were monoassociated with either Bifidobacterium (B.) adolescentis or Bacteroides (B.) thetaiotaomicron and the development of bacteria-specific IgG and IgA in serum and specific secretory IgA (sIgA) in feces of the animals were measured. Knowing the antibody levels in gnotobiotic rats induced by monoassociation, we subsequently diassociated two groups of rats in order to investigate the impact of B. adolescentis on the immune reaction against B. thetaiotaomicron. One group was diassociated simultaneously with B. adolescentis and B. thetaiotaomicron, the second group was diassociated with these bacteria in sequence. In contrast to B. thetaiotaomicron, B. adolescentis was not able to induce a systemic immune response in monoassociated animals as evident from serum IgG and IgA. However, both bacterial species challenged the mucosal immune system as indicated by an increase in sIgA in the feces. The specific immune response to B. thetaiotaomicron was significantly lower in diassociated animals than in animals monoassociated with B. thetaiotaomicron. This effect was more pronounced in the rats, that had been associated sequentially. The presence of B. adolescentis down-regulated the humoral immunity to B. thetaiotaomicron.

Promotion of a favorable gut flora in inflammatory bowel disease

Recent evidence suggests that the composition of colonic flora plays a role in intestinal inflammation in inflammatory bowel disease (IBO). This review examines the evidence that altering the concentrations of colonic bacteria might benefit patients with this condition.

Immune response to orally consumed antigens and probiotic bacteria

The gut mucosal system must fulfil conflicting roles in suppressing immune responses against orally fed antigens (tolerance) while still retaining the ability to respond to potential enteric pathogens. It must also, to a large degree, not mount an immune response against commensal enteric bacteria and the administration of large numbers of probiotic bacteria formulated as dietary supplements in food products. Contrary to this dogma, it has been found that feeding ovalbumin as a marker antigen, in association with selected probiotic bacteria, appears to prime for an intestinal immune response that is further augmented by skin vaccination. Skin immunization is known to stimulate a strong innate, humoral and cellular immune response. Such dominant immunogenic signals appear to override tolerogenic signals engendered by oral feeding of antigen. High-dose antigen feeding stimulated a strong Th2-dependent antibody response to skin vaccination but completely suppressed cytotoxic T cell responses. This was true even when ovalbumin was administered in conjunction with various selected probiotic bacteria. However, while yeast appeared to be better at priming for an enhanced humoral response, Lactobacillus fermentum and Staphylococcus carnosus were more effective in enhancing the postvaccinal lymphoproliferative response against ovalbumin.

Diversion of intestinal flow decreases the numbers of interleukin 4 secreting and interferon gamma secreting T lymphocytes in small bowel mucosa

BACKGROUND/AIMS

The intestinal immune system faces large amounts of antigens, and its regulation is tightly balanced by cytokines. In this study, the effect of intestinal flow diversion on spontaneous secretion of interleukin (IL)-4 and interferon (IFN)- gamma was analysed.

METHODS

Eight patients (two with Crohn's disease, four with ulcerative colitis, and two with previous colon cancer) carrying a double lumen small bowel stoma after a total colectomy procedure were included in the study. For each patient, eight biopsy samples were taken endoscopically from both the diverted and non-diverted part of the small bowel. Intraepithelial lymphocytes (IELs) and lamina propria lymphocytes (LPLs) were isolated separately and assayed for numbers of cells spontaneously secreting IL-4 and/or IFN-gamma by an ELISPOT technique.

RESULTS

Compared with the non-diverted mucosa, a significant decrease in the number of spontaneously IFN-gamma secreting CD3 lymphocytes was observed in the diverted small bowel mucosa among both IELs (p = 0.008) and LPLs (p = 0.007). The same results, although less significant, were obtained for IL-4, especially in LPLs (p = 0.01).

CONCLUSION

The intestinal content influences the spontaneous secretion of IFN-gamma and IL-4 by intestinal lymphocytes. These results could help to elucidate the anti-inflammatory role of split ileostomy in patients suffering from inflammatory bowel diseases.

Experimental colitis induced by trinitrobenzenesulfonic acid: an ultrastructural and histochemical study

Inflammatory bowel disease (IBD) of humans is a chronic and devastating disease of unknown etiology. Models of acute colitis in animals have been achieved by intrarectal administration of agents such as 2,4,6-trinitrobenzenesulfonic acid (TNBS) into rat colon. This agent induces focal inflammation and alterations in the colon with features similar to those found in chronic inflammatory diseases in humans. The aim of this study was to assess the effect of TNBS administration on histological and ultrastructural features of the rat colon, especially in areas not affected by transmural inflammation. Also in areas without transmural inflammation, we observed a significant increase in crypt diameter and in the number and area of the goblet cells, as well as alterations in the contents of mucin in goblet cells. We conclude that TNBS treatment in rats led to severe changes in normal architecture of the colon and also in damaged areas where no direct inflammation was produced.

The role of IL-10 in inflammatory bowel disease: "of mice and men"

Inflammatory bowel disease (IBD) is a generic term typically used to describe a group of idiopathic inflammatory intestinal conditions in humans that are generally divided into Crohn's disease and ulcerative colitis. Although the etiology of these diseases remains unknown, a number of rodent models of IBD have recently been identified, all sharing the concept that the development of chronic intestinal inflammation occurs as a consequence of alterations in the immune system that lead to a failure of normal immunoregulation in the intestine. On the basis of these models, it has been hypothesized that the development of IBD in humans may be related to a dysregulated immune response to normal flora in the gut. Immunodeficient scid mice injected with CD4+ CD45RB(high) T cells and mice deficient in interleukin (IL)-10 (IL-10-/-) are among the rodent models of IBD. In both models, there is inflammation and evidence of a Th1-like response in the large intestine, characterized by CD4+ T-cell and macrophage infiltrates, and elevated levels of interferon-gamma. Because IL-10 is an immunomodulatory cytokine that is capable of controlling Th1-like responses, the role of IL-10 was investigated in these models. IL-10 was shown to be important in regulating the development of intestinal inflammation in both models. These results provided key data that supported initiation of clinical trials evaluating the efficacy of IL-10 in patients with IBD.

Autoimmunity, immunodeficiency and mucosal infections: chronic intestinal inflammation as a sensitive indicator of immunoregulatory defects in response to normal luminal microflora

Despite the fact that target antigens and the genetic basis of several autoimmune diseases are now better understood, the initial events leading to a loss of tolerance towards self-components remain unknown. One of the most attractive explanations for autoimmune phenomena involves various infections as possible natural events capable of initiating the process in genetically predisposed individuals. The most accepted explanation of how infection causes autoimmunity is based on the concept of "molecular mimicry" (similarity between the epitopes of an autoantigen and the epitopes in the environmental antigen). Infectious stimuli may also participate in the development of autoimmunity by inducing an increased expression of stress proteins (hsp), chaperones and transplantation antigens, which leads to abnormal processing and presentation of self antigens. Superantigens are considered to be one of the most effective bacterial components to induce inflammatory reactions and to take part in the development and course of autoimmune mechanisms. It has long been known that defects in the host defense mechanism render the individual susceptible to infections caused by certain microorganisms. Impaired exclusion of microbial antigens can lead to chronic immunological activation which can affect the tolerance to self components. Defects in certain components of the immune system are associated with a higher risk of a development of autoimmune disease. The use of animal models for the studies of human diseases with immunological pathogenesis has provided new insights into the influence of immunoregulatory factors and the lymphocyte subsets involved in the development of disease. One of the most striking conclusion arising from work with genetically engineered immunodeficient mouse models is the existence of a high level of redundancy of the components of the immune system. However, when genes encoding molecules involved in T cell immunoregulatory functions are deleted, spontaneous chronic inflammation of the gut mucosa (similar to human inflammatory bowel disease) develops. Surprisingly, when such immunocompromised animals were placed into germfree environment, intestinal inflammation did not develop. Impairment of the mucosal immune response to the normal bacterial flora has been proposed to play a crucial role in the pathogenesis of chronic intestinal inflammation. The use of immunodeficient models colonized with defined microflora for the analysis of immune reactivity will shed light on the mode of action of different immunologically important molecules responsible for the delicate balance between luminal commensals, nonspecific and specific components of the mucosal immune system.

IL-7 Deficiency Prevents Development of a Non-T Cell Non-B Cell-Mediated Colitis

IL-7 is a stromal cell-derived cytokine with a well-established physiologic role in lymphocyte biology. This report describes an unexpected role for IL-7 in the development of colitis in a T and B cell-deficient environment. Recombination-activating gene-2 (RAG-2)-deficient mice (RAG-2−/−) were exposed to and subsequently maintained a horizontally transmitted microbial flora that included Helicobacter hepaticus. These animals mounted a strong myeloid cell response and developed both systemic and local signs of a severe colitis. A striking infiltration of F4/80 and MHC class II-positive cells was seen in the colon and cecum of animals undergoing the disease. Mice mutant for both IL-7 and RAG-2 (IL-7/RAG-2−/−) that were colonized by the same flora showed no signs of myeloid responses or colitis, indicating that IL-7 plays a critical role in exacerbating a non-T cell/non-B cell-mediated chronic inflammatory response. Recombinant IL-10 protein therapy was able to prevent the occurrence of colitis in susceptible mice, suggesting a pivotal role for macrophages. The implications of a role for IL-7 in this disease model with respect to human inflammatory bowel disease are discussed.

A Novel Model of Inflammatory Bowel Disease: Mice Deficient for the Multiple Drug Resistance Gene, mdr1a, Spontaneously Develop Colitis

The murine multiple drug resistance (mdr) gene, mdr1a, encodes a 170-kDa transmembrane protein that is expressed in many tissues including intestinal epithelial cells, a subset of lymphoid cells and hematopoietic cells. We report that mdr1a knockout (mdr1a−/−) mice are susceptible to developing a severe, spontaneous intestinal inflammation when maintained under specific pathogen-free animal facility conditions. The intestinal inflammation seen in mdr1a−/− mice has a pathology similar to that of human inflammatory bowel disease (IBD) and is defined by dysregulated epithelial cell growth and leukocytic infiltration into the lamina propria of the large intestine. Treating mdr1a−/− mice with oral antibiotics can both prevent the development of disease and resolve active inflammation. Lymphoid cells isolated from mice with active colitis are functionally reactive to intestinal bacterial Ags, providing evidence that there is enhanced immunologic responsiveness to the normal bacterial flora during IBD. This study is the first description of spontaneous colitis in a gene knockout mouse with an apparently intact immune system. This novel model of spontaneous colitis may provide new insight into the pathogenesis of IBD, the nature of dysregulated immune reactivity to intestinal bacterial Ags, and the potential functional role of mdr genes expressed in the cells and tissues of the colonic microenvironment.

Oral microbial ecology and the role of salivary immunoglobulin A

In the oral cavity, indigenous bacteria are often associated with two major oral diseases, caries and periodontal diseases. These diseases seem to appear following an imbalance in the oral resident microbiota, leading to the emergence of potentially pathogenic bacteria. To define the process involved in caries and periodontal diseases, it is necessary to understand the ecology of the oral cavity and to identify the factors responsible for the transition of the oral microbiota from a commensal to a pathogenic relationship with the host. The regulatory forces influencing the oral ecosystem can be divided into three major categories: host related, microbe related, and external factors. Among host factors, secretory immunoglobulin A (SIgA) constitutes the main specific immune defense mechanism in saliva and may play an important role in the homeostasis of the oral microbiota. Naturally occurring SIgA antibodies that are reactive against a variety of indigenous bacteria are detectable in saliva. These antibodies may control the oral microbiota by reducing the adherence of bacteria to the oral mucosa and teeth. It is thought that protection against bacterial etiologic agents of caries and periodontal diseases could be conferred by the induction of SIgA antibodies via the stimulation of the mucosal immune system. However, elucidation of the role of the SIgA immune system in controlling the oral indigenous microbiota is a prerequisite for the development of effective vaccines against these diseases. The role of SIgA antibodies in the acquisition and the regulation of the indigenous microbiota is still controversial. Our review discusses the importance of SIgA among the multiple factors that control the oral microbiota. It describes the oral ecosystems, the principal factors that may control the oral microbiota, a basic knowledge of the secretory immune system, the biological functions of SIgA, and, finally, experiments related to the role of SIgA in oral microbial ecology.

Mechanisms of gastrointestinal reactions to food

Much of the genetic information that modulates mucosal immune responses was encoded several million years ago and has subsequently been subjected to modifications selected by the impact of microorganisms and food antigens. Confronted with these challenges, the intestinal immune system has developed two arms: (1) immune exclusion performed mainly by secretory IgA antibodies to inhibit colonization of pathogenic microorganisms and penetration of harmful antigens; and (2) down-regulatory mechanisms to avoid local and peripheral overreaction (hypersensitivity) towards innocuous substances. The latter phenomenon is called oral tolerance and apparently explains why most individuals show no adverse immune reactions food. When the mucosal barrier function is insufficient, tolerance to dietary antigens is abrogated in genetically susceptible individuals. This is most likely to occur during the vulnerable period after birth before the immunoregulatory network has been established. Breast-feeding appears to be immunologically important during this period, not only to substitute for the infant's lacking secretory antibodies but also because of its immune-modulating effects.

Characterization of the mucosal cell-mediated immune response in IL-2 knockout mice before and after the onset of colitis

One of the major advances in the understanding of inflammatory bowel disease has been the observation that mice with immunoregulatory defects, such as interleukin-2 knockout (IL-2 -/-) mice, develop spontaneous gut inflammation. Here we have characterized the immune response in the ileum, caecum and colon of these mice before and after the onset of colitis by examining the cellular infiltrate, the cytokines produced by these cells and the mucosal vascular addressin MAdCAM-1. IL-2 -/- mice developed colitis after 35 days of age and before this the mice were apparently healthy. IL-2 -/- mice aged over 35 days with colitis had large numbers of CD4+, CD8+, alpha beta T-cell receptor (TCR)+ and gamma delta TCR+ T cells, macrophages, dendritic cells and MAdCAM-1+ endothelial cells in the caecum and colon. This was associated with an increase in the number of interferon-gamma (IFN-gamma), IL-1 and tumour necrosis factor-alpha (TNF-alpha) transcripts and a decrease in IL-4 and IL-10 transcripts. Treatment of IL-2 -/- mice with cyclosporin A significantly delayed mortality. Interestingly, IL-2 -/- mice under 35 days, although healthy, did show some subtle immunological signs of preclinical disease. There was a significant increase in the number of macrophages and dendritic cells in the colonic lamina propria and increased mRNA for IL-1 and TNF-alpha. There were also increased numbers of MAdCAM-1+ endothelial cells, but IFN-gamma transcripts were not elevated. These results suggest that T-cell-mediated colitis in IL-2 -/- mice may be secondary to an initial non-specific inflammation.

No apparent influence of immunoglobulins on indigenous oral and intestinal microbiota of mice

The role of secretory immunoglobulin A (sIgA) in the control of the indigenous microbiota is not well understood. In this study, we compared the oral and intestinal microbiota of transgenic B-cell-deficient (microMT) mice with their heterozygous (microMT/+) normal littermates. The levels of salivary IgA and serum IgA and IgG were normal in microMT/+ mice, while no immunoglobulins were detected in microMT/microMT mice. The acquisition and proportions of the different species of the oral and intestinal indigenous bacterial populations were not significantly different between the two groups of mice. Our results thus suggest that secretory IgA does not play a major role in the regulation of the indigenous microbiota of mice.

T helper cell 1-type CD4+ T cells, but not B cells, mediate colitis in interleukin 10-deficient mice

Mice rendered deficient in the production of interleukin 10 (IL-10-/-) develop a chronic inflammatory bowel disease (IBD) that predominates in the colon and shares histopathological features with human IBD. Our aim was to identify which cell type(s) can mediate colitis in IL-10-/- mice. We detected an influx of immunoglobulin-positive cells into the colon and the presence of colon-reactive antibodies in the serum of IL-10-/- mice. To assess a pathogenic role for B cells, we generated a B cell-deficient (B-/-) strain of IL-10-/- mice. B-/-IL-10-/- mice acquired a severe colitis analogous to that IL-10-/- mice, implying that B cells were not the primary mediator of IBD in this model. A series of cell transfer experiments was performed to assess a pathogenic role for T cells. When IL-10-/- T cell-enriched lamina propria lymphocytes (LPL) or intraepithelial lymphocytes (IEL) were transferred into immunodeficient recombinase-activating gene (RAG)-2-/- recipients, a mild to severe colitis developed, depending on the cell number transferred. Lymphocytes recovered from the colon of transplanted RAG-2-/- mice with colitis were predominantly alpha beta TCR+CD4+, including a large proportion of CD4+CD8 alpha + cells. These cells were also CD45RB-/low and CD44+, indicative of an activated/memory population. Individual populations of CD4+CD8 alpha-, CD4+CD8 alpha + and CD4-CD8 alpha + T cells were then isolated from the lamina propria compartment of IL-10-/- mice and transferred into RAG-2-/- recipients. Only IL-10-/- CD4-expressing LPL, including both the CD4+CD8 alpha- and CD4+CD8 alpha + populations, induced colitis in recipient mice. Interferon-gamma, but little to no IL-4, was produced by CD4+CD8 alpha- and CD4+CD8 alpha + LPL recovered from the inflamed colons of RAG-2-/- recipients implicating alpha T helper cell 1 (TH1)-mediated response. We thus conclude that colitis in IL-10-/- mice is predominantly mediated by TH1-type alpha beta TCR+ T cells expressing CD4 alone, or in combination with the CD8 alpha molecule.