Stool antigen immunodetection for diagnosis of Giardia duodenalis infection in human subjects with HIV and cancer

Human infection with the protozoan parasite Giardia duodenalis is one the most common parasitic diseases worldwide. Higher incidence rates of giardiasis have been reported from human subjects with multiple debilitating chronic conditions, including hypogammaglobulinemia and common variable immunodeficiency (CVID). In the current study, stool specimens were collected from 199 individuals diagnosed with HIV or cancer and immunocompetent subjects. The sensitivity of microscopy-based detection on fresh stool preparations, trichrome staining and stool antigen immunodetection for the diagnosis of G. duodenalis were 36%, 45.5% and 100%, respectively when compared with a highly sensitive stool-based PCR method as the gold standard. Further multilocus molecular analyses using glutamate dehydrogenase (gdh) and triose phosphate isomerase (tpi) loci demonstrated that the AI genotype of G. duodenalis was the most prevalent, followed by the AII genotype and mixed (AI+B) infections. We concluded that stool antigen immunodetection-based immunoassays and stool-based PCR amplification had comparable sensitivity and specificity for the diagnosis of G. duodenalis infections in these populations. Stool antigen detection-based diagnostic modalities are rapid and accurate and may offer alternatives to conventional microscopy and PCR-based diagnostic methods for the diagnosis of G. duodenalis in human subjects living with HIV or cancer.

TLR3 signaling is downregulated by a MAVS isoform in epithelial cells

Innate immune responses to dsRNA result in signaling through the TLR3 pathway and/or the RIG-I/MDA-5/MAVS pathway which can activate type I IFN, proinflammatory cytokines and apoptosis. It is not clear whether MAVS could play a role in TLR3-dependent responses to extracellular dsRNA. Using a model of epithelial cells that express a functional TLR3 signaling pathway, we found that TLR3-dependent responses to extracellular dsRNA are negatively regulated by MAVS, precisely "miniMAVS", a recently described 50kDa isoform of MAVS. This regulation of TLR3 by a MAVS isoform constitutes an endogenous regulatory mechanism in epithelial cells that could help prevent a potentially damaging excessive inflammatory response.

Lack of the programmed death-1 receptor renders host susceptible to enteric microbial infection through impairing the production of the mucosal natural killer cell effector molecules

The programmed death-1 receptor is expressed on a wide range of immune effector cells, including T cells, natural killer T cells, dendritic cells, macrophages, and natural killer cells. In malignancies and chronic viral infections, increased expression of programmed death-1 by T cells is generally associated with a poor prognosis. However, its role in early host microbial defense at the intestinal mucosa is not well understood. We report that programmed death-1 expression is increased on conventional natural killer cells but not on CD4(+), CD8(+) or natural killer T cells, or CD11b(+) or CD11c(+) macrophages or dendritic cells after infection with the mouse pathogen Citrobacter rodentium. Mice genetically deficient in programmed death-1 or treated with anti-programmed death-1 antibody were more susceptible to acute enteric and systemic infection with Citrobacter rodentium. Wild-type but not programmed death-1-deficient mice infected with Citrobacter rodentium showed significantly increased expression of the conventional mucosal NK cell effector molecules granzyme B and perforin. In contrast, natural killer cells from programmed death-1-deficient mice had impaired expression of those mediators. Consistent with programmed death-1 being important for intracellular expression of natural killer cell effector molecules, mice depleted of natural killer cells and perforin-deficient mice manifested increased susceptibility to acute enteric infection with Citrobacter rodentium. Our findings suggest that increased programmed death-1 signaling pathway expression by conventional natural killer cells promotes host protection at the intestinal mucosa during acute infection with a bacterial gut pathogen by enhancing the expression and production of important effectors of natural killer cell function.

The intestinal epithelium is an integral component of a communications network

The epithelial lining of the intestine forms a barrier that separates the intestinal lumen from the host's internal milieu and is critical for fluid and electrolyte secretion and nutrient absorption. In the early 1990s, my laboratory discovered that intestinal epithelial cells could alter their phenotype and produce proinflammatory chemokines and cytokines when stimulated by pathogenic enteric luminal microbes or proinflammatory agonists produced by cells in the underlying mucosa. It is now well accepted that intestinal epithelial cells can be induced to express and secrete specific arrays of cytokines, chemokines, and antimicrobial defense molecules. The coordinated release of molecules by intestinal epithelial cells is crucial for activating intestinal mucosal inflammatory responses as well as mucosal innate and adaptive immune responses. More recent studies have focused on the intestinal epithelial signaling pathways that culminate in immune activation as well as the role of these pathways in host defense, mucosal injury, mucosal wound healing, and tumorigenesis. The emerging picture indicates that intestinal epithelial cells represent an integral component of a highly regulated communications network that can transmit essential signals to cells in the underlying intestinal mucosa, and that intestinal epithelial cells, in turn, serve as targets of mucosal mediators. These signals are essential for maintaining intestinal mucosal defense and homeostasis.

Barriers impeding serologic screening for celiac disease in clinically high-prevalence populations

BACKGROUND

Celiac disease is present in ~1% of the general population in the United States and Europe. Despite the availability of inexpensive serologic screening tests, ~85% of individuals with celiac disease remain undiagnosed and there is an average delay in diagnosis of symptomatic individuals with celiac disease that ranges from ~5.8-11 years. This delay is often attributed to the use of a case-based approach for detection rather than general population screening for celiac disease, and deficiencies at the level of health care professionals. This study aimed to assess if patient-centered barriers have a role in impeding serologic screening for celiac disease in individuals from populations that are clinically at an increased risk for celiac disease.

METHODS

119 adults meeting study inclusion criteria for being at a higher risk for celiac disease were recruited from the general population. Participants completed a survey/questionnaire at the William K. Warren Medical Research Center for Celiac Disease that addressed demographic information, celiac disease related symptoms (gastrointestinal and extraintestinal), family history, co-morbid diseases and conditions associated with celiac disease, and patient-centered barriers to screening for celiac disease. All participants underwent serologic screening for celiac disease using the IgA tissue transglutaminase antibody (IgA tTG) and, if positive, testing for IgA anti-endomysial antibody (IgA EMA) as a confirmatory test.

RESULTS

Two barriers to serologic testing were significant across the participant pool. These were participants not knowing they were at risk for celiac disease before learning of the study, and participants not knowing where to get tested for celiac disease. Among participants with incomes less than $25,000/year and those less than the median age, not having a doctor to order the test was a significant barrier, and this strongly correlated with not having health insurance. Symptoms and co-morbid conditions were similar among those whose IgA tTG were negative and those who tested positive.

CONCLUSION

There are significant patient-centered barriers that impede serologic screening and contribute to the delayed detection and diagnosis of celiac disease. These barriers may be lessened by greater education of the public and health care professionals about celiac disease symptoms, risk factors, and serologic testing.

Persistence of elevated deamidated gliadin peptide antibodies on a gluten-free diet indicates nonresponsive coeliac disease

BACKGROUND

Histologically nonresponsive coeliac disease (NRCD) is a potentially serious condition diagnosed during the follow-up of coeliac disease (CD) when patients have persistent villous atrophy despite following a gluten-free diet (GFD).

AIM

As current assessments of recovery are limited to invasive and costly serial duodenal biopsies, we sought to identify antibody biomarkers for CD patients that do not respond to traditional therapy.

METHODS

Bacterial display peptide libraries were screened by flow cytometry to identify epitopes specifically recognised by antibodies from patients with NRCD, but not by antibodies from responsive CD patients. Deamidated gliadin was confirmed to be the antigen mimicked by library peptides using ELISA with sera from NRCD (n = 15) and responsive CD (n = 45) patients on a strict GFD for at least 1 year.

RESULTS

The dominant consensus epitope sequence identified by unbiased library screening QPxx(A/P)FP(E/D) was highly similar to reported deamidated gliadin peptide (dGP) B-cell epitopes. Measurement of anti-dGP IgG titre by ELISA discriminated between NRCD and responsive CD patients with 87% sensitivity and 89% specificity. Importantly, dGP antibody titre correlated with the severity of mucosal damage indicating that IgG dGP titres may be useful to monitor small intestinal mucosal recovery on a GFD.

CONCLUSIONS

The finding of increased levels of anti-dGP IgG antibodies in CD patients on strict GFDs effectively identifies patients with NRCD. Finally, anti-dGP IgG assays may be useful to monitor mucosal damage and histological improvement in CD patients on a strict GFD.

GM-CSF produced by nonhematopoietic cells is required for early epithelial cell proliferation and repair of injured colonic mucosa

GM-CSF is a growth factor that promotes the survival and activation of macrophages and granulocytes, as well as dendritic cell differentiation and survival in vitro. The mechanism by which exogenous GM-CSF ameliorates the severity of Crohn's disease in humans and colitis in murine models has mainly been considered to reflect its activity on myeloid cells. We used GM-CSF-deficient (GM-CSF(-/-)) mice to probe the functional role of endogenous host-produced GM-CSF in a colitis model induced after injury to the colon epithelium. Dextran sodium sulfate (DSS), at doses that resulted in little epithelial damage and mucosal ulceration in wild type mice, caused marked colon ulceration and delayed ulcer healing in GM-CSF(-/-) mice. Colon crypt epithelial cell proliferation in vivo was significantly decreased in GM-CSF(-/-) mice at early times after DSS injury. This was paralleled by decreased expression of crypt epithelial cell genes involved in cell cycle, proliferation, and wound healing. Decreased crypt cell proliferation and delayed ulcer healing in GM-CSF(-/-) mice were rescued by exogenous GM-CSF, indicating the lack of a developmental abnormality in the epithelial cell proliferative response in those mice. Nonhematopoietic cells, and not myeloid cells, produced the GM-CSF important for colon epithelial proliferation after DSS-induced injury, as revealed by bone marrow chimera and dendritic cell-depletion experiments, with colon epithelial cells being the cellular source of GM-CSF. Endogenous epithelial cell-produced GM-CSF has a novel nonredundant role in facilitating epithelial cell proliferation and ulcer healing in response to injury of the colon crypt epithelium.

TLR3, TRIF, and caspase 8 determine double-stranded RNA-induced epithelial cell death and survival in vivo

TLR3 signaling is activated by dsRNA, a virus-associated molecular pattern. Injection of dsRNA into mice induced a rapid, dramatic, and reversible remodeling of the small intestinal mucosa with significant villus shortening. Villus shortening was preceded by increased caspase 3 and 8 activation and apoptosis of intestinal epithelial cells (IECs) located in the mid to upper villus with ensuing luminal fluid accumulation and diarrhea because of an increased secretory state. Mice lacking TLR3 or the adaptor molelcule TRIF mice were completely protected from dsRNA-induced IEC apoptosis, villus shortening, and diarrhea. dsRNA-induced apoptosis was independent of TNF signaling. Notably, NF-κB signaling through IκB kinase β protected crypt IECs but did not protect villus IECs from dsRNA-induced or TNF-induced apoptosis. dsRNA did not induce early caspase 3 activation with subsequent villus shortening in mice lacking caspase 8 in IECs but instead caused villus destruction with a loss of small intestinal surface epithelium and death. Consistent with direct activation of the TLR3-TRIF-caspase 8 signaling pathway by dsRNA in IECs, dsRNA-induced signaling of apoptosis was independent of non-TLR3 dsRNA signaling pathways, IL-15, TNF, IL-1, IL-6, IFN regulatory factor 3, type I IFN receptor, adaptive immunity, as well as dendritic cells, NK cells, and other hematopoietic cells. We conclude that dsRNA activation of the TLR3-TRIF-caspase 8 signaling pathway in IECs has a significant impact on the structure and function of the small intestinal mucosa and suggest signaling through this pathway has a host protective role during infection with viral pathogens.

Introduction: celiac disease

This is the introduction for the Special Issue on Celiac Disease.

Can consumers trust web-based information about celiac disease? Accuracy, comprehensiveness, transparency, and readability of information on the internet

Background

Celiac disease is an autoimmune disease that affects approximately 1% of the US population. Disease is characterized by damage to the small intestinal lining and malabsorption of nutrients. Celiac disease is activated in genetically susceptible individuals by dietary exposure to gluten in wheat and gluten-like proteins in rye and barley. Symptoms are diverse and include gastrointestinal and extraintestinal manifestations. Treatment requires strict adherence to a gluten-free diet. The Internet is a major source of health information about celiac disease. Nonetheless, information about celiac disease that is available on various websites often is questioned by patients and other health care professionals regarding its reliability and content.

Objectives

To determine the accuracy, comprehensiveness, transparency, and readability of information on 100 of the most widely accessed websites that provide information on celiac disease.

Methods

Using the search term celiac disease, we analyzed 100 of the top English-language websites published by academic, commercial, nonprofit, and other professional (nonacademic) sources for accuracy, comprehensiveness, transparency, and reading grade level. Each site was assessed independently by 3 reviewers. Website accuracy and comprehensiveness were probed independently using a set of objective core information about celiac disease. We used 19 general criteria to assess website transparency. Website readability was determined by the Flesch-Kincaid reading grade level. Results for each parameter were analyzed independently. In addition, we weighted and combined parameters to generate an overall score, termed website quality.

Results

We included 98 websites in the final analysis. Of these, 47 (48%) provided specific information about celiac disease that was less than 95% accurate (ie, the predetermined cut-off considered a minimum acceptable level of accuracy). Independent of whether the information posted was accurate, 51 of 98 (52%) websites contained less than 50% of the core celiac disease information that was considered important for inclusion on websites that provide general information about celiac disease. Academic websites were significantly less transparent (P = .005) than commercial websites in attributing authorship, timeliness of information, sources of information, and other important disclosures. The type of website publisher did not predict website accuracy, comprehensiveness, or overall website quality. Only 4 of 98 (4%) websites achieved an overall quality score of 80 or above, which a priori was set as the minimum score for a website to be judged trustworthy and reliable.

Conclusions

The information on many websites addressing celiac disease was not sufficiently accurate, comprehensive, and transparent, or presented at an appropriate reading grade level, to be considered sufficiently trustworthy and reliable for patients, health care providers, celiac disease support groups, and the general public. This has the potential to adversely affect decision making about important aspects of celiac disease, including its appropriate and proper diagnosis, treatment, and management.

Constitutive intestinal NF-κB does not trigger destructive inflammation unless accompanied by MAPK activation

Constitutive NF-κB activation in IECs induces inflammatory cytokines and chemokines in the lamina propria, but does not result in overt tissue damage unless acute inflammatory insults are present, causing TNF-dependent destruction and barrier disruption.

Nuclear factor (NF)-κB, activated by IκB kinase (IKK), is a key regulator of inflammation, innate immunity, and tissue integrity. NF-κB and one of its main activators and transcriptional targets, tumor necrosis factor (TNF), are up-regulated in many inflammatory diseases that are accompanied by tissue destruction. The etiology of many inflammatory diseases is poorly understood, but often depends on genetic factors and environmental triggers that affect NF-κB and related pathways. It is unknown, however, whether persistent NF-κB activation is sufficient for driving symptomatic chronic inflammation and tissue damage. To address this question, we generated IKKβ(EE)^IEC mice, which express a constitutively active form of IKKβ in intestinal epithelial cell (IECs). IKKβ(EE)^IEC mice exhibit NF-κB activation in IECs and express copious amounts of inflammatory chemokines, but only small amounts of TNF. Although IKKβ(EE)^IEC mice exhibit inflammatory cell infiltration in the lamina propria (LP) of their small intestine, they do not manifest tissue damage. Yet, upon challenge with relatively mild immune and microbial stimuli, IKKβ(EE)^IEC mice succumb to destructive acute inflammation accompanied by enterocyte apoptosis, intestinal barrier disruption, and bacterial translocation. Inflammation is driven by massive TNF production, which requires additional activation of p38 and extracellular-signal–regulated kinase mitogen-activated protein kinases (MAPKs).

RIG-I/MDA5/MAVS are required to signal a protective IFN response in rotavirus-infected intestinal epithelium

Rotavirus is a dsRNA virus that infects epithelial cells that line the surface of the small intestine. It causes severe diarrheal illness in children and ∼500,000 deaths per year worldwide. We studied the mechanisms by which intestinal epithelial cells (IECs) sense rotavirus infection and signal IFN-β production, and investigated the importance of IFN-β production by IECs for controlling rotavirus production by intestinal epithelium and virus excretion in the feces. In contrast with most RNA viruses, which interact with either retinoic acid-inducible gene I (RIG-I) or melanoma differentiation-associated gene 5 (MDA5) inside cells, rotavirus was sensed by both RIG-I and MDA5, alone and in combination. Rotavirus did not signal IFN-β through either of the dsRNA sensors TLR3 or dsRNA-activated protein kinase (PKR). Silencing RIG-I or MDA5, or their common adaptor protein mitochondrial antiviral signaling protein (MAVS), significantly decreased IFN-β production and increased rotavirus titers in infected IECs. Overexpression of laboratory of genetics and physiology 2, a RIG-I-like receptor that interacts with viral RNA but lacks the caspase activation and recruitment domains required for signaling through MAVS, significantly decreased IFN-β production and increased rotavirus titers in infected IECs. Rotavirus-infected mice lacking MAVS, but not those lacking TLR3, TRIF, or PKR, produced significantly less IFN-β and increased amounts of virus in the intestinal epithelium, and shed increased quantities of virus in the feces. We conclude that RIG-I or MDA5 signaling through MAVS is required for the activation of IFN-β production by rotavirus-infected IECs and has a functionally important role in determining the magnitude of rotavirus replication in the intestinal epithelium.

GM-CSF: a role in immune and inflammatory reactions in the intestine

Granulocyte macrophage colony-stimulating factor (GM-CSF) is a cytokine that promotes myeloid cell development and maturation, and dendritic cell differentiation and survival in vitro. Growing evidence supports the notion that GM-CSF has a major role in some inflammatory and autoimmune reactions and in the host's response to pulmonary infection, but few studies have addressed its functions and importance in the GI tract. Recent studies demonstrated that administration of GM-CSF can result in clinical improvement in patients with Crohn's disease. Mice deficient in GM-CSF (GM-CSF(-/-) ) developed more severe intestinal and systemic infection after an enteric infection, and more severe colitis in response to enteric exposure to dextran sodium sulfate. Both the severity of infection and colitis were largely prevented by GM-CSF administration. Such studies indicate that GM-CSF has an important role in the regulation of intestinal immune and inflammatory responses.

Activation of innate immune defense mechanisms by signaling through RIG-I/IPS-1 in intestinal epithelial cells

Intestinal epithelial cells (IECs) are a first line of defense against microbial pathogens that enter the host through the intestinal tract. Moreover, viral pathogens that infect the host via the intestinal epithelium are an important cause of morbidity and mortality. However, the mechanisms by which viral pathogens activate antiviral defense mechanisms in IECs are largely unknown. The synthetic dsRNA analog polyinosinic-polycytidylic acid and infection with live virus were used to probe the molecules that are activated and the mechanisms of signaling in virus-infected human IECs. Polyinosinic-polycytidylic acid activated IFN regulatory factor 3 dimerization and phosphorylation, increased activity of the IFN-stimulated response element, induced a significant increase in IFN-beta mRNA transcripts and IFN-beta secretion, and up-regulated the expression of IFN-regulated genes in IECs. Those responses were dependent upon activation of the dsRNA binding protein retinoic acid inducible gene I (RIG-I) and the RIG-I interacting protein IFN promoter stimulator-1, but not on dsRNA-activated protein kinase or TLR3, which also were expressed by IECs. Virus replication and virus-induced cell death increased in IECs in which RIG-I was silenced, consistent with the importance of the RIG-I signaling pathway in IEC antiviral innate immune defense mechanisms.

Celiac disease: pathogenesis of a model immunogenetic disease

Celiac disease is characterized by small-intestinal mucosal injury and nutrient malabsorption in genetically susceptible individuals in response to the dietary ingestion of wheat gluten and similar proteins in barley and rye. Disease pathogenesis involves interactions among environmental, genetic, and immunological factors. Although celiac disease is predicted by screening studies to affect approximately 1% of the population of the United States and is seen both in children and in adults, 10%-15% or fewer of these individuals have been diagnosed and treated. This article focuses on the role of adaptive and innate immune mechanisms in the pathogenesis of celiac disease and how current concepts of immunopathogenesis might provide alternative approaches for treating celiac disease.

Epithelial cell I kappa B-kinase beta has an important protective role in Clostridium difficile toxin A-induced mucosal injury

Toxin A released by Clostridium difficile interacts with the single layer of intestinal epithelial cells that lines the host's intestinal tract and leads to mucosal damage and inflammation that manifests clinically as antibiotic-associated diarrhea and pseudomembranous colitis. Activation of the transcription factor NF-kappaB in intestinal epithelial cells is important for regulating the expression of epithelial cell proinflammatory genes and cell survival. However, the role of NF-kappaB activation in the pathogenesis of C. difficile toxin A-induced colitis is unknown. To determine the functional importance in vivo of NF-kappaB activation in intestinal epithelium in the pathogenesis of C. difficile-induced colitis, we used mutant mice that do not activate the classical NF-kappaB signaling pathway in intestinal epithelial cells due to a conditional deficiency in those cells of the IkappaB-kinase beta (IKKbeta) subunit of IKK. C. difficile toxin A challenge of intestinal loops in intestinal epithelial cell IKKbeta-deficient mice induced a rapid and significant increase in intestinal epithelial apoptosis compared with littermate controls. This was accompanied by a significant increase in acute mucosal inflammation, mucosal injury, luminal fluid secretion, and bacterial translocation. We conclude that activation of intestinal epithelial cell NF-kappaB by toxin A plays an important host mucosal protective role after C. difficile toxin A exposure that is mediated, at least in part, through promoting epithelial cell survival by abrogating epithelial cell apoptosis.

Microbial-Epithelial Cell Crosstalk during Inflammation: The Host Response

The intestinal epithelium forms a single cell barrier that separates the host's internal milieu from luminal contents. This article examines the role of the intestinal epithelium as a critical component of a communications network that is essential for transmitting signals generated in response to infection with microbial pathogens to cells of the innate and acquired immune systems in the underlying intestinal mucosa. It further highlights the importance of intestinal epithelium in mediating host antimicrobial defense through the production of antimicrobial peptides of the defensin and cathelicidin families.

Role of Shiga toxin versus H7 flagellin in enterohaemorrhagic Escherichia coli signalling of human colon epithelium in vivo

Enterohaemorrhagic Escherichia coli O157:H7 (EHEC) is a clinically important foodborne pathogen that colonizes human colon epithelium and induces acute colonic inflammation, but does not invade the epithelial cells. Whereas Shiga toxin (Stx) and bacterial flagellin have been studied for their ability to upregulate the production of proinflammatory chemokines by cultured human colon cancer cell lines, the relevance of studies in colon cancer cell lines to the production of proinflammatory signals by normal epithelial cells in EHEC-infected human colon is not known. We show herein that Stx does not bind to human colon epithelium in vivo. Moreover, globotriaosylceramide (Gb3/CD77) synthase, the enzyme required for synthesis of the Gb3/CD77 receptor for Stx, was not expressed by normal or inflamed human colon epithelium in vivo. In contrast, Toll-like receptor (TLR) 5, the receptor for bacterial flagellin, was expressed by normal human colon epithelium and by colon epithelium in human intestinal xenografts. EHEC H7 flagellin instilled in the lumen of human colon xenografts that contain an intact human epithelium upregulated the expression of epithelial cell proinflammatory chemokines, which was accompanied by a subepithelial influx of neutrophils. Isogenic mutants of EHEC that lacked flagellin did not significantly upregulate prototypic neutrophil and dendritic cell chemoattractants by model human colon epithelia, irrespective of Stx production. We conclude that EHEC H7 flagellin and not Stx is the major EHEC factor that directly upregulates proinflammatory chemokine production by human colon epithelium in vivo.

Intestinal mucosal responses to microbial infection

Infections of the human intestinal tract with foodborne and waterborne pathogens are among the leading causes of morbidity and death in the world. Upon ingestion, such pathogens commonly pass through the stomach in sufficient numbers to establish infection in the small intestine or colon. The subsequent interactions with the host depend critically on the particular pathogen, ranging from mere presence in the intestinal lumen and minimal interaction with the epithelium to highly mucosal invasive with rapid systemic spread. This article addresses the morphological and molecular changes that occur in the intestinal mucosa after infection with a selected yet representative spectrum of enteric pathogens, ranging from luminally restricted but epithelial adherent, epithelial invasive, to mucosally invasive, with a focus on intestinal epithelial responses.

Cathelicidin mediates innate intestinal defense against colonization with epithelial adherent bacterial pathogens

Cathelicidin-related antimicrobial peptide (mCRAMP), the sole murine cathelicidin, is encoded by the gene Cnlp. We show that mCRAMP expression in the intestinal tract is largely restricted to surface epithelial cells in the colon. Synthetic mCRAMP had antimicrobial activity against the murine enteric pathogen Citrobacter rodentium, which like the related clinically important human pathogens enteropathogenic Escherichia coli and enterohemorrhagic E. coli, adheres to the apical membrane of intestinal epithelial cells. Colon epithelial cell extracts from Cnlp+/+ mice had significantly greater antimicrobial activity against C. rodentium than those of mutant Cnlp-/- mice that lack mCRAMP. Cnlp-/- mice developed significantly greater colon surface and crypt epithelial cell colonization, surface epithelial cell damage, and systemic dissemination of infection than Cnlp+/+ mice after oral infection with C. rodentium. Moreover, Cnlp+/+ mice were protected from oral infections with C. rodentium inocula that infected the majority of Cnlp-/- mice. These results establish cathelicidin as an important component of innate antimicrobial defense in the colon.

Nod2 mutation in Crohn's disease potentiates NF-kappaB activity and IL-1beta processing

Variants of NOD2, an intracellular sensor of bacteria-derived muramyl dipeptide (MDP), increase susceptibility to Crohn's disease (CD). These variants are thought to be defective in activation of nuclear factor kappaB (NF-kappaB) and antibacterial defenses, but CD clinical specimens display elevated NF-kappaB activity. To illuminate the pathophysiological function of NOD2, we introduced such a variant to the mouse Nod2 locus. Mutant mice exhibited elevated NF-kappaB activation in response to MDP and more efficient processing and secretion of the cytokine interleukin-1beta (IL-1beta). These effects are linked to increased susceptibility to bacterial-induced intestinal inflammation and identify NOD2 as a positive regulator of NF-kappaB activation and IL-1beta secretion.

Regulated production of the chemokine CCL28 in human colon epithelium

The chemokine CCL28 is constitutively expressed by epithelial cells at several mucosal sites and is thought to function as a homeostatic chemoattractant of subpopulations of T cells and IgA B cells and to mediate antimicrobial activity. We report herein on the regulation of CCL28 in human colon epithelium by the proinflammatory cytokine IL-1, bacterial flagellin, and n-butyrate, a product of microbial metabolism. In vivo, CCL28 was markedly increased in the epithelium of pathologically inflamed compared with normal human colon. Human colon and small intestinal xenografts were used to model human intestinal epithelium in vivo. Xenografts constitutively expressed little, if any, CCL28 mRNA or protein. After stimulation with the proinflammatory cytokine IL-1, CCL28 mRNA and protein were significantly increased in the epithelium of colon but not small intestinal xenografts, although both upregulated the expression of another prototypic chemokine, CXCL8, in response to the identical stimulus. In studies of CCL28 regulation using human colon epithelial cell lines, proinflammatory stimuli, including IL-1, bacterial flagellin, and bacterial infection, significantly upregulated CCL28 mRNA expression and protein production. In addition, CCL28 mRNA expression and protein secretion by those cells were significantly increased by the short-chain fatty acid n-butyrate, and IL-1- or flagellin-stimulated upregulation of CCL28 by colon epithelial cells was synergistically increased by pretreatment of cells with n-butyrate. Consistent with its upregulated expression by proinflammatory stimuli, CCL28 mRNA expression was attenuated by pharmacological inhibitors of NF-kappaB activation. These findings indicate that CCL28 functions as an "inflammatory" chemokine in human colon epithelium and suggest the notion that CCL28 may act to counterregulate colonic inflammation.

Chemokine receptor CCR6 transduces signals that activate p130Cas and alter cAMP-stimulated ion transport in human intestinal epithelial cells

Human colon epithelial cells express the G protein-coupled receptor CCR6, the sole receptor for the chemokine CCL20 (also termed MIP-3alpha). CCL20 produced by intestinal epithelial cells is upregulated in response to proinflammatory stimuli and microbial infection, and it chemoattracts leukocytes, including CCR6-expressing immature myeloid dendritic cells, into sites of inflammation. The aim of this study was to determine whether CCR6 expressed by intestinal epithelial cells acts as a functional receptor for CCL20 and whether stimulation with CCL20 alters intestinal epithelial cell functions. The human colon epithelial cell lines T84, Caco-2, HT-29, and HCA-7 were used to model colonic epithelium. Polarized intestinal epithelial cells constitutively expressed CCR6, predominantly on the apical side. Consistent with this, apical stimulation of polarized intestinal epithelial cells resulted in tyrosine phosphorylation of the p130 Crk-associated substrate (Cas), an adaptor/scaffolding protein that localizes in focal adhesions and has a role in regulating cytoskeletal elements important for cell attachment and migration. In addition, CCL20 stimulation inhibited agonist-stimulated production of the second messenger cAMP and cAMP-mediated chloride secretory responses by intestinal epithelial cells. Inhibition was abrogated by pertussis toxin, consistent with signaling through Galphai proteins that negatively regulate adenylyl cyclases and cAMP production. These data indicate that signaling events, occurring via the activation of the apically expressed chemokine receptor CCR6 on polarized intestinal epithelial cells, alter specialized intestinal epithelial cell functions, including electrogenic ion secretion and possibly epithelial cell adhesion and migration.

IKKbeta links inflammation and tumorigenesis in a mouse model of colitis-associated cancer

A link between inflammation and cancer has long been suspected, but its molecular nature remained ill defined. A key player in inflammation is transcription factor NF-kappaB whose activity is triggered in response to infectious agents and proinflammatory cytokines via the IkappaB kinase (IKK) complex. Using a colitis-associated cancer model, we show that although deletion of IKKbeta in intestinal epithelial cells does not decrease inflammation, it leads to a dramatic decrease in tumor incidence without affecting tumor size. This is linked to increased epithelial apoptosis during tumor promotion. Deleting IKKbeta in myeloid cells, however, results in a significant decrease in tumor size. This deletion diminishes expression of proinflammatory cytokines that may serve as tumor growth factors, without affecting apoptosis. Thus, specific inactivation of the IKK/NF-kappaB pathway in two different cell types can attenuate formation of inflammation-associated tumors. In addition to suppressing apoptosis in advanced tumors, IKKbeta may link inflammation to cancer.

Expression of Epstein-Barr virus-induced gene 3 and other interleukin-12-related molecules by human intestinal epithelium

Antigen-presenting cells, including dendritic cells, monocytes and macrophages, produce members of the interleukin-12 (IL-12) family that are important in initiating and maintaining cell-mediated immune responses. These include IL-12p35 and p19 that dimerize with IL-12p40 to form IL-12 (also termed IL-12p75) and IL-23, respectively, and Epstein-Barr virus-induced gene 3 (EBI3) protein (a protein related to IL-12p40), that forms a dimer with p28, termed IL-27. Intestinal epithelial cells, which are the initial site of contact between the host and enteric pathogens, can act as antigen-presenting cells, and are known to express mediators important in inflammatory and immune responses. In the current studies, we hypothesized that intestinal epithelial cells express members of the IL-12 family, which can function as an early signalling system important in mucosal immunity. Using in vitro and in vivo model systems of human intestinal epithelium, we demonstrate the regulated expression of EBI3, IL-12p35 and p19 by human intestinal epithelial cells. However, intestinal epithelial cells do not coexpress IL-12p40 or p28 that are required to generate heterodimeric IL-12p75, IL-23 and IL-27. To the extent that IL-12p35, p19 and EBI3 cannot form IL-12p75, IL-23 or IL-27 heterodimers in intestinal epithelial cells, these data suggest that those cells may express other, currently unknown, molecules that can associate with EBI3, IL-12p35 and/or p19 or, alternatively, intestinal epithelial cells may release IL-12-related molecules that by themselves, or in combination with other molecules in the mucosal microenvironment, mediate biological activities.

Clearance of Citrobacter rodentium requires B cells but not secretory immunoglobulin A (IgA) or IgM antibodies

Citrobacter rodentium, a murine model pathogen for human enteropathogenic Escherichia coli, predominantly colonizes the lumen and mucosal surface of the colon and cecum and causes crypt hyperplasia and mucosal inflammation. Mice infected with C. rodentium develop a secretory immunoglobulin A (IgA) response, but the role of B cells or secretory antibodies in host defense is unknown. To address this question, we conducted oral C. rodentium infections in mice lacking B cells, IgA, secreted IgM, polymeric Ig receptor (pIgR), or J chain. Normal mice showed peak bacterial numbers in colon and feces at 1 week and bacterial eradication after 3 to 4 weeks. B-cell-deficient mice were equally susceptible initially but could not control infection subsequently. Tissue responses showed marked differences, as infection of normal mice was accompanied by transient crypt hyperplasia and mucosal inflammation in the colon and cecum at 2 but not 6 weeks, whereas B-cell-deficient mice had few mucosal changes at 2 weeks but severe epithelial hyperplasia with ulcerations and mucosal inflammation at 6 weeks. The functions of B cells were not mediated by secretory antibodies, since mice lacking IgA or secreted IgM or proteins required for their transport into the lumen, pIgR or J chain, cleared C. rodentium normally. Nonetheless, systemic administration of immune sera reduced bacterial numbers significantly in normal and pIgR-deficient mice, and depletion of IgG abrogated this effect. These results indicate that host defense against C. rodentium depends on B cells and IgG antibodies but does not require production or transepithelial transport of IgA or secreted IgM.

SDF-1/CXCL12 regulates cAMP production and ion transport in intestinal epithelial cells via CXCR4

Human colonic epithelial cells express CXCR4, the sole cognate receptor for the chemokine stromal cell-derived factor (SDF)-1/CXC chemokine ligand (CXCL) 12. The aim of this study was to define the mechanism and functional consequences of signaling intestinal epithelial cells through the CXCR4 chemokine receptor. CXCR4, but not SDF-1/CXCL12, was constitutively expressed by T84, HT-29, HT-29/-18C1, and Caco-2 human colon epithelial cell lines. Studies using T84 cells showed that CXCR4 was G protein-coupled in intestinal epithelial cells. Moreover, stimulation of T84 cells with SDF-1/CXCL12 inhibited cAMP production in response to the adenylyl cyclase activator forskolin, and this inhibition was abrogated by either anti-CXCR4 antibody or receptor desensitization. Studies with pertussis toxin suggested that SDF-1/CXCL12 activated negative regulation of cAMP production through G(i)alpha subunits coupled to CXCR4. Consistent with the inhibition of forskolin-stimulated cAMP production, SDF-1/CXCL12 also inhibited forskolin-induced ion transport in voltage-clamped polarized T84 cells. Taken together, these data indicate that epithelial CXCR4 can transduce functional signals in human intestinal epithelial cells that modulate important cAMP-mediated cellular functions.

Nod1 is an essential signal transducer in intestinal epithelial cells infected with bacteria that avoid recognition by toll-like receptors

The transcription factor NF-kappaB in human intestinal epithelial cells plays a central role in regulating genes that govern the onset of mucosal inflammatory responses following intestinal microbial infection. Nod1 is a cytosolic pattern recognition receptor in mammalian cells that senses components of microbial peptidoglycans and signals the activation of NF-kappaB. The aim of these studies was to assess the functional importance of Nod1 in activating NF-kappaB and NF-kappaB proinflammatory target genes in human intestinal epithelium. Human colon epithelial cells that constitutively express Nod1 were used as a model intestinal epithelium. These cells do not signal through Toll-like receptor 4 (TLR4) or respond to bacterial lipopolysaccharide, but they express functional TLR5 and interleukin 1 (IL-1) receptors that signal the activation of NF-kappaB in response to bacterial flagellin or IL-1 stimulation. Stable expression of dominant negative (DN) Nod1 in colon epithelial cells prevented IkappaB kinase and NF-kappaB activation in response to infection with enteroinvasive Escherichia coli. In contrast, DN Nod1 did not eliminate IL-1 or flagellin-stimulated NF-kappaB activation. Inhibition of NF-kappaB was accompanied by inhibition of NF-kappaB target genes that provide signals for the mucosal influx of neutrophils during intestinal infection. We conclude that signaling through Nod1 is required for activating NF-kappaB in human intestinal epithelial cells infected with gram-negative enteric bacteria that can bypass TLR activation. Signaling through Nod1 provides the intestinal epithelium with a backup mechanism for rapidly activating innate immunity during infection with a group of highly invasive pathogenic gram-negative bacteria.

IkappaB-kinasebeta-dependent NF-kappaB activation provides radioprotection to the intestinal epithelium

Acute injury to the intestinal mucosa is a major dose-limiting complication of abdominal radiation therapy. We studied the role of the transcription factor NF-kappaB in protection against radiation-induced apoptosis in the intestinal epithelium in vivo. We use mice in which NF-kappaB signaling through IkappaB-kinase (IKK)-beta is selectively ablated in intestinal epithelial cells to show that failure to activate epithelial cell NF-kappaB in vivo results in a significant increase in radiation-induced epithelial cell apoptosis. Furthermore, bacterial lipopolysaccharide, which is normally a radioprotective agent, is radiosensitizing in IKKbeta-deficient intestinal epithelial cells. Increased apoptosis in IKKbeta-deficient intestinal epithelial cells was accompanied by increased expression and activation of the tumor suppressor p53 and decreased expression of antiapoptotic Bcl-2 family proteins. These results demonstrate the physiological importance of the NF-kappaB system in protection against radiation-induced death in the intestinal epithelium in vivo and identify IKKbeta as a key molecular target for radioprotection in the intestine. Selective preactivation of NF-kappaB through IKKbeta in intestinal epithelial cells could provide a therapeutic modality that allows higher doses of radiation to be tolerated during cancer radiotherapy.

Expression of LL-37 by human gastric epithelial cells as a potential host defense mechanism against Helicobacter pylori

BACKGROUND & AIMS

LL-37/human cationic antimicrobial peptide 18 (hCAP18) is a human cathelicidin with broad-spectrum antimicrobial, lipopolysaccharide binding, and chemotactic activities. This study examined the role of LL-37/hCAP18 in gastric innate immune defense by characterizing its constitutive and regulated expression by human gastric mucosa and its bactericidal activity against the gastric pathogen Helicobacter pylori.

METHODS

LL-37/hCAP18 messenger RNA expression in normal and H. pylori -infected gastric mucosa and gastric epithelial cells was determined by in situ hybridization, real-time polymerase chain reaction, immunostaining, and immunoblot analysis. Bactericidal activity was measured by using a colony-forming unit assay.

RESULTS

LL-37/hCAP18 messenger RNA and protein were expressed in a distinct distribution by surface epithelial cells as well as chief and parietal cells in the fundic glands of normal gastric mucosa. LL-37/hCAP18 was significantly increased in the epithelium and gastric secretions of H. pylori -infected patients, but not in individuals with non-H. pylori -induced gastric inflammation. Infection of cultured gastric epithelial cells with a wild-type but not an isogenic Delta cagE mutant strain of H. pylori increased LL-37/hCAP18 expression, indicating that H. pylori -induced regulation of LL-37/hCAP18 production required an intact type IV secretion system. LL-37, the C-terminal peptide of LL-37/hCAP18, alone or in synergy with human beta-defensin 1, was bactericidal for several H. pylori strains.

CONCLUSIONS

These data indicate that H. pylori up-regulates production of LL-37/hCAP18 by gastric epithelium and suggest this cathelicidin contributes to determining the balance between host mucosal defense and H. pylori survival mechanisms that govern chronic infection with this gastric pathogen.

Nuclear factor-kappa B activation promotes restitution of wounded intestinal epithelial monolayers

Epithelial restitution, the movement of wound-edge cells into an area of epithelial cell denudation, is an important early step in the ulcer healing process. Growth factors regulate epithelial restitution, yet little is known about the transcriptional pathways that mediate their effects on cell migration. The transcription factor nuclear factor (NF)-kappaB is a master regulator of the host inflammatory response that is activated in the epithelium in intestinal inflammation, which often accompanies epithelial injury. We hypothesized that NF-kappaB may be an important transcriptional regulator of epithelial restitution. In an in vitro model of scrape-wounded monolayers of nontransformed rat intestinal epithelial (RIE-1) cells, NF-kappaB was activated in epithelial cells at the wound edge. Blocking of NF-kappaB activation by either pharmacological or genetic approaches inhibited intestinal epithelial restitution. Moreover, scrape wounding activated the epidermal growth factor receptor (EGFR) in cells at the wound edge, and, importantly, inhibiting EGFR tyrosine kinase activity decreased scrape wound-induced NF-kappaB activation and cell migration. These results indicate a novel role of NF-kappaB activation in a signaling pathway important for restitution and healing of intestinal epithelia. To the extent NF-kappaB may have parallel functions in vivo, they also suggest a need for caution in the proposed use of NF-kappaB inhibitors for the treatment of conditions associated with inflammation and injury of intestinal and other mucosal surfaces.

The two faces of IKK and NF-kappaB inhibition: prevention of systemic inflammation but increased local injury following intestinal ischemia-reperfusion

We studied the role of NF-kappaB in acute inflammation caused by gut ischemia-reperfusion through selective ablation of IkappaB kinase (IKK)-beta, the catalytic subunit of IKK that is essential for NF-kappaB activation. Ablation of IKK-beta in enterocytes prevented the systemic inflammatory response, which culminates in multiple organ dysfunction syndrome (MODS) that is normally triggered by gut ischemia-reperfusion. IKK-beta removal from enterocytes, however, also resulted in severe apoptotic damage to the reperfused intestinal mucosa. These results show the dual function of the NF-kappaB system, which is responsible for both tissue protection and systemic inflammation, and underscore the caution that should be exerted in using NF-kappaB and IKK inhibitors.

Genes in the Salmonella pathogenicity island 2 and the Salmonella virulence plasmid are essential for Salmonella-induced apoptosis in intestinal epithelial cells

Intestinal epithelial cells are an important site of the host's interaction with enteroinvasive bacteria. Genes in the chromosomally encoded Salmonella pathogenicity island 2 (SPI 2) that encodes a type III secretion system and genes on the virulence plasmid pSDL2 of Salmonella enteritica serovar Dublin (spv genes) are thought to be important for Salmonella dublin survival in host cells. We hypothesized that genes in those loci may be important also for prolonged Salmonella growth and the induction of apoptosis induced by Salmonella in human intestinal epithelial cells. HT-29 human intestinal epithelial cells were infected with wild-type S. dublin or isogenic mutants deficient in the expression of spv genes or with SPI 2 locus mutations. Neither the spv nor the SPI 2 mutations affected bacterial entry into epithelial cells or intracellular proliferation of Salmonella during the initial 8 h after infection. However, at later periods, bacteria with mutations in the SPI 2 locus or in the spv locus compared to wild-type bacteria, manifested a marked decrease in intracellular proliferation and a different distribution pattern of bacteria within infected cells. Epithelial cell apoptosis was markedly increased in response to infection with wild-type, but not the mutant Salmonella. However, apoptosis of epithelial cells infected with wild-type S. dublin was delayed for approximately 28 h after bacterial entry. Apoptosis was preceded by caspase 3 activation, which was also delayed for approximately 24 h after infection. Despite its late onset, the cellular commitment to apoptosis was determined in the early period after infection as inhibition of bacterial protein synthesis during the first 6 h after epithelial cell infection with wild-type S. dublin, but not at later times, inhibited the induction of apoptosis. These studies indicate that genes in the SPI 2 and the spv loci are crucial for prolonged bacterial growth in intestinal epithelial cells. In addition to their influence on intracellular proliferation of Salmonella, genes in those loci determine the ultimate fate of infected epithelial cells with respect to caspase 3 activation and undergoing death by apoptosis.

Role of EHEC O157:H7 virulence factors in the activation of intestinal epithelial cell NF-kappaB and MAP kinase pathways and the upregulated expression of interleukin 8

Enterohaemorrhagic Escherichia coli O157:H7 (EHEC) is a gastrointestinal pathogen that is generally non-invasive for intestinal epithelial cells, yet causes acute intestinal inflammation, diarrhoea, haemorrhagic colitis and haemolytic uraemic syndrome. To study signal transduction pathways activated in human intestinal epithelial cells by EHEC, we took advantage of EHEC O157:H7 and isogenic mutants deficient in the major EHEC virulence factors, intimin (eae-) and Shiga toxin (stx-). Infection with wild-type EHEC activated p38 and ERK MAP kinases and the nuclear translocation of the transcription factor NF-kappaB. Downstream, this was accompanied by increased expression of mRNA and protein for the neutrophil chemoattractant IL-8. Isogenic eae- and stx- mutants also activated p38 and ERK MAP kinases, and NF-kappaB and stimulated increases in IL-8 protein secretion similar to those of wild-type EHEC. Further, inhibition of either p38, ERK or NF-kappaB activation abrogated the IL-8 response induced by wild-type EHEC and the mutants. Epithelial cell MAP kinase and NF-kappaB pathways leading to IL-8 secretion were also activated by isolated EHEC H7 flagellin, which was active when added to either the apical or basolateral surface of polarized human intestinal epithelial cells. We conclude that EHEC interacting with intestinal epithelial cells activates intracellular signalling pathways and an epithelial cell proinflammatory response independent of either Shiga toxin or intimin, two of the major known virulence factors of EHEC. The activation of proinflammatory signals in human colon epithelial cells in response to this non-invasive pathogen appears to depend to a significant extent on H7 flagellin.

Role of the intestinal epithelium in orchestrating innate and adaptive mucosal immunity

The mucosa that lines the human colon and small intestine is a site of chronic regulated "physiologic" inflammation. This contrasts markedly with other mucosal sites in that if the numbers of T and B cells, eosinophils, mast cells, macrophages, and dendritic cells that are present in the human intestinal tract were to be present in other sites, those sites would be considered to be sites of chronic pathological inflammation. This review examines the role of the intestinal epithelium in the development of "physiologic" intestinal mucosal inflammation and focuses on its role in signalling and mediating host innate and adaptive mucosal immune responses.

Ubiquitous production of macrophage migration inhibitory factor by human gastric and intestinal epithelium

BACKGROUND & AIMS

Macrophage migration inhibitory factor (MIF) inhibits macrophage migration and has pleiotropic activities on immune and inflammatory responses, cell growth, and glucose metabolism. MIF is produced by T cells, macrophages, and endothelial cells. Because intestinal epithelial cells produce mediators important for regulating mucosal immune and inflammatory responses, we sought to determine if these cells produce MIF.

METHODS

MIF expression was determined by immunostaining of human intestinal mucosa, intestinal xenografts, and cultured cells. MIF protein levels were quantitated by enzyme-linked immunosorbent assay and immunoblot analysis, messenger RNA was assessed by real-time reverse-transcription polymerase chain reaction, and functional activity was assessed by enzymatic and migration assays.

RESULTS

MIF was abundantly expressed in vivo in gastric, small intestinal, and colonic epithelium and in epithelium lining human intestinal xenografts. MIF was also constitutively expressed at the messenger RNA and protein level by several cultured colon and gastric epithelial cell lines, and its expression in those cells was not up-regulated by the proinflammatory cytokines interleukin 1alpha, tumor necrosis factor alpha, or interferon gamma. Epithelial MIF from cultured cells was released predominantly from the apical side after Salmonella infection, had tautomerase activity, and arrested macrophage migration.

CONCLUSIONS

Human intestinal epithelial cells are a major source of MIF, a molecule that can regulate macrophage migration, inflammation, and cell metabolism.

Cell differentiation is a key determinant of cathelicidin LL-37/human cationic antimicrobial protein 18 expression by human colon epithelium

Antimicrobial peptides are highly conserved evolutionarily and are thought to play an important role in innate immunity at intestinal mucosal surfaces. To better understand the role of the antimicrobial peptide human cathelicidin LL-37/human cationic antimicrobial protein 18 (hCAP18) in intestinal mucosal defense, we characterized the regulated expression and production of this peptide by human intestinal epithelium. LL-37/hCAP18 is shown to be expressed within epithelial cells located at the surface and upper crypts of normal human colon. Little or no expression was seen within the deeper colon crypts or within epithelial cells of the small intestine. Paralleling its expression in more differentiated epithelial cells in vivo, LL-37/hCAP18 mRNA and protein expression was upregulated in spontaneously differentiating Caco-2 human colon epithelial cells and in HCA-7 human colon epithelial cells treated with the cell differentiation-inducing agent sodium butyrate. LL-37/hCAP18 expression by colon epithelium does not require commensal bacteria, since LL-37/hCAP18 is produced with a similar expression pattern by epithelial cells in human colon xenografts that lack a luminal microflora. LL-37/hCAP18 mRNA was not upregulated in response to tumor necrosis factor alpha, interleukin 1alpha (IL-1alpha), gamma interferon, lipopolysaccharide, or IL-6, nor did the expression patterns and levels of LL-37/hCAP18 in the epithelium of the normal and inflamed colon differ. On the other hand, infection of HCA-7 cells with Salmonella enterica serovar Dublin or enteroinvasive Escherichia coli modestly upregulated LL-37/hCAP18 mRNA expression. We conclude that differentiated human colon epithelium expresses LL-37/hCAP18 as part of its repertoire of innate defense molecules and that the distribution and regulated expression of LL-37/hCAP18 in the colon differs markedly from that of other enteric antimicrobial peptides, such as defensins.

Central importance of immunoglobulin A in host defense against Giardia spp

The protozoan pathogen Giardia is an important cause of parasitic diarrheal disease worldwide. It colonizes the lumen of the small intestine, suggesting that effective host defenses must act luminally. Immunoglobulin A (IgA) antibodies are presumed to be important for controlling Giardia infection, but direct evidence for this function is lacking. B-cell-independent effector mechanisms also exist and may be equally important for antigiardial host defense. To determine the importance of the immunoglobulin isotypes that are transported into the intestinal lumen, IgA and IgM, for antigiardial host defense, we infected gene-targeted mice lacking IgA-expressing B-cells, IgM-secreting B-cells, or all B-cells as controls with Giardia muris or Giardia lamblia GS/M-83-H7. We found that IgA-deficient mice could not eradicate either G. muris or G. lamblia infection, demonstrating that IgA is required for their clearance. Furthermore, although neither B-cell-deficient nor IgA-deficient mice could clear G. muris infections, IgA-deficient mice controlled infection significantly better than B-cell-deficient mice, suggesting the existence of B-cell-dependent but IgA-independent antigiardial defenses. In contrast, mice deficient for secreted IgM antibodies cleared G. muris infection normally, indicating that they have no unique functions in antigiardial host defense. These data, together with the finding that B-cell-deficient mice have some, albeit limited, residual capacity to control G. muris infection, show that IgA-dependent host defenses are central for eradicating Giardia spp. Moreover, B-cell-dependent but IgA-independent and B-cell-independent antigiardial host defenses exist but are less important for controlling infection.

Cytokines in host defense against Salmonella

Cytokines are key communication molecules between host cells in the defense against the enteric pathogen, Salmonella. Infection with Salmonella induces expression of multiple chemokines and proinflammatory cytokines in cultured intestinal epithelial cells and macrophages. In animal models, protective roles have been shown for IL-1alpha, TNFalpha, IFN-gamma, IL-12, IL-18 and IL-15, whereas IL-4 and IL-10 inhibit host defenses against Salmonella.

Production of MDC/CCL22 by human intestinal epithelial cells

The intestinal mucosa contains a subset of lymphocytes that produce Th2 cytokines, yet the signals responsible for the recruitment of these cells are poorly understood. Macrophage-derived chemokine (MDC/CCL22) is a recently described CC chemokine known to chemoattract the Th2 cytokine producing cells that express the receptor CCR4. The studies herein demonstrate the constitutive production of MDC/CCL22 in vivo by human colon epithelium and by epithelium of human intestinal xenografts. MDC/CCL22 mRNA expression and protein secretion was upregulated in colon epithelial cell lines in response to proinflammatory cytokines or infection with enteroinvasive bacteria. Inhibition of nuclear factor (NF)-kappaB activation abolished MDC/CCL22 expression in response to proinflammatory stimuli, demonstrating that MDC/CCL22 is a NF-kappaB target gene. In addition, tumor necrosis factor-alpha-induced MDC/CCL22 secretion was differentially modulated by Th1 and Th2 cytokines. Supernatants from the basal, but not apical, side of polarized epithelial cells induced a MDC/CCL22-dependent chemotaxis of CCR4-positive T cells. These studies demonstrate the constitutive and regulated production by intestinal epithelial cells of a chemokine known to function in the trafficking of T cells that produce anti-inflammatory cytokines.

Analysis of host responses to microbial infection using gene expression profiling

Gene expression profiling offers new opportunities for understanding host-cell responses to microbial pathogens and their products. Current strategies involve either first identifying mRNAs that differ in their expression status under different experimental conditions and later defining the identity of the respective genes (for example, differential display or serial analysis of gene expression), or alternatively assessing changes in the expression of already defined genes (for example, cDNA or oligonucleotide microarrays). Early studies indicate the power of gene expression profiling for providing new insights into groups of genes whose expression is altered during the course of host-microbe interactions, and for the discovery of cellular genes that were not previously recognized to be regulated by infection.

Regulated MIP-3alpha/CCL20 production by human intestinal epithelium: mechanism for modulating mucosal immunity

Human intestinal epithelial cells secrete an array of chemokines known to signal the trafficking of neutrophils and monocytes important in innate mucosal immunity. We hypothesized that intestinal epithelium may also have the capacity to play a role in signaling host adaptive immunity. The CC chemokine macrophage inflammatory protein (MIP)-3alpha/CCL20 is chemotactic for immature dendritic cells and CD45RO(+) T cells that are important components of the host adaptive immune system. In these studies, we demonstrate the widespread production and regulated expression of MIP-3alpha by human intestinal epithelium. Several intestinal epithelial cell lines were shown to constitutively express MIP-3alpha mRNA. Moreover, MIP-3alpha mRNA expression and protein production were upregulated by stimulation of intestinal epithelial cells with the proinflammatory cytokines tumor necrosis factor-alpha or interleukin-1alpha or in response to infection with the enteric bacterial pathogens Salmonella or enteroinvasive Escherichia coli. In addition, MIP-3alpha was shown to function as a nuclear factor-kappaB target gene. In vitro findings were paralleled in vivo by increased expression of MIP-3alpha in the epithelium of cytokine-stimulated or bacteria-infected human intestinal xenografts and in the epithelium of inflamed human colon. Mucosal T cells, other mucosal mononuclear cells, and intestinal epithelial cells expressed CCR6, the cognate receptor for MIP-3alpha. The constitutive and regulated expression of MIP-3alpha by human intestinal epithelium is consistent with a role for epithelial cell-produced MIP-3alpha in modulating mucosal adaptive immune responses.

Regulated production of the T helper 2-type T-cell chemoattractant TARC by human bronchial epithelial cells in vitro and in human lung xenografts

The chemokine TARC is a ligand for the chemokine receptor CCR4 expressed on T helper (Th)2-type CD4 T cells. Allergic airway inflammation is characterized by a local increase in cells secreting Th2-type cytokines. We hypothesized that bronchial epithelial cells may be a source of chemokines known to chemoattract Th2 cells. Regulated TARC expression was studied using normal human bronchial epithelial cells and a human lung xenograft model. TARC expression was increased in normal human bronchial epithelial cells in response to tumor necrosis factor-alpha stimulation, and further upregulation of TARC was observed with interferon (IFN)-gamma but not interleukin (IL)-4 costimulation. TARC functions as a nuclear factor (NF)-kappa B target gene, as shown by the abrogation of TARC expression in response to proinflammatory stimuli when NF-kappa B activation is inhibited. In an in vivo model, minimal constitutive TARC expression was observed in human lung xenografts. Consistent with our findings in vitro, TARC messenger RNA (mRNA) expression was upregulated in the xenografts in response to IL-1, and costimulation with IFN-gamma but not IL-4 further increased TARC mRNA and protein expression. In addition, bronchoalveolar lavage fluid from asthmatic subjects after allergen challenge contained significantly increased levels of TARC, suggesting that TARC production by bronchial epithelial cells may play a role in the pathogenesis of allergic asthma.