Stimulation of lamina propria lymphocytes by intestinal epithelial cells: evidence for recognition of nonclassical restriction elements

Bovine Endometrial Epithelial Cells Scale Their Pro-inflammatory Response In vitro to Pathogenic Trueperella pyogenes Isolated from the Bovine Uterus in a Strain-Specific Manner

Among different bacteria colonizing the bovine uterus, Trueperella pyogenes is found to be associated with clinical endometritis (CE). The ability of cows to defend against T. pyogenes infections depends on the virulence of invading bacteria and on the host's innate immunity. Therefore, to gain insights into bacterial factors contributing to the interplay of this host pathogen, two strains of T. pyogenes were included in this study: one strain (TP2) was isolated from the uterus of a postpartum dairy cow developing CE and a second strain (TP5) was isolated from a uterus of a healthy cow. The two strains were compared in terms of their metabolic fingerprints, growth rate, virulence gene transcription, and effect on bovine endometrial epithelial cells in vitro. In addition, the effect of the presence of peripheral blood mononuclear cells (PBMCs) on the response of endometrial epithelial cells was evaluated. TP2, the strain isolated from the diseased cow, showed a higher growth rate, expressed more virulence factors (cbpA, nanH, fimE, and fimG), and elicited a higher mRNA expression of pro-inflammatory factors (PTGS2, CXCL3, and IL8) in bovine endometrial epithelial cells compared with TP5, the strain isolated from the healthy cow. The presence of PBMCs amplified the mRNA expression of pro-inflammatory factors (PTGS2, CXCL3, IL1A, IL6, and IL8) in bovine endometrial epithelial cells co-cultured with live TP2 compared with untreated cells, especially as early as after 4 h. In conclusion, particular strain characteristics of T. pyogenes were found to be important for the development of CE. Furthermore, immune cells attracted to the site of infection might also play an important role in up-regulation of the pro-inflammatory response in the bovine uterus and thus significantly contribute to the host-pathogen interaction.

Loss of T-cell protein tyrosine phosphatase in the intestinal epithelium promotes local inflammation by increasing colonic stem cell proliferation

T-cell protein tyrosine phosphatase (TC-PTP) has a critical role in the development of the immune system and has been identified as a negative regulator of inflammation. Single-nucleotide polymorphisms in the TC-PTP locus have been associated with increased susceptibility to inflammatory bowel diseases (IBDs) in patients. To further understand how TC-PTP is related to IBDs, we investigated the role of TC-PTP in maintaining the intestinal epithelial barrier using an in vivo genetic approach. Intestinal epithelial cell (IEC)-specific deletion of TC-PTP was achieved in a mouse model at steady state and in the context of dextran sulphate sodium (DSS)-induced colitis. Knockout (KO) of TC-PTP in IECs did not result in an altered intestinal barrier. However, upon DSS treatment, IEC-specific TC-PTP KO mice displayed a more severe colitis phenotype with a corresponding increase in the immune response and inflammatory cytokine profile. The absence of TC-PTP caused an altered turnover of IECs, which is further explained by the role of the tyrosine phosphatase in colonic stem cell (CoSC) proliferation. Our results suggest a novel role for TC-PTP in regulating the homeostasis of CoSC proliferation. This supports the protective function of TC-PTP against IBDs, independently of its previously demonstrated role in intestinal immunity.

Intestinal epithelial cells modulate CD4 T cell responses via the thymus leukemia antigen

The intestinal epithelium is comprised of a monolayer of intestinal epithelial cells (IEC), which provide, among other functions, a physical barrier between the high Ag content of the intestinal lumen and the sterile environment beyond the epithelium. IEC express a nonclassical MHC class I molecule known as the thymus leukemia (TL) Ag. TL is known to interact with CD8αα-expressing cells, which are abundant in the intestinal intraepithelial lymphocyte compartment. In this report, we provide evidence indicating that expression of TL by IEC modulates the cytokine profile of CD4(+) T cells favoring IL-17 production. We show in an adoptive transfer model of colitis that donor-derived cells become more pathogenic when TL is expressed on IEC in recipient animals. Moreover, TL(+)IEC promote development of IL-17-mediated responses capable of protecting mice from Citrobacter rodentium infection. We also show that modulation of IL-17-mediated responses by TL(+)IEC is controlled by the expression of CD8α on CD4(+) T cells. Overall, our results provide evidence for an important interaction between IEC and CD4(+) T cells via TL, which modulates mucosal immune responses.

Variants in ZNF365 isoform D are associated with Crohn's disease

OBJECTIVE

Genome-wide association studies have identified multiple Crohn's disease (CD) susceptibility loci, including association with non-coding intergenic single-nucleotide polymorphisms (SNPs) at 10q21.

DESIGN

To fine-map the 10q21 locus, the authors genotyped 86 SNPs in 1632 CD cases and 961 controls and performed single-marker and conditional analyses using logistic regression.

RESULTS

Association with CD risk spanning 11 SNPs (p<0.001) was observed. The most significant association observed was at the non-synonymous SNP, rs7076156 (Ala62Thr), in ZNF365. The alanine allele was over-represented in CD (p=5.23×10⁻⁷; OR=1.39 (95% CI 1.22 to 1.58)); allele frequency of 76% in CD and 69.7% in controls). Conditional analysis on rs7076156 nullified all other significant associations, suggesting that this is the causative variant at this locus. Four isoforms of ZNF365 have previously been identified, and rs7076156 is located in an exon unique to ZNF365 isoform D. The authors demonstrated, using reverse transcription-PCR, expression of ZNF365D in intestinal resections from both CD subjects and controls. Markedly reduced mean expression levels of ZNF365D were identified in Epstein-Barr virus-transformed lymphoblastoid cell lines from CD subjects homozygous for the risk allele (Ala). A whole-genome microarray expression study further suggested that the Ala62Thr change in ZNF365 isoform D is related to differential expression of the genes ARL4A, MKKS, RRAGD, SUMF2, TDR1 and ZNF148 in CD.

CONCLUSIONS

Collectively, these data support the hypothesis that the non-synonymous Ala62Thr SNP, rs7076156, underlies the association between 10q21 and CD risk and suggest that this SNP acts by altering expression of genes under the control of ZNF365 isoform D.

Function of the intestinal epithelium and its dysregulation in inflammatory bowel disease

The intestinal epithelium not only acts as a physical barrier to commensal bacteria and foreign antigens but is also actively involved in antigen processing and immune cell regulation. The inflammatory bowel diseases (IBDs) are characterized by inflammation at this mucosal surface with well-recognized defects in barrier and secretory function. In addition to this, defects in intraepithelial lymphocytes, chemokine receptors, and pattern recognition receptors promote an abnormal immune response, with increased differentiation of proinflammatory cells and a dysregulated relationship with professional antigen-presenting cells. This review focuses on recent developments in the structure of the epithelium, including a detailed account of the apical junctional complex in addition to the role of the enterocyte in antigen recognition, uptake, processing, and presentation. Recently described cytokines such as interleukin-22 and interleukin-31 are highlighted as is the dysregulation of chemokines and secretory IgA in IBD. Finally, the effect of the intestinal epithelial cell on T effector cell proliferation and differentiation are examined in the context of IBD with particular focus on T regulatory cells and the two-way interaction between the intestinal epithelial cell and certain immune cell populations.

CD74 is a survival receptor on colon epithelial cells

AIM: To investigate the expression and function of CD74 in normal murine colon epithelial cells (CEC) and colon carcinoma cells.

METHODS: Expression of CD74 mRNA and protein were measured by reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and fluorescence-activated cell sorter (FACS). The effect of migration inhibitory factor (MIF) on the survival of normal CEC from C57BL/6, NOD/SCID, and CD74 deficient mice both in vitro and in vivo, and on the CT26 carcinoma cell line was analyzed by (quantitative) qRT-PCR, RT-PCR, Western blotting and FACS.

RESULTS: CD74 was found to be expressed on normal CEC. Stimulation of CD74 by MIF induced a signaling cascade leading to up-regulation of Bcl-2 expression, resulting in a significant increased survival of CEC. CD74 was also expressed on the CT26 colon carcinoma cell line and its stimulation by MIF resulted in enhanced cell survival, up-regulation of Akt phosphorylation and Bcl-2 expression.

CONCLUSION: CD74 is expressed on CEC and colon carcinoma cells and serves as a survival receptor in these cells. These results may have implications on colorectal cancer research.

Membrane markers of the immune cells in swine: an update

Besides their breeding value, swine are increasingly used as biomedical models. As reported in three international swine clusters of differentiation (CD) workshops and in the animal homologue section of the last workshop for the determination of human leukocyte differentiation antigens (HLDA 8), characterisation of leukocyte surface antigens by monoclonal antibodies and other molecular studies have determined the cell lineages and blood leukocyte subsets implicated in the immune response, including cell adhesion molecules involved in cell trafficking. This review focusses on the current state of knowledge of porcine leukocyte differentiation and major histocompatibility complex (SLA) molecules. Examples of porcine particularities such as the double-positive T lymphocytes with the phenotype CD(4+)CD8(low) and CD(4-)CD8(low) alphabeta T cell subsets and the persistence of SLA class II after T-lymphocyte activation are illustrated, as well as the shared characteristics of the Artiodactyla group, such as the high proportion of gammadelta TcR (T cell receptor) T cells in blood and other lymphoid tissues. Furthermore, discrepancies between swine and humans, such as CD16 expression on dendritic cells and CD11b (wCD11R1) tissue distribution are outlined. The rapidly growing information should facilitate manipulation of the swine immune system towards improving disease control, and open new avenues for biomedical research using the pig as a model.

MIP-3alpha neutralizing monoclonal antibody protects against TNBS-induced colonic injury and inflammation in mice

A characteristic feature of human inflammatory bowel disease, particularly Crohn's disease, is the presence of activated CD4(+) T cells. Recently, we have shown that colonic epithelial cell production of macrophage inflammatory protein (MIP)-3alpha, a CD4 T cell-directed chemokine, is elevated in inflammatory bowel disease. However, the functional relevance of MIP-3alpha production during intestinal inflammation is poorly understood. The aim of this study was to determine whether MIP-3alpha production is increased during murine 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis and to examine the effect of anti-MIP-3alpha neutralizing monoclonal antibody administration in this model. We found that the administration of TNBS significantly increased colonic MIP-3alpha protein levels in Balb/c mice. Consistent with this, a marked increase in the number of CCR6-bearing lamina propria CD4(+) and CD8(+) T cells was also observed in TNBS-treated animals. Treatment of mice with an anti-MIP-3alpha neutralizing monoclonal antibody significantly reduced TNBS-mediated increases in colonic weight-to-length ratio, mucosal ulceration, histological damage, and myeloperoxidase activity. TNBS-mediated increases in the number of CCR6-bearing lamina propria T cells were also substantially reduced by anti-MIP-3alpha neutralizing monoclonal antibody treatment. Taken together, our findings indicate that blockade of MIP-3alpha bioactivity can significantly reduce TNBS-mediated colonic injury and T cell recruitment, suggesting a role for this chemokine in the pathophysiology of intestinal inflammation.

Mechanisms of type I food allergy

The gastrointestinal tract represents the biggest immune organ of the human body and has 3 distinct functions: (1) barrier and defense against potential pathogens, (2) ignorance or tolerance of innocuous agents, and (3) digestion and nutritional uptake of alimentary compounds. Recent studies have indicated that especially structural features of dietary proteins seem to be a precondition for the induction of immediate type immune responses. Crystallographic studies of allergen molecules have been fundamental for epitope studies in a 3-dimensional format using peptides or mimotopes. The identified IgE epitopes were all conformational and responsible for high-affinity interactions with specific IgE. Moreover, numerous studies have indicated that allergens, among them food allergens, preferentially form di-, tri-, or multimers, thus leading to a repetitive display of epitopes. As B-lymphocytes are pattern recognizers, this feature is essential for a memory response, but may also be critical for the very first allergen contact and initiation of the IgE response. Here we review the key candidate cells in the gut, which are capable of recognizing conformation and molecular patterns, but may also be involved in skewing the immune response towards Th2. Animal models have been basic for understanding the molecular principles of food allergy and they will be increasingly indispensable for the definition of novel vaccination strategies. Therefore, the available models are critically analyzed in this review.

Polarized uterine epithelial cells preferentially present antigen at the basolateral surface: role of stromal cells in regulating class II-mediated epithelial cell antigen presentation

To study Ag presentation in the female reproductive tract, DO11.10 TCR transgenic mice specific for the class II MHC-restricted OVA(323-339) peptide and non-transgenic BALB/c mice were used. We report here that freshly isolated uterine epithelial cells, uterine stromal, and vaginal APCs present OVA and OVA(323-339) peptide to naive- and memory T cells, which is reduced when cells are incubated with Abs to CD80 and 86. To determine whether polarized primary epithelial cells present Ags, uterine epithelial cells were cultured on cell inserts in either the upright or inverted position. After reaching confluence, as indicated by high transepithelial resistance (>2000 ohms/well), Ag presentation by epithelial cells incubated with memory T cells and OVA(323-339) peptide placed on the basolateral surface (inverted) was 2- to 3-fold greater than that seen with epithelial cells in contact with T cells and peptide on the apical surface (upright). In contrast, whereas freshly isolated epithelial cells process OVA, polarized epithelial cells did not. When epithelial cells grown upright on inserts were incubated with T cells and OVA(323-339) peptide, coculture with either hepatocyte growth factor or conditioned stromal medium increased epithelial cell Ag presentation (approximately 90% higher than controls). These studies indicate that uterine stromal cells produce a soluble factor(s) in addition to a hepatocyte growth factor, which regulates epithelial cell Ag presentation. Overall, these results demonstrate that polarized epithelial cells are able to present Ags and suggest that uterine stromal cells communicate with epithelial cells via a soluble factor(s) to regulate Ag presentation in the uterus.

Defects in CD8+ regulatory T cells in the lamina propria of patients with inflammatory bowel disease

Mucosal tolerance is believed to be partly mediated by regulatory T cells. Intestinal epithelial cells (IECs) may play an important role in the generation of such regulatory cells, because they are able to process and present Ag to T cells. Furthermore, we have previously demonstrated that IECs are able to generate regulatory CD8(+) T cells in vitro. In the present study, we have analyzed lamina propria (LP) lymphocytes for the presence of such regulatory CD8(+) T cells in normal individuals as well as in patients with inflammatory bowel disease (IBD). The results of the present study show that LP CD8(+) T cells derived from normal controls possess regulatory activity, whereas both unfractionated LP lymphocytes and purified LP CD4(+) T cells do not. The LP CD8(+) T cells suppress Ig production by pokeweed mitogen-stimulated PBMCs by 31-80%, in a cell contact-dependent manner. No significant difference in suppression between CD28(+) and CD28(-)CD8(+) LP T cells was observed. In contrast to CD8(+) T cells from normal LP, CD8(+) T cells isolated from LP of IBD patients, did not suppress Ig production by pokeweed mitogen-stimulated PBMC (five of six ulcerative colitis specimens; six of six Crohn's disease specimens). Furthermore, we demonstrate that the frequency of TCR Vbeta5.1-positive CD8(+) T cells, which we previously have demonstrated to be regulatory and to be expanded by IECs in vitro, is decreased in IBD LP compared with normal LP. In conclusion, this study demonstrates that CD8(+) T cells with regulatory activity are present in the LP of normal healthy individuals, but not in patients with IBD, suggesting that these cells might play an active role in mucosal tolerance.

Modulation of Cytokine Release by Differentiated CACO-2 Cells in a Compartmentalized Coculture Model with Mononuclear Leucocytes and Nonpathogenic Bacteria

To further investigate the interaction between human mononuclear leucocytes [peripheral blood mononuclear cells (PBMC)] and enterocytes, the effect of a confluent layer of differentiated CACO-2 cells on cytokine kinetics during challenge with bacteria in a compartmentalized coculture model was investigated. Nonpathogenic Escherichia coli were added either to the apical or the basolateral compartment of this transwell cell culture system, the latter of which contained human leucocytes. The synthesis of tumour necrosis factor (TNF-alpha) and interleukin (IL)-12 was significantly suppressed by CACO-2 cells when leucocytes were stimulated directly with bacteria. This suppression was not paralleled by changes in the production of IL-10, IL-6 and transforming growth factor (TGF)-beta. When the bacteria were applied apically to the CACO-2 cell layer, the production of TNF-alpha, IL-12, IL-1beta, IL-8, IL-6, IL-10, TGF-beta and interferon-gamma was pronouncedly lower as compared to the bacterial stimulation of leucocytes beneath the CACO-2 cells. In the latter experiments, IL-6, IL-8 and TNF-alpha were the cytokines being mostly induced by apical addition of E. coli. Quantitative mRNA expression analysis revealed that IL-8 gene expression was equally induced in both CACO-2 and PBMC after apical stimulation with bacteria. Of note, bacteria-stimulated CACO-2 cells produced little or no cytokines in the absence of leucocytes, supporting the concept of leucocyte-epithelial cell cross-talk in modulating cytokine responses in the gut mucosa.

Expansion of CD8+ T cells with regulatory function after interaction with intestinal epithelial cells

BACKGROUND & AIMS

Regulatory T cells play a role in the control of immune responses in the intestinal mucosa and their absence may predispose to inflammatory bowel disease (IBD). We have previously shown that T cells activated by intestinal epithelial cells (IECs) are suppressive in function. Our goal was to characterize the phenotype and function of T cells proliferating after interaction with IECs.

METHODS

Irradiated human IECs, isolated from normal resection specimens, were cultured with carboxy fluorescein succinimidyl ester (CFSE) labeled T cells. Flow cytometric analysis of T cells was performed at days 5-10. CD8+ T cells proliferating in culture with IECs were sorted and added to suppressive assays.

RESULTS

The precursor frequency of T cells proliferating in response to IECs ranged from 0.3%-0.9%. Several subpopulations were shown to proliferate (CD8+CD28-/CD8+CD28+/CD4+CD25+), but one population (CD8+CD28-CD101+CD103+) appeared to be dependent on contact with the CD8 ligand gp180. After sorting, culture in the presence of interleukin (IL)-7 and IL-15 allowed for the generation of cell lines. IEC-activated CD8+ T cells, but not nonactivated CD8+ T cells, were suppressive in function. Suppression belonged to the CD101+CD103+ subset of IEC-activated CD8+ T cells and appeared to require cell contact. CD8+ lamina propria T cells also showed suppressive function, suggesting the presence of CD8+ regulatory T cells in the mucosa.

CONCLUSIONS

IECs are able to induce the proliferation of a small fraction of CD8+ peripheral T cells. The CD8+CD28- subset of IEC-activated CD8+ T cells, which express CD101 and CD103, interacts with IECs through gp180 and has regulatory function.

IKK beta and phosphatidylinositol 3-kinase/Akt participate in non-pathogenic Gram-negative enteric bacteria-induced RelA phosphorylation and NF-kappa B activation in both primary and intestinal epithelial cell lines

Pathogenic and enteroinvasive bacteria have been shown to trigger the I kappa B/NF-kappa B transcriptional system and proinflammatory gene expression in epithelial cells. In this study, we investigated the molecular mechanism of the commensal Gram-negative Bacteroides vulgatus-induced NF-kappa B signal transduction in intestinal epithelial cells (IEC). We report that B. vulgatus induced interleukin-1 receptor-associated kinase-1 degradation, I kappa B alpha phosphorylation/degradation, RelA and Akt phosphorylation, as well as NF-kappa B DNA binding and NF-kappa B transcriptional activity in rat non-transformed IEC-6 cells. B. vulgatus- but not interleukin-1 beta-mediated NF-kappa B transcriptional activity was inhibited by dominant negative (dn) toll-like receptor 4. Of importance, B. vulgatus induced I kappa B alpha phosphorylation/degradation and IKK alpha/beta and RelA phosphorylation in primary IEC derived from germ-free or mono-associated HLA-B27 transgenic and wild type rats, demonstrating the physiological relevance of non-pathogenic bacterial signaling in IEC. Adenoviral delivery of dn IKK beta or treatment with wortmannin inhibited B. vulgatus-induced endogenous RelA Ser-536 and GST-p65TAD (Ser-529/Ser-536) phosphorylation as well as NF-kappa B transcriptional activity in IEC-6 cells, suggesting a critical role of IKK beta and phosphatidylinositol 3-kinase/Akt in bacteria-induced RelA phosphorylation and NF-kappa B activation. Interestingly, B. vulgatus-induced I kappa B alpha degradation and NF-kappa B transcriptional activity in IEC transwell cultures were inhibited in the presence of lymphocytes. We propose that non-pathogenic B. vulgatus activates the NF-kappa B signaling pathway through both I kappa B degradation and RelA phosphorylation but that immune cells mediate tolerance of IEC to this commensal bacteria.

The state of CD4+ T cell activation is a major factor for determining the kinetics and location of T cell responses to oral antigen

Current models suggest that inductive immune responses to enteric Ag are initiated in Peyer's patches (PP) and mesenteric lymph nodes (MLN) followed by migration of activated, memory-like CD4(+) T cells to extralymphoid sites in the intestinal lamina propria (LP). The resultant immune system contains both naive and activated T cells. To examine the differential responses of naive and memory-like T cells to oral Ag, bone marrow chimeras (BMC) were generated. Irradiated BALB/c hosts were reconstituted with a mix of DO11.10 x RAG-1(-/-) and BALB/c bone marrow. In unprimed DO11.10 and BMC models, LP and PP DO11.10 T cells responded to oral Ag with similar kinetics. Responses of activated, memory-like T cells to oral Ag were examined in thymectomized BMC 60 days after i.p. immunization with OVA peptide in Freund's adjuvant (OVA(323-339)/CFA). Results indicate that i.p. OVA(323-339)/CFA generated a high proportion of memory-like CD45RB(low) DO11.10 T cells in peripheral lymphoid (40%) and intestinal LP (70%) tissue. Previously activated DO11.10 T cells in the LP responded to oral Ag earlier and at 50% higher levels compared with memory CD4(+) T cells localized to PP tissue. These data indicate that responses to oral Ag in antigenically naive animals are initiated in PP whereas in Ag-experienced animals LP T cells respond earlier and more vigorously than cells in PP. Taken together, these data suggest that previous activation alters the hierarchy of T cell responses to oral Ag by enhancing the efficiency of LP T cell activation.

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.

Patients with inflammatory bowel disease (IBD) reveal increased induction capacity of intracellular interferon-gamma (IFN-gamma) in peripheral CD8+ lymphocytes co-cultured with intestinal epithelial cells

Intestinal epithelial cells seem to play a key role during IBD. The network of cellular interactions between epithelial cells and lamina propria mononuclear cells is still incompletely understood. In the following co-culture model we investigated the influence of intestinal epithelial cells on cytokine expression of T cytotoxic and T helper cells from patients with IBD and healthy controls. Peripheral blood mononuclear cells (PBMC) were purified by a Ficoll-Hypaque gradient followed by co-incubation with epithelial cells in multiwell cell culture insert plates in direct contact as well as separated by transwell filters. We used Caco-2 cells as well as freshly isolated colonic epithelia obtained from surgical specimens. Three-colour immunofluorescence flow cytometry was performed after collection, stimulation and staining of PBMC with anti-CD4, anti-CD8, anti-IFN-gamma and anti-IL-4. Patients with IBD (Crohn's disease (CD), n = 12; ulcerative colitis (UC), n = 16) and healthy controls (n = 10) were included in the study. After 24 h of co-incubation with Caco-2 cells we found a significant increase of IFN-gamma-producing CD8+ lymphocytes in patients with IBD. In contrast, healthy controls did not respond to the epithelial stimulus. No significant differences could be found between CD and UC or active and inactive disease. A significant increase of IFN-gamma+/CD8+ lymphocytes in patients with UC was also seen after direct co-incubation with primary cultures of colonic crypt cells. The observed epithelial-lymphocyte interaction seems to be MHC I-restricted. No significant epithelial cell-mediated effects on cytokine expression were detected in the PBMC CD4+ subsets. Patients with IBD-even in an inactive state of disease-exert an increased capacity for IFN-gamma induction in CD8+ lymphocytes mediated by intestinal epithelial cells. This mechanism may be important during chronic intestinal inflammation, as in the case of altered mucosal barrier function epithelial cells may become targets for IFN-gamma-producing CD8+ lymphocytes.

Genetic dissection of primary and secondary responses to a widespread natural pathogen of the gut, Eimeria vermiformis

Because most pathogens initially challenge the body at epithelial surfaces, it is important to dissect the mechanisms that underlie T-cell responses to infected epithelial cells in vivo. The coccidian parasites of the genus Eimeria are protozoan gut pathogens that elicit a potent, protective immune response in a wide range of host species. CD4+ alpha beta T cells and gamma interferon (IFN-gamma) are centrally implicated in the primary immunoprotective response. To define any additional requirements for the primary response and to develop a comparison between the primary and the secondary response, we have studied Eimeria infections of a broad range of genetically altered mice. We find that a full-strength primary response depends on beta(2)-microglobulin (class I major histocompatibility complex [MHC] and class II MHC and on IFN-gamma and interleukin-6 (IL-6) but not on TAP1, perforin, IL-4, Fas ligand, or inducible nitric oxide synthetase. Indeed, MHC class II-deficient and IFN-gamma-deficient mice are as susceptible to primary infection as mice deficient in all alpha beta T cells. Strikingly, the requirements for a highly effective alpha beta-T-cell-driven memory response are less stringent, requiring neither IFN-gamma nor IL-6 nor class I MHC. The class II MHC dependence was also reduced, with adoptively transferable immunity developing in MHC class II(-/-) mice. Besides the improved depiction of an immune response to a natural gut pathogen, the finding that effective memory can be elicited in the absence of primary effector responses appears to create latitude in the design of vaccine strategies.

Antigen uptake and trafficking in human intestinal epithelial cells

Primary intestinal epithelial cells, human colonic adenocarcinoma cell lines (DLD-1, Caco-2, and HT-29), and monocytes were used as model systems to study antigen uptake, antigen-presenting cell properties, as well as the kinetics of antigen uptake in intestinal epithelial cells (IEC). Intracellular staining of fluoresceinated tetanus toxoid was not evident in the IEC until after 30 min of incubation at 37 degrees C, whereas in monocytes intracellular punctate staining of fluoresceinated tetanus toxoid was evident after 5 mins. In polarized Caco-2 cells antigen could be internalized at both the apical and basolateral surfaces with polarized transport. When analyzed by electron microscopy, gold-labeled tetanus toxoid was internalized and found within endosomes and multivesicular bodies, but not within the lysosomal compartments by 60 min. By 2 hrs, gold-labeled tetanus toxoid was evident in the secondary lysosomes. These results demonstrate that tetanus toxoid follows an endocytic pathway in intestinal epithelial cells and that the kinetics of antigen uptake is slower than that of conventional antigen-presenting cells.

Non-pathogenic bacteria elicit a differential cytokine response by intestinal epithelial cell/leucocyte co-cultures

BACKGROUND AND AIM

Intestinal epithelial cells (IEC) are thought to participate in the mucosal defence against bacteria and in the regulation of mucosal tissue homeostasis. Reactivity of IEC to bacterial signals may depend on interactions with immunocompetent cells. To address the question of whether non-pathogenic bacteria modify the immune response of the intestinal epithelium, we co-cultivated enterocyte-like CaCO-2 cells with human blood leucocytes in separate compartments of transwell cultures.

METHODS

CaCO-2/PBMC co-cultures were stimulated with non-pathogenic bacteria and enteropathogenic Escherichia coli. Expression of tumour necrosis factor alpha (TNF-alpha), interleukin (IL)-1beta, IL-8, monocyte chemoattracting protein 1 (MCP-1), and IL-10 was studied by enzyme linked immunosorbent assays (cytokine secretion) and by semiquantitative reverse transcription-polymerase chain reaction.

RESULTS

Challenge of CaCO-2 cells with non-pathogenic E coli and Lactobacillus sakei induced expression of IL-8, MCP-1, IL-1beta, and TNF-alpha mRNA in the presence of underlying leucocytes. Leucocyte sensitised CaCO-2 cells produced TNF-alpha and IL-1beta whereas IL-10 was exclusively secreted by human peripheral blood mononuclear cells. CaCO-2 cells alone remained hyporesponsive to the bacterial challenge. Lactobacillus johnsonii, an intestinal isolate, showed reduced potential to induce proinflammatory cytokines but increased transforming growth factor beta mRNA in leucocyte sensitised CaCO-2 cells. TNF-alpha was identified as one of the early mediators involved in cellular cross talk. In the presence of leucocytes, discriminative activation of CaCO-2 cells was observed between enteropathogenic E coli and non-pathogenic bacteria.

CONCLUSION

The differential recognition of non-pathogenic bacteria by CaCO-2 cells required the presence of underlying leucocytes. These results strengthen the hypothesis that bacterial signalling at the mucosal surface is dependent on a network of cellular interactions.

Defensins are dominant HLA-DR-associated self-peptides from CD34− peripheral blood mononuclear cells of different tumor patients (plasmacytoma, chronic myeloid leukemia)

The HLA-DR-associated peptides from peripheral blood mononuclear cells of 2 patients with plasmacytoma and 1 with chronic myeloid leukemia were isolated, identified, and compared. Several were identified as derivatives of the defensin family. Defensins (or human neutrophil peptides [HNP]) are antimicrobial, cationic peptides of 29 to 35 amino acids in length and are the major constituents of the azurophilic granules of human neutrophils. Using peripheral blood cells from leukapheresis, containing about 90% of polymorphonuclear cells, we could identify HNP-1, -2, and -4 and propeptides of up to 49 amino acids in length, eluted from HLA class II molecules. Binding of isolated and synthetic defensin peptides to various HLA-DR alleles using an in vitro binding/competition assay based on size exclusion chromatography revealed that defensin may bind into the peptide-binding groove. In a T-cell competition assay, defensins were able to reduce the proliferation of an HLA-DR-restricted T-cell line after preincubation of stimulating cells (CHO-DRB1*0401 transfectants) with defensin. Therefore, binding of defensins might prevent T-cell recognition of HLA class II molecules expressed on different blood precursor cells (all of which are “nonprofessional” antigen-presenting cells) by blocking the HLA peptide-binding groove or, alternatively, might protect defensin-expressing cells from self-destruction.

The luminal short-chain fatty acid butyrate modulates NF-kappaB activity in a human colonic epithelial cell line

BACKGROUND & AIMS

The transcription factor nuclear factor-kappaB (NF-kappaB) plays a central role in regulating immune and inflammatory responses. Because butyrate deficiency has been associated with inflammatory bowel disease, we examined the effect of butyrate on NF-kappaB activity in the human HT-29 colonic cell line.

METHODS

The influence of butyrate (4 mmol/L) on NF-kappaB activity was determined using the gel mobility shift assay. The effect of butyrate on the expression of NF-kappaB subunits and inhibitory proteins was determined by immunoblotting. NF-kappaB-regulated gene expression was assayed by primer extension of intercellular adhesion molecule 1 and Mn superoxide dismutase messenger RNA, and by analysis of a transfected luciferase reporter.

RESULTS

Exposure of HT-29 cells to butyrate eliminated their constitutive NF-kappaB, p50 dimer activity. This inhibition corresponded with a reduction in p50 nuclear localization, without a reduction in expression. Butyrate also selectively modulated activation of NF-kappaB, suppressing its activation by tumor necrosis factor alpha and phorbol ester more than 10-fold, without affecting the activity induced by interleukin (IL)-1beta. Butyrate did, however, enhance formation of the stronger p65-p50 transcriptional activator in IL-1beta-stimulated cells. The changes in NF-kappaB activation did not correlate with changes in IkappaBalpha levels. Gene expression reflected DNA binding. The influence of butyrate on NF-kappaB may result in part from its ability to inhibit deacetylases because the specific deacetylase inhibitor trichostatin A has a similar effect.

CONCLUSIONS

These findings suggest that the influences of butyrate on colonic inflammatory responses may result in part from its influence on NF-kappaB activation. This activity of butyrate apparently involves its ability to inhibit deacetylases.

Human intestinal epithelial cells secrete interleukin-1 receptor antagonist and interleukin-8 but not interleukin-1 or interleukin-6

BACKGROUND

There is growing evidence that intestinal epithelial cells (IECs) are involved in the mucosal immune system.

AIM

To assess the pattern of cytokines secreted by IECs and lamina propria mononuclear cells (LPMNCs). To achieve this, the expression and secretion of interleukin (IL)-1, IL-1 receptor antagonist (IL-1ra), IL-6, and IL-8 in human primary colonic and ileal IECs and LPMNCs from the same patient were studied.

METHODS

IECs and LPMNCs were isolated from surgical specimens or endoscopic biopsy samples. mRNA expression was investigated by northern blot analysis. Secretion of IL-1beta, IL-6, IL-8, and IL-1ra was measured by enzyme linked immunosorbent assay.

RESULTS

IL-1ra mRNA levels were higher in IECs than in LPMNCs in all probands. IL-8 mRNA was only present in low amounts in the IECs from two controls. In none of the specimens were IL-1beta and IL-6 mRNA present in IECs. Transcripts encoding IL-1beta, IL-1ra, IL-6, and IL-8 were identified in LPMNC preparations of all specimens. IECs from normal mucosa produced no detectable amounts of IL-1beta or IL-6, whereas LPMNCs did. IECs secreted some IL-8 (65 (9) pg/10(5) cells) but significantly more was generated by LPMNCs (408 (43) pg/10(5) cells, p<0.0001). However, IECs secreted more IL-1ra than did LPMNCs (120 (12) v 94 (11) pg/10(5) cells). In acute inflammation, IEC IL-1ra secretion was significantly increased. A correlation between secreted IL-1ra and the macroscopical degree of inflammation was found in Crohn's disease (r = 0.64, p<0.0001, n = 36) and ulcerative colitis (r = 0. 76, p<0.0001, n = 24).

CONCLUSIONS

IECs from normal mucosa express and secrete IL-1ra and low amounts of IL-8, but no IL-1 or IL-6. In inflamed mucosa the secretion of IL-1ra by IECs is slightly increased but may be not sufficient to antagonise the greatly increased production of proinflammatory cytokines by LPMNCs and the IECs themselves.

The Differentiated State of Intestinal Lamina Propria CD4+ T Cells Results in Altered Cytokine Production, Activation Threshold, and Costimulatory Requirements

Intestinal lamina propria (LP) CD4+ T cells are memory-like effector cells that proliferate at relatively low levels and require high levels of TCR signaling and costimulation for full activation in vitro. To study LP CD4+ T cell functional potential we used DO11.10 TCR transgenic (Tg) mice specific for the class II MHC-restricted OVA323–339 peptide and nontransgenic BALB/c mice. Activation of LP Tg+ T cells with Ag using mucosal explants induced high levels of IL-2, IL-4, and IFN-γ. Culturing isolated LP cells with IL-12 enhanced IFN-γ production and down-regulated IL-4 and IL-2, whereas addition of IL-4 maintained IL-4 production without inhibiting IFN-γ production. Systemic administration of relatively high dose (HD; 100 nM) OVA323–339 peptide induced similar levels of bromodeoxyuridine (BrdU) incorporation by LP and splenic Tg+ T cells in vivo, whereas low dose (LD; 4.5 nM) peptide injections induced 4-fold greater levels of BrdU incorporation for LP compared with splenic Tg+ T cells. Coadministration of CTLA-4Ig reduced BrdU incorporation for splenic cells by 70% with HD and LD stimulation, but had little effect on LP responses to HD stimulation. Results of in vivo studies were confirmed in nontransgenic BALB/c mice using HD (200 μg) and LD (10 μg) anti-CD3 mAb+/− CTLA-4Ig. These results suggest that LP T cells are differentiated effector cells that respond at high levels when activated with relatively low levels of Ag- and B7-mediated costimulation in vivo. The reduced activation threshold of LP T cells may facilitate responses to low levels of Ag derived from mucosal pathogens.

The intestinal epithelial cell: processing and presentation of antigen to the mucosal immune system

The immunologic tone of the intestinal tract is one of suppressed or highly regulated responses. While there are several components (intrinsic and extrinsic to the gut-associated lymphoid tissue) responsible for this immunologically suppressed tone, the intestinal epithelial call (IEC) has been proposed as a key player in this process. IECs can take up and process antigen but distinct surface molecules and restriction elements allow them to present these antigens to unique regulatory T cells. These include the expression of the class Ib molecule CD1d as well as a novel CD8 ligand, gp180. These molecules come together to activate a subpopulation of CD8+ regulatory cells whose function is to suppress immune responses in an antigen non-specific fashion most likely through cognate interactions. This form of regulation may be unique to the gut-associated lymphoid tissue which is consistent with the unusual demands upon this part of the immune system.

In situ hybridization as a technique for the immunological investigation of canine intestine: jejunal expression of IFNgamma and IL10 in Irish setters and beagles

In situ hybridization (ISH) has found numerous applications in biology and medicine. However, its use to demonstrate expression of cytokines within the canine small intestine has not been described. Digoxigenin-labelled riboprobes complementary to mRNA encoding canine IFNgamma and IL10 were used to demonstrate expression of these cytokines within formalin-fixed, paraffin-embedded sections of jejunum obtained from healthy control Irish setter (IS) dogs (n = 4), gluten-sensitive IS in remission (n = 7), and beagles with high enteric bacterial populations (n = 5). Proportional areas of cells within the lamina propria showing one of three mutually exclusive staining intensities were measured, as well as the total stained area. Intensity categories were chosen arbitrarily to represent cells showing weak, moderate or dense staining (grades 1-3 respectively), reflecting increasing expression of mRNA. Control and gluten-sensitive IS showed similar total and grade-by-grade areas of expression of IFNgamma and IL10 in the lamina propria (p>0.05), in contrast to beagles, which showed greater total and grade 1 areas of expression of IFNgamma, and greater total, grade 1 and grade 2 areas of expression of IL10, than both groups of IS (p<0.05). Epithelial expression of both cytokines was demonstrated in beagles and IS, but differences between groups for each cytokine were not apparent (p>0.05). This study has validated the use of in situ hybridization for the detection of IFNgamma and IL10 mRNA within canine intestinal biopsies, andhas shown heightened jejunal expression of both cytokines in beagles with high enteric bacterial populations.

Molecular Cloning and Characterization of a Novel CD1 Gene from the Pig

Much effort is underway to define the immunological functions of the CD1 multigene family, which encodes a separate lineage of Ag presentation molecules capable of presenting lipid and glycolipid Ags. To identify porcine CD1 homologues, a cosmid library was constructed and screened with a degenerate CD1 α3 domain probe. One porcine CD1 gene (pCD1.1) was isolated and fully characterized. The pCD1.1 gene is organized similarly to MHC class I and other CD1 genes and contains an open reading frame of 1020 bp encoding 339 amino acids. Expression of pCD1.1 mRNA was observed in CD3− thymocytes, B lymphocytes, and tissue macrophages and dendritic cells. The pCD1.1 cDNA was transfected into Chinese hamster ovary cells, and subsequent FACS analysis demonstrated that mAb 76-7-4, previously suggested to be a pig CD1 mAb, recognizes cell surface pCD1.1. Structurally, the pCD1.1 α1 and α2 domains are relatively dissimilar to those of other CD1 molecules, whereas the α3 domain is conserved. Overall, pCD1.1 bears the highest similarity with human CD1a, and the ectodomain sequences characteristically encode a hydrophobic Ag-binding pocket. Distinct from other CD1 molecules, pCD1.1 contains a putative serine phosphorylation motif similar to that found in human, pig, and mouse MHC class Ia molecules and to that found in rodent, but not human, MHC class-I related (MR1) cytoplasmic tail sequences. Thus, pCD1.1 encodes a molecule with a conventional CD1 ectodomain and an MHC class I-like cytoplasmic tail. The unique features of pCD1.1 provoke intriguing questions about the immunologic functions of CD1 and the evolution of Ag presentation gene families.

Colitis in transgenic and knockout animals as models of human inflammatory bowel disease

Spontaneous colitis in knockout (KO) and transgenic rodents provides experimental models to study the development of mucosal inflammation and inflammatory bowel disease (Crohn's disease and ulcerative colitis). Genetic and environmental factors, particularly the normal enteric flora, are important factors in the development of mucosal inflammation. The normal mucosal homeostasis is disrupted when there is either cytokine imbalance, abrogation of oral tolerance, alteration of epithelial barrier and function or loss of immunoregulatory cells. Some but not all immunodeficiencies, in the appropriate setting, lead to colitis. CD4+ T cells have been identified as the pathogenic T cells in colitis, which mediate inflammation by either the Th1 or the Th2 pathway. The Th1 pathway dominates most colitis models and in Crohn's disease. In contrast, the colitis in TCR alpha KO mice shares many features of ulcerative colitis including the dominance of Th2 pathway in colonic inflammation. A major benefit of these models is in the development of therapeutic strategies for the treatment of inflammatory bowel disease.

Regulation by human uterine cells of PBMC proliferation: influence of the phase of the menstrual cycle and menopause

To determine the influence of human uterine cells recovered at different stages of the menstrual cycle and following menopause on the proliferation of peripheral blood mononuclear cells (PBMC), whole cell suspensions of uterine tissues were co-cultured with autologous and heterologous PBMC. PBMC proliferation in response to tetanus toxoid (TT) or Con A was inhibited by uterine endometrial cells and was dependent on the phase of the menstrual cycle. Inhibition by cells from the proliferative phase was significantly greater than by cells from the secretory phase. Uterine cells isolated from post-menopausal women also inhibited proliferation of PBMC. Cell fractionation studies indicated that epithelial cells are the primary source of uterine inhibitory activity. When epithelial cells and PBMC were cultured in separate compartments, epithelial cells released a soluble factor(s) that inhibited the PBMC proliferation. These results suggest that uterine epithelial cells produce cytokines that down-regulate the proliferation of PBMC in response to antigens and mitogens. This may be important for the control of uterine immune responses, as well as the growth of the reproductive tract in preparation for implantation during the secretory phase of the menstrual cycle.

The Regulation and Functional Consequence of Proinflammatory Cytokine Binding on Human Intestinal Epithelial Cells

Products of an activated immune system may affect cells within the immune system as well as nonlymphoid cells in the local environment. Given the immunologically activated state of the intestinal tract, it is conceivable that locally produced cytokines could regulate epithelial cell function. To assess whether epithelial cells are targets for particular cytokines, we initiated studies on the binding of a panel of proinflammatory cytokines in freshly isolated epithelial cells from normal and inflammatory bowel disease (IBD) patients as well as in cell lines. Isolated intestinal epithelial cells (IEC) were stained with phycoerythrin-conjugated or biotinylated cytokines to determine the expression and density of receptors for IL-1β, IL-6, granulocyte-macrophage CSF (GM-CSF), and TNF-α. Receptors for IL-1β, IL-6, and GM-CSF were readily detectable in all epithelial cell preparations at levels equal to (GM-CSFR) or lower than those seen on monocytes. However TNFα-R were not detectable on freshly isolated IECs. Receptor density was greater in surface vs crypt epithelial cells, but no significant differences were seen between normal and IBD epithelial cells. Expression of IL-1R and IL-6R was enhanced by LPS and IFN-γ. Functionally, IL-1β enhanced proliferation of the IEC cell line, DLD1, whereas GM-CSF treatment of de-differentiated crypt-like DLD1 and HT29 cells resulted in enhanced expression of ICAM-1. Furthermore, TNF-α treatment enhanced the secretion of IL-8 and GRO-α in HT29 cells, but not in freshly isolated IEC cultures. The differential binding and function of proinflammatory cytokines on IEC support the hypothesis that these cytokines may be involved in normal physiological processes as well as in regulating mucosal immune responses.

Substance P receptor expression in intestinal epithelium in clostridium difficile toxin A enteritis in rats

We previously reported that the inflammatory effects of Clostridium difficile toxin A on rat intestine can be significantly inhibited with a specific neurokinin-1 receptor (NK-1R) antagonist. In this study we investigated the localization and expression of NK-1R mRNA and protein in rat intestine by in situ hybridization, Northern blot analysis, and immunohistochemistry, respectively, after exposure to toxin A. Northern blot analysis showed increased mucosal levels of NK-1R mRNA starting 30 min after toxin A administration. In situ hybridization showed that toxin A increased NK-1R mRNA expression in intestinal epithelial cells after 30, 120, and 180 min. In rats pretreated with the NK-1R antagonist CP-96345 the increase in NK-1R mRNA levels after exposure to toxin A was inhibited, indicating that NK-1R upregulation is substance P (SP) dependent. One hour after exposure to toxin A many of the intestinal epithelial cells showed staining for NK-1R compared with controls. Specific 125I-SP binding to purified epithelial cell membranes obtained from ileum exposed to toxin A for 15 min was increased twofold over control and persisted for 4 h. This report provides evidence that NK-1R expression is increased in the intestinal epithelium shortly after exposure to toxin A and may be important in toxin A-induced inflammation.

Mediation by NF-kappa B of cytokine induced expression of intercellular adhesion molecule 1 (ICAM-1) in an intestinal epithelial cell line, a process blocked by proteasome inhibitors

BACKGROUND/AIMS

The gene promoter for the intercellular adhesion molecule ICAM-1 possesses binding sites for several transcriptional factors, including nuclear factor kappa B (NF-kappa B). The role of NF-kappa B in ICAM-1 gene regulation was therefore examined by using different proteasome inhibitors in tumour necrosis factor alpha (TNF-alpha) stimulated IEC-6 rat intestinal epithelial cells.

METHODS

ICAM-1 expression was analysed by enzyme linked immunosorbent assay (ELISA), reverse transcriptase polymerase chain reaction, and immunohistochemistry. Steady state levels of cytoplasmic I kappa B protein were evaluated by western blot, and nuclear translocation of NF-kappa B was determined by electrophoretic mobility shift assay and immunofluorescence staining. Cell adhesion was assayed by measuring the binding of fluorescence labelled MOLT-4 cells.

RESULTS

TNF-alpha induced ICAM-1 mRNA and protein expression in IEC-6 cells, which was followed by increased adhesion of MOLT-4 lymphocytes. Blocking TNF-alpha induced I kappa B alpha degradation with proteasome inhibitors reduced TNF-alpha induced NF-kappa B activation and ICAM-1 gene induction and notably decreased MOLT-4 cell adhesion without affecting Jun N-terminal kinase (JNK/SAPK) activity or de novo protein synthesis.

CONCLUSION

TNF-alpha induction of ICAM-1 expression is mediated by the transcription factor NF-kappa B and can be inhibited by blocking I kappa B alpha degradation. Thus the I kappa B/NF-kappa B system is a promising target for pharmacological modulation of the expression of adhesion molecules and other inflammatory genes in the intestine.

Interactions between peripheral blood CD8 T lymphocytes and intestinal epithelial cells (iEC)

Intestinal intraepithelial lymphocytes (iIEL) are primarily CD8 cells and most of them have a CD28- phenotype, the phenotype of effector cytotoxic T cells. We asked whether the predominance of CD8+CD28- T cells in the gut may result from peripheral blood T cells preferentially migrating to the iIEL compartment and adhering to iEC. Compared with CD4 cells, adhesion of resting CD8+ T cells to iEC cell lines was significantly higher. Adhesion could be blocked with a MoAb to gp180, a molecule expressed on iEC which is known to interact with CD8/lck. No significant difference in the level of adhesion was observed between CD8+CD28+ and CD8+CD28- T cells. Thus CD8 cells may preferentially migrate to the iIEL compartment, but loss of CD28 expression could occur in situ after migration. Consistent with this hypothesis, the CD8+CD28- cells became enriched after co-culturing T cells with iEC cell lines and primary iEC. Induction of the CD8+CD28- phenotype in cord blood and adult T cells was observed in co-cultures with iEC and also with mitogens and superantigens. In the latter case, CD28 down-modulation was seen specifically in the Vbeta subset targeted by the superantigen, indicating that loss of CD28 expression is a direct result of T cell receptor (TCR)-mediated stimulation. The combined results suggest that CD8+CD28- T cells are antigen experienced T cells, and that they may have a survival advantage in the presence of gut epithelial cells in vitro. This may contribute to the predominance of CD8+CD28- T cells in the iIEL compartment.

A Mucosal Intranet: Intestinal Epithelial Cells Down-Regulate Intraepithelial, But Not Peripheral, T Lymphocytes

Epithelial cells and lymphocytes, including γδ and αβ T cells, in the gastrointestinal tract epithelium represent a major host defense intranet that is incompletely understood. Cell-to-cell interactions between intraepithelial lymphocytes (IELs) and intestinal epithelial cells (IECs) comprise this intranet, and we have assessed the role of IECs in the regulation of γδ and αβ T cell responses. When highly purified CD3+ IEL T cells were stimulated via the TCR-CD3 complex, high proliferative responses and cytokine synthesis were induced. However, the addition of viable IECs or purified IEC membranes (mIEC) down-regulated T cell proliferative and cytokine responses. Further, the inhibitory effect of mIEC was not restored by antibodies to TGF-β, CD1d, E-cadherin, or MHC class I or II. This inhibitory effect was noted for both γδ and αβ T cell subsets from IELs, and mRNA levels were reduced for both Th1 (IL-2 and IFN-γ) and Th2 (IL-4 and IL-5) cytokines in γδ and αβ IELs. In contrast, a purified membrane fraction obtained from thymocytes did not inhibit IEL proliferative responses. Further, mIEC did not inhibit splenic αβ T cell proliferative responses. These findings show that cell-to-cell interactions between intraepithelial γδ and αβ T cells and IECs occur via cell surface molecules, suggesting an intranet to prevent potential inflammatory responses at the intestinal mucosal surface.

Lack of Local Suppression in Orally Tolerant CD8-Deficient Mice Reveals a Critical Regulatory Role of CD8+ T Cells in the Normal Gut Mucosa

We found that feeding keyhole limpet hemocyanin (KLH) to CD8-deficient (CD8−/−) mice induced oral tolerance that was comparable in both magnitude and quality to that induced in wild-type (wt) mice. The tolerance was dose dependent, and only higher doses of KLH caused significant reduction in specific Ab and T cell responses. Both Th1 and Th2 CD4+ T cell functions were affected. Feeding KLH together with cholera toxin (CT) adjuvant, however, abrogated the induction of oral tolerance equally well in CD8−/− and wt mice. On the contrary, CT adjuvant was unable to abrogate already established oral tolerance in both CD8−/− and wt mice. Most importantly, whereas Ag feeding induced hyporesponsiveness in systemic as well as in local gut IgA responses in wt mice, a lack of local suppression was evident in orally tolerant CD8−/− mice following oral immunizations. Thus, contrary to the situation in wt mice, Ag feeding induces systemic, but not local, gut IgA hyporesponsiveness in CD8−/− mice, suggesting that CD8+ T cells in the normal gut mucosa exert an important down-regulatory function. In wt mice the local suppression extended to an unrelated Ag, OVA, given together with KLH and CT adjuvant, i.e., bystander suppression. Based on these results we propose that tolerance induced by feeding Ag is highly compartmentalized, requiring CD8+ T cells for local suppression of IgA responses, whereas systemic tolerance may affect CD4+ T cells of both Th1 and Th2 types independently of CD8+ T cells. Finally, the adjuvant effect of CT abrogates induction, but not established, oral tolerance through a mechanism that does not require CD8+ T cells.

Inhibition of Proinflammatory Molecule Production by Adenovirus-Mediated Expression of a Nuclear Factor κB Super-Repressor in Human Intestinal Epithelial Cells

NF-κB plays a major role in the transcriptional regulation of many proinflammatory genes in multiple cell lineages, including intestinal epithelial cells (IEC). Activation of NF-κB requires both phosphorylation and degradation of its natural cytoplasmic inhibitor, IκB. We tested whether a super-repressor of NF-κB activity, which is a mutated nondegradable IκBα resistant to phosphorylation and degradation, could be delivered into IEC using an adenoviral vector (Ad5IκB) and determined the anti-inflammatory potential of this inhibitor following different stimuli. We showed for the first time that recombinant adenovirus efficiently infected (&gt;80%) transformed as well as primary IEC. Cytoplasmic levels of the NF-κB super-repressor protein were more than 50-fold higher than those of endogenous IκB, and this mutated IκB was resistant to IL-1β-induced degradation. Immunofluorescent RelA nuclear staining was strongly inhibited in Ad5IκB-infected IEC compared with control Ad5LacZ, and NF-κB, but not AP-1 binding activity, was reduced by more than 70% as measured by electrophoretic mobility shift assay (EMSA). Induction of inducible nitric-oxide synthase (iNOS), IL-1β, and IL-8 genes by IL-1β, TNF-α, or PMA was blocked in Ad5IκB-infected cells but not in Ad5LacZ controls as assayed by RT-PCR and ELISA. In addition, IL-1β-induced IL-8 secretion was totally inhibited by Ad5IκB in primary colonic IEC. We conclude that an adenoviral vector efficiently transfers a nondegradable IκB in both transformed and native IEC. The strong inhibition of NF-κB activity and the resulting down-regulation of multiple proinflammatory molecules by Ad5IκB suggests an exciting approach for in vivo intestinal gene therapy and illustrates the key role of NF-κB in transcriptional regulation of the inflammatory phenotype of IEC.

The effect of interleukin-10 and transforming growth factor beta-1 on HLA-DR expression in colonic epithelial cells

The aim of this study was to assess whether interleukin-10 (IL-10) and/or transforming growth factor beta-1 (TGFbeta1) downregulate HLA-DR expression using the HT29 cell line as a model of colonic epithelial cells. HLA-DR expression was induced in HT29 cells with gamma-interferon. The effects of IL-10 alone, TGFbeta1 alone, and IL-10 and TGFbeta1 in combination were studied. HLA-DR expression was assessed using flow cytometric analysis. Gamma-interferon induced HLA-DR expression in a dose-dependent fashion. In the absence of gamma-interferon, neither IL-10 nor TGFbeta1 induced HLA-DR expression. In isolation, neither IL-10 nor TGFbeta1 downregulated HLA-DR expression. When IL-10 and TGFbeta1 were added in combination, small (6-30%) statistically significant reductions in HLA-DR expression were seen. The biological significance is unclear.

Review article: Local and systemic regulation of mucosal immunity

An increased interest in mucosal immunity has stemmed from the identification of novel T-cell populations and developments in oral vaccines and oral tolerance. The development of physiological inflammation is antigen driven. Upon recognition of antigen, the lamina propria (LP) is populated with lymphocytes and activated peripheral cells acquire the capacity to home to the gut. Antigen entry to the gut is via follicle-associated epithelium or M cells. The antigen now interacts with macrophages or CD4+ cells, and go on to the Peyer's patch where B cells undergo a transforming growth factor beta (TGF-beta)-mediated isotope switch to immunoglobulin (Ig) A. TGF-beta may also play a role in the development of oral tolerance. The intestinal epithelium is seen as the site for the activation of CD8+ suppressor cells. Controlled inflammation is therefore explained by the interaction of LP lymphocytes and intra-epithelial cells (IEC). IECs are capable of extending processes that express regulatory surface molecules coupled with antigen processed from luminal uptake. CD8+ T-cell activation is favoured over CD4+ T-cell activation due to the size of the antigenic binding peptide. The result is suppressed inflammation. Other antigen-presenting cells (APCs) and dendritic cells may also contribute to local immunosuppression.

Review article: In vitro models in inflammatory bowel disease research--a critical review

Research efforts in inflammatory bowel disease (IBD) have been directed towards the epithelium as it has become clear that epithelial cells play a critical role in inflammatory response. Most research involving IBD employs in vitro techniques. In vitro epithelial cell studies have played and are continuing to play a major role in providing specific information relevant to IBD. Thus, such studies have provided irrefutable evidence that epithelial responses can be induced by microbes/microbial products and by immune activation. Culture experiments have provided insights into the effects of individual cytokines and other inflammatory mediators on epithelial pathophysiology, injury and repair, apoptosis, necrosis, and other processes that may be involved in IBD. Activated epithelial cells can participate in and even orchestrate immune responses, by stimulating T cells (and possibly others) and by producing cytokines that recruit specific inflammatory cells. Physiological regulation of epithelial tight junctions has been demonstrated by in vitro studies; the implication of this information for treating IBD is just beginning to be explored. It is becoming increasingly clear that epithelial processing and presentation of antigens is critical to the outcome of the immune response.

Defective expression of gp180, a novel CD8 ligand on intestinal epithelial cells, in inflammatory bowel disease

Previous studies support a role for intestinal epithelial cells (IEC) as antigen-presenting cells in mucosal immune responses. T cells activated by IEC are CD8+, suppressor in function, and dependent upon CD8-associated p56lck activation. A 180-kD glycoprotein (gp180) recognized by mAbs B9 and L12 has been identified and shown to be important in CD8+ T cell activation by IEC. Since IEC derived from patients with inflammatory bowel disease (IBD) are incapable of activating CD8+ T cells, we asked whether this correlated with gp180 expression. While frozen sections of normal bowel revealed bright gp180 staining on all IEC, both inflamed and uninflamed ulcerative colitis (UC) specimens showed patchy staining. In Crohn's disease (CD), staining was faint to absent. Flow cytometry confirmed immunohistochemical data. The staining patterns correlated with the ability of IEC to activate CD8-associated p56lck. Normal IEC induced phosphorylation of p56lck in CD8alpha but not CD4+ transfectants. In contrast, both UC and CD IEC activated CD4 and, to a much lesser extent, CD8-associated p56lck. Thus, gp180 expression by IBD IEC appears to be altered, and correlates with a functional alteration of lck activation. This defect may reflect a more proximal event in the pathogenesis of IBD.

Crohn's disease and ulcerative colitis mucosal T cells are stimulated by intestinal epithelial cells: implications for immunosuppressive therapy

BACKGROUND

Crohn's disease (CD) and ulcerative colitis (UC) are chronic inflammatory diseases, and their pathogenesis is attributed, in part, to alterations of the mucosal immune system. This study was designed to define the possible contribution of epithelial cells to the activation of lamina propria T lymphocytes (LPTs) in CD and UC.

METHODS

LPTs isolated from CD, UC, and control surgical specimens were cocultured with freshly isolated allogeneic or autologous epithelial cells or epithelial cell lines. Resulting T-cell proliferation was evaluated by tritiated thymidine incorporation on day 5.

RESULTS

When intestinal epithelial cells were used to stimulate mucosal T-cell proliferation, CD and UC LPTs were less responsive than control LPTs (p < 0.05 and p < 0.03, respectively). This difference between inflamed and control T cells was consistently observed by using a variety of different intestinal epithelial cell types.

CONCLUSIONS

CD and UC mucosal T cells are hyporesponsive to activation by intestinal epithelial cells when compared with control LPTs. Elucidating the mechanism underlying the differential activation of CD and UC LPTs may help to better understand the immunopathogenesis of these conditions.

A comparison of the antigen-presenting capabilities of class II MHC-expressing human lung epithelial and endothelial cells

Human lung alveolar epithelial cells constitutively express class II major histocompatibility complex (MHC). Human lung microvascular endothelial and small airway epithelial cells can be induced to express class II MHC by stimulation with the pro-inflammatory cytokine interferon-gamma. The levels of class II MHC on lung epithelial and endothelial cells were comparable to those seen on an Epstein-Barr virus (EBV)-transformed B-cell line. However, the costimulatory molecules B7-1 and B7-2 were not expressed. The ability of the class II MHC expressing human lung parenchymal cells to present alloantigen to CD4+ T lymphocytes was investigated. Freshly isolated human alveolar epithelial cells (type II pneumocytes) and monolayers of interferon-gamma-stimulated small airway epithelial and lung microvascular endothelial cells were co-cultured with allogeneic CD4+ T lymphocytes and proliferation determined by [3H]thymidine incorporation. A clear difference was observed between effects of the epithelial and endothelial cells on CD4+ T-lymphocyte activation. Alveolar and small airway epithelial cells failed to stimulate the proliferation of allogeneic CD4+ T lymphocytes whereas lung microvascular endothelial cells did stimulate proliferation. This difference could not be explained by the levels of class II MHC or the lack of B7-1 and B7-2 solely. Microvascular endothelial cells, and not alveolar or small airway epithelial cells, possess B7-independent costimulatory pathways.

Intestinal epithelial cells use two distinct pathways for HLA class II antigen processing

Intestinal epithelial cells express a low level of HLA class II molecules constitutively, with elevated levels seen in the setting of mucosal inflammation including inflammatory bowel disease. The ability of intestinal epithelial cells to act as antigen presenting cells for alphabeta CD4(+) T lymphocytes was examined through a molecular analysis of the HLA class II antigen processing pathway. We have shown that intestinal epithelial cells contain abundant constitutive levels of the cathepsin proteases proven to function in HLA class II mediated antigen presentation. Activation of these cells by gamma-IFN induced the expression of invariant chain and HLA-DM alphabeta, thus facilitating the formation of compact, SDS-stable HLA- DR alphabeta heterodimers. Using HLA-DR-restricted T cells and retroviral mediated gene transfer of HLA-DR alleles into the intestinal epithelial cell lines HT-29 and T84, we demonstrated efficient antigen processing and presentation to CD4(+) T lymphocytes in the presence of the proinflammatory cytokine gamma-IFN. The class II processing pathway and presentation in the presence of gamma-IFN was indistinguishable from that observed with a conventional antigen presenting cell. Antigen processing also occurred in intestinal epithelial cells in the absence of gamma-IFN, and in contrast to that seen after stimulation with gamma-IFN, required high concentration of antigen and was not inhibited by the protease inhibitor leupeptin. These data suggest the use of two distinct pathways of HLA class II antigen processing in enterocytes with differential immunomodulatory properties in the presence or absence of mucosal inflammation.

The intestinal epithelial cell: immunological aspects

IECs likely play an important role in immunological defense mechanism. Apart from being a passive barrier against luminal bacteria, IECs secrete protective and microbiocidal products such as ITF, complement components and cryptdins into the lumen. Moreover, IECs produce secretory component that is essential for the transport of IgA from the lamina propria into the lumen. IECs also have regulatory functions. They express adhesion molecules important in the homing of T cells and other leukocytes, and likely modulate T cell functions in a paracrine way. Furthermore, IECs secrete cytokines, either constitutively or after bacterial challenge, and they express cytokine receptors. Lastly, IECs may play an important role as non-professional antigen-presenting cells by expressing classical MHC class I and class II and nonclassical MHC class I molecules on the cell surface. This aspect is particularly intriguing in that IECs also express a FcR that may have a function in luminal antigen sampling.

Gastric mucosa abnormalities and tumorigenesis in mice lacking the pS2 trefoil protein

To determine the function of the pS2 trefoil protein, which is normally expressed in the gastric mucosa, the mouse pS2 (mpS2) gene was inactivated. The antral and pyloric gastric mucosa of mpS2-null mice was dysfunctional and exhibited severe hyperplasia and dysplasia. All homozygous mutant mice developed antropyloric adenoma, and 30 percent developed multifocal intraepithelial or intramucosal carcinomas. The small intestine was characterized by enlarged villi and an abnormal infiltrate of lymphoid cells. These results indicate that mpS2 is essential for normal differentiation of the antral and pyloric gastric mucosa and may function as a gastric-specific tumor suppressor gene.