Thomas T. MacDonald

Tumor necrosis factor α-producing cells in the intestinal mucosa of children with inflammatory bowel disease

Abstract Background/Aims: Cytokines are thought to be important in mediating tissue damage in inflammatory bowel disease (IBD). Many of the in vivo activities of tumor necrosis factor α (TNF-α) match the changes found in IBD, but its importance is controversial. Methods: A sensitive, reverse hemolytic plaque assay was used to determine the frequency of TNF-α secreting cells isolated from mucosal biopsy specimens of children with Crohns disease or ulcerative colitis (UC) and non-IBD controls before and after medical treatment. Results: Frequency of TNF-α secreting cells was significantly increased in biopsy specimens from children with mild, nonspecific inflammation compared with those with histologically normal intestine. Frequency did not increase in UC compared with children with nonspecific inflammation but was significantly greater in Crohns disease than in UC. After treatment, the frequency of TNF-α secreting cells was reduced in patients receiving cyclosporin A, not reduced in patients with steroids or enteral nutrition, and not changed with treatment in UC. Conclusions: TNF-α secreting cells are increased in the mucosa of inflamed intestine, regardless of pathogenesis. In patients with IBD, higher levels are seen in Crohns disease than in UC, probably reflecting the extensive T-cell activation in Crohns disease. No relation existed between histological healing and the frequency of TNF-α-secreting cells.

Blocking Smad7 restores TGF-β1 signaling in chronic inflammatory bowel disease

TGF-beta1 functions as a negative regulator of T cell immune responses, signaling to target cells using the Smad family of proteins. We show here that Smad7, an inhibitor of TGF-beta1 signaling, is overexpressed in inflammatory bowel disease (IBD) mucosa and purified mucosal T cells. Both whole tissue and isolated cells exhibit defective signaling through this pathway, as measured by phospho-Smad3 immunoreactivity. Specific antisense oligonucleotides for Smad7 reduce Smad7 protein expression in cells isolated from patients with IBD, permitting the cells to respond to exogenous TGF-beta1. TGF-beta1 cannot inhibit proinflammatory cytokine production in isolated lamina propria mononuclear cells from patients with Crohn disease (CD), but inhibition of Smad7 restores TGF-beta1 signaling and enables TGF-beta1 to inhibit cytokine production. In inflamed mucosal tissue explants from patients with CD, inhibition of Smad7 also restores p-Smad3 and decreases proinflammatory cytokine production, an effect that is partially blocked by anti-TGF-beta1. These results show that Smad7 blockade of TGF-beta1 signaling helps maintain the chronic production of proinflammatory cytokines that drives the inflammatory process in IBD and that inhibition of Smad7 enables endogenous TGF-beta to downregulate this response.

Location of tumour necrosis factor alpha by immunohistochemistry in chronic inflammatory bowel disease.

This study determined the location and tissue density of cells immunoreactive for tumour necrosis factor alpha (TNF alpha) in intestinal specimens from 24 patients with chronic inflammatory bowel disease (15 with Crohns disease, nine with ulcerative colitis) and 11 controls. There was significantly increased density of TNF alpha immunoreactive cells in the lamina propria of both ulcerative colitis and Crohns disease specimens, although the distribution of these cells differed in the two conditions. In ulcerative colitis most of the TNF alpha immunoreactivity was seen in the subepithelial macrophages, with comparatively less in the deep lamina propria, while in Crohns disease immunoreactive cells were distributed evenly throughout the lamina propria. Increased submucosal immunoreactivity was found only in Crohns disease, in which TNF alpha positive macrophages tended to cluster around arterioles and venules, often infiltrating and disrupting vascular endothelium. It is suggested that this degree of TNF alpha production probably contributes significantly to the pathogenesis of both Crohns disease and ulcerative colitis, by impairing the integrity of epithelial and endothelial membranes, increasing inflammatory cell recruitment, and by prothrombotic effects on the vascular endothelium.

Serum concentrations of tumour necrosis factor alpha in childhood chronic inflammatory bowel disease.

Serum tumour necrosis factor alpha (TNF alpha) concentrations were measured by enzyme linked immunoadsorbent assay in 31 normal children and during 65 episodes of clinical remission and 54 episodes of relapse in 92 children with chronic inflammatory bowel disease. An appreciable rise in TNF alpha was found only in children in relapse of ulcerative colitis and colonic Crohns disease. The group of children with small bowel Crohns disease in relapse did not show increases of TNF alpha above control concentrations, despite an equivalent rise in disease indices. Height velocity was depressed in children with relapse of large bowel Crohns disease and ulcerative colitis compared with the equivalent condition in remission. The impairment of growth velocity was significantly greater in relapse of large bowel Crohns disease and ulcerative colitis than in small bowel Crohns disease alone, although for the subgroups in stage 1 puberty (prepubertal) the differences were not significant. Inadequate growth in chronic inflammatory bowel disease is currently ascribed to inadequate nutrition and TNF alpha may contribute to this through its cachexia inducing effects. It may, in addition, diminish pituitary growth hormone release. These results suggest that production of TNF alpha may be associated with growth failure in relapse of colonic inflammatory bowel disease.

The mucosal immune system

This article outlines the lymphoid structures and cell types important in the intestinal immune response. Particular attention is paid to differences between rodents and man where there appears to be fundamental differences in the sources of the T and B cells which populate the mucosa. The majority of the data still suggest that Peyers patches are the inductive site of mucosal immunity and the mucosa (lamina propria and epithelium) is the effector site, but there is growing realization that mucosal immune responses can occur in the absence of Peyers patches and that antigen sampling may also occur in the lamina propria.

Citrobacter rodentium of mice and man

The major classes of enteric bacteria harbour a conserved core genomic structure, common to both commensal and pathogenic strains, that is most likely optimized to a life style involving colonization of the host intestine and transmission via the environment. In pathogenic bacteria this core genome framework is decorated with novel genetic islands that are often associated with adaptive phenotypes such as virulence. This classical genome organization is well illustrated by a group of extracellular enteric pathogens, which includes enteropathogenic Escherichia coli (EPEC), enterohaemorrhagic E. coli (EHEC) and Citrobacter rodentium, all of which use attaching and effacing (A/E) lesion formation as a major mechanism of tissue targeting and infection. Both EHEC and EPEC are poorly pathogenic in mice but infect humans and domestic animals. In contrast, C. rodentium is  a  natural  mouse  pathogen  that  is  related  to E.  coli, hence providing an excellent in vivo model for A/E lesion forming pathogens. C. rodentium also provides a model of infections that are mainly restricted to the lumen of the intestine. The mechanisms by which the immune system deals with such infections has become a topic of great interest in recent years. Here we review the literature of C. rodentium from its emergence in the mid‐1960s to the most contemporary reports of colonization, pathogenesis, transmission and immunity.

Mucosal healing and a fall in mucosal pro-inflammatory cytokine mRNA induced by a specific oral polymeric diet in paediatric Crohn’s disease

Although enteral nutrition is a recognized form of treatment for intestinal Crohn’s disease, there are persisting problems with feed palatability and only limited data as to its mode of action.

Inflammatory processes have differential effects on claudins 2, 3 and 4 in colonic epithelial cells

Claudin proteins comprise a recently described family of tight junction proteins that differentially regulate paracellular permeability. Since other tight junction proteins show alterations in distribution or expression in inflammatory bowel disease (IBD) we assessed expression of claudins (CL) 2, 3 and 4 in IBD. CL 2 was strongly expressed along the inflamed crypt epithelium, whilst absent or barely detectable in normal colon. In contrast, CL 3 and 4 were present throughout normal colonic epithelium and were reduced or redistributed in the diseased surface epithelium. In a T84-cell culture model of the gut barrier, paracellular permeability decreased with time after plating and correlated with a marked decrease in the expression of CL 2. Addition of IFNγ/TNFα led to further decreases in CL 2 and 3, the redistrbution of CL 4 and a marked increase in paracellular permeability. Conversely, IL-13 dramatically increased CL 2, with little effect on CL 3 or 4, but also resulted in increased paracellular permeability. Expression of CL 2 did not correlate with proliferation or junctional reorganisation after calcium ion depletion. Re-expression of CL 2 in response to IL-13 was inhibited by phophatidylinositol 3 kinase inhibitor, LY294002, which also restored the ion permeability to previous levels. CL 2 expression could be stimulated in the absence of IL-13 by activation of phospho-Akt in the phophatidylinositol 3 kinase pathway. These results suggest that INFγ/TNFα and IL-13 have differential effects on CL 2, 3 and 4 in tight junctions, which may lead to increased permeability via different mechanisms.

Curcumin as a therapeutic agent: the evidence from in vitro , animal and human studies

Curcumin is the active ingredient of turmeric. It is widely used as a kitchen spice and food colorant throughout India, Asia and the Western world. Curcumin is a major constituent of curry powder, to which it imparts its characteristic yellow colour. For over 4000 years, curcumin has been used in traditional Asian and African medicine to treat a wide variety of ailments. There is a strong current public interest in naturally occurring plant-based remedies and dietary factors related to health and disease. Curcumin is non-toxic to human subjects at high doses. It is a complex molecule with multiple biological targets and different cellular effects. Recently, its molecular mechanisms of action have been extensively investigated. It has anti-inflammatory, antioxidant and anti-cancer properties. Under some circumstances its effects can be contradictory, with uncertain implications for human treatment. While more studies are warranted to further understand these contradictions, curcumin holds promise as a disease-modifying and chemopreventive agent. We review the evidence for the therapeutic potential of curcumin from in vitro studies, animal models and human clinical trials.

Characterisation of Acute Murine Dextran Sodium Sulphate Colitis: Cytokine Profile and Dose Dependency

Background/Aims: In our experience with the acute murine dextran sodium sulphate (DSS) model of experimental colitis, we noted both interstrain and interanimal variations in daily water consumption. One might critically question whether observed differences in injuries are just a dose dependency phenomenon reflecting variations in DSS intake. To clarify this important topic, we performed a dose and concentration dependency study of DSS in Balb/c mice. We also determined Th1 and Th2 cytokine levels to compare the cytokine profile to that from inflammatory bowel disease (IBD). Methods: In four groups (14 animals each group) different concentrations of DSS (0, 2.5, 5 and 7.5%) were given for 7 days ad libitum. Mucosal injury of the entire colon was histologically assessed and graded. Cytokine levels were determined by competitive quantitative RT-PCR. Results: A linear increase in the crypt damage score was noted with increasing concentrations (0, 4.9 ± 0.7, 11.9 ± 0.5 and 18.9 ± 1.3, respectively), but the total dose of DSS intake did not correlate with mucosal damage. Progressive upregulation in the transcripts for Th1 cytokines (IL-12, IFN-γ, IL-1, TNF-α) was observed with increasing dosage of DSS. Interestingly, an increase in IL-10, but not IL-4 mRNA transcripts was also noted. Discussion: Acute DSS-induced mucosal injury is dependent on the administered DSS water concentration but not on the consumed DSS dose. The cytokine profile is a classic Th1 response and is similar to that of various inflammatory conditions in the colon. Conclusions: Minor variations in fluid consumption do not affect the severity of DSS-induced injury in mice. The acute murine DSS colitis model is useful for studying the pathophysiological aspects of colonic inflammatory diseases as IBD and for evaluating new potential therapeutic agents