Nonclassical CD1d-restricted NK T cells that produce IL-13 characterize an atypical Th2 response in ulcerative colitis

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Osteopontin/Eta-1 upregulated in Crohn's disease regulates the Th1 immune response

BACKGROUND AND AIMS

The pathogenesis of Crohn's disease (CD), a chronic inflammatory bowel disease characterised by a Th1 immune response, remains unclear. Osteopontin (OPN) is a phosphoprotein known as an adhesive bone matrix protein. Recent studies have shown that OPN plays an important role in lymphocyte migration, granuloma formation, and interleukin 12 (IL-12) production. The present study investigated expression and the pathophysiological role of OPN in CD.

METHODS

Plasma OPN concentration was measured by enzyme linked immunosorbent assay. Expression of OPN in human intestinal mucosa was determined using reverse transcription-polymerase chain reaction and western blot, and localisation of OPN was examined by immunohistochemistry. Expression of integrin beta3, an OPN receptor, on lamina propria mononuclear cells (LPMC) was assessed by flow cytometry. Functional activation of OPN in LPMC was investigated by measuring the production of cytokines.

RESULTS

Plasma OPN concentration was significantly higher in patients with CD compared with normal controls or patients with ulcerative colitis (UC). OPN was upregulated in intestinal mucosa from UC and CD patients. OPN producing cells were epithelial or IgG producing plasma cells, or partial macrophages. OPN was detected in areas surrounding granuloma from mucosa in CD. Integrin beta3 expressing macrophages infiltrated inflamed mucosa in UC and CD; in contrast, there was no expression of integrin beta3 on intestinal macrophages in normal mucosa. OPN induced production of IL-12 from LPMC in CD but not in normal controls or UC.

CONCLUSIONS

Increased OPN expression facilitates cytokine production and is closely involved in the Th1 immune response associated with CD.

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 IFNgamma/TNFalpha 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 INFgamma/TNFalpha and IL-13 have differential effects on CL 2, 3 and 4 in tight junctions, which may lead to increased permeability via different mechanisms.

Interleukin-13 is the key effector Th2 cytokine in ulcerative colitis that affects epithelial tight junctions, apoptosis, and cell restitution

BACKGROUND & AIMS

Ulcerative colitis (UC) is characterized by a Th2 immune response with inflammation and epithelial barrier dysfunction. So far, Th2 cytokines have not been shown to directly influence epithelial barrier function.

METHODS

Lamina propria mononuclear cells (LPMCs) were stimulated and interleukin (IL)-13 was measured by enzyme-linked immunosorbent assay. Functional IL-13 and IL-4 effects were studied on HT-29/B6 colonic epithelial cells in Ussing chambers and by conductance scanning. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assays. IL-13/IL-4 receptors were analyzed by reverse-transcription polymerase chain reaction and immunofluorescence. Western blotting combined with immunofluorescence was used to detect tight junction proteins. Furthermore, restitution velocity was measured. Finally, mucosal biopsy specimens from patients with UC were compared with cultured cells for these features.

RESULTS

LPMCs from patients with UC produced large amounts of IL-13 (985 +/- 73 pg/mL), much more than from controls or patients with Crohn's disease. IL-13Ralpha1 and IL-4Ralpha receptors were present in HT-29/B6 cells and colonic epithelial cells of control patients and patients with UC. IL-13 had a dose-dependent effect on transepithelial resistance of HT-29/B6 monolayers (reduction to 60% +/- 4%), whereas IL-4 had no effect. This was due to an increased number of apoptotic cells (5.6-fold +/- 0.9-fold) and an increased expression of the pore-forming tight junction protein claudin-2 to 295% +/- 37%, both of which contributed equally. Finally, epithelial restitution velocity decreased from 15.1 +/- 0.6 to 10.6 +/- 0.5 microm/h after treatment with IL-13. Parallel changes were observed in human samples, with an increase in claudin-2 expression to 956% +/- 252%.

CONCLUSIONS

IL-13 was identified as an important effector cytokine in UC that impairs epithelial barrier function by affecting epithelial apoptosis, tight junctions, and restitution velocity.

Recognition of lipid antigens by T cells

Recent studies have shown that the recognition of lipid antigens by the immune system is important for defence against infection and other diseases, and that lipid-specific responses occur at higher frequencies than previously suspected. Thanks to several recent advances in this field, we now have a better appreciation of the molecular and cellular requirements of T-cell stimulation by lipids. These findings have raised new questions about the mechanisms of lipid presentation, the priming and clonal expansion of lipid-specific T cells, and their differentiation into memory cells. A greater understanding of lipid-specific T cells and the molecular mechanisms of lipid immunogenicity should facilitate the development of lipid-based vaccines.

Signal transducers and activators of transcription 3 signaling pathway: an essential mediator of inflammatory bowel disease and other forms of intestinal inflammation

Crohn's disease (CD) and ulcerative colitis (UC), the two major forms of chronic inflammatory bowel disease (IBD), are characterized by mucosal immune cell activation that is driven by a cytokine imbalance. Several cytokines involved in IBD act through the activation of the signal transducers and activators of transcription (STAT) family. We investigated the activation of STAT3 in the mucosa of CD and UC patients, and evaluated whether this event is specific for IBD patients. Using immunofluorescence and immunoblotting, total and phosphorylated STAT3 levels were assessed in biopsy specimens, isolated lamina propria mononuclear cells, and peripheral blood mononuclear cells from patients with CD, UC, other forms of intestinal inflammation, and control subjects. Immunoblotting revealed phosphorylated STAT3 in mucosal biopsy specimens from patients with CD, UC, celiac disease, and acute self-limited colitis, but not in the normal mucosa of control subjects. In IBD patients, STAT3 activation was confined to actively inflamed areas. Accordingly, activated STAT3 was detected in isolated lamina propria mononuclear cells from inflamed IBD tissues, but not in peripheral blood mononuclear cells from control subjects or IBD patients. Immunofluorescence demonstrated that the sources of activated STAT3 were macrophages and T lymphocytes, but not neutrophils. STAT3 activation also was detected in T cells infiltrating the duodenal mucosa of celiac disease patients. We conclude that STAT3 signaling occurs in both CD and UC, where it is strictly confined to areas of active inflammation and is limited to infiltrating macrophages and T cells. The occurrence of STAT3 signaling in other acute and chronic intestinal inflammatory conditions suggests that, rather than a specific feature of IBD, it represents a fundamental signaling pathway that is shared by multiple forms of gut inflammation.

Etiology of Crohn’s disease: Do certain food additives cause intestinal inflammation by molecular mimicry of mycobacterial lipids?

Crohn's disease is a chronic granulomatous inflammation of the gastrointestinal tract which was first described in the beginning of the 20th century. The histological similarity with intestinal tuberculosis has led to the assumption of an involvement of mycobacteria and mycobacterial antigens, respectively, in the etiology. A major defense mechanism against mycobacterial lipid antigens is the CD1 system which includes CD1 molecules for antigen presentation and natural killer T cells for recognition and subsequent production of cytokines like interferon-gamma and tumour necrosis factor-alpha. These cytokines promote granulomatous transformation. Various food additives, especially emulsifiants, thickeners, surface-finishing agents and contaminants like plasticizers share structural domains with mycobacterial lipids. It is therefore hypothesized, that these compounds are able to stimulate by molecular mimicry the CD1 system in the gastrointestinal mucosa and to trigger the pro-inflammatory cytokine cascade. The understanding of Crohn's disease as a CD1-mediated delayed-type hypersensitivity to certain food additives would lead to strong emphasis on a dietary treatment. Related aspects of pathology, physiology and epidemiology of Crohn's disease are presented.

Single dose of OCH improves mucosal T helper type 1/T helper type 2 cytokine balance and prevents experimental colitis in the presence of valpha14 natural killer T cells in mice

BACKGROUND AND AIMS

Valpha14 natural killer T (NKT) cells seem to play important roles in the development of various autoimmune diseases. However, the pathophysiologic role of NKT cells in inflammatory bowel disease remains unclear. To clarify the mechanism by which the activation of NKT cells mediates protection against intestinal inflammation, we investigated the antiinflammatory role of specifically activated Valpha14 NKT cells by glycolipids in a mouse experimental model of colitis induced by dextran sulfate sodium (DSS).

METHODS

Colitis was induced in C57BL/6 mice by the oral administration of 1.5% DSS for 9 days. A single dose of OCH or alpha-galactosylceramide, a ligand for NKT cells, was administered on day 3 after the induction of colitis. Body weights and colonic mucosal injury were assessed in each glycolipid-treated group. Interferon-gamma and interleukin-4 levels in the supernatants from colonic lamina propria lymphocytes (LPLs) were measured by enzyme-linked immunosorbent assay.

RESULTS

The administration of a single dose of OCH attenuated colonic inflammation, as defined by body weights and histologic injury. The protective effects of OCH could not be observed in Valpha14 NKT cell-deficient mice. In vivo treatment with OCH had improved the interferon-gamma/interleukin-4 ratio from colonic LPLs on day 9 after DSS treatment.

CONCLUSION

The present data indicated that the activation of Valpha14 NKT cells by OCH plays a pivotal role in mediating intestinal inflammation via altered mucosal T-helper type 1/type 2 responses. Therapeutic strategies that are designed to activate specifically Valpha14 NKT cells may prove to be beneficial in treating intestinal inflammation.

New insights into the pathogenesis of inflammatory bowel disease

Several important advances have been made over the past few years that have expanded our knowledge of the immunology of the gut and its complex interactions with commensal organisms. Critical developments in our understanding of the pathogenesis of inflammatory bowel diseases include the discovery of Toll-like receptors and the identification of not one but two susceptibility genes for Crohn's disease. We have furthered our understanding significantly concerning the role of dendritic cells in the development of gut inflammation. In addition, a novel hypothesis suggesting a protective role for helminthic infections is gaining experimental evidence and direct clinical applicability. In this review we summarize these key developments in the pathophysiology of inflammatory bowel disease and attempt to ascribe clinical relevance where applicable.

To be or not to be NKT: natural killer T cells in the liver

Much of the hepatology literature to date has focused on the adaptive, antigen-specific response mediated by classical T-cell populations in both the protection and pathogenesis of liver disease. However, the liver is selectively enriched for cells representative of innate immunity, including natural killer T (NKT) cells. In particular, certain CD1d-reactive T cells are present at much higher frequencies in the liver than in the peripheral blood. Although these cells have previously been defined mostly on the basis of phenotypic markers, recent emerging literature regarding NKT cell populations has revealed considerable functional complexity. This review summarizes the recent literature regarding NKT cells, which may have important roles in a variety of liver diseases. Although there is an abundance of literature on the phenotype, distribution, and function of these cells in mice, much less is known about them in human health or liver diseases.