Tumor necrosis factor family members and inflammatory bowel disease

LIGHT-related molecular network in the regulation of innate and adaptive immunity

The LIGHT-related molecular network is composed of at least seven interacting receptors and ligands. Recent studies reveal that this network has profound immune regulatory functions for both innate and adaptive immunity. Experimental data support the concept that this network may also play roles in the pathogenesis of human diseases including cancer, infection, transplantation tolerance, and autoimmune diseases. In this review, we attempt to dissect each molecular interaction in detail and assemble them in the context of their roles in the pathogenesis and possible therapeutic potential in human diseases.

Colonic involvement in Stevens-Johnson syndrome

Severe gastrointestinal tract involvement is a rare manifestation of Stevens-Johnson syndrome (SJS). The case is described of a 17 year old man who developed SJS secondary to phenytoin. In addition to the cutaneous, ocular, and oral mucosal lesions typical of SJS, he also developed persistent, bloody diarrhoea associated with life threatening malnutrition. Serial colonoscopy showed severe and progressive colitis. He was treated with a combination of long term nutritional support, probiotic therapy, and supportive measures. He was eventually discharged from hospital six months after admission when the diarrhoea improved and he began to gain weight.

A new transcription factor that regulates TNF-alpha gene expression, LITAF, is increased in intestinal tissues from patients with CD and UC

BACKGROUND

The proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) plays a key role in the pathogenesis of Crohn's disease (CD) and ulcerative colitis (UC). Recently, a new transcription factor termed LITAF (lipopolysaccharide-induced TNF-alpha factor) was shown to mediate TNF-alpha expression in human macrophages by direct binding to specific sequences in the promoter region of the TNF-alpha gene.

METHODS

In this report, we identified LITAF in resected ileal and colonic tissues from patients with CD and UC by immunohistochemistry, real-time polymerase chain reaction, and Western blot analysis. LITAF expression in inflamed and noninflamed areas of the tissues was compared.

RESULTS

This is the first demonstration of LITAF, a newly discovered transcription factor that regulates TNF-alpha gene transcription in ileal and colonic tissues from patients with either CD or UC. LITAF immunostaining was localized to lamina propria macrophages and was markedly increased relative to tissues from controls without inflammatory bowel disease. In patients with CD, a 5-fold increase in LITAF mRNA was measurable in noninflamed colonic tissues compared with controls without inflammatory bowel disease. LITAF mRNA in tissues from inflamed areas of the colon was increased by an additional 60% compared with noninflamed tissues. In patients with UC, LITAF mRNA levels in colonic tissues resected from noninflamed areas were elevated 15-fold above nondisease controls, but they were not different in tissues resected from inflamed areas. Western blot analysis showed that in patients with CD, there was a marked increase in LITAF protein in inflamed areas compared with noninflamed areas. LITAF protein levels were not different between noninflamed and inflamed tissues obtained from patients with UC. TNF-alpha mRNA and protein levels paralleled LITAF. Similarly, in inflamed ileal tissues from patients with CD, LITAF is also localized to lamina propria macrophages. LITAF mRNA and LITAF protein were significantly increased in inflamed ileal tissues compared with noninflamed areas.

CONCLUSIONS

LITAF is readily detectable in ileal and colonic tissues from patients with either CD or UC, is significantly elevated above controls, and is localized to macrophages, a major source of TNF-alpha. These data provide strong evidence of a role for LITAF in the pathophysiological regulation of the TNF-alpha gene and underscore the potential value of anti-LITAF strategies in the clinical management of these diseases.

Role of tumor necrosis factor alpha (TNF-alpha) and interleukin-10 in the pathogenesis of severe murine monocytotropic ehrlichiosis: increased resistance of TNF receptor p55- and p75-deficient mice to fatal ehrlichial infection

Intraperitoneal (i.p.) infection with a high dose of a highly virulent Ehrlichia strain (IOE) results in a toxic shock-like syndrome characterized by severe liver injury and systemic overproduction of tumor necrosis factor alpha (TNF-alpha) by CD8+ T cells. We examined the role of TNF-alpha and TNF receptors in high-dose-IOE-induced shock/liver injury. TNF receptor (TNFR) I/II-/- mice lacking both the p55 and p75 receptors for this cytokine were more resistant to IOE-induced liver injury than their wild-type background controls. TNFR I/II-/- mice survived longer, dying between 15 and 18 days, with evidence of mild liver necrosis/apoptosis. In contrast, wild-type mice were not rescued from the lethal effect of IOE by TNF-alpha neutralization. TNF-alpha-depleted mice developed severe liver injury and succumbed to disease between days 9 and 11 postinfection, similar to sham-treated, infected wild-type mice. Although IFN-gamma production in the spleens of IOE-infected TNFR I/II-/- and TNF-alpha-depleted mice was higher than that detected in wild-type controls, these mice had higher bacterial burdens than infected controls. Following high-dose IOE challenge, TNFR I/II-/- and TNF-alpha-depleted mice have an early increase in IL-10 levels in sera and spleens, which was produced mainly by adherent spleen cells. In contrast, a late burst of interleukin-10 (IL-10) was observed in control mice. Nonadherent spleen cells were the major source of IL-10 in IOE-infected wild-type mice. We conclude that TNFR I/II and TNF-alpha participate in Ehrlichia-induced shock and host defense by regulating liver injury and controlling ehrlichial burden. Our data suggest that fatal ehrlichiosis could be a multistep process, where TNF-alpha is not solely responsible for mortality.

Proinflammatory CD4+CD45RBhi Lymphocytes Promote Mammary and Intestinal Carcinogenesis in ApcMin/+ Mice

Cancers of breast and bowel are increasingly frequent in humans. Chronic inflammation is known to be a risk factor for these malignancies, yet cellular and molecular mechanisms linking inflammation and carcinogenesis remain poorly understood. Here, we apply a widely used T-cell transfer paradigm, involving adoptive transfer of proinflammatory CD4+ CD45RB(hi) (T(E)) cells to induce inflammatory bowel disease (IBD) in mice, to investigate roles of inflammation on carcinogenesis in the Apc(Min/+) mouse model of intestinal polyposis. We find that transfer of T(E) cells significantly increases adenoma multiplicity and features of malignancy in recipient Apc(Min/+) mice. Surprisingly, we find that female Apc(Min/+) recipients of T(E) cells also rapidly develop mammary tumors. Both intestinal polyposis and mammary adenocarcinoma are abolished by cotransfer of anti-inflammatory CD4+ CD45RB(lo) regulatory lymphocytes or by neutralization of key proinflammatory cytokine tumor necrosis factor-alpha. Lastly, down-regulation of cyclooxygenase-2 and c-Myc expression is observed coincident with tumor regression. These findings define a novel mouse model of inflammation-driven mammary carcinoma and suggest that epithelial carcinogenesis can be mitigated by anti-inflammatory cells and cytokines known to regulate IBD in humans and mice.

Alterations in intestinal fatty acid metabolism in inflammatory bowel disease

Inflammatory bowel disease (IBD) constitutes a severe intestinal disorder in developed countries with increasing incidence worldwide. Upcoming evidence indicates an important role of intestinal epithelial barrier function in the development of IBD. Fatty acids exert nutritional and protective effects on enterocytes, serve as activators of transcription and constitute precursors of inflammatory mediators. The aim of this study was to investigate differential regulation of genes involved in fatty acid uptake and endogenous fatty acid biosynthesis in IBD. Mucosal biopsy specimens from non-affected regions of the intestine were subjected to DNA microarray analysis. Gene array analysis revealed a variety of genes involved in fatty acid uptake and synthesis to be differentially expressed in ileum and colon of selected IBD patients. To verify these results, real-time RT-PCR was performed for selected regulated candidate genes in larger IBD sample numbers. In single biopsy analysis long chain acyl-CoA synthetase (ACSL) 1 and 4 were upregulated in IBD (P<0.05), while a significant decrease in fatty acid synthase expression was found in ileum and colon of ulcerative colitis patients (P<0.001). Expression of the transcription factor liver X receptor (LXR) which was previously shown to induce fatty acid synthase gene expression was not altered on mRNA level in IBD. However, in cell culture experiments using the human intestinal cell line LS174T induction of fatty acid synthase by the LXR ligand T0901317 was inhibited by TNFalpha. Moreover, these experiments indicated a decrease of LXR protein levels by TNFalpha treatment. These data suggest that the decrease of fatty acid synthase expression in ulcerative colitis patients could be at least partially due to a loss of LXR expression and function in the presence of pro-inflammatory cytokines. Observed alterations in expression of genes of fatty acid metabolism may contribute to the pathophysiology of ulcerative colitis.

Lymphotoxin-beta receptor signaling is required for the homeostatic control of HEV differentiation and function

The lymphotoxin axis is important for the maintenance of several specialized lymphoid microenvironments in secondary lymphoid tissue. Lymphoid-tissue architecture is highly plastic and requires continual homeostatic signaling to maintain its basal functional state. The cellularity of lymph nodes in adult mice was reduced by systemic blockade of lymphotoxin-beta receptor (LTbeta R) signaling with a soluble decoy receptor both in resting and reactive settings. This reduction in cellularity resulted from greatly impaired lymphocyte entry into lymph nodes due to decreased levels of peripheral lymph node addressing (PNAd) and MAdCAM on high endothelial venules (HEV). LTbeta R signaling was required to maintain normal levels of RNA expression of MAdCAM, and also of PNAd by regulating the expression of key enzymes and scaffold proteins required for its assembly. Thus, the homeostatic maintenance of functional HEV status in adult mice relies largely on LTbeta R signaling.