CD40-mediated immune-nonimmune cell interactions induce mucosal fibroblast chemokines leading to T-cell transmigration

Contribution of Blood Vessel Activation, Remodeling and Barrier Function to Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBDs) consist of a group of chronic inflammatory disorders with a complex etiology, which represent a clinical challenge due to their often therapy-refractory nature. In IBD, inflammation of the intestinal mucosa is characterized by strong and sustained leukocyte infiltration, resulting in the loss of epithelial barrier function and subsequent tissue destruction. This is accompanied by the activation and the massive remodeling of mucosal micro-vessels. The role of the gut vasculature in the induction and perpetuation of mucosal inflammation is receiving increasing recognition. While the vascular barrier is considered to offer protection against bacterial translocation and sepsis after the breakdown of the epithelial barrier, endothelium activation and angiogenesis are thought to promote inflammation. The present review examines the respective pathological contributions of the different phenotypical changes observed in the microvascular endothelium during IBD, and provides an overview of potential vessel-specific targeted therapy options for the treatment of IBD.

PD-L1 Inhibits T Cell-Induced Cytokines and Hyaluronan Expression via the CD40-CD40L Pathway in Orbital Fibroblasts From Patients With Thyroid Associated Ophthalmopathy

Thyroid associated ophthalmopathy (TAO), characterized by T cell infiltration and orbital fibroblast activation, is an organ-specific autoimmune disease which is still short of effective and safety therapeutic drugs. The PD-1/PD-L1 pathway has been reported hindering the progression of Graves’ disease to some extent by inhibiting T cell activity, and tumor therapy with a PD-1 inhibitor caused some adverse effects similar to the symptoms of TAO. These findings suggest that the PD-1/PD-L1 pathway may be associated with the pathogenesis of TAO. However, it remains unknown whether the PD-1/PD-L1 pathway is involved in orbital fibroblast activation. Here, we show that orbital fibroblasts from patients with TAO do not express PD-L1. Based on in vitro OF-T cell co-culture system, exogenous PD-L1 weakens T cell-induced orbital fibroblast activation by inhibiting T cell activity, resulting in reduced production of sICAM-1, IL-6, IL-8, and hyaluronan. Additionally, exogenous PD-L1 treatment also inhibits the expression of CD40 and the phosphorylation levels of MAPK and NF-κB pathways in orbital fibroblasts of the OF-T cell co-culture system. Knocking down CD40 with CD40 siRNA or down-regulating the phosphorylation levels of MAPK and NF-κB pathways with SB203580, PD98059, SP600125, and PDTC can both reduce the expression of these cytokines and hyaluronan. Our study demonstrates that the orbital immune tolerance deficiency caused by the lack of PD-L1 in orbital fibroblasts may be one of the causes for the active orbital inflammation in TAO patients, and the utilization of exogenous PD-L1 to reconstruct the orbital immune tolerance microenvironment may be a potential treatment strategy for TAO.

The Future of Precision Medicine to Predict Outcomes and Control Tissue Remodeling in Inflammatory Bowel Disease

Inflammatory bowel disease is characterized by significant interindividual heterogeneity. With a wider selection of pharmacologic and nonpharmacologic interventions available and in advanced developmental stages, a priority for the coming decade is to determine accurate methods of predicting treatment response and disease course. Precision medicine strategies will allow tailoring of preventative and therapeutic decisions to individual patient needs. In this review, we consider the future of precision medicine in inflammatory bowel disease. We discuss the critical need to extend from research focused on short-term symptomatic response to integrative multi-omic systems biology strategies to identify and validate biomarkers that underpin precision approaches. Crucially, the international community has collective responsibility to provide well-phenotyped and -curated longitudinal datasets for scientific discovery and validation. Research must also study broader aspects of the immune response, including components of the extracellular matrix, to better understand biological pathways initiating and perpetuating tissue fibrosis and longer-term disease complications.

Molecular basis and therapeutic implications of CD40/CD40L immune checkpoint

The CD40 receptor and its ligand CD40L is one of the most critical molecular pairs of the stimulatory immune checkpoints. Both CD40 and CD40L have a membrane form and a soluble form generated by proteolytic cleavage or alternative splicing. CD40 and CD40L are widely expressed in various types of cells, among which B cells and myeloid cells constitutively express high levels of CD40, and T cells and platelets express high levels of CD40L upon activation. CD40L self-assembles into functional trimers which induce CD40 trimerization and downstream signaling. The canonical CD40/CD40L signaling is mediated by recruitment of TRAFs and NF-κB activation, which is supplemented by signal pathways such as PI3K/AKT, MAPKs and JAK3/STATs. CD40/CD40L immune checkpoint leads to activation of both innate and adaptive immune cells via two-way signaling. CD40/CD40L interaction also participates in regulating thrombosis, tissue inflammation, hematopoiesis and tumor cell fate. Because of its essential role in immune activation, CD40/CD40L interaction has been regarded as an attractive immunotherapy target. In recent years, significant advance has been made in CD40/CD40L-targeted therapy. Various types of agents, including agonistic/antagonistic monoclonal antibodies, cellular vaccines, adenoviral vectors and protein antagonist, have been developed and evaluated in early-stage clinical trials for treating malignancies, autoimmune diseases and allograft rejection. In general, these agents have demonstrated favorable safety and some of them show promising clinical efficacy. The mechanisms of benefits include immune cell activation and tumor cell lysis/apoptosis in malignancies, or immune cell inactivation in autoimmune diseases and allograft rejection. This review provides a comprehensive overview of the structure, processing, cellular expression pattern, signaling and effector function of CD40/CD40L checkpoint molecules. In addition, we summarize the progress, targeted diseases and outcomes of current ongoing and completed clinical trials of CD40/CD40L-targeted therapy.

CD40 Receptor Knockout Protects against Microcystin-LR (MC-LR) Prolongation and Exacerbation of Dextran Sulfate Sodium (DSS)-Induced Colitis

Inflammatory Bowel Disease (IBD) is one of the most common gastrointestinal (GI) disorders around the world, and includes diagnoses such as Crohn’s disease and ulcerative colitis. The etiology of IBD is influenced by genetic and environmental factors. One environmental perturbagen that is not well studied within the intestines is microcystin-leucine arginine (MC-LR), which is a toxin produced by cyanobacteria in freshwater environments around the world. We recently reported that MC-LR has limited effects within the intestines of healthy mice, yet interestingly has significant toxicity within the intestines of mice with pre-existing colitis induced by dextran sulfate sodium (DSS). MC-LR was found to prolong DSS-induced weight loss, prolong DSS-induced bloody stools, exacerbate DSS-induced colonic shortening, exacerbate DSS-induced colonic ulceration, and exacerbate DSS-induced inflammatory cytokine upregulation. In addition, we previously reported a significant increase in expression of the pro-inflammatory receptor CD40 in the colons of these mice, along with downstream products of CD40 activation, including plasminogen activator inhibitor-1 (PAI-1) and monocyte chemoattractant protein-1 (MCP-1). In the current study, we demonstrate that knocking out CD40 attenuates the effects of MC-LR in mice with pre-existing colitis by decreasing the severity of weight loss, allowing a full recovery in bloody stools, preventing the exacerbation of colonic shortening, preventing the exacerbation of colonic ulceration, and preventing the upregulation of the pro-inflammatory and pro-fibrotic cytokines IL-1β, MCP-1, and PAI-1. We also demonstrate the promising efficacy of a CD40 receptor blocking peptide to ameliorate the effects of MC-LR exposure in a proof-of-concept study. Our findings suggest for the first time that MC-LR acts through a CD40-dependent mechanism to exacerbate colitis.

Platelet hyaluronidase-2 regulates the early stages of inflammatory disease in colitis

Platelets are specialized cells essential for hemostasis that also function as crucial effectors capable of mediating inflammatory and immune responses. These sentinels continually survey their environment and discriminate between homeostatic and danger signals such as modified components of the extracellular matrix. The glycosaminoglycan hyaluronan (HA) is a major extracellular matrix component that coats the vascular lumen and, under normal conditions, restricts access of inflammatory cells. In response to tissue damage, the endothelial HA matrix enhances leukocyte recruitment and regulates the early stages of the inflammatory response. We have shown that platelets can degrade HA from the surface of activated endothelial cells via the enzyme hyaluronidase-2 (HYAL2) and that HYAL2 is deficient in platelets isolated from patients with inflammatory bowel disease (IBD). Platelets are known to be involved in the pathogenesis of several chronic disease states, including IBD, but they have been largely overlooked in the context of intestinal inflammation. We therefore wanted to define the mechanism by which platelet HYAL2 regulates the inflammatory response during colitis. In this study, we provide evidence that HA catabolism is disrupted in human intestinal microvascular endothelial cells isolated from patients with IBD. Furthermore, mice deficient in HYAL2 are more susceptible to an acute model of colitis, and this increased susceptibility is abrogated by transfusion of HYAL2-competent platelets. Finally, we show that platelets, via HYAL2-dependent degradation of endothelial HA, regulate the early stages of inflammation in colitis by limiting leukocyte extravasation.

Targeting the CD40-CD40L pathway in autoimmune diseases: Humoral immunity and beyond

CD40 is a TNF receptor superfamily member expressed on both immune and non-immune cells. Interactions between B cell-expressed CD40 and its binding partner, CD40L, predominantly expressed on activated CD4+ T cells, play a critical role in promoting germinal center formation and the production of class-switched antibodies. Non-hematopoietic cells expressing CD40 can also engage CD40L and trigger a pro-inflammatory response. This article will highlight what is known about the biology of the CD40-CD40L axis in humans and describe the potential contribution of CD40 signaling on both hematopoietic and non-hematopoietic cells to autoimmune disease pathogenesis. Additionally, novel therapeutic approaches to target this pathway, currently being evaluated in clinical trials, are discussed.

Disruption of the Hedgehog signaling pathway in inflammatory bowel disease fosters chronic intestinal inflammation

Hedgehog (Hh) signaling is essential for intestinal homeostasis and has been associated with inflammation and tissue repair. We hypothesized that Hh signaling could affect the inflammatory process in inflammatory bowel disease (IBD). For this purpose, colon specimens from the inflamed and non-inflamed mucosa of 15 patients with Crohn's disease (CD), 15 with ulcerative colitis, and 15 controls were analyzed by immunohistochemistry and real-time PCR. The production and modulation of cytokines were measured by ELISA from culture explants. Apoptosis was assessed by TUNEL and caspase-3 activity assays. Chemotaxis was evaluated using a transwell system. Primary human intestinal and skin fibroblasts were used for analyzing migration and BrdU incorporation. Hh proteins were generally expressed at the superficial epithelium, and a marked reduction was observed in CD. In the lamina propria, Gli-1 predominantly co-localized with vimentin- and alpha-smooth muscle actin-positive cells, with lower levels observed in CD. In colon explants, Hh stimulation resulted in reduction, while blockade increased, TNF α, IL-17, and TGF β levels. Apoptotic rates were higher in inflamed samples, and they increased after Hh blockade. Levels of Gli-1 mRNA were negatively correlated with caspase-3 activity. Hh blockade increased chemoattraction of monocytes. Primary fibroblasts incorporated more BrdU, but migrated less after Hh blockade. These results suggest that Hh signaling provides a negative feedback to the lamina propria, down-regulating inflammatory cytokines, and inhibiting leukocyte migration and fibroblast proliferation, while favoring fibroblast migration. Therefore, Hh signaling is strongly implicated in the pathogenesis of intestinal inflammation, and it may represent a novel therapeutic target for IBD.

T-helper 2 cytokines, transforming growth factor β1, and eosinophil products induce fibrogenesis and alter muscle motility in patients with eosinophilic esophagitis

BACKGROUND & AIMS

Patients with eosinophilic esophagitis (EoE) often become dysphagic from the combination of organ fibrosis and motor abnormalities. We investigated mechanisms of dysphagia, assessing the response of human esophageal fibroblasts (HEFs), human esophageal muscle cells (HEMCs), and esophageal muscle strips to eosinophil-derived products.

METHODS

Biopsy specimens were collected via endoscopy from the upper, middle, and lower thirds of the esophagus of 18 patients with EoE and 21 individuals undergoing endoscopy for other reasons (controls). Primary cultures of esophageal fibroblasts and muscle cells were derived from 12 freshly resected human esophagectomy specimens. Eosinophil distribution was investigated by histologic analyses of full-thickness esophageal tissue. Active secretion of EoE-related mediators was assessed from medium underlying mucosal biopsy cultures. We quantified production of fibronectin and collagen I by HEF and HEMC in response to eosinophil products. We also measured the expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 by, and adhesion of human eosinophils to, HEFs and HEMCs. Eosinophil products were tested in an esophageal muscle contraction assay.

RESULTS

Activated eosinophils were present in all esophageal layers. Significantly higher concentrations of eosinophil-related mediators were secreted spontaneously in mucosal biopsy specimens from patients with EoE than controls. Exposure of HEFs and HEMCs to increasing concentrations of eosinophil products or co-culture with eosinophils caused HEFs and HEMCs to increase secretion of fibronectin and collagen I; this was inhibited by blocking transforming growth factor β1 and p38 mitogen-activated protein kinase signaling. Eosinophil binding to HEFs and HEMCs increased after incubation of mesenchymal cells with eosinophil-derived products, and decreased after blockade of transforming growth factor β1 and p38 mitogen-activated protein kinase blockade. Eosinophil products reduced electrical field-induced contraction of esophageal muscle strips, but not acetylcholine-induced contraction.

CONCLUSIONS

In an analysis of tissues samples from patients with EoE, we linked the presence and activation state of eosinophils in EoE with altered fibrogenesis and motility of esophageal fibroblasts and muscle cells. This process might contribute to the development of dysphagia.

The Role of STAT1 for Crosstalk between Fibroblasts and Colon Cancer Cells

Signaling between tumor cells and the associated stroma has an important impact on cancer initiation and progression. The tumor microenvironment has a paradoxical role in tumor progression and fibroblasts, a major component of the tumor stroma, have been shown to either inhibit or promote cancer development. In this study, we established that normal intestinal fibroblasts activate STAT1 signaling in colon cancer cells and, in contrast to cancer-associated fibroblasts, inhibit growth of tumor cells. Treatment of 18Co fibroblasts with the proinflammatory cytokine TNFα interfered with their ability to trigger STAT1 signaling in cancer cells. Accordingly, intestinal myofibroblasts isolated from patients with ulcerative colitis or Crohn’s disease, which are activated and produce high levels of TNFα, failed to stimulate STAT1 signaling in tumor cells, demonstrating that activated myofibroblasts lose the ability to trigger growth-inhibitory STAT1 signaling in tumor cells. Finally, we confirmed that silencing of STAT1 in tumor cells alters the crosstalk between tumor cells and fibroblasts, suggesting STAT1 as a novel link between intestinal inflammation and colon cancer. We demonstrated that normal fibroblasts restrain the growth of carcinoma cells, at least in part, through the induction of STAT1 signaling in cancer cells and showed that changes in the microenvironment, as they occur in inflammatory bowel disease, alter the crosstalk between carcinoma cells and fibroblasts, perturb the homeostasis of intestinal tissue, and thereby contribute to tumor progression.

Stromal cells induce Th17 during Helicobacter pylori infection and in the gastric tumor microenvironment

Gastric cancer is associated with chronic inflammation and Helicobacter pylori infection. Th17 cells are CD4(+) T cells associated with infections and inflammation; but their role and mechanism of induction during carcinogenesis is not understood. Gastric myofibroblasts/fibroblasts (GMF) are abundant class II MHC expressing cells that act as novel antigen presenting cells. Here we have demonstrated the accumulation of Th17 in H. pylori-infected human tissues and in the gastric tumor microenvironment. GMF isolated from human gastric cancer and H. pylori infected tissues co-cultured with CD4(+) T cells induced substantially higher levels of Th17 than GMF from normal tissues in an IL-6, TGF-β, and IL-21 dependent manner. Th17 required interaction with class II MHC on GMF for activation and proliferation. These studies suggest that Th17 are induced during both H. pylori infection and gastric cancer in the inflammatory milieu of gastric stroma and may be an important link between inflammation and carcinogenesis.

The role of portal vein thrombosis in the clinical course of inflammatory bowel diseases: report on three cases and review of the literature

Inflammatory bowel diseases are associated with an increased risk of vascular complications. The most important are arterial and venous thromboembolisms, which are considered as specific extraintestinal manifestations of inflammatory bowel diseases. Among venous thromboembolism events, portal vein thrombosis has been described in inflammatory bowel diseases. We report three cases of portal vein thrombosis occurring in patients with active inflammatory bowel disease. In two of them, hepatic abscess was present. Furthermore, we performed a systematic review based on the clinical literature published on this topic.

Inflammation-induced endothelial-to-mesenchymal transition: a novel mechanism of intestinal fibrosis

In addition to mesenchymal cells, endothelial cells may contribute to fibrosis through the process of endothelial-to-mesenchymal transition (EndoMT). We investigated whether human intestinal microvascular endothelial cells (HIMEC) undergo EndoMT and contribute to fibrosis in human and experimental inflammatory bowel disease (IBD). HIMEC were exposed to TGF-β1, IL-1β, and TNF-α or supernatants of lamina propria mononuclear cells (LPMC) and evaluated for morphological, phenotypic, and functional changes compatible with EndoMT. Genomic analysis was used to identify transcription factors involved in the transformation process. Evidence of in situ and in vivo EndoMT was sought in inflamed human and murine intestine. The combination of TGF-β1, IL-1β and TNF-α, or activated LPMC supernatants induced morphological and phenotypic changes consistent with EndoMT with a dominant effect by IL-1. These changes persisted after removal of the inducing agents and were accompanied by functional loss of acetylated LDL-uptake and migratory capacity, and acquisition of de novo collagen synthesis capacity. Sp1 appeared to be the main transcriptional regulator of EndoMT. EndoMT was detected in microvessels of inflammatory bowel disease (IBD) mucosa and experimental colonic fibrosis of Tie2-green fluorescent protein (GFP) reporter-expressing mice. In conclusion, chronic inflammation induces transdifferentiation of intestinal mucosal microvascular cells into mesenchymal cells, suggesting that the intestinal microvasculature contributes to IBD-associated fibrosis through the novel process of EndoMT.

Inflammation-induced endothelial-to-mesenchymal transition: a novel mechanism of intestinal fibrosis

In addition to mesenchymal cells, endothelial cells may contribute to fibrosis through the process of endothelial-to-mesenchymal transition (EndoMT). We investigated whether human intestinal microvascular endothelial cells (HIMEC) undergo EndoMT and contribute to fibrosis in human and experimental inflammatory bowel disease (IBD). HIMEC were exposed to TGF-β1, IL-1β, and TNF-α or supernatants of lamina propria mononuclear cells (LPMC) and evaluated for morphological, phenotypic, and functional changes compatible with EndoMT. Genomic analysis was used to identify transcription factors involved in the transformation process. Evidence of in situ and in vivo EndoMT was sought in inflamed human and murine intestine. The combination of TGF-β1, IL-1β and TNF-α, or activated LPMC supernatants induced morphological and phenotypic changes consistent with EndoMT with a dominant effect by IL-1. These changes persisted after removal of the inducing agents and were accompanied by functional loss of acetylated LDL-uptake and migratory capacity, and acquisition of de novo collagen synthesis capacity. Sp1 appeared to be the main transcriptional regulator of EndoMT. EndoMT was detected in microvessels of inflammatory bowel disease (IBD) mucosa and experimental colonic fibrosis of Tie2-green fluorescent protein (GFP) reporter-expressing mice. In conclusion, chronic inflammation induces transdifferentiation of intestinal mucosal microvascular cells into mesenchymal cells, suggesting that the intestinal microvasculature contributes to IBD-associated fibrosis through the novel process of EndoMT.

Enhanced platelet adhesion induces angiogenesis in intestinal inflammation and inflammatory bowel disease microvasculature

Although angiogenesis is viewed as a fundamental component of inflammatory bowel disease (IBD) pathogenesis, we presently lack a thorough knowledge of the cell type(s) involved in its induction and maintenance in the inflamed intestinal mucosa. This study aimed to determine whether platelet (PLT) adhesion to inflamed intestinal endothelial cells of human origin may favour angiogenesis. Unstimulated or thrombin-activated human PLT were overlaid on resting or tumour necrosis factor (TNF)-α-treated human intestinal microvascular endothelial cells (HIMEC), in the presence or absence of blocking antibodies to either vascular cell adhesion molecule (VCAM)-1, intercellular adhesion molecule (ICAM)-1, integrin α_vβ₃, tissue factor (TF) or fractalkine (FKN). PLT adhesion to HIMEC was evaluated by fluorescence microscopy, and release of angiogenic factors (VEGF and soluble CD40L) was measured by ELISA. A matrigel tubule formation assay was used to estimate PLT capacity to induce angiogenesis after co-culturing with HIMEC. TNF-α up-regulated ICAM-1, α_vβ₃ and FKN expression on HIMEC. When thrombin-activated PLT were co-cultured with unstimulated HIMEC, PLT adhesion increased significantly, and this response was further enhanced by HIMEC activation with TNF-α. PLT adhesion to HIMEC was VCAM-1 and TF independent but ICAM-1, FKN and integrin α_vβ₃ dependent. VEGF and sCD40L were undetectable in HIMEC cultures either before or after TNF-α stimulation. By contrast, VEGF and sCD40L release significantly increased when resting or activated PLT were co-cultured with TNF-α-pre-treated HIMEC. These effects were much more pronounced when PLT were derived from IBD patients. Importantly, thrombin-activated PLT promoted tubule formation in HIMEC, a functional estimate of their angiogenic potential. In conclusion, PLT adhesion to TNF-α-pre-treated HIMEC is mediated by ICAM-1, FKN and α_vβ₃, and is associated with VEGF and sCD40L release. These findings suggest that inflamed HIMEC may recruit PLT which, upon release of pro-angiogenic factors, actively contribute to inflammation-induced angiogenesis.

Blood platelets and inflammation: their relationship with liver and digestive diseases

An expansion of knowledge from basic and clinical research has highlighted the critical role of platelets in inflammation and tissue repair in addition to their established contribution to hemostasis. Activated platelets are a rich source of mediators participating to inflammation and tissue regeneration. Platelet-derived microparticles recapitulate essential platelet functions and their contribution to the pathogenesis of inflammatory diseases has been emphasized. Recent findings suggest that platelets are both friends and foes for the liver. Platelets are essential to liver regeneration, platelet-derived serotonin being critical. However platelets can also exacerbate liver damage, as in immune-mediated injury. The dual role of platelets has recently been exemplified in animal models of liver fibrosis. Platelets release profibrogenic mediators, such as CXC Chemokine Ligand 4, that is instrumental in the progression of liver fibrosis. On the other hand, thrombocytopenia aggravates liver fibrosis, an outcome linked to the downregulation of hepatic stellate cell collagen production by platelet derived hepatocyte growth factor. CD154, a key molecule in inflammation, is expressed by platelets and is a pathogenic mediator in inflammatory bowel disease. Here, we summarize some of the mechanisms linking platelets with inflammation and comment few recent articles indicating why platelets may prove to be important pathogenic mediators in liver and gastrointestinal diseases.

Cytokine loaded biopolymers as a novel strategy to study stem cells during wound-healing processes

The biopolymer matrigel loaded with cytokine can be used for the recruitment in vivo of specific cell populations and as a vector for the preparation of cell cultures. Data demonstrate that the injection of the matrigel biopolymer supplemented with interleukin-8 (IL-8) in the leech Hirudo medicinalis can be used to purify cell populations showing the same morphofunctional and molecular mechanisms of specific populations of vertebrate hematopoietic precursor cells involved in tissue repair. These cells spontaneously differentiated into myofibroblasts. This approach highlights how the innovative use of a cytokine-loaded biopolymer for an in vivo cell sorting method, applied to a simple invertebrate model, can be a tool for studying myofibroblast cell biology and its regulation, step by step.

Role of the endothelium in inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are a complex group of diseases involving alterations in mucosal immunity and gastrointestinal physiology during both initiation and progressive phases of the disease. At the core of these alterations are endothelial cells, whose continual adjustments in structure and function coordinate vascular supply, immune cell emigration, and regulation of the tissue environment. Expansion of the endothelium in IBD (angiogenesis), mediated by inflammatory growth factors, cytokines and chemokines, is a hallmark of active gut disease and is closely related to disease severity. The endothelium in newly formed or inflamed vessels differs from that in normal vessels in the production of and response to inflammatory cytokines, growth factors, and adhesion molecules, altering coagulant capacity, barrier function and blood cell recruitment in injury. This review examines the roles of the endothelium in the initiation and propagation of IBD pathology and distinctive features of the intestinal endothelium contributing to these conditions.

Mesenteric vascular thromboembolism in inflammatory bowel disease: a single center experience

BACKGROUND

Vascular thrombotic complications in inflammatory bowel disease (IBD) are well recognized, although mesenteric vascular thrombotic disease is rare.

METHODS

We describe nine patients in a tertiary care center with IBD that developed thrombosis of the mesenteric arterial or venous vasculature (e.g., mesenteric thrombosis, MT).

RESULTS

Eight subjects developed mesenteric venous thrombosis (five located in the superior mesenteric vein and three located in a branch of the portal vein) and one had a mesenteric arterial embolus, located in the splenic artery. Five subjects had Crohn's disease (CD), and four had ulcerative colitis. The one subject diagnosed with an arterial thrombosis had CD. Mean time from diagnosis of IBD to diagnosis of thrombosis was 24.6 ± 13.5 years. Five of the nine subjects developed mesenteric venous thrombosis while their IBD was clinically in remission. Seven of nine subjects were symptomatic from the development of MT, including bowel infarction that led to development of short bowel syndrome.

CONCLUSION

Mesenteric thrombosis is a rare complication of IBD and may develop during clinical remission, suggesting a potential role for factors other than clinically significant inflammation in its pathogenesis.

Mesenchymal cells of the intestinal lamina propria

The mesenchymal elements of the intestinal lamina propria reviewed here are the myofibroblasts, fibroblasts, mural cells (pericytes) of the vasculature, bone marrow-derived stromal stem cells, smooth muscle of the muscularis mucosae, and smooth muscle surrounding the lymphatic lacteals. These cells share similar marker molecules, origins, and coordinated biological functions previously ascribed solely to subepithelial myofibroblasts. We review the functional anatomy of intestinal mesenchymal cells and describe what is known about their origin in the embryo and their replacement in adults. As part of their putative role in intestinal mucosal morphogenesis, we consider the intestinal stem cell niche. Lastly, we review emerging information about myofibroblasts as nonprofessional immune cells that may be important as an alarm system for the gut and as a participant in peripheral immune tolerance.

New and emerging biologics in the treatment of inflammatory bowel disease: quo vadis?

Inflammatory bowel diseases (IBD) are pathological conditions characterized by chronic inflammation that is primarily the consequence of dysregulation of the immune response. Over the last decade, the advances in the pathophysiology of IBD have paved the way for the development of a number of biological agents that selectively target specific molecules and/or pathways involved in gut inflammation. Although numerous, so far, the only biological therapeutics that are approved for the treatment for IBD are monoclonal antibodies against tumor necrosis factor alpha. This paper systematically reviews the mechanismof-action, efficacy, short-term and, where available, long-term safety of biological agents that target molecules other than tumor necrosis factor alpha, in IBD.

Expression, localization and systemic concentration of vascular endothelial growth factor (VEGF) and its receptors in patients with ulcerative colitis

Vascular endothelial grow factor (VEGF) promotes angiogenesis by activating the specific receptors KDR and Flt-1. We investigate the expression of genes encoding VEGF and its receptors KDR and Flt- 1 by RT-QPCR reaction using Quanti Tect SYBR Green RT-PCR in patients with active and inactive ulcerative colitis (UC) and control subjects. The localization and level of VEGF protein and its receptors protein in intestinal tissue were estimated by immunohistochemistry. VEGF concentration in serum and plasma was determined by ELISA. We found a significant increase of VEGF gene expression and increase expression of genes encoding receptor Flt-1 in patients with active UC when compared with controls, but KDR was present in trace amount. VEGF and Flt-1 proteins were colocalized in enterocytes as well as in endothelium and muscularis layer of the intestine. The specific staining reaction for VEGF protein as well as for Flt-1 protein was significantly higher in active UC compared with controls. Serum level of VEGF was significantly higher in active UC patients as compared with inactive UC patients as well as with controls. The plasma VEGF level was found to be significantly higher in active UC patients as compared with controls. The increase of gene expression as well as protein level for VEGF and its receptor in UC - inflamed colon, and VEGF action via Flt-1 receptor may have a functional role in UC. Increased VEGF levels in both serum and plasma in active UC patients may reflect VEGF overexpression in intestinal inflammatory tissue.

CD40 glycoforms and TNF-receptors 1 and 2 in the formation of CD40 receptor(s) in autoimmunity

The CD40-CD154 dyad is an intensely studied field as is glycosylation status and both impact immunological functions and autoimmune conditions. CD40 has several isoforms, is modified by glycosylation, and trimerizes to form the functional receptor. We described a CD4(+)CD40(+) T cell (Th40) subset which is expanded in autoimmunity and is necessary and sufficient in transferring type 1 diabetes. Glycosylation impacts immunological events and T cells from autoimmune mouse strains express 30-40% less GlcNAc-branched N-glycans than T cells from non-autoimmune strains, a decrease known to activate T cells. Here we demonstrate that several CD40 receptor constellations exist on CD4 T cells. However, rather than containing different isoforms of CD40 they contain different glycoforms of isoform I. The glycoform profile is dependent on availability of CD154 and autoimmune NOD mice express a high level of a less glycosylated form. Interestingly, CD40 stimulation induces some CD40 receptor constellations that contain TNF-receptors 1 and 2 and targeting of those alters CD40 signaling outcomes in NOD Th40 cells. CD40-stimulation in vivo of non-autoimmune BALB/c mice expands the Th40 population and alters the CD40 glycoform profile of those cells to appear more like that of autoimmune prone NOD mice. Further understanding the dynamics and composition of the different CD40 receptor constellations will provide important insights into treatment options in autoimmunity.

Antibodies against gonadotropin-releasing hormone (GnRH) and destruction of enteric neurons in 3 patients suffering from gastrointestinal dysfunction

BACKGROUND

Antibodies against gonadotropin-releasing hormone (GnRH) and gastrointestinal dysmotility have been found after treatment with GnRH analogues. The aim of this study was to examine the presence of such antibodies in patients with dysmotility not subjected to GnRH treatment and study the anti-GnRH antibody effect on enteric neurons viability in vitro.

METHODS

Plasma and sera from 3 patients suffering from either enteric dysmotility, irritable bowel syndrome (IBS) or gastroparesis were analysed for C-reactive protein (CRP), and for GnRH antibodies and soluble CD40 by ELISA methods. Primary cultures of small intestinal myenteric neurons were prepared from rats. Neuronal survival was determined after the addition of sera either from the patients with dysmotility, from healthy blood donors, antiserum raised against GnRH or the GnRH analogue buserelin. Only for case 1 a full-thickness bowel wall biopsy was available for immunohistochemical analysis.

RESULTS

All 3 patients expressed antibodies against GnRH. The antibody titer correlated to the levels of CD40 (rs = 1.000, p < 0.01), but not to CRP. Serum from case 3 with highest anti-GnRH antibody titer, and serum concentrations of sCD40 and CRP, when added to cultured rat myenteric neurons caused remarkable cell death. In contrast, serum from cases 1 and 2 having lower anti-GnRH antibody titer and lower sCD40 levels had no significant effect. Importantly, commercial antibodies against GnRH showed no effect on neuron viability whereas buserelin exerted a protective effect. The full-thickness biopsy from the bowel wall of case 1 showed ganglioneuritis and decrease of GnRH and GnRH receptor.

CONCLUSION

Autoantibodies against GnRH can be detected independently on treatment of GnRH analogue. Whether the generation of the antibody is directly linked to neuron degeneration and chronic gastrointestinal symptoms in patients with intestinal dysmotility, remains to be answered.

Inflammatory mediators in gastroesophageal reflux disease: impact on esophageal motility, fibrosis, and carcinogenesis

Gastroesophageal reflux disease (GERD) is one of the most common problems in clinical practice today. It is widely believed that functional and structural abnormalities of the gastroesophageal junction as well as an abnormal exposure to gastroduodenal contents are the main contributors to its pathogenesis. Novel findings of the inflammatory process in GERD suggest a far more complex process involving multifaceted inflammatory mechanisms. This review summarizes knowledge about the expression of inflammatory mediators in GERD and their potential cellular sources and provides an integrated concept of disease pathogenesis. In addition we evaluate the contribution of inflammatory mediators to well-known complications of GERD, namely motility abnormalities, fibrosis, and carcinogenesis. Novel findings regarding the pathophysiology of esophageal inflammation should enhance our understanding of GERD and its complications and provide new treatment insights.

CD154 deficiency uncouples allograft CD8+ T-cell effector function from proliferation and inhibits murine airway obliteration

Obliterative bronchiolitis (OB) limits the long-term success of lung transplantation, while T-cell effector mechanisms in this process remain incompletely understood. Using the murine heterotopic tracheal transplant model of obliterative airway disease (OAD) to characterize airway allograft rejection, we previously reported an important role for CD8(+) T cells in OAD. Herein, we studied the role of CD154/CD40 costimulation in the regulation of allospecific CD8(+) T cells, as airway rejection has been reported to be CD154-dependent. Airway allografts from CD154(-/-) recipients had significantly lower day 28 OAD scores compared to wild-type (WT) recipients, and adoptive transfer of CD8(+) T cells from WT recipients, but not CD154(-/-) recipients, were capable of airway rejection in fresh CD154(-/-) allograft recipients. Intragraft CD8(+) T cells from CD154(-/-) mice showed similar expression of the surface markers CD69, CD62L(low) CD44(high) and PD-1, but markedly impaired IFN-gamma and TNF-alpha secretion and granzyme B expression versus WT controls. Unexpectedly, intragraft and systemic CD8(+) T cells from CD154(-/-) recipients demonstrated robust in vivo expansion similar to WT recipients, consistent with an uncoupling of proliferation from effector function. Together, these data suggest that a lack of CD154/CD40 costimulation results in ineffective allospecific priming of CD8(+) T cells required for murine OAD.

Exaggerated inflammatory response of primary human myeloid dendritic cells to lipopolysaccharide in patients with inflammatory bowel disease

Inflammatory bowel disease (IBD) results from a breakdown of tolerance towards the indigenous flora in genetically susceptible hosts. Failure of dendritic cells (DC) to interpret molecular microbial patterns appropriately when directing innate and adaptive immune responses is conceivable. Primary (conventional, non-monocyte generated) CD1c(+)CD11c(+)CD14(-)CD16(-)CD19(-) myeloid blood or mucosal dendritic cells (mDC) from 76 patients with Crohn's disease (CD) or ulcerative colitis (UC) in remission, during flare-ups (FU) and 76 healthy or non-IBD controls were analysed by fluorescence activated cell sorter (FACS) flow cytometry and real-time polymerase chain reaction. Cytokine secretion of freshly isolated, cultured and lipopolysaccharide (LPS)-stimulated highly purified mDC (purity >95%) was assessed using cytometric bead arrays (CBA). More cultured and stimulated circulating mDC express CD40 in IBD patients. Stimulated circulating mDC from IBD patients secrete significantly more tumour necrosis factor (TNF)-alpha and interleukin (IL)-8. Toll-like receptor (TLR)-4 expression by mDC was higher in remission and increased significantly in flaring UC and CD patients compared with remission (P < 0.05) and controls (P < 0.001). Fluorochrome-labelled LPS uptake by mDC was evaluated at different time-points over 24 h by measuring mean fluorescence intensity (MFI). Circulating mDC from IBD patients take up more LPS and the uptake begins earlier compared with controls (P < 0.05 in CD-FU and UC-FU at 24 h). The frequency of mucosal mDC (P < 0.05) and the number of CD40 expressing mucosal mDC is significantly greater in UC and CD compared with non-IBD controls (P < 0.001 versus P < 0.01, respectively). Our data suggest an aberrant LPS response of mDC in IBD patients, resulting in an inflammatory phenotype and possibly intestinal homing in acute flares.

Differential expression of leukocyte functions associated antigen-1 (LFA-1) on peripheral blood mononuclear cells in patients with Crohn's disease

BACKGROUND

The leukocyte function associated antigen-1 (LFA-1) intracellular adhesion molecule-1 pathway is presumed to play a pivotal role in the perpetuation of inflammatory bowel disease. We aimed to elucidate the effect of 2 different therapies on LFA-1 expression in patients with Crohn's disease (CD) and correlate LFA-1 expression with disease activity.

METHODS

In all, 30 patients with active CD were recruited for the present investigation. Eleven patients were treated with infliximab and 19 patients with total parenteral nutrition. The clinical activity and the expression of LFA-1 in peripheral blood mononuclear cells were assessed prior to and 4 weeks after treatment. Clinical activity was determined by measuring the Crohn's Disease Activity Index and LFA-1 expression was measured by mean fluorescence intensity (MFI) under fluorescence-activated cell sorter analysis.

RESULTS

In each treatment group the clinical disease activity index decreased significantly 4 weeks after treatment. In patients treated with infliximab, LFA-1 expression decreased significantly (mean MFI decreased from 1983 to 1487, P < 0.05). However, LFA-1 expression remained unchanged in the total parenteral nutrition group (mean MFI elevated from 1684 to 1902, P > 0.05).

CONCLUSIONS

The mechanism of therapeutic action on CD is different between infliximab and total parenteral nutrition.

Nonimmune cells in inflammatory bowel disease: from victim to villain

Nonimmune cells have traditionally been viewed as target cells of the aberrant inflammatory process present in chronic immune-mediated conditions such as inflammatory bowel disease (IBD). However, the discovery that many of the functions traditionally attributed to immune cells are also performed by nonimmune cells has caused a shift to a multidirectional hypothesis in which nonimmune cells and acellular elements play active roles. Many types of interactions occur within this multidirectional system, and the difficulties associated with modeling these complex interactions currently limit our understanding of the cellular network that occurs in IBD. I describe the current knowledge of the roles played by nonimmune cells in the pathogenesis of IBD, as they emerge as crucial alternative targets for therapeutic intervention.

VEGF-A links angiogenesis and inflammation in inflammatory bowel disease pathogenesis

BACKGROUND & AIMS

Vascular endothelial growth factor A (VEGF-A) mediates angiogenesis and might also have a role in inflammation and immunity. We examined whether VEGF-A signaling has a role in inflammatory bowel disease (IBD).

METHODS

Expression levels of VEGF-A, and its receptors VEGFR-1 and VEGFR-2, were examined in samples from patients with IBD and compared with those of controls. The capacity of VEGF-A to induce angiogenesis was tested in human intestinal microvascular endothelial cells using cell-migration and matrigel tubule-formation assays. Levels of vascular cellular adhesion molecule-1 and intercellular adhesion molecule were measured by flow cytometry to determine induction of inflammation; neutrophil adhesion was also assayed. Expression patterns were determined in tissues from mice with dextran sulfate sodium (DSS)-induced colitis; the effects of VEGF-A overexpression and blockade were assessed in these mice by adenoviral transfer of VEGF-A and soluble VEGFR-1. Intestinal angiogenesis was measured by quantitative CD31 staining and leukocyte adhesion in vivo by intravital microscopy.

RESULTS

Levels of VEGF-A and VEGFR-2 increased in samples from patients with IBD and colitic mice. VEGF-A induced angiogenesis of human intestinal microvascular endothelial cells in vitro as well as an inflammatory phenotype and adherence of neutrophils to intestinal endothelium. Overexpression of VEGF-A in mice with DSS-induced colitis worsened their condition, whereas overexpression of soluble VEGFR-1 had the opposite effect. Furthermore, overexpression of VEGF-A increased mucosal angiogenesis and stimulated leukocyte adhesion in vivo.

CONCLUSIONS

VEGF-A appears to be a novel mediator of IBD by promoting intestinal angiogenesis and inflammation. Agents that block VEGF-A signaling might reduce intestinal inflammation in patients with IBD.

Intestinal fibrosis in inflammatory bowel disease - Current knowledge and future perspectives

BACKGROUND AND AIMS

Intestinal fibrosis is a common complication of IBD that can become seriously symptomatic and may require surgical intervention if stricture formation ensues. This review discusses existing and developing knowledge of intestinal fibrosis and its implications for therapy.

METHODS

Review of the literature, personal communications, unpublished observations.

RESULTS

Known mechanisms of intestinal fibrosis include fibroblast proliferation and migration, activation of stellate cells, and extraintestinal fibroblast recruitment. However, novel mechanisms are being uncovered, including epithelial-to-mesenchymal transition, endothelial-to-mesenchymal transition, pericyte differentiation, and fibrocyte recruitment. Most of the traditional and novel mechanisms underlying intestinal fibrosis are associated to the presence of chronic inflammation, but is also possible that fibrosis develops independently of persistent immune activation in the gut. At the moment, the development of preventive, non-interventional, and more effective management of intestinal fibrosis is hampered by the lack of a greater knowledge of its basic pathophysiology and predisposing factors.

CONCLUSIONS

It is reasonable to expect that therapy of IBD-associated fibrosis will radically improve once the underlying mechanisms are better understood, and therapeutic modalities will emerge that prevent or reverse this complication of IBD.

CD40-mediated death and cytokine secretion in colorectal cancer: a potential target for inflammatory tumour cell killing

CD40, a member of the tumour necrosis factor family, is expressed in a variety of epithelial cells. Although soluble CD40 agonists are growth-inhibitory, membrane-presented CD40 ligand (CD40L) induces extensive apoptosis in carcinoma cells. This study investigated whether CD40 is expressed in human colorectal carcinoma (CRC) cells and explored the functional consequences of CD40 ligation. CD40 expression in a panel of CRC lines was assessed by flow cytometry and in resected human CRCs by immunohistochemistry. CRC cells were treated in vitro with soluble CD40 agonists or cocultured with fibroblasts expressing membrane-bound CD40 ligand. Apoptosis was determined by flow cytometry using Annexin V/propidium iodide labelling and by a DNA fragmentation assay. Cytokine secretion induced by CD40 ligation was quantified by a multiplex-bead array approach. We show that CD40 is expressed in a proportion of established CRC lines in culture and that receptor expression is functional. Activation of CD40 by membrane-presented CD40L, but not soluble agonists, causes high levels of death in CD40-positive CRC cells and induces secretion of proinflammatory cytokines. In agreement with our in vitro observations, immunohistochemical studies demonstrated that CD40 is highly expressed in a proportion of colorectal cancer specimens. The high level of susceptibility of CRC cells to CD40-killing combined with the ability of CD40 to induce concomitant secretion of proinflammatory cytokines suggest that CD40 ligation may represent a novel mechanism for elimination of CRC cells and render CD40 a promising therapeutic target for the eradication of colorectal tumours.

Crucial role of the protein C pathway in governing microvascular inflammation in inflammatory bowel disease

Endothelial protein C receptor (EPCR) and thrombomodulin (TM) are expressed at high levels in the resting microvasculature and convert protein C (PC) into its activated form, which is a potent anticoagulant and antiinflammatory molecule. Here we provide evidence that in Crohn disease (CD) and ulcerative colitis (UC), the 2 major forms of inflammatory bowel disease (IBD), there was loss of expression of endothelial EPCR and TM, which in turns caused impairment of PC activation by the inflamed mucosal microvasculature. In isolated human intestinal endothelial cells, administration of recombinant activated PC had a potent antiinflammatory effect, as demonstrated by downregulated cytokine-dependent cell adhesion molecule expression and chemokine production as well as inhibited leukocyte adhesion. In vivo, administration of activated PC was therapeutically effective in ameliorating experimental colitis as evidenced by reduced weight loss, disease activity index, and histological colitis scores as well as inhibited leukocyte adhesion to the inflamed intestinal vessels. The results suggest that the PC pathway represents a new system crucially involved in governing intestinal homeostasis mediated by the mucosal microvasculature. Restoring the PC pathway may represent a new therapeutic approach to suppress intestinal inflammation in IBD.

Progress in basic inflammatory bowel disease research

A modern approach to inflammatory bowel disease (IBD) research has been under way for little over one-half century, but only during the last two decades has progress accelerated and finally generated tangible results that have been translated into practical and better therapeutic strategies. The areas where progress has been more evident are those currently believed to be the key components of IBD pathogenesis, and include the environment, genetics, enteric microbiology, and immune reactivity. Progress in these different areas has been somewhat uneven, yielding a better understanding of the mechanisms behind gut inflammation and tissue injury rather than of specific etiological agents or predisposing factors. However, with the rapidly increasing utilization of novel methodological approaches like genetics, genomics, proteomics, and pharmacogenomics, it is reasonable to anticipate that the etiopathogenesis of IBD will be unveiled in the next couple of decades and more definitive, perhaps disease-modifying, approaches will be uncovered and implemented.

Monocyte chemoattractant protein-1 production by intestinal myofibroblasts in response to staphylococcal enterotoxin a: relevance to staphylococcal enterotoxigenic disease

Food poisoning due to staphylococcal enterotoxins A and B (SEA and SEB) affects hundreds of thousands of people annually. SEA and SEB induce massive intestinal cytokine production, which is believed to be the key factor in staphylococcal enterotoxin enteropathy. MHC class II molecules are the major receptors for staphylococcal enterotoxins. We recently demonstrated that normal human subepithelial intestinal myofibroblasts (IMFs) express MHC class II molecules. We hypothesized that IMFs are among the first cells to respond to staphylococcal enterotoxins and contribute to the cytokine production associated with staphylococcal enterotoxin pathogenesis. We demonstrated here that primary cultured IMFs bind staphylococcal enterotoxins in a MHC class II-dependent fashion in vitro. We also demonstrated that staphylococcal enterotoxins can cross a CaCo-2 epithelial monolayer in coculture with IMFs and bind to the MHC class II on IMFs. IMFs responded to SEA, but not SEB, exposure with 3- to 20-fold increases in the production of proinflammatory chemokines (MCP-1, IL-8), cytokines (IL-6), and growth factors (GM-CSF and G-CSF). The SEA induction of the proinflammatory mediators by IMFs resulted from the efficient cross-linking of MHC class II molecules because cross-linking of class II MHC by biotinylated anti-HLA-DR Abs induced similar cytokine patterns. The studies presented here show that MCP-1 is central to the production of other cytokines elicited by SEA in IMFs because its neutralization with specific Abs prevented the expression of IL-6 and IL-8 by IMFs. Thus, MCP-1 may play a leading role in initiation of inflammatory injury associated with staphylococcal enterotoxigenic disease.

Oxidant stress, immune dysregulation, and vascular function in type I diabetes

Although high glucose is an important contributor to diabetic vasculopathies, complications still occur in spite of tight glycemic control, suggesting that some critical event prior to or concurrent with hyperglycemia may contribute to early vascular changes. Utilizing previously published and new experimental evidence, this review will discuss how prior to the hyperglycemic state, an imbalance between oxidants and antioxidants may contribute to early vascular dysfunction and set in motion proinflammatory insults that are further amplified as the diabetes develops. This imbalance results from the resetting of the equilibrium between vessel superoxide/H(2)O(2) production and/or decreased antioxidant defenses. Such an imbalance may cause endothelial dysfunction, characterized by abnormal endothelium-dependent vasoreactivity, as the first sign of blood vessel damage, followed by morphological changes of the vessel wall and inflammation. As such, increased oxidant stress in preglycemic states may be a critically central initiating event that underlies the pathogenesis of life-threatening vascular diseases in autoimmune diabetes. This review focuses on the relationship between oxidative stress, immune dysregulation, and vascular injury in type 1 diabetes, and how the discovery of novel pathways of vascular disease in nonobese diabetic mice may direct future studies in patients with type 1 diabetes.

The transdifferentiation of bone-marrow-derived cells in colonic mucosal regeneration after dextran-sulfate-sodium-induced colitis in mice

Bone-marrow-derived cells (BMDCs) transdifferentiate into various types of gastrointestinal cells. The precise transdifferentiation of BMDCs in gut regeneration, however, is controversial. In this study, we examined the transdifferentiation of BMDCs in the regeneration of damaged colonic epithelia. Lethally irradiated wild-type female mice (C57BL/6) were rescued by bone marrow transplantation from male green fluorescent protein transgenic mouse donors. Chronic colitis was induced by administering 3% dextran sulfate sodium (DSS) in the drinking water for 5 days on day 28 after the bone marrow transplantation. The mice were killed on day 25 after DSS administration. BMDC phenotypes were examined by confocal microscopy and fluorescence immunohistochemistry. BMDCs were frequently observed in the vimentin-positive colonic interstitial cells, which also expressed alpha-smooth muscle actin and had a spindle-like morphology, but did not express leukocyte common antigen. Green-fluorescent-protein-positive cells were rarely or less frequently found in Ki-67-positive proliferating cells, cytokeratin-positive epithelial cells, or CD31-positive endothelial cells. BMDCs frequently transdifferentiated into subepithelial myofibroblasts and fibroblasts, and often continued to reside in the colonic subepithelia after the experimental colitis had healed. In conclusion, our data indicate the fate of BMDCs, which might be involved in the healing process of the colon after DSS-induced colitis. Our data show that BMDCs contribute to colonic interstitial cells after the colitis has healed. Understanding the fate of BMDCs may be important for stem cell therapy by BMDCs.

[Fibrogenesis and inflammatory bowel disease]

A substantial proportion of patients with Crohn's disease develops intestinal stenosis due to anomalous fiber deposits. These patients frequently require resection of the affected segment. Despite its evident clinical significance, intestinal fibrogenesis has received little attention in comparison with research into hepatic, pulmonary, renal or cutaneous fibrosis. There seems to be a certain genetic predisposition to developing intestinal fibrosis. A meta-analysis has demonstrated that the three main variants of the NOD2/CARD15 gene are associated with this complication. In Crohn's disease, a series of alterations in collagen synthesis, expression of various pro- and anti-fibrogenic factors and intestinal fibroblast function have been described in the last few years. More recently, the development of intestinal fibrosis has been attenuated in several experimental models. Nevertheless, further studies are required to improve our understanding of intestinal fibrogenesis and to develop effective strategies for its prevention and treatment.

Proinflammatory cytokine synthesis by mucosal fibroblasts from mouse colitis is enhanced by interferon-gamma-mediated up-regulation of CD40 signalling

Gut mesenchymal fibroblasts form complex phenotypical and functional populations. They participate actively in homeostatic maintenance of the extracellular matrix, epithelial barrier function, repair mechanisms and leucocyte migration. In inflammation, they become activated, change matrix expression and synthesize proinflammatory mediators. Subpopulations of mucosal fibroblasts express CD40 and the aim of this study was to define its role in their proinflammatory function. Stable primary fibroblast lines derived from normal mouse colon and inflamed colon from CD4(+) CD45RB(high)-transplanted SCID mice were used as models to explore the role of mucosal fibroblast CD40 in the inflammatory process. Phenotype correlated with in situ fibroblast phenotype in the tissues of origin. Lines from both sources co-expressed CD40 and Thy1.2 independently of alpha-smooth muscle actin. A subpopulation of CD40(+) fibroblasts from normal colon expressed CD40 at high levels and expression was enhanced by interferon (IFN)-gamma treatment, whereas all CD40(+) fibroblasts from colitis expressed at low levels and expression was unaffected by IFN-gamma treatment. Despite lower-level expression of CD40 by cells from colitis, they secreted constitutively interleukin (IL)-6 and C-C chemokine (CCL)2. Ligation of CD40 enhanced secretion of these mediators and induced secretion of CCL3. CD40 in cells from colitis was more responsive to ligation than CD40 on cells from normal tissue and this sensitivity was amplified selectively by the action of IFN-gamma. We conclude that the inflammatory milieu in colitis induces long-lasting changes in phenotype and proinflammatory function in colonic fibroblasts. In particular, proinflammatory signalling from fibroblast CD40 is amplified synergistically by the Th1 effector T cell cytokine, IFN-gamma.

CD40-CD40 ligand mediates the recruitment of leukocytes and platelets in the inflamed murine colon

BACKGROUND AND AIMS

Although the CD40-CD40 ligand (CD40L) signaling pathway has been implicated in the pathogenesis of a variety of diseases, including inflammatory bowel disease, the nature of its contribution to intestinal inflammation remains poorly understood. The aim of this study was to determine whether CD40-CD40L contributes to the intestinal inflammatory response, tissue injury, and disease activity elicited by dextran sodium sulphate (DSS) through the modulation of leukocyte and platelet recruitment in the colonic microvasculature.

METHODS

Wild-type (WT), CD40(-/-), and CD40L(-/-) mice were fed DSS drinking water. On day 6, intravital videomicroscopy was performed to monitor leukocyte and platelet recruitment in colonic venules, with measurements obtained for tissue myeloperoxidase and histology. CD40 expression on colonic endothelium was measured using the dual-radiolabeled antibody technique.

RESULTS

A comparison of the responses to DSS-induced colitis in CD40(-/-) and CD40L(-/-) mice to WT mice revealed a significant attenuation of disease activity and histologic damage, as well as profound reductions in the recruitment of adherent leukocytes and platelets in the mutant mice. Similar down-regulation of the blood cell recruitment responses to DSS was noted in WT mice treated with the CD40-CD40L pathway inhibitor Trapidil. CD40 expression in the colonic vasculature was greatly elevated during DSS-induced inflammation in WT mice, but not in CD40(-/-) mice.

CONCLUSIONS

These findings implicate CD40-CD40L in the pathogenesis of DSS-induced intestinal inflammation, and suggest that modulation of leukocyte and platelet recruitment by activated, CD40-positive endothelial cells in colonic venules may represent a major action of this signaling pathway.

Enhanced recruitment of CX3CR1+ T cells by mucosal endothelial cell-derived fractalkine in inflammatory bowel disease

BACKGROUND & AIMS

Fractalkine (FKN/CX3CL1) is a unique chemokine combining adhesive and chemotactic properties. We investigated FKN production by the mucosal microvasculature in inflammatory bowel disease (IBD), its capacity for leukocyte recruitment into the gut, and the number of CX3CR1+ cells in the circulation and mucosa of IBD patients.

METHODS

The expression of FKN by human intestinal microvascular endothelial cells (HIMECs) and CX3CR1 by circulating cells was evaluated by flow cytometry, and mucosal CX3CR1+ cells were enumerated by immunohistochemistry. The capacity of FKN to mediate leukocyte binding to HIMECs was assessed by immunoblockade, and to induce HIMEC transmigration by a Transwell system.

RESULTS

The spontaneously low HIMEC FKN expression was enhanced markedly by tumor necrosis factor-alpha plus interferon-gamma stimulation, or direct leukocyte contact. This effect was significantly stronger in IBD than control HIMECs. Up-regulation of HIMEC FKN expression was dependent on p38 and extracellular signal-regulated kinase phosphorylation, as was abrogated by selective mitogen-activated protein kinase inhibitors. Circulating T cells contained significantly higher numbers of CX3CR1+ cells in active IBD than inactive IBD or healthy subjects, and IBD mucosa contained significantly more CX3CR1+ cells than control mucosa. Antibody-blocking experiments showed that FKN was a major contributor to T- and monocytic-cell adhesion to HIMECs. Finally, FKN enhanced the expression of active beta1 integrin on leukocytes and mediated leukocyte HIMEC transmigration.

CONCLUSIONS

In view of the capacity of FKN to mediate leukocyte adhesion, chemoattraction, and transmigration, its increased production by mucosal microvascular cells and increased numbers of circulating and mucosal CX3CR1+ cells in IBD point to a significant role of FKN in disease pathogenesis.

The proportion of CD40+ mucosal macrophages is increased in inflammatory bowel disease whereas CD40 ligand (CD154)+ T cells are relatively decreased, suggesting differential modulation of these costimulatory molecules in human gut lamina propria

BACKGROUND

Signal transduction through binding of CD40 on antigen-presenting cells and CD40 ligand (CD154) on T cells appears to be crucial for mutual cellular activation. Antibodies aimed at blocking the CD40-CD154 costimulatory pathway dampen the severity of experimental colitis. To elucidate the microanatomical basis for signaling through this costimulatory pathway in human inflammatory bowel disease, we studied in situ the cellular distribution of these 2 molecules on lamina propria macrophages and T cells, respectively.

METHODS

Colonic specimens from 8 patients with ulcerative colitis and 8 with Crohn's disease, 8 small bowel specimens of Crohn's disease, and histologically normal control samples (6 from colon and 6 from small bowel) were included. Multicolor immunofluorescence in situ staining was performed to determine the percentage of subepithelial macrophages expressing CD40 and that of lamina propria T cells expressing CD154 while avoiding cells in lymphoid aggregates.

RESULTS

The proportion of subepithelial CD40CD68 macrophages was significantly increased in normal colon compared with normal small bowel and showed further elevation in both colon and small bowel afflicted with inflammatory bowel disease. In addition, on a per-CD68-cell basis, CD40 expression was significantly increased in severely inflamed compared with moderately inflamed colonic specimens. Conversely, the proportion of CD154 T cells was similar in colon and small bowel, and interestingly, it was significantly reduced in colonic inflammatory bowel disease.

CONCLUSIONS

Our findings suggested that modulation of CD40 expression by subepithelial macrophages and CD154 by lamina propria T cells is inversely modulated in the human gut.

Subepithelial Myofibroblasts are Novel Nonprofessional APCs in the Human Colonic Mucosa

The human gastrointestinal mucosa is exposed to a diverse normal microflora and dietary Ags and is a common site of entry for pathogens. The mucosal immune system must respond to these diverse signals with either the initiation of immunity or tolerance. APCs are important accessory cells that modulate T cell responses which initiate and maintain adaptive immunity. The ability of APCs to communicate with CD4+ T cells is largely dependent on the expression of class II MHC molecules by the APCs. Using immunohistochemistry, confocal microscopy, and flow cytometry, we demonstrate that alpha-smooth muscle actin(+), CD90+ subepithelial myofibroblasts (stromal cells) constitutively express class II MHC molecules in normal colonic mucosa and that they are distinct from professional APCs such as macrophages and dendritic cells. Primary isolates of human colonic myofibroblasts (CMFs) cultured in vitro were able to stimulate allogeneic CD4+ T cell proliferation. This process was dependent on class II MHC and CD80/86 costimulatory molecule expression by the myofibroblasts. We also demonstrate that CMFs, engineered to express a specific DR4 allele, can process and present human serum albumin to a human serum albumin-specific and DR4 allele-restricted T cell hybridoma. These studies characterize a novel cell phenotype which, due to its strategic location and class II MHC expression, may be involved in capture of Ags that cross the epithelial barrier and present them to lamina propria CD4+ T cells. Thus, human CMFs may be important in regulating local immunity in the colon.

Etiopathogenesis of inflammatory bowel diseases

Theories explaining the etiopathogenesis of inflammatory bowel disease (IBD) have been proposed ever since Crohn’s disease (CD) and ulcerative colitis (UC) were recognized as the two major forms of the disease. Although the exact cause(s) and mechanisms of tissue damage in CD and UC have yet to be completely understood, enough progress has occurred to accept the following hypothesis as valid: IBD is an inappropriate immune response that occurs in genetically susceptible individuals as the result of a complex interaction among environmental factors, microbial factors, and the intestinal immune system. Among an almost endless list of environmental factors, smoking has been identified as a risk factor for CD and a protective factor for UC. Among microbial factors, no convincing evidence indicates that classical infectious agents cause IBD, while mounting evidence points to an abnormal immune response against the normal enteric flora as being of central importance. Gut inflammation is mediated by cells of the innate as well as adaptive immune systems, with the additional contribution of non-immune cells, such as epithelial, mesenchymal and endothelial cells, and platelets.

Angiogenesis as a novel component of inflammatory bowel disease pathogenesis

BACKGROUND & AIMS

Angiogenesis is a critical component of neoplastic and chronic inflammatory disorders, but whether angiogenesis also occurs in inflammatory bowel disease (IBD) has yet to be established. We assessed mucosal vascularization, expression of endothelial alphaVbeta3 integrin, angiogenic factors, and their bioactivity in Crohn's disease (CD) and ulcerative colitis (UC) mucosa.

METHODS

Mucosal endothelium was immunostained for CD31 and factor VIII and quantified by digital morphometry. alphaVbeta3 expression was studied in vivo by confocal microscopy and in vitro by flow cytometric analysis of human intestinal microvascular endothelial cells (HIMECs). Vascular endothelial growth factor (VEGF), interleukin (IL)-8, and bFGF levels were measured in mucosal extracts and cells and angiogenic bioactivity shown by induction of HIMEC migration and the corneal and chorioallantoic membrane angiogenesis assays.

RESULTS

Microvessel density was increased in IBD mucosa. Endothelial alphaVbeta3 was strongly expressed in IBD but only sporadically in normal mucosa and was up-regulated in HIMECs by VEGF, tumor necrosis factor alpha, and bFGF. IBD mucosal extracts induced a significantly higher degree of HIMEC migration than control mucosa, and this response was mostly dependent on IL-8 and less on basic fibroblast growth factor or vascular endothelial growth factor. Compared with normal mucosa, IBD mucosal extracts induced a potent angiogenic response in both the corneal and chorioallantoic membrane assays.

CONCLUSIONS

These results provide morphological, phenotypic and functional evidence of potent angiogenic activity in both CD and UC mucosa, indicating that the local microvasculature undergoes an intense process of inflammation-dependent angiogenesis. Thus, angiogenesis appears to be an integral component of IBD pathogenesis, providing the practical and conceptual framework for anti-angiogenic therapies in IBD.

TNF-alpha blockade down-regulates the CD40/CD40L pathway in the mucosal microcirculation: a novel anti-inflammatory mechanism of infliximab in Crohn's disease

The CD40/CD40 ligand (CD40L) pathway is involved in Crohn's disease (CD) pathogenesis. In the patients' circulation, soluble CD40L (sCD40L) levels are elevated and surface CD40L is increased in platelets and T cells, whereas in the intestine CD40 is overexpressed in the microvasculature and CD40L in platelets and T cells. The therapeutic effects of infliximab in CD are attributed to its systemic anti-TNF-alpha action, but because TNF-alpha modulates both CD40 and CD40L, we investigated whether infliximab affects the CD40/CD40L pathway in the intestine. Eighteen CD patients were evaluated before and after infliximab therapy. Plasma sCD40L was measured by ELISA and platelet and peripheral blood T cell (PBT) CD40L expression by flow cytometry. Microvascular CD40 and VCAM-1 expression were assessed in mucosal biopsies by immunohistochemistry and by flow cytometry in human intestinal microvascular endothelial cells (HIMEC). Cell cultures were performed in the presence and absence of infliximab. Infliximab treatment significantly reduced plasma sCD40L levels and eliminated CD40 and VCAM-1 from mucosal microvessels. In vitro infliximab prevented TNF-alpha-induced CD40 and VCAM-1 expression by HIMEC, and reduced PBT, but not platelet, surface CD40L expression and sCD40L release. In addition, infliximab decreased T cell-induced VCAM-1 expression in HIMEC by down-regulating CD40L in T cells and promoting T cells apoptosis. These findings point to a novel mechanism of action of infliximab, i.e., the disruption of CD40/CD40L-dependent cognate interactions between intestinal microvessels and T cells. Thus, in addition to neutralizing TNF-alpha and inducing T cell death, the therapeutic effects of infliximab in CD appear to be also mediated by inhibition of vascular inflammation in the gut.

Tumour necrosis factor-alpha production stimulated by heat shock protein 70 and its inhibition in circulating dendritic cells and cells eluted from mucosal tissues in Crohn's disease

Summaryand interleukin (IL)-12 by dendritic cells (DC) from patients with Crohn's disease. TNF-alpha concentration was increased significantly when DC from Crohn's disease were stimulated with HSP70 or CD40L and this was associated with signalling by the extracellular signal regulated kinase (ERK) 1/2 and p38 mitogen activated protein (MAP) kinase pathway. IL-12 production was also increased when DC were stimulated with HSP70. Cells eluted from inflamed intestinal mucosa from Crohn's disease, stimulated with HSP70, CD40L or lipopolysaccharide produced significantly greater TNF-alpha and IL-12 concentrations than cells from uninflamed mucosa. Significant inhibition of TNF-alpha production was demonstrated when DC from peripheral blood mononuclear cells or cells eluted from intestinal mucosa of Crohn's disease were treated with either the HSP70 inhibitory peptide (aa 457-496) or peptides derived from CD40 and CD40L. These inhibitory peptides target the CD40-CD40L and the emerging CD40-HSP70 co-stimulatory pathway. Our findings offer a novel strategy to prevent excessive production of TNF-alpha in Crohn's disease.

Cytokines and the regulation of hypoxia-inducible factor (HIF)-1alpha

Hypoxia-inducible factor (HIF)--an oxygen sensor? The HIF-oxygen sensing association type of dogma is, unequivocally, well anchored. But this is only one face of, at least, a double-sided coin. Current concepts charge HIF of taking sides with a yet not well-founded identity--an immunologic sensor and/or regulator. Or, is it really a sensor, put it more correctly, a key player in sensing mechanisms? The evolving association between HIF and immunity emanates from an established linkage that bonds oxidative stress and inflammation--notably the 'biologic response modifiers', or cytokines. HIF is a redox(y)-sensitive transcription factor, and so are cytokines. Recently, cytokines emerged as major regulators of HIF, under physiologic conditions extending the realm of hypoxia. Alternatively, can HIF, like the so infamous inflammatory transcription factor NF-(kappa)B, prove itself as a key player in the regulation of cytokines and, subsequently, the inflammatory process. The targeting of HIF would be, at least theoretically, of therapeutic value, but does it make sense given its intricate role in hypoxia signaling? It is the theme of HIF being an immunologic sensor that will be explored therein--with special emphasis on the regulatory role of cytokines.