Human intestinal microvascular endothelial cells express Toll-like receptor 5: a binding partner for bacterial flagellin

Microbiota and angiogenesis in the intestinal vasculature

The gut microbiota is responsible for several metabolic functions, producing various metabolites with numerous roles for the host. The gut microbiota plays a key role in constructing the microvascular network in the intestinal villus, depending on the Paneth cells, strategically positioned to coordinate the development of both the microbiota and the microvasculature. The gut microbiota secretes several molecules and chemokines involved in the induction of the secretion of pro-angiogenic factors.

TLR5-deficiency controls dendritic cell subset development in an autoimmune diabetes-susceptible model

Introduction

The incidence of the autoimmune disease, type 1 diabetes (T1D), has been increasing worldwide and recent studies have shown that the gut microbiota are associated with modulating susceptibility to T1D. Toll-like receptor 5 (TLR5) recognizes bacterial flagellin and is widely expressed on many cells, including dendritic cells (DCs), which are potent antigen-presenting cells (APCs). TLR5 modulates susceptibility to obesity and alters metabolism through gut microbiota; however, little is known about the role TLR5 plays in autoimmunity, especially in T1D.

Methods

To fill this knowledge gap, we generated a TLR5-deficient non-obese diabetic (NOD) mouse, an animal model of human T1D, for study.

Results

We found that TLR5-deficiency led to a reduction in CD11c+ DC development in utero, prior to microbial colonization, which was maintained into adulthood. This was associated with a bias in the DC populations expressing CD103, with or without CD8α co-expression, and hyper-secretion of different cytokines, both in vitro (after stimulation) and directly ex vivo. We also found that TLR5-deficient DCs were able to promote polyclonal and islet antigen-specific CD4+ T cell proliferation and proinflammatory cytokine secretion. Interestingly, only older TLR5-deficient NOD mice had a greater risk of developing spontaneous T1D compared to wild-type mice.

Discussion

In summary, our data show that TLR5 modulates DC development and enhances cytokine secretion and diabetogenic CD4+ T cell responses. Further investigation into the role of TLR5 in DC development and autoimmune diabetes may give additional insights into the pathogenesis of Type 1 diabetes.

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.

Mechanisms modulating the activities of intestinal stem cells upon radiation or chemical agent exposure

Intestinal stem cells (ISCs) are essential for the regeneration of intestinal cells upon radiation or chemical agent damage. As for radiation-induced damage, the expression of AIM2, YAP, TLR3, PUMA or BVES can aggravate ISCs depletion, while the stimulation of TLR5, HGF/MET signaling, Ass1 gene, Slit/Robo signaling facilitate the radio-resistance of ISCs. Upon chemical agent treatment, the activation of TRAIL or p53/PUMA pathway exacerbate injury on ISCs, while the increased levels of IL-22, β-arrestin1 can ease the damage. The transformation between reserve ISCs (rISCs) maintaining quiescent states and active ISCs (aISCs) that are highly proliferative has obtained much attention in recent years, in which ISCs expressing high levels of Hopx, Bmi1, mTert, Krt19 or Lrig1 are resistant to radiation injury, and SOX9, MSI2, clusterin, URI are essential for rISCs maintenance. The differentiated cells like Paneth cells and enteroendocrine cells can also obtain stemness driven by radiation injury mediated by Wnt or Notch signaling. Besides, Mex3a-expressed ISCs can survive and then proliferate into intestinal epithelial cells upon chemical agent damage. In addition, the modulation of symbiotic microbes harboring gastrointestinal (GI) tract is also a promising strategy to protect ISCs against radiation damage. Overall, the strategies targeting mechanisms modulating ISCs activities are conducive to alleviating GI injury of patients receiving chemoradiotherapy or victims of nuclear or chemical accident.

The Interplay between Nutrition, Innate Immunity, and the Commensal Microbiota in Adaptive Intestinal Morphogenesis

The gastrointestinal tract is a functionally and anatomically segmented organ that is colonized by microbial communities from birth. While the genetics of mouse gut development is increasingly understood, how nutritional factors and the commensal gut microbiota act in concert to shape tissue organization and morphology of this rapidly renewing organ remains enigmatic. Here, we provide an overview of embryonic mouse gut development, with a focus on the intestinal vasculature and the enteric nervous system. We review how nutrition and the gut microbiota affect the adaptation of cellular and morphologic properties of the intestine, and how these processes are interconnected with innate immunity. Furthermore, we discuss how nutritional and microbial factors impact the renewal and differentiation of the epithelial lineage, influence the adaptation of capillary networks organized in villus structures, and shape the enteric nervous system and the intestinal smooth muscle layers. Intriguingly, the anatomy of the gut shows remarkable flexibility to nutritional and microbial challenges in the adult organism.

Anesthetics isoflurane and sevoflurane attenuate flagellin-mediated inflammation in the lung

Isoflurane and sevoflurane are volatile anesthetics (VA) widely used in clinical practice to provide general anesthesia. We and others have previously shown that VAs have immunomodulatory effects and may have a significant impact on the progression of disease states. Flagellin is a component of Gram negative bacteria and plays a significant role in the pathophysiology of bacterial pneumonia through its binding to Toll-like Receptor 5 (TLR5). Our results showed that VAs, not an intravenous anesthetic, significantly attenuated the activation of TLR5 and the release of the neutrophil chemoattractant IL-8 from lung epithelial cells. Furthermore, flagellin-induced lung injury was significantly attenuated by VAs by inhibiting neutrophil migration to the bronchoalveolar space. The lungs of cystic fibrosis (CF) patients are highly colonized by Pseudomonas aeruginosa, which causes inflammation. The retrospective study of oxygenation in patients with CF who had received VA versus intravenous anesthesia suggested that VAs might have the protective effect for gas exchange. To understand the interaction between VAs and TLR5, a docking simulation was performed, which indicated that isoflurane and sevoflurane docked into the binding interphase between TLR5 and flagellin.

Comparative analysis on the anti-inflammatory/immune effect of mesenchymal stem cell therapy for the treatment of pulmonary arterial hypertension

Despite the advancement of targeted therapy for pulmonary arterial hypertension (PAH), poor prognosis remains a reality. Mesenchymal stem cells (MSCs) are one of the most clinically feasible alternative treatment options. We compared the treatment effects of adipose tissue (AD)-, bone marrow (BD)-, and umbilical cord blood (UCB)-derived MSCs in the rat monocrotaline-induced pulmonary hypertension (PH) model. The greatest improvement in the right ventricular function was observed in the UCB-MSCs treated group. The UCB-MSCs treated group also exhibited the greatest improvement in terms of the largest decrease in the medial wall thickness, perivascular fibrosis, and vascular cell proliferation, as well as the lowest levels of recruitment of innate and adaptive immune cells and associated inflammatory cytokines. Gene expression profiling of lung tissue confirmed that the UCB-MSCs treated group had the most notably attenuated immune and inflammatory profiles. Network analysis further revealed that the UCB-MSCs group had the greatest therapeutic effect in terms of the normalization of all three classical PAH pathways. The intravenous injection of the UCB-MSCs, compared with those of other MSCs, showed superior therapeutic effects in the PH model for the (1) right ventricular function, (2) vascular remodeling, (3) immune/inflammatory profiles, and (4) classical PAH pathways.

When Innate Immunity Meets Angiogenesis-The Role of Toll-Like Receptors in Endothelial Cells and Pulmonary Hypertension

Toll-like receptors serve a central role in innate immunity, but they can also modulate cell function in various non-immune cell types including endothelial cells. Endothelial cells are necessary for the organized function of the vascular system, and part of their fundamental role is also the regulation of immune function and inflammation. In this review, we summarize the current knowledge of how Toll-like receptors contribute to the immune and non-immune functions of the endothelial cells.

Effects of Short-Peptide-Based Enteral Nutrition on the Intestinal Microcirculation and Mucosal Barrier in Mice with Severe Acute Pancreatitis

SCOPE

Short-peptide-based enteral nutrition (SPEN) is absorbed more efficiently in patients with severe acute pancreatitis (SAP). More importantly, SPEN decreases SAP-induced enterogenous infection risk. This study aims to investigate whether SPEN alleviates intestinal bacterial translocation in mice with SAP, and the underlying mechanisms.

METHODS AND RESULTS

The SAP model is established after pre-treatment with SPEN or intact-protein-based enteral nutrition. Although there is no improvement in pancreas injury, as evaluated through Hematoxylin-Eosin staining or serum amylase, SPEN obviously attenuates intestinal bacterial translocation after SAP. To unveil the mechanisms, it is found that the intestinal mechanical barrier destroyed by SAP is significantly relieved by SPEN, which presents with recovered ZO-1 expression, mucus layer, and goblet cell function. Additionally, SPEN alleviates local CCR6/CCL20 induced CD11c+ dendritic cell infiltration, systemic immunosuppression, and inhibits the secretion of luminal secretory immunoglobulin A. Possibly responsible for SAP-induced mucosal dysfunctions, destroyed intestinal mucosal microcirculation and local hypoxia are largely improved in SAP+SPEN group.

CONCLUSION

SPEN can improve downregulated intestinal mucosal microcirculation secondary to SAP, which may be responsible for mucosal inflammation relief, maintenance of the mechanical barrier and mucosal immunity, the correction of systemic immunosuppression, and play a protective role in defending commensal bacterial translocation after SAP.

Inflammatory Response to Different Toxins in Experimental Sepsis Models

Sepsis is defined as life-threatening organ dysfunction caused by the dysregulated host response to infection. Despite serious mortality and morbidity, no sepsis-specific drugs exist. Endotoxemia is often used to model the hyperinflammation associated with early sepsis. This model classically uses lipopolysaccharide (LPS) from Gram-negative pathogens to activate the immune system, leading to hyperinflammation, microcirculatory disturbances and death. Other toxins may also be used to activate the immune system including Gram-positive peptidoglycan (PG) and lipoteichoic acid (LTA). In addition to these standard toxins, other bacterial components can induce inflammation. These molecules activate different signaling pathways and produce different physiological responses which can be taken advantage of for sepsis modeling. Endotoxemia modeling can provide information on pathways to inflammation in sepsis and contribute to preclinical drug development.

Species-specific enhancement of enterohemorrhagic E. coli pathogenesis mediated by microbiome metabolites

BACKGROUND

Species-specific differences in tolerance to infection are exemplified by the high susceptibility of humans to enterohemorrhagic Escherichia coli (EHEC) infection, whereas mice are relatively resistant to this pathogen. This intrinsic species-specific difference in EHEC infection limits the translation of murine research to human. Furthermore, studying the mechanisms underlying this differential susceptibility is a difficult problem due to complex in vivo interactions between the host, pathogen, and disparate commensal microbial communities.

RESULTS

We utilize organ-on-a-chip (Organ Chip) microfluidic culture technology to model damage of the human colonic epithelium induced by EHEC infection, and show that epithelial injury is greater when exposed to metabolites derived from the human gut microbiome compared to mouse. Using a multi-omics approach, we discovered four human microbiome metabolites-4-methyl benzoic acid, 3,4-dimethylbenzoic acid, hexanoic acid, and heptanoic acid-that are sufficient to mediate this effect. The active human microbiome metabolites preferentially induce expression of flagellin, a bacterial protein associated with motility of EHEC and increased epithelial injury. Thus, the decreased tolerance to infection observed in humans versus other species may be due in part to the presence of compounds produced by the human intestinal microbiome that actively promote bacterial pathogenicity.

CONCLUSION

Organ-on-chip technology allowed the identification of specific human microbiome metabolites modulating EHEC pathogenesis. These identified metabolites are sufficient to increase susceptibility to EHEC in our human Colon Chip model and they contribute to species-specific tolerance. This work suggests that higher concentrations of these metabolites could be the reason for higher susceptibility to EHEC infection in certain human populations, such as children. Furthermore, this research lays the foundation for therapeutic-modulation of microbe products in order to prevent and treat human bacterial infection.

MiR-3926 inhibits synovial fibroblasts proliferation and inflammatory cytokines secretion through targeting toll like receptor 5

Rheumatoid arthritis synovial fibroblasts (RASFs) play a key role in the pathogenesis of rheumatoid arthritis (RA). This study was aimed to investigate the effects of miR-3926 on the biological activities of RASFs. The results showed that miR-3926 was significantly down-regulated in RASFs and RA synovial tissue. Overexpression of miR-3926 significantly inhibited RASFs proliferation and decreased the secretion of inflammatory cytokines including TNF-α, IL-1β and IL-6 in RASFs. TLR5 was identified to be a direct target of miR-3926. TLR5 showed an opposite expression trends with miR-3926 in RASFs and RA synovial tissue. Overexpression of miR-3926 led to a reduction of endogenous TLR5 in RASFs, whereas down-regulation of miR-3926 increased TLR5 expression. Knocking down of TLR5 significantly inhibited RASFs proliferation and inflammatory cytokines secretion. Rescue experiments with a miR-3926-resistant variant of TLR5 showed that overexpression of TLR5 restored RASFs proliferation and inflammatory cytokines secretion in miR-3926-overexpressing RASFs. In conclusion, miR-3926 is downregulated in RA synovial tissues and its overexpression caused the inhibitory effects on RASF proliferation and inflammatory cytokines secretion by targeting TLR5. The miR-3926/TLR5 pathway may represent a novel target for prevention and treatment of RA.

Functional expression of TLR5 in murine salivary gland epithelial cells

Toll-like receptors (TLR) recognize microbe-associated molecular patterns and induce the innate immune response. Among them, TLR5 recognizes the Gram-negative bacterial component flagellin. The aim of this study was to examine the expression of TLR5 in mouse salivary gland (SG). The SG was excised from 8- to 10-week-old female C57BL/6 mice. Salivary gland epithelial cells (SGECs) were purified and subjected to reverse transcription polymerase chain reaction (RT-PCR). Western blotting was performed to detect TLR5 expression at the protein level in several organs. The localization of TLR5 in SG was examined using immunohistochemical staining. The responsiveness of SGECs to flagellin was further examined by evaluating the induction of CXCL1 by real-time PCR and immunoprecipitation followed by Western blotting. TLR5 expression in SG was confirmed at the gene and protein levels. Immunohistochemical staining detected TLR5 in both acinic and ductal cells of the sublingual gland, but not in serous acinic cells of the submandibular gland. Although TLR5 was detected throughout the cytoplasm in ductal cells, positive staining was observed on the basal side of the mucous acinic cells. The purified SGECs responded to flagellin and induced the production of CXCL1. These findings suggest that TLR5 is functionally expressed in the SG and responds to its cognate ligand flagellin. (J Oral Sci 58, 317-323, 2016).

Toll-like receptors elicit different recruitment kinetics of monocytes and neutrophils in mouse acute inflammation

Leukocyte recruitment is an important process in combating pathogens. The largest class of circulating leukocytes are neutrophils, which rapidly invade inflamed tissue, followed by inflammatory Ly6C⁺ monocytes. Ly6C^low monocytes patrol the endothelial wall routinely in the steady state. We recently reported early luminal recruitment of Ly6C^low monocytes, which preceded and orchestrated neutrophil arrival and extravasation in response to TLR7/8-mediated vascular inflammation. Here we dissected the kinetics of recruitment of monocytes and neutrophils and examined the dynamics of Ly6C^low monocytes in response to several other Toll-like receptor (TLR) agonists, using intravital confocal microscopy. We observed two types of kinetics in mesenteric veins. TLR2, TLR5 and TLR9 agonists caused early monocyte and neutrophil influx whereas TLR3 and TLR4 agonists rapidly recruited neutrophils and caused Ly6C^low monocytes to arrive at low levels later on. All TLR agonists, except TLR9, led Ly6C^low monocytes to meticulously patrol the vascular wall. Finally, these monocytes released pro-inflammatory cytokines and chemokines implicated in neutrophil recruitment in response to TLR2, TLR4, and TLR9 stimulation but not to TLR3 and TLR5 agonists. These results refine our understanding of the early events in the leukocyte recruitment cascade, including the patrolling behavior of Ly6C^low monocytes, in TLR-mediated acute vascular inflammation.

Modulation of endothelial function by Toll like receptors

Endothelial cells (EC) are able to actively control vascular permeability, coagulation, blood pressure and angiogenesis. Most recently, a role for endothelial cells in the immune response has been described. Therefore, the endothelium has a dual role controlling homeostasis but also being the first line for host defence and tissue damage repair thanks to its ability to mount an inflammatory response. Endothelial cells have been shown to express pattern-recognition receptors (PRR) including Toll-like receptors (TLR) that are activated in response to stimuli within the bloodstream including pathogens and damage signals. TLRs are strategic mediators of the immune response in endothelial cells but they also regulate the angiogenic process critical for tissue repair. Nevertheless, endothelial activation and angiogenesis can contribute to some pathologies. Thus, inappropriate endothelial activation, also known as endothelial dysfunction, through TLRs contributes to tissue damage during autoimmune and inflammatory diseases such as atherosclerosis, hypertension, ischemia and diabetes associated cardiovascular diseases. Also TLR induced angiogenesis is required for the growth of some tumors, atherosclerosis and rheumatoid arthritis, among others. In this review we discuss the importance of various TLRs in modulating the activation of endothelial cells and their importance in immunity to infection and vascular disease as well as their potential as therapeutic targets.

Vascular endothelial cell Toll-like receptor pathways in sepsis

The endothelium forms a vast network that dynamically regulates vascular barrier function, coagulation pathways and vasomotor tone. Microvascular endothelial cells are uniquely situated to play key roles during infection and injury, owing to their widespread distribution throughout the body and their constant interaction with circulating blood. While not viewed as classical immune cells, endothelial cells express innate immune receptors, including the Toll-like receptors (TLRs), which activate intracellular inflammatory pathways mediated through NF-κB and the MAP kinases. TLR agonists, including LPS and bacterial lipopeptides, directly upregulate microvascular endothelial cell expression of inflammatory mediators. Intriguingly, TLR activation also modulates microvascular endothelial cell permeability and the expression of coagulation pathway intermediaries. Microvascular thrombi have been hypothesized to trap microorganisms thereby limiting the spread of infection. However, dysregulated activation of endothelial inflammatory pathways is also believed to lead to coagulopathy and increased vascular permeability, which together promote sepsis-induced organ failure. This article reviews vascular endothelial cell innate immune pathways mediated through the TLRs as they pertain to sepsis, highlighting links between TLRs and coagulation and permeability pathways, and their role in healthy and pathologic responses to infection and sepsis.

Role of translocated bacterial flagellin in monocyte activation among individuals with chronic HIV-1 infection

Monocyte activation has been identified as a predictor of mortality and morbidity in HIV-1 infection. This study investigated translocated bacterial flagellin as a potential contributor to systemic monocyte activation via Toll-like receptor 5 (TLR5) stimulation.We demonstrated that circulating flagellin correlated to anti-flagellin, which was associated with soluble markers of microbial translocation (LPS, LBP) and monocyte activation (sCD14, sCD163). Flagellin exposure in vitro reduced monocyte TLR5 expression and the magnitude of reduction was correlated to anti-flagellin levels, indicative of previous flagellin exposure. Circulating anti-flagellin and basal TLR5 expression were both associated with basal and flagellin-stimulated monocyte cytokine production, where HIV + and HIV − differed in their cytokine patterns (IL-1β, IL-6, IL-8).Our results suggest that translocated flagellin contributes to systemic immune activation in HIV-1 infection and reduces monocyte surface TLR5 expression resulting in a hyperactivated state with elevated basal cytokine production and reduced ability to respond to further TLR5 stimulation.

Suppression of Toll-like receptor-mediated innate immune responses at the ocular surface by the membrane-associated mucins MUC1 and MUC16

Membrane-associated mucins (MAMs) expressed on the ocular surface epithelium form a dense glycocalyx that is hypothesized to protect the cornea and conjunctiva from external insult. In this study, the hypothesis that the MAMs MUC1 and MUC16, expressed on the apical surface of the corneal epithelium, suppress Toll-like receptor (TLR)-mediated innate immune responses was tested. Using an in vitro model of corneal epithelial cells that are cultured to express MAMs, we show that reduced expression of either MUC1 or MUC16 correlates with increased message and secreted protein levels of the proinflammatory cytokines interleukin (IL)-6, IL-8, and tumor necrosis factor-α (TNF-α) following exposure of cells to the TLR2 and TLR5 agonists, heat-killed Listeria monocytogenes and flagellin, respectively. As mice express Muc1 (but not Muc16) in the corneal epithelium, a Muc1(-/-) mouse model was used to extend in vitro findings. Indeed, IL-6 and TNF-α message levels were increased in the corneal epithelium of Muc1(-/-) mice, in comparison with wild-type mice, following exposure of enucleated eyes to the TLR2 and TLR5 agonists. Our results suggest that the MAMs MUC1 and MUC16 contribute to the maintenance of immune homeostasis at the ocular surface by limiting TLR-mediated innate immune responses.

TLR5 Ligand-Secreting T Cells Reshape the Tumor Microenvironment and Enhance Antitumor Activity

The tumor microenvironment counters antitumor T-cell responses, in part, by blunting their activation and infiltration. Ligands that engage Toll-like receptors (TLR) on T cells and antigen-presenting cells can act as potent immune adjuvants. In this study, we show how tumor-reactive T cells engineered to secrete bacterial flagellin, a TLR5 ligand (TLR5L), can engender a costimulatory signal that augments antitumor activity. Human T cells engineered to express TLR5L along with DMF5, a T-cell receptor that recognizes the melanoma antigen MART-127-35 (DMF5(TLR5L) T cells), displayed increased proliferation, cytokine production, and cytolytic activity against melanoma cells. In a xenogenetic model, adoptive transfer of DMF5(TLR5L) T cells reduced tumor growth kinetics and prolonged mouse survival. In a syngeneic model, similarly engineered melanoma-reactive T cells (pmel(TLR5L)) displayed a relative increase in antitumor activity against established tumors, compared with unmodified T cells. In this model, we documented increased T-cell infiltration associated with increased levels of CCR1 and CXCR3 levels on T cells, a reduction in PD-1(+)Lag3(+) T cells and CD11(+)Gr1(+) myeloid-derived suppressor cells, and changes in the chemokine/cytokine profile of tumors. Our findings show how T cell-mediated delivery of a TLR agonist to the tumor site can contribute to antitumor efficacy, in the context of adoptive T-cell immunotherapy.

Intestinal mucosal tolerance and impact of gut microbiota to mucosal tolerance

The mucosal barriers are very sensitive to pathogenic infection, thereby assuming the capacity of the mucosal immune system to induce protective immunity to harmful antigens and tolerance against harmless substances. This review provides current information about mechanisms of induction of mucosal tolerance and about impact of gut microbiota to mucosal tolerance.

Interferons and interferon regulatory factors in malaria

Malaria is one of the most serious infectious diseases in humans and responsible for approximately 500 million clinical cases and 500 thousand deaths annually. Acquired adaptive immune responses control parasite replication and infection-induced pathologies. Most infections are clinically silent which reflects on the ability of adaptive immune mechanisms to prevent the disease. However, a minority of these can become severe and life-threatening, manifesting a range of overlapping syndromes of complex origins which could be induced by uncontrolled immune responses. Major players of the innate and adaptive responses are interferons. Here, we review their roles and the signaling pathways involved in their production and protection against infection and induced immunopathologies.

Toll-like receptor regulation of intestinal development and inflammation in the pathogenesis of necrotizing enterocolitis

Toll-like receptors (TLRs) are a structurally related family of molecules that respond to a wide variety of endogenous and exogenous ligands, and which serve as important components of the innate immune system. While TLRs have established roles in host defense, these molecules have also been shown to play important roles in the development of various disease states. A particularly important example of the role of TLRs in disease induction includes necrotizing enterocolitis (NEC), which is the most common gastrointestinal disease in preterm infants, and which is associated with extremely high morbidity and mortality rates. The development of NEC is thought to reflect an abnormal interaction between microorganisms and the immature intestinal epithelium, and emerging evidence has clearly placed the spotlight on an important and exciting role for TLRs, particularly TLR4, in NEC pathogenesis. In premature infants, TLR4 signaling within the small intestinal epithelium regulates apoptosis, proliferation and migration of enterocytes, affects the differentiation of goblet cells, and reduces microcirculatory perfusion, which in combination result in the development of NEC. This review will explore the signaling properties of TLRs on hematopoietic and non-hematopoietic cells, and will examine the role of TLR4 signaling in the development of NEC. In addition, the effects of dampening TLR4 signaling using synthetic and endogenous TLR4 inhibitors and active components from amniotic fluid and human milk on NEC severity will be reviewed. In so doing, we hope to present a balanced approach to the understanding of the role of TLRs in both immunity and disease pathogenesis, and to dissect the precise roles for TLR4 in both the cause and therapeutic intervention of necrotizing enterocolitis.

Identification of granulocyte colony-stimulating factor and interleukin-6 as candidate biomarkers of CBLB502 efficacy as a medical radiation countermeasure

Given an ever-increasing risk of nuclear and radiological emergencies, there is a critical need for development of medical radiation countermeasures (MRCs) that are safe, easily administered, and effective in preventing and/or mitigating the potentially lethal tissue damage caused by acute high-dose radiation exposure. Because the efficacy of MRCs for this indication cannot be ethically tested in humans, development of such drugs is guided by the Food and Drug Administration's Animal Efficacy Rule. According to this rule, human efficacious doses can be projected from experimentally established animal efficacious doses based on the equivalence of the drug's effects on efficacy biomarkers in the respective species. Therefore, identification of efficacy biomarkers is critically important for drug development under the Animal Efficacy Rule. CBLB502 is a truncated derivative of the Salmonella flagellin protein that acts by triggering Toll-like receptor 5 (TLR5) signaling and is currently under development as a MRC. Here, we report identification of two cytokines, granulocyte colony-stimulating factor (G-CSF) and interleukin-6 (IL-6), as candidate biomarkers of CBLB502's radioprotective/mitigative efficacy. Induction of both G-CSF and IL-6 by CBLB502 1) is strictly TLR5-dependent, 2) occurs in a CBLB502 dose-dependent manner within its efficacious dose range in both nonirradiated and irradiated mammals, including nonhuman primates, and 3) is critically important for the ability of CBLB502 to rescue irradiated animals from death. After evaluation of CBLB502 effects on G-CSF and IL-6 levels in humans, these biomarkers will be useful for accurate prediction of human efficacious CBLB502 doses, a key step in the development of this prospective radiation countermeasure.

TLR5, a novel and unidentified inflammatory mediator in rheumatoid arthritis that correlates with disease activity score and joint TNF-α levels

The innate immune system plays an important role in rheumatoid arthritis (RA) pathogenesis. Previous studies support the role of TLR2 and 4 in RA and experimental arthritis models; however, the regulation and pathogenic effect of TLR5 is undefined in RA. In this study, we show that TLR5 is elevated in RA and osteoarthritis ST lining and sublining macrophages and endothelial cells compared with normal individuals. Furthermore, expression of TLR5 is elevated in RA synovial fluid macrophages and RA peripheral blood monocytes compared with RA and normal peripheral blood in vitro-differentiated macrophages. We also found that TLR5 on RA monocytes is an important modulator of TNF-α in RA synovial fluid and that TLR5 expression on these cells strongly correlates with RA disease activity and TNF-α levels. Interestingly, TNF-α has a feedback regulation with TLR5 expression in RA monocytes, whereas expression of this receptor is regulated by IL-17 and IL-8 in RA macrophages and fibroblasts. We show that RA monocytes and macrophages are more responsive to TLR5 ligation compared with fibroblasts despite the proinflammatory response being mediated through the same signaling pathways in macrophages and fibroblasts. In conclusion, we document the potential role of TLR5 ligation in modulating transcription of TNF-α from RA synovial fluid and the strong correlation of TLR5 and TNF-α with each other and with disease activity score in RA monocytes. Our results suggest that expression of TLR5 may be a predictor for RA disease progression and that targeting TLR5 may suppress RA.

Toll-like receptor 5 deficiency protects from wasting disease in a T cell transfer colitis model in T cell receptor-β-deficient mice

BACKGROUND

Toll-like receptor 5 (TLR5) is implicated in the innate and adaptive immune responses that are associated with inflammatory bowel disease (IBD). In humans TLR5 is expressed on CD4(+) T cells and costimulation with flagellin potentiates effector and regulatory T cell responses. The aim of this study was to determine the role of TLR5 in CD4(+) T cell subsets versus other cells in induction of disease in a model of T cell-dependent colitis.

METHODS

TLR5 expression on CD4(+) T cells was assessed by real-time reverse-transcriptase polymerase chain reaction (RT-PCR). Wildtype (WT) or TLR5-deficient (5-/-) CD4(+) T conventional cells (Tconv) and T regulatory cells (Treg) were compared for their ability to induce and suppress T cell transfer colitis, respectively. In addition, the role of TLR5 expression in recipient mice was analyzed.

RESULTS

TLR5 is preferentially expressed on mouse Treg compared to Tconv, although expression levels were low. The colitogenic capacity of WT and 5-/- Tconv was found to be similar and Treg from WT or 5-/- donor animals both prevented T cell transfer colitis in TLR-competent hosts. TLR5 deficiency in recipient mice, however, did affect the disease process, as T cell receptor-β (TCRβ) 5-/- recipients had decreased weight loss compared to TCRβ recipient mice when WT Tconv were used.

CONCLUSIONS

TLR5 expression on T cells is not required for induction of or protection from T cell-dependent colitis. Expression of TLR5 in non-T cells has a pathogenic role, since TLR5 deficiency in recipient mice protects against weight loss induced by WT T cells.

B cell toll-like receptors with respect to the pathogenesis of Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune immunopathological disease of unknown aetiology. It is characterized by focal lymphocyte infiltration and inflammation in exocrinne glands, involving especially salivary and lacrimal glands. Hypofunction of the glands leads to the decreased glandular secretion together with impaired production of saliva and tears, resulting in dryness of the mouth and eyes (xerostomia and xerophthalmia, respectively). Some of the studies have suggested that Toll-like receptors and B cells play a pivotal role in the pathogenesis of autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis and SS etc. Stimulation of B cells via the TLRs pathway leads to several important changes including increase in antibody production, differentiation to plasma cells, cytokine production and up-regulation of molecules essential for antigen presentation to (autoreactive) T cells. Experimental data support the idea that co-engagement of BCR and TLR might be sufficient for B cell activation and lead to the failure of tolerance. In human naive B cells, most TLRs are expressed at very low or undetectable level, but expression of TLR 7 and 9 is rapidly induced by B cell receptor triggering. This review will focus on the possible role of B cells and TLRs signaling in the pathogenesis of SS.

Heterogeneous expression of toll-like receptors in lymphatic endothelial cells derived from different tissues

As lymphatic endothelial cells (LECs) express different lymphatic and vascular markers depending on the organ they are derived from, we analysed whether they also show a heterogeneity of response against pathogens. To this end we analysed, for the presence of mRNA encoding for all human toll-like receptor (TLR), LECs isolated from lymph nodes and thymuses. RNA for TLR1-6 and 9 was identified in thymus-derived cells, whereas cells derived from lymph nodes contained mRNA for TLR1-4, 6 and 9, but failed to express mRNA specific for TLR5. The differential expression of TLRs was confirmed by the phosphorylation of nuclear factor-κB p65 only when the two types of LECs were incubated with the appropriate TLR agonists. The stimulation with specific agonists gives rise to a heterogeneous pattern of cytokine and chemokine secretion: thymus-derived LECs produced preferentially interleukin-6, interferon-inducible protein (IP)-10 and tumour necrosis factor-α, whereas cells prepared from lymph nodes mainly released interleukin-8, monocyte chemotactic protein-1, RANTES and (IP)-10. Finally, cells purified from lymph nodes expressed a higher level of intercellular adhesion molecule-1 than did cells prepared from the thymus when stimulated with several TLR agonists. The expression of a large set of TLRs and the responsiveness to specific agonists suggest that LECs are able to respond to pathogens, and the observed differences reflect specialized functions, redundancy and/or roles of LECs of different origin.

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.

Toll-like receptor 5 stimulation protects mice from acute Clostridium difficile colitis

Clostridium difficile is a spore-forming bacterium that infects the lower intestinal tract of humans and is the most common known cause of diarrhea among hospitalized patients. Clostridium difficile colitis is mediated by toxins and develops during or following antibiotic administration. We have used a murine model of C. difficile infection, which reproduces the major features of the human disease, to study the effect of innate immune activation on resistance to C. difficile infection. We found that administration of purified Salmonella-derived flagellin, a Toll-like receptor 5 (TLR5) agonist, protects mice from C. difficile colitis by delaying C. difficile growth and toxin production in the colon and cecum. TLR5 stimulation significantly improves pathological changes in the cecum and colon of C. difficile-infected mice and reduces epithelial cell loss. Flagellin treatment reduces epithelial apoptosis in the large intestine, thereby protecting the integrity of the intestinal epithelial barrier during C. difficile infection. We demonstrate that restoring intestinal innate immune tone by TLR stimulation in antibiotic-treated mice ameliorates intestinal inflammation and prevents death from C. difficile colitis, potentially providing an approach to prevent C. difficile-induced pathology.

Flagellin as an adjuvant: cellular mechanisms and potential

Flagellin is a potent activator of a broad range of cell types involved in innate and adaptive immunity. An increasing number of studies have demonstrated the effectiveness of flagellin as an adjuvant, as well as its ability to promote cytokine production by a range of innate cell types, trigger a generalized recruitment of T and B lymphocytes to secondary lymphoid sites, and activate TLR5(+)CD11c(+) cells and T lymphocytes in a manner that is distinct from cognate Ag recognition. The plasticity of flagellin has allowed for the generation of a range of flagellin-Ag fusion proteins that have proven to be effective vaccines in animal models. This review summarizes the state of our current understanding of the adjuvant effect of flagellin and addresses important areas of current and future research interest.

Radioprotectors and mitigators of radiation-induced normal tissue injury

Radiation is used in the treatment of a broad range of malignancies. Exposure of normal tissue to radiation may result in both acute and chronic toxicities that can result in an inability to deliver the intended therapy, a range of symptoms, and a decrease in quality of life. Radioprotectors are compounds that are designed to reduce the damage in normal tissues caused by radiation. These compounds are often antioxidants and must be present before or at the time of radiation for effectiveness. Other agents, termed mitigators, may be used to minimize toxicity even after radiation has been delivered. Herein, we review agents in clinical use or in development as radioprotectors and mitigators of radiation-induced normal tissue injury. Few agents are approved for clinical use, but many new compounds show promising results in preclinical testing.

IFN-γ induces IFN-α and IFN-β expressions in cultured rat intestinal mucosa microvascular endothelial cells

Although researchers have recently begun to pay more attention to the immunological characteristics of microvascular endothelial cells (MVECs), there are no reports on whether activation of MVECs by interferon-γ (IFN-γ) exerts any influence on the expressions of IFN-α/β. In the present study, we examined the influence of IFN-γ on the expressions of IFN-α/β in rat intestinal mucous MVECs (RIMMVECs). Different concentrations of IFN-γ were used to stimulate cultured RIMMVECs in vitro, and the cells and cell supernatants were collected at different time intervals. The influence of IFN-γ on the expressions of IFN-α/β in the RIMMVECs was examined at the mRNA and protein levels by real-time quantitative PCR and enzyme-linked immunosorbent assay (ELISA), respectively. The results indicated that IFN-γ was able to activate RIMMVECs, thereby leading to upregulated expressions of IFN-α/β. The real-time quantitative PCR analyses indicated that the IFN-α/β mRNA expression levels in RIMMVECs achieved their peak values after stimulation with IFN-γ at 20 ng/mL for 6 h and were increased by 14.88- and 3.82-fold, respectively, when compared with the levels in negative control cells. The ELISA analyses revealed that the IFN-α/β protein expression levels achieved their peak values after stimulation with IFN-γ at 40 ng/mL. The expression of IFN-α protein achieved its peak value at 12 h, while the expression of IFN-β protein achieved its peak value after 6 h. The present results suggest that the expression and secretion of IFNs may participate in the immunologic barrier function of MVECs.

The response of the host microcirculation to bacterial sepsis: does the pathogen matter?

Sepsis results from the interaction between a host and an invading pathogen. The microcirculatory dysfunction is now considered central in the development of the often deadly multiple organ dysfunction syndrome in septic shock patients. The microcirculatory flow shutdown and flow shunting leading to oxygen demand and supply mismatch at the cellular level and the local activation of inflammatory pathways resulting from the leukocyte–endothelium interactions are both features of the sepsis-induced microcirculatory dysfunction. Although the host response through the inflammatory and immunologic response appears to be critical, there are also evidences that Gram-positive and Gram-negative bacteria can exert different effects at the microcirculatory level. In this review we discuss available data on the potential bacterial-specific microcirculatory alterations observed during sepsis.

Direct stimulation of tlr5+/+ CD11c+ cells is necessary for the adjuvant activity of flagellin

Flagellin is a highly effective adjuvant, but the cellular mechanism underlying this activity remains uncertain. More specifically, no consensus exists as to whether flagellin activates dendritic cells (DC) directly or indirectly. Intramuscular immunization with flagellin-OVA fusion protein resulted in enhanced in vivo T cell clustering in draining lymph nodes and IL-2 production by OVA-specific CD4(+) T cells. Immunization with flagellin-OVA also triggered greater levels of Ag-specific CD4(+) T cell proliferation than immunization with flagellin and OVA as separate proteins. To determine whether flagellin, in the context of a fusion protein with OVA, was acting directly on DC, we used a combination of CD4(+) T cell adoptive transfers and bone marrow chimera mice in which the presence or absence of potential tlr5(+/+) CD11c(+) cells was controlled by injection of diphtheria toxin. The Ag-specific CD4(+) T cell response in mice with CD11c(+) cells from a tlr5(-/-) background and mixed populations of all other hematopoietic cells was dramatically reduced in comparison to mice that had DC from tlr5(-/-) and wild-type backgrounds. Immunization of MyD88(-/-)tlr5(+/+) mice revealed that the enhanced response following immunization with flagellin-OVA is dependent on signaling via the TLR5-MyD88 pathway as well as enhanced Ag uptake and processing resulting from Ag targeting via TLR5. In summary, our data are consistent with the conclusion that direct stimulation of tlr5(+/+) CD11c(+) cells is necessary for the adjuvant activity of a flagellin fusion protein and that this adjuvant effect requires signaling through TLR5.

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.

Up-regulation of intestinal Toll-Like receptors and cytokines expressions change after TPN administration and a lack of enteral feeding

BACKGROUND

Total parenteral nutrition (TPN) increases the risk of severe infectious complications such as septic shock, which are believed to be the result of a breakdown of intestinal barrier function and subsequent bacterial translocation. Toll-like receptors (TLRs) comprise a family of membrane proteins that serve as pattern recognition receptors for a variety of microbe-derived molecules and stimulate innate immune responses to microbes. Alteration of intraepithelial lymphocytes (IELs) to TPN administration has been studied extensively. However, few studies have examined the effect of TPN administration on intestinal TLRs. We hypothesized that the expressions of intestinal TLRs and cytokines may change with TPN administration and a lack of enteral feeding.

MATERIALS AND METHODS

TPN-treated mice and sham operation mice (control) were killed at 10 days after operation. mRNA expression of intestinal cytokines and TLRs were analyzed with reverse transcription-polymerase chain reaction (RT-PCR) methods. Change in IEL populations was analyzed with flow cytometry.

RESULTS

RT-PCR showed varying expression levels of TLRs at different sites on the small intestine and colon. TLR4, TLR5, TLR7, and TLR9 mRNAs were up-regulated in response to TPN administration, particularly in the distal small intestine.

CONCLUSIONS

Up-regulation of TLRs in intestine in response to TPN administration and a lack of enteral nutrition may be associated with an increased risk of septic shock due to bacterial translocation caused by Interferon gamma-mediated intestinal epithelial cell apoptosis.

The ex vivo response of human intestinal mucosa to enteropathogenic Escherichia coli infection

In vitro organ culture (IVOC) represents a gold standard model to study enteropathogenic E. coli (EPEC) infection of human intestinal mucosa. However, the optimal examination of the bacterial-host cell interaction requires a directional epithelial exposure, without serosal or cut surface stimulation. A polarized IVOC system (pIVOC) was developed in order to overcome such limitations: apical EPEC infection produced negligible bacterial leakage via biopsy edges, resulted in enhanced colonization compared with standard IVOC, and showed evidence of bacterial detachment, as in natural rabbit EPEC infections. Examination of mucosal innate immune responses in pIVOC showed both interleukin (IL)-8 mRNA and protein levels were significantly increased after apical EPEC infection. Increased IL-8 levels mainly depended on flagellin expression as fliC-negative EPEC did not elicit a significant IL-8 response despite increased mucosal colonization compared with wild-type EPEC. In addition, apical application of purified flagella significantly increased IL-8 protein levels over non-infected controls. Immunofluorescence staining of EPEC-infected small intestinal biopsies revealed apical and basolateral distribution of Toll-like receptor (TLR) 5 on epithelium, suggesting that EPEC can trigger mucosal IL-8 responses by apical flagellin/TLR5 interaction ex vivo and does not require access to the basolateral membrane as postulated in cell culture models.

The role of T-regulatory cells and Toll-like receptors in the pathogenesis of human inflammatory bowel disease

Two related chronic inflammatory diseases, Crohn's disease and ulcerative colitis, are together often referred to as inflammatory bowel disease (IBD). Current treatment options are not curative, and patients face lifelong therapy and debilitation. IBD is thought to be the product of a combination of genetic and environmental factors that result in the abnormal regulation of immune responses. Experimental models have demonstrated that normal CD4+ T-regulatory (Treg) cell responses and commensal bacteria are required for the maintenance of gut immune homeostasis. Recent evidence that CD4+ T cells express Toll-like receptors (TLRs) and respond directly to TLR ligands, suggests that signals from commensal bacteria may directly affect T-cell responses in the gut. In this review, we focus on evidence that defects in Treg cells may underlie IBD in humans. In addition, we discuss evidence that direct signaling via TLRs to T cells can affect IBD and that T-cell-dependent responses to bacterial proteins, such as flagellin, are central to the aetiology of this disease.

The role of T-regulatory cells and Toll-like receptors in the pathogenesis of human inflammatory bowel disease

Two related chronic inflammatory diseases, Crohn's disease and ulcerative colitis, are together often referred to as inflammatory bowel disease (IBD). Current treatment options are not curative, and patients face lifelong therapy and debilitation. IBD is thought to be the product of a combination of genetic and environmental factors that result in the abnormal regulation of immune responses. Experimental models have demonstrated that normal CD4+ T-regulatory (Treg) cell responses and commensal bacteria are required for the maintenance of gut immune homeostasis. Recent evidence that CD4+ T cells express Toll-like receptors (TLRs) and respond directly to TLR ligands, suggests that signals from commensal bacteria may directly affect T-cell responses in the gut. In this review, we focus on evidence that defects in Treg cells may underlie IBD in humans. In addition, we discuss evidence that direct signaling via TLRs to T cells can affect IBD and that T-cell-dependent responses to bacterial proteins, such as flagellin, are central to the aetiology of this disease.

Molecular pathogenesis of inflammatory bowel disease: relevance for novel therapies

The immense load of microorganisms within the gastrointestinal tract is a great challenge for the mucosal immune system. Whereas the vast majority of commensal bacteria should be tolerated, pathogenic organisms have to be attacked. During inflammatory bowel disease, the balanced interaction between the mucosal flora and the intestinal immune system is disturbed. Various defective components of this complex interaction have been described, such as different susceptibility genes, impaired innate immune responses and environmental factors, suggesting that inflammatory bowel diseases are multifactorial diseases. Based on new insights into the pathogenesis of inflammatory bowel disease, various targets for future drugs have been identified and new substances are emerging. The following article will review the current understanding of inflammatory bowel disease pathogenesis in context with genetic risk factors, imbalanced innate and acquired immune responses, and altered barrier function. Clinical treatment of the diseases will be summarized and emerging therapies as well as individual management based on recent insights into pathogenesis will be discussed.

Vascular cell responsiveness to Toll-like receptor ligands in carotid atheroma

BACKGROUND

Atherosclerosis is potentiated by stimulation of Toll-like receptors (TLRs), which serve to detect pathogen associated molecular patterns (PAMPs). However little is known of which PAMPs may be present in atheroma, or capable of stimulating inflammatory signalling in vascular cells.

MATERIALS AND METHODS

DNA extracted from human carotid atheroma samples was amplified and sequenced using broad-range 16S gene specific primers to establish historical exposure to bacterial PAMPs. Responsiveness of primary human arterial and venous endothelial and smooth muscle cells to PAMPs specific for each of the TLRs was assessed by measurement of interleukin-8 secretion and E-selectin expression.

RESULTS

Extracts of atheromatous tissue stimulated little or no signalling in TLR-transfected HEK-293 cells. However, sequencing of bacterial DNA amplified from carotid atheroma revealed the presence of DNA from 17 different bacterial genera, suggesting historical exposure to bacterial lipopeptide, lipopolysaccharide and flagellin. All cells examined were responsive to the ligands of TLR3 and TLR4, poly inosine:cytosine and lipopolysaccharide. Arterial cells were responsive to a wider range of PAMPs than venous cells, being additionally responsive to bacterial flagellin and unmethylated cytosine-phosphate-guanosine DNA motifs, the ligands of TLR5 and TLR9, respectively. Cells were generally unresponsive towards the ligands of human TLR7 and TLR8, loxoribine and single stranded RNA. Only coronary artery endothelial cells expressed TLR2 mRNA and responded to the TLR2 ligand Pam(3)CSK(4).

CONCLUSIONS

Vascular cells are responsive to a relatively diverse range of TLR ligands and may be exposed, at least transiently, to ligands of TLR2, TLR4, TLR5 and TLR9 during the development of carotid atheroma.

Vascular cells contribute to atherosclerosis by cytokine- and innate-immunity-related inflammatory mechanisms

Cardiovascular diseases are the human diseases with the highest death rate and atherosclerosis is one of the major underlying causes of cardiovascular diseases. Inflammatory and innate immune mechanisms, employing monocytes, innate receptors, innate cytokines, or chemokines are suggested to be involved in atherogenesis. Among the inflammatory pathways the cytokines are central players. Plasma levels of cytokines and related proteins, such as CRP, have been investigated in cardiovascular patients, tissue mRNA expression was analyzed and correlations to vascular diseases established. Consistent with these findings the generation of cytokine-deficient animals has provided direct evidence for a role of cytokines in atherosclerosis. In vitro cell culture experiments further support the suggestion that cytokines and other innate mechanisms contribute to atherogenesis. Among the initiation pathways of atherogenesis are innate mechanisms, such as toll-like-receptors (TLRs), including the endotoxin receptor TLR4. On the other hand, innate cytokines, such as IL-1 or TNF, or even autoimmune triggers may activate the cells. Cytokines potently activate multiple functions relevant to maintain or spoil homeostasis within the vessel wall. Vascular cells, not least smooth muscle cells, can actively contribute to the inflammatory cytokine-dependent network in the blood vessel wall by: (i) production of cytokines; (ii) response to these potent cell activators; and (iii) cytokine-mediated interaction with invading cells, such as monocytes, T-cells, or mast cells. Activation of these pathways results in accumulation of cells and increased LDL- and ECM-deposition which may serve as an 'immunovascular memory' resulting in an ever-growing response to subsequent invasions. Thus, vascular cells may potently contribute to the inflammatory pathways involved in development and acceleration of atherosclerosis.

Multiple pathogenic roles of microvasculature in inflammatory bowel disease: a Jack of all trades

The etiology of Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD), is still largely unknown. However, it is now clear that the abnormalities underlying pathogenesis of intestinal inflammation are not restricted to those mediated by classic immune cells but also involve nonimmune cells. In particular, advances in vascular biology have outlined a central and multifaceted pathogenic role for the microcirculation in the initiation and perpetuation of IBD. The microcirculation and its endothelial lining play a crucial role in mucosal immune homeostasis through tight regulation of the nature and magnitude of leukocyte migration from the intravascular to the interstitial space. Chronically inflamed IBD microvessels display significant alterations in microvascular physiology and function compared with vessels from healthy and uninvolved IBD intestine. The investigation into human IBD has demonstrated how endothelial activation present in chronically inflamed IBD microvessels results in a functional phenotype that also includes leakiness, chemokine and cytokine expression, procoagulant activity, and angiogenesis. This review contemplates the newly uncovered contribution of intestinal microcirculation to pathogenesis and maintenance of chronic intestinal inflammation. In particular, we assess the multiple roles of the microvascular endothelium in innate immunity, leukocyte recruitment, coagulation and perfusion, and immune-driven angiogenesis in IBD.

Multiple pathogenic roles of microvasculature in inflammatory bowel disease: a Jack of all trades

The etiology of Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD), is still largely unknown. However, it is now clear that the abnormalities underlying pathogenesis of intestinal inflammation are not restricted to those mediated by classic immune cells but also involve nonimmune cells. In particular, advances in vascular biology have outlined a central and multifaceted pathogenic role for the microcirculation in the initiation and perpetuation of IBD. The microcirculation and its endothelial lining play a crucial role in mucosal immune homeostasis through tight regulation of the nature and magnitude of leukocyte migration from the intravascular to the interstitial space. Chronically inflamed IBD microvessels display significant alterations in microvascular physiology and function compared with vessels from healthy and uninvolved IBD intestine. The investigation into human IBD has demonstrated how endothelial activation present in chronically inflamed IBD microvessels results in a functional phenotype that also includes leakiness, chemokine and cytokine expression, procoagulant activity, and angiogenesis. This review contemplates the newly uncovered contribution of intestinal microcirculation to pathogenesis and maintenance of chronic intestinal inflammation. In particular, we assess the multiple roles of the microvascular endothelium in innate immunity, leukocyte recruitment, coagulation and perfusion, and immune-driven angiogenesis in IBD.

An agonist of toll-like receptor 5 has radioprotective activity in mouse and primate models

The toxicity of ionizing radiation is associated with massive apoptosis in radiosensitive organs. Here, we investigate whether a drug that activates a signaling mechanism used by tumor cells to suppress apoptosis can protect healthy cells from the harmful effects of radiation. We studied CBLB502, a polypeptide drug derived from Salmonella flagellin that binds to Toll-like receptor 5 (TLR5) and activates nuclear factor-kappaB signaling. A single injection of CBLB502 before lethal total-body irradiation protected mice from both gastrointestinal and hematopoietic acute radiation syndromes and resulted in improved survival. CBLB502 injected after irradiation also enhanced survival, but at lower radiation doses. It is noteworthy that the drug did not decrease tumor radiosensitivity in mouse models. CBLB502 also showed radioprotective activity in lethally irradiated rhesus monkeys. Thus, TLR5 agonists could potentially improve the therapeutic index of cancer radiotherapy and serve as biological protectants in radiation emergencies.

Effects of flagellin on innate and adaptive immunity

Flagella are locomotive organelles present on a wide range of bacteria and are important for the pathogenesis of many species. Cells of the innate immune system lack memory per se, but recognize conserved pathogen-associated molecular patterns (PAMPs) through a family of type I membrane receptors known as Toll-like receptors (TLRs). Flagellin, the major structural component of flagella, is a highly conserved protein recognized in hosts by TLR5. Signaling of flagellin via TLR5/TLR4 heteromeric complexes enhances the diversity of the response, likely by engaging MyD88-independent adaptors to activate the interferon pathway. Flagellin is a potent immune activator, stimulating diverse biologic effects that mediate both innate inflammatory responses as well as the development of adaptive immunity. Binding of flagellin to the extracellular domain of TLR5 rapidly induces a signal cascade that culminates in the production of proinflammatory mediators such as cytokines, chemokines, and costimulatory molecules. This review focuses on the mechanisms of action of flagellin and its effects on both innate and adaptive immunity.

Expression of IL-12-related molecules in human intestinal microvascular endothelial cells is regulated by TLR3

Members of the interleukin (IL)-12 family constitute subunits of IL-12, -23, and -27. These ILs represent pivotal mediators in the regulation of cell-mediated immune responses and in animal models of human inflammatory bowel disease. Recent work has suggested that intestinal endothelial cells might serve as a second line of defense in bacterial sensing of invading pathogens. The purpose of this study was to examine the production of IL-12 family members in intestinal endothelial cells (HIMEC). HIMEC were stimulated with proinflammatory agents (TNF-alpha, IFN-gamma, IL-1beta) and microbial antigens [LPS, lipoteichoic acid, peptidoglycan, CpG-DNA, flagellin, poly(I:C)]. Expression of IL-12 family members and of Toll-like receptor (TLR)3 in HIMEC was assessed by real-time RT-PCR, immunostaining, flow cytometry, and immunoblot analysis. HIMEC display an induction of Epstein-Barr virus-induced gene 3 (EBI3), IL-12p35, and IL-23p19, whereas no expression of IL-12p40 and IL-27p28 was detectable. The strongest induction was induced by proinflammatory factors known to utilize the NF-kappaB pathway, and expression of EBI3 and IL-23p19 was diminished by an NF-kappaB inhibitor. HIMEC display regulated expression of TLR3. Adhesion and transmigration assays showed proinflammatory responses after HIMEC stimulation. HIMEC are capable of producing IL-12 family members as a response to microbial stimuli. The TLR3 agonist, poly(I:C), was shown to enhance leukocyte adhesion in vitro in HIMEC. Our data suggest that the intestinal microvasculature is responsive to ligands of TLR3 expressed on intestinal endothelial cells, thereby adding to the regulation of adaptive immunity and leukocyte recruitment.