A calculated response: control of inflammation by the innate immune system

STAT1-regulated lung MDSC-like cells produce IL-10 and efferocytose apoptotic neutrophils with relevance in resolution of bacterial pneumonia

Bacterial pneumonia remains a significant burden worldwide. Although an inflammatory response in the lung is required to fight the causative agent, persistent tissue-resident neutrophils in non-resolving pneumonia can induce collateral tissue damage and precipitate acute lung injury. However, little is known about mechanisms orchestrated in the lung tissue that remove apoptotic neutrophils to restore tissue homeostasis. In mice infected with Klebsiella pneumoniae, a bacterium commonly associated with hospital-acquired pneumonia, we show that interleukin (IL)-10 is essential for resolution of lung inflammation and recovery of mice after infection. Although IL-10(-/-) mice cleared bacteria, they displayed increased morbidity with progressive weight loss and persistent lung inflammation in the later phase after infection. A source of tissue IL-10 was found to be resident CD11b(+)Gr1(int)F4/80(+) cells resembling myeloid-derived suppressor cells (MDSCs) that appeared with a delayed kinetics after infection. These cells efficiently efferocytosed apoptotic neutrophils, which was aided by IL-10. The lung neutrophil burden was attenuated in infected signal transducer and activator of transcription 1 (STAT1)(-/-) mice with concomitant increase in the frequency of the MDSC-like cells and lung IL-10 levels. Thus, inhibiting STAT1 in combination with antibiotics may be a novel therapeutic strategy to address inefficient resolution of bacterial pneumonia.

Induction of nuclear factor-κB responses by the S100A9 protein is Toll-like receptor-4-dependent

Interactions between danger-associated molecular patterns (DAMP) and pathogen-associated molecular patterns (PAMP) and pattern recognition receptors such as Toll-like receptors (TLRs) are critical for the regulation of the inflammatory process via activation of nuclear factor-κB (NF-κB) and cytokine secretion. In this report, we investigated the capacity of lipopolysaccharide (LPS) -free S100A9 (DAMP) protein to activate human and mouse cells compared with lipoprotein-free LPS (PAMP). First, we showed that LPS and S100A9 were able to increase NF-κB activity followed by increased cytokine and nitric oxide (NO) secretion both in human THP-1 cells and in mouse bone marrow-derived dendritic cells. Surprisingly, although S100A9 triggered a weaker cytokine response than LPS, we found that S100A9 more potently induced IκBα degradation and hence NF-κB activation. Both the S100A9-induced response and the LPS-induced response were completely absent in TLR4 knockout mice, whereas it was only slightly affected in RAGE knockout mice. Also, we showed that LPS and S100A9 NF-κB induction were strongly reduced in the presence of specific inhibitors of TLR-signalling. Chloroquine reduced S100A9 but not LPS signalling, indicating that S100A9 may need to be internalized to be fully active as a TLR4 inducer. This was confirmed using A488-labelled S100A9 that was internalized in THP-1 cells, showing a raise in fluorescence after 30 min at 37°. Chloroquine treatment significantly reduced the fluorescence. In summary, our data indicate that both human and mouse S100A9 are TLR4 agonists. Importantly, S100A9 induced stronger NF-κB activation albeit weaker cytokine secretion than LPS, suggesting that S100A9 and LPS activated NF-κB in a qualitatively distinct manner.

Regulation of Inflammation by Bidirectional Signaling through CD137 and Its Ligand

Although the majority of research on CD137 has been directed to T cells, it is becoming clear that this molecule has distinct functions in other lineages of cells, including non-hematopoietic cells. In particular, emerging evidence suggests that the CD137-its ligand (CD137L) network involving immune cells and non-immune cells, directly or indirectly regulates inflammation in both positive and negative manners. Bidirectional signaling through both CD137 and CD137L is critical in the evolution of inflammation: 1) CD137L signaling plays an indispensible role in the activation and recruitment of neutrophils by inducing the production of proinflammatory cytokines and chemokines in hematopoietic and non-hematopoietic cells such as macrophages, endothelial cells and epithelial cells; 2) CD137 signaling in NK cells and T cells is required for their activation and can influence other cells participating in inflammation via either their production of proinflammatory cytokines or engagement of CD137L by their cell surface CD137: 3) CD137 signaling can suppress inflammation by controlling regulatory activities of dendritic cells and regulatory T cells. As recognition grows of the role of dysregulated CD137 or CD137L stimulation in inflammatory diseases, significant efforts will be needed to develop antagonists to CD137 or CD137L.

Oligodendroglia are limited in type I interferon induction and responsiveness in vivo

Type I interferons (IFNα/β) provide a primary defense against infection. Nevertheless, the dynamics of IFNα/β induction and responsiveness by central nervous system (CNS) resident cells in vivo in response to viral infections are poorly understood. Mice were infected with a neurotropic coronavirus with tropism for oligodendroglia and microglia to probe innate antiviral responses during acute encephalomyelitis. Expression of genes associated with the IFNα/β pathways was monitored in microglia and oligodendroglia purified from naïve and infected mice by fluorescent activated cell sorting. Compared with microglia, oligodendroglia were characterized by low basal expression of mRNA encoding viral RNA sensing pattern recognition receptors (PRRs), IFNα/β receptor chains, interferon sensitive genes (ISG), as well as kinases and transcription factors critical in IFNα/β signaling. Although PRRs and ISGs were upregulated by infection in both cell types, the repertoire and absolute mRNA levels were more limited in oligodendroglia. Furthermore, although oligodendroglia harbored higher levels of viral RNA compared with microglia, Ifnα/β was only induced in microglia. Stimulation with the double stranded RNA analogue poly I:C also failed to induce Ifnα/β in oligodendroglia, and resulted in reduced and delayed induction of ISGs compared with microglia. The limited antiviral response by oligodendroglia was associated with a high threshold for upregulation of Ikkε and Irf7 transcripts, both central to amplifying IFNα/β responses. Overall, these data reveal that oligodendroglia from the adult CNS are poor sensors of viral infection and suggest they require exogenous IFNα/β to establish an antiviral state.

The nuclear factor kappa B signaling pathway: integrating metabolism with inflammation

Nuclear factor kappa B (NF-κB) transcription factors are evolutionarily conserved, coordinating regulators of immune and inflammatory responses. They also play a pivotal role in oncogenesis and metabolic disorders. Several studies during the past two decades have highlighted the key role of the IKK/NF-κB pathway in the induction and maintenance of the state of inflammation that underlies metabolic diseases such as obesity and type 2 diabetes. Recent reports, however, reveal an even more intimate connection between NF-κB and metabolism. These studies demonstrate that NF-κB regulates energy homeostasis via direct engagement of the cellular networks governing glycolysis and respiration, with profound implications beyond metabolic diseases, including cancer, ageing and anticancer therapy. In this review, we discuss these emerging bioenergetic functions of NF-κB and their significance to oncogenesis.

Resolution of inflammation in obesity-induced liver disease

Low-grade inflammation in adipose tissue is recognized as a critical event in the development of obesity-related co-morbidities. This chronic inflammation is powerfully augmented through the infiltration of macrophages, which together with adipocytes, perpetuate a vicious cycle of inflammatory cell recruitment and secretion of free fatty acids and deleterious adipokines that predispose to greater incidence of metabolic complications. In the last decade, many factors have been identified to contribute to mounting unresolved inflammation in obese adipose tissue. Among them, pro-inflammatory lipid mediators (i.e., leukotrienes) derived from the omega-6 polyunsaturated arachidonic acid have been shown to play a prominent role. Of note, the same lipid mediators that initially trigger the inflammatory response also signal its termination by stimulating the formation of anti-inflammatory signals. Resolvins and protectins derived from the omega-3 polyunsaturated docosahexaenoic and eicosapentaenoic acids have emerged as a representative family of this novel class of autacoids with dual anti-inflammatory and pro-resolving properties that act as “stop-signals” of the inflammatory response. This review discusses the participation of these endogenous autacoids in the resolution of adipose tissue inflammation, with a special emphasis in the amelioration of obesity-related metabolic dysfunctions, namely insulin resistance and non-alcoholic fatty liver disease.

Leptospiral hemolysins induce proinflammatory cytokines through Toll-like receptor 2-and 4-mediated JNK and NF-κB signaling pathways

BACKGROUND

Infection with pathogenic Leptospira species causes serious systemic inflammation in patients. Although a few leptospiral proinflammatory molecules have been identified, Leptospira likely encodes other unidentified strong inflammation stimulators. The pathogenic L. interrogans genome encodes numerous putative hemolysin genes. Since hemolysins from other bacteria can cause inflammatory reactions, we hypothesized that leptospiral hemolysins may function as proinflammatory stimulators that contribute to the strong inflammation associated with Leptospira infection.

METHODOLOGY/PRINCIPAL FINDINGS

We first used cytokine protein microarrays for systematic analysis of serum cytokine profiles in leptospirosis patients and leptospire-infected mice. We found that IL-1β, IL-6 and TNF-α were the main proinflammatory cytokines in the sera of both the patients and the mice. We then analyzed eight putative hemolysins in L. interrogans strain Lai. The results showed that five of them, Sph1, Sph2, Sph3, HlpA and TlyA were secreted and had hemolytic activity. More importantly, these five hemolysins induced the strong production of IL-1β, IL-6 and TNF-α in human and mouse macrophages (although a bit lower in the latter). Furthermore, blockade of TLR2 or TLR4 with either antibodies or inhibitors of the NF-κB or JNK signaling pathways significantly reduced the production of hemolysin-induced IL-1β, IL-6 and TNF-α. Macrophages isolated from TLR2-, TLR4-or double TLR2-and 4-deficient mice also confirmed that the leptospiral hemolysins that induce proinflammatory cytokines are both TLR2-and TLR4-dependent.

CONCLUSIONS/SIGNIFICANCE

Our findings demonstrate that L. interrogans secretes many hemolysins that function as powerful inducers of proinflammatory cytokines through both TLR2-and TLR4-dependent JNK and NF-κB pathways.

Characterization of fatty acid modifying enzyme activity in staphylococcal mastitis isolates and other bacteria

Background

Fatty acid modifying enzyme (FAME) has been shown to modify free fatty acids to alleviate their bactericidal effect by esterifying fatty acids to cholesterol or alcohols. Although it has been shown in previous studies that FAME is required for Staphylococcus aureus survival in skin abscesses, FAME is poorly studied compared to other virulence factors. FAME activity had also been detected in coagulase-negative staphylococci (CNS). However, FAME activity was only surveyed after a bacterial culture was grown for 24 h. Therefore if FAME activity was earlier in the growth phase, it would not have been detected by the assay and those strains would have been labeled as FAME negative.

Results

Fifty CNS bovine mastitis isolates and several S. aureus, Escherichia coli, and Streptococcus uberis strains were assayed for FAME activity over 24 h. FAME activity was detected in 54% of CNS and 80% S. aureus strains surveyed but none in E. coli or S. uberis. While some CNS strains produced FAME activity comparable to the lab strain of S. aureus, the pattern of FAME activity varied among strains and across species of staphylococci. All CNS that produced FAME activity also exhibited lipase activity. Lipase activity relative to colony forming units of these CNS decreased over the 24 h growth period. No relationship was observed between somatic cell count in the milk and FAME activity in CNS.

Conclusions

Some staphylococcal species surveyed produced FAME activity, but E. coli and S. uberis strains did not. All FAME producing CNS exhibited lipase activity which may indicate that both these enzymes work in concert to alter fatty acids in the bacterial environment.

Reverse signaling through the co-stimulatory ligand, CD137L, as a critical mediator of sterile inflammation

CD137 (also called 4-1BB and TNFRSF9) has recently received attention as a therapeutic target for cancer and a variety of autoimmune and inflammatory diseases. Stimulating CD137 in vivo enhances CD8(+) T cell-activity and results in strong immunosuppression in some contexts. This paradoxical phenomenon may be partially explained by the ability of CD137-stimulating reagents (usually agonistic monoclonal antibodies against CD137) to overactivate T cells and other CD137-expressing cells. This over-activity is associated with deleting pathogenic T cells and B cells or generating a tolerogenic microenvironment. Recent studies, however, suggest that the biology of CD137 and its ligand (CD137L) are more complex, mainly due to bidirectional signaling between CD137 and CD137L. For example, signaling through CD137L in non-hematopoietic cells such as epithelial cells and endothelial cells has been shown to play an essential role in sterile inflammation by regulating immune cell recruitment. One outstanding, and clinically important, issue is understanding how bidirectional signaling through CD137 and CD137L controls the vicious cycle of sterile inflammation (e.g., ischemia-reperfusion tissue injury and meta-inflammatory diseases).

Streptococcal M1 protein-provoked CXC chemokine formation, neutrophil recruitment and lung damage are regulated by Rho-kinase signaling

Streptococcal toxic shock syndrome is frequently caused by Streptococcus pyogenes of the M1 serotype. The aim of this study was to determine the role of Ras-homologous (Rho)-kinase signaling in M1 protein-provoked lung damage. Male C57BL/6 mice received the Rho-kinase-specific inhibitor Y-27632 before administration of M1 protein. Edema, neutrophil accumulation and CXC chemokines were quantified in the lung 4 h after M1 protein challenge. Flow cytometry was used to determine Mac-1 expression. Quantitative RT-PCR was used to determine gene expression of CXC chemokine mRNA in alveolar macrophages. M1 protein increased neutrophil accumulation, edema and CXC chemokine formation in the lung as well as enhanced Mac-1 expression on neutrophils. Inhibition of Rho-kinase signaling significantly reduced M1 protein-provoked neutrophil accumulation and edema formation in the lung. M1 protein-triggered pulmonary production of CXC chemokine and gene expression of CXC chemokines in alveolar macrophages was decreased by Y-27632. Moreover, Rho-kinase inhibition attenuated M1 protein-induced Mac-1 expression on neutrophils. We conclude that Rho-kinase-dependent neutrophil infiltration controls pulmonary tissue damage in response to streptococcal M1 protein and that Rho-kinase signaling regulates M1 protein-induced lung recruitment of neutrophils via the formation of CXC chemokines and Mac-1 expression.

Cutaneous microdialysis: cytokine evidence for altered innate reactivity in the skin of psoriasis patients?

Cutaneous microdialysis demonstrates cytokine production in living human skin. In the present study, microdialysis samples taken from uninvolved and lesional skin in three test subjects with psoriasis over 24 h have been investigated for cytokine content with a bead-based multiplex immunoassay from Luminex. Concentration curves for a set of Th1/Th2 and pro-inflammatory cytokines measured differed from a reference group of ten subjects without psoriasis. The time to return to near baseline values after innate insertion reactivity is between 9 and 16 h. Post-equilibration levels (17-24 h) for the three main cytokines elevated in the reference group were differentially elevated outside the range of the reference group for interleukin-1β (IL1β) and IL8 but not so for IL6. Two further cytokines, granulocyte-macrophage colony-stimulating factor and tumor necrosis factor-α not generally elevated in the reference group, showed elevated values in the test subjects. Multivariate time series analysis (chemometry) showed that cytokine patterns for the individual test subjects often fell outside the 99% confidence intervals of a model generated from the reference group. In a clinical research situation, cutaneous microdialysis is feasible, gives generally higher cytokine levels than in the blood and generates interpretable data on an individual's reactivity compared with a reference group. This may well prove useful in delineation of pathogenetic issues, selection of appropriate therapy and monitoring of subsequent response in inflammatory dermatoses such as psoriasis.

Microbes and asthma: the missing cellular and molecular links

PURPOSE OF REVIEW

In this review, we describe the 'state-of-the-art' in our knowledge of asthma and what gaps exist, which can be exploited in the future for effective translation of our knowledge from the bench or population studies to diagnosis and therapy.

RECENT FINDINGS

The advent of microbiome research has expanded the potential role of microbes in asthma. There has been a significant increase in our understanding of the pathologic, genetic, cellular and molecular mechanisms of asthma. Nonetheless, the contribution of microbes to the genesis, exacerbation and treatment of asthma are poorly understood.

SUMMARY

Asthma is a complex chronic disease of the lung whose incidence is growing at all ages despite the progress that has been made in the areas of diagnosis and treatment of asthma. The complexity is partly due to the environmental insults such as allergens and microbial infections that play differential roles in the pathogenesis of childhood vis-à-vis elderly asthma. Microbes may play important roles in the exacerbation of asthma and hence in the comorbidities due to asthma, and also in the causation of asthma.

CGI-58/ABHD5-derived signaling lipids regulate systemic inflammation and insulin action

Mutations of comparative gene identification 58 (CGI-58) in humans cause Chanarin-Dorfman syndrome, a rare autosomal recessive disease in which excess triacylglycerol (TAG) accumulates in multiple tissues. CGI-58 recently has been ascribed two distinct biochemical activities, including coactivation of adipose triglyceride lipase and acylation of lysophosphatidic acid (LPA). It is noteworthy that both the substrate (LPA) and the product (phosphatidic acid) of the LPA acyltransferase reaction are well-known signaling lipids. Therefore, we hypothesized that CGI-58 is involved in generating lipid mediators that regulate TAG metabolism and insulin sensitivity. Here, we show that CGI-58 is required for the generation of signaling lipids in response to inflammatory stimuli and that lipid second messengers generated by CGI-58 play a critical role in maintaining the balance between inflammation and insulin action. Furthermore, we show that CGI-58 is necessary for maximal TH1 cytokine signaling in the liver. This novel role for CGI-58 in cytokine signaling may explain why diminished CGI-58 expression causes severe hepatic lipid accumulation yet paradoxically improves hepatic insulin action. Collectively, these findings establish that CGI-58 provides a novel source of signaling lipids. These findings contribute insight into the basic mechanisms linking TH1 cytokine signaling to nutrient metabolism.

Role of reactive oxygen and nitrogen species in the vascular responses to inflammation

Inflammation is a complex and potentially life-threatening condition that involves the participation of a variety of chemical mediators, signaling pathways, and cell types. The microcirculation, which is critical for the initiation and perpetuation of an inflammatory response, exhibits several characteristic functional and structural changes in response to inflammation. These include vasomotor dysfunction (impaired vessel dilation and constriction), the adhesion and transendothelial migration of leukocytes, endothelial barrier dysfunction (increased vascular permeability), blood vessel proliferation (angiogenesis), and enhanced thrombus formation. These diverse responses of the microvasculature largely reflect the endothelial cell dysfunction that accompanies inflammation and the central role of these cells in modulating processes as varied as blood flow regulation, angiogenesis, and thrombogenesis. The importance of endothelial cells in inflammation-induced vascular dysfunction is also predicated on the ability of these cells to produce and respond to reactive oxygen and nitrogen species. Inflammation seems to upset the balance between nitric oxide and superoxide within (and surrounding) endothelial cells, which is necessary for normal vessel function. This review is focused on defining the molecular targets in the vessel wall that interact with reactive oxygen species and nitric oxide to produce the characteristic functional and structural changes that occur in response to inflammation. This analysis of the literature is consistent with the view that reactive oxygen and nitrogen species contribute significantly to the diverse vascular responses in inflammation and supports efforts that are directed at targeting these highly reactive species to maintain normal vascular health in pathological conditions that are associated with acute or chronic inflammation.

Reverse signaling through the costimulatory ligand CD137L in epithelial cells is essential for natural killer cell-mediated acute tissue inflammation

Renal ischemia-reperfusion injury (IRI) after kidney transplantation is a major cause of delayed graft function. Even though IRI is recognized as a highly coordinated and specific process, the pathways and mechanisms through which the innate response is activated are poorly understood. In this study, we used a mouse model of acute kidney IRI to examine whether the interactions of costimulatory receptor CD137 and its ligand (CD137L) are involved in the early phase of acute kidney inflammation caused by IRI. We report here that the specific expressions of CD137 on natural killer cells and of CD137L on tubular epithelial cells (TECs) are required for acute kidney IRI. Reverse signaling through CD137L in TECs results in their production of the chemokine (C-X-C motif) receptor 2 ligands CXCL1 and CXCL2 and the subsequent induction of neutrophil recruitment, resulting in a cascade of proinflammatory events during kidney IRI. Our findings identify an innate pathogenic pathway for renal IRI involving the natural killer cell-TEC-neutrophil axis, whereby CD137-CD137L interactions provide the causal contribution of epithelial cell dysregulation to renal IRI. The CD137L reverse signaling pathway in epithelial cells therefore may represent a good target for blocking the initial stage of inflammatory diseases, including renal IRI.

Cells, cytokines and inflammatory bowel disease: a clinical perspective

Ulcerative colitis and Crohn's disease are chronic inflammatory disorders of the GI tract. Although the disorders can usually be distinguished on clinical and pathological criteria, there are similarities in natural history and response to therapy. The purpose of this article is to examine the inflammatory infiltrate in both disorders and the cytokine profiles in intestinal mucosa and peripheral blood. For both disorders, the predominant cells in inflamed mucosa are neutrophils and lymphocytes positive for CD4. There are also increases in the number of B cells, macrophages, dendritic cells, plasma cells, eosinophils and perhaps mast cells. Cytokine levels and cytokine expression are also similar for both disorders, with increases in TNF-α and IFN-γ consistent with a Th1 response. As inflammation occurs in a microbial environment, one possibility is that the nature of the inflammatory response is largely independent of initiating factors. One concept that might be useful is that of initiating cells and cytokines and effector cells and cytokines. Persuasive evidence exists for a defect in phagocytic cells in Crohn's disease, perhaps with the expansion of a subset of activated macrophages. There are also possible links to natural killer cells and changes in the regulation of IL-8 and perhaps IL-22. For ulcerative colitis, the cellular events are less clear, but natural killer T cells may be important as initiating cells, and there is some evidence for upregulation of cytokines involved in Th2 responses, including IL-4 and IL-13. For both disorders, proinflammatory cytokines include TNF-α, IL-12, IL-23, and perhaps IL-17 and IFN-γ. Research challenges include the identification, activation and function of subsets of inflammatory cells, as well as new ways to terminate the inflammatory response.

Cellular regulation of the inflammatory response

In simple terms, inflammation can be defined as a beneficial, nonspecific response of tissues to injury that generally leads to restoration of normal structure and function. In this concept, resolution of the inflammatory response, once it has achieved its protective and pro-immunogenic functions, becomes a critical determinant of what might be considered the paradox of inflammation. On one hand, inflammation is essential to resolve tissue injury and maintain homeostasis. On the other, inflammation is a key participant in the great majority of human diseases. Accordingly, to achieve complete resolution of inflammation, it is necessary to both turn off inflammatory mediator production and inflammatory cell accumulation and to remove inflammatory cells and debris without initiating an autoimmune response. Much of this process involves key activities of the mononuclear phagocyte series of cells, including resident and recruited macrophages. Recognition of activated and dying acute inflammatory cells by mononuclear phagocytes has been shown to (a) enhance macropinocytic activity for removal of debris, (b) enhance uptake of the effete inflammatory cells themselves, (c) induce inflammosuppressive and immunosuppressive mediators such as TGFβ and IL-10 that can down-regulate and limit proinflammatory mediator production, and (d) induce production of growth factors for tissue cells that may play key roles in tissue repair. Defects in these highly regulated processes are associated with persistent inflammation and/or autoimmunity in overaggressive resolution mechanisms such as nonresolving fibrosis or persistent tissue destruction as in emphysema.

Activation of hypoxia-inducible factor 1 in skeletal muscle cells after exposure to damaged muscle cell debris

Skeletal muscle damage provokes complex repair mechanisms including recruitment of leukocytes as well as activation of myogenic precursor cells such as satellite cells. To study muscle cell repair mechanisms after muscle fiber damage, we used an in vitro model of scrape-injured myotubes. Exposing vital C2C12 myoblasts and myotubes to cell debris of damaged myotubes revealed mRNA upregulation of adrenomedullin (ADM), insulin-like growth factors 1 and 2, metallopeptidase 9, and monocyte chemoattractant protein11. When cell debris was treated with ultrasound, frozen in liquid nitrogen, or heat inactivated before addition to C2C12 cells, gene expression was drastically reduced or completely absent. Moreover, incubations of myoblasts with debris separated by transwell inserts indicated that direct cell contact is required for gene induction. Incubation with albumin and PolyIC ruled out that ADM induction by cell debris simply results from increased protein or nucleic acid concentrations in the supernatant. Because the genes, which were upregulated by cell debris, are potential target genes of hypoxia-inducible factor (HIF), cells were analyzed for HIF-1α expression. Western blot analysis showed accumulation of the α-subunit upon contact to cell debris. Knockdown of HIF-1α in C2C12 cells proved that activation of HIF-1 in response to cell debris was responsible for upregulating ADM and monocyte chemoattractant protein 1. Furthermore, by incubating cells on gas-permeable culture dishes, we excluded a reduced pericellular pO2 induced by cell debris as the cause for ADM upregulation. Our data suggest that damaged myofibers activate HIF-1 in neighboring myotubes and precursor myoblasts by direct contact, concomitantly upregulating factors necessary for angiogenesis, tissue regeneration, and phagocyte recruitment.

The role of photopheresis in the treatment of graft-versus-host disease

Hematopoietic stem-cell transplantation [...]

Metallothionein and brain inflammation

Since the seminal discoveries of Bert Vallee regarding zinc and metallothioneins (MTs) more than 50 years ago, thousands of studies have been published concerning this fascinating story. One of the most active areas of research is the involvement of these proteins in the inflammatory response in general, and in neuroinflammation in particular. We describe the general aspects of the inflammatory response, highlighting the essential role of the major cytokine interleukin-6, and review briefly the expression and function of MTs in the central nervous system in the context of neuroinflammation. Particular attention is paid to the Tg2576 Alzheimer disease mouse model and the preliminary results obtained in mice into which human Zn(7)MT-2A was injected, which suggest a reversal of the behavioral deficits while enhancing amyloid plaque load and gliosis.

A trio of microRNAs that control Toll-like receptor signalling

Toll-like receptors (TLRs) in the host recognize conserved microbial products and defend against pathogenic attack by initiating an immune response via signalling pathways that lead to an increase in immune and inflammatory gene expression. TLR signalling must be stringently regulated in order to ensure sufficient clearance of pathogens and a timely return to homeostasis after infection. MicroRNAs (miRNAs) are a newly discovered class of gene regulators which bind to the 3' untranslated region of target mRNA and direct their post-transcriptional repression. They are global regulators potentially controlling up to 30% of the human genome. Several miRNAs have been shown to be up-regulated in response to TLR ligands, and many directly target components of the TLR signalling system, revealing a whole extra level of control of TLR signalling which is being extensively researched. The dysregulation of miRNAs may be involved in many inflammatory diseases and cancers and thus merits further investigation. In this review, we focus in on a trio of miRNA which have proven to be key in many immune and inflammatory pathways; miR-155, miR-21 and miR-146.

Early interleukin 6 production by leukocytes during ischemic acute kidney injury is regulated by TLR4

Although leukocytes infiltrate the kidney during ischemic acute kidney injury (AKI) and release interleukin 6 (IL6), their mechanism of activation is unknown. Here, we tested whether Toll-like receptor 4 (TLR4) on leukocytes mediated this activation by interacting with high-mobility group protein B1 (HMGB1) released by renal cells as a consequence of ischemic kidney injury. We constructed radiation-induced bone marrow chimeras using C3H/HeJ and C57BL/10ScNJ strains of TLR4 (-/-) mice and their respective TLR4 (+/+) wild-type counterparts and studied them at 4 h after an ischemic insult. Leukocytes adopted from TLR4 (+/+) mice infiltrated the kidneys of TLR4 (-/-) mice, and TLR4 (-/-) leukocytes infiltrated the kidneys of TLR4 (+/+) mice but caused little functional renal impairment in each case. Maximal ischemic AKI required both radiosensitive leukocytes and radioresistant renal parenchymal and endothelial cells from TLR4 (+/+) mice. Only TLR4 (+/+) leukocytes produced IL6 in vivo and in response to HMGB1 in vitro. Thus, following infiltration of the injured kidney, leukocytes produce IL6 when their TLR4 receptors interact with HMGB1 released by injured renal cells. This underscores the importance of TLR4 in the pathogenesis of ischemic AKI.

Activation of hypoxia-inducible factor-1α (Hif-1α) delays inflammation resolution by reducing neutrophil apoptosis and reverse migration in a zebrafish inflammation model

The oxygen-sensing transcription factor hypoxia-inducible factor-1α (HIF-1α) plays a critical role in the regulation of myeloid cell function. The mechanisms of regulation are not well understood, nor are the phenotypic consequences of HIF modulation in the context of neutrophilic inflammation. Species conservation across higher metazoans enables the use of the genetically tractable and transparent zebrafish (Danio rerio) embryo to study in vivo resolution of the inflammatory response. Using both a pharmacologic approach known to lead to stabilization of HIF-1α, and selective genetic manipulation of zebrafish HIF-1α homologs, we sought to determine the roles of HIF-1α in inflammation resolution. Both approaches reveal that activated Hif-1α delays resolution of inflammation after tail transection in zebrafish larvae. This delay can be replicated by neutrophil-specific Hif activation and is a consequence of both reduced neutrophil apoptosis and increased retention of neutrophils at the site of tissue injury. Hif-activated neutrophils continue to patrol the injury site during the resolution phase, when neutrophils would normally migrate away. Site-directed mutagenesis of Hif in vivo reveals that hydroxylation of Hif-1α by prolyl hydroxylases critically regulates the Hif pathway in zebrafish neutrophils. Our data demonstrate that Hif-1α regulates neutrophil function in complex ways during inflammation resolution in vivo.

Toll-like receptor 9 signaling is critical for early experimental deep vein thrombosis resolution

OBJECTIVE

Toll-like receptors (TLR) bridge innate immunity and host responses, including inflammation. Sterile inflammation such as a venous thrombus (Vt) may involve TLR signaling, including TLR9.

METHODS AND RESULTS

TLR9 signaling on thrombus resolution was investigated using a mouse model of stasis Vt. Vt were significantly larger in TLR9-/- mice compared with wild-type (WT) at 2 and 8 days, despite a 2-fold increase in thrombus polymorphonucleic neutrophils at 2 days and monocytes at 8 days, whereas thrombus collagen and neovascularization was 55% and 37% less, respectively, at 8 days. Coincidently, decreased fibrinogen and increased thrombin-antithrombin complex were observed in TLR9-/- mouse thrombi. Vein wall interferon-α, interleukin-1α, and interleukin-2 were significantly reduced in TLR9-/- mice compared with WT. Thrombus cell death pathway markers were not significantly altered at 2 days, but caspase-1 was reduced in TLR9-/- thrombi at 8 days. MyD88 confers TLR9 intracellular signaling, but MyD88-/- mice had Vt resolution similar to that of WT. However, inhibition of the NOTCH ligand δ-like 4 was associated with larger Vt. Finally, stimulation with a TLR9 agonist was associated with smaller Vt.

CONCLUSIONS

TLR9 signaling is integral for early and mid-Vt resolution through modulation of sterile inflammation, maintaining a TH1 milieu, and effects on the thrombosis pathway.

Mechanistically probing lipid-siRNA nanoparticle-associated toxicities identifies Jak inhibitors effective in mitigating multifaceted toxic responses

A major hurdle for harnessing small interfering RNA (siRNA) for therapeutic application is an effective and safe delivery of siRNA to target tissues and cells via systemic administration. While lipid nanoparticles (LNPs) composed of a cationic lipid, poly-(ethylene glycol) lipid and cholesterol, are effective in delivering siRNA to hepatocytes via systemic administration, they may induce multi-faceted toxicities in a dose-dependent manner, independently of target silencing. To understand the underlying mechanism of toxicities, pharmacological probes including anti-inflammation drugs and specific inhibitors blocking different pathways of innate immunity were evaluated for their abilities to mitigate LNP-siRNA-induced toxicities in rodents. Three categories of rescue effects were observed: (i) pretreatment with a Janus kinase (Jak) inhibitor or dexamethasone abrogated LNP-siRNA-mediated lethality and toxicities including cytokine induction, organ impairments, thrombocytopenia and coagulopathy without affecting siRNA-mediated gene silencing; (ii) inhibitors of PI3K, mammalian target of rapamycin (mTOR), p38 and IκB kinase (IKK)1/2 exhibited a partial alleviative effect; (iii) FK506 and etoricoxib displayed no protection. Furthermore, knockout of Jak3, tumor necrosis factor receptors (Tnfr)p55/p75, interleukin 6 (IL-6) or interferon (IFN)-γ alone was insufficient to alleviate LNP-siRNA-associated toxicities in mice. These indicate that activation of innate immune response is a primary trigger of systemic toxicities and that multiple innate immune pathways and cytokines can mediate toxic responses. Jak inhibitors are effective in mitigating LNP-siRNA-induced toxicities.

Islet-expressed TLR2 and TLR4 sense injury and mediate early graft failure after transplantation

Although islet transplantation is an effective treatment for Type 1 diabetes, primary engraftment failure contributes to suboptimal outcomes. We tested the hypothesis that islet isolation and transplantation activate innate immunity through TLR expressed on islets. Murine islets constitutively express TLR2 and TLR4, and TLR activation with peptidoglycan or LPS upregulates islet production of cytokines and chemokines. Following transplantation into streptozotocin-induced diabetic, syngeneic mice, islets exposed to LPS or peptidoglycan had primary graft failure with intra- and peri-islet mononuclear cell inflammation. The use of knockout mice showed that recipient CD8(+) T cells caused engraftment failure and did so in the absence of islet-derived DC. To mimic physiological islet injury, islets were transplanted with exocrine debris. Transplantation of TLR2/4(-/-) islets reduced proinflammatory cytokine production and improved islet survival. Stressed islets released the alarmin high-mobility group box protein 1 (HMGB1) and recombinant HMGB1 (rHMGB1) induced NFkB activation. NFkB activation was prevented in the absence of both TLR2 and TLR4. rHMGB1 pretreatment also prevented primary engraftment through a TLR2/4-dependent pathway. Our results show that islet graft failure can be initiated by TLR2 and TLR4 signaling and suggest that HMGB1 is one likely early mediator. Subsequent downstream signaling results in intra-islet inflammation followed by T-cell-mediated graft destruction.

Lipopolysaccharide (LPS) induction of nitric oxide synthase-2 and cyclooxygenase-2 is impaired in fructose overloaded rats

AIMS

Fructose (F) overload in rats induces metabolic dysfunctions that resemble the human metabolic syndrome. In this paper, we aimed to investigate the response of F overload rats to lipopolysaccharide (LPS) challenge in terms of nitric oxide (NO) production and prostanoids (PR) release.

MAIN METHODS

NO blood steady-state concentration was monitored through the detection of nitrosyl-hemoglobin complexes (NO-Hb) by electronic spin resonance. Production of 6-keto PGF(1)α, PGE(2), PGF(2)α and TXB(2) was measured in aorta and mesenteric beds by HPLC. Western blot analysis was used to examine the changes in the expression levels of NOS-2 and COX-2 in aorta.

KEY FINDINGS

Our results showed that increases in NO circulating steady-state concentration and PR production by aorta and mesenteric beds 6h after LPS administration were significantly attenuated in F overload rats with respect to control animals. Oxidative stress parameters were equally affected in the presence or absence of the F treatment. Aorta protein levels of NOS-2 and COX-2, two enzymes inducible by LPS, were significantly lower in F overload rats with respect to control rats at the end of the treatment (-39% and -61% for NOS-2 and COX-2 respectively).

SIGNIFICANCE

These results suggest that the metabolic alterations established by 15 weeks of F overload should affect the response to LPS challenge due to an attenuation in the induction of NOS-2 and COX-2. This effect would be one of the components contributing to abnormalities in the course of the inflammatory response in other conditions associated to insulin resistance, such as diabetes.

Genome wide transcriptome profiling of a murine acute melioidosis model reveals new insights into how Burkholderia pseudomallei overcomes host innate immunity

BACKGROUND

At present, very little is known about how Burkholderia pseudomallei (B. pseudomallei) interacts with its host to elicit melioidosis symptoms. We established a murine acute-phase melioidosis model and used DNA microarray technology to investigate the global host/pathogen interaction. We compared the transcriptome of infected liver and spleen with uninfected tissues over an infection period of 42 hr to identify genes whose expression is altered in response to an acute infection.

RESULTS

Viable B. pseudomallei cells were consistently detected in the blood, liver and spleen during the 42 hr course of infection. Microarray analysis of the liver and spleen over this time course demonstrated that genes involved in immune response, stress response, cell cycle regulation, proteasomal degradation, cellular metabolism and signal transduction pathways were differentially regulated. Up regulation of toll-like receptor 2 (TLR2) gene expression suggested that a TLR2-mediated signalling pathway is responsible for recognition and initiation of an inflammatory response to the acute B. pseudomallei infection. Most of the highly elevated inflammatory genes are a cohort of "core host immune response" genes commonly seen in general inflammation infections. Concomitant to this initial inflammatory response, we observed an increase in transcripts associated with cell-death, caspase activation and peptidoglysis that ultimately promote tissue injury in the host. The complement system responsible for restoring host cellular homeostasis and eliminating intracellular bacteria was activated only after 24 hr post-infection. However, at this time point, diverse host nutrient metabolic and cellular pathways including glycolysis, fatty acid metabolism and tricarboxylic acid (TCA) cycle were repressed.

CONCLUSIONS

This detailed picture of the host transcriptional response during acute melioidosis highlights a broad range of innate immune mechanisms that are activated in the host within 24 hrs, including the core immune response commonly seen in general inflammatory infections. Nevertheless, this activation is suppressed at 42 hr post-infection and in addition, suboptimal activation and function of the downstream complement system promotes uncontrolled spread of the bacteria.

Design of a composite drug delivery system to prolong functionality of cell-based scaffolds

Cell encapsulation technology raises hopes in medicine and biotechnology. However, despite important advances in the field in the past three decades, several challenges associated with the biocompatibility are still remaining. In the present study, the effect of a temporary release of an anti-inflammatory agent on co-administered encapsulated allogeneic cells was investigated. The aim was to determine the biocompatibility and efficacy of the approach to prevent the inflammatory response. A composite delivery system comprised of alginate-poly-l-lysine-alginate (APA)-microencapsulated Epo-secreting myoblasts and dexamethasone (DXM)-releasing poly(lactic-co-glycolic acid) (PLGA) microspheres was implanted in the subcutaneous space of Balb/c mice for 45 days. The use of independently co-implanted DXM-loaded PLGA microspheres resulted in an improved functionality of the cell-based graft, evidenced by significantly higher hematocrit levels found in the cell-implanted groups by day 45, which was found to be more pronounced when higher cell-doses (100 μL) were employed. Moreover, no major host reaction was observed upon implantation of the systems, showing good biocompatibility and capability to partially avoid the inflammatory response, probably due to the immunosuppressive effects related to DXM. The findings of this study imply that DXM-loaded PLGA microspheres show promise as release systems to enhance biocompatibility and offer advantage in the development of long-lasting and effective implantable microencapsulated cells by generating a potential immunopriviledged local environment and an effective method to limit the structural ensheathing layer caused by inflammation.

Major stress hormones suppress the response of macrophages through down-regulation of TLR2 and TLR4

BACKGROUND

Severe trauma often leads to diminished cytokines especially from macrophages to Toll-like receptor (TLR) agonists. However, the molecular mechanisms remain to be elucidated. As surgical trauma could also induce neuroendocrine hormones to modulate the immune system, we investigated the effects of major hormones, including endogenous glucocorticoid (corticosterone (CORT)), epinephrine (E), and norepinephrine (NE) on the expression and response of TLR2 and TLR4 in macrophages.

MATERIALS AND METHODS

Rat macrophages were pretreated by each hormone (1000 ng/mL of CORT, E, and NE) for 24 h, then restimulated with Pam3CSK4 or lipopolysaccharide (LPS) for further 24 h, and supernatant tumor necrosis factor-alpha (TNF-α) was measured. Additionally, macrophages were incubated with different concentrations of hormones (0-10,000 ng/mL) for 48 h or with 1000 ng/mL of hormones for 0-48 h, the expressions of TLR2 and TLR4 and intracellular molecules (MyD88, IRAK1, and TRAF6) in macrophages were analyzed by real-time quantitative polymerase chain reaction (PCR) and RT-PCR, respectively.

RESULTS

Pam3CSK4-stimulated TNF-α production was significantly reduced from macrophages pretreated with CORT, and both Pam3CSK4- and LPS-stimulated TNF-α were suppressed with E. Moreover, CORT down-regulated only TLR2 expression in both time- and dose-dependent manner, but both TLR2 and TLR4 mRNA expressions were down-regulated in time- and dose-dependent manner after exposure to E. However, the transcript expression of MyD88, IRAK1, and TRAF6 remained unchanged after exposure to each hormone.

CONCLUSIONS

These results suggested that the down-regulation of TLR2 and TLR4 expressions by CORT and E is involved in the hyporesponsiveness of macrophages.

Deconvoluting post-transplant immunity: cell subset-specific mapping reveals pathways for activation and expansion of memory T, monocytes and B cells

A major challenge for the field of transplantation is the lack of understanding of genomic and molecular drivers of early post-transplant immunity. The early immune response creates a complex milieu that determines the course of ensuing immune events and the ultimate outcome of the transplant. The objective of the current study was to mechanistically deconvolute the early immune response by purifying and profiling the constituent cell subsets of the peripheral blood. We employed genome-wide profiling of whole blood and purified CD4, CD8, B cells and monocytes in tandem with high-throughput laser-scanning cytometry in 10 kidney transplants sampled serially pre-transplant, 1, 2, 4, 8 and 12 weeks. Cytometry confirmed early cell subset depletion by antibody induction and immunosuppression. Multiple markers revealed the activation and proliferative expansion of CD45RO⁺CD62L⁻ effector memory CD4/CD8 T cells as well as progressive activation of monocytes and B cells. Next, we mechanistically deconvoluted early post-transplant immunity by serial monitoring of whole blood using DNA microarrays. Parallel analysis of cell subset-specific gene expression revealed a unique spectrum of time-dependent changes and functional pathways. Gene expression profiling results were validated with 157 different probesets matching all 65 antigens detected by cytometry. Thus, serial blood cell monitoring reflects the profound changes in blood cell composition and immune activation early post-transplant. Each cell subset reveals distinct pathways and functional programs. These changes illuminate a complex, early phase of immunity and inflammation that includes activation and proliferative expansion of the memory effector and regulatory cells that may determine the phenotype and outcome of the kidney transplant.

Klebsiella pneumoniae subverts the activation of inflammatory responses in a NOD1-dependent manner

Klebsiella pneumoniae is an important cause of community-acquired and nosocomial pneumonia. Subversion of inflammation is essential for pathogen survival during infection. Evidence indicates that K. pneumoniae infections are characterized by lacking an early inflammatory response although the molecular bases are currently unknown. Here we unveil a novel strategy employed by a pathogen to counteract the activation of inflammatory responses. K. pneumoniae attenuates pro-inflammatory mediators-induced IL-8 secretion. Klebsiella antagonizes the activation of NF-κB via the deubiquitinase CYLD and blocks the phosphorylation of mitogen-activated protein kinases (MAPKs) via the MAPK phosphatase MKP-1. Our studies demonstrate that K. pneumoniae has evolved the capacity to manipulate host systems dedicated to control the immune balance. To exert this anti-inflammatory effect, Klebsiella engages NOD1. In NOD1 knock-down cells, Klebsiella neither induces the expression of CYLD and MKP-1 nor blocks the activation of NF-κB and MAPKs. Klebsiella inhibits Rac1 activation; and inhibition of Rac1 activity triggers a NOD1-mediated CYLD and MKP-1 expression which in turn attenuates IL-1β-induced IL-8 secretion. A capsule (CPS) mutant does not attenuate the inflammatory response. However, purified CPS neither reduces IL-1β-induced IL-8 secretion nor induces the expression of CYLD and MKP-1 thereby indicating that CPS is necessary but not sufficient to attenuate inflammation.

Toll-like receptor 4 regulates early endothelial activation during ischemic acute kidney injury

Ischemic acute kidney injury (AKI) triggers an inflammatory response which exacerbates injury that requires increased expression of endothelial adhesion molecules. To study this further, we used in situ hybridization, immunohistology, and isolated endothelial cells, and found increased Toll-like receptor 4 (TLR4) expression on endothelial cells of the vasa rectae of the inner stripe of the outer medulla of the kidney 4 h after reperfusion. This increase was probably due to reactive oxygen species, known to be generated early during ischemic AKI, because the addition of hydrogen peroxide increased TLR4 expression in MS1 microvascular endothelial cells in vitro. Endothelial TLR4 may regulate adhesion molecule (CD54 and CD62E) expression as they were increased on endothelia of wild-type but not TLR4 knockout mice in vivo. Further, the addition of high-mobility group protein B1, a TLR4 ligand released by injured cells, increased adhesion molecule expression on endothelia isolated from wild-type but not TLR4 knockout mice. TLR4 was localized to proximal tubules in the cortex and outer medulla after 24 h of reperfusion. Thus, at least two different cell types express TLR4, each of which contributes to renal injury by temporally different mechanisms during ischemic AKI.

Bench-to-bedside review: Glucose and stress conditions in the intensive care unit

The physiological response to blood glucose elevation is the pancreatic release of insulin, which blocks hepatic glucose production and release, and stimulates glucose uptake and storage in insulin-dependent tissues. When this first regulatory level is overwhelmed (that is, by exogenous glucose supplementation), persistent hyperglycaemia occurs with intricate consequences related to the glucose acting as a metabolic substrate and as an intracellular mediator. It is thus very important to unravel the glucose metabolic pathways that come into play during stress as well as the consequences of these on cellular functions. During acute injuries, activation of serial hormonal and humoral responses inducing hyperglycaemia is called the 'stress response'. Central activation of the nervous system and of the neuroendocrine axes is involved, releasing hormones that in most cases act to worsen the hyperglycaemia. These hormones in turn induce profound modifications of the inflammatory response, such as cytokine and mediator profiles. The hallmarks of stress-induced hyperglycaemia include 'insulin resistance' associated with an increase in hepatic glucose output and insufficient release of insulin with regard to glycaemia. Although both acute and chronic hyperglycaemia may induce deleterious effects on cells and organs, the initial acute endogenous hyperglycaemia appears to be adaptive. This acute hyperglycaemia participates in the maintenance of an adequate inflammatory response and consequently should not be treated aggressively. Hyperglycaemia induced by an exogenous glucose supply may, in turn, amplify the inflammatory response such that it becomes a disproportionate response. Since chronic exposure to glucose metabolites, as encountered in diabetes, induces adverse effects, the proper roles of these metabolites during acute conditions need further elucidation.

B7-H3 augments the inflammatory response and is associated with human sepsis

B7-H3, a new member of the B7 superfamily, acts as both a T cell costimulator and coinhibitor, and thus plays a key role in the regulation of T cell-mediated immune responses. However, it is unclear whether B7-H3 is involved in the innate immune monocyte/macrophage-mediated inflammatory response. In this paper, we show that, although B7-H3 alone failed to stimulate proinflammatory cytokine release from murine macrophages, it strongly augmented both LPS- and bacterial lipoprotein-induced NF-kappaB activation and inflammatory response. This occurred in both a TLR4- and TLR2-dependent manner. Blockage of B7-H3 in vivo attenuated LPS-induced proinflammatory cytokine release and endotoxic shock-related lethality. Furthermore, we found that patients diagnosed with sepsis, in contrast to healthy individuals, exhibited significant levels of raised plasma soluble B7-H3 (sB7-H3) and that this level correlated with the clinical outcome and levels of plasma TNF-alpha and IL-6. In addition, a putative receptor for B7-H3 was detected on monocytes and peritoneal macrophages from septic patients but not on monocytes from healthy donors. Stimulation of human monocytes with LPS and inflammatory cytokines led to a substantial release of sB7-H3. Taken together, our data indicate that significantly elevated plasma sB7-H3 in septic patients may predict a poor outcome. Furthermore, we demonstrate that B7-H3 functions as a costimulator of innate immunity by augmenting proinflammatory cytokine release from bacterial cell wall product-stimulated monocytes/macrophages and may contribute positively to the development of sepsis.

Genome-wide expression profiling deciphers host responses altered during dengue shock syndrome and reveals the role of innate immunity in severe dengue

Background

Deciphering host responses contributing to dengue shock syndrome (DSS), the life-threatening form of acute viral dengue infections, is required to improve both the differential prognosis and the treatments provided to DSS patients, a challenge for clinicians.

Methodology/Principal Findings

Based on a prospective study, we analyzed the genome-wide expression profiles of whole blood cells from 48 matched Cambodian children: 19 progressed to DSS while 16 and 13 presented respectively classical dengue fever (DF) or dengue hemorrhagic fever grades I/II (DHF). Using multi-way analysis of variance (ANOVA) and adjustment of p-values to control the False Discovery Rate (FDR<10%), we identified a signature of 2959 genes differentiating DSS patients from both DF and DHF, and showed a strong association of this DSS-gene signature with the dengue disease phenotype. Using a combined approach to analyse the molecular patterns associated with the DSS-gene signature, we provide an integrative overview of the transcriptional responses altered in DSS children. In particular, we show that the transcriptome of DSS children blood cells is characterized by a decreased abundance of transcripts related to T and NK lymphocyte responses and by an increased abundance of anti-inflammatory and repair/remodeling transcripts. We also show that unexpected pro-inflammatory gene patterns at the interface between innate immunity, inflammation and host lipid metabolism, known to play pathogenic roles in acute and chronic inflammatory diseases associated with systemic vascular dysfunction, are transcriptionnally active in the blood cells of DSS children.

Conclusions/Significance

We provide a global while non exhaustive overview of the molecular mechanisms altered in of DSS children and suggest how they may interact to lead to final vascular homeostasis breakdown. We suggest that some mechanisms identified should be considered putative therapeutic targets or biomarkers of progression to DSS.

Expression, biological activities and mechanisms of action of A20 (TNFAIP3)

A20 (also known as TNFAIP3) is a cytoplasmic protein that plays a key role in the negative regulation of inflammation and immunity. Polymorphisms in the A20 gene locus have been identified as risk alleles for multiple human autoimmune diseases, and A20 has also been proposed to function as a tumor suppressor in several human B-cell lymphomas. A20 expression is strongly induced by multiple stimuli, including the proinflammatory cytokines TNF and IL-1, and microbial products that trigger pathogen recognition receptors, such as Toll-like receptors. A20 functions in a negative feedback loop, which mediates its inhibitory functions by downregulating key proinflammatory signaling pathways, including those controlling NF-κB- and IRF3-dependent gene expression. Activation of these transcription factors is controlled by both K48- and K63- polyubiquitination of upstream signaling proteins, respectively triggering proteasome-mediated degradation or interaction with other signaling proteins. A20 turns off NF-κB and IRF3 activation by modulating both types of ubiquitination. Induction of K48-polyubiquitination by A20 involves its C-terminal zinc-finger ubiquitin-binding domain, which may promote interaction with E3 ligases, such as Itch and RNF11 that are involved in mediating A20 inhibitory functions. A20 is thought to promote de-ubiquitination of K63-polyubiquitin chains either directly, due to its N-terminal deubiquitinase domain, or by disrupting the interaction between E3 and E2 enzymes that catalyze K63-polyubiquitination. A20 is subject to different mechanisms of regulation, including phosphorylation, proteolytic processing, and association with ubiquitin binding proteins. Here we review the expression and biological activities of A20, as well as the underlying molecular mechanisms.

Cystic fibrosis transmembrane conductance regulator (CFTR) expression in human platelets: impact on mediators and mechanisms of the inflammatory response

Inflammatory lung disease is a primary cause of morbidity and mortality in cystic fibrosis (CF). Mechanisms of unresolved acute inflammation in CF are not completely known, although the involvement of cystic fibrosis transmembrane conductance regulator (CFTR) in nonrespiratory cells is emerging. Here we examined CFTR expression and function in human platelets (PLTs) and found that they express a biologically active CFTR. CFTR blockade gave an ∼50% reduction in lipoxin A(4) (LXA(4)) formation during PLT/polymorphonuclear leukocytes (PMN) coincubations by inhibiting the lipoxin synthase activity of PLT 12-lipoxygenase. PLTs from CF patients generated ∼40% less LXA(4) compared to healthy subject PLTs. CFTR inhibition increased PLT-dependent PMN viability (33.0±5.7 vs. 61.2±8.2%; P=0.033), suppressed nitric oxide generation (0.23±0.04 vs. 0.11±0.002 pmol/10(8) PLTs; P=0.004), while reducing AKT (1.02±0.12 vs. 0.71±0.007 U; P=0.04), and increasing p38 MAPK phosphorylation (0.650±0.09 vs. 1.04±0.24 U; P=0.03). Taken together, these findings indicate that PLTs from CF patients are affected by the molecular defect of CFTR. Moreover, this CF PLT abnormality may explain the failure of resolution in CF.

The inflammatory response to injury in children

PURPOSE OF REVIEW

Severely injured children have a decreased incidence and different pattern of multiple organ failure when compared with adults. This article reviews recent advances in understanding the mechanisms leading to this discrepancy.

RECENT FINDINGS

Post injury, inflammation-related outcomes are age-related, as demonstrated by epidemiological and laboratory investigations that confirm a relative protection from acute lung injury and multiple organ failure in children. The importance of the innate immune system in initiating and regulating the inflammatory response to injury is also increasingly well understood, but relatively little research has focused on the implications of a maturing innate immune system for the inflammatory response to injury in children. The development of age-appropriate immunomodulatory interventions for the prevention and treatment of postinjury inflammatory dysregulation depends on continued investigation of mechanisms responsible for the unique pediatric inflammatory response to trauma.

SUMMARY

The inflammatory response to injury in children is functionally and mechanistically unique, as suggested by age-related differences in the incidence and pattern of systemic inflammation and multiple organ failure after major trauma. We review the current clinical and basic science literature related to postinjury inflammation in childhood, focusing on the developmental biology of innate immunity and the implications of a maturing immune system for trauma-related interventions and outcomes.

The neuroinflammatory hypothesis of delirium

Delirium is a neuropsychiatric syndrome characterized by a sudden and global impairment in consciousness, attention and cognition. It is particularly frequent in elderly subjects with medical or surgical conditions and is associated with short- and long-term adverse outcomes. The pathophysiology of delirium remains poorly understood as it involves complex multi-factorial dynamic interactions between a diversity of risk factors. Several conditions associated with delirium are characterized by activation of the inflammatory cascade with acute release of inflammatory mediators into the bloodstream. There is compelling evidence that acute peripheral inflammatory stimulation induces activation of brain parenchymal cells, expression of proinflammatory cytokines and inflammatory mediators in the central nervous system. These neuroinflammatory changes induce neuronal and synaptic dysfunction and subsequent neurobehavioural and cognitive symptoms. Furthermore, ageing and neurodegenerative disorders exaggerate microglial responses following stimulation by systemic immune stimuli such as peripheral inflammation and/or infection. In this review we explore the neuroinflammatory hypothesis of delirium based on recent evidence derived from animal and human studies.

A minimally invasive human in vivo cutaneous wound model for the evaluation of innate skin reactivity and healing status

Individual variability in skin reactivity and healing capacity after trauma are important clinical issues. The aims were to develop an in vivo, human wound model based on a standardised minimal skin injury and to demonstrate therapeutic effect of simple wound therapies in terms of morphological wound outcome with changes in skin blood perfusion as a quantified indicator of wound healing. In a series of experiments, wounds were induced on the normal forearm skin of volunteers using a blood collection lancet. This was well tolerated. Wounds were assessed by naked eye examination or laser Doppler perfusion imaging (LDPI) at baseline and at up to 6 further time points up to 96 h in control wounds and wounds treated by commonly used occlusive dressing options. Assessment by clinical observation with 10x magnification showed over 96 h a progression of erythema, surface crust, a new keratinisation layer and finally healed areas. LDPI quantifying wound erythema showed a peak at 24 h and near normal levels at 96 h. Inter-individual variability was evident but intra-individual variability was much less pronounced. Wounds treated with occlusion showed a statistically significant more rapid return to baseline blood perfusion as measured by LDPI compared to controls supported by favourable healing parameters in the clinical assessment. The paper exemplifies use of non-invasive, bioengineering technique for quantification of individual innate variability in skin reactivity, wound healing capacity and therapeutic effect in a well-tolerated in vivo, human, minimal skin trauma model.

MDA5 and PTPN2, two candidate genes for type 1 diabetes, modify pancreatic beta-cell responses to the viral by-product double-stranded RNA

β-Cell destruction in type 1 diabetes (T1D) is at least in part consequence of a ‘dialog’ between β-cells and immune system. This dialog may be affected by the individual's genetic background. We presently evaluated whether modulation of MDA5 and PTPN2, two candidate genes for T1D, affects β-cell responses to double-stranded RNA (dsRNA), a by-product of viral replication. These genes were selected following comparison between known candidate genes for T1D and genes expressed in pancreatic β-cells, as identified in previous array analysis. INS-1E cells and primary fluorescence-activated cell sorting-purified rat β-cells were transfected with small interference RNAs (siRNAs) targeting MDA5 or PTPN2 and subsequently exposed to intracellular synthetic dsRNA (polyinosinic–polycitidilic acid—PIC). Real-time RT–PCR, western blot and viability assays were performed to characterize gene/protein expression and viability. PIC increased MDA5 and PTPN2 mRNA expression, which was inhibited by the specific siRNAs. PIC triggered apoptosis in INS-1E and primary β-cells and this was augmented by PTPN2 knockdown (KD), although inhibition of MDA5 did not modify PIC-induced apoptosis. In contrast, MDA5 silencing decreased PIC-induced cytokine and chemokine expression, although inhibition of PTPN2 induced minor or no changes in these inflammatory mediators. These findings indicate that changes in MDA5 and PTPN2 expression modify β-cell responses to dsRNA. MDA5 regulates inflammatory signals, whereas PTPN2 may function as a defence mechanism against pro-apoptotic signals generated by dsRNA. These two candidate genes for T1D may thus modulate β-cell apoptosis and/or local release of inflammatory mediators in the course of a viral infection by acting, at least in part, at the pancreatic β-cell level.

The evolution of an inflammatory response

BACKGROUND

The past 25 years have witnessed immense progress in our understanding of the systemic, tissue-specific, and cellular consequences of severe injury and infection. Despite such insights, considerable controversy remains regarding appropriate biologic and management interventions to prevent or ameliorate the associated adverse outcomes.

METHODS

A review of several scientific developments arising from studies initiated at Cornell University Medical College during the tenure of Dr. G. Tom Shires. The implications of those and subsequent studies are discussed.

RESULTS

An understanding of patient-specific variation and adaptability could direct individualized biologic and management interventions for severe injury and infection.

CONCLUSION

Despite more detailed appreciation of the molecular mechanisms of danger and pathogen recognition and response biology, we have much to learn about the complexity of severe injury and infection. There is a great need to extend our investigation of these mechanisms to experimental and stress-modified clinical scenarios.