The interferon in TLR signaling: more than just antiviral

Toll-like receptors are potential therapeutic targets in rheumatoid arthritis

Toll-like receptors (TLRs) are found on the membranes of pattern recognition receptors and not only play important roles in activating immune responses but are also involved in the pathogenesis of inflammatory disease, injury and cancer. Furthermore, TLRs are also able to recognize endogenous alarmins released by damaged tissue and necrosis and/or apoptotic cells and are present in numerous autoimmune diseases. Therefore, the release of endogenous TLR ligands plays an important role in initiating and driving inflammatory diseases. Increasing data suggest a role for TLR signaling in rheumatoid arthritis, which is an autoimmune disease. Although their involvement is not comprehensively understood, the TLRs signaling transducers may provide potential therapeutic targets.

STAT1 as a novel therapeutical target in pro-atherogenic signal integration of IFNγ, TLR4 and IL-6 in vascular disease

Inflammation participates importantly in host defenses against infectious agents and injury, but it also contributes to the pathophysiology of atherosclerosis. Recruitment of blood leukocytes to the injured vascular endothelium characterizes the initiation and progression of atherosclerosis and involves many inflammatory mediators, modulated by cells of both innate and adaptive immunity. The pro-inflammatory cytokine, interferon (IFN)-γ derived from T cells, is vital for both innate and adaptive immunity and is also expressed at high levels in atherosclerotic lesions. As such IFN-γ plays a crucial role in the pathology of atherosclerosis through activation of signal transducer and activator of transcription (STAT) 1. Toll-like receptors (TLRs) are innate immune pattern recognition receptors (PRRs) expressed on a variety of cells, and thus initiate and sustain the inflammatory response in atherosclerosis. More recent studies have revealed that STAT1 is involved in the signaling events mediated by TLR4, leading to increased expression of several pro-inflammatory and pro-atherogenic mediators. By upregulating members of the Suppressors Of Cytokine Signaling (SOCS) family that regulate cellular responsiveness to immune signals, IFNγ and TLR4-activated pathways have also shown to inhibit IL-6 STAT3-dependent anti-inflammatory signaling and potentially shift IL-6 to a STAT1 activating pro-inflammatory cytokine. Consequently, STAT1 has been identified as a point of convergence for the cross-talk between the pro-atherogenic IFN-γ, TLR4 and IL-6 activated pathways in immune as well as vascular cells, as such amplifying pro-inflammatory signals. This results in augmented smooth muscle cell (SMC) and leukocyte migration, leukocyte to endothelial cell (EC) adhesion and foam cell formation, and could encompass a novel mechanism involved in the initiation and progression of atherosclerosis. Therefore, application of small inhibitory compounds that specifically interact with the SH2-phosphotyrosine pocket of STAT1, proposed here as a novel working mechanism for the known STAT1 inhibitor fludarabine, could be a promising tool in the development of a therapeutical strategy for atherosclerosis.

The regulation and functions of activin and follistatin in inflammation and immunity

The activins are members of the transforming growth factor β superfamily with broad and complex effects on cell growth and differentiation. Activin A has long been known to be a critical regulator of inflammation and immunity, and similar roles are now emerging for activin B, with which it shares 65% sequence homology. These molecules and their binding protein, follistatin, are widely expressed, and their production is increased in many acute and chronic inflammatory conditions. Synthesis and release of the activins are stimulated by inflammatory cytokines, Toll-like receptor ligands, and oxidative stress. The activins interact with heterodimeric serine/threonine kinase receptor complexes to activate SMAD transcription factors and the MAP kinase signaling pathways, which mediate inflammation, stress, and immunity. Follistatin binds to the activins with high affinity, thereby obstructing the activin receptor binding site, and targets them to cell surface proteoglycans and lysosomal degradation. Studies on transgenic mice and those with gene knockouts, together with blocking studies using exogenous follistatin, have established that activin A plays critical roles in the onset of cachexia, acute and chronic inflammatory responses such as septicemia, colitis and asthma, and fibrosis. However, activin A also directs the development of monocyte/macrophages, myeloid dendritic cells, and T cell subsets to promote type 2 and regulatory immune responses. The ability of both endogenous and exogenous follistatin to block the proinflammatory and profibrotic actions of activin A has led to interest in this binding protein as a potential therapeutic for limiting the severity of disease and to improve subsequent damage associated with inflammation and fibrosis. However, the ability of activin A to sculpt the subsequent immune response as well means that the full range of effects that might arise from blocking activin bioactivity will need to be considered in any therapeutic applications.

Classical swine fever virus N(pro) limits type I interferon induction in plasmacytoid dendritic cells by interacting with interferon regulatory factor 7

Viruses are detected by different classes of pattern recognition receptors that lead to the activation of interferon regulatory factors (IRF) and consequently to the induction of alpha/beta interferon (IFN-α/β). In turn, efficient viral strategies to escape the type I IFN-induced antiviral mechanisms have evolved. Previous studies established that pestivirus N(pro) antagonizes the early innate immune response by targeting the transcription factor IRF3 for proteasomal degradation. Here, we report that N(pro) of classical swine fever virus (CSFV) interacts also with IRF7, another mediator of type I IFN induction. We demonstrate that the Zn-binding domain of N(pro) is essential for the interaction of N(pro) with IRF7. For IRF3 and IRF7, the DNA-binding domain, the central region, and most of the regulatory domain are required for the interaction with N(pro). Importantly, the induction of IRF7-dependent type I IFN responses in plasmacytoid dendritic cells (pDC) is reduced after wild-type CSFV infection compared with infection with virus mutants unable to interact with IRF7. This is associated with lower levels of IRF7 in pDC. Consequently, wild-type but not N(pro) mutant CSFV-infected pDC show reduced responses to other stimuli. Taken together, the results of this study show that CSFV N(pro) is capable of manipulating the function of IRF7 in pDC and provides the virus with an additional strategy to circumvent the innate defense.

Computational identification of transcriptional regulators in human endotoxemia

One of the great challenges in the post-genomic era is to decipher the underlying principles governing the dynamics of biological responses. As modulating gene expression levels is among the key regulatory responses of an organism to changes in its environment, identifying biologically relevant transcriptional regulators and their putative regulatory interactions with target genes is an essential step towards studying the complex dynamics of transcriptional regulation. We present an analysis that integrates various computational and biological aspects to explore the transcriptional regulation of systemic inflammatory responses through a human endotoxemia model. Given a high-dimensional transcriptional profiling dataset from human blood leukocytes, an elementary set of temporal dynamic responses which capture the essence of a pro-inflammatory phase, a counter-regulatory response and a dysregulation in leukocyte bioenergetics has been extracted. Upon identification of these expression patterns, fourteen inflammation-specific gene batteries that represent groups of hypothetically ‘coregulated’ genes are proposed. Subsequently, statistically significant cis-regulatory modules (CRMs) are identified and decomposed into a list of critical transcription factors (34) that are validated largely on primary literature. Finally, our analysis further allows for the construction of a dynamic representation of the temporal transcriptional regulatory program across the host, deciphering possible combinatorial interactions among factors under which they might be active. Although much remains to be explored, this study has computationally identified key transcription factors and proposed a putative time-dependent transcriptional regulatory program associated with critical transcriptional inflammatory responses. These results provide a solid foundation for future investigations to elucidate the underlying transcriptional regulatory mechanisms under the host inflammatory response. Also, the assumption that coexpressed genes that are functionally relevant are more likely to share some common transcriptional regulatory mechanism seems to be promising, making the proposed framework become essential in unravelling context-specific transcriptional regulatory interactions underlying diverse mammalian biological processes.

Melatonin protects liver against ischemia and reperfusion injury through inhibition of toll-like receptor signaling pathway

This study investigated the immunomodulating effect of melatonin on toll-like receptor (TLR)-stimulated signal transduction. Rats were subjected to 60 min of ischemia followed by 1 or 5 hr of reperfusion. Melatonin (10 mg/kg) or the vehicle was administered intraperitoneally 15 min prior to ischemia and immediately before reperfusion. Melatonin treatment significantly reduced the level of serum alanine aminotransferase activity. Increased levels of TLR3 and TLR4 protein expression induced by ischemia/reperfusion (I/R) were attenuated by melatonin. Serum level of high-mobility group box 1 (HMGB1), a potent alarmin of the TLR system, increased significantly in the I/R group, and melatonin inhibited this release. Melatonin suppressed the increase in myeloid differentiation factor 88 (MyD88) protein expression, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) phosphorylation and nuclear translocation of nuclear factor κB (NF-κB) and phosphorylated c-Jun, a component of activator protein 1. The increased level of toll-receptor-associated activator of interferon (TRIF) expression, phosphorylation of interferon (IFN) regulatory factor 3 (IRF3) and serum IFN-β was attenuated by melatonin. Melatonin attenuated the levels of tumor necrosis factor alpha (TNF-α), interleukin (IL)-6 and inducible nitric oxide synthase (iNOS) protein and mRNA expression, while the level of heme oxygenase-1 (HO-1) was augmented. Our results suggest that melatonin ameliorates I/R-induced liver damage by modulation of TLR-mediated inflammatory responses.

STAT1-mediated signal integration between IFNγ and LPS leads to increased EC and SMC activation and monocyte adhesion

Inflammation plays an important role in host defenses against infectious agents and injury, but it also contributes to the pathophysiology of atherosclerosis. Signal transducer and activated transcription 1 (STAT1) has been identified as a point of convergence for the cross talk between the pro-inflammatory cytokine interferon γ (IFNγ) and the Toll-like receptor-4 (TLR4) ligand LPS in immune cells. However, there is no information available on the role of STAT1 in TLR4-mediated progression of atherosclerosis and on potential synergism between lipopolysaccharides (LPS) and IFNγ signaling in cells from the vasculature. Cultured human microvascular endothelial cells (HMECs) exposed to LPS activated STAT1 in a delayed manner that was inhibited by cycloheximide treatment. Pretreatment of HMECs as well as primary vascular smooth muscle cells (VSMCs) with IFNγ followed by LPS resulted in a significant increase in STAT1 phosphorylation compared with both factors alone. Increased STAT1 protein levels, strictly mediated by IFNγ, correlated with the augmented STAT1 phosphorylation that was absent in TLR4(-/-) cells. As assessed by PCR, Western analysis, and ELISA, this coincided with increased expression of the chemokine interferon gamma-induced protein 10 kDa (IP-10) and the adhesion molecule ICAM-1 in a TLR4-dependent manner.The STAT1-inhibitor fludarabine markedly reduced these effects as well as IFNγ and LPS-dependent adhesion of U937 cells to endothelial cells, emphasizing the potential importance of STAT1 in the integration of both signals. With the established roles of IFNγ and TLRs in atherosclerotic pathology, the STAT1-dependent signal integration between IFNγ and TLR in ECs and VSMCs in response to exogenous and endogenous atherogenic ligands could result in amplification of pro-inflammatory responses in the damaged vessel and be a novel mechanism involved in the initiation and progression of atherosclerosis.

Toll-like receptors and signalling in spermatogenesis and testicular responses to inflammation--a perspective

It is self-evident that infection and inflammation in the reproductive tract can inhibit male fertility, but the observation that fertility may also be compromised by systemic inflammation and disease is more difficult to explain. Recent studies implicating microbial pattern-recognition receptors, such as the Toll-like receptors (TLRs), as well as inflammatory cytokines and their signalling pathways, in testicular function have cast new light on this mysterious link between infection/inflammation and testicular dysfunction. It is increasingly evident that signalling pathways normally involved in controlling inflammation play fundamental roles in regulating Sertoli cell activity and responses to reproductive hormones, in addition to promoting immune responses within the testis. Many of the negative effects of inflammation on spermatogenesis may be attributed to elevated production of inflammation-related gene products within the circulation and the testis, which subsequently exert disruptive effects on spermatogenic cell development and survival, as well as the ability of the Sertoli cells to provide support for spermatogenesis. These interactions have important implications for testicular dysfunction and disease, and may eventually provide new opportunities for therapeutic interventions.

Remote ischemic preconditioning protects the brain against injury after hypothermic circulatory arrest

BACKGROUND

Ischemic preconditioning (IPC) is a mechanism protecting tissues from injury during ischemia and reperfusion. Remote IPC (RIPC) can be elicited by applying brief periods of ischemia to tissues with ischemic tolerance, thus protecting vital organs more susceptible to ischemic damage. Using a porcine model, we determined whether RIPC of the limb is protective against brain injury caused by hypothermic circulatory arrest (HCA).

METHODS AND RESULTS

Twelve piglets were randomized to control and RIPC groups. RIPC was induced in advance of cardiopulmonary bypass by 4 cycles of 5 minutes of ischemia of the hind limb. All animals underwent cardiopulmonary bypass followed by 60 minutes of HCA at 18°C. Brain metabolism and electroencephalographic activity were monitored for 8 hours after HCA. Assessment of neurological status was performed for a week postoperatively. Finally, brain tissue was harvested for histopathological analysis. Study groups were balanced for baseline and intraoperative parameters. Brain lactate concentration was significantly lower (P<0.0001, ANOVA) and recovery of electroencephalographic activity faster (P<0.05, ANOVA) in the RIPC group. RIPC had a beneficial effect on neurological function during the 7-day follow-up (behavioral score; P<0.0001 versus control, ANOVA). Histopathological analysis demonstrated a significant reduction in cerebral injury in RIPC animals (injury score; mean [interquartile range]: control 5.8 [3.8 to 7.5] versus RIPC 1.5 [0.5 to 2.5], P<0.001, t test).

CONCLUSIONS

These data demonstrate that RIPC protects the brain against HCA-induced injury, resulting in accelerated recovery of neurological function. RIPC might be neuroprotective in patients undergoing surgery with HCA and improve long-term outcomes. Clinical trials to test this hypothesis are warranted.

Peroxisome proliferator-activated receptor gamma negatively regulates IFN-beta production in Toll-like receptor (TLR) 3- and TLR4-stimulated macrophages by preventing interferon regulatory factor 3 binding to the IFN-beta promoter

Toll-like receptors 3 and 4 utilize adaptor TRIF to activate interferon regulatory factor 3 (IRF3), resulting in IFN-β production to mediate anti-viral and bacterial infection. Peroxisome proliferator-activated receptor (PPAR)-γ is a ligand-activated transcription factor expressed in various immune cells and acts as a transcriptional repressor to inhibit the transcription of many proinflammatory cytokines. But, the function of PPAR-γ in TLR3- and -4-mediated IFN-β production is not well elucidated. Here, we have analyzed the effect of the PPAR-γ agonists on IFN-β production in peritoneal primary macrophages in response to LPS and poly(I:C). PPAR-γ agonists inhibited LPS and poly(I:C)-induced IFN-β transcription and secretion. siRNA knockdown of PPAR-γ expression and transfection of PPAR-γ expression plasmid demonstrated that PPAR-γ agonist inhibits IFN-β production in a PPAR-γ-dependent manner. The ability of the PPAR-γ agonist to inhibit IFN-β production was confirmed in vivo as mice treated with troglitazone exhibited decreased levels of IFN-β upon LPS and poly(I:C) challenge. Chromatin immunoprecipitation (CHIP) assay and electrophoretic mobility shift assay (EMSA) demonstrated that troglitazone treatment impaired IRF3 binding to the IFN-β promoter. Furthermore, troglitazone could inhibit LPS and poly(I:C)-induced STAT1 phosphorylation and subsequent ISRE activation. These results demonstrate that PPAR-γ negatively regulates IFN-β production in TLR3- and 4-stimulated macrophages by preventing IRF3 binding to the IFN-β promoter.

Innate immune signaling in the myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are heterogeneous clonal hematologic malignancies characterized by cytopenias caused by ineffective hematopoiesis and propensity to progress to acute myeloid leukemia. Innate immunity provides immediate protection against pathogens by coordinating activation of signaling pathways in immune cells. Given the prominent role of the innate immune pathway in regulating hematopoiesis, it is not surprising that aberrant signaling of this pathway is associated with hematologic malignancies. Increased activation of the innate immune pathway may contribute to dysregulated hematopoiesis, dysplasia, and clonal expansion in myelodysplastic syndromes.

The expression of SOCS1 and TLR4-NFkappaB pathway molecules in neoplastic cells as potential biomarker for the aggressive tumor phenotype in laryngeal carcinoma

Suppressor of cytokine signaling 1 (SOCS1) is the key regulator of cytokine-mediated innate and adaptive immunity. One of the molecular mechanisms of SOCS1 is connected with inhibition of TLR4-NFkappaB pathway. The relationships among these molecules in laryngeal carcinoma are not exactly known. In this preliminary study we focused on their special activity and role in regulation of development and progression of laryngeal carcinoma. To investigate NFkappaB (p65 subunit) nuclear and cytoplasmic expression in 45 tumor samples of advanced laryngeal carcinoma IHC staining was performed. To determine the mRNA expression levels of TLR4, IRAK1, TRAF6 and SOCS1 in isolated neoplasm cells and non-cancerous adjacent mucosa epithelial cells RT-PCR was used. The invasiveness of laryngeal carcinomas was evaluated according to tumor front grading, TFG, which included tumor-related features (cytoplasmic differentiation, nuclear polymorphism, number of mitoses) and adjacent stroma-related characteristics of the peripheral edge of tumor infiltration (mode of infiltration, depth of invasion and plasmalymphocytic infiltration). The relationships between pT, pN status, the histological G grade, certain clinicopathological characteristics as well as postoperative observation time and the mRNA expression of the molecules mentioned earlier were investigated. Significant differences of TLR4-NFkappaB pathway molecules and SOCS1 mRNA expression in laryngeal tumor cells and normal adjacent mucosa cells as well as significant interconnections of TLR4, SOCS1 and NFkappaB(p65) in isolated tumor cells were obtained. This preliminary study demonstrated that the expression of SOCS1 and TLR4-NFkappaB pathway molecules had a strong association with the aggressiveness of laryngeal carcinoma. Positive relationships of TRAF6 in tumor margin cells with the histological grade and the mode of tumor invasion as well as the TFG total score were highlighted. Significant positive correlations were found between the TLR4 in tumor central cells and the TFG total score. Negative relationships of SOCS1 in tumor central cells with the histological grade were also noted. Significant positive correlations were found between the cytoplasmic NFkappaB(p65) and the mode of invasion as well as TFG total score. Our findings confirmed the importance of SOCS1 and TLR4-NFkappaB pathway molecules as potential biomarkers for assessment of the aggressive tumor phenotype in laryngeal carcinoma.

SIGIRR inhibits toll-like receptor 4, 5, 9-mediated immune responses in human airway epithelial cells

Human airway epithelial cells (HAEC) may contribute to acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) through toll-like receptors (TLRs)-mediated molecular mechanisms. TLRs exist on the surface of HAEC where binding to their cognate ligands initiates airway inflammation. Single immunoglobulin interleukin-1 receptor-related protein (SIGIRR) is a member of the toll-interleukin-1 receptor (TIR) family that can negatively modulate the immune response. We carried out studies to characterize SIGIRR modulation of TLR-mediated immune response in HAEC and to define its mechanisms of action. Following treatment with various concentrations of LPS, flagellin and CpG DNA, the levels of cognate TLRs 4, 5, and 9 were measured in the supernatants of HAEC over-expressing the SIGIRR molecule. Moreover, the interaction of the TLR adaptor myeloid differentiation factor 88 (MyD88) with SIGIRR in response to LPS-, flagellin- and CpG DNA-stimulation was examined by co-immunoprecipitation. The findings from this study revealed that overexpression of SIGIRR in HAEC stimulated by LPS, flagellin or CpG DNA resulted in attenuated production of the inflammatory mediators IL-6 and TNF-α. This attenuation was not the result of decreased expression of TLR4, 5 or 9, but rather a sequestration of MyD88 to the TLRs. In conclusion, SIGIRR can inhibit TLR4, 5, and 9-mediated immune responses in HAEC and may be a valuable therapeutic target for the prevention of ALI/ARDS.

Functional genomics to identify therapeutic prophylactic targets

Infectious diseases are a leading cause of global human mortality. The use of antimicrobials remains the most common strategy for treatment. However, the isolation of pathogens resistant to virtually all antimicrobials makes it urgent to develop effective therapeutics based on new targets. Here we review a new drug discovery paradigm focusing on identifying and targeting host factors important for infection as well as pathogen determinants involved in disease progression. We summarize innovative strategies which by combining bioinformatics with transcriptomics and chemical genetics have already identified host factors essential for pathogen entry, survival and replication. We describe how the discovery of RNA interference which allows loss-of-function studies has facilitated functional genomic studies in human cells. It is expected that these studies will identify targets to be used as host-directed drug therapy which, together with antimicrobials targeting microbial virulence factors, will efficiently eliminate the invading pathogen.

Immunology of the Testis and Male Reproductive Tract

A large body of evidence points to the existence of a close, dynamic relationship between the immune system and the male reproductive tract, which has important implications for our understanding of both systems. The testis and the male reproductive tract provide an environment that protects the otherwise highly immunogenic spermatogenic cells and sperm from immunological attack. At the same time, secretions of the testis, including androgens, influence the development and mature functions of the immune system. Activation of the immune system has negative effects on both androgen and sperm production, so that systemic or local infection and inflammation compromise male fertility. The mechanisms underlying these interactions have begun to receive the attention from reproductive biologists and immunologists that they deserve, but many crucial details remain to be uncovered. A complete picture of male reproductive tract function and its response to toxic agents is contingent upon continued exploration of these interactions and the mechanisms involved.

PolyI:C plus IL-2 or IL-12 induce IFN-gamma production by human NK cells via autocrine IFN-beta

NK lymphocytes and type I IFN (IFN-alpha/beta) are major actors of the innate anti-viral response that also influence adaptive immune responses. We evaluated type I IFN production by human NK cells in response to polyI:C, a potent type I IFN-inducing TLR3 agonist. PolyI:C plus IL-2/IL-12 induced IFN-beta (but not IFN-alpha) mRNA expression and protein production by highly pure human NK cells and by the human NK cell line NK92. Neutralizing anti-IFNAR1 or anti-IFN-beta Ab prevented the production of IFN-gamma induced by polyI:C plus IL-2/IL-12. Similarly, IFN-gamma production induced by polyI:C plus IL-12 was reduced in NK cells isolated from IFNAR1(-/-) compared with WT mice. The ability of polyI:C plus IL-12 to induce IFN-gamma production was related to an increase of TLR3, Mda5 and IFNAR expression and by an increase of STAT1 and STAT4 phosphorylation. Collectively, these data demonstrate that NK cells, in response to polyI:C plus IL-2/IL-12, produce IFN-beta that induce, in an autocrine manner, the production of IFN-gamma and thereby highlight that NK cells may control the outcome of protective or injurious immune responses through type I IFN secretion.

SOCS2 influences LPS induced human monocyte-derived dendritic cell maturation

Dendritic cells (DCs) are highly specific antigen presenting cells, which link innate and adaptive immune responses and participate in protecting hosts from invading pathogens. DCs can be generated in vitro by culturing human monocytes with GM-CSF and IL-4 followed by LPS induced DC maturation. We set out to study the suppressor of cytokine signaling (SOCS) proteins during maturation and activation of human monocyte-derived DCs from peripheral blood in vitro. We found that the expression of SOCS2 mRNA and protein is dramatically up-regulated during DC maturation. Silencing of SOCS2 using siRNA, inhibited DC maturation as evidenced by a decreased expression of maturation markers such as CD83, co-stimulatory molecules CD40, CD86 and HLA-DR. Furthermore, silencing of SOCS2 decreased LPS induced activation of MAP kinases (SAKP/JNK, p38, ERK), IRF3, decreased the translocation of the NF-kappaB transcription factor and reduced downstream gene mRNA expression. These results suggest a role for SOCS2 in the MyD88-dependent and -independent TLR4 signaling pathways. In conclusion, our results demonstrate that SOCS2 is required for appropriate TLR4 signaling in maturating human DCs via both the MyD88-dependent and -independent signaling pathway.

The major outer membrane protein of a periodontopathogen induces IFN-beta and IFN-stimulated genes in monocytes via lipid raft and TANK-binding kinase 1/IFN regulatory factor-3

Surface molecules of pathogens play an important role in stimulating host immune responses. Elucidation of the signaling pathways activated by critical surface molecules in host cells provides insight into the molecular pathogenesis resulting from bacteria-host interactions. MspTL is the most abundant outer membrane protein of Treponema lecithinolyticum, which is associated with periodontitis, and induces expression of a variety of proinflammatory factors. Although bacteria and bacterial components like LPS and flagellin are known to induce IFN-beta, induction by bacterial surface proteins has not been reported. In the present study, we investigated MspTL-mediated activation of signaling pathways stimulating up-regulation of IFN-beta and IFN-stimulated genes in a human monocytic cell line, THP-1 cells, and primary cultured human gingival fibroblasts. MspTL treatment of the cells induced IFN-beta and the IFN-stimulated genes IFN-gamma-inducible protein-10 (IP-10) and RANTES. A neutralizing anti-IFN-beta Ab significantly reduced the expression of IP-10 and RANTES, as well as STAT-1 activation, which was also induced by MspTL. Experiments using specific small interfering RNA showed that MspTL activated TANK-binding kinase 1 (TBK1), but not inducible IkappaB kinase (IKKi). MspTL also induced dimerization of IFN regulatory factor-3 (IRF-3) and translocation into the nucleus. The lipid rapid-disrupting agents methyl-beta-cyclodextrin, nystatin, and filipin inhibited the MspTL internalization and cellular responses, demonstrating that lipid raft activation was a prerequisite for MspTL cellular signaling. Our results demonstrate that MspTL, the major outer protein of T. lecithinolyticum, induced IFN-beta expression and subsequent up-regulation of IP-10 and RANTES via TBK1/IRF-3/STAT-1 signaling secondary to lipid raft activation.

CC chemokine ligand 2 down-modulation by selected Toll-like receptor agonist combinations contributes to T helper 1 polarization in human dendritic cells

Toll-like receptor (TLR) signaling activation by pathogens is critical to the induction of immune responses, and demands tight regulation. We describe in this study that CC chemokine ligand 2 (CCL2) secretion triggered by TLR4 or TLR8 engagement is strongly inhibited upon simultaneous activation of both TLRs in human monocyte-derived dendritic cells (DCs). Impaired CCL2 secretion occurs concomitantly to interleukin-12 up-regulation, being part of a complex regulatory circuit ensuring optimal T helper type 1 polarization. Interestingly, triggering selected TLRs or their combinations differently affects nuclear factor-kappaB p65 activation and microRNA expression. Overall, these results indicate that CCL2 supplies an important immunomodulatory role to DCs, and may contribute to dictate the cytokine profile in T helper type 1 responses induced by DCs.

GM-CSF- and M-CSF-dependent macrophage phenotypes display differential dependence on type I interferon signaling

M-CSF and GM-CSF are mediators involved in regulating the numbers and function of macrophage lineage populations and have been shown to contribute to macrophage heterogeneity. Type I IFN is an important mediator produced by macrophages and can have profound regulatory effects on their properties. In this study, we compared bone marrow-derived macrophages (BMM) and GM-CSF-induced BMM (GM-BMM) from wild-type and IFNAR1(-/-) mice to assess the contribution of endogenous type I IFN to the phenotypic differences between BMM and GM-BMM. BMM were capable of higher constitutive IFN-beta production, which contributed significantly to their basal transcriptome. Microarray analysis found that of the endogenous type I IFN-regulated genes specific to either BMM or GM-BMM, 488 of these gene alterations were unique to BMM, while only 50 were unique to GM-BMM. Moreover, BMM displayed enhanced basal mRNA levels, relative to GM-BMM, of a number of genes identified as being dependent on type I IFN signaling, including Stat1, Stat2, Irf7, Ccl5, Ccl12, and Cxcl10. As a result of prior type I IFN "priming," upon LPS stimulation BMM displayed increased activation of the MyD88-independent IRF-3/STAT1 pathways compared with GM-BMM, which correlated with the distinct cytokine/chemokine profiles of the two macrophage subsets. Furthermore, the autocrine type I IFN signaling loop regulated the production of the M1 and M2 signature cytokines, IL-12p70 and IL-10. Collectively, these findings demonstrate that constitutive and LPS-induced type I IFN play significant roles in regulating the differences in phenotype and function between BMM and GM-BMM.

Double-stranded RNA analog poly(I:C) inhibits human immunodeficiency virus amplification in dendritic cells via type I interferon-mediated activation of APOBEC3G

Human immunodeficiency virus (HIV) is taken up by and replicates in immature dendritic cells (imDCs), which can then transfer virus to T cells, amplifying the infection. Strategies known to boost DC function were tested for their ability to overcome this exploitation when added after HIV exposure. Poly(I:C), but not single-stranded RNA (ssRNA) or a standard DC maturation cocktail, elicited type I interferon (IFN) and interleukin-12 (IL-12) p70 production and the appearance of unique small (15- to 20-kDa) fragments of APOBEC3G (A3G) and impeded HIV(Bal) replication in imDCs when added up to 60 h after virus exposure. Comparable effects were mediated by recombinant alpha/beta IFN (IFN-alpha/beta). Neutralizing the anti-IFN-alpha/beta receptor reversed poly(I:C)-induced inhibition of HIV replication and blocked the appearance of the small A3G proteins. The poly(I:C)-induced appearance of small A3G proteins was not accompanied by significant differences in A3G mRNA or A3G monomer expression. Small interfering RNA (siRNA) knockdown of A3G could not be used to reverse the poly(I:C)-induced protective effect, since siRNAs nonspecifically activated the DCs, inducing the appearance of the small A3G proteins and inhibiting HIV infection. Notably, the appearance of small A3G proteins coincided with the shift of high-molecular-mass inactive A3G complexes to the low-molecular-mass (LMM) active A3G complexes. The unique immune stimulation by poly(I:C) with its antiviral effects on imDCs marked by the expression of IFN-alpha/beta and active LMM A3G renders poly(I:C) a promising novel strategy to combat early HIV infection in vivo.

INTERFEROME: the database of interferon regulated genes

INTERFEROME is an open access database of types I, II and III Interferon regulated genes (http://www.interferome.org) collected from analysing expression data sets of cells treated with IFNs. This database of interferon regulated genes integrates information from high-throughput experiments with annotation, ontology, orthologue sequences from 37 species, tissue expression patterns and gene regulatory information to enable a detailed investigation of the molecular mechanisms underlying IFN biology. INTERFEROME fulfils a need in infection, immunity, development and cancer research by providing computational tools to assist in identifying interferon signatures in gene lists generated by high-throughput expression technologies, and their potential molecular and biological consequences.

Interferon and cytokine responses to Crimean Congo hemorrhagic fever virus; an emerging and neglected viral zonoosis

Crimean Congo hemorrhagic fever virus (CCHFV) causes an acute disease with the potential of a fatal outcome. The virus is prevalent in about 30 countries. Clinical symptoms of infection commonly include fever, myalgia, and hemorrhages. Levels of liver enzymes are raised, and bleeding markers are often increased. A role of inflammatory cytokines in the pathogenesis has been suggested, and CCHFV employs a range of passive and active mechanisms to avoid induction of the antiviral type I interferons. Here, we review the most recent findings on the molecular pathogenesis and the interaction of CCHFV with the type I interferon and cytokine responses and discuss implications for pathogenesis.

Effect of pretreatment with toll-like receptor agonists in a mouse model of herpes simplex virus type 1 encephalitis

BACKGROUND

We evaluated the effect of pretreatment with Toll-like receptor (TLR) agonists in a mouse model of herpes simplex virus type 1 (HSV-1) encephalitis.

METHODS

BALB/c mice received a single intraperitoneal or intranasal injection of polyinosinic:polycytidylic acid (poly I:C), a TLR3 agonist; lipopolysaccharide (LPS), a TLR4 agonist; oligodeoxynucleotide (ODN), a TLR9 agonist; or control vehicle. Twenty-four hours later, animals were infected with 5000 plaque-forming units of HSV-1.

RESULTS

Mice that received intraperitoneal pretreatment with vehicle, LPS, and poly I:C had survival rates of 7%, 13%, and 56%, respectively, and mean life expectancies of 156.80+/-9.56, 176.00+/-9.24, and 213.00+/-7.71 h, respectively (p< .05, poly I:C group vs. other groups). Similarly, intranasal pretreatment with vehicle, LPS, ODN, and poly I:C were associated with survival rates of 20%, 47%, 60%, and 94%, respectively, and mean life expectancies of 153.60+/-11.71, 188.80+/-12.97, 204.80+/-11.73, and 234.00+/-5.81 h, respectively (p< .05, ODN and poly I:C groups vs. vehicle group). Pretreatment with intranasal poly I:C induced early expression of several immune genes in the brain and resulted in a significantly lower virus load.

CONCLUSION

TLR3 stimulation by poly I:C 24 h before infection reinforces a natural innate immune mechanism of neuroprotection against HSV-1.

Preconditioning with a TLR2 specific ligand increases resistance to cerebral ischemia/reperfusion injury

The brain's resistance to ischemic injury can be transiently augmented by prior exposure to a sub-lethal stress stimulus, i.e. preconditioning. It has been reported that Toll-like receptors (TLRs) are involved in the preconditioning-induced protective effect against ischemic brain injury. In this study, we investigated the effect of preconditioning with a TLR2 specific ligand, Pam3CSK4, on focal cerebral ischemia/reperfusion (I/R) injury in mice. Pam3CSK4 was administered systemically 24 h before the mice were subjected to focal cerebral ischemia (1 h) followed by reperfusion. Cerebral infarct size was determined, blood brain barrier (BBB) permeability was evaluated, and expression of tight-junction proteins were examined after focal cerebral I/R. Results showed that pre-treatment with Pam3CSK significantly reduced brain infarct size (1.9+/-0.5% vs 9.4+/-2.2%) compared with the untreated I/R group. Pam3CSK4 pre-treatment also significantly reduced acute mortality (4.3% vs 24.2%), preserved neurological function (8.22+/-0.64 vs 3.91+/-0.57), and attenuated brain edema (84.61+/-0.08% vs 85.29+/-0.09%) after cerebral I/R. In addition, Pam3CSK4 pre-treatment preserved BBB function as evidenced by decreased leakage of serum albumin (0.528+/-0.026 vs 0.771+/-0.059) and Evans Blue (9.23+/-0.72 microg/mg vs 12.56+/-0.65 microg/mg) into brain tissue. Pam3CSK4 pre-treatment also attenuated the loss of the tight junction protein occludin in response to brain I/R injury. These results suggest that TLR2 is a new target of ischemic preconditioning in the brain and preconditioning with a TLR2 specific ligand will protect the brain from I/R injury.

The E3 ubiquitin ligase Ro52 negatively regulates IFN-beta production post-pathogen recognition by polyubiquitin-mediated degradation of IRF3

Induction of type I IFNs is a fundamental cellular response to both viral and bacterial infection. The role of the transcription factor IRF3 is well established in driving this process. However, equally as important are cellular mechanisms for turning off type I IFN production to limit this response. In this respect, IRF3 has previously been shown to be targeted for ubiquitin-mediated degradation postviral detection to turn off the IFN-beta response. In this study, we provide evidence that the E3 ligase Ro52 (TRIM21) targets IRF3 for degradation post-pathogen recognition receptor activation. We demonstrate that Ro52 interacts with IRF3 via its C-terminal SPRY domain, resulting in the polyubiquitination and proteasomal degradation of the transcription factor. Ro52-mediated IRF3 degradation significantly inhibits IFN-beta promoter activity, an effect that is reversed in the presence of the proteasomal inhibitor MG132. Specific targeting of Ro52 using short hairpin RNA rescues IRF3 degradation following polyI:C-stimulation of HEK293T cells, with a subsequent increase in IFN-beta production. Additionally, shRNA targeting of murine Ro52 enhances the production of the IRF3-dependent chemokine RANTES following Sendai virus infection of murine fibroblasts. Collectively, this demonstrates a novel role for Ro52 in turning off and thus limiting IRF3-dependent type I IFN production by targeting the transcription factor for polyubiquitination and subsequent proteasomal degradation.

Expression of toll-like receptors in the Fusarium solani infected cornea

PURPOSE

To investigate the expression of toll-like receptors (TLRs) in the human cornea with Fusarium solani (F. solani) keratitis.

METHODS

Five human corneas with F. solani keratitis and 5 healthy human corneas were evaluated for TLR1-10 mRNA by reverse transcribed polymerase chain reaction (RT-PCR) and relative real-time PCR. The proteins of TLR2, 4, and 9 were also compared by Western blot. The mean times between these corneas were collected, and the onset of treatment to surgery was 34.4 +/- 12.4 days, ranging from 15 to 47 days. The data were analyzed with SPSS15.0.

RESULTS

TLR1-10 mRNA was expressed in both healthy and F. solani infected human corneas. The expression of TLR2, 4, 6, and 9 mRNA in the F. solani infected human corneas were upregulated. The Western blot showed the protein expression of TLR2, 4, and 9 was also upregulated in the corneas with F. solani keratitis than that of the healthy corneas.

CONCLUSIONS

TLRs are expressed diversely in the F. solani infected human cornea, and TLR2, 4, and 9 may be implicated in the pathogenesis of F. solani infection in the cornea.

The role of toll-like receptor ligands/agonists in protection against genital HSV-2 infection

Control of virus replication initially depends on rapid activation of the innate immune responses. Toll-like receptor (TLR) ligands are potent inducers of innate immunity against viral infections, including herpes simplex virus (HSV). HSV-2 is currently one of the most common sexually transmitted infections in developed nations and is becoming more prevalent in adolescents. HSV-2 infects the genital mucosa and is associated with an increased risk of obtaining other sexually transmitted infections such as HIV. There is currently no vaccine available against HSV-2. In the last several years, there has been an interest in utilizing Toll-like receptor (TLR) ligands to initiate innate immune responses in order to provide an early line of defence against viral replication. This review highlights recent studies investigating the effect of various TLR ligands on genital HSV-2 infection. A considerable body of information has been published on the effect of local delivery of TLR ligands on HSV-2 replication in genital mucosa. We have outlined ligands that have a potential to provide protection against HSV-2 infection. In addition, we have presented possible mechanisms by which the local delivery of TLR ligands provides innate protection against genital HSV-2.

Induction and sequencing of Rousette bat interferon alpha and beta genes

Bats are considered to be natural reservoirs for several viruses of clinical importance, including rabies virus, Nipah virus, and Hendra virus. Type I interferons (IFNs) is an important part of the immune system in the defense against viral infection. To investigate the function of type I IFNs upon viral infection in bats, the nucleic acid, and amino acid sequences of Egyptian Rousette (Rousettus aegyptiacus) IFN-α and -β were characterized. Sequence data indicated that bat IFN-α consists of 562-bp encoded 187-aa, and IFN-β consisted of 558-bp encoded 186-aa. Phylogenetic analysis of the overall identity of IFN-β shared the highest sequence homology with pig IFN-β in both nucleotide and amino acid level. Stimulation of bat primary kidney cells (BPKCs) and bat lung cell lines, Tb-1 Lu, with polyinosinic–polycytidylic acid (poly(I:C)) or exogenous bat type I IFNs resulted in increased type I IFNs mRNA expression in BPKCs, but not in Tb-1 Lu. Characterization of the bat IFN-α and -β genes allows understanding of the immune responses upon stimulation in different tissues, thus providing practical strategies for control and treatment of clinically important diseases. These results are important especially for the virus infection, and suggest that future molecular studies on virus infection experiment of bats in vitro will require careful consideration of the differences of type I IFN expression patterns in different cell types.

Interferon and cytokine responses to SARS-coronavirus infection

The sudden emergence of severe acute respiratory syndrome (SARS) has boosted research on innate immune responses to coronaviruses. It is now well established that the causative agent, a newly identified coronavirus termed SARS-CoV, employs multiple passive and active mechanisms to avoid induction of the antiviral type I interferons in tissue cells. By contrast, chemokines such as IP-10 or IL-8 are strongly upregulated. The imbalance in the IFN response is thought to contribute to the establishment of viremia early in infection, whereas the production of chemokines by infected organs may be responsible for (i) massive immune cell infiltrations found in the lungs of SARS victims, and (ii) the dysregulation of adaptive immunity. Here, we will review the most recent findings on the interaction of SARS-CoV and related Coronaviridae members with the type I interferon and cytokine responses and discuss implications for pathogenesis and therapy.

Critical role for transcription factor C/EBP-beta in regulating the expression of death-associated protein kinase 1

Transcription factor C/EBP-beta regulates a number of physiological responses. During an investigation of the growth-suppressive effects of interferons (IFNs), we noticed that cebpb(-/-) cells fail to undergo apoptosis upon gamma IFN (IFN-gamma) treatment, compared to wild-type controls. To examine the basis for this response, we have performed gene expression profiling of isogenic wild-type and cebpb(-/-) bone marrow macrophages and identified a number of IFN-gamma-regulated genes that are dependent on C/EBP-beta for their expression. These genes are distinct from those regulated by the JAK-STAT pathways. Genes identified in this screen appear to participate in various cellular pathways. Thus, we identify a new pathway through which the IFNs exert their effects on cellular genes through C/EBP-beta. One of these genes is death-associated protein kinase 1 (dapk1). DAPK1 is critical for regulating the cell cycle, apoptosis, and metastasis. Using site-directed mutagenesis, RNA interference, and chromatin immunoprecipitation assays, we show that C/EBP-beta binds to the promoter of dapk1 and is required for the regulation of dapk1. Both mouse dapk1 and human dapk1 exhibited similar dependences on C/EBP-beta for their expression. The expression of the other members of the DAPK family occurred independently of C/EBP-beta. Members of the C/EBP family of transcription factors other than C/EBP-beta did not significantly affect dapk1 expression. We identified two elements in this promoter that respond to C/EBP-beta. One of these is a consensus C/EBP-beta-binding site that constitutively binds to C/EBP-beta. The other element exhibits homology to the cyclic AMP response element/activating transcription factor binding sites. C/EBP-beta binds to this site in an IFN-gamma-dependent manner. Inhibition of ERK1/2 or mutation of an ERK1/2 site in the C/EBP-beta protein suppressed the IFN-gamma-induced response of this promoter. Together, our data show a critical role for C/EBP-beta in a novel IFN-induced cell growth-suppressive pathway via DAPK1.

CXCL10 regulates liver innate immune response against ischemia and reperfusion injury

We have shown that activation of toll-like receptor 4 (TLR4) and its interferon regulatory factor 3 (IRF3)-dependent downstream signaling pathway are required for the development of liver ischemia/reperfusion injury (IRI). This study focused on the role of TLR4-IRF3 activation pathway products, in particular, chemokine (C-X-C motif) ligand 10 (CXCL10). The induction of CXCL10 by liver IR was rapid (1 hour postreperfusion), restricted (ischemic lobes), and specific (no CXCL9 and CXCL11 induction). Functionally, CXCL10 was critical for IR-induced liver inflammation and hepatocellular injury. CXCL10 knockout (KO) mice were protected from IRI, as evidenced by reduced serum alanine aminotransferase (sALT) levels and preserved liver histological detail. The induction of pro-inflammatory genes, such as tumor necrosis factor alpha (TNF-alpha), interleukin 1beta (IL-1beta), IL-6, and IL-12beta was diminished, whereas the induction of the IL-10 gene remained intact in CXCL10 KO mice, indicating an altered liver response against IR. This was accompanied by selective down-regulation of extracellular signal-regulated kinase (ERK), but intact Jun N-terminal kinase (JNK), activation in the KO IR livers. This altered liver inflammation response was (1) specific to IR, because lipopolysaccharide (LPS) induced a comparable pro-inflammatory response in CXCL10 KO and wild-type (WT) mice; and (2) responsible for liver cytoprotection from IR, because neutralization of IL-10 restored local inflammation and hepatocellular damage.

CONCLUSION

CXCL10 regulates liver inflammation response against IRI, and its deficiency protected livers from IRI by local IL-10-mediated cytoprotection. Targeting CXCL10 may provide a novel therapeutic means to ameliorate liver IRI in clinics.

Systems biology approach for mapping the response of human urothelial cells to infection by Enterococcus faecalis

Background

To better understand the response of urinary epithelial (urothelial) cells to Enterococcus faecalis, a uropathogen that exhibits resistance to multiple antibiotics, a genome-wide scan of gene expression was obtained as a time series from urothelial cells growing as a layered 3-dimensional culture similar to normal urothelium. We herein describe a novel means of analysis that is based on deconvolution of gene variability into technical and biological components.

Results

Analysis of the expression of 21,521 genes from 30 minutes to 10 hours post infection, showed 9553 genes were expressed 3 standard deviations (SD) above the system zero-point noise in at least 1 time point. The asymmetric distribution of relative variances of the expressed genes was deconvoluted into technical variation (with a 6.5% relative SD) and biological variation components (>3 SD above the mode technical variability). These 1409 hypervariable (HV) genes encapsulated the effect of infection on gene expression. Pathway analysis of the HV genes revealed an orchestrated response to infection in which early events included initiation of immune response, cytoskeletal rearrangement and cell signaling followed at the end by apoptosis and shutting down cell metabolism. The number of poorly annotated genes in the earliest time points suggests heretofore unknown processes likely also are involved.

Conclusion

Enterococcus infection produced an orchestrated response by the host cells involving several pathways and transcription factors that potentially drive these pathways. The early time points potentially identify novel targets for enhancing the host response. These approaches combine rigorous statistical principles with a biological context and are readily applied by biologists.

Th1 polarization of CD4+ T cells by Toll-like receptor 3-activated human microglia

Toll-like receptors (TLRs) are expressed by human microglia and translate environmental cues into distinct activation programs. We addressed the impact of TLR ligation on the capacity of human microglia to activate and polarize CD4 T cell responses. As microglia exist under distinct states of activation, we examined both ramified and ameboid microglia isolated from adult and fetal CNS, respectively. In vitro, ligation of TLR3 significantly increased major histocompatibility complex and costimulatory molecule expression on adult microglia and induced high levels of interferon-alpha, interleukin-12p40, and interleukin-23. TLR4 and, in particular, TLR2 had a more limited capacity to induce such responses. Coculturing allogeneic CD4 T cells with microglia preactivated with TLR3 did not increase T cell proliferation above basal levels but consistently led to elevated levels of interferon-gamma secretion and Th1 polarization. Fetal microglial TLR3 responses were comparable; in contrast, TLR2 and TLR4 decreased major histocompatibility complex class II expression on fetal cells and reduced CD4 T cell proliferation to levels below those found in untreated cocultures. All 3 TLRs induced comparable interleukin-6 secretion by microglia. Our findings illustrate how activation of human microglia via TLRs, particularly TLR3, can change the profile of local CNS immune responses by translating Th1 polarizing signals to CD4 T cells.

Expression of toll-like receptors in the healthy and herpes simplex virus-infected cornea

PURPOSE

To study the expression of toll-like receptors (TLRs) in healthy corneas and corneas with active or nonactive herpetic stromal keratitis (HSK).

METHODS

Eight corneas with HSK (including 5 active and 3 nonactive cases) and 8 healthy corneas were evaluated for TLR1-10 mRNA by reverse transcription-polymerase chain reaction (RT-PCR) and relative real-time PCR. The proteins of TLR2, 9 in 3 different groups, were also compared by immunofluorescence staining. The data were analyzed with SPSS 11.5.

RESULTS

TLR1-10 mRNA was expressed in both healthy and HSK corneas. In the healthy cornea, the mRNA expression of TLR1, 2, 3, 4, and 6 was higher, whereas the expression of TLR7, 8, and 9 was lower relative to TLR 5 and 10. All the TLRs mRNA expression in the active HSK corneas were upregulated, especially TLR4, 7, 8, and 9, compared with the healthy corneas. However, in nonactive HSK corneas, only TLR7 mRNA expression upregulated, whereas the others downregulated. The immunofluorescence staining showed that the expression of TLR 9 was slightly stronger in the cornea with active HSK than that of nonactive and healthy corneas.

CONCLUSIONS

TLRs are expressed diversely in the healthy cornea and could have an important role in innate corneal immunity. TLR4, 8, and 9 may be implicated in the pathogenesis of active HSV infection in the cornea, whereas TLR7 may play a key role in HSK whether it is active or not.

Biological characters of bats in relation to natural reservoir of emerging viruses

Many investigators focused on bats (Chiroptera) for their specific character, i.e. echolocation system, phylogenic tree, food practice and unique reproduction. However, most of basic information about the vital functions related to anti-viral activity has been unclear. For evaluating some animals as a natural reservoir or host of infectious pathogens, it is necessary that not only their immune system but also their biology, the environment of their living, food habits and physiological features should be clarified and they should be analyzed from these multi-view points. The majority of current studies on infectious diseases have been conducted for the elucidation of viral virulence using experimental animals or viral gene function in vitro, but in a few case, researchers focused on wild animal itself. In this paper, we described basic information about bats as follows; genetic background, character of the immunological factors, histological character of immune organs, the physiological function and sensitivity of bat cells to viral infection.

The role of Toll-like receptors in the regulation of neutrophil migration, activation, and apoptosis

Toll-like receptors (TLRs) play an essential role in the detection of invading pathogens and in the induction of host antimicrobial defenses. TLR4, the major endotoxin receptor, and TLR2, with agonists derived principally from gram-positive organisms, are likely to be important in the pathogenesis of sepsis. Both TLR2 and TLR4 agonists regulate important neutrophil functions, including adhesion, generation of reactive oxygen species, and release of chemokines, and activate major proinflammatory signaling pathways, including the nuclear factor- kappa B pathway. TLR stimulation produces only a modest direct inhibition of neutrophil apoptosis, although this signal is greatly amplified by the presence of monocytes, suggesting that regulation of the life span of neutrophils by TLR agonists may be principally mediated by responses of other endotoxin-responsive cells. We suggest that activation of neutrophils by TLRs is highly regulated, permitting acute neutrophil antimicrobial responses to TLR activation while providing a "brake" on inflammation by requiring the presence of mononuclear cells to significantly extend neutrophil survival.

Lipopolysaccharide preconditioning induces robust protection against brain injury resulting from deep hypothermic circulatory arrest

OBJECTIVE

Delayed preconditioning genetically reprograms the response to ischemic injury. Subclinical bacterial lipopolysaccharide acts through preconditioning, powerfully protecting against experimental stroke. We investigated the potential for lipopolysaccharide to protect against brain injury related to cardiopulmonary bypass.

METHODS

Neonatal piglets were blindly and randomly preconditioned with lipopolysaccharide (n = 6) or saline (n = 6). Three days later, they experienced 2 hours of deep hypothermic circulatory arrest before being weaned and supported anesthetized for 20 hours in an intensive care setting. Controls included cardiopulmonary bypass without deep hypothermic circulatory arrest (n = 3) and no cardiopulmonary bypass (n = 3). Brain injury was quantified by light and fluorescent microscopy (Fluoro-Jade; Histo-Chem, Inc, Jefferson, Ark).

RESULTS

All animals were clinically indistinguishable before surgery. Perioperative and postoperative parameters between experimental groups were similar. No control animal scored falsely positive. Histologic scores were 0.33 +/- 0.21, 0.66 +/- 0.42, and 0.5 +/- 0.24 in the cortex, basal ganglia, and hippocampus, respectively, in the lipopolysaccharide-treated animals but significantly worse in all saline control animals (1.33 +/- 0.21, P < .01; 1.66 +/- 0.33, P = .09; and 6.0 +/- 1.5, P < .01). One lipopolysaccharide-treated brain was histologically indistinguishable from controls.

CONCLUSION

This is the first evidence that lipopolysaccharide can precondition against cardiopulmonary bypass-related injury. Because lipopolysaccharide preconditioning is a systemic phenomenon offering proven protection against myocardial, hepatic, and pulmonary injury, this technique offers enormous potential for protecting against systemic neonatal injury related to cardiopulmonary bypass.

Type I IFN signaling is crucial for host resistance against different species of pathogenic bacteria

It is known that host cells can produce type I IFNs (IFN-alphabeta) after exposure to conserved bacterial products, but the functional consequences of such responses on the outcome of bacterial infections are incompletely understood. We show in this study that IFN-alphabeta signaling is crucial for host defenses against different bacteria, including group B streptococci (GBS), pneumococci, and Escherichia coli. In response to GBS challenge, most mice lacking either the IFN-alphabetaR or IFN-beta died from unrestrained bacteremia, whereas all wild-type controls survived. The effect of IFN-alphabetaR deficiency was marked, with mortality surpassing that seen in IFN-gammaR-deficient mice. Animals lacking both IFN-alphabetaR and IFN-gammaR displayed additive lethality, suggesting that the two IFN types have complementary and nonredundant roles in host defenses. Increased production of IFN-alphabeta was detected in macrophages after exposure to GBS. Moreover, in the absence of IFN-alphabeta signaling, a marked reduction in macrophage production of IFN-gamma, NO, and TNF-alpha was observed after stimulation with live bacteria or with purified LPS. Collectively, our data document a novel, fundamental function of IFN-alphabeta in boosting macrophage responses and host resistance against bacterial pathogens. These data may be useful to devise alternative strategies to treat bacterial infections.

Immunopathogenesis in hepatitis C virus cirrhosis

HCV (hepatitis C virus) has a high propensity to persist and to cause chronic hepatitis C, eventually leading to cirrhosis. Since HCV itself is not cytopathic, liver damage in chronic hepatitis C is commonly attributed to immune-mediated mechanisms. HCV proteins interact with several pathways in the host's immune response and disrupt pathogen-associated pattern recognition pathways, interfere with cellular immunoregulation via CD81 binding and subvert the activity of NK (natural killer) cells as well as CD4(+) and CD8(+) T-cells. Finally, HCV-specific T-cells become increasingly unresponsive and apparently disappear, owing to several possible mechanisms, such as escape mutations in critical viral epitopes, lack of sufficient help, clonal anergy or expansion of regulatory T-cells. The role of neutralizing antibodies remains uncertain, although it is still possible that humoral immunity contributes to bystander damage of virally coated cells via antibody-dependent cellular cytotoxicity. Cytotoxic lymphocytes kill HCV-infected cells via the perforin/granzyme pathway, but also release Fas ligand and inflammatory cytokines such as IFNgamma (interferon gamma). Release of soluble effector molecules helps to control HCV infection, but may also destroy uninfected liver cells and can attract further lymphocytes without HCV specificity to invade the liver. Bystander damage of these non-specific inflammatory cells will expand the tissue damage triggered by HCV infection and ultimately activate fibrogenesis. A clear understanding of these processes will eventually help to develop novel treatment strategies for HCV liver disease, independent from direct inhibition of HCV replication.

MicroRNA-155 is induced during the macrophage inflammatory response

The mammalian inflammatory response to infection involves the induction of several hundred genes, a process that must be carefully regulated to achieve pathogen clearance and prevent the consequences of unregulated expression, such as cancer. Recently, microRNAs (miRNAs) have emerged as a class of gene expression regulators that has also been linked to cancer. However, the relationship between inflammation, innate immunity, and miRNA expression is just beginning to be explored. In the present study, we use microarray technology to identify miRNAs induced in primary murine macrophages after exposure to polyriboinosinic:polyribocytidylic acid or the cytokine IFN-beta. miR-155 was the only miRNA of those tested that was substantially up-regulated by both stimuli. It also was induced by several Toll-like receptor ligands through myeloid differentiation factor 88- or TRIF-dependent pathways, whereas up-regulation by IFNs was shown to involve TNF-alpha autocrine signaling. Pharmacological inhibition of the kinase JNK blocked induction of miR-155 in response to either polyriboinosinic:polyribocytidylic acid or TNF-alpha, suggesting that miR-155-inducing signals use the JNK pathway. Together, these findings characterize miR-155 as a common target of a broad range of inflammatory mediators. Importantly, because miR-155 is known to function as an oncogene, these observations identify a potential link between inflammation and cancer.

p50 nuclear factor-kappaB overexpression in tumor-associated macrophages inhibits M1 inflammatory responses and antitumor resistance

Tumor-associated macrophages (TAM) are a major inflammatory infiltrate in tumors and a major component of the protumor function of inflammation. TAM in established tumors generally have an M2 phenotype with defective production of interleukin-12 (IL-12) and high IL-10. Here, we report that defective responsiveness of TAM from a murine fibrosarcoma and human ovarian carcinoma to M1 activation signals was associated with a massive nuclear localization of the p50 nuclear factor-kappaB (NF-kappaB) inhibitory homodimer. p50 overexpression inhibited IL-12 expression in normal macrophages. TAM isolated from p50(-/-) mice showed normal production of M1 cytokines, associated with reduced growth of transplanted tumors. Bone marrow chimeras showed that p50 inactivation in hematopoietic cells was sufficient to result in reduced tumor growth. Thus, p50 NF-kappaB overexpression accounts for the inability of TAM to mount an effective M1 antitumor response capable of inhibiting tumor growth.

Human cytomegalovirus envelope glycoproteins B and H are necessary for TLR2 activation in permissive cells

Human CMV (HCMV) is a ubiquitous member of the Herpesviridae family and an opportunistic pathogen that poses significant health risks for immunocompromised patients. HCMV pathogenesis is intimately tied to the immune status of the host, thus characterization of the innate immune response to HCMV infection is critical for understanding disease progression. Previously, we identified TLR2 as a host factor that detects and initiates inflammatory cytokine secretion in response to HCMV independent of viral replication. In this study, we show that two entry-mediating envelope gp, gp B (gB) and gp H (gH), display determinants recognized by TLR2. Neutralizing Abs against TLR2, gB and gH inhibit inflammatory cytokine responses to HCMV infection, suggesting that inflammatory cytokine stimulation by HCMV is mediated by interactions between these envelope gp and TLR2. Furthermore, both gB and gH coimmunoprecipitate with TLR2 and TLR1, indicating that these envelope gp directly interact with TLR2 and that a TLR2/TLR1 heterodimer is a functional sensor for HCMV. Because our previous studies were conducted in model cell lines, we also show that TLR2 is expressed by HCMV permissive human fibroblast cell strains, and that TLR2 is a functional sensor in these cells. This study further elucidates the importance and potency of envelope gp as a class of molecules displaying pathogen-associated molecular patterns that are recognized with immediate kinetics by TLRs in permissive cells.

Modulation of the human cytokine response by interferon lambda-1 (IFN-lambda1/IL-29)

The interferon lambda family (IFN-lambda1/2/3) is a newly described group of cytokines that are related to both the type-1 interferons and IL-10 family members. These novel cytokines are induced during viral infection and, like type-1 interferons, display significant anti-viral activity. In order to understand their function in more depth, we have examined the ability of IFN-lambda1/IL-29 to regulate cytokine production by human immune cells. Whole peripheral blood mononuclear cells (PBMC) exposed to IFN-lambda1 specifically upregulated IL-6, -8 and -10 but there were no visible effects on TNF or IL-1. This response was produced in a dose-dependant fashion and was inhibited by IL-10. Examination of purified cell populations isolated from PBMC demonstrated that monocytes, rather than lymphocytes, were the major IFN-lambda1-responsive cellular subset, producing IL-6, -8 and -10 in response to IFN-lambda1. Monocyte responses induced by low-level LPS stimulation were also synergistically enhanced by the presence of IFN-lambda1. Human macrophages were also shown to react to IFN-lambda1 similarly to monocytes, by producing the cytokines IL-6, -8 and -10. In conclusion, we have shown that IFN-lambda1, a cytokine produced in response to viral infection, activates both monocytes and macrophages producing a restricted panel of cytokines and may therefore be important in activating innate immune responses at the site of viral infection.

Differential expression of toll-like receptor mRNA in treatment non-responders and sustained virologic responders at baseline in patients with chronic hepatitis C

BACKGROUND/AIMS

The contribution of the host immune response to sustained virologic response is not clear in patients with chronic hepatitis C (CHC). The aim of this study was to explore the relationship of the toll-like receptor (TLR) expression with the outcome of antiviral therapy in hepatitis C viral infection.

METHODS

Peripheral blood mononuclear cells (PBMC) were obtained from 15 CHC patients before a 48-week treatment with pegylated interferon (PEG IFN) alpha-2a and ribavirin. A multiplex semi-quantitative reverse-trancriptase polymerase chain reaction (RT-PCR) was used to compare the relative abundance of TLR2-9 transcripts.

RESULTS

mRNA levels of TLR2, 3 and 6 were significantly higher in CHC subjects compared with normal controls (n=8). When patients were classified into non-responders (n=8) and sustained virological responders (n=7) according to the virological outcome of the treatment, there was a clear difference in baseline mRNA expression of TLRs and T-helper (Th) 1/2 cytokines. In addition, the mRNA expression of IFN-gamma and nuclear factor of activated T cells (NFAT), which is exclusively expressed in activated T cells, was inversely correlated with that of TLR4, 6 and 9 in non-responders.

CONCLUSIONS

TLRs mRNA levels are differentially expressed in baseline PBMC of chronic HCV-infected subjects with or without responsiveness to antiviral therapy.

Immunostimulants revisited: focus on the pharmacology of Ribomunyl

Ribomunyl is an immunostimulant that was developed and commercialized in the 1980s in France and has subsequently been made available in a large number of countries. The formulation is composed of proteoglycans from Klebsiella pneumoniae and of ribosomes from four of the most commonly encountered bacterial strains in recurrent respiratory tract infections. While it is obviously difficult to present a thorough summary of all historical data, here we revisit the mode of action of this immunostimulant and present a perspective in the context of the most recent data and hypotheses on the mechanisms of the antibacterial immune responses. We provide various examples of these mechanisms in innate immunity (phagocytosis, cell adhesion, dendritic cell maturation, Toll-like receptors, interferon production, proinflammatory cytokines, activation of natural killer cells), as well as in adaptative immunity (polyclonal activation of T and B cells, specific immunoglobulin A immune response in an integrated view of the mucosal immune system, and T helper type 1/type 2 [Th1/Th2] regulation and balance). The effect of this immunostimulant on anti-infectious responses can be explained, not only by a stimulation of the antibacterial defense directly assumed by innate immunity, but also by a stimulation of the specific (adaptative) immune response related to the activation of dendritic cells, of which the pivotal role in T-cell differentiation is already well known. This supports the potential of bacterial immunostimulants such as Ribomunyl in anti-infective therapy.

Protective and destructive immunity in the periodontium: Part 1--innate and humoral immunity and the periodontium

Based on the results of recent research in the field, the present paper will discuss the protective and destructive aspects of the innate vs. adaptive (humoral and cell-mediated) immunity associated with the bacterial virulent factors or antigenic determinants during periodontal pathogenesis. Attention will be focused on: (i) the Toll-like receptors (TLR), the innate immune repertoire for recognizing the unique molecular patterns of microbial components that trigger innate and adaptive immunity for effective host defenses, in some general non-oral vs. periodontal microbial infections; (ii) T-cell-mediated immunity, Th-cytokines, and osteoclastogenesis in periodontal disease progression; and (iii) some molecular techniques developed and used to identify critical microbial virulence factors or antigens associated with host immunity (using Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis as the model species). Therefore, further understanding of the molecular interactions and mechanisms associated with the host's innate and adaptive immune responses will facilitate the development of new and innovative therapeutics for future periodontal treatments.

Arbidol: a broad-spectrum antiviral that inhibits acute and chronic HCV infection

Arbidol (ARB) is an antiviral compound that was originally proven effective for treatment of influenza and several other respiratory viral infections. The broad spectrum of ARB anti-viral activity led us to evaluate its effect on hepatitis C virus (HCV) infection and replication in cell culture. Long-term ARB treatment of Huh7 cells chronically replicating a genomic length genotype 1b replicon resulted in sustained reduction of viral RNA and protein expression, and eventually cured HCV infected cells. Pre-treatment of human hepatoma Huh7.5.1 cells with 15 μM ARB for 24 to 48 hours inhibited acute infection with JFH-1 virus by up to 1000-fold. The inhibitory effect of ARB on HCV was not due to generalized cytotoxicity, nor to augmentation of IFN antiviral signaling pathways, but involved impaired virus-mediated membrane fusion. ARB's affinity for membranes may inhibit several aspects of the HCV lifecycle that are membrane-dependent.

Anti-interferon autoantibodies in autoimmune polyendocrinopathy syndrome type 1

BACKGROUND

The autoimmune regulator (AIRE) gene influences thymic self-tolerance induction. In autoimmune polyendocrinopathy syndrome type 1 (APS1; OMIM 240300), recessive AIRE mutations lead to autoimmunity targetting endocrine and other epithelial tissues, although chronic candidiasis usually appears first. Autoimmunity and chronic candidiasis can associate with thymomas as well. Patients with these tumours frequently also have high titre immunoglobulin G autoantibodies neutralising type I interferon (IFN)-alpha and IFN-omega, which are secreted signalling proteins of the cytokine superfamily involved in both innate and adaptive immunity.

METHODS AND FINDINGS

We tested for serum autoantibodies to type I IFNs and other immunoregulatory cytokines using specific binding and neutralisation assays. Unexpectedly, in 60/60 Finnish and 16/16 Norwegian APS1 patients with both AIRE alleles mutated, we found high titre neutralising immunoglobulin G autoantibodies to most IFN-alpha subtypes and especially IFN-omega (60% homologous to IFN-alpha)-mostly in the earliest samples. We found lower titres against IFN-beta (30% homologous to IFN-alpha) in 23% of patients; two-thirds of these (from Finland only) also had low titres against the distantly related "type III IFN" (IFN-lambda1; alias interleukin-29). However, autoantibodies to the unrelated type II IFN, IFN-gamma, and other immunoregulatory cytokines, such as interleukin-10 and interleukin-12, were much rarer and did not neutralise. Neutralising titres against type I IFNs averaged even higher in patients with APS1 than in patients with thymomas. Anti-type I IFN autoantibodies preceded overt candidiasis (and several of the autoimmune disorders) in the informative patients, and persisted for decades thereafter. They were undetectable in unaffected heterozygous relatives of APS1 probands (except for low titres against IFN-lambda1), in APS2 patients, and in isolated cases of the endocrine diseases most typical of APS1, so they appear to be APS1-specific. Looking for potentially autoimmunising cell types, we found numerous IFN-alpha(+) antigen-presenting cells-plus strong evidence of local IFN secretion-in the normal thymic medulla (where AIRE expression is strongest), and also in normal germinal centres, where it could perpetuate these autoantibody responses once initiated. IFN-alpha2 and IFN-alpha8 transcripts were also more abundant in antigen-presenting cells cultured from an APS1 patient's blood than from age-matched healthy controls.

CONCLUSIONS

These apparently spontaneous autoantibody responses to IFNs, particularly IFN-alpha and IFN-omega, segregate like a recessive trait; their high "penetrance" is especially remarkable for such a variable condition. Their apparent restriction to APS1 patients implies practical value in the clinic, e.g., in diagnosing unusual or prodromal AIRE-mutant patients with only single components of APS1, and possibly in prognosis if they prove to predict its onset. These autoantibody responses also raise numerous questions, e.g., about the rarity of other infections in APS1. Moreover, there must also be clues to autoimmunising mechanisms/cell types in the hierarchy of preferences for IFN-omega, IFN-alpha8, IFN-alpha2, and IFN-beta and IFN-lambda1.