The interface between innate and adaptive immunity

Role for MyD88 signaling in murine gammaherpesvirus 68 latency

Toll-like receptors (TLRs) are known predominantly for their role in activating the innate immune response. Recently, TLR signaling via MyD88 has been reported to play an important function in development of a B-cell response. Since B cells are a major latency reservoir for murine gammaherpesvirus 68 (MHV68), we investigated the role of TLR signaling in the establishment and maintenance of MHV68 latency in vivo. Mice deficient in MyD88 (MyD88(-/-)) or TLR3 (TLR3(-/-)) were infected with MHV68. Analysis of splenocytes recovered at day 16 postinfection from MyD88(-/-) mice compared to those from wild-type control mice revealed a lower frequency of (i) activated B cells, (ii) germinal-center B cells, and (iii) class-switched B cells. Accompanying this substantial defect in the B-cell response was an approximately 10-fold decrease in the establishment of splenic latency. In contrast, no defect in viral latency was observed in TLR3(-/-) mice. Analysis of MHV68-specific antibody responses also demonstrated a substantial decrease in the kinetics of the response in MyD88(-/-) mice. Analysis of wild-type x MyD88(-/-) mixed-bone-marrow chimeric mice demonstrated that there is a selective failure of MyD88(-/-) B cells to participate in germinal-center reactions as well as to become activated and undergo class switching. In addition, while MHV68 established latency efficiently in the MyD88-sufficient B cells, there was again a ca. 10-fold reduction in the frequency of MyD88(-/-) B cells harboring latent MHV68. This phenotype indicates that MyD88 is important for the establishment of MHV68 latency and is directly related to the role of MyD88 in the generation of a B-cell response. Furthermore, the generation of a B-cell response to MHV68 was intrinsic to B cells and was independent of the interleukin-1 receptor, a cytokine receptor that also signals through MyD88. These data provide evidence for a unique role for MyD88 in the establishment of MHV68 latency.

Innate immunity in Drosophila: Pathogens and pathways

Following in the footsteps of traditional developmental genetics, research over the last 15 years has shown that innate immunity against bacteria and fungi is governed largely by two NF-kappaB signal transduction pathways, Toll and IMD. Antiviral immunity appears to stem from RNA interference, whereas resistance against parasitoids is conferred by Toll signaling. The identification of these post-transcriptional regulatory mechanisms and the annotation of most Drosophila immunity genes have derived from functional genomic studies using "model" pathogens, intact animals and cell lines. The D. melanogaster host has thus provided the core information that can be used to study responses to natural microbial and metazoan pathogens as they become identified, as well as to test ideas of selection and evolutionary change. These analyses are of general importance to understanding mechanisms of other insect host-pathogen interactions and determinants of variation in host resistance.

A comparative analysis of cytokine responses, cell surface marker expression and MAPKs in DCs matured with LPS compared with a panel of TLR ligands

Dendritic cells (DCs) are professional antigen-presenting cells that play a vital role in shaping adaptive immunity. DC maturation begins when exogenous danger signals bind to the appropriate toll-like receptor (TLR) and initiate expression of cell surface markers and the secretion of cytokines. This process occurs through defined mitogen-activated protein kinase (MAPK) signalling pathways. Of the 13 known mammalian TLRs, lipopolysaccharide (LPS), which activates TLR4, is the most commonly used ligand for the maturation of DCs in vitro. This comprehensive study measures cytokine secretion and cell surface marker expression in murine bone-marrow-derived DCs following maturation with LPS compared to DCs matured with a panel of other TLR-ligands (zymosan A (TLR2/6), PGN (TLR2), poly(I:C) (TLR3), flagellin (TLR5) and CpG-ODN1826 (TLR9)). The role of MAPK signalling pathways in the maturation process was also examined. Results demonstrate that zymosan A and CpG induce comparable cytokine and cell surface marker profiles to LPS. The remaining ligands differed significantly for cytokine and CD40 expression, but not for CD80 and CD86 expression. While there were differences for MAPK signalling pathways for all ligands, the effect of the inhibitors were broadly similar. These findings broaden our knowledge of TLR ligand-matured DCs.

Dissecting innate immunity by germline mutagenesis

The innate arm of our immune system is the first line of defence against infections. In addition, it is believed to drive adaptive immune responses, which help fight pathogens and provide long-term memory. As such, the innate immune system is instrumental for protection against pathogens that would otherwise destroy their host. Although our understanding of the innate immune components involved in pathogen sensing and fighting is improving, it is still limited. This is particularly exemplified by increased documentation of innate immune deficiencies in humans that often result in high and recurrent susceptibility to infections or even death, without the genetic cause being evident. To provide further insight into the mechanisms by which pathogen sensing and eradication occur, several strategies can be used. The current review focuses on the forward genetic approaches that have been used to dissect innate immunity in the fruit fly and the mouse. For both animal models, forward genetics has been instrumental in the deciphering of innate immunity and has greatly improved our understanding of how we respond to invading pathogens.

The zinc finger protein and transcriptional repressor Gfi1 as a regulator of the innate immune response

Gfi1 is a transcriptional repressor with a molecular weight between 47 and 55kDa. The protein has six C-terminal C(2)H(2)-type zinc finger domains and a characteristic stretch of 20 amino acids, called the SNAG-domain, at its N-terminus. Expression of Gfi1 ranges from the hematopoietic and lymphoid system to sensory epithelia, lung and parts of the CNS. Gene knockout studies revealed that Gfi1 is essential for the development of granulocytes and plays a role in macrophage-dependent cytokine production, indicating that this protein shares the responsibility for different lines of defense against pathogens. Strikingly, Gfi1-deficient mice are highly sensitive to both endotoxin and bacterial infections and die rapidly after an experimental application of endotoxin or induction of infection with symptoms of septic shock. This sensitivity is mediated by an overproduction of tumor necrosis factor (TNF) and other inflammatory cytokines. The lung could be identified as the principal organ in which the accelerated inflammatory reactions take place in challenged Gfi1-deficient mice. Several lines of experimental evidence support a role of Gfi1 as a regulator of the Toll-like receptor (TLR) pathways, and, in general, as an essential modulator preventing an overshooting of the inflammatory response.

Cloning, characterization and expression analysis of the gene for a putative lipopolysaccharide-induced TNF-alpha factor of the Pacific oyster, Crassostrea gigas

Lipopolysaccharide-induced TNF-alpha factor (LITAF) is an important transcription factor that mediates the expression of inflammatory cytokines, including TNF-alpha, in lipopolysaccharide (LPS)-induced processes. In the present study, the Pacific oyster Crassostrea gigas LITAF (Cg-LITAF) gene was cloned and characterized. The full-length Cg-LITAF cDNA consists of 906bp and encodes a polypeptide of 115 amino acids. The Cg-LITAF gene consists of three exons and two introns, with a length of approximately 1.8kb. The Cg-LITAF protein showed 34-45% amino acid sequence identity with other known LITAF sequences. Although the Cg-LITAF coding sequence (115 aa) is shorter than all previously reported LITAF genes, the LITAF domain which contains two CXXC motifs is well conserved. An in vivo expression study showed that Cg-LITAF mRNA was expressed predominantly in gills and moderately in digestive gland and labial palps of healthy oysters. The accumulation of Cg-LITAF mRNA in oyster haemocytes determined by real-time PCR showed the peak 12h after bacterial challenge. This expression pattern suggests that Cg-LITAF is a potent factor in the regulation of genes that are involved in innate defence mechanisms.

Immunomodulatory activity of acidic polysaccharides isolated from Tanacetum vulgare L

Tanacetum vulgare L. (Tansy) has been extensively used in folk medicine for treatment of a variety of medical disorders. In the present study, we isolated and purified four acidic polysaccharide fractions (designated T-I to T-IV) from Tansy florets by the sequential use of hot-water extraction, ethanol precipitation, ultra-filtration, anion-exchange, and size-exclusion chromatography. The average M(r) of fractions T-I through T-IV was estimated to be 326, 151, 64 and 9 kDa, respectively, as determined by high performance size-exclusion chromatography analysis. Sugar composition analysis revealed that Tansy polysaccharides consisted primarily of galacturonic acid, galactose, arabinose, and rhamnose. Fractions T-II through T-IV contained an arabinogalactan type II structure, as determined by reaction with Yariv reagent. High M(r) fractions T-I and T-II exhibited potent macrophage/monocyte-activating activity, enhancing production of reactive oxygen species (ROS), nitric oxide (NO), and tumor necrosis factor alpha (TNF-alpha) by J774.A1 murine macrophages, and activating nuclear factor kappaB (NF-kappaB) in THP-1 human monocytes. In addition, Tansy polysaccharides stimulated human neutrophil function by greatly enhancing neutrophil myeloperoxidase (MPO) release. Furthermore, the low M(r) fraction T-IV had potent complement-fixing activity, which may also contribute to the anti-inflammatory and would-healing properties of Tansy extracts. Taken together, our results provide a molecular basis to explain at least part of the beneficial therapeutic effects of Tansy extracts, and support the concept of using Tansy polysaccharides as an immunotherapeutic adjuvant.

The anti-tumor effect of allogeneic bone marrow/stem cell transplant without graft vs. host disease toxicity and without a matched donor requirement?

The anti-tumor immune response that occurs in allogeneic bone marrow/stem cell transplant (BMT) settings is capable of eradicating tumors that are resistant to chemotherapy/radiation treatment. This anti-tumor immune response, known as the graft vs. tumor (GVT) effect, is the most effective immunotherapy treatment ever discovered. Unfortunately, the clinical application of GVT is severely limited due to the intimate association of GVT with the extremely toxic and often lethal side-effect known as graft vs. host disease (GVHD). It is a major research focus in the field of BMT to develop methods to separate the beneficial GVT effect from the detrimental GVHD toxicity. However, due to the intimate association of these effects, attempts to limit GVHD also have a tendency to limit the GVT effect. We propose a new concept for harnessing the power of the GVT effect without the toxicity of GVHD. Rather than trying to separate GVT from GVHD, we propose that these naturally coupled effects can 'mirrored' onto the host immune system and maintain their intimate association. The 'mirror' of GVHD is a host rejection of a graft (HVG). As rejection of an allograft would not be toxic, an HVG effect coupled to a host vs. tumor (HVT) effect, the 'mirror' of the GVT effect, would provide the anti-tumor effect of BMT without GVHD toxicity. In the 'mirror' setting, the HVT effect must occur against syngeneic tumors, while in the BMT setting the GVT effect occurs in the allogeneic setting. Previous attempts to elicit syngeneic anti-tumor immunity using therapeutic tumor vaccines have had disappointing results in the clinic due to the influence of tumor immunoavoidance mechanisms. We propose that the 'danger' signals that are released as a result of GVHD in the allogeneic BMT setting serve as an adjuvant to the GVT effect disabling tumor immunoavoidance. The chemotherapy/radiation conditioning prior to transplant is a required initiating event to the coupled GVT/GVHD effects. The conditioning releases 'danger' signals that mediate this adjuvant effect. To imitate this immunological event in immunocompetent, non-conditioned patients we propose that infusion of freshly activated, polyclonal CD4+ memory Th1 cells which express CD40L on the cell surface will stimulate a HVT/HVG 'mirror' effect, providing a non-toxic means to elicit the effective immune-mediated anti-tumor effect of BMT without the GVHD toxicity and without the requirement for a matched donor.

Update on toll-like receptor-directed therapies for human disease

Innate responses to microbes are mediated in large part by toll-like receptors (TLRs), which recognise a diverse range of molecules produced by viruses, bacteria and fungi. Great effort has been directed towards translating this knowledge into the development of new therapies for a wide spectrum of diseases, including infectious, malignant, autoimmune and allergic diseases. This review will provide a brief update on completed, ongoing and planned clinical trials of TLR ligand-based therapies for the treatment of diseases in humans.

Maturation-dependent responses of human neuronal cells to western equine encephalitis virus infection and type I interferons

Innate cell-autonomous antiviral responses are essential first lines of defense against central nervous system infections but may also contribute to neuropathogenesis. We investigated the relationships between innate immunity and neuronal differentiation using an in vitro culture system with human cell lines to analyze cellular responses to the neurotropic alphavirus western equine encephalitis virus. Human neuronal cells displayed a maturation-dependent reduction in virus-induced cytopathology that was independent of autocrine interferon alpha or beta activity. In addition, maturation was associated with enhanced responsiveness to exogenous stimuli, such that differentiated neurons required five- to ten-fold less type I interferon to suppress viral replication or virus-induced cytopathology compared to immature cells, although this enhanced responsiveness extended to only a subset of unique type I interferons. These results demonstrate that maturation-dependent changes in human neuronal cells may be key determinants in the innate immune response to infections with neurotropic alphaviruses.

Challenges for modeling and interpreting the complex biology of severe injury and inflammation

Human injury is associated with inflammatory responses that are modulated by the acute and chronic activity of endogenous factors and exogenous interventions. A characteristic feature of chronic, severe inflammatory states is the diminished signal output variability of many organ systems, including innate immune responsiveness and endogenous neural and endocrine-mediated functions. The attenuation of signal/response variability and integration of feedback capacity may contribute to systemic and tissue-specific deterioration of function. Some well-intentioned therapies directed toward support of systemic and tissue functions may actually promote the loss of system(s) adaptability and contribute to adverse outcomes in severely stressed patients. In vivo and in silico models of stress, injury, and infection have yet to fully define the influences of ongoing stressful stimulae as well as genetic variation and epigenetic factors in the context of an evolving inflammatory state. Experimental and human models incorporating variable, antecedent stress(es) and altered neuroendocrine rhythms might approximate the altered adaptability in immune and organ function responses. Such models may also provide insights into the salient mechanisms of risk and outcome more precisely than do the constrained study conditions of current animal or human models of systemic inflammation.

Protease-activated receptors: novel PARtners in innate immunity

Protease-activated receptors (PARs) belong to a family of G protein-coupled receptors activated by serine proteases via proteolytic cleavage. PARs are expressed on epithelial cells, endothelial cells, and leukocytes, indicating a role in controlling barrier function against external danger. During inflammation, microorganisms as well as host immune cells release various proteases activating PARs. Thus, PARs can be viewed as an integral component of the host antimicrobial alarm system. When stimulated, PARs regulate various functions of leukocytes in vivo and in vitro, revealing a novel pathway by which proteases affect innate immune responses. Understanding protease-immune interactions could lead to novel strategies for the treatment of infectious and immune-related diseases.

CSF-1 and TPA stimulate independent pathways leading to lysosomal degradation or regulated intramembrane proteolysis of the CSF-1 receptor

The CSF-1 receptor is a protein-tyrosine kinase that has been shown to undergo regulated intramembrane proteolysis, or RIPping. Here, we have compared receptor downregulation and RIPping in response to CSF-1 and TPA. Our studies show that CSF-1 is a relatively poor inducer of RIPping and that CSF-1-induced receptor downregulation is largely independent of RIPping. TPA is a strong inducer of RIPping and TPA-induced receptor downregulation is mediated by RIPping. We further found that RIPping is dependent on TACE or a TACE-like protease, that CSF-1 and TPA use independent pathways to initiate RIPping, and that the intracellular domain is targeted for degradation through ubiquitination.

Dendritic cells have a crucial role in the production of cytokines in mesenteric lymph nodes of B10.BR mice infected with Trichuris muris

Dendritic cells bridge innate and adaptive immunity and establish protective immunity to pathogens. Protection against the murine nematode parasite Trichuris muris depends on the T helper 2 (Th2) response and requires the Th2 cytokines interleukin 4 (IL-4), IL-10, or IL-13. To examine if the Th2 response to T. muris infection is regulated by CD11c(+)B220(-) dendritic cells in mesenteric lymph nodes, dendritic cell-enriched and dendritic cell-depleted fractions were obtained from mesenteric lymph node cells of T. muris-infected mice, and production of cytokines in cultures of these fractions was measured. At day 14 postinfection, no worm expulsion was observed, and high levels of interferon gamma production occurred in dendritic cell-enriched fractions. Expulsion of worms occurred on days 20 and 25 postinfection, and IL-10 production was induced in dendritic cell-enriched fractions on these 2 days. No cytokine production was observed in mesenteric lymph node cells and dendritic cell-depleted fractions during T. muris infection. The occurrence of worm expulsion was consistent with IL-10 production in dendritic cell-enriched fractions. IL-10 inhibits Th1 cells and promotes the Th2 response, and results from this study suggest that CD11c(+)B220(-) dendritic cells in the mesenteric lymph nodes are required for IL-10 production and the IL-10-dependent protective Th2 response.

Signaling pathways downstream of pattern-recognition receptors and their cross talk

Pattern-recognition receptors (PRRs) initiate innate immunity through pathogen recognition. Serum PRRs opsonize pathogens for enhanced phagocytic clearance. Toll-like receptors (TLRs) initiate common NF-kappaB/AP-1 and distinct IRF3/7 pathways to coordinate innate immunity and to initiate adaptive immunity against diverse pathogens. Cytoplasmic caspase-recruiting domain (CARD) helicases, such as RIG-I/MDA5, mediate antiviral immunity by inducing the production of type I interferons via the adaptor IPS-1, whereas nucleotide-binding oligomerization domain (NOD)-like receptors mediate mainly antibacterial immunity by activating NF-kappaB or inflammasomes. Dectin-1 is important for antifungal immunity, promoting phagocytosis and activating NF-kappaB. Potentially harmful TLR signaling pathways can be negatively regulated by negative feedback mechanisms and also by anti-inflammatory factors such as TGFbeta, interleukin (IL)-10, and steroids. Many combinations of TLR-TLR and TLR-NOD modulate inflammatory responses. TLRs and NALP3 interplay to produce mature IL-1beta. Thus signaling pathways downstream of PRRs and their cross talk control immune responses in effective manners.

Immune cells as anti-cancer therapeutic targets and tools

Chronic inflammation is a contributing factor to overall cancer risk as well as cancer promotion and progression; however, pathways regulating onset of cancer-promoting inflammatory responses are still poorly understood. Clinical data suggest that deficient anti-tumor cell-mediated immunity, in combination with enhanced pro-tumor humoral and/or innate immunity (inflammation), are significant factors influencing malignant outcome. Here, we discuss therapeutic implications from clinical data and experimental studies using de novo immune-competent mouse models of cancer development that together are revealing molecular and cellular mechanisms underlying interactions between immune cells and evolving neoplastic cells that regulate cancer outcome. Understanding the functionally significant links between adaptive and innate immunity that regulate cancer development will open new therapeutic opportunities to manipulate aspects of immunobiology and minimize lethal effects of cancer development.

The immunocompetence of Schwann cells

Schwann cells are the myelinating glial cells of the peripheral nervous system that support and ensheath axons with myelin to enable rapid saltatory signal propagation in the axon. Immunocompetence, however, has only recently been recognized as an important feature of Schwann cells. An autoimmune response against components of the peripheral nervous system triggers disabling inflammatory neuropathies in patients and corresponding animal models. The immune system participates in nerve damage and disease manifestation even in non-inflammatory hereditary neuropathies. A growing body of evidence suggests that Schwann cells may modulate local immune responses by recognizing and presenting antigens and may also influence and terminate nerve inflammation by secreting cytokines. This review summarizes current knowledge on the interaction of Schwann cells with the immune system, which is involved in diseases of the peripheral nervous system.

Complement activating soluble pattern recognition molecules with collagen-like regions, mannan-binding lectin, ficolins and associated proteins

Mannan-binding lectin (MBL), L-ficolin, M-ficolin and H-ficolin are all complement activating soluble pattern recognition molecules with recognition domains linked to collagen-like regions. All four may form complexes with four structurally related proteins, the three MBL-associated serine proteases (MASPs), MASP-1, MASP-2 and MASP-3, and a smaller MBL-associated protein (MAp19). The four recognition molecules recognize patterns of carbohydrate or acetyl-group containing ligands. After binding to the relevant targets all four are able to activate the complement system. We thus have a system where four different and/or overlapping patterns of microbial origin or patterns of altered-self may be recognized, but in all cases the signalling molecules, the MASPs, are shared. MASP-1 and MASP-3 are formed from one gene, MASP1/3, by alternative splicing generating two different mRNAs from a single primary transcript. Similarly MASP-2 and MAp19 are both generated from one gene, MASP-2/MAp19, by alternative splicing. A number of non-synonymous polymorphisms of the four recognition molecules and of the MASPs are known, and the implications of these alterations are being studied. The clinical impact of deficiencies will be discussed.

Increased lipopolysaccharide-induced tumour necrosis factor-alpha, interferon-gamma and interleukin-10 production in atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is based on a genetic predisposition, but environmental factors may trigger skin inflammation. According to the hygiene hypothesis, decreased exposure to microbial products in early childhood does not allow sufficient maturation of the immune system that is associated with an increased risk of atopic sensitization.

OBJECTIVES

The effect of lipopolysaccharide (LPS) on the cytokine production of peripheral blood mononuclear cells (PBMC) of AD patients and nonatopic controls was studied.

PATIENTS AND METHODS

PBMC were isolated from heparinized blood of 10 patients with AD and 10 nonatopic individuals, suspended in culture medium and stimulated with LPS. Cytokine levels in the supernatants were measured by immunoassays. Results Upon stimulation with LPS, PBMC from AD patients produced significantly higher amounts of tumour necrosis factor-alpha, interferon-gamma and interleukin (IL)-10 compared with control PBMC. LPS stimulation blocked the increased spontaneous production of IL-4 and IL-5 by PBMC from AD patients, but had no effect on IL-13 production.

CONCLUSIONS

These results demonstrate that the effects of LPS stimulation depend on both the type of cytokine and the origin of PBMC. Endotoxin exposure is suggested to modulate the disease course of AD.

Specificity and complexity of the Caenorhabditis elegans innate immune response

In response to infection, Caenorhabditis elegans produces an array of antimicrobial proteins. To understand the C. elegans immune response, we have investigated the regulation of a large, representative sample of candidate antimicrobial genes. We found that all these putative antimicrobial genes are expressed in tissues exposed to the environment, a position from which they can ward off infection. Using RNA interference to inhibit the function of immune signaling pathways in C. elegans, we found that different immune response pathways regulate expression of distinct but overlapping sets of antimicrobial genes. We also show that different bacterial pathogens regulate distinct but overlapping sets of antimicrobial genes. The patterns of genes induced by pathogens do not coincide with any single immune signaling pathway. Thus, even in this simple model system for innate immunity, striking specificity and complexity exist in the immune response. The unique patterns of antimicrobial gene expression observed when C. elegans is exposed to different pathogens or when different immune signaling pathways are perturbed suggest that a large set of yet to be identified pathogen recognition receptors (PRRs) exist in the nematode. These PRRs must interact in a complicated fashion to induce a unique set of antimicrobial genes. We also propose the existence of an "antimicrobial fingerprint," which will aid in assigning newly identified C. elegans innate immunity genes to known immune signaling pathways.

Double-stranded RNA increases kinin B1 receptor expression and function in human airway epithelial cells

Increased levels of kinins have been detected within the airways during upper respiratory viral infections (URIs). Rhinovirus, the major URI associated with acute exacerbations of asthma, is an ssRNA virus that primarily infects the airway epithelium and produces dsRNA during replication. We asked whether dsRNA could increase the expression of kinin receptors in airway epithelial cells, thereby potentiating the inflammatory consequences of kinin generation. Human airway epithelial cell line BEAS-2B was stimulated with the dsRNA analog Poly I:C and kinin receptor expression detected by quantitative RT-PCR as well as radioligand binding. Poly I:C induced an increase in B1 and B2 receptor mRNA levels in BEAS-2B and primary human normal bronchial epithelial cells. At the cell surface, only B1 receptor expression was increased by Poly I:C. Furthermore, pretreatment of BEAS-2B cells with Poly I:C enhanced the induction of phospho-ERK following B1 receptor ligand stimulation. To investigate whether these finding had potential in vivo relevance, we assessed B1 receptor expression in nasal tissue obtained from 8 normal human subjects with URIs and 3 control subjects. Five of the URI subjects demonstrated increased B1 receptor mRNA compared to the 3 control subjects. We suggest that increased expression of B1 receptor in the human airway following a URI could increase the risk of an exacerbation of asthma by contributing to increased inflammation in the airway.

Inflammatory arthritis can be reined in by CpG-induced DC-NK cell cross talk

Unmethylated CpG-oligodeoxynucleotides (ODNs) are generally thought of as potent adjuvants with considerable therapeutic potential to enhance immune responses against microbes and tumors. Surprisingly, certain so-called stimulatory CpG-ODNs strongly inhibited the effector phase of inflammatory arthritis in the K/BxN serum transfer system, either preventively or therapeutically. Also unexpected was that the inhibitory influence did not depend on the adaptive immune system cells mobilized in an immunostimulatory context. Instead, they relied on cells of the innate immune system, specifically on cross talk between CD8α⁺ dendritic cells and natural killer cells, resulting in suppression of neutrophil recruitment to the joint, orchestrated through interleukin-12 and interferon-γ. These findings highlight potential applications of CpG-ODNs and downstream molecules as antiinflammatory agents.

Application of beta-lactamase enzyme complementation to the high-throughput screening of toll-like receptor signaling inhibitors

We describe a successful application of beta-lactamase fragment complementation to high-throughput screening (HTS) for Toll-like receptor 4 (TLR4) signaling inhibitors. We developed a stable cell line, HeLa/CL3-4, expressing MyD88/Bla(a) and TLR4/Bla(b), in which the two beta-lactamase fragments complement with each other by virtue of spontaneous MyD88-TLR4 binding via their Toll/IL-1R (TIR) domains. Inhibition of the MyD88-TLR4 binding leads to the disruption of the enzyme complementation and a loss of the lactamase activity. We used a 384-well plate format to screen 16,000 compounds using this assay and obtained 45 primary hits. After rescreening these 45 hits and eliminating compounds that directly inhibited beta-lactamase, we had five candidate inhibitors. We show that these five act as inhibitors of TLR4-MyD88 binding and are variously effective at inhibiting lipopolysaccharide-stimulated cytokine release from RAW264.7 cells. One compound is effective near 100 nM. None of the compounds showed any cytotoxicity at 20 microM.

Dendritic cell quiescence during systemic inflammation driven by LPS stimulation of radioresistant cells in vivo

Dendritic cell (DC) activation is a prerequisite for T cell priming. During infection, activation can ensue from signaling via pattern-recognition receptors after contact with pathogens or infected cells. Alternatively, it has been proposed that DCs can be activated indirectly by signals produced by infected tissues. To address the contribution of tissue-derived signals, we measured DC activation in a model in which radioresistant cells can or cannot respond to lipopolysaccharide (LPS). We report that recognition of LPS by the radioresistant compartment is sufficient to induce local and systemic inflammation characterized by high circulating levels of tumor necrosis factor (TNF) α, interleukin (IL) 1β, IL-6, and CC chemokine ligand 2. However, this is not sufficient to activate DCs, whether measured by migration, gene expression, phenotypic, or functional criteria, or to render DC refractory to subsequent stimulation with CpG-containing DNA. Similarly, acute or chronic exposure to proinflammatory cytokines such as TNF-α ± interferon α/β has marginal effects on DC phenotype in vivo when compared with LPS. In addition, DC activation and migration induced by LPS is unimpaired when radioresistant cells cannot respond to the stimulus. Thus, inflammatory mediators originating from nonhematopoietic tissues and from radioresistant hematopoietic cells are neither sufficient nor required for DC activation in vivo.

Proinflammatory response of human leukemic cells to dsRNA transfection linked to activation of dendritic cells

Leukemic cells exert immunosuppressive effects that interfere with dendritic cell (DC) function and hamper effective antileukemic immune responses. Here, we sought to enhance the immunogenicity of leukemic cells by loading them with the double-stranded (ds) RNA Toll-like receptor 3 (TLR3) ligand polyriboinosinic polyribocytidylic acid (poly(I:C)), mimicking viral infection of the tumor cells. Given the responsiveness of DC to TLR ligands, we hypothesized that the uptake of poly(I:C)-loaded leukemic cells by immature DC (iDC) would lead to DC activation. Primary acute myeloid leukemia (AML) cells and AML cell lines markedly responded to poly(I:C) electroporation by apoptosis, upregulation of TLR3 expression, enhanced expression of major histocompatibility complex (MHC) and costimulatory molecules and by production of type I interferons (IFN). Upon phagocytosis of poly(I:C)-electroporated AML cells, DC maturation and activation were induced as judged by an increased expression of MHC and costimulatory molecules, production of proinflammatory cytokines and an increase of T helper 1 (T(H)1)-polarizing capacity. These immune effects were suboptimal when AML cells were passively pulsed with poly(I:C), indicating the superiority of poly(I:C) transfection over pulsing. Our results demonstrate that poly(I:C) electroporation is a promising strategy to increase the immunogenicity of AML cells and to convert iDC into activated mature DC following the phagocytosis of AML cells.

The zebrafish lysozyme C promoter drives myeloid-specific expression in transgenic fish

Background

How different immune cell compartments contribute to a successful immune response is central to fully understanding the mechanisms behind normal processes such as tissue repair and the pathology of inflammatory diseases. However, the ability to observe and characterize such interactions, in real-time, within a living vertebrate has proved elusive. Recently, the zebrafish has been exploited to model aspects of human disease and to study specific immune cell compartments using fluorescent reporter transgenic lines. A number of blood-specific lines have provided a means to exploit the exquisite optical clarity that this vertebrate system offers and provide a level of insight into dynamic inflammatory processes previously unavailable.

Results

We used regulatory regions of the zebrafish lysozyme C (lysC) gene to drive enhanced green fluorescent protein (EGFP) and DsRED2 expression in a manner that completely recapitulated the endogenous expression profile of lysC. Labeled cells were shown by co-expression studies and FACS analysis to represent a subset of macrophages and likely also granulocytes. Functional assays within transgenic larvae proved that these marked cells possess hallmark traits of myelomonocytic cells, including the ability to migrate to inflammatory sources and phagocytose bacteria.

Conclusion

These reporter lines will have utility in dissecting the genetic determinants of commitment to the myeloid lineage and in further defining how lysozyme-expressing cells participate during inflammation.

Neisseria meningitidis type C capsular polysaccharide inhibits lipooligosaccharide-induced cell activation by binding to CD14

Encapsulated Neisseria meningitidis can invade mucosal barriers and cause systemic diseases. Activation of the innate immune system by conserved meningococcal molecules such as lipooligosaccharides (LOS) is essential for the generation of an effective host immune response. Here we show that the type C capsular polysaccharide of N. meningitidis (MCPS) inhibited LOS-induced interleukin-6 and TNF-alpha secretion from monocytes, and blocked the maturation of dendritic cells induced by LOS, while the capsular polysaccharide from group B streptococcus type III and t(4-hydroxy-3-nitrophenyl) acetyl (NP)-Ficoll had no such effect. MCPS also inhibited the LOS-induced NF-kappaB activation and phosphorylation of signalling molecules such as ERK1/2, p38 and Jun N-terminal kinase. In a direct binding assay, MCPS manifested a concentration-dependent binding to recombinant lipoprotein binding protein and CD14, the two members of the LOS receptor complex. In addition, the binding of LOS to CD14 and lipopolysaccharide binding protein was inhibited by MCPS. We established that MCPS binding to CD14 is responsible for the inhibition of LOS-mediated cell activation because MCPS inhibition of LOS was reversed when access amounts of CD14 were added to culture media of HEK293 cells expressing TLR4 and MD-2, and the magnitude of recovery in LOS stimulation correlated with the increase in CD14 concentration. These results suggest a new virulence property of meningococcal capsular polysaccharides.

The SPINK gene family and celiac disease susceptibility

The gene family of serine protease inhibitors of the Kazal type (SPINK) are functional and positional candidate genes for celiac disease (CD). Our aim was to assess the gut mucosal gene expression and genetic association of SPINK1, -2, -4, and -5 in the Dutch CD population. Gene expression was determined for all four SPINK genes by quantitative reverse-transcription polymerase chain reaction in duodenal biopsy samples from untreated (n=15) and diet-treated patients (n=31) and controls (n=16). Genetic association of the four SPINK genes was tested within a total of 18 haplotype tagging SNPs, one coding SNP, 310 patients, and 180 controls. The SPINK4 study cohort was further expanded to include 479 CD cases and 540 controls. SPINK4 DNA sequence analysis was performed on six members of a multigeneration CD family to detect possible point mutations or deletions. SPINK4 showed differential gene expression, which was at its highest in untreated patients and dropped sharply upon commencement of a gluten-free diet. Genetic association tests for all four SPINK genes were negative, including SPINK4 in the extended case/control cohort. No SPINK4 mutations or deletions were observed in the multigeneration CD family with linkage to chromosome 9p21-13 nor was the coding SNP disease-specific. SPINK4 exhibits CD pathology-related differential gene expression, likely derived from altered goblet cell activity. All of the four SPINK genes tested do not contribute to the genetic risk for CD in the Dutch population.

Immunological research using RNA interference technology

RNA interference (RNAi) is a potent method of gene silencing that has developed rapidly over the past few years as a result of its extensive importance in the study of genetics, molecular biology and physiology. RNAi technology has also recently yielded significant insight into the innate and adaptive immune systems by helping to elucidate numerous mechanisms that regulate the development, activation and function of cells that mediate immunity. In addition, because of its ability to suppress gene expression effectively, this technique may be used to regulate the immune response for clinical purposes. Nonetheless, before RNAi can be successfully administered into human patients as a medical treatment, it is necessary to overcome several major limitations of this technology, such as inefficient in vivo delivery, incomplete silencing of target genes, non-specific immune responses, and off-target effects. As novel developments and discoveries in molecular biology swiftly continue to unfold, it is likely that RNAi may soon translate into a potent form of in vivo gene silencing with profound applications to vaccination and immunotherapy. In the present review, we examine the current progress of immunological studies employing RNAi and discuss the prospects for the implementation of this technique in the clinical arena.

Evidence for phagocytosis of influenza virus-infected, apoptotic cells by neutrophils and macrophages in mice

Influenza virus-infected cells undergo apoptosis and become susceptible to phagocytosis by macrophages in vitro, and this leads to the propagation of the virus being inhibited. We previously showed that inhibitors of phagocytosis increased the rate of mortality among influenza virus-infected mice. However, the mode of the phagocytosis of influenza virus-infected cells in vivo has not been investigated. We, in this study, assessed this issue by histochemically analyzing bronchoalveolar lavage cells and lung tissue obtained from C57BL/6 mice infected with influenza A/WSN (H1N1) virus. Both neutrophils and macrophages accumulated in the lung soon after the viral challenge, and either type of cell was capable of phagocytosing influenza virus-infected, apoptotic cells. Changes in the level of phagocytosis and the amount of virus in lung tissue roughly correlated with each other. Furthermore, alveolar macrophages prepared from influenza virus-infected mice showed greater phagocytic activity than those from uninfected mice. The phagocytic activity of macrophages was stimulated in vitro by a heat-labile substance(s) released from influenza virus-infected cells undergoing apoptosis. These results suggested that the level of phagocytosis is augmented both quantitatively and qualitatively in the lung of influenza virus-infected animals so that infected cells are effectively eliminated. Finally, lack of TLR4 caused an increase in the rate of mortality among influenza virus-challenged mice and a decrease in the level of phagocytosis of apoptotic cells in the lung. TLR4 could thus play an important role in the host defense against influenza by positively regulating the phagocytic elimination of infected cells.

Cytokines are a therapeutic target for the prevention of inflammation-induced cancers

Interleukin-6 (IL-6) is an inflammatory cytokine with a well-documented role in cancer. The cytokine binds to a membrane-bound IL-6 receptor (IL-6R) and this complex associates with two molecules of the signal transducing protein gp130, initiating intracellular signaling. Whereas gp130 is expressed on all cells of the body, the IL-6R is only found on some cells, mainly hepatocytes and several leukocytes. Cells, which only express gp130 and no IL-6R, cannot respond to IL-6. We have shown that the IL-6R exists as a soluble protein generated by limited proteolysis of the membrane-bound receptor or by translation from an alternatively spliced mRNA. The complex of soluble IL-6R (sIL-6R) and IL-6 can bind to gp130 on cells that lack the membrane-bound IL-6R and trigger gp130 signaling. We have named this process trans-signaling. We review data that show that IL-6 uses classical signaling via the membrane-bound receptor and trans-signaling via the soluble receptor in physiological and pathophysiological situations. We have developed designer cytokines, which specifically enhance or inhibit IL-6 trans-signaling. These designer cytokines have been shown to be extremely useful in therapeutic applications such as blockade of chronic inflammation and cancer.

Organ-specific regulation of innate immunity

Immune responses to microbial challenge in various tissues are not the same. Organ-specific immune responses are adapted to maintain organ physiology.

Regulation of innate immunity by MAPK dual-specificity phosphatases: knockout models reveal new tricks of old genes

Throughout evolution, mammals have developed an elaborate network of positive and negative regulatory mechanisms, which provide balance between defensive measures against bacterial and viral pathogens and protective measures against unwarranted destruction of the host by the activated immune system. Kinases and phosphatases encompassing the MAPK pathway are key players in the orderly action of pro- and anti-inflammatory processes, forming numerous promiscuous interactions. Several lines of evidence demonstrate that the phosphorylation and activation status of kinases in the MAPK system has crucial impact on the outcome of downstream events that regulate cytokine production. At least 13 members of the family of dual-specificity phosphatases (DUSP) display unique substrate specificities for MAPKs. Despite the considerable amount of information obtained about the contribution of the different DUSP to MAPK-mediated signaling and innate immunity, the interpretation of available data remains problematic. The in vitro and ex vivo findings are often complicated by functional redundancy of signaling molecules and do not always accurately predict the situation in vivo. Until recently, DUSP research has been hampered by the lack of relevant mammalian knockout (KO) models, which is a powerful tool for delineating in vivo function and redundancy in gene families. This situation changed dramatically over the last year, and this review integrates recent insights into the precise biological role of the DUSP family in innate immunity gained from a comprehensive analysis of mammalian KO models.

Toll-like Receptor 9 Triggers an Innate Immune Response to Helper-dependent Adenoviral Vectors

A major obstacle to the clinical application of systemic adenoviral gene replacement therapy is the host innate immune response. Although recent studies have attempted to characterize the cellular basis for this response to systemically administered helper-dependent adenoviral vector (HD-Ad), the underlying molecular components of the innate immune repertoire required to recognize the viral vector have yet to be identified. Here, we show that primary macrophages can sense HD-Ad vectors via the Toll-like Receptor 9 (TLR9) and respond by increasing pro-inflammatory cytokine secretion. Moreover, TLR9 sensing is involved in the rapid innate immune response to HD-Ad in vivo. TLR9 deficiency attenuates the innate immune response to HD-Ad, whereas TLR9 blockade reduces the acute inflammatory response after intravenous injection of the vector. Moreover, HD-Ad upregulates TLR9 gene expression independent of TLR9 function, suggesting that additional innate signaling pathways work cooperatively with TLR9. The identification of the components of the innate immune response to adenovirus will facilitate the development of combinatorial therapy directed at increasing the maximal tolerated dose of systemically delivered adenoviral vectors.

The human IgM antibody SAM-6 induces tumor-specific apoptosis with oxidized low-density lipoprotein

Lipids are essential for normal and malignant cells during growth and differentiation. The turnover is strictly regulated because an uncontrolled uptake and accumulation is cytotoxic and can lead to lipoapoptosis: lipoptosis. The human monoclonal antibody SAM-6 binds to a cell surface receptor on malignant cells and to oxidized low-density lipoprotein (LDL). SAM-6 induces an excess of intracellular lipids, by overfeeding malignant cells with oxidized LDL, via a receptor-mediated endocytosis. The treated cells overaccumulate depots of cholesteryl esters and triglycerides. This lipid overaccumulation is tumor specific; nonmalignant cells neither bind the antibody nor harvest lipids after incubation. Because for both forms of apoptosis, the death domain dependent ("extrinsic") and independent ("intrinsic"), the activation of proteases is crucial, we also investigated this pathway in more detail. It was found that shortly after internalization of antibody/oxidized LDL/receptor complex and formation of lipid depots, cytochrome c is released by mitochondria. Followed by this, initiator caspase-8 and caspase-9 and effector caspase-3 and caspase-6 are activated. The mechanism of mitochondrial trigger (e.g., by free fatty acids) is under investigation. However, the present data indicate that the SAM-6 antibody induces an intrinsic-like form of apoptosis by overfeeding malignant cells with lipoproteins.

Bv8, the amphibian homologue of the mammalian prokineticins, induces a proinflammatory phenotype of mouse macrophages

1.--The small protein Bv8, isolated from the amphibian skin, belongs to a novel family of secreted proteins linked to several biological effects. We describe the expression of Bv8/prokineticins and their receptors in mouse macrophages, and characterize their proinflammatory activities. 2.--The rodent analogue of Bv8, prokineticin-2, is expressed by macrophages, as well as its G-protein-coupled receptor prokineticin receptor (PKR-1 and PKR-2). PKR-1 is expressed more abundantly. 3.-- Bv8 induces potent chemotaxis of macrophages at concentrations as low as 10(-12) M. 4.-- It stimulates lipopolysaccharide-induced production of the proinflammatory cytokines IL-1 and IL-12, reducing that of the anti-inflammatory cytokine IL-10. The effects are observed starting at the very low concentration of 10(-11) M. 5.--Effects on chemotaxis and cytokine are not pertussis-toxin sensitive, but are completely prevented by addition of the phospholipase inhibitor U73122, suggesting a G(q) protein is involved in the Bv8-induced effects. 6.--Studies in PKR-1 knockout mice indicate that all the activities exerted by Bv8 on macrophages are mediated by the PKR-1 receptor. 7.--In conclusion, Bv8 appears to be able to induce the macrophage to migrate and to acquire a proinflammatory phenotype.

Essential role for caspase-8 in Toll-like receptors and NFkappaB signaling

In addition to its pro-apoptotic function in the death receptor pathway, roles for caspase-8 in mediating T-cell proliferation, maintaining lymphocyte homeostasis, and suppressing immunodeficiency have become evident. Humans with a germline point mutation of CASPASE-8 have multiple defects in T cells, B cells, and NK cells, most notably attenuated activation and immunodeficiency. By generating mice with B-cell-specific inactivation of caspase-8 (bcasp8(-/-)), we show that caspase-8 is dispensable for B-cell development, but its loss in B cells results in attenuated antibody production upon in vivo viral infection. We also report an important role for caspase-8 in maintaining B-cell survival following stimulation of the Toll-like receptor (TLR)2, -3, and -4. In response to TLR4 stimulation, caspase-8 is recruited to a complex containing IKKalphabeta, and its loss resulted in delayed NFkappaB nuclear translocation and impaired NFkappaB transcriptional activity. Our study supports dual roles for caspase-8 in apoptotic and nonapoptotic functions and demonstrates its requirement for TLR signaling and in the regulation of NFkappaB function.

The solution structure of horseshoe crab antimicrobial peptide tachystatin B with an inhibitory cystine-knot motif

Tachystatin B is an antimicrobial and a chitin-binding peptide isolated from the Japanese horseshoe crab (Tachypleus tridentatus) consisting of two isopeptides called tachystatin B1 and B2. We have determined their solution structures using NMR experiments and distance geometry calculations. The 20 best converged structures of tachystatin B1 and B2 exhibited root mean square deviations of 0.46 and 0.49 A, respectively, for the backbone atoms in Cys(4)-Arg(40). Both structures have identical conformations, and they contain a short antiparallel beta-sheet with an inhibitory cystine-knot (ICK) motif that is distributed widely in the antagonists for voltage-gated ion channels, although tachystatin B does not have neurotoxic activity. The structural homology search provided several peptides with structures similar to that of tachystatin B. However, most of them have the advanced functions such as insecticidal activity, suggesting that tachystatin B may be a kind of ancestor of antimicrobial peptide in the molecular evolutionary history. Tachystatin B also displays a significant structural similarity to tachystatin A, which is member of the tachystatin family. The structural comparison of both tachystatins indicated that Tyr(14) and Arg(17) in the long loop between the first and second strands might be the essential residues for binding to chitin.

Update on toll-like receptor ligands and allergy: implications for immunotherapy

Innate responses to microbes are mediated in large part via toll-like receptors (TLRs) that recognize a diverse family of ligands produced by viruses, bacteria, and fungi. Great effort has been directed toward translating this knowledge into the development of therapies for the prevention and treatment of diseases, including those fueled by allergic (Th2-biased) hypersensitivities. In this review, we consider the ways in which ligands for different TLRs influence the allergic phenotype. In addition, an update on safety and efficacy data from clinical trials of allergic patients treated with TLR9 ligand-based interventions is provided. Finally, recent experimental results that help elucidate how ambient TLR ligand exposures influence allergic risk and their relevance to the development of TLR ligand-based therapeutics are discussed. Investigations presented within this opinion paper suggest that several TLR ligands could have clinical utility in the treatment of allergic diseases, whereas other TLR ligands appear less attractive, as they facilitate development of Th2-biased hypersensitivities in murine studies.

Association of CD14 promoter polymorphism with otitis media and pneumococcal vaccine responses

Innate immunity is of particular importance for protection against infection during early life, when adaptive immune responses are immature. CD14 plays key roles in innate immunity, including in defense against pathogens associated with otitis media, a major pediatric health care issue. The T allele of the CD14 C-159T polymorphism has been associated with increased serum CD14 levels. Our objective was to investigate the hypothesis that the CD14 C-159T allele is protective against recurrent acute otitis media in children. The association between the CD14 promoter genotype and the number of acute otitis media episodes was evaluated both retrospectively and prospectively in a cohort of 300 children. Serotype-specific immunoglobulin G (IgG) antibody responses after pneumococcal vaccinations were examined according to CD14 genotype to compare immune responsiveness across genotypes. An age-dependent association was found: compared with that for CC homozygotes aged between 12 to 24 months, TT homozygotes had fewer episodes of acute otitis media (79 versus 41%, respectively; P = 0.004); this relationship was absent in older children. Additionally, TT homozygotes showed higher serotype-specific anti-pneumococcal IgG antibody levels. Our data suggest that genetic variation in CD14, a molecule at the interface of innate and adaptive immune responses, plays a key role in the defense against middle ear disease in childhood and in pneumococcal vaccine responsiveness. These findings are likely to be important to these and other immune-mediated outcomes in early life.

HIV-1 infection of mononuclear phagocytic cells: the case for bacterial innate immune deficiency in AIDS

HIV-1 infection of mononuclear phagocytic cells, comprising monocytes, macrophages, and dendritic cells, has been the subject of extensive research over the past 20 years. The roles of mononuclear phagocytic cells in transmission of HIV-1 infection and as reservoirs of actively replicating virus have received particular attention. Experimental data have also accumulated about the effects of HIV-1 on the physiological function of mononuclear phagocytic cells, particularly their role in innate immunity to bacteria. The effects of HIV-1 on bacterial innate immune responses by mononuclear phagocytic cells are discussed here together with reports of direct interactions between HIV-encoded products and bacterial innate immune signalling pathways. These reports demonstrate mechanisms for HIV-mediated disruption of innate immune responses by mononuclear phagocytic cells that could provide novel therapeutic targets in HIV-infected patients. The clinical urgency is highlighted by greatly increased risk of invasive bacterial disease in this population, even in the era of highly active antiretroviral therapy. HIV-mediated injury to bacterial innate immunity provides an experimental paradigm that could broaden our overall understanding of innate immunity and be used to study responses to pathogens other than bacteria.