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Protection of mice from LPS-induced shock by CD14 antisense oligonucleotide.

CD14 is a pattern recognition receptor on myeloid cells and plays a pivotal role in an innate immune system that is responsible for Gram-negative and Gram-positive bacteria infection. Lipopolysaccharide (LPS), a cell wall component of Gram-negative bacteria, can induce production of a large quantity of proinflammatory cytokines into the circulation mediated by CD14-mediated macrophages and monocytes. These cytokines eventually cause septic shock. Several in vitro and in vivo studies have shown that suppression of a CD14 function by a CD14 antibody led to an inhibition of the production of proinflammatory cytokines such as TNF-alpha, IL-1 beta, and IL-8. In the present study, we found that CD14 antisense oligonucleotide (ODN) can prevent lethal LPS shock in D-galactosamine-sensitized mice. This ODN inhibited CD14 expression in a mouse macrophage cell line, RAW264.7, and suppressed production of TNF-alpha in LPS-stimulated RAW264.7 cells. Furthermore, we designed a consensus antisense ODN that could hybridize human and mouse CD14 RNA, and we evaluated its efficacy. The consensus antisense ODN rescued mice primed with Mycobacterium bovis bacillus Calmette-Guerin (BCG) from the LPS-induced lethal shock. In this model, the CD14 antisense ODN down-regulated LPS-elicited CD14 expression in the liver, resulting in a decrease in LPS-induced TNF-alpha production. These findings suggest that the CD14 antisense ODN is distributed in the liver and efficiently suppresses LPS-induced TNF-alpha production by reducing CD14 expression on Kupffer cells. This CD14 antisense ODN may be useful for the development of a therapeutic agent against sepsis and septic shock.

Animals↗

Pulmonary surfactant proteins A and D: innate immune functions and biomarkers for lung diseases.

Pulmonary surfactant, a complex of lipids and proteins, functions to keep alveoli from collapsing at expiration. Surfactant proteins A (SP-A) and D (SP-D) belong to the collectin family and play pivotal roles in the innate immunity of the lung. Pulmonary collectins directly bind with broad specificities to a variety of microorganism and possess anti-microbial effects. These proteins also exhibit both inflammatory and anti-inflammatory functions, which occur through interactions with pattern recognition receptors including Toll-like receptor and CD14, signal inhibitory regulatory protein alpha and a receptor complex of calreticulin and CD91. The collectins enhance phagocytosis of microbes by macrophages through opsonic and/or non-opsonic activities. The proteins stimulate cell surface expression of phagocytic receptors including scavenger receptor A and mannose receptor. Since the expression of SP-A and SP-D is abundant and restricted within the lung, the proteins are now clinically used as biomarkers for lung diseases. The levels of SP-A and SP-D in bronchoalveolar lavage fluids, amniotic fluids, tracheal aspirates and pleural effusions reflect alterations in alveolar compartments and epithelium, and lung maturity. The determination of SP-A and SP-D in sera is a non-invasive and useful tool for understanding some pathological changes of the lung in the diseases, including pulmonary fibrosis, collagen vascular diseases complicated with interstitial lung disease, pulmonary alveolar proteinosis, acute respiratory distress syndrome and radiation pneumonitis.

Animals↗

Innate immunity in lophotrochozoans: the annelids.

Innate immunity plays a major role as a first defense against microbes. Effectors of the innate response include pattern recognition receptors (PRR), phagocytic cells, proteolytic cascades and peptides/proteins with antimicrobial properties. Each element of these events has been well studied in vertebrates and in some invertebrates such as annelids. From these different researches, it appears that mammalian innate immunity could be considered as a mosaic of invertebrate immune responses. Annelids belonging to the lophotrochozoans' group are primitive coelomates that possess specially developed cellular immunity against pathogens including phagocytosis, encapsulation and spontaneous cytotoxicity of coelomocytes against allogenic or xenogenic cells. They have also developed an important humoral immunity that is based on antimicrobial, hemolytic and clotting properties of their body fluid. In the present review, we will emphasize the different immunodefense strategies that adaptation has taken during the course of evolution of two classes of annelids i.e. oligochaetes and achaetes.

Animals↗

Effect of CD14 blockade in rabbits with Escherichia coli pneumonia and sepsis.

CD14, a pattern recognition receptor found on myeloid cells, is a critical component of the innate immune system that mediates local and systemic host responses to Gram-negative and Gram-positive bacterial products. Previous studies in normal animals have tested the effect of CD14 blockade on the systemic response to i.v. LPS. The goals of the study were to determine whether CD14 blockade protected against the deleterious systemic response associated with Escherichia coli pneumonia and to determine whether this strategy affected the pulmonary response to tissue infection. Rabbits were pretreated with either anti-CD14 mAb or isotype control mAb at 2.5 mg/kg. E. coli (1 x 109 CFU) was inoculated into the lungs, and the animals were observed for either 4 or 24 h. The blockade of CD14 improved the mean arterial blood pressure (p = 0.001) and decreased the i.v. fluid requirements (p = 0.01). Although this therapy protected the vascular compartment, rabbits treated with anti-CD14 mAb had increased bacterial burdens in the bronchoalveolar lavage fluid recovered from the instilled lung (p = 0.005) and widened alveolar-arterial oxygen difference. Blockade of CD14 prevents the deleterious systemic responses that occur in sepsis; however, other measures are necessary to control bacterial proliferation at the primary site of infection.

Animals↗

A common single nucleotide polymorphism in the CD14 promoter decreases the affinity of Sp protein binding and enhances transcriptional activity.

CD14 is a pattern recognition receptor that plays a central role in innate immunity through recognition of bacterial lipoglycans, primarily LPS. Recently, our group has identified a common single nucleotide polymorphism, -159C-->T, in the CD14 proximal promoter. Homozygous carriers of the T allele have a significant increase in soluble CD14, but a decreased total serum IgE. This epidemiologic evidence led us to investigate the molecular basis for the effects of CD14/-159C-->T on CD14 regulation in monocytes and hepatocytes, the two major cell types known to express this gene in vivo. EMSA analysis showed that the T allele results in decreased affinity of DNA/protein interactions at a GC box that contains a binding site for Sp1, Sp2, and Sp3 transcription factors. In reporter assays, the transcriptional activity of the T allele was increased in monocytic Mono Mac 6 cells, which express low levels of Sp3, a member of the Sp family with inhibitory potential relative to activating Sp1 and Sp2. By contrast, both alleles were transcribed equivalently in Sp3-rich hepatocytic HepG2 cells. Our data indicate that the interplay between CD14 promoter affinity and the [Sp3]:[Sp1 + Sp2] ratio plays a critical mechanistic role in regulating transcription of the two CD14 alleles. Variation in a key gene of innate immunity may be important for the pathogenesis of allergy and inflammatory disease through gene-by-gene and/or gene-by-environment interactions.

Base Sequence↗

Peptidoglycan molecular requirements allowing detection by the Drosophila immune deficiency pathway.

Innate immune recognition of microbes is a complex process that can be influenced by both the host and the microbe. Drosophila uses two distinct immune signaling pathways, the Toll and immune deficiency (Imd) pathways, to respond to different classes of microbes. The Toll pathway is predominantly activated by Gram-positive bacteria and fungi, while the Imd pathway is primarily activated by Gram-negative bacteria. Recent work has suggested that this differential activation is achieved through peptidoglycan recognition protein (PGRP)-mediated recognition of specific forms of peptidoglycan (PG). In this study, we have further analyzed the specific PG molecular requirements for Imd activation through the pattern recognition receptor PGRP-LC in both cultured cell line and in flies. We found that two signatures of Gram-negative PG, the presence of diaminopimelic acid in the peptide bridge and a 1,6-anhydro form of N-acetylmuramic acid in the glycan chain, allow discrimination between Gram-negative and Gram-positive bacteria. Our results also point to a role for PG oligomerization in Imd activation, and we demonstrate that elements of both the sugar backbone and the peptide bridge of PG are required for optimum recognition. Altogether, these results indicate multiple requirements for efficient PG-mediated activation of the Imd pathway and demonstrate that PG is a complex immune elicitor.

Animals↗

Essential role of MD-2 in TLR4-dependent signaling during Helicobacter pylori-associated gastritis.

TLR4, a member of pattern recognition receptors, is the main receptor of LPS. MD-2 physically associates with TLR4 on the cell surface and confers LPS responsiveness. Helicobacter pylori LPS is one of the major virulence factors for induction of gastritis. We demonstrated in this study the role of MD-2 in TLR4-dependent signaling in H. pylori-associated gastritis. Gastric biopsy samples collected from patients with and without H. pylori infection and four gastric cancer cell lines were used for this study. TLR-4 and MD-2 expression in biopsy specimens and the cell lines was examined by using RT-PCR. Localization of TLR-4 in histological sections was evaluated by immunohistochemistry. For in vitro functional assays, we established stable transfectants of AGS cells expressing TLR4 and MD-2. Cellular distribution of TLR4 was examined by flow cytometry. NF-kappaB activation and activation of IL-8 and MD-2 promoters were assessed by reporter gene assay. H. pylori infection up-regulated the TLR4 and MD-2 expression in gastric mucosa. TLR4 staining was observed predominantly in epithelial cells, located in both the cytoplasm and at the apical surface. MD-2 transfection in AGS cells markedly increased cell surface expression of TLR4 and augmented the activation of NF-kappaB and IL-8 promoter upon stimulation with H. pylori LPS. Live H. pylori also stimulated transcriptional activation of MD-2. This study revealed that MD-2 expression is elevated in gastric epithelial cells during H. pylori infection, suggesting that the TLR4/MD-2 system is a potent receptor complex involved in the response to H. pylori LPS in the stomach.

Adult↗

CpG DNA induces IgG class switch DNA recombination by activating human B cells through an innate pathway that requires TLR9 and cooperates with IL-10.

TLRs are pattern recognition receptors that initiate innate immune responses. TLR9 detects microbial DNA with hypomethylated CpG motifs and in humans is preferentially expressed by IFN-alpha-producing plasmacytoid dendritic cells and B cells. In addition to favoring IFN-alpha release, TLR9 signals B cell activation, proliferation, and IgM production. Recent findings suggest that CpG DNA-TLR9 interaction plays a key role in systemic lupus erythematosus and rheumatoid arthritis, two autoimmune disorders characterized by dysregulated production of DNA-reactive IgG. We show that CpG DNA initiates germline C(gamma)1, C(gamma)2, and C(gamma)3 gene transcription by activating B cells through a TLR9-mediated NF-kappaB-Rel-dependent innate pathway that cooperates with IL-10 through STAT proteins and IFN-responsive factors. This pathway is inhibited by chloroquine, a drug that attenuates the clinical manifestations of IgG-mediated autoimmune disorders. Germline C(gamma) gene transcription is associated with up-regulation of activation-induced cytidine deaminase, a key element of the B cell class switch-inducing machinery, and is followed by class switch DNA recombination from C(micro) to C(gamma)1, C(gamma)2, and C(gamma)3. Subsequent IgG production requires additional signals from BCR and a B cell-activating factor of the TNF family (BAFF), produced by dendritic cells upon exposure to IFN-alpha. Our findings suggest that CpG DNA-TLR9 interaction may be important to initiate or amplify early T cell-independent IgG responses against pathogens. This implies that CpG DNA released during infections may exacerbate autoimmunity by stimulating autoreactive B cells to switch from an IgM to a more pathogenic IgG isotype.

Adaptor Proteins, Signal Transducing↗

Expression of functional TLR4 confers proinflammatory responsiveness to Trypanosoma cruzi glycoinositolphospholipids and higher resistance to infection with T. cruzi.

TLRs function as pattern recognition receptors in mammals and play an essential role in the recognition of microbial components. We found that the injection of glycoinositolphospholipids (GIPLs) from Trypanosoma cruzi into the peritoneal cavity of mice induced neutrophil recruitment in a TLR4-dependent manner: the injection of GIPL in the TLR4-deficient strain of mice (C57BL/10ScCr) caused no inflammatory response. In contrast, in TLR2 knockout mice, neutrophil chemoattraction did not differ significantly from that seen in wild-type controls. GIPL-induced neutrophil attraction and MIP-2 production were also severely affected in TLR4-mutant C3H/HeJ mice. The role of TLR4 was confirmed in vitro by testing genetically engineered mutants derived from TLR2-deficient Chinese hamster ovary (CHO)-K1 fibroblasts that were transfected with CD14 (CHO/CD14). Wild-type CHO/CD14 cells express the hamster TLR4 molecule and the mutant line, in addition, expresses a nonfunctional form of MD-2. In comparison to wild-type cells, mutant CHO/CD14 cells failed to respond to GIPLs, indicating a necessity for a functional TLR4/MD-2 complex in GIPL-induced NF-kappaB activation. Finally, we found that TLR4-mutant mice were hypersusceptible to T. cruzi infection, as evidenced by a higher parasitemia and earlier mortality. These results demonstrate that natural resistance to T. cruzi is TLR4 dependent, most likely due to TLR4 recognition of their GIPLs.

Animals↗

The mucosal adjuvant macrophage-activating lipopeptide-2 directly stimulates B lymphocytes via the TLR2 without the need of accessory cells.

The macrophage-activating lipopeptide-2 (MALP-2) is an agonist of the TLR heterodimer 2/6, which exhibits potent activity as mucosal adjuvant, promoting strong humoral and cellular responses. Although B cells expressing TLR2/6 are potential targets, very little is known about the effect of MALP-2 on B cells. Studies were performed using total spleen cells or purified B cells from WT mice or animals deficient in TLR2, T cells, B cells, or specific subpopulations of B cells. They demonstrated that MALP-2 promotes a T cell-independent activation and maturation of B cells (mainly follicular but also B-1a and marginal zone B cells) via TLR2. MALP-2 also increased the frequency of IgM- and IgG-secreting cells, but bystander cells were required for IgA secretion. Activated B cells exhibited increased expression of activation markers and ligands that are critical for cross-talk with T cells (CD19, CD25, CD80, CD86, MHC I, MHC II, and CD40). Immunization of mice lacking T cells showed that MALP-2-mediated stimulation of TLR2/6 was unable to circumvent the need of T cell help for efficient Ag-specific B cell activation. Immunization of mice lacking B cells demonstrated that B cells are critical for MALP-2-dependent improvement of T cell responses. The knowledge emerging from this work suggests that MALP-2-mediated activation of B cells through TLR2/6 is critical for adjuvanticity. B cell stimulation by pattern recognition receptors seems to be a basic mechanism that can be exploited to improve the immunogenicity of vaccine formulations.

Adjuvants, Immunologic↗

Transcriptional profiling reveals complex regulation of the monocyte IL-1 beta system by IL-13.

IL-4 and IL-13 are prototypic Th2 cytokines that generate an "alternatively activated" phenotype in macrophages. We used high-density oligonucleotide microarrays to investigate the transcriptional profile induced in human monocytes by IL-13. After 8-h stimulation with IL-13, 142 genes were regulated (85 increased and 57 decreased). The majority of these genes were related to the inflammatory response and innate immunity; a group of genes related to lipid metabolism was also identified, with clear implications for atherosclerosis. In addition to characteristic markers of alternatively activated macrophages, a number of novel IL-13-regulated genes were seen. These included various pattern recognition receptors, such as CD1b/c/e, TLR1, and C-type lectin superfamily member 6. Several components of the IL-1 system were regulated. IL-1RI, IL-1RII, and IL-1Ra were all up-regulated, whereas the IL-1beta-converting enzyme, caspase 1, and IRAK-M were down-regulated. LPS-inducible caspase 1 enzyme activity was also reduced in IL-13-stimulated monocytes, with a consequent decrease in pro-IL-1beta processing. These data reveal that IL-13 has a potent effect on the transcriptional profile in monocytes. The IL-13-induced modulation of genes related to IL-1 clearly highlights the tightly controlled and complex levels of regulation of the production and response to this potent proinflammatory cytokine.

Caspase 1↗

TLR signaling in the gut in health and disease.

The human intestine has evolved in the presence of diverse enteric microflora. TLRs convert the recognition of pathogen-associated molecules in the gut into signals for anti-microbial peptide expression, barrier fortification, and proliferation of epithelial cells. Healing of injured intestinal epithelium and clearance of intramucosal bacteria require the presence of intact TLR signaling. Nucleotide oligomerization domain (Nod)1 and Nod2 are additional pattern recognition receptors that are required for defense against invasive enteric pathogens. Through spatial and functional localization of TLR and Nod molecules, the normal gut maintains a state of controlled inflammation. By contrast, patients with inflammatory bowel disease demonstrate inflammation in response to the normal flora. A subset of these patients carry polymorphisms in TLR and CARD15/NOD2 genes. A better understanding of the delicate regulation of TLR and Nod molecules in the gut may lead to improved treatment for enteric infections and idiopathic inflammatory bowel diseases.

Adaptor Proteins, Signal Transducing↗

The complex mechanism of antibody-mediated clearance of Bordetella from the lungs requires TLR4.

Although the antibacterial effects of Abs are well studied in in vitro systems, the in vivo effects of Abs cannot always be accurately predicted. Complicated cross-talk between different effector functions of Abs and various arms of the immune system can affect their activities in vivo. Using the mouse respiratory pathogen Bordetella bronchiseptica, we examined the mechanisms of Ab-mediated clearance of bacteria from the respiratory tract. Interestingly, although TLR4 was not necessary for protective immunity following infection, it was required for rapid bacterial clearance in mice that were vaccinated or adoptively transferred Abs. TLR4 was important for the rapid recruitment of neutrophils that are necessary for Ab-mediated bacterial clearance via a mechanism that requires both FcgammaR and CR3. These data are consistent with a model in which TLR4-mediated inflammatory responses aid in the recruitment of neutrophils, which phagocytose Ab- and complement-opsonized bacteria via FcgammaRs and CR3. Although pattern recognition receptors are known to be involved in innate immunity and the generation of adaptive immunity, their contributions to specific adaptive immune functions should be considered in ongoing efforts to improve vaccine-induced protective immunity.

Adoptive Transfer↗

TNFalpha-induced long pentraxin PTX3 expression in human lung epithelial cells via JNK.

Long pentraxin 3 (PTX3), an acute-phase protein, is a newly clarified mediator for innate immunity and inflammation. As a soluble pattern recognition receptor, it has a nonredundant role in antifungal infection. Overexpression of PTX3 worsens acute lung injury. The lung epithelium is a critical factor in defense against pulmonary pathogens; it is also involved in acute inflammatory responses related to tissue injury. However, very little is known about how PTX3 is regulated in the lung epithelium. In this study, we found that i.v. injection of LPS induced PTX3 expression in rat lung alveolar epithelium. Using human lung cell lines and primary epithelial cells, we found that PTX3 expression was significantly up-regulated by TNF-alpha in a time- and dose-dependent manner, but not by LPS. Pretreatment with either actinomycin D or cycloheximide abolished TNF-alpha-induced PTX3 expression, indicating the requirement for both transcriptional and translational regulation. The TNF-alpha-induced PTX3 expression was blocked by SP600125, a JNK-specific inhibitor, but not by the inhibitors against NF-kappaB, ERKs, or p38 MAPK. Knockdown of either JNK1 or JNK2 with small interfering RNA also significantly reduced the regulated PTX3 expression. Thus, lung epithelial cells appear to be a major local source for PTX3 production, which could be induced in vivo from these cells by LPS or other inflammatory stimuli, and may be an important mediator for host defense and tissue damage. The importance of the JNK pathway for the regulated PTX3 expression may be a potential target for its regulation in the lung.

Animals↗

Identification of a macrophage-specific chromatin signature in the IL-10 locus.

The molecular mechanisms that regulate expression of the immunosuppressive cytokine IL-10 remain poorly understood. In this study, by measuring sensitivity to DNase I digestion, we show that production of IL-10 by primary mouse bone marrow-derived macrophages stimulated through pattern recognition receptors was associated with chromatin remodeling of the IL-10 locus. We also demonstrate that the IL-10 locus is remodeled in primary Th2 cells and IL-10-producing regulatory T cells that have been differentiated in vitro. Strikingly, a novel DNase I-hypersensitive site (HSS-4.5) was identified in stimulated macrophages, but not in T cells. We show that hyperacetylated histones were recruited to this site in stimulated macrophages. Furthermore, HSS-4.5 is highly conserved and contains a putative NF-kappaB binding site. In support of a function for this site, NF-kappaB p65/RelA was recruited to HSS-4.5 in vivo and its activation was required for optimal IL-10 gene expression in LPS-stimulated macrophages.

Animals↗

Gene family clustering identifies functionally associated subsets of human in vivo blood and tonsillar dendritic cells.

Human dendritic cells (DCs) are a distinct but heterogeneous lineage of APCs operating as the link between innate and adaptive immune responses, with the function to either maintain tolerance or trigger immunity. The DC lineage consists of several subpopulations with unique phenotypes; however, their functional characteristics and transcriptional similarities remain largely unknown. To further characterize the phenotypes and transcriptomes of the subsets, we purified myeloid CD16(+), blood DC Ag 1(+) (BDCA1(+)), and BDCA3(+) DC populations, as well as plasmacytoid CD123(+) DCs, from tonsillar tissue and peripheral blood. Transcriptional profiling and hierarchical clustering visualized that BDCA1(+) DCs clustered with BDCA3(+) DCs, whereas CD16(+) DCs and CD123(+) DCs clustered as distinct populations in blood. Differential expression levels of chemokines, ILs, and pattern recognition receptors were demonstrated, which emphasize innate DC subset specialization. Even though highly BDCA1(+) and BDCA3(+) DC-specific gene expression was identified in blood, the BDCA1(+) DCs and BDCA3(+) DCs from tonsils displayed similar transcriptional activity, most likely due to the pathogenic or inflammatory maturational signals present in tonsillar tissues. Of note, plasmacytoid DCs displayed less plasticity in their transcriptional activity compared with myeloid DCs. The data demonstrated a functionally distinct association of each of the seven subsets based on their signatures, involving regulatory genes in adaptive and innate immunity.

Antigens, CD↗

Increased expression of TLR3 in lymph nodes during simian immunodeficiency virus infection: implications for inflammation and immunodeficiency.

As pattern recognition receptors, TLRs signal and induce expression of multiple host defense genes including proinflammatory cytokines and chemokines. To investigate the mechanisms of up-regulation of proinflammatory cytokines and chemokines during SIV infection in rhesus macaques, we measured the relative levels of expression of TLRs 1-10 in lymphoid tissues during different stages of SIV infection. By real-time RT-PCR, TLR3 was determined to be up-regulated in macaque lymph nodes (LN) throughout the course of infection, whereas TLR9 was down-regulated during early stages of infection. CXCL9/Mig, CXCL10/IP-10, IFN-gamma, and IFN-alpha mRNAs were also increased during acute SIV infection and AIDS. Treatment of macaque spleen and LN cells with TLR3 and TLR9 ligands led to the induction of these same genes. TLR3 stimulation had disparate effects on viral transcription and viral replication, because poly(I:C), a model TLR3 ligand, stimulated the viral promoter but potently inhibited SIV replication in primary cultures of macaque spleen and LN cells. These findings identify roles for TLR3 inflammation in lymphoid tissues and in the immunopathogenesis of HIV-1/SIV, and suggest that TLR3 ligands could potentially be used to flush out latently infected cells that persist during antiretroviral therapies.

Animals↗

The envelope protein of a human endogenous retrovirus-W family activates innate immunity through CD14/TLR4 and promotes Th1-like responses.

Multiple sclerosis-associated retroviral element (MSRV) is a retroviral element, the sequence of which served to define the W family of human endogenous retroviruses. MSRV viral particles display proinflammatory activities both in vitro in human mononuclear cell cultures and in vivo in a humanized SCID mice model. To understand the molecular basis of such properties, we have investigated the inflammatory potential of the surface unit of the MSRV envelope protein (ENV-SU), the fraction that is poised to naturally interact with host cells. We report in this study that MSRV ENV-SU induces, in a specific manner, human monocytes to produce major proinflammatory cytokines through engagement of CD14 and TLR4, which are pattern recognition receptors of primary importance in innate immunity. ENV-SU could also trigger a maturation process in human dendritic cells. Finally, ENV-SU endowed dendritic cells with the capacity to support a Th1-like type of Th cell differentiation. The data are discussed in the context of immune responses and chronic proinflammatory disorders.

Amino Acid Sequence↗