Pneumolysin-dependent and -independent gene expression identified by cDNA microarray analysis of THP-1 human mononuclear cells stimulated by Streptococcus pneumoniae

The Role of Macrophage Phenotype in the Vascularization of Prevascularized Human Bone Marrow Mesenchymal Stem Cell Sheets

With the development of tissue engineering and regenerative medicine, prevascularized bone marrow mesenchymal stem cell (BMSC) sheets have been regarded as a promising method for tissue regeneration. Furthermore, the inflammatory response is one of the main regulators of vascularization and the restoration of engineered tissue function; among them, macrophages and cytokines produced by them are considered to be the decisive factors of the downstream outcomes. This study investigated the effect of macrophages on the formation of microvascular-like structures of human umbilical vein endothelial cells (HUVECs) in BMSC sheets. First, a human monocytic leukemia cell line (THP-1 cells) was differentiated into derived macrophages (M0) with phorbol 12-myristate 13-acetate and further activated into proinflammatory macrophages (M1 macrophages) with interferon-γ and lipopolysaccharide or anti-inflammatory macrophages (M2 macrophages) with interleukin-4. Then, HUVECs and prevascularized sheets were treated with conditioned media (CM) from different macrophages, and the impact of macrophage phenotypes on vascularized network formation in prevascularized cell sheets was examined by hematoxylin and eosin staining, CD31 immunofluorescence staining and enzyme-linked immunosorbent assay. Our study showed that macrophages may guide the arrangement of endothelial cells through a paracrine pathway. Cell sheets that were cultured in the CM from M2 macrophages were thinner than those cultured in other media. At various time points, the levels of tumor necrosis factor alpha and vascular endothelial growth factor in prevascularized sheets cultured with CM(M1) was higher than that in sheets cultured with other media; however, the levels of platelet-derived growth factor in prevascularized sheets cultured with CM(M2) was higher than that in sheets cultured with other media. These findings suggest that the paracrine effect of macrophages can influence the formation of microvascular networks in prevascularized sheets by regulating the arrangement of cells, the thickness of the cell sheet and the secretion of cytokines related to angiogenesis. Macrophages with different phenotypes have unique effects on prevascularized sheets.

CAR-cell therapy in the era of solid tumor treatment: current challenges and emerging therapeutic advances

In the last decade, Chimeric Antigen Receptor (CAR)-T cell therapy has emerged as a promising immunotherapeutic approach to fight cancers. This approach consists of genetically engineered immune cells expressing a surface receptor, called CAR, that specifically targets antigens expressed on the surface of tumor cells. In hematological malignancies like leukemias, myeloma, and non-Hodgkin B-cell lymphomas, adoptive CAR-T cell therapy has shown efficacy in treating chemotherapy refractory patients. However, the value of this therapy remains inconclusive in the context of solid tumors and is restrained by several obstacles including limited tumor trafficking and infiltration, the presence of an immunosuppressive tumor microenvironment, as well as adverse events associated with such therapy. Recently, CAR-Natural Killer (CAR-NK) and CAR-macrophages (CAR-M) were introduced as a complement/alternative to CAR-T cell therapy for solid tumors. CAR-NK cells could be a favorable substitute for CAR-T cells since they do not require HLA compatibility and have limited toxicity. Additionally, CAR-NK cells might be generated in large scale from several sources which would suggest them as promising off-the-shelf product. CAR-M immunotherapy with its capabilities of phagocytosis, tumor-antigen presentation, and broad tumor infiltration, is currently being investigated. Here, we discuss the emerging role of CAR-T, CAR-NK, and CAR-M cells in solid tumors. We also highlight the advantages and drawbacks of CAR-NK and CAR-M cells compared to CAR-T cells. Finally, we suggest prospective solutions such as potential combination therapies to enhance the efficacy of CAR-cells immunotherapy.

Induced CAR-Macrophages as a Novel Therapeutic Cell Type for Cancer Immune Cell Therapies

The Chimeric antigen receptor (CAR)-T cell therapy has made inroads in treating hematological malignancies. Nonetheless, there are still multiple hurdles in CAR-T cell therapy for solid tumors. Primary CAR-expressing macrophage cells (CAR-Ms) and induced pluripotent stem cells (iPSCs)-derived CAR-expressing macrophage cells (CAR-iMacs) have emerged as attractive alternatives in our quest for an efficient and inexpensive approach for tumor immune cell therapy. In this review, we list the current state of development of human CAR-macrophages and provide an overview of the crucial functions of human CAR-macrophages in the field of tumor immune cell therapy.

The Yin and Yang of Pneumolysin During Pneumococcal Infection

Pneumolysin (PLY) is a pore-forming toxin produced by the human pathobiont Streptococcus pneumoniae, the major cause of pneumonia worldwide. PLY, a key pneumococcal virulence factor, can form transmembrane pores in host cells, disrupting plasma membrane integrity and deregulating cellular homeostasis. At lytic concentrations, PLY causes cell death. At sub-lytic concentrations, PLY triggers host cell survival pathways that cooperate to reseal the damaged plasma membrane and restore cell homeostasis. While PLY is generally considered a pivotal factor promoting S. pneumoniae colonization and survival, it is also a powerful trigger of the innate and adaptive host immune response against bacterial infection. The dichotomy of PLY as both a key bacterial virulence factor and a trigger for host immune modulation allows the toxin to display both "Yin" and "Yang" properties during infection, promoting disease by membrane perforation and activating inflammatory pathways, while also mitigating damage by triggering host cell repair and initiating anti-inflammatory responses. Due to its cytolytic activity and diverse immunomodulatory properties, PLY is integral to every stage of S. pneumoniae pathogenesis and may tip the balance towards either the pathogen or the host depending on the context of infection.

Clinical factors associated with composition of lung microbiota and important taxa predicting clinical prognosis in patients with severe community-acquired pneumonia

Few studies have described the key features and prognostic roles of lung microbiota in patients with severe community-acquired pneumonia (SCAP). We prospectively enrolled consecutive SCAP patients admitted to ICU. Bronchoscopy was performed at bedside within 48 h of ICU admission, and 16S rRNA gene sequencing was applied to the collected bronchoalveolar lavage fluid. The primary outcome was clinical improvements defined as a decrease of 2 categories and above on a 7-category ordinal scale within 14 days following bronchoscopy. Sixty-seven patients were included. Multivariable permutational multivariate analysis of variance found that positive bacteria lab test results had the strongest independent association with lung microbiota (R² = 0.033; P = 0.018), followed by acute kidney injury (AKI; R² = 0.032; P = 0.011) and plasma MIP-1β level (R² = 0.027; P = 0.044). Random forest identified that the families Prevotellaceae, Moraxellaceae, and Staphylococcaceae were the biomarkers related to the positive bacteria lab test results. Multivariable Cox regression showed that the increase in α-diversity and the abundance of the families Prevotellaceae and Actinomycetaceae were associated with clinical improvements. The positive bacteria lab test results, AKI, and plasma MIP-1β level were associated with patients’ lung microbiota composition on ICU admission. The families Prevotellaceae and Actinomycetaceae on admission predicted clinical improvements.

Pneumolysin Is Responsible for Differential Gene Expression and Modifications in the Epigenetic Landscape of Primary Monocyte Derived Macrophages

Epigenetic modifications regulate gene expression in the host response to a diverse range of pathogens. The extent and consequences of epigenetic modification during macrophage responses to Streptococcus pneumoniae, and the role of pneumolysin, a key Streptococcus pneumoniae virulence factor, in influencing these responses, are currently unknown. To investigate this, we infected human monocyte derived macrophages (MDMs) with Streptococcus pneumoniae and addressed whether pneumolysin altered the epigenetic landscape and the associated acute macrophage transcriptional response using a combined transcriptomic and proteomic approach. Transcriptomic analysis identified 503 genes that were differentially expressed in a pneumolysin-dependent manner in these samples. Pathway analysis highlighted the involvement of transcriptional responses to core innate responses to pneumococci including modules associated with metabolic pathways activated in response to infection, oxidative stress responses and NFκB, NOD-like receptor and TNF signalling pathways. Quantitative proteomic analysis confirmed pneumolysin-regulated protein expression, early after bacterial challenge, in representative transcriptional modules associated with innate immune responses. In parallel, quantitative mass spectrometry identified global changes in the relative abundance of histone post translational modifications (PTMs) upon pneumococcal challenge. We identified an increase in the relative abundance of H3K4me1, H4K16ac and a decrease in H3K9me2 and H3K79me2 in a PLY-dependent fashion. We confirmed that pneumolysin blunted early transcriptional responses involving TNF-α and IL-6 expression. Vorinostat, a histone deacetylase inhibitor, similarly downregulated TNF-α production, reprising the pattern observed with pneumolysin. In conclusion, widespread changes in the macrophage transcriptional response are regulated by pneumolysin and are associated with global changes in histone PTMs. Modulating histone PTMs can reverse pneumolysin-associated transcriptional changes influencing innate immune responses, suggesting that epigenetic modification by pneumolysin plays a role in dampening the innate responses to pneumococci.

Pneumolysin: Pathogenesis and Therapeutic Target

Streptococcus pneumoniae is an opportunistic pathogen responsible for widespread illness and is a major global health issue for children, the elderly, and the immunocompromised population. Pneumolysin (PLY) is a cholesterol-dependent cytolysin (CDC) and key pneumococcal virulence factor involved in all phases of pneumococcal disease, including transmission, colonization, and infection. In this review we cover the biology and cytolytic function of PLY, its contribution to S. pneumoniae pathogenesis, and its known interactions and effects on the host with regard to tissue damage and immune response. Additionally, we review statins as a therapeutic option for CDC toxicity and PLY toxoid as a vaccine candidate in protein-based vaccines.

The Autoimmune Susceptibility Gene C5orf30 Regulates Macrophage-Mediated Resolution of Inflammation

Genetic variants in C5orf30 have been associated with development of the autoimmune conditions primary biliary cirrhosis and rheumatoid arthritis. In rheumatoid arthritis, C5orf30 expression is cell-specific, with highest expression found in macrophages and synovial fibroblasts. C5orf30 is highly expressed in inflamed joints and is a negative regulator of tissue damage in a mouse model of inflammatory arthritis. Transcriptomic analysis from ultrasound-guided synovial biopsy of inflamed joints in a well characterized clinical cohort of newly diagnosed, disease-modifying antirheumatic drugs-naive rheumatoid arthritis patients was used to determine the clinical association of C5orf30 expression with disease activity. A combined molecular and computational biology approach was used to elucidate C5orf30 function in macrophages both in vitro and in vivo. Synovial expression of C5orf30 is inversely correlated with both clinical measures of rheumatoid arthritis disease activity and with synovial TNF mRNA expression. C5orf30 plays a role in regulating macrophage phenotype and is differentially turned over in inflammatory and anti-inflammatory macrophages. Inhibition of C5orf30 reduces wound healing/repair-associated functions of macrophages, reduces signaling required for resolution of inflammation, and decreases secretion of anti-inflammatory mediators. In an animal model of wound healing (zebrafish), C5orf30 inhibition increases the recruitment of macrophages to the wound site. Finally, we demonstrate that C5orf30 skews macrophage immunometabolism, demonstrating a mechanism for C5orf30-mediated immune regulation.

Apoptosis, Toll-like, RIG-I-like and NOD-like Receptors Are Pathways Jointly Induced by Diverse Respiratory Bacterial and Viral Pathogens

Lower respiratory tract infections are among the top five leading causes of human death. Fighting these infections is therefore a world health priority. Searching for induced alterations in host gene expression shared by several relevant respiratory pathogens represents an alternative to identify new targets for wide-range host-oriented therapeutics. With this aim, alveolar macrophages were independently infected with three unrelated bacterial (Streptococcus pneumoniae, Klebsiella pneumoniae, and Staphylococcus aureus) and two dissimilar viral (respiratory syncytial virus and influenza A virus) respiratory pathogens, all of them highly relevant for human health. Cells were also activated with bacterial lipopolysaccharide (LPS) as a prototypical pathogen-associated molecular pattern. Patterns of differentially expressed cellular genes shared by the indicated pathogens were searched by microarray analysis. Most of the commonly up-regulated host genes were related to the innate immune response and/or apoptosis, with Toll-like, RIG-I-like and NOD-like receptors among the top 10 signaling pathways with over-expressed genes. These results identify new potential broad-spectrum targets to fight the important human infections caused by the bacteria and viruses studied here.

Pyruvate oxidase of Streptococcus pneumoniae contributes to pneumolysin release

Background

Streptococcus pneumoniae is one of the leading causes of community acquired pneumonia and acute otitis media. Certain aspects of S. pneumoniae’s virulence are dependent upon expression and release of the protein toxin pneumolysin (PLY) and upon the activity of the peroxide-producing enzyme, pyruvate oxidase (SpxB). We investigated the possible synergy of these two proteins and identified that release of PLY is enhanced by expression of SpxB prior to stationary phase growth.

Results

Mutants lacking the spxB gene were defective in PLY release and complementation of spxB restored PLY release. This was demonstrated by cytotoxic effects of sterile filtered supernatants upon epithelial cells and red blood cells. Additionally, peroxide production appeared to contribute to the mechanism of PLY release since a significant correlation was found between peroxide production and PLY release among a panel of clinical isolates. Exogenous addition of H₂O₂ failed to induce PLY release and catalase supplementation prevented PLY release in some strains, indicating peroxide may exert its effect intracellularly or in a strain-dependent manner. SpxB expression did not trigger bacterial cell death or LytA-dependent autolysis, but did predispose cells to deoxycholate lysis.

Conclusions

Here we demonstrate a novel link between spxB expression and PLY release. These findings link liberation of PLY toxin to oxygen availability and pneumococcal metabolism.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0881-6) contains supplementary material, which is available to authorized users.

MicroRNAs Constitute a Negative Feedback Loop in Streptococcus pneumoniae-Induced Macrophage Activation

Streptococcus pneumoniae causes high mortality as a major pneumonia-inducing pathogen. In pneumonia, control of innate immunity is necessary to prevent organ damage. We assessed the role of microRNAs (miRNAs) as regulators in pneumococcal infection of human macrophages. Exposure of primary blood-derived human macrophages with pneumococci resulted in transcriptional changes in several gene clusters and a significant deregulation of 10 microRNAs. Computational network analysis retrieved miRNA-146a as one putatively important regulator of pneumococci-induced host cell activation. Its induction depended on bacterial structural integrity and was completely inhibited by blocking Toll-like receptor 2 (TLR-2) or depleting its mediator MyD88. Furthermore, induction of miRNA-146a release did not require the autocrine feedback of interleukin 1β and tumor necrosis factor α released from infected macrophages, and it repressed the TLR-2 downstream mediators IRAK-1 and TRAF-6, as well as the inflammatory factors cyclooxygenase 2 and interleukin 1β. In summary, pneumococci recognition induces a negative feedback loop, preventing excessive inflammation via miR-146a and potentially other miRNAs.

Defying death: Cellular survival strategies following plasmalemmal injury by bacterial toxins

The perforation of the plasmalemma by pore-forming toxins causes an influx of Ca(2+) and an efflux of cytoplasmic constituents. In order to ensure survival, the cell needs to identify, plug and remove lesions from its membrane. Quarantined by membrane folds and isolated by membrane fusion, the pores are removed from the plasmalemma and expelled into the extracellular space. Outward vesiculation and microparticle shedding seem to be the strategies of choice to eliminate toxin-perforated membrane regions from the plasmalemma of host cells. Depending on the cell type and the nature of injury, the membrane lesion can also be taken up by endocytosis and degraded internally. Host cells make excellent use of an initial, moderate rise in intracellular [Ca(2+)], which triggers containment of the toxin-inflicted damage and resealing of the damaged plasmalemma. Additional Ca(2+)-dependent defensive cellular actions range from the release of effector molecules in order to warn neighbouring cells, to the activation of caspases for the initiation of apoptosis in order to eliminate heavily damaged, dysregulated cells. Injury to the plasmalemma by bacterial toxins can be prevented by the early sequestration of bacterial toxins. Artificial liposomes can act as a decoy system preferentially binding and neutralizing bacterial toxins.

In vitro expression of Streptococcus pneumoniae ply gene in human monocytes and pneumocytes

BACKGROUND

Streptococcus pneumoniae is one major cause of pneumonia in human and contains various virulence factors that contribute to pathogenesis of pneumococcal disease. This study investigated the role of pneumolysin, Ply, in facilitating S. pneumoniae invasion into the host blood stream.

METHODS

S. pneumoniae strains were isolated from clinical blood and sputum samples and confirmed by PCR. Expression of ply gene was assessed by infecting human monocytes and pneumocytes.

RESULTS

A total of 23 strains of S. pneumoniae isolated from blood (n = 11) and sputum (n = 12) along with S. pneumoniae ATCC49619 were used to infect human monocyte (THP-1) and Type II pneumocyte (A549) cell lines. All clinical strains of S. pneumoniae showed higher expression of ply mRNA than the American Type Culture Collection (ATCC) strain. Among the clinical strains, blood isolates showed higher expression of ply genes than sputum isolates, i.e., 2(1.5)- to 2(1.6)-folds in THP-1 and 2(0.4)- to 2(4.9)-folds in A549 cell lines.

CONCLUSIONS

The data from the current study demonstrated that ply gene of blood- and sputum-derived S. pneumoniae is differentially expressed in two different cell lines. Under survival pressure, ply is highly expressed in these two cell lines for blood-derived S. pneumoniae, indicating that ply gene may facilitate S. pneumoniae invasion into the host blood system.

Differential bacterial gene expression during experimental pneumococcal endophthalmitis

Streptococcus pneumoniae (pneumococcus) is a potential cause of bacterial endophthalmitis in humans that can result in ocular morbidity. We sought to identify pneumococcal genes that are differentially expressed during growth in the vitreous humor of the eye in an experimental endophthalmitis model. Microarray analysis was used to identify genes that were differentially expressed when pneumococci replicated in the vitreous of rabbit eyes as compared with bacteria grown in vitro in Todd Hewitt medium. Array results were verified by quantitative real-time PCR analysis of representative genes. Select genes potentially playing a role in virulence during endophthalmitis were deleted, and mutants were tested for reduced eye pathogenesis and altered adhesion to host cells. Array analysis identified 134 genes that were differentially expressed during endophthalmitis; 112 genes demonstrated increased expression during growth in the eye whereas 22 were downregulated. Real-time analysis verified increased expression of neuraminidase A (NanA; SP1693), neuraminidase B (NanB; SP1687) and serine protease (SP1954), and decreased expression of RlrA (SP0461) and choline transporter (SP1861). Mutation of NanA and NanB had no major effect on pathogenesis. Loss of SP1954 led to increased adherence to host cells. S. pneumoniae enhances and represses the expression of a variety of genes during endophthalmitis. While some of these genes reflect changes in metabolic requirements, some appear to play a role in immune evasion and pathogenesis in the eye.

Enhanced antidepressant-like effects of the macromolecule trefoil factor 3 by loading into negatively charged liposomes

Immunocytes, mainly neutrophils and monocytes, exhibit an intrinsic homing property, enabling them to migrate to sites of injury and inflammation. They can thus act as Trojan horses carrying concealed drug cargoes while migrating across impermeable barriers to sites of disease, especially the blood–brain barrier (BBB). In this study, to target circulating phagocytic cells, we formulated negatively charged nanosize liposomes and loaded trefoil factor 3 (TFF3) into liposomes by the pH-gradient method. According to the optimized formulation (5:1.5 of lipid to cholesterol, 10:1 of lipid to drug, 10 mg/mL of lipid concentration, and 10 mmol/L of phosphate-buffered saline), 44.47% entrapment efficiency was obtained for TFF3 liposomes with 129.6 nm particle size and −36.6 mV zeta potential. Compared with neutrally charged liposomes, the negatively charged liposomes showed a strong binding capacity with monocytes and were effectively carried by monocytes to cross the BBB in vitro. Furthermore, enhanced antidepressant-like effects were found in the tail-suspension and forced-swim tests in mice, as measured by decreased immobility time, as well as increased swimming time and reduced immobility in rats. These results suggested that negatively charged liposomes could improve the behavioral responses of TFF3, and our study opens up a new way for the development of effective therapies for brain disease by increasing the permeability of the BBB.

The role of macrophages in the innate immune response to Streptococcus pneumoniae and Staphylococcus aureus: mechanisms and contrasts

Macrophages are critical mediators of innate immune responses against bacteria. The Gram-positive bacteria Streptococcus pneumoniae and Staphylococcus aureus express a range of virulence factors, which challenge macrophages' immune competence. We review how macrophages respond to this challenge. Macrophages employ a range of strategies to phagocytose and kill each pathogen. When the macrophages capacity to clear bacteria is overwhelmed macrophages play important roles in orchestrating the inflammatory response through pattern recognition receptor-mediated responses. Macrophages also ensure the inflammatory response is tightly constrained, to avoid tissue damage, and play an important role in downregulating the inflammatory response once initial bacterial replication is controlled.

Ca²⁺-dependent repair of pneumolysin pores: A new paradigm for host cellular defense against bacterial pore-forming toxins

Pneumolysin (PLY), a key virulence factor of Streptococcus pneumoniae, permeabilizes eukaryotic cells by forming large trans-membrane pores. PLY imposes a puzzling multitude of diverse, often mutually excluding actions on eukaryotic cells. Whereas cytotoxicity of PLY can be directly attributed to the pore-mediated effects, mechanisms that are responsible for the PLY-induced activation of host cells are poorly understood. We show that PLY pores can be repaired and thereby PLY-induced cell death can be prevented. Pore-induced Ca²⁺ entry from the extracellular milieu is of paramount importance for the initiation of plasmalemmal repair. Nevertheless, active Ca²⁺ sequestration that prevents excessive Ca²⁺ elevation during the execution phase of plasmalemmal repair is of no less importance. The efficacy of plasmalemmal repair does not only define the fate of targeted cells but also intensity, duration and repetitiveness of PLY-induced Ca²⁺ signals in cells that were able to survive after PLY attack. Intracellular Ca²⁺ dynamics evoked by the combined action of pore formation and their elimination mimic the pattern of receptor-mediated Ca²⁺ signaling, which is responsible for the activation of host immune responses. Therefore, we postulate that plasmalemmal repair of PLY pores might provoke cellular responses that are similar to those currently ascribed to the receptor-mediated PLY effects. Our data provide new insights into the understanding of the complexity of cellular non-immune defense responses to a major pneumococcal toxin that plays a critical role in the establishment and the progression of life-threatening diseases. Therapies boosting plasmalemmal repair of host cells and their metabolic fitness might prove beneficial for the treatment of pneumococcal infections. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

TLR-mediated inflammatory responses to Streptococcus pneumoniae are highly dependent on surface expression of bacterial lipoproteins

Streptococcus pneumoniae infections induce inflammatory responses that contribute toward both disease pathogenesis and immunity, but the host–pathogen interactions that mediate these effects are poorly defined. We used the surface lipoprotein-deficient ∆lgt pneumococcal mutant strain to test the hypothesis that lipoproteins are key determinants of TLR-mediated immune responses to S. pneumoniae. We show using reporter assays that TLR2 signaling is dependent on pneumococcal lipoproteins, and that macrophage NF-κB activation and TNF-α release were reduced in response to the ∆lgt strain. Differences in TNF-α responses between Δlgt and wild-type bacteria were abrogated for macrophages from TLR2- but not TLR4-deficient mice. Transcriptional profiling of human macrophages revealed attenuated TLR2-associated responses to ∆lgt S. pneumoniae, comprising many NF-κB–regulated proinflammatory cytokine and chemokine genes. Importantly, non-TLR2–associated responses were preserved. Experiments using leukocytes from IL-1R–associated kinase-4–deficient patients and a mouse pneumonia model confirmed that proinflammatory responses were lipoprotein dependent. Our data suggest that leukocyte responses to bacterial lipoproteins are required for TLR2- and IL-1R–associated kinase-4–mediated inflammatory responses to S. pneumoniae.

The biology of pneumolysin

Cholesterol dependent cytolysins are important in the ability of some bacteria to cause disease in man and animals. Pneumolysin (PLY) plays a key role in the diseases caused by Streptococcus pneumoniae (the pneumococcus). This chapter describes the role of PLY in some of the key process in disease. These include induction of cell death by pore formation and toxin-induced apoptosis as well as more subtle effects on gene expression of host cells including epigenetic effects of the toxin. The use of bacterial mutants that either do not express the toxin or express altered versions in biological systems is described. Use of isolated tissue and whole animal systems to dissect the structure/function relationships of the toxin as well as the role played by different activities in the pathogenesis of infection are described. The role of PLY in meningitis and the associated deafness is discussed as well as the role of the toxin in promoting increased lung permeability and inflammation during pneumococcal pneumonia. Different clinical strains of the pneumococcus produce different forms of PLY and the impact of this on disease caused by these strains is discussed. Finally, the impact of this knowledge on the development of treatment and prevention strategies for pneumococcal disease is discussed.

Protection against pneumococcal infection elicited by immunization with glutamyl tRNA synthetase, polyamine transport protein D and sortase A

Protein-based vaccines are considered to be the next-generation of pneumococcal vaccines. Here we evaluated the protection elicited by immunization with recombinant glutamyl tRNA synthetase (Gts), polyamine transport protein D (PotD) and sortase A (SrtA) antigens in preclinical mouse models. In mucosal immunization studies, intranasal immunization with either Gts, PotD or SrtA could significantly reduce pneumococcal nasopharyngeal and lung colonization and significantly increase mice survival times following invasive pneumococcal challenge, and combinations of these antigens could enhance this protection. In systemic immunization studies, intraperitoneal immunization with multiple protein antigens also provided better protection against pneumococcal sepsis caused by different pneumococcal strains. Finally, passive immunization studies showed an additive effect by using multiple anti-sera when compared to single anti-sera. Therefore, a multicomponent protein-based pneumococcal vaccine composed of Gts, PotD or SrtA could confer protection against pneumococcal colonization as well as invasive infections in terms of efficacy of protection and serotype coverage.

Transcriptome signature in young children with acute otitis media due to Streptococcus pneumoniae

Streptococcus pneumoniae (Spn) is the predominant causative organism of acute otitis media in children. To better understand the genes that are regulated at the onset of AOM caused by Spn infection in the middle ear, the transcriptome profile of peripheral blood mononuclear cells isolated from children prior to and during an AOM event was evaluated by microarray. We found that 1903 (6.2%) of 29,187 genes were differentially regulated greater than 2-fold at the onset of AOM compared to the pre-infection stage of the same children. The ontology of differentially regulated genes was dominated by those involved with the immune response. At onset of infection, genes associated with bacterial defenses were significantly up-regulated, including beta-defensin123, S100 protein A12, Toll-like receptor 5, IL-10, and those involved in the classical and alternative complement pathways. Genes associated with inhibition of bacterial entry through clathrin-dependent endocytosis were also up-regulated. In contrast, genes associated with cell-mediated immune responses were broadly down-regulated. The results provide the first human transcriptome data identifying genes differentially regulated at the onset of AOM in children.

The use of THP-1 cells as a model for mimicking the function and regulation of monocytes and macrophages in the vasculature

Since their establishment thirty years ago, THP-1 cells have become one of most widely used cell lines to investigate the function and regulation of monocytes and macrophages in the cardiovascular system. However, because this cell line was derived from the blood of a patient with acute monocytic leukemia, the extent to which THP-1 cells mimic monocytes and macrophages in the vasculature is not entirely known. This article serves as a meaningful attempt to address this question by reviewing the recent publications. The interactions between THP-1 cells and various vascular cells (such as endothelial cells, smooth muscle cells, adipocytes, and T cells) provide insight into the roles of the interconnection of monocytes-macrophages with other vascular cells during vascular inflammation, particularly atherogenesis and obesity. Transcriptome, microRNA profile, and histone modifications of THP-1 cells shed new light on the regulatory mechanism of the monocytes-macrophages in response to various inflammatory mediators, such as oxidized low density lipoprotein, lipopolysaccharide, and glucose. These studies hint that under certain defined conditions, THP-1 cells not only resemble primary monocytes-macrophages isolated from healthy donors or donors with disease, such as diabetes mellitus, but also mimic the in situ alteration of macrophages in the adipose tissue of obese subjects and in atherosclerotic lesions. A potential trajectory is to use this cell line to study the novel molecular mechanisms in monocytes and macrophages in relation to the physiology and pathophysiology of the cardiovascular system, however, the conclusion of studies employing THP-1 cells requires further verification using primary cells and/or in vivo models to be generalized to monocytes and macrophages.

A sensitive high-throughput assay for evaluating host-pathogen interactions in Cryptococcus neoformans infection

BACKGROUND

Cryptococcus neoformans causes serious disease in immunocompromised individuals, leading to over 600,000 deaths per year worldwide. Part of this impact is due to the organism's ability to thwart what should be the mammalian hosts' first line of defense against cryptococcal infection: internalization by macrophages. Even when C. neoformans is engulfed by host phagocytes, it can survive and replicate within them rather than being destroyed; this ability is central in cryptococcal virulence. It is therefore critical to elucidate the interactions of this facultative intracellular pathogen with phagocytic cells of its mammalian host.

METHODOLOGY/PRINCIPAL FINDINGS

To accurately assess initial interactions between human phagocytic cells and fungi, we have developed a method using high-throughput microscopy to efficiently distinguish adherent and engulfed cryptococci and quantitate each population. This method offers significant advantages over currently available means of assaying host-fungal cell interactions, and remains statistically robust when implemented in an automated fashion appropriate for screening. It was used to demonstrate the sensitivity of human phagocytes to subtle changes in the cryptococcal capsule, a major virulence factor of this pathogen.

CONCLUSIONS/SIGNIFICANCE

Our high-throughput method for characterizing interactions between C. neoformans and mammalian phagocytic cells offers a powerful tool for elucidating the relationship between these cell types during pathogenesis. This approach will be useful for screens of this organism and has potentially broad applications for investigating host-pathogen interactions.

Proteomic evaluation and validation of cathepsin D regulated proteins in macrophages exposed to Streptococcus pneumoniae

Macrophages are central effectors of innate immune responses to bacteria. We have investigated how activation of the abundant macrophage lysosomal protease, cathepsin D, regulates the macrophage proteome during killing of Streptococcus pneumoniae. Using the cathepsin D inhibitor pepstatin A, we demonstrate that cathepsin D differentially regulates multiple targets out of 679 proteins identified and quantified by eight-plex isobaric tag for relative and absolute quantitation. Our statistical analysis identified 18 differentially expressed proteins that passed all paired t-tests (α = 0.05). This dataset was enriched for proteins regulating the mitochondrial pathway of apoptosis or inhibiting competing death programs. Five proteins were selected for further analysis. Western blotting, followed by pharmacological inhibition or genetic manipulation of cathepsin D, verified cathepsin D-dependent regulation of these proteins, after exposure to S. pneumoniae. Superoxide dismutase-2 up-regulation was temporally related to increased reactive oxygen species generation. Gelsolin, a known regulator of mitochondrial outer membrane permeabilization, was down-regulated in association with cytochrome c release from mitochondria. Eukaryotic elongation factor (eEF2), a regulator of protein translation, was also down-regulated by cathepsin D. Using absence of the negative regulator of eEF2, eEF2 kinase, we confirm that eEF2 function is required to maintain expression of the anti-apoptotic protein Mcl-1, delaying macrophage apoptosis and confirm using a murine model that maintaining eEF2 function is associated with impaired macrophage apoptosis-associated killing of Streptococcus pneumoniae. These findings demonstrate that cathepsin D regulates multiple proteins controlling the mitochondrial pathway of macrophage apoptosis or competing death processes, facilitating intracellular bacterial killing.

Gram-positive pathogenic bacteria induce a common early response in human monocytes

BACKGROUND

We infected freshly isolated human peripheral monocytes with live bacteria of three clinically important gram-positive bacterial species, Staphylococcus aureus, Streptococcus pneumoniae and Listeria monocytogenes and studied the ensuing early transcriptional response using expression microarrays. Thus the observed response was unbiased by signals originating from other helper and effector cells of the host and was not limited to induction by solitary bacterial constituents.

RESULTS

Activation of monocytes was demonstrated by the upregulation of chemokine rather than interleukin genes except for the prominent expression of interleukin 23, marking it as the early lead cytokine. This activation was accompanied by cytoskeleton rearrangement signals and a general anti-oxidative stress and anti-apoptotic reaction. Remarkably, the expression profiles also provide evidence that monocytes participate in the regulation of angiogenesis and endothelial function in response to these pathogens.

CONCLUSION

Regardless of the invasion properties and survival mechanisms of the pathogens used, we found that the early response comprised of a consistent and common response. The common response was hallmarked by the upregulation of interleukin 23, a rather unexpected finding regarding Listeria infection, as this cytokine has been linked primarily to the control of extracellular bacterial dissemination.

Pneumolysin-induced CXCL8 production by nasopharyngeal epithelial cells is dependent on calcium flux and MAPK activation via Toll-like receptor 4

The natural niche of Streptococcus pneumoniae is the nasopharyngeal mucosa and nasopharyngeal carriage of pneumococci is widely prevalent. Pneumolysin (Ply), a pore-forming protein produced by S. pneumonia, may be important in driving the innate immune response of the nasopharynx. We studied the Ply-induced production of CXCL8 by nasopharyngeal cells and further analysed the mechanism of this induction. Detroit nasopharyngeal cells were stimulated with supernatants derived from bacterial cultures of Ply-deficient, wild-type pneumococci and recombinant Ply, and CXCL8 measured by ELISA. The role of MAP kinase family members in Ply-induced CXCL8 production was analysed using specific inhibitors, NF-κB activity was measured by immunoblot and Ply-mediated TLR4 activation analysed by a CXCL8 promotor luciferase assay. Ply significantly increased production of CXCL8 in Detroit and primary nasal cells. Flow cytometric analysis showed that Detroit cells express cell surface TLR4. CXCL8 production was dependent on changes in the intracellular Ca(2+) levels and also by NF-κB via activation of TLR4, and MAP kinase signalling. Ply induces production of CXCL8 by nasopharyngeal cells using signalling mechanisms involving Ca(2+) mobilisation and activation of MAPK and NF-κB via TLR4. This may be important in regulating nasopharyngeal immunity against pneumococcal colonization.

Mammalian cell transcriptome in response to meningitis-causing pathogens

Bacterial meningitis continues to be a major cause of mortality and morbidity, despite improved antimicrobial therapy. A key factor that contributes to this situation is the incomplete understanding of its pathogenesis. High-throughput methods (e.g., DNA microarray technology) can provide a holistic picture of the transcriptional events that underlie the host response to bacterial infections, including that during bacterial meningitis. Since 2001, several studies have been reported on the cellular host's responses to infections with Neisseria meningitidis and Streptococcus pneumoniae (the leading causes of bacterial meningitis) using DNA microarrays and have described numerous differentially expressed genes. The present review summarizes the main recent findings with gene expression analyses in the field of bacterial meningitis. Experiments that defined a common host response, as well as pathogen-specific host responses, will be discussed. This review will also outline the contributions of global gene analyses to our understanding of the pathophysiology of bacterial meningitis.

Streptococcus pneumoniae nasopharyngeal colonization induces type I interferons and interferon-induced gene expression

Background

We employed DNA microarray technology to investigate the host response to Streptococcus pneumoniae in a mouse model of asymptomatic carriage. Over a period of six weeks, we profiled transcript abundance and complexity in the Nasal Associated Lymphoid Tissue (NALT) to identify genes whose expression differed between pneumococcal-colonized and uncolonized states.

Results

Colonization with S. pneumoniae altered the expression of hundreds of genes over the course of the study, demonstrating that carriage is a dynamic process characterized by increased expression of a set of early inflammatory responses, including induction of a Type I Interferon response, and the production of several antimicrobial factors. Subsequent to this initial inflammatory response, we observed increases in transcripts associated with T cell development and activation, as well as wounding, basement membrane remodeling, and cell proliferation. Our analysis suggests that microbial colonization induced expression of genes encoding components critical for controlling JAK/STAT signaling, including stat1, stat2, socs3, and mapk1, as well as induction of several Type I Interferon-inducible genes and other antimicrobial factors at the earliest stages of colonization.

Conclusion

Examining multiple time points over six weeks of colonization demonstrated that asymptomatic carriage stimulates a dynamic host response characterized by temporal waves with distinct biological programs. Our data suggest that the usual response to the presence of the pneumocccus is an initial controlled inflammatory response followed by activation of host physiological processes such as response to wounding, basement membrane remodeling, and increasing cellular numbers that ultimately allow the host to maintain an intact epithelium and eventually mount a preventive adaptive immune response.

Virulence factors in pneumococcal respiratory pathogenesis

Streptococcus pneumoniae (the pneumococcus) is a major global cause of human disease. Since the publication of the entire sequence of TIGR4 in 2001, our understanding of this human pathogen has increased significantly. Genetic studies, and the use of mutant strains have refined our understanding of the pathogenic mechanisms of classic pneumococcal virulence factors, including the polysaccharide capsule, pneumolysin and surface-expressed proteins. Genetic screens are identifying novel virulence factors. Characterization of pili and bacteriocins, as well as genes associated with competence, metabolism and resistance to oxidative stress has provided new insights into the genetic diversity of the pneumococcus. Further appreciation of the molecular basis of pneumococcal pathogenesis will lead to more effective strategies for the prevention and management of pneumococcal disease.

Histone-like DNA binding protein of Streptococcus intermedius induces the expression of pro-inflammatory cytokines in human monocytes via activation of ERK1/2 and JNK pathways

Streptococcus intermedius is a commensal associated with serious, deep-seated purulent infections in major organs, such as the brain and liver. Histone-like DNA binding protein (HLP) is an accessory architectural protein in a variety of bacterial cellular processes. In this study, we investigated the mechanisms of pro-inflammatory cytokine inductions in THP-1 cells by stimulation with recombinant HLP of S. intermedius (rSi-HLP). rSi-HLP stimulation-induced production of pro-inflammatory cytokines (IL-8, IL-1 beta and TNF-alpha) occurred in a time- and dose-dependent manner. In contrast with the heat-stable activity of DNA binding, the induction activity of rSi-HLP was heat-unstable. In subsequent studies, rSi-HLP acted cooperatively with lipoteichoic acid, the synthetic Toll-like receptor 2 agonist, Pam3CSK4, and the cytosolic nucleotide binding oligomerization domain 2 receptor agonist, muramyldipeptide. Furthermore, Western blot and blocking assays with specific inhibitors showed that rSi-HLP stimulation induced the activation of cell signal transduction pathways, extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK). In addition to its physiological role in bacterial growth through DNA binding, these results indicate that Si-HLP can trigger a cascade of events that induce pro-inflammatory responses via ERK1/2 and JNK signal pathways, and suggest that bacterial HLP may contribute to the activation of host innate immunity during bacterial infection.

Analysis of the in vitro transcriptional response of human pharyngeal epithelial cells to adherent Streptococcus pneumoniae: evidence for a distinct response to encapsulated strains

Infection of the human host by Streptococcus pneumoniae begins with colonization of the nasopharynx, which is mediated by the adherence of bacteria to the respiratory epithelium. Several studies have indicated an important role for the pneumococcal capsule in this process. Here, we used microarrays to characterize the in vitro transcriptional response of human pharyngeal epithelial Detroit 562 cells to the adherence of serotype 2 encapsulated strain D39, serotype 19F encapsulated strain G54, serotype 4 encapsulated strain TIGR4, and their nonencapsulated derivatives (Deltacps). In total, 322 genes were found to be upregulated in response to adherent pneumococci. Twenty-two genes were commonly induced, including those encoding several cytokines (e.g., interleukin 1beta [IL-1beta] and IL-6), chemokines (e.g., IL-8 and CXCL1/2), and transcriptional regulators (e.g., FOS), consistent with an innate immune response mediated by Toll-like receptor signaling. Interestingly, 85% of genes were induced specifically by one or more encapsulated strains, suggestive of a capsule-dependent response. Importantly, purified capsular polysaccharides alone had no effect. Over a third of these loci encoded products predicted to be involved in transcriptional regulation and signal transduction, in particular mitogen-activated protein kinase signaling pathways. Real-time PCR of a subset of 10 genes confirmed the microarray data and showed a time-dependent upregulation of, especially, innate immunity genes. The downregulation of epithelial genes was most pronounced upon adherence of D39Deltacps, as 68% of the 161 genes identified were repressed only by this nonencapsulated strain. In conclusion, we identified a subset of host genes specifically induced by encapsulated strains during in vitro adherence and have demonstrated the complexity of interactions occurring during the initial stages of pneumococcal infection.

Cholesterol as treatment for pneumococcal keratitis: cholesterol-specific inhibition of pneumolysin in the cornea

PURPOSE

The purpose of this study was to determine whether cholesterol, the host cell receptor for pneumolysin of Streptococcus pneumoniae, could effectively treat pneumococcal keratitis.

METHODS

New Zealand White rabbits were intrastromally injected with 10(5) colony-forming units (CFUs) of S. pneumoniae D39. Corneas were treated with topical drops of 1% cholesterol every 2 hours beginning 25 hours after infection and were examined by slit lamp microscopy 24, 36, and 48 hours after infection. Rabbits were killed, and CFUs were recovered from the corneas after the final slit lamp examination (SLE). Minimal inhibitory concentration (MIC) assays of cholesterol against bacteria were performed. Specific inhibition of pneumolysin by cholesterol in the rabbit cornea was tested by intrastromal injection of pneumolysin with or without cholesterol and was compared with cholesterol inhibition of pneumolysin in vitro using hemolysis assays with rabbit erythrocytes.

RESULTS

Corneas treated with cholesterol had significantly lower SLE scores 48 hours after infection than corneas treated with vehicle (P = 0.0015). Treated corneas also had significantly less log(10) CFUs than vehicle-treated corneas (P = 0.0006). Cholesterol at a 1% concentration was bactericidal to bacteria in vitro, and lower concentrations of cholesterol were partially inhibitory in a concentration-dependent manner. Cholesterol also specifically inhibited 1 mug pneumolysin in vivo and up to 50 ng pneumolysin in vitro.

CONCLUSIONS

Topical cholesterol is an effective treatment for S. pneumoniae keratitis. Cholesterol not only inhibits pneumolysin, it is also bactericidal.

Pneumolysin, PspA, and PspC contribute to pneumococcal evasion of early innate immune responses during bacteremia in mice

The pneumococcal virulence factors include capsule, PspA, PspC, and Ply. Cytometric analysis demonstrated that the greatest levels of C3 deposition were on a Deltaply PspA(-) PspC(-) mutant. Also, Ply, PspA, and PspC expression resulted in C3 degradation in vitro and in vivo. Finally, blood clearance assays demonstrated that there was enhanced clearance of Deltaply PspA(-) PspC(-) pneumococci compared to the clearance of nonencapsulated pneumococci.

Tex, a putative transcriptional accessory factor, is involved in pathogen fitness in Streptococcus pneumoniae

We have identified a pneumococcal gene, tex, which has the potential to regulate gene expression. The tex gene is named for its role in toxin expression in Bordetella pertussis, where it was characterized as an essential gene. Homologous sequences have been found in both Gram-positive and Gram-negative bacteria and are highly conserved at the protein level. Tex family proteins contain a S1 RNA-binding domain at the C-terminus. Members of this family are putative transcriptional accessory factors. Although tex in Streptococcus pneumoniae is homologous to that in B. pertussis, there are distinct differences. Since the tex gene in S. pneumoniae is not an essential gene, we were able to delete tex in strain D39. The tex knockout mutant, DeltaTex, did not affect production of the pneumococcal toxin pneumolysin. However, we observed decreased growth of DeltaTex in the presence of the wild-type strain both in vitro and in vivo as determined by generation numbers and competitive index (CI). The interaction between recombinant Tex and nucleic acids was confirmed by southwestern and northwestern analysis, supporting its role as a transcriptional accessory factor.

Reovirus Strain-Dependent Inflammatory Cytokine Responses and Replication Patterns in a Human Monocyte Cell Line

Mammalian Orthoreoviruses are important models for studies of viral pathogenesis. In the rat lung, Reovirus strain type 3 Dearing (T3D) induces substantially more inflammation than does strain type 1 Lang (T1L). To better understand mechanisms underlying differences in the host inflammatory response elicited by T1L and T3D, we characterized cytokine expression patterns induced by those strains after infection of THP-1 monocyte cells. THP-1 cells were adsorbed with either viable or ultraviolet- inactivated T1L and T3D and assayed for mRNA and protein production of growth-regulated oncogene-alpha (GRO-alpha), interleukin-8 (IL-8), or tumor necrosis factor-alpha (TNF-alpha). T3D stimulated mRNA and protein production of all three cytokines, whereas T1L stimulated mRNA and protein production of IL-8 and TNF-alpha but not GRO-alpha. In each case, T3D induced greater cytokine mRNA and protein expression than did T1L. Nonviable virus did not stimulate detectable cytokine secretion, suggesting a requirement for viral RNA synthesis in cytokine induction by THP-1 cells. A greater percentage of THP-1 cells was infected with T1L than T3D as assessed by infectious center assay, and T1L achieved higher yields of infectious progeny than did T3D in infected THP-1 cells as determined by plaque assay. These strain-dependent differences in cytokine responses and corresponding replication patterns in monocyte cells parallel findings made in studies of rat models of pneumonia and provide clues about how Reovirus interfaces with the host innate immune response to produce pulmonary disease.

Host gene expression profiling in pathogen–host interactions

Microarray technology is a powerful high-throughput tool for the analysis of host-pathogen interactions that permits simultaneous interrogation of the transcriptional status of thousands of genes. Emerging topics from microarray-based studies employing diverse pathogens and cell types suggest an initial common host response largely characterised by features of the innate immune response. However, specific host gene expression patterns that reflect differences between bacteria of related genera, different species of a particular genus, as well as strains within a single species can also be discerned. These differences are indicative of virulence determinant functions and suggest adaptive survival strategies. These studies have led to a more comprehensive understanding of the host response and identified new avenues of research for potential control strategies against pathogens.

Molecular analysis of colonic transformation in the ileum after total colectomy in rats

BACKGROUND

Colonic transformation is thought to be a phenotypic alteration in the ileum after total colectomy (TC) but has not been well addressed at the molecular level. We previously demonstrated roles of aldosterone in enhancement of ileal sodium absorption after TC. However, the significance of aldosterone in intestinal adaptation has been unknown.

METHODS

Rat epithelial gene expression was compared between the ileum and distal colon by complementary DNA microarray. Genes were categorized into "colonic," "common," and "ileal" genes according to signal intensity. Ileal gene expressions in (1) the control and TC rats and (2) the control and aldosterone-infused rats were compared to detect altered genes or to assess the role of aldosterone in intestinal adaptation. Differential expression of MUC3 and lysozyme was confirmed by quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

A total of 6109 genes were categorized into "colonic," "common," or "ileal" gene pools. A comparison of the control and TC rats yielded 82 and 91 genes that were induced and suppressed in the ileum after TC, respectively. Thirty-five percent of them were associated with colonlike transformation (ie, the induction of colonic genes or the suppression of ileal genes). The expressions of MUC3 and lysozyme messenger RNAs were enhanced significantly in the TC ileum, compared with the control. In comparison, aldosterone infusion modulated a total of only 21 genes in the ileum.

CONCLUSION

Those data demonstrate that altered gene expression after TC is, in part, characterized by colonlike transformation. Furthermore, circulating aldosterone appears to play a part in the altering and/or adapting of gene expression in intestinal epithelium.

Innate immunity and the pneumococcus

The innate immune system provides a non-specific first line of defence against microbes and is crucial both in the development and effector stages of subsequent adaptive immune responses. Consistent with its importance, study of the innate immune system is a broad and fast-moving field. Here we provide an overview of the recent key advances made in this area with relation to the important pathogen Streptococcus pneumoniae (the pneumococcus).

Proinflammatory cytokine and chemokine modulation byStreptococcus suisin a whole-blood culture system

Streptococcus suis is an important swine and human pathogen. Inflammation, a hallmark of S. suis infection, is thought to be responsible for most clinical signs of meningitis, septicaemia and sudden death. In this work, using a porcine whole blood model, S. suis serotype 2 was shown to trigger the release of several pro-inflammatory cytokines as evaluated by reverse transcriptase-PCR and enzyme-linked immunosorbent assay. Although individual variations were observed among different S. suis strains, no correlations were observed between the strain origin/phenotype and cytokine levels. Live bacteria induced higher tumour necrosis factor alpha, interleukin-1 beta (IL-1beta) and IL-6 levels than did heat-killed bacteria. In contrast, heat-killed bacteria stimulated higher levels of IL-8 and monocyte chemotactic protein one (MCP-1). The bacterial cell wall was observed to be the major cytokine-inducting components, whereas capsule expression was important for MCP-1 activation. The presence of specific antibodies suppressed bacterial growth resulting in significantly reduced levels of cytokine production. Thus, antibody-mediated bacterial phagocytosis combined with suppressed inflammation may be beneficial for infection control strategies. We provide first evidence of S.suis-induction of pro-inflammatory swine cytokines and demonstrate the strength and relevance of the whole blood culture systems in the investigation of S. suis modulation of cytokine production.

Enhanced protective immunity against pneumococcal infection with PspA DNA and protein

The effect of priming and boosting with pspA/EF5668 and purified recombinant PspA/EF5668 was examined. With this strategy CBA/N mice were protected against fatal challenge with Streptococcus pneumoniae EF5668. Anti-PspA antibody titers were elevated, and Western analysis with the immune serum demonstrated cross-reactivity with PspA from several different pneumococcal isolates, representing different PspA clades. Immune serum localized cross-reactive epitopes to the alpha-helical domain of PspA/Rx1 and PspA/EF5668. We demonstrated that DNA/protein prime-boost immunizations can enhance protective immunity against pneumococcal challenge.

THP-1 monocytes up-regulate intercellular adhesion molecule 1 in response to pneumolysin from Streptococcus pneumoniae

Pneumolysin (PLY) is a major virulence factor of Streptococcus pneumoniae that elicits a variety of proinflammatory responses from cells of the host immune system. Intercellular adhesion molecule 1 (ICAM-1) is a cell adhesion molecule involved in leukocyte trafficking toward inflammatory stimuli in extravascular sites. In this study, we evaluated the effect of PLY on expression of ICAM-1 in THP-1 monocytic cells exposed to S. pneumoniae. Exposure of cells to PLY-expressing S. pneumoniae strain WU2 for 6 h led to significantly higher levels of ICAM-1 message than those in cells exposed to either medium alone or DeltaPLY1, a PLY-negative isogenic mutant of WU2. Cells exposed to purified recombinant PLY also showed a dose-dependent increase in ICAM-1 mRNA compared to cells exposed to medium alone. Exposure to recombinant PLY containing a single amino acid substitution (Trp433-->Phe) that decreases cytolytic activity did not increase ICAM-1 mRNA to levels seen with wild-type PLY. In addition, THP-1 cells exposed to wild-type strain WU2 or D39 had increased ICAM-1 on their surface compared to cells exposed to medium alone or their PLY-negative isogenic mutants DeltaPLY1 and DeltaPLY2, respectively. These data indicate that PLY induces transcription and production of a cell adhesion molecule involved in the inflammatory response that may play a role in pneumococcal infection.

Reduced interleukin-8 response to Streptococcus pneumoniae by alveolar macrophages from adults with HIV/AIDS

BACKGROUND

HIV-infected adults are highly susceptible to pneumococcal disease.

OBJECTIVE

To examine if alveolar macrophages from HIV-infected subjects exhibited a failure of cytokine production in response to Streptococcus pneumoniae in vitro.

DESIGN

Case-control comparison of alveolar macrophages from 11 HIV-infected and 13 non-infected adults.

METHODS

Type 1 opsonized S. pneumoniae were used to challenge the alveolar macrophages in vitro. Cell supernatant fluid was collected from unstimulated cells, and cells challenged with bacteria for 0, 6, 12 and 24 h. Cytokine production (interleukins 1beta, 6 and 8) was measured in all fluids using an enzyme-linked immunosorbent assay.

RESULTS

All the cytokines tested increased over time in both HIV-infected and uninfected subjects. Interleukin-8 release was significantly lower in HIV-infected than in non-HIV-infected subjects (P = 0.02).

CONCLUSION

Reduced interleukin-8 production may result in decreased neutrophil recruitment, and hence increased susceptibility to pneumococcal infection in HIV-infected subjects.

Innate immune defence in the human gastrointestinal tract

The mucosal surface of the gastrointestinal tract represents a major entry point and ecological niche for many microbes. It forms an important immune barrier, absorbing nutrients, whilst preventing invasion by organisms. Of the extra-ordinarily diverse species that comprise the microbial world, relatively few organisms are able to succeed in breaching this barrier in an otherwise healthy host. The production and secretion of antimicrobial peptides (AMPs) from surface epithelia and circulating immune cells are likely to play a key role in host protection and homeostasis. A number of these peptides are constitutively produced providing resident protection, whereas others are induced during infection and inflammation. In addition to directly eradicating microorganisms, it is becoming increasingly apparent that AMPs are multi-functional with diverse immuno-modulatory properties. This review focuses on three families of AMPs, defensins, cathelicidins, and lysozyme, and discusses their role in mucosal defence.

Pneumolysin-mediated activation of NFkappaB in human neutrophils is antagonized by docosahexaenoic acid

This study was designed to investigate the relationship between influx of extracellular Ca(2+), activation of NFkappaB and synthesis of interleukin-8 (IL-8) following exposure of human neutrophils to subcytolytic concentrations (8.37 and 41.75 ng/ml) of the pneumococcal toxin, pneumolysin, as well as the potential of the omega-3 polyunsaturated fatty acid, docosahexaenoic acid, to antagonize these events. Activation and translocation of NFkappaB were measured using a radiometric electrophoretic mobility shift assay, while influx of extracellular Ca(2+) and synthesis of IL-8 were determined using a radioassay and an ELISA procedure, respectively. Exposure of neutrophils to pneumolysin was accompanied by influx of Ca(2+), activation of NFkappaB, and synthesis of IL-8, all of which were eliminated by inclusion of the Ca(2+)-chelating agent, EGTA (10 m m), in the cell-suspending medium, as well as by pretreatment of the cells with docosahexaenoic acid (5 and 10 microg/ml). The antagonistic effects of docosahexaenoic acid on these pro-inflammatory interactions of pneumolysin with neutrophils were not attributable to inactivation of the toxin, and required the continuous presence of the fatty acid. These observations demonstrate that activation of NFkappaB and synthesis of IL-8, following exposure of neutrophils to pneumolysin are dependent on toxin-mediated influx of Ca(2+) and that these potentially harmful activities of the toxin are antagonized by docosahexaenoic acid.

Identification of a detrimental role for NK cells in pneumococcal pneumonia and sepsis in immunocompromised hosts

Gram-positive sepsis is a major disease problem. However, the contribution of various immune cell types to pathogenesis remains unclear. By infecting scid and wild type BALB/c mice with Streptococcus pneumoniae we have found a situation in which natural killer (NK) cells can play a detrimental role in the response to infection. scid mice were found to be significantly more susceptible to local and systemic pneumococcal infection than controls; they had significantly higher bacterial loads, elevated inflammatory responses and more widespread lung pathology. Interestingly, depletion of NK cells in scid mice resulted in significantly lower bacteraemia and inflammatory cytokine production. Infection with pneumococci deficient in pneumolysin revealed the toxin was involved in cytokine production. Overall results indicate that elevated NK cell activity during pneumococcal pneumonia amplifies pulmonary and systemic inflammation, increases bacteraemia and results in poor outcome.

Insights into host responses against pathogens from transcriptional profiling

DNA microarrays have allowed us to monitor the effects of pathogens on host-cell gene expression programmes in great depth and on a broad scale. The comparison of results that have been generated by these studies is complex, and such a comparison has not previously been attempted in a systematic manner. In this review, we have collated and compared published transcriptional-profiling data from 32 studies that involved 77 different host-pathogen interactions, and have defined a common host-transcriptional-response. We outline gene expression patterns in the context of Toll-like receptor and pathogen-mediated signalling pathways, and summarize the contributions that transcriptional-profiling studies have made to our understanding of the infectious disease process.

IMMUNOMODULATION AND SEPSIS: IMPACT OF THE PATHOGEN

Infection begins when microorganisms overcome host barriers and multiply within host tissues. To contain the infection, the host mounts an inflammatory response that mobilizes defense systems and kills the invading microorganisms. A focal inflammatory response is usually sufficient to eradicate the organisms. However, when it fails to contain the infection, the organisms, their toxins, and numerous host mediators are released into the bloodstream, producing a systemic inflammatory response and organ failure. Microorganisms have coevolved with their hosts, thereby acquiring means of overcoming host defense mechanisms or even taking advantage of innate host responses. Many pathogens avoid recognition by the host or dampen host immune responses via sophisticated pathogen-host interactions. Some pathogens benefit from the inflammatory response. According to current hypotheses regarding the pathogenesis of sepsis, the host generates both an innate immune response identical for all pathogens and an adaptive pathogen-specific response. Determining whether the innate response benefits the pathogen or the host is essential for understanding host-pathogen interactions. In this review, we discuss how pathogens interfere with innate and adaptive immune responses to escape eradication by the host.