Beta 2 integrins are involved in cytokine responses to whole Gram-positive bacteria

Engagement of α3β1 and α2β1 integrins by hypervirulent Streptococcus agalactiae in invasion of polarized enterocytes

The gut represents an important site of colonization of the commensal bacterium Streptococcus agalactiae (group B Streptococcus or GBS), which can also behave as a deadly pathogen in neonates and adults. Invasion of the intestinal epithelial barrier is likely a crucial step in the pathogenesis of neonatal infections caused by GBS belonging to clonal complex 17 (CC17). We have previously shown that the prototypical CC17 BM110 strain invades polarized enterocyte-like cells through their lateral surfaces using an endocytic pathway. By analyzing the cellular distribution of putative GBS receptors in human enterocyte-like Caco-2 cells, we find here that the alpha 3 (α3) and alpha 2 (α2) integrin subunits are selectively expressed on lateral enterocyte surfaces at equatorial and parabasal levels along the vertical axis of polarized cells, in an area corresponding to GBS entry sites. The α3β1 and α2β1 integrins were not readily accessible in fully differentiated Caco-2 monolayers but could be exposed to specific antibodies after weakening of intercellular junctions in calcium-free media. Under these conditions, anti-α3β1 and anti-α2β1 antibodies significantly reduced GBS adhesion to and invasion of enterocytes. After endocytosis, α3β1 and α2β1 integrins localized to areas of actin remodeling around GBS containing vacuoles. Taken together, these data indicate that GBS can invade enterocytes by binding to α3β1 and α2β1 integrins on the lateral membrane of polarized enterocytes, resulting in cytoskeletal remodeling and bacterial internalization. Blocking integrins might represent a viable strategy to prevent GBS invasion of gut epithelial tissues.

Complement Receptor 3 Mediates HIV-1 Transcytosis across an Intact Cervical Epithelial Cell Barrier: New Insight into HIV Transmission in Women

Transmission of HIV across the mucosal surface of the female reproductive tract to engage subepithelial CD4-positive T cells is not fully understood. Cervical epithelial cells express complement receptor 3 (CR3) (integrin αMβ2 or CD11b/CD18). In women, the bacterium Neisseria gonorrhoeae uses CR3 to invade the cervical epithelia to cause cervicitis. We hypothesized that HIV may also use CR3 to transcytose across the cervical epithelia. Here, we show that HIV-1 strains bound with high affinity to recombinant CR3 in biophysical assays. HIV-1 bound CR3 via the I-domain region of the CR3 alpha subunit, CD11b, and binding was dependent on HIV-1 N-linked glycans. Mannosylated glycans on the HIV surface were a high-affinity ligand for the I-domain. Man5 pentasaccharide, representative of HIV N-glycans, could compete with HIV-1 for CR3 binding. Using cellular assays, we show that HIV bound to CHO cells by a CR3-dependent mechanism. Antibodies to the CR3 I-domain or to the HIV-1 envelope glycoprotein blocked the binding of HIV-1 to primary human cervical epithelial (Pex) cells, indicating that CR3 was necessary and sufficient for HIV-1 adherence to Pex cells. Using Pex cells in a Transwell model system, we show that, following transcytosis across an intact Pex cell monolayer, HIV-1 is able to infect TZM-bl reporter cells. Targeting the HIV-CR3 interaction using antibodies, mannose-binding lectins, or CR3-binding small-molecule drugs blocked HIV transcytosis. These studies indicate that CR3/Pex may constitute an efficient pathway for HIV-1 transmission in women and also demonstrate strategies that may prevent transmission via this pathway. IMPORTANCE In women, the lower female reproductive tract is the primary site for HIV infection. How HIV traverses the epithelium to infect CD4 T cells in the submucosa is ill-defined. Cervical epithelial cells have a protein called CR3 on their surface. We show that HIV-1 binds to CR3 with high affinity and that this interaction is necessary and sufficient for HIV adherence to, and transcytosis across, polarized, human primary cervical epithelial cells. This suggests a unique role for CR3 on epithelial cells in dually facilitating HIV-1 attachment and entry. The HIV-CR3 interaction may constitute an efficient pathway for HIV delivery to subepithelial lymphocytes following virus transmission across an intact cervical epithelial barrier. Strategies with potential to prevent transmission via this pathway are presented.

The Relevance of IL-1-Signaling in the Protection against Gram-Positive Bacteria

Previous studies performed using a model of group B streptococcus (GBS)-induced peritoneal inflammation indicate that the interleukin-1 receptor (IL-1R) family plays an important role in the innate host defense against this encapsulated Gram-positive bacteria. Since the role of IL-1-dependent signaling in peritoneal infections induced by other Gram-positive bacteria is unknown, in the present study we sought to investigate the contribution of IL-1R signaling in host defenses against Streptococcus pyogenes (group A streptococcus or GAS) or Staphylococcus aureus, two frequent and global human Gram-positive extracellular pathogens. We analyzed here the outcome of GAS or S. aureus infection in IL-1R-deficient mice. After inoculated intraperitoneal (i.p.) inoculation with group A Streptococcus or S. aureus, all the wild-type (WT) control mice survived the challenge, while, respectively, 63% or 50% of IL-1-defective mice died. Lethality was due to the ability of both bacterial species to replicate and disseminate to the target organs of IL-1R-deficient mice. Moreover, the experimental results indicate that IL-1 signaling promotes the production of leukocyte attractant chemokines CXCL-1 and CXCL-2 and recruitment of neutrophils to bacterial infection sites. Accordingly, the reduced neutrophil recruitment in IL-1R-deficient mice was linked with decreased production of neutrophil chemokines. Collectively, our findings indicate that IL-1 signaling, as previously showed in host defense against GBS, plays a fundamental role also in controlling the progression and outcome of GAS or S. aureus disease.

Repurposed Drugs That Block the Gonococcus-Complement Receptor 3 Interaction Can Prevent and Cure Gonococcal Infection of Primary Human Cervical Epithelial Cells

Novel therapies that avert the problem of Neisseria gonorrhoeae with acquired antibiotic resistance are urgently needed. Gonococcal infection of the human cervix is initiated by an interaction between a galactose modification made to its surface appendages, pili, and the I-domain region of (host) complement receptor 3 (CR3). By targeting this crucial gonococcal–I-domain interaction, it may be possible to prevent cervical infection in females. To this end, we identified the I-domain galactose-binding epitope of CR3 and characterized its galactose lectin activity. Moreover, we identified two drugs, carbamazepine and methyldopa, as effective host-targeted therapies for gonorrhea treatment. At doses below those currently used for their respective existing indications, both carbamazepine and methyldopa were more effective than ceftriaxone in curing cervical infection ex vivo. This host-targeted approach would not be subject to N. gonorrhoeae drug resistance mechanisms. Thus, our data suggest a long-term solution to the growing problem of multidrug-resistant N. gonorrhoeae infections.

In the absence of a vaccine, multidrug-resistant Neisseria gonorrhoeae has emerged as a major human health threat, and new approaches to treat gonorrhea are urgently needed. N. gonorrhoeae pili are posttranslationally modified by a glycan that terminates in a galactose. The terminal galactose is critical for initial contact with the human cervical mucosa via an interaction with the I-domain of complement receptor 3 (CR3). We have now identified the I-domain galactose-binding epitope and characterized its galactose-specific lectin activity. Using surface plasmon resonance and cellular infection assays, we found that a peptide mimic of this galactose-binding region competitively inhibited the N. gonorrhoeae-CR3 interaction. A compound library was screened for potential drugs that could similarly prohibit the N. gonorrhoeae-CR3 interaction and be repurposed as novel host-targeted therapeutics for multidrug-resistant gonococcal infections in women. Two drugs, methyldopa and carbamazepine, prevented and cured cervical cell infection by multidrug-resistant gonococci by blocking the gonococcal-CR3 I-domain interaction.

In vitro complement activation, adherence to red blood cells and induction of mononuclear cell cytokine production by four strains of Aggregatibacter actinomycetemcomitans with different fimbriation and expression of leukotoxin

BACKGROUND AND OBJECTIVE

The periodontal pathogen Aggregatibacter actinomycetemcomitans has been proposed as pro-atherogenic, and complement-mediated adherence to red blood cells (RBCs) may facilitate its systemic spread. We investigated the ability of four strains of A. actinomycetemcomitans with differential expression of leukotoxin A (LtxA) and fimbriae to activate complement, adhere to RBCs and elicit cytokine responses by mononuclear cells (MNCs).

MATERIAL AND METHODS

Aggregatibacter actinomycetemcomitans serotype b strains HK 921, HK 1651, HK 2092 and HK 2108 were fluorescence-labeled, incubated with human whole blood cells in the presence of autologous serum, and assessed for RBC adherence by flow cytometry and for capacity to induce cytokine production by cytometric bead array analysis. The levels of IgG to A. actinomycetemcomitans serotype b were quantified by ELISA, as was consumption of complement.

RESULTS

The JP2 clone variants HK 1651 and, to a lesser extent, HK 2092, consumed complement efficiently, while HK 2108 (= strain Y4) consumed complement poorly. Nonetheless, the four tested strains adhered equally well to RBCs in the presence of autologous serum, without causing RBC lysis. The JP2 clone variant HK 2092, selectively lacking LtxA production, induced higher production of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-10 by MNCs than did the other three strains, while the four strains induced similar production of IL-12p70. RBCs facilitated the HK 2092-induced production of TNF-α and IL-1β, and IL-6 was enhanced by RBCs, and this facilitation could be counteracted by blockade of complement receptor 3 (CD11b/CD18).

CONCLUSION

Our data suggest that the JP2 clone of A. actinomycetemcomitans, most closely resembled by the variant HK 1651, activates complement well, while strain Y4, represented by HK 2108, activates complement poorly. However, all strains of A. actinomycetemcomitans adhere to RBCs and, when capable of producing LtxA, prevent production of inflammatory cytokines by MNCs. This "immunologically silent" immune adherence may facilitate systemic spread and atherogenesis.

Staphylococcus epidermidis Bacteremia Induces Brain Injury in Neonatal Mice via Toll-like Receptor 2-Dependent and -Independent Pathways

BACKGROUND

Staphylococcus epidermidis causes late-onset sepsis in preterm infants. Staphylococcus epidermidis activates host responses in part via Toll-like receptor 2 (TLR2). Epidemiologic studies link bacteremia and neonatal brain injury, but direct evidence is lacking.

METHODS

Wild-type and TLR2-deficient (TLR2-/-) mice were injected intravenously with S. epidermidis at postnatal day 1 prior to measuring plasma and brain cytokine and chemokine levels, bacterial clearance, brain caspase-3 activation, white/gray matter volume, and innate transcriptome.

RESULTS

Staphylococcus epidermidis bacteremia spontaneously resolved over 24 hours without detectable bacteria in the cerebrospinal fluid (CSF). TLR2-/- mice demonstrated delayed S. epidermidis clearance from blood, spleen, and liver. Staphylococcus epidermidis increased the white blood cell count in the CSF, increased interleukin 6, interleukin 12p40, CCL2, and CXCL1 concentrations in plasma; increased the CCL2 concentration in the brain; and caused rapid (within 6 hours) TLR2-dependent brain activation of caspase-3 and TLR2-independent white matter injury.

CONCLUSIONS

Staphylococcus epidermidis bacteremia, in the absence of bacterial entry into the CSF, impairs neonatal brain development. Staphylococcus epidermidis bacteremia induced both TLR2-dependent and -independent brain injury, with the latter occurring in the absence of TLR2, a condition associated with an increased bacterial burden. Our study indicates that the consequences of transient bacteremia in early life may be more severe than commonly appreciated, and our findings may inform novel approaches to reduce bacteremia-associated brain injury.

Activation of the NLRP3 inflammasome by group B streptococci

Group B Streptococcus (GBS) is a frequent agent of life-threatening sepsis and meningitis in neonates and adults with predisposing conditions. We tested the hypothesis that activation of the inflammasome, an inflammatory signaling complex, is involved in host defenses against this pathogen. We show in this study that murine bone marrow-derived conventional dendritic cells responded to GBS by secreting IL-1β and IL-18. IL-1β release required both pro-IL-1β transcription and caspase-1-dependent proteolytic cleavage of intracellular pro-IL-1β. Dendritic cells lacking the TLR adaptor MyD88, but not those lacking TLR2, were unable to produce pro-IL-1β mRNA in response to GBS. Pro-IL-1β cleavage and secretion of the mature IL-1β form depended on the NOD-like receptor family, pyrin domain containing 3 (NLRP3) sensor and the apoptosis-associated speck-like protein containing a caspase activation and recruitment domain adaptor. Moreover, activation of the NLRP3 inflammasome required GBS expression of β-hemolysin, an important virulence factor. We further found that mice lacking NLRP3, apoptosis-associated speck-like protein, or caspase-1 were considerably more susceptible to infection than wild-type mice. Our data link the production of a major virulence factor by GBS with the activation of a highly effective anti-GBS response triggered by the NLRP3 inflammasome.

Deciphering the complexity of Toll-like receptor signaling. Cell Mol Life Sci. 2010;67:4109-4134. [PMID: 20680392 DOI: 10.1007/s00018-010-0464-x]

Toll-like receptors (TLRs) are essential players in the innate immune response to invading pathogens. Although extensive research efforts have provided a considerable wealth of information on how TLRs function, substantial gaps in our knowledge still prevent the definition of a complete picture of TLR signaling. However, several recent studies describe additional layers of complexity in the regulation of TLR ligand recognition, adaptor recruitment, posttranslational modifications of signaling proteins, and the newly described, autonomous role of the TLR4 co-receptor CD14. In this review, by using it as model system for the whole TLR family, we attempt to provide a complete description of the signal transduction pathways triggered by TLR4, with a particular emphasis on the molecular and cell biological aspects regulating its function. Finally, we discuss a recently reported model of CD14-dependent signaling and highlight its biological implications.

iC3b-opsonized apoptotic cells mediate a distinct anti-inflammatory response and transcriptional NF-kappaB-dependent blockade

In recent years, it has become apparent that the removal of apoptotic cells by macrophages and DC is not only noninflammatory, but also immune-inhibitory, in most although not all circumstances. Complement may be involved in the uptake of apoptotic cells via direct binding of bridging factors in some physiological circumstances, by opsonization and engagement of the complement receptors. In the current study, we use a complement-dependent system of apoptotic cell clearance by human-derived macrophages and DC. Using a luciferase reporter gene and measuring immune response to non-opsonic zymosan, we show that iC3b-apoptotic cells induce NF-kappaB inhibition in response to zymosan and LPS at the nuclear translocation, transcriptional and post-transcriptional levels, leading to profound inhibition of proinflammatory cytokines. In addition, interaction with iC3b-opsonized apoptotic cells is characterized by macrophage secretion of IL-10 and lack of TGF-beta secretion. In conclusion, in cells with iC3b receptors, opsonized apoptotic cells mediate a distinct anti-inflammatory response and transcriptional NF-kappaB-dependent blockage.

TLR2 mediates recognition of live Staphylococcus epidermidis and clearance of bacteremia

Background

Staphylococcus epidermidis (SE) is a nosocomial pathogen that causes catheter-associated bacteremia in the immunocompromised, including those at the extremes of age, motivating study of host clearance mechanisms. SE-derived soluble components engage TLR2; but additional signaling pathways have also been implicated, and TLR2 can play complex, at times detrimental, roles in host defense against other Staphylococcal spp. The role of TLR2 in responses of primary blood leukocytes to live SE and in clearance of SE bacteremia, the most common clinical manifestation of SE infection, is unknown.

Methodology/Principal Findings

We studied TLR2-mediated recognition of live clinical SE strain 1457 employing TLR2-transfected cells, neutralizing anti-TLR antibodies and TLR2-deficient mice. TLR2 mediated SE-induced cytokine production in human embryonic kidney cells, human whole blood and murine primary macrophages, in part via recognition of a soluble TLR2 agonist. After i.v. challenge with SE, early (1 h) cytokine/chemokine production and subsequent clearance of bacteremia (24–48 h) were markedly impaired in TLR2-deficient mice.

Conclusions/Significance

TLR2 mediates recognition of live SE and clearance of SE bacteremia in vivo.

Induction and termination of inflammatory signaling in group B streptococcal sepsis

SUMMARY

Group B streptococcus (GBS) is part of the normal genital and gastrointestinal flora in healthy humans. However, GBS is a major cause of sepsis and meningitis in newborn infants in the Western world and an important pathogen in many developing countries. The dissection of the host response to GBS may increase the general understanding of innate immunity in sepsis, because newborn infants lack a sufficient adaptive response. Inflammatory signal induction in macrophages by GBS seems largely preserved in newborn infants, as shown both in vitro and in vivo. The engagement of Toll-like receptor 2 (TLR2) by lipoproteins and a myeloid differentiation factor 88 (MyD88)--dependent pathway induced by GBS cell wall are both important in this context. TLR2 activation of microglia by GBS induces neuronal damage, which might account for the high morbidity of GBS meningitis. At the same time, TLR2 mediates activation-induced cell death (AICD), a process involved in the containment of inflammation. In newborn infants, AICD and anti-bacterial polymorphonuclear leukocyte activity appears to be compromised. Accordingly, neonatal aberrations in the pathogen-specific negative control of inflammatory signaling are likely to contribute to excessive inflammation and neurological sequelae in GBS sepsis and meningitis.

Cross-regulation of signaling by ITAM-associated receptors

An important function of receptors that signal through immunoreceptor tyrosine-based activation motifs (ITAMs) is to regulate signaling by heterologous receptors. This review describes mechanisms by which ITAM-associated receptors modulate signaling by Toll-like receptors (TLRs), tumor necrosis factor receptor family members and cytokine receptors that use the Jak-STAT signaling pathway, and the biological importance of this signal transduction cross-talk. ITAM-mediated cross-regulation can either augment or dampen signaling by other receptors. Conversely, TLRs and cytokines modulate ITAM-mediated signaling, by means including activation of beta2 integrins that are coupled to the ITAM-containing adaptors DAP12 and FcRgamma. Integration of ITAM signaling into signaling networks through cross-talk with other signal transduction pathways results in tight regulation and fine tuning of cellular responses to various extracellular stimuli and contributes to induction of specific activation and differentiation pathways.

Chemokines are secreted by monocytes following OK-432 (lyophilized Streptococcus pyogenes) stimulation

BACKGROUND

OK-432, penicillin-killed Streptococcus pyogenes, is used in treating lymphangiomas and carcinomas. We have studied in vitro the role of mononuclear phagocytes (MNPs), including purified monocytes (MOs), in the immune response to OK-432. MIP-1alpha/beta and MCP-1 secretions were assessed in whole blood (WB), peripheral blood mononuclear cells (PBMCs) and purified MOs, after in vitro stimulation with OK-432 with or without adherence for 24 hours.

RESULTS

OK-432 stimulated MNPs to secrete MCP-1 and MIP-1alpha/beta in healthy individuals and in head and neck squamous cell carcinoma (HNSCC) patients, except for OK-432 stimulation of WB giving a minimal MIP-1alpha/beta response. Upon culture on low-attachment wells, a spontaneous chemokine secretion was observed, with an unchanged secretion following OK-432 stimulation. Inhibition of Syk kinase and/or PI-3 kinase did not significantly change the chemokine response to OK-432, except for MIP-1alpha production being increased upon Syk inhibitor addition and an increased MCP-1 response upon addition of both inhibitors. Adhesion may possibly involve beta1 and/or beta3 integrins, not beta2, whereas beta(1-3) integrins may act as co-stimulatory receptors for OK-432. Based on direct blockage of CD36 or CD18 by antibodies, MCP-1 production may be mediated by CD18 while MIP-1beta and MCP-1 production may occur upon binding to CD36.

CONCLUSION

Adherent human MOs produce MCP-1 and MIP-1alpha/beta upon stimulation with OK-432. CD36 modulates MIP-1beta and MCP-1 response. Thus, to some extent OK-432 acts as a substance whereby only MOs adhered to surfaces secrete MCP-1 and MIP-1alpha/beta, in part explaining why OK-432 is suited as a biological response modifying drug.

Different sequence strains of Streptococcus agalactiae elicit various levels of cytokine production

Group B streptococcus (GBS) is the most common cause of neonatal and obstetric sepsis and an increasingly important cause of septicemia in elderly subjects and immunocompromised patients. Our aim was to evaluate whether different genotypes of GBS may induce a different production of pro-inflammatory and anti-inflammatory cytokines. We used multilocus sequence typing to identify 71 clones isolated from asymptomatic healthy carriers and symptomatic individuals. All these clinical isolates were used to infect purified human monocytes. TNF-alpha, IL-6, IL-8 and IL-10 secretion was measured. Fifteen allelic sequence types (STs) were identified. The MLST (multilocus sequence typing) analysis grouped the bacteria into four different lineages (clonal cluster) and two of these were closely involved in the infection of symptomatic subjects: CC17 and CC19. Furthermore, CC17 and CC19 stimulated TNF-alpha, IL-6 and IL-8 production significantly more than the other lineages, while CC17 induced a decreased IL-10 production. These results suggest the existence of differences in immune response to infection with particular genotypes of GBS.

A Toll-like receptor 2-integrin beta3 complex senses bacterial lipopeptides via vitronectin

Toll-like receptor 2 (TLR2) initiates inflammation in response to bacterial lipopeptide (BLP). However, the molecular mechanisms enabling the detection of BLP by TLR2 are unknown. Here we investigated the interaction of BLP with human serum proteins and identified vitronectin as a BLP-recognition molecule. Vitronectin and its receptor, integrin beta(3), were required for BLP-induced TLR2-mediated activation of human monocytes. Furthermore, monocytes from patients with Glanzmann thrombasthenia, which lack integrin beta(3), were completely unresponsive to BLP. In addition, integrin beta(3) formed a complex with TLR2 and this complex dissociated after BLP stimulation. Notably, vitronectin and integrin beta(3) coordinated responses to other TLR2 agonists such as lipoteichoic acid and zymosan. Our findings show that vitronectin and integrin beta(3) contribute to the initiation of TLR2 responses.

Human CD34+ CD11b- cord blood stem cells generate in vitro a CD34- CD11b+ subset that is enriched in langerin+ Langerhans dendritic cell precursors

OBJECTIVE

We investigated whether the expression of CD11b on precursors derived in vitro from CD34+ hematopoietic stem cells was related to their ability to generate CD11b- and CD11b+ Langerhans dendritic cells (LC).

METHODS

Human CD34+ cells purified from cord blood were cultured with FLT3 ligand, thrombopoietin, and stem cell factor (FTS) for 2 weeks, analyzed, and sorted by FACS. Sorted fractions were cultured as above, or differentiated into LC with GM-CSF, IL-4, and TGF-beta1 (G4-TGF) for 6 days. The capacity of LC to internalize langerin and dextran was assessed.

RESULTS

Ex vivo, human CD34+ cells were CD11b- and mostly CLA+. After 2 weeks of culture with FTS, CD34- CLA- CD11b- and CD34- CLA- CD11b+ cells emerged. CD11b- cells were the most ancestral because they were the only ones to proliferate with FTS, and constantly generated CD11b+ cells. Both CD11b- and CD11b+ sorted cells generated E-cadherin+ langerin+ LC after incubation with G4-TGF. The former fraction contained 46% +/- 15% of E-cadherin+ and 10% +/- 5% of langerin+ cells, whereas in the latter fraction these values reached respectively 66% +/- 23% and 30% +/- 16% (mean +/- SD, n = 7, p < 0.056). Looking at functional properties, CD11b- and CD11b+ LC were similar in terms of langerin and dextran endocytosis. By contrast, only CD11b+ LC internalized fluorescent LPS.

CONCLUSION

Human CD34+ CD11b- cells differentiate in FTS culture into a CD34- CD11b- precursor that in turn generates CD34- CD11b+ cells. These cells are enriched in LC precursors compared to CD34- CD11b- cells. Both CD11b- and CD11b+ LC are generated in vitro, and each fraction may assume different functions in inflammatory situations.

Differential regulation of lipopolysaccharide and Gram-positive bacteria induced cytokine and chemokine production in macrophages by Galpha(i) proteins

Heterotrimeric G(i) proteins play a role in signalling activated by lipopolysaccharide (LPS), Staphylococcus aureus (SA) and group B streptococci (GBS), leading to production of inflammatory mediators. We hypothesized that genetic deletion of G(i) proteins would alter cytokine and chemokine production induced by LPS, SA and GBS stimulation. LPS-induced, heat-killed SA-induced and heat-killed GBS-induced cytokine and chemokine production in peritoneal macrophages from wild-type (WT), Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice were investigated. LPS induced production of tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), IL-10 and interferon-gamma-inducible protein-10 (IP-10); SA induced TNF-alpha, and IL-1beta production; and GBS induced TNF-alpha, IL-6, IL-1beta, macrophage inflammatory protein-1alpha (MIP-1alpha) and keratinocyte chemoattract (KC) production were all decreased (P < 0.05) in Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice compared with WT mice. In contrast to the role of G(i) proteins as a positive regulator of mediators, LPS-induced production of MIP-1alpha and granulocyte-macrophage colony-stimulating factor (GM-CSF) were increased in macrophages from Galpha(i1/3) (-/-) mice, and SA-induced MIP-1alpha production was increased in both groups of Galpha(i) protein-depleted mice. LPS-induced production of KC and IL-1beta, SA-induced production of GM-CSF, KC and IP-10, and GBS-induced production of IL-10, GM-CSF and IP-10 were unchanged in macrophages from Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice compared with WT mice. These data suggest that G(i2) and G(i1/3) proteins are both involved and differentially regulate murine inflammatory cytokine and chemokine production in response to both LPS and Gram-positive microbial stimuli.

Contribution of Toll-like receptors to the innate immune response to Gram-negative and Gram-positive bacteria

Innate recognition of bacteria is a key step in the activation of inflammation and coagulation, and it is dependent on pathogen-associated molecular pattern (PAMP) ligation to Toll-like receptors (TLRs) and CD14. The dominant receptors activated when cells encounter a whole bacterium, which express several PAMPs, are poorly defined. Herein, we have stimulated various human cells with prototypic Gram-negative and Gram-positive bacteria. Receptor-dependent responses to whole bacteria were assessed using both TLR-transfected cells and specific monoclonal antibodies against TLRs, MD-2, and CD14. Enterobacteria-activated leukocytes and endothelial cells in a TLR4/MD-2-dependent manner, most likely via lipopolysaccharide (LPS). TLR2 activation was observed with a high bacterial inoculum, and in epithelial cells expressing TLR2 but not TLR4. Pseudomonas aeruginosa stimulated cells by both TLR2 and TLR4/MD-2. Gram-positive bacteria activated cells only at high concentrations, in a partially TLR2-dependent but TLR4/MD-2-independent manner. Either TLR or CD14 neutralization blocked activation to all bacterial strains tested with the exception of some Gram-positive strains in whole blood in which partial inhibition was noted. This study identifies dominant TLRs involved in responses to whole bacteria. It also validates the concept that host cell activation by bacterial pathogens can be therapeutically reduced by anti-TLR4, -TLR2, and -CD14 mAbs.

Differential regulation of lipopolysaccharide and Gram-positive bacteria induced cytokine and chemokine production in splenocytes by Galphai proteins

Heterotrimeric Gi proteins play a role in lipopolysaccharide (LPS) and Staphylococcus aureus (SA) activated signaling leading to inflammatory mediator production. We hypothesized that genetic deletion of Gi proteins would alter cytokine and chemokine production induced by LPS and SA. LPS- and heat killed SA-induced cytokine and chemokine production in splenocytes from wild type (WT), Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice were investigated. LPS- or SA-induced production of TNFalpha, IL-6, IFNgamma, IL-12, IL-17, GM-CSF, MIP-1alpha, MCP-1, MIG and IP-10 were significantly increased (1.2 to 33 fold, p<0.05) in splenocytes harvested from Galpha(i2)(-/-) mice compared with WT mice. The effect of Galpha(i) protein depletion was remarkably isoform specific. In splenocytes from Galpha(i1/3) (-/-) mice relative to WT mice, SA-induced IL-6, IFNgamma, GM-CSF, and IP-10 levels were decreased (59% to 86%, p<0.05), whereas other LPS- or SA-stimulated cytokines and chemokines were not different relative to WT mice. LPS- and SA-induced production of KC were unchanged in both groups of the genetic deficient mice. Splenocytes from both Galpha(i2) (-/-) and Galpha(i1/3) (-/-) mice did not exhibit changes in TLR2 and TLR4 expression. Also analysis of splenic cellular composition by flow cytometry demonstrated an increase in splenic macrophages and reduced CD4 T cells in both Galpha(i2) (-/-) and Galpha(i1/3) (-/-) mice relative to WT mice. The disparate response of splenocytes from the Galpha(i2) (-/-) relative to Galpha(i1/3) (-/-) mice therefore cannot be attributed to major differences in spleen cellular composition. These data demonstrate that G(i2) and G(i1/3) proteins are both involved and differentially regulate splenocyte inflammatory cytokine and chemokine production in a highly Gi isoform specific manner in response to LPS and Gram-positive microbial stimuli.

Streptococcus pyogenes induces epithelial inflammatory responses through NF-kappaB/MAPK signaling pathways

Innate immunity involves a cascade of inflammatory events, resulting in the secretion of chemokines and cytokines to recruit mediator cells in adaptive immunity. To study epithelial inflammatory responses initiated by Streptococcus pyogenes infection, we investigated chemotaxis ability in the supernatant of infected human respiratory epithelial HEp-2 cells. Our results showed that these supernatants showed significantly increased ability to attract monocytes, implying the release of inflammatory chemoattractants into the medium. Expression of interleukin (IL)-8 and IL-6 in HEp-2 cells was significantly increased at both the mRNA and protein levels after infection with S. pyogenes. Electrophoretic mobility shift and reporter-gene assays demonstrated that the transcription factors NF-kappaB and AP-1, regulated by mitogen-activated protein (MAP) kinase, were activated after streptococcal infection. The increases in mRNAs for IL-8 and IL-6 were abrogated by addition of NF-kappaB and MAP kinase inhibitors, suggesting that the upregulation of IL-8 and IL-6 is mediated through NF-kappaB and MAP kinase signaling pathways. Taken together, our results indicate that S. pyogenes infection of epithelial cells induces the secretion of pro-inflammatory chemokines/cytokines through activation of NF-kappaB and MAP kinase signaling pathways. These early innate responses initiated by S. pyogenes-infected respiratory epithelial cells may recruit immune cells to the airway and induce inflammation.

Responses of microglia in vitro to the gram-positive bacterial component, lipoteichoic acid

An increase in incidence and severity of gram-positive infections has emerged in the past decade. In this regard, attention has been focused recently on immune responses of microglial cells in the central nervous system to gram-positive bacteria. The underlying immunological and cellular events in microglial activation induced by specific bacterial toxin of gram-positive bacteria, however, have not yet been clarified fully. This study reports that a simple cell wall product, lipoteichoic acid (LTA), derived from gram-positive bacteria (Staphylococcus aureus) could trigger microglial activation in vitro. Microglia challenged with LTA showed intense ruffling of plasma membrane in the form of lamellipodia or rounded up forming cell aggregates. MTT assay and Western blot analysis with anti-proliferating cell nuclear antigen antibody showed a significant microglial proliferation that may be induced at the later phases of LTA treatment with low doses but at the early period with a high dose. Concentrated LTA also caused apoptotic death of cultured microglia showing fragmented nuclei and increased expression of annexin V or caspase 3. In response to LTA, isolated microglia increased the expression of inducible nitric oxide synthase and major histocompatibility complex class II antigen. Microglial LTA receptors such as CD14 molecule, complement receptor type 3, and macrophage scavenger receptor were upregulated concurrently. In conclusion, staphylococcal LTA can exert an immunomodulatory effect on microglial morphology, cell cycle, and immunomolecules, including its receptors.

Signal transduction pathways of nitric oxide release in primary microglial culture challenged with gram-positive bacterial constituent, lipoteichoic acid

Between one-third and one-half of all cases of sepsis are known to be caused by gram-positive microorganisms through the cell wall component, e.g. lipoteichoic acid (LTA). Gram-positive bacteria are also known to induce encephalomyelitis and meningeal inflammation, and enhance the production of nitric oxide (NO) via expression of inducible nitric oxide synthase (iNOS) in murine tissue macrophages. It remains to be explored if LTA could activate microglia considered to be resident brain macrophages. We report here that LTA derived from gram-positive bacteria (Staphylococcus aureus) significantly induces NO release and iNOS expression in primary microglia. LTA-induced NO accumulation was detected at 2 h in microglial culture and was significantly attenuated by pretreatment with anti-CD14, complement receptor type 3 (CR3) or scavenger receptor (SR) antibodies. LTA activated mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase, p38 MAPK or c-Jun N-terminal kinase in cultured microglia. LTA-elicited microglial NO production was also drastically suppressed by SB203580 (p38 MAPK inhibitor) or pyrrolidine dithiocarbamate (an inhibitor of nuclear factor kappaB), indicating that p38 MAPK and nuclear factor kappaB were involved in microglial NO release after LTA challenge. These results suggest that gram-positive bacterial product such as LTA can activate microglia to release NO via the signal transduction pathway involving multiple LTA receptors (e.g. CD14, CR3 or SR), p38 MAPK and nuclear factor kappaB. The in vivo study further confirmed that administered intracerebrally LTA induced considerable noticeable iNOS, phospho-IkappaB and phospho-p38 MAPK expression in microglia/macrophages.

C3 binding glycoprotein from Cuscuta europea induced different cytokine profiles from human PBMC compared to other plant and bacterial immunomodulators

The immunomodulatory properties of bioactive agents include the ability to induce cytokine production by the activated target cell. The effect of immunomodulatory C3 binding glycoprotein isolated from Cuscuta europea on the induction of human PBMC cytokine synthesis and the cell viability was investigated. Isolated PBMC from healthy donors were cultured for 24 h with C3bgp. We also studied the influence of C3bgp on the cytokine production in LPS, PHA, PWM and Dex treated PBMC. The quantitative determination of TNF-alpha, IL-12, IL-6 and IL-10 was performed in culture supernatant by ELISA. Results obtained demonstrated that C3bgp induced proinflammatory and immunoregulatory cytokine production, in the highest degree IL-12, followed by IL-6 and in lower degree TNF-alpha. IL-12 quantity was significantly increased in C3bgp stimulated cultures in comparison with LPS, PHA and PWM stimulated PBMC. C3bgp also increased IL-12 in PHA or PWM stimulated cultures, but not in LPS stimulated culture. C3bgp significantly increased IL-6 production compared to the PHA and PWM but not to LPS stimulation. On the other side, C3bgp inhibited IL-10 production after LPS, PHA and PWM stimulation. Cell viability in C3bgp stimulated cultures retained on the same level from 72 to 120 h of culturing, in contrast to LPS and PHA stimulated cultures. Based on the results presented, we conclude that the C3bgp exhibited immunomodulatory properties on the human PBMC. The ability of PDTC and Dex to down-regulate the effect of C3bgp on the proinflammatory cytokine production suggests that a part of the mechanism of action of C3bgp is mediated through NF-kB signal transduction pathway.

Lipopolysaccharide- and gram-positive bacteria-induced cellular inflammatory responses: role of heterotrimeric Galpha(i) proteins

Heterotrimeric G(i) proteins may play a role in lipopolysaccharide (LPS)-activated signaling through Toll-like receptor 4 (TLR4), leading to inflammatory mediator production. Although LPS is a TLR4 ligand, the gram-positive bacterium Staphylococcus aureus (SA) is a TLR2 ligand, and group B streptococci (GBS) are neither TLR2 nor TLR4 ligands but are MyD88 dependent. We hypothesized that genetic deletion of G(i) proteins would alter mediator production induced by LPS and gram-positive bacterial stimulation. We examined genetic deletion of Galpha(i2) or Galpha(i1/3) protein in Galpha(i2)-knockout (Galpha(i2)-/-) or Galpha(i1/3)-knockout (Galpha(i1/3)-/-) mice. LPS-, heat-killed SA-, or GBS-induced mediator production in splenocytes or peritoneal macrophages (MPhi) was investigated. There were significant increases in LPS-, SA-, and GBS-induced production of TNF-alpha and IFN-gamma in splenocytes from Galpha(i2)-/- mice compared with wild-type (WT) mice. Also, LPS-induced TNF-alpha was increased in splenocytes from Galpha(i1/3)-/- mice. In contrast to splenocytes, LPS-, SA-, and GBS-induced TNF-alpha, IL-10, and thromboxane B(2) (TxB(2)) production was decreased in MPhi harvested from Galpha(i2)-/- mice. Also, LPS-induced production of IL-10 and TxB(2) was decreased in MPhi from Galpha(i1/3)-/- mice. In subsequent in vivo studies, TNF-alpha levels after LPS challenge were significantly greater in Galpha(i2)-/- mice than in WT mice. Also, myeloperoxidase activity, a marker of tissue neutrophil infiltration, was significantly increased in the gut and lung of LPS-treated Galpha(i2)-/- mice compared with WT mice. These data suggest that G(i) proteins differentially regulate murine TLR-mediated inflammatory cytokine production in a cell-specific manner in response to both LPS and gram-positive microbial stimuli.

Interleukin-18 is an essential element in host resistance to experimental group B streptococcal disease in neonates

Previous studies demonstrated that interleukin-12 (IL-12)-dependent gamma interferon (IFN-gamma) responses have a major role in restricting in vivo bacterial growth during infection of mice with group B streptococci (GBS), important human pathogens. Like IL-12, IL-18 is a potent IFN-gamma inducer. The role of IL-18 in experimental GBS infection was investigated here. Significant elevations of IL-18 levels over baseline values were detected in plasma samples from neonatal mice rendered septic with GBS. Neutralization of IL-18 significantly increased mortality and bacterial burden (P < 0.05). In contrast, administration of recombinant IL-18 (rIL-18) before or after GBS challenge remarkably improved survival and decreased blood colony counts, in association with increased IFN-gamma production by spleen cells. The beneficial effects of rIL-18 were counteracted by administration of neutralizing anti-IFN-gamma monoclonal antibodies, indicating that the effects of IL-18 were mediated by IFN-gamma. Finally, low rIL-18 doses that had no effect of their own on bacterial burden could act in synergy with rIL-12 to protect neonatal mice during GBS infection. Collectively, our data indicate that IL-18 responses have an important role in host defenses against GBS and that rIL-18 may be useful in alternative strategies to treat neonatal GBS disease.

Critical role of the complement system in group B streptococcus-induced tumor necrosis factor alpha release

Group B Streptococcus (GBS) is a major cause of newborn sepsis and meningitis and induces systemic release of tumor necrosis factor alpha (TNF-alpha), believed to play a role in morbidity and mortality. While previous studies have shown that GBS can induce TNF-alpha release from monocytes and macrophages, little is known about the potential modulating effect of plasma or serum on GBS-induced TNF-alpha release, and there are conflicting reports as to the host receptors involved. In a human whole-blood assay system, GBS type III COH-1 potently induced substantial monocyte TNF-alpha release in adult peripheral blood and, due to a higher concentration of monocytes, 10-fold-greater TNF-alpha release in newborn cord blood. Remarkably, GBS-induced TNF-alpha release from human monocytes was enhanced approximately 1000-fold by heat-labile serum components. Experiments employing C2-, C3-, or C7-depleted serum demonstrated that C3 activation via the alternative pathway is crucial for potent GBS-induced TNF-alpha release. Accordingly, whole blood from C3-deficient mice demonstrated significantly reduced GBS-induced TNF-alpha release. Preincubation with human serum enhanced the TNF-alpha-inducing activity of GBS in a C3- and factor B-dependent manner, implying deposition of complement components via the alternative pathway. GBS-induced TNF-alpha release was inhibited by monoclonal antibodies directed against each of the components of CR3 and CR4: the common integrin beta subunit CD18 and the alpha subunits CD11b (of CR3) and CD11c (of CR4). Blood derived from CR3 (CD11b/CD18)-deficient mice demonstrated a markedly diminished TNF-alpha response to GBS. We conclude that the ability of plasma and serum to greatly amplify GBS-induced TNF-alpha release reflects the activity of the alternative complement pathway that deposits fragments on GBS and thereby enhances CR3- and CR4-mediated monocyte activation.

Up-regulation of ICAM-1, CD11a/CD18 and CD11c/CD18 on human THP-1 monocytes stimulated by Streptococcus suis serotype 2

Streptococcus suis serotype 2 is known to be a major pathogen of swine, causing mainly meningitis. It is also a zoonotic agent leading predominantly to meningitis in humans working in close contact with pigs. In this study, we investigated the ability of S. suis to up-regulate the expression of adhesion molecules involved in inflammation, using an enzyme-linked immunosorbent assay. S. suis serotype 2 stimulated the up-regulation of the expression of intercellular adhesion molecule-1 (ICAM-1, CD54), CD11a/CD18 and CD11c/CD18 on human THP-1 monocytes, but did not change that of ICAM-1, vascular cell adhesion molecule-1 (VCAM-1, CD106) and E-selectin (CD62E) on human endothelial cells. The up-regulation of adhesion molecules was time- and bacterial concentration-dependent, and cell wall components were largely responsible for such stimulation. To a lesser extent, purified haemolysin of S. suis also stimulated adhesion molecule expression. Stimulation of monocytes with strains of different origin showed that there was no clear tendency for human strains to induce a higher expression of adhesion molecules than strains from diseased pigs. Finally, monocytes stimulated with S. suis also showed an increase in adherence to endothelial cells. Hence, S. suis is capable of up-regulating important adhesion molecules involved in inflammation, which may result in an increased leucocyte recruitment into sites of infection, thus providing a possible mechanism for some of the inflammatory features of meningitis caused by this pathogen.

Receptors, mediators, and mechanisms involved in bacterial sepsis and septic shock

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

Involvement of G(i) proteins and Src tyrosine kinase in TNFalpha production induced by lipopolysaccharide, group B Streptococci and Staphylococcus aureus

Previous studies have suggested that heterotrimeric G(i) proteins, Src tyrosine kinase and phosphatidylinositol-3 kinase (PI3 Kinase) are involved in signaling events induced by lipopolysaccharide (LPS) leading to pro-inflammatory cytokines gene expression. To investigate the involvement of these mediators in Gram-positive bacteria induced pro-inflammatory cytokine expression, LPS (10 ng/ml), heat killed group B Streptococci (GBS 1 microg/ml) and Staphylococcus aureus (SA 10 microg/ml) were used to induce TNFalpha production in the murine J774A.1 macrophage (MØ) cell line and human promonocytic THP-1 cell line. Pertussis toxin (PTx, 1 microg/ml), an inhibitor of G(i) protein; pyrazolopyrimidine-2 (PP2, 1 or 25 microM), a Src tyrosine kinase inhibitor; and LY294002 (100 nM), an inhibitor of PI3 Kinase were used to examine the involvement of G(i), Src tyrosine kinase and PI3 Kinase, respectively, in TNFalpha production. In J774A.1 cells, pretreatment with PTx and PP2 attenuated TNFalpha production induced by LPS (60+/-9% and 81+/-11% inhibition, n=3, p<0.05, respectively), GBS (95+/-1% and 80+/-6% inhibition, n=3, p<0.05, respectively) and SA (51+/-18% and 68+/-16% inhibition, n=4, p<0.05, respectively). However, pretreatment with LY 294002 inhibited LPS induced TNFalpha production (82+/-13% inhibition, n=3, p<0.05), but did not inhibit GBS or SA induced TNFalpha production. In THP-1 cells, pretreatment with PTx, PP2 and LY 294002 inhibited TNFalpha production induced by LPS (84+/-3%, 59+/-12% and 84+/-4% inhibition, n=3, p<0.05, respectively) and SA (56+/-7%, 87+/-1% and 35+/-6% inhibition, n=3, p<0.05, respectively). These data support our hypothesis that G(i)-coupled and Src tyrosine kinase-coupled signaling pathways are involved in both Gram-negative and Gram-positive bacteria induced pro-inflammatory cytokine expression. However, unlike LPS, involvement of PI3 Kinase in Gram-positive bacteria induced signaling pathways are species dependent.

Infection by Streptococcus pyogenes induces the receptor activator of NF-kappaB ligand expression in mouse osteoblastic cells

Group A Streptococcus pyogenes is known to induce nongonococcal septic arthritis in addition to pharyngitis, scarlet fever, and poststreptococcal sequelae. However, little is known about the interaction between S. pyogenes and bone cells. We report here that S. pyogenes strain JRS4 (M6) attached to and invaded mouse primary osteoblasts. Reverse transcription-PCR demonstrated that S. pyogenes infection of osteoblasts stimulated expression of mRNA for the receptor activator of NF-kappaB ligand (RANKL). Western blot analysis followed by ligand precipitation with the receptor activator of NF-kappaB receptor showed that there was an increase in RANKL protein in infected osteoblasts. Production of interleukin-6 was also stimulated, but no production of interleukin-1beta or tumor necrosis factor alpha was observed. Stimulation of RANKL production was not observed in osteoblasts stimulated with heat-inactivated S. pyogenes, suggesting that an active interaction of S. pyogenes with osteoblasts is essential for this phenomenon. A Western blot analysis performed with antibodies specific for phosphorylated signal transduction proteins demonstrated that S. pyogenes infection induces phosphorylation of p38 mitogen-activated protein kinase. A specific inhibitor of this kinase, SB203580, inhibited RANKL production by infected osteoblasts. These results suggest that infection of osteoblasts by S. pyogenes stimulates RANKL production and may trigger bone destruction in infected bone tissue.

Inflammatory cytokine (interleukin 6 and tumour necrosis factor alpha) release in a human whole blood system in response to Streptococcus pneumoniae serotype 14 and its capsular polysaccharide

Gram-positive bacteria, which lack lipopolysaccharide (LPS), produce a septic-shock-like condition, accompanied by release of pro-inflammatory cytokines. Various components of the bacteria may be responsible for this. We stimulated a whole blood system with heat-inactivated Streptococcus pneumoniae serotype 14 (S14) bacteria, with pneumococcal S14 capsular polysaccharide (PPS S14) and with PPS S14 coated on to latex beads, to compare interleukin 6 (IL-6) and tumour necrosis factor alpha (TNFalpha) production over a six hour period, to ascertain the contribution of PPS to the inflammatory response. This was compared with the response to LPS. After sonication of the bacteria, their PPS content was estimated by an enzyme-linked immunoabsorbent assay, to compare this with the concentration of free PPS needed to generate cytokine release. The whole bacteria elicited a much larger cytokine response than the equivalent amount of PPS alone, whereas the PPS-coated beads gave minimal response. The different cytokine responses to PPS and LPS suggest that there are differences in the receptors and/or signalling pathways for Gram-negative and Gram-positive bacteria. We conclude that the estimated amount of PPS in the bacteria is not enough to account for the large cytokine response we observed. Since PPS could not be shown to contribute significantly to cytokine induction, specific antibodies to PPS would not play any significant role in combating cytokine release associated with pneumococcal infection and possible septic shock. This needs to be considered in production of future vaccines.

Cellular Activation, Phagocytosis, and Bactericidal Activity Against Group B Streptococcus Involve Parallel Myeloid Differentiation Factor 88-Dependent and Independent Signaling Pathways

Group B streptococci (GBS) vigorously activate inflammatory responses. We reported previously that a secreted GBS "factor" activates phagocytes via Toll-like receptor (TLR)2 and TLR6, but that GBS cell walls activate cells independently of these receptors. We hypothesized that the phagocytic immune functions in response to GBS, such as inflammation, uptake, and elimination of bacteria, occur through a coordinated engagement of TLRs, along with the coreceptors CD14 and CD11b/CD18. Using various knockout mice we show that GBS-induced activation of p38 and NF-kappaB depends upon the expression of the cytoplasmic TLR adapter protein, myeloid differentiation factor 88 (MyD88), but not TLR2 and/or TLR4. Macrophages with deletions of CD14 and complement receptor 3 had a normal cytokine response to whole bacteria, although the response to GBS factor was abrogated in CD14-null cells. The intracellular formation of bactericidal oxygen species proved to be MyD88 dependent; however, uptake of GBS, a prerequisite for intracellular killing by O(2) radicals, occurred independently of MyD88. While deletion of complement receptor 3 greatly diminished the uptake of opsonized GBS, it did not affect the formation of bactericidal O(2) radicals or inflammatory signaling intermediates. We conclude that the inflammatory, bactericidal, and phagocytic responses to GBS occur via parallel but independent processes.

Mitogen-activated protein kinases and NF-kappa B are involved in TNF-alpha responses to group B streptococci

TNF-alpha is a mediator of lethality in experimental infections by group B streptococcus (GBS), an important human pathogen. Little is known of signal transduction pathways involved in GBS-induced TNF-alpha production. Here we investigate the role of mitogen-activated protein kinases (MAPKs) and NF-kappa B in TNF-alpha production by human monocytes stimulated with GBS or LPS, used as a positive control. Western blot analysis of cell lysates indicates that extracellular signal-regulated kinase 1/2 (ERK 1/2), p38, and c-Jun N-terminal kinase MAPKs, as well as I kappa B alpha, became phosphorylated, and hence activated, in both LPS- and GBS-stimulated monocytes. The kinetics of these phosphorylation events, as well as those of TNF-alpha production, were delayed by 30-60 min in GBS-stimulated, relative to LPS-stimulated, monocytes. Selective inhibitors of ERK 1/2 (PD98059 or U0126), p38 (SB203580), or NF-kappa B (caffeic acid phenetyl ester (CAPE)) could all significantly reduce TNF-alpha production, although none of the inhibitors used alone was able to completely prevent TNF-alpha release. However, this was completely blocked by combinations of the inhibitors, including PD98059-SB203580, PD98059-CAPE, or SB203580-CAPE combinations, in both LPS- and GBS-stimulated monocytes. In conclusion, our data indicate that the simultaneous activation of multiple pathways, including NF-kappa B, ERK 1/2, and p38 MAPKs, is required to induce maximal TNF-alpha production. Accordingly, in septic shock caused by either GBS or Gram-negative bacteria, complete inhibition of TNF-alpha release may require treatment with drugs or drug combinations capable of inhibiting multiple activation pathways.

Activation of human NK cells by staphylococci and lactobacilli requires cell contact-dependent costimulation by autologous monocytes

NK cells are instrumental in innate immune responses, in particular for the early production of gamma interferon (IFN-gamma) and other cytokines necessary to control certain bacterial, parasitic, and viral infections. NK cell-mediated effector functions are controlled by a fine balance between distinct receptors mediating activating and inhibitory signals; however, little is known about activating receptors on NK cells and their corresponding ligands. Several studies have shown that commensal lactobacilli isolated from the human gastrointestinal tract activate human mononuclear cells and are potent inducers of IFN-gamma and monocyte-derived interleukin 12 (IL-12). NK cell activation was shown for Lactobacillus johnsonii La1. In this study the cellular mechanisms of in vitro NK cell activation by gram-positive bacteria were analyzed. Staphylococcus aureus- and L. johnsonii La1-mediated activation of CD3(-) CD16(+) CD56(+) human peripheral blood NK cells, including expression of the activation antigen CD69 and secretion of IFN-gamma, required cell contact-dependent costimulation by autologous monocytes. S. aureus- and L. johnsonii-preactivated monocytes retained their capacity to induce NK cell activation. In contrast, cytokine-primed monocytes completely failed to induce NK cell activation unless bacteria were present. This suggests that phagocytosis of bacteria provided additional coactivation signals on accessory cells that may differ from those induced by tumor necrosis factor and IFN-gamma. Blocking of costimulatory molecules by B7.1, B7.2, and IL-12 but not CD14 monoclonal antibodies inhibited S. aureus- and L. johnsonii-induced effector function of NK cells. Our data suggest an important role for accessory cell-derived signals in the process of NK cell activation by gram-positive bacteria.

Cytokine expression of cord and adult blood mononuclear cells in response to Streptococcus agalactiae

Neonatal bacterial sepsis is often characterized by a fulminant clinical course and highly elevated plasma levels of proinflammatory cytokines. To evaluate in vitro activation of the neonatal immune system by specific infectious stimuli, cord blood cells from healthy neonates were examined for expression of tumor necrosis factor-alpha (TNF-alpha), IL-1beta, IL-6, and IL-8 in response to Streptococcus agalactiae (GBS), lipopolysaccharide (LPS), and lipoteichoic acid (LTA). Cytokine-expression was compared in mononuclear cells from cord and adult peripheral blood. TNF-alpha and IL-6 levels in the supernatant of cord blood cell cultures were significantly higher after stimulation with heat-killed GBS (10(7)/mL) than with LPS (2 microg/mL) or LTA (2 microg/mL) (TNF-alpha: 2215 versus 267.5 versus 40 pg/mL, p = 0.001; IL-6: 9667 versus 4909 versus 919 pg/mL, p = 0.006). mRNA expression of TNF-alpha, IL-1beta, IL-6, and IL-8 was equally pronounced after stimulation with either GBS, LPS, or LTA in cord or adult blood cells at various times. A MAb directed against the monocyte receptor molecule CD14 did not inhibit the release of cytokines in cord blood mononuclear cells after stimulation with GBS. In summary, activation of cord blood cells by infectious stimuli is comparable to the adult immune response in terms of expression of proinflammatory cytokines. GBS in particular proves to be a potent activator of the neonatal immune system when compared with LPS and LTA. CD14 seems not to be a crucial molecule for activation of cord blood cells by GBS.

Elevated levels of lipopolysaccharide-binding protein and soluble CD14 in plasma in neonatal early-onset sepsis

No data on lipopolysaccharide-binding protein (LBP) in newborns with sepsis have been available up to now. We therefore determined levels of LBP and soluble CD14 (sCD14) in plasma of healthy and septic neonates in order to evaluate their potential diagnostic role. The study included prospectively collected patient samples of two recently published studies on cytokine expression in neonatal sepsis. Twenty-nine septic patients were enrolled in the present analysis. Samples--either cord blood or peripheral blood--from patients admitted within the first 24 h of life for suspicion of sepsis and cord blood samples of a control group of 40 healthy mature infants delivered spontaneously were analyzed. For seven patients of the septic group, a second sample collected between 24 and 48 h of life was available. Levels of sCD14 and LBP in plasma were determined by an enzyme immunoassay using recombinant CD14 and LBP as standards. LBP and sCD14 were correlated to cytokine plasma levels. In septic neonates, LBP (median, 36.6 versus 7.8 microg/ml; P < 0.001) and sCD14 (median, 0.42 versus 0.28 microg/ml; P < 0.001) levels were highly elevated when compared to those of healthy neonates and strongly correlated to granulocyte colony-stimulating factor (G-CSF), interleukin-1beta (IL-1beta), IL-6, and IL-8 levels. LBP levels in septic neonates analyzed between 24 and 48 h of life even increased when compared to samples obtained at or shortly after delivery (median, 36.6 versus 60 microg/ml; P = 0.038). In summary, levels of LBP in plasma of neonates with early-onset sepsis are significantly elevated; the elevated plasma levels seem to persist for more than 24 h, which could provide the clinician with a prolonged time period to identify the newborn with bacterial sepsis.

Leukocyte integrin Mac-1 recruits toll/interleukin-1 receptor superfamily signaling intermediates to modulate NF-kappaB activity

The leukocyte integrin Mac-1 (alphaMbeta2, CD11b/CD18) regulates important cell functions in inflammation, including adhesion, phagocytosis, and oxidative burst. Deficiency of Mac-1 reduces vessel wall inflammation and neointimal thickening after murine carotid artery injury. Although Mac-1 has been implicated in modulating AP-1 and NF-kappaB activity, the signal transduction pathways involved are undefined. cDNA array analysis of Mac-1-clustered compared with -nonclustered monocytic THP-1 cells showed increased expression of the signal transducer TRAF6 (TNF receptor-associated factor 6), leading us to consider the possibility that Mac-1 used a Toll/IL-1 receptor family-like signaling pathway. Mac-1-dependent activation of NF-kappaB was potentiated by wild-type, and attenuated by dominant negative, TRAF6- and TGF-beta-activated kinase (TAK1) constructs. IRAK1 (IL-1 receptor associated kinase), a kinase immediately upstream of TRAF6, coimmunoprecipitated with Mac-1. Taken together, these observations indicate that Mac-1 recruits a Toll/IL-1 receptor family-like cascade to modulate NF-kappaB activity. This represents a new pathway for integrin-dependent modulation of gene expression.

Different cytokine expression in cord blood mononuclear cells after stimulation with neonatal sepsis or colonizing strains of Streptococcus agalactiae

Streptococcus agalactiae (group B streptococcus, GBS) is the major pathogen of neonatal sepsis. In some newborns, GBS sepsis may have a severe course, including septic shock with a high mortality rate, whereas other newborns are colonized with GBS on their surfaces without any clinical signs of bacterial infection. The reason for this discrepancy is far from clear. We sought, in this study, to compare cytokine expression in cord blood mononuclear cells after stimulation with GBS strains isolated from newborns with sepsis, and strains isolated from newborns without any symptoms of invasive infection. Cord blood mononuclear cells were incubated with either heat-killed bacteria of different strains or lipopolysaccharide, respectively. After 6 and 24 h, cells were harvested and cytokine mRNA-expression was analyzed by reverse-transcriptase PCR. Likewise, supernatants were tested for IL-6 and tumor necrosis factor-alpha concentrations by enzyme immunoassay. When comparing IL-6 and tumor necrosis factor-alpha secretion, there were significantly higher IL-6 levels after stimulation with sepsis than with colonizing isolates. Likewise, mRNA expression of IL-6, IL-1 beta, and IL-12p40 was significantly higher after stimulation with sepsis isolates. This was also true when normalizing to cytokine expression after stimulation with lipopolysaccharide. These findings indicate that the different clinical pictures in response to GBS, either septic infection or colonization, might reflect strain-specific properties. If the respective characteristics can be defined, it might become possible to distinguish by molecular methods potentially "dangerous" from "harmless" strains. Moreover, our findings underline the essential role of these cytokines in the pathogenesis of neonatal GBS sepsis.

Involvement of CD14 and beta2-integrins in activating cells with soluble and particulate lipopolysaccharides and mannuronic acid polymers

Lipopolysaccharide (LPS) and related bacterial products can be recognized by host inflammatory cells in a particulate, bacterium-bound form, as well as in various soluble, released forms. In the present study we have compared the mechanisms used by LPS, detoxified LPS (DLPS), and mannuronic acid polymers (M-polymers), in solution or covalently linked to particles, in stimulating monocytes to tumor necrosis factor (TNF) production. The addition of recombinant LPS binding protein (LBP) and/or soluble CD14 (sCD14) enhanced the production of TNF from monocytes stimulated with soluble LPS, DLPS, or M-polymer, but did not affect the response to M-polymer or DLPS attached to particles. Treatment of monocytes with antibody to CD14, CD18, or CD11b showed that CD14, but not CR3 (CD11b/CD18), mediated monocyte TNF production in response to the soluble antigens. In contrast, anti-CD14, anti-CD11b and anti-CD18 monoclonal antibodies all inhibited the response to the particulate stimuli. On the other hand, B975, a synthetic analog of Rhodobacter capsulatus lipid A, completely abrogated the monocyte TNF response induced by LPS but did not affect the TNF induction by DLPS or M-polymer, either in soluble or particulate forms. These data demonstrate that the engagement of immune receptors by bacterial products such as LPS, DLPS, and M-polymer is dependent upon the presentation form of their constituent carbohydrates, and that factors such as aggregation state, acylation, carbohydrate chain length, and solid versus liquid phase of bacterial ligands influence the mechanisms used by cells in mediating proinflammatory responses.