Activation of human dendritic cells by the PorA protein of Neisseria meningitidis

Vibrio cholerae Porin OmpU Activates Dendritic Cells via TLR2 and the NLRP3 Inflammasome

OmpU is one of the major porins of Vibrio cholerae, a Gram-negative human pathogen. Previously, we showed that OmpU stimulates host monocytes and macrophages and induces the production of proinflammatory mediators via activation of the Toll-like receptor 1/2 (TLR1/2)-MyD88-dependent pathways. In the present study, we show that OmpU activates murine dendritic cells (DCs) via activation of the TLR2-mediated pathway and the NLRP3 inflammasome, leading to the production of proinflammatory cytokines and DC maturation. Our data reveal that although TLR2 plays an important role in providing both priming and the activation signal for the NLRP3 inflammasome in OmpU-activated DCs, OmpU is capable of activating the NLRP3 inflammasome, even in the absence of TLR2, if a priming signal is given. Furthermore, we show that the OmpU-mediated interleukin-1β (IL-1β) production in DCs depends on calcium flux and mitochondrial reactive oxygen species (mitoROS) generation. Interestingly, both OmpU translocation to the mitochondria of DCs as well as calcium signaling contribute to mitoROS production and prompt NLRP3 inflammasome activation. We also demonstrate that OmpU induces downstream signaling via activation of phosphoinositide-3-kinase (PI3K)-AKT, protein kinase C (PKC), mitogen-activated protein kinases (MAPKs), and transcription factor NF-κB. Furthermore, our data reveal that OmpU-mediated activation of TLR2 induces signaling via PKC, MAPKs p38 and extracellular signal-regulated kinase (ERK), and transcription factor NF-κB; however, PI3K and MAPK Jun N-terminal protein kinase (JNK) are activated in TLR2 independent manner.

The Host-Pathogen Interactions and Epicellular Lifestyle of Neisseria meningitidis

Neisseria meningitidis is a gram-negative diplococcus and a transient commensal of the human nasopharynx. It shares and competes for this niche with a number of other Neisseria species including N. lactamica, N. cinerea and N. mucosa. Unlike these other members of the genus, N. meningitidis may become invasive, crossing the epithelium of the nasopharynx and entering the bloodstream, where it rapidly proliferates causing a syndrome known as Invasive Meningococcal Disease (IMD). IMD progresses rapidly to cause septic shock and meningitis and is often fatal despite aggressive antibiotic therapy. While many of the ways in which meningococci survive in the host environment have been well studied, recent insights into the interactions between N. meningitidis and the epithelial, serum, and endothelial environments have expanded our understanding of how IMD develops. This review seeks to incorporate recent work into the established model of pathogenesis. In particular, we focus on the competition that N. meningitidis faces in the nasopharynx from other Neisseria species, and how the genetic diversity of the meningococcus contributes to the wide range of inflammatory and pathogenic potentials observed among different lineages.

Modulation of host cellular responses by gram-negative bacterial porins

The outer membrane of a gram-negative bacteria encapsulates the plasma membrane thereby protecting it from the harsh external environment. This membrane acts as a sieving barrier due to the presence of special membrane-spanning proteins called "porins." These porins are β-barrel channel proteins that allow the passive transport of hydrophilic molecules and are impermeable to large and charged molecules. Many porins form trimers in the outer membrane. They are abundantly present on the bacterial surface and therefore play various significant roles in the host-bacteria interactions. These include the roles of porins in the adhesion and virulence mechanisms necessary for the pathogenesis, along with providing resistance to the bacteria against the antimicrobial substances. They also act as the receptors for phage and complement proteins and are involved in modulating the host cellular responses. In addition, the potential use of porins as adjuvants, vaccine candidates, therapeutic targets, and biomarkers is now being exploited. In this review, we focus briefly on the structure of the porins along with their important functions and roles in the host-bacteria interactions.

Adjuvant effects elicited by novel oligosaccharide variants of detoxified meningococcal lipopolysaccharides on Neisseria meningitidis recombinant PorA protein: a comparison in mice

Neisseria meningitidis lipopolysaccharide (LPS) has adjuvant properties that can be exploited to assist vaccine immunogenicity. The modified penta-acylated LPS retains the adjuvant properties of hexa-acylated LPS but has a reduced toxicity profile. In this study we investigated whether two modified glycoform structures (LgtE and IcsB) of detoxified penta-acylated LPS exhibited differential adjuvant properties when formulated as native outer membrane vesicles (nOMVs) as compared to the previously described LgtB variant. Detoxified penta-acylated LPS was obtained by disruption of the lpxL1 gene (LpxL1 LPS), and three different glycoforms were obtained by disruption of the lgtB, lgtE or icsB genes respectively. Mice (mus musculus) were immunized with a recombinant PorA P1.7-2,4 (rPorA) protein co-administered with different nOMVs (containing a different PorA serosubtype P1.7,16), each of which expressed one of the three penta-acylated LPS glycoforms. All nOMVs induced IgG responses against the rPorA, but the nOMVs containing the penta-acylated LgtB-LpxL1 LPS glycoform induced significantly greater bactericidal activity compared to the other nOMVs or when the adjuvant was Alhydrogel. Compared to LgtE or IcsB LPS glycoforms, these data support the use of nOMVs containing detoxified, modified LgtB-LpxL1 LPS as a potential adjuvant for future meningococcal protein vaccines.

Disease-associated Neisseria meningitidis isolates inhibit wound repair in respiratory epithelial cells in a type IV pilus-independent manner

Neisseria meningitidis is the causative agent of meningococcal disease. Onset of meningococcal disease can be extremely rapid and can kill within a matter of hours. However, although a much-feared pathogen, Neisseria meningitidis is frequently found in the nasopharyngeal mucosae of healthy carriers. The bacterial factors that distinguish disease- from carriage-associated meningococci are incompletely understood. Evidence suggesting that disruptions to the nasopharynx may increase the risk of acquiring meningococcal disease led us to evaluate the ability of disease- and carriage-associated meningococcal isolates to inhibit cell migration, using an in vitro assay for wound repair. We found that disease-associated isolates in our collection inhibited wound closure, while carriage-associated isolates were more variable, with many isolates not inhibiting wound repair at all. For isolates selected for further study, we found that actin morphology, such as presence of lamellipodia, correlated with cell migration. We demonstrated that multiple meningococcal virulence factors, including the type IV pili, are dispensable for inhibition of wound repair. Inhibition of wound repair was also shown to be an active process, i.e., requiring live bacteria undergoing active protein synthesis.

Saccharomyces boulardii and Bacillus subtilis B10 modulate TLRs mediated signaling to induce immunity by chicken BMDCs

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that play a critical role to activate immune response. They may be targeted for immunomodulation by microbes, including probiotics. In this study, chicken bone marrow dendrite cells (chi-BMDCs) were stimulated with lipopolysachride (LPS), Saccharomyces boulardii (Sb), Bacillus subtilis B10 (Bs), co-culture of Sb + Bs and phosphate buffer saline (PBS) as a control group (Ctr) at 3, 6, and 12 h intervals. Results revealed that treatment groups modulated the phenotype and biological functions of chi-BMDCs. Scan electron microscopy showed attachment of probiotics on the surface of chi-BMDCs. Additionally transmission electron microscopy (TEM) revealed efficiently engulfing and degradation of probiotics. Gene expression levels of MHC-II, CD40, CD80 and CD86 up-regulated in stimulated groups. Furthermore, toll-like receptors TLR1, TLR2, TLR4, and chicken specific TLR15 expressions were improved and downstream associated factors MyD88, TRAF6, TAB1, and NFκ-B mRNA levels increased in all treatment groups as compared to control. Surprisingly, NFκ-B response was noted significant higher in LPS treatment among all groups. Moreover, IL-1β, IL-17, IL-4, TGF-β, and IL-10 production levels were found higher, and lower concentration of INF-γ and IL-8 were observed in Sb, Bs, and Sb + Bs treatment groups. In contrast, LPS groups showed prominent increase in IL-12, INF-γ, and IL-8 concentration levels as compared to control group. Altogether, these results emphasize a potentially important role of Saccharomyces boulardii and Bacillus subtilis B10 in modulating immunological functions of chi-BMDCs by targeting specific toll like receptors (TLRs) and associated factors. The role of probiotics on chi-BMDCs functionality in a non-mammalian species have been presented for the first time.

The biology of Neisseria adhesins

Members of the genus Neisseria include pathogens causing important human diseases such as meningitis, septicaemia, gonorrhoea and pelvic inflammatory disease syndrome. Neisseriae are found on the exposed epithelia of the upper respiratory tract and the urogenital tract. Colonisation of these exposed epithelia is dependent on a repertoire of diverse bacterial molecules, extending not only from the surface of the bacteria but also found within the outer membrane. During invasive disease, pathogenic Neisseriae also interact with immune effector cells, vascular endothelia and the meninges. Neisseria adhesion involves the interplay of these multiple surface factors and in this review we discuss the structure and function of these important molecules and the nature of the host cell receptors and mechanisms involved in their recognition. We also describe the current status for recently identified Neisseria adhesins. Understanding the biology of Neisseria adhesins has an impact not only on the development of new vaccines but also in revealing fundamental knowledge about human biology.

Human dendritic cell culture and bacterial infection

Dendritic cells (DC) play a key role in the development of natural immunity to microbes. The DC form a bridge between the innate and adaptive immune system by providing key instructions particularly to antigen naïve T-cells. The interaction of DC with T lymphocytes involves three signals: (1) antigen processing and presentation in context of MHC Class I and/or II, (2) expression of T cell co-stimulatory molecules, and (3) cytokine production. Studying the interactions of DCs with specific pathogens allows for better understanding of how protective immunity is generated, and may be particularly useful for assessing vaccine components. In this chapter, we describe methods to generate human monocyte-derived DCs and assess their maturation, activation, and function, using interaction with the gram-negative bacterial pathogen Neisseria meningitidis as a model.

Mycobacterium avium subsp. paratuberculosis fibronectin attachment protein activates dendritic cells and induces a Th1 polarization

Paratuberculosis is a chronic infectious disorder and a major problem in farmed ruminants. This disease is caused by Mycobacterium avium subsp. paratuberculosis. M. avium subsp. paratuberculosis is an important pathogen that causes Johne's disease in animals and also has been implicated as a possible cause of Crohn's disease in humans, but little is known about the protective immune responses to this microorganism. Fibronectin attachment protein (FAP) is a member of a family of fibronectin-binding proteins produced by several species of mycobacteria which is important in the pathogenesis of M. avium. Addition of recombinant FAP to human respiratory tract organ cultures inhibits M. avium binding to areas where there is epithelial damage. We characterized the role of FAP in promoting adaptive and innate immune responses. FAP functionally activated dendritic cells by augmenting the expression of CD80, CD86, major histocompatibility complex class I, and major histocompatibility complex class II. Moreover, FAP induced the allogeneic immunostimulatory capacity of dendritic cells by stimulating dendritic cell production of Th1-promoting interleukin-12. FAP also increased the production of gamma interferon by T cells in mixed-lymphocyte reactions, which would be expected to contribute to the Th1 polarization of the immune response. The expression of surface markers and cytokine production in dendritic cells was mediated by both mitogen-activated protein kinases and NF-kappaB pathways. These results show that FAP modulates the adaptive immune responses to M. avium subsp. paratuberculosis by inducing maturation and activation of dendritic cells, which drives Th1 polarization.

Induction of CC and CXC chemokines in human antigen-presenting dendritic cells by the pneumococcal proteins pneumolysin and CbpA, and the role played by toll-like receptor 4, NF-kappaB, and mitogen-activated protein kinases

BACKGROUND

Choline-binding protein A (CbpA) and pneumolysin (Ply) can induce the expression and release of chemokines by human cells, which might modulate specific immune responses. In dendritic cells (DCs), such effects could be important for the size and character of the immunity induced if administered as vaccines. We studied the induction of CCL and CXCL chemokines by CbpA and Ply in DCs and related signaling pathways.

METHODS

Proteins derived from bacterial cultures and cloning were used as stimulants. DCs were generated from CD14+ human monocytes by negative selection, followed by coculture with recombinant human granulocyte-macrophage colony-stimulating factor and recombinant interleukin-4. The role played by Toll-like receptors (TLRs) was assessed using anti-TLR antibodies. Likewise, specific inhibitors (given in parentheses) of signaling molecules were used: NF-kappaB (SN50), extracellular signal-regulated kinase (PD98059), p38 (SB203580), and Jun N-terminal kinase (SP600125).

RESULTS

Both CbpA and Ply significantly up-regulated DC mRNA of several CCL (2, 4, 5, and 8) and CXCL (8 and 10) chemokines studied as well as the expression of 3 proteins studied: CCL2, CCL5, and CXCL8. Ply stimulation was blocked by anti-TLR4. Inhibition of NF-kappaB and several mitogen-activated protein kinase signaling pathways also reduced chemokine release.

CONCLUSION

Chemokine induction in DCs by CbpA and Ply may be important for their potential use in future pneumococcal vaccines.

Anti-tumor activity of Acinetobacter baumannii outer membrane protein A on dendritic cell-based immunotherapy against murine melanoma

Acinetobacter baumannii outer membrane protein A (AbOmpA) is a major surface protein that is an important pathogen-associated molecular pattern. Based on our previous findings that AbOmpA induced the phenotypic maturation of dendritic cells (DCs) and drove the Th1 immune response in vitro, we investigated the therapeutic efficacy of AbOmpA-pulsed DC vaccines in a murine melanoma model. The surface expression of co-stimulatory molecules (CD80 and CD86) and major histocompatibility complex class I and II molecules was higher in DCs pulsed with AbOmpA alone or with a combination of B16F10 cell lysates than that of DCs pulsed with B16F10 cell lysates. AbOmpA stimulated the maturation of murine splenic DCs in vivo. In a therapeutic model of murine melanoma, AbOmpA-pulsed DCs significantly retarded tumor growth and improved the survival of tumor-bearing mice. AbOmpA-pulsed DCs significantly enhanced CD8+, interleukin-2+ T cells and CD4+, interferon-gamma+ T cells in tumor-bearing mice. These results provide evidence that AbOmpA may be therapeutically useful in adjuvant DC immunotherapy against poorly immunogenic melanoma without tumor-specific antigens.

The differential response of human dendritic cells to live and killed Neisseria meningitidis

There is currently no effective vaccine for Neisseria meningitidis (Nm) serogroup B. Generation of optimal immune responses to meningococci could be achieved by targeting meningococcal antigens to human dendritic cells (DCs). Recent studies have shown that diverse DC responses and subsequent generation of protective immunity can be observed if the microbes are viable or killed. This is important because the host is likely to be exposed to both live and killed bacteria during natural infection. There are currently few data on comparative DC responses to live and killed meningococci. We show here that exposure of human DC to live meningococci does not result in a typical maturation response, as determined by the failure to upregulate CD40, CD86, HLA-DR and HLA-Class I. Despite this, live meningococci were potent inducers of IL-12 and IL-10, although the ratios of these cytokines differed from those to killed organisms. Our data also suggest that enhanced phagocytosis of killed organisms compared with live may be responsible for the differential cytokine responses, involving an autocrine IL-10-dependent mechanism. The consequences of these findings upon the effectiveness of antigen presentation and T-cell responses are currently under investigation.

IFN-gamma and R-848 dependent activation of human monocyte-derived dendritic cells by Neisseria meningitidis adhesin A

A soluble recombinant form of Neisseria meningitidis adhesin A (NadADelta351-405), proposed as a constituent of anti-meningococcal B vaccines, is here shown to specifically interact with and immune-modulate human monocyte-derived dendritic cells (mo-DCs). After priming with IFN-gamma and stimulation with NadADelta351-405, mo-DCs strongly up-regulated maturation markers CD83, CD86, CD80, and HLA-DR, secreted moderate quantities of TNF-alpha, IL-6, and IL-8, and produced a slight, although significant, amount of IL-12p70. Costimulation of mo-DCs with NadADelta351-405 and the imidoazoquinoline drug R-848, believed to mimic bacterial RNA, increased CD86 in an additive way, but strongly synergized the secretion of IL-12p70, IL-1, IL-6, TNF-alpha, and MIP-1alpha, especially after IFN-gamma priming. CD86/CD80 overexpression correlated with the occupation of high-(kd approximately 80 nM) and low-(kd approximately 4 muM) affinity binding sites for NadADelta351-405. Alternatively, secretion of IL-12p70 and TNF-alpha, IL-6, and IL-8 corresponded to the occupation of high- or low-affinity receptors, respectively. Mo-DCs matured by IFN-gamma and NadADelta351-405 supported the proliferation of naive CD4+ T lymphocytes, inducing the differentiation of both IFN-gamma and IL-4 producing phenotypes. Our data show that NadA not only is a good immunogen but is as well endowed with a proimmune, self-adjuvating, activity.

A Novel Role for the Bactericidal/Permeability Increasing Protein in Interactions of Gram-Negative Bacterial Outer Membrane Blebs with Dendritic Cells

The bactericidal/permeability-increasing protein (BPI) is thought to play an important role in killing and clearance of Gram-negative bacteria and the neutralization of endotoxin. A possible role for BPI in clearance of cell-free endotoxin has also been suggested based on studies with purified endotoxin aggregates and blood monocytes. Because the interaction of BPI with cell-free endotoxin, during infection, occurs mainly in tissue and most likely in the form of shed bacterial outer membrane vesicles ("blebs"), we examined the effect of BPI on interactions of metabolically labeled ([(14)C]-acetate) blebs purified from Neisseria meningitidis serogroup B with either human monocyte-derived macrophages or monocyte-derived dendritic cells (MDDC). BPI produced a dose-dependent increase (up to 3-fold) in delivery of (14)C-labeled blebs to MDDC, but not to monocyte-derived macrophages in the presence or absence of serum. Both, fluorescently labeled blebs and BPI were internalized by MDDC under these conditions. The closely related LPS-binding protein, in contrast to BPI, did not increase association of the blebs with MDDC. BPI-enhanced delivery of the blebs to MDDC did not increase cell activation but permitted CD14-dependent signaling by the blebs as measured by changes in MDDC morphology, surface expression of CD80, CD83, CD86, and MHC class II and secretion of IL-8, RANTES, and IP-10. These findings suggest a novel role of BPI in the interaction of bacterial outer membrane vesicles with dendritic cells that may help link innate immune recognition of endotoxin to Ag delivery and presentation.

The bactericidal/permeability-increasing protein (BPI) in infection and inflammatory disease

Gram-negative bacteria (GNB) and their endotoxin present a constant environmental challenge. Endotoxins can potently signal mobilization of host defenses against invading GNB but also potentially induce severe pathophysiology, necessitating controlled initiation and resolution of endotoxin-induced inflammation to maintain host integrity. The bactericidal/permeability-increasing protein (BPI) is a pluripotent protein expressed, in humans, mainly neutrophils. BPI exhibits strong antimicrobial activity against GNB and potent endotoxin-neutralizing activity. BPI mobilized with neutrophils in response to invading GNB can promote intracellular and extracellular bacterial killing, endotoxin neutralization and clearance, and delivery of GNB outer membrane antigens to dendritic cells. Tissue expression by dermal fibroblasts and epithelia could further amplify local levels of BPI and local interaction with GNB and endotoxin, helping to constrain local tissue infection and inflammation and prevent systemic infection and systemic inflammation. This review article focuses on the structural and functional properties of BPI with respect to its contribution to host defense during GNB infections and endotoxin-induced inflammation and the genesis of autoantibodies against BPI that can blunt BPI activity and potentially contribute to chronic inflammatory disease.

A critical contribution of both CD28 and ICOS in the adjuvant activity of Neisseria meningitidis H44/76 LPS and lpxL1 LPS

The development of novel vaccines against Neisseria meningitidis recently gained momentum by the generation of penta-acylated lpxL1 LPS which has similar adjuvant activity, but reduced endotoxic activity as compared to hexa-acylated wild type (H44/76) LPS. We investigated the costimulation requirements for the adjuvant activity of both forms of LPS by immunizing CD28-, ICOS- and B7.1/2/ICOS-deficient mice. Both ICOS and CD28 appeared essential for optimal adjuvant activity of H44/76 LPS or lpxL1 LPS. Interestingly, ICOS-mediated costimulation predominates in the adjuvant activity of lpxL1 LPS, while both ICOS and CD28 are required for H44/76 LPS adjuvant activity.

Outer membrane protein A of Acinetobacter baumannii induces differentiation of CD4+ T cells toward a Th1 polarizing phenotype through the activation of dendritic cells

Acinetobacter baumannii is an increasing hospital-acquired pathogen that causes a various type of infections, but little is known about the protective immune response to this microorganism. Outer membrane protein A of A. baumannii (AbOmpA) is a major porin protein and plays an important role in pathogenesis. We analyzed interaction between AbOmpA and dendritic cells (DCs) to characterize the role of this protein in promoting innate and adaptive immune responses. AbOmpA functionally activates bone marrow-derived DCs by augmenting expression of the surface markers, CD40, CD54, B7 family (CD80 and CD86) and major histocompatibility complex class I and II. AbOmpA induces production of Th1-promoting interleukin-12 from DCs and augments the syngeneic and allogeneic immunostimulatory capacity of DCs. AbOmpA stimulates production of interferon-gamma from T cells in mixed lymphocyte reactions, which suggesting Th1-polarizing capacity. CD4(+) T cells stimulated by AbOmpA-stimulated DCs show a Th1-polarizing cytokine profile. The expression of surface markers on DCs is mediated by both mitogen-activated protein kinases and NF-kappaB pathways. Our findings suggest that AbOmpA induces maturation of DCs and drives Th1 polarization, which are important properties for determining the nature of immune response against A. baumannii.

Regulation of Th-1 T cell-dominated immunity to Neisseria meningitidis within the human mucosa

Neisseria meningitidis is commonly carried asymptomatically in the upper respiratory tract and only occasionally invades the bloodstream and meninges to cause disease. Naturally acquired immunity appears protective but the nature of the cellular immune response within the mucosa is uncertain. We show that following in vitro stimulation with N. meningitidis serogroup B (MenB) antigens, approximately 66% of the dividing mucosal CD4(+)CD45RO(+) memory population express the Th1-associated IL18-R while the remainder express CRTH2, a Th2-associated marker. The pro-inflammatory bias of this anti-MenB response is not evident in blood, demonstrating compartmentalization at the induction site; and occurs in the presence or absence of lipopolysacharide indicating that these responses are already fully committed. Depletion of CD25(+) cells reveals suppression of the effector CD4(+) T cell response restricted to the mucosa and most marked in children (i.e. those at greatest risk of disease). Mucosal T-regulatory cell (Treg) activity is partially overcome by blocking the human glucocorticoid-induced TNF receptor (GITR) and is not seen following stimulation with antigens from another mucosal pathogen, influenza virus. Pro-inflammatory, antimeningococcal T cell responses may limit invasive disease at the mucosa but Treg induction while reducing immunopathological damage, may also restrict the effectiveness of the protective response, particularly in children.

Non-lipooligosaccharide-mediated signalling via Toll-like receptor 4 causes fatal meningococcal sepsis in a mouse model

Meningococcal lipooligosaccharide (LOS) is a major inflammatory mediator of fulminant meningococcal sepsis and meningitis with disease severity correlating with circulating concentrations of LOS and proinflammatory cytokines. In this study we show that the proinflammatory response to live meningococci in a mouse model of sepsis involves TLR4, but can develop independently of the expression of LOS. This is supported by data showing that in vivo an isogenic LOS-deficient strain, lpxA, induced equivalent disease severity and similar proinflammatory responses as the serogroup C wild-type parent strain FAM20. This response was abolished in TLR4-/- mice, and neither the wild-type strain of meningococci nor the LOS-deficient mutant was able to cause fatal sepsis in these mice. Mouse survival correlated with low levels of cytokines and chemokines, the chemotactic complement factor C5a and neutrophil levels in blood at 24 h post infection. These data suggest that during meningococcal sepsis the recognition of one or more unidentified non-LOS component(s) by TLR4 is important in stimulating proinflammatory responses, and that fatality associated with meningococcal sepsis in mice is induced by the proinflammatory host response.

Outer membrane vesicles of the VA-MENGOC-BC vaccine against serogroup B of Neisseria meningitidis: Analysis of protein components by two-dimensional gel electrophoresis and mass spectrometry

Neisseria meningitidis is a Gram-negative bacterium responsible for significant mortality worldwide. While effective polysaccharides-based vaccines exist against serogroups A, C, W135, and Y, no similar vaccine is suitable for children under 4 years against disease caused by serogroup B strains. Therefore, major vaccine efforts against this serogroup are based on outer membrane vesicles (OMVs), containing major outer membrane proteins. The OMV-based vaccine produced by the Finlay Institute in Cuba (VA-MENGOC-BC) contributed to the rapid decline of the epidemic in this Caribbean island. While the content of major proteins in this vaccine has been discussed, no detailed work of an outer membrane proteomic map of this, or any other, commercially available OMV-derived product has been published so far. Since OMVs exhibit a large bias toward a few major proteins and usually contain a high content of lipids, establishing the adequate conditions for high resolution, 2-DE of this kind of preparation was definitely a technical challenge. In this work, 2-DE and MS have been used to generate a proteomic map of this product, detailing the presence of 31 different proteins, and it allows the identification of new putative protective protein components it contains.

Carbohydrate composition of meningococcal lipopolysaccharide modulates the interaction of Neisseria meningitidis with human dendritic cells

Meningococcal lipopolysaccharide (LPS) is of crucial importance for the pathogenesis of invasive infection. We show that sialylation and elongation of the alpha-chain effectively shields viable unencapsulated Neisseria meningitidis from recognition by human dendritic cells (DC). In contrast, beta- and gamma- chain of the LPS carbohydrate moiety play only a minor role in the interaction with DC. The protective function of the LPS for the bacteria can be counteracted in vivo by phase variation of the lgtA gene encoding LPS glycosyltransferase A. Capsule expression protects N. meningitidis efficiently from recognition and phagocytosis by DC independent of the LPS structure. Despite the significant impact of LPS composition on the adhesion and phagocytosis of N. meningitidis no differences were found in terms of cytokine levels secreted by DC for IL1-beta, IL-6, IL-8, TNF-alpha, IFN-gamma and GM-CSF. However, significantly lower levels of the regulatory mediator IL-10 were induced by encapsulated strains in comparison to isogenic unencapsulated derivatives. IL-10 secretion was shown to depend on phagocytosis because poly alpha-2,8 sialic acid did not influence IL-10 secretion. The use of truncated LPS isoforms in vaccine preparations can therefore not only result in attenuation but also in more efficient targeting of DC.

Activation of human meningeal cells is modulated by lipopolysaccharide (LPS) and non-LPS components of Neisseria meningitidis and is independent of Toll-like receptor (TLR)4 and TLR2 signalling

The interactions of Neisseria meningitidis with cells of the meninges are critical to progression of the acute, compartmentalized intracranial inflammatory response that is characteristic of meningococcal meningitis. An important virulence mechanism of the bacteria is the ability to shed outer membrane (OM) blebs containing lipopolysaccharide (LPS), which has been assumed to be the major pro-inflammatory molecule produced during meningitis. Comparison of cytokine induction by human meningeal cells following infection with wild-type meningococci, LPS-deficient meningococci or after treatment with OM isolated from both organisms, demonstrated the involvement of non-LPS bacterial components in cell activation. Significantly, recognition of LPS-replete OM did not depend on host cell expression of Toll-like receptor (TLR)4, the accessory protein MD-2 or CD14, or the recruitment of LPS-accessory surface proteins heat shock protein (HSP)70, HSP90alpha, chemokine receptor CXCR4 and growth differentiation factor (GDF)5. In addition, recognition of LPS-deficient OM was not associated with the expression of TLR2 or any of these other molecules. These data suggest that during meningococcal meningitis innate recognition of both LPS and non-LPS modulins is dependent on the expression of as yet uncharacterized pattern recognition receptors on cells of the meninges. Moreover, the biological consequences of cellular activation by non-LPS modulins suggest that clinical intervention strategies based solely on abrogating the effects of LPS are likely to be only partially effective.

Improved purification of native meningococcal porin PorB and studies on its structure/function

The outer membrane protein PorB of Neisseria meningitidis is a pore-forming protein which has various effects on eukaryotic cells. It has been shown to (1) up-regulate the surface expression of the co-stimulatory molecule CD86 and of MHC class II (which are TLR2/MyD88 dependent and related to the porin's immune-potentiating ability), (2) be involved in prevention of apoptosis by modulating the mitochondrial membrane potential, and (3) form pores in eukaryotic cells. As an outer membrane protein, its native trimeric form isolation is complicated by its insoluble nature, requiring the presence of detergent throughout the whole procedure, and by its tight association with other outer membrane components, such as neisserial LOS or lipoproteins. In this study, an improved chromatographic purification method to obtain an homogeneous product free of endotoxin and lipoprotein is described, without loss of any of the above-mentioned properties of the porin. Furthermore, we have investigated the requirement of the native trimeric structure for the porin's activity. Inactivation of functional PorB trimers into non-functional monomers was achieved by incubation on ice. Thus, routine long- and medium-term storage at low temperature may be a cause of porin inactivation.

Neisserial porin-induced dendritic cell activation is MyD88 and TLR2 dependent

Neisserial porins have been shown to act as B cell mitogens and immune adjuvants. PorA and PorB are the major outer membrane porin proteins of the human pathogen Neisseria meningitidis. We have shown that the mechanism of the immunopotentiating capability of porin involves up-regulation of the T cell costimulatory ligand, CD86. Due to neisserial porin's ability to activate B cells and potentiate immune responses, we hypothesized that porin also employs the potent immune stimulatory function of dendritic cells (DC). We examined the ability of purified N. meningitidis PorB to induce maturation of murine splenic and bone marrow-derived DC. PorB treatment induced DC maturation, as demonstrated by increased expression of CD86 and class I and II MHC molecules. In addition, PorB not only enhanced the allostimulatory activity of DC, but also augmented the ability of DC to stimulate T cells in an Ag-specific manner. PorB-matured DC secreted the inflammatory cytokine IL-6, which may have implications for the adjuvant property of porin. Induction of IL-6 by PorB is also significant because IL-6 is one of a number of cytokines produced during infection with N. meningitidis and may be involved in the inflammatory process observed during infection and disease. We previously demonstrated the requirement of MyD88 and TLR2 for PorB-induced B cell activation. In the present study, MyD88 and TLR2 were also essential for PorB-induced DC activation. This work is significant for elucidating the mechanism(s) of neisserial porin's immune stimulatory activity.