Current concepts in the role of the host response in Neisseria meningitidis septic shock

Innate immune recognition and inflammation in Neisseria meningitidis infection

Neisseria meningitidis (Nme) can cause meningitis and sepsis, diseases which are characterised by an overwhelming inflammatory response. Inflammation is triggered by host pattern recognition receptors (PRRs) which are activated by pathogen-associated molecular patterns (PAMPs). Nme contains multiple PAMPs including lipooligosaccharide, peptidoglycan, proteins and metabolites. Various classes of PRRs including Toll-like receptors, NOD-like receptors, C-type lectins, scavenger receptors, pentraxins and others are expressed by the host to respond to any given microbe. While Toll-like receptors and NOD-like receptors are pivotal in triggering inflammation, other PRRs act as modulators of inflammation or aid in functional antimicrobial responses such as phagocytosis or complement activation. This review aims to give an overview of the various Nme PAMPs reported to date, the PRRs they activate and their implications during the inflammatory response to infection.

Interactions of meningococcal virulence factors with endothelial cells at the human blood-cerebrospinal fluid barrier and their role in pathogenicity

The Gram-negative extracellular bacterium Neisseria meningitidis is one of the most common aetiological agents of bacterial meningitis affecting predominantly young children worldwide. This bacterium is normally a quiescent coloniser of the upper respiratory tract, but in some individuals it enters the blood stream and causes invasive diseases, such as septicaemia and meningitis. Interactions of N. meningitidis with human endothelial cells are crucially involved in pathogencitiy, and great efforts have been made to understand these molecular interactions. The aim of this review article is to provide an overview of the interactions of meningococcal virulence factors with host endothelial cells at the blood-cerebrospinal fluid barrier.

Infectious Diseases and the Kidney in Children

The kidney is involved in a wide range of bacterial, viral, fungal, and parasitic diseases. In most systemic infections, renal involvement is a minor component of the illness, but in some, renal failure may be the presenting feature and the major problem in management. Although individual infectious processes may have a predilection to involve the renal vasculature, glomeruli, interstitium, or collecting systems, a purely anatomic approach to the classification of infectious diseases affecting the kidney is rarely helpful because most infections may involve several different aspects of renal function. In this chapter, a microbiological classification of the organisms affecting the kidney is adopted. Although they are important causes of renal dysfunction in infectious diseases, urinary tract infections and hemolytic uremic syndrome (HUS) are not discussed in detail because they are considered separately in chapters XX and XX, respectively.

Lipopolysaccharide engineering in Neisseria meningitidis: structural analysis of different pentaacyl lipid A mutants and comparison of their modified agonist properties

Engineering the lipopolysaccharide (LPS) biosynthetic pathway offers the potential to obtain modified derivatives with optimized adjuvant properties. Neisseria meningitidis strain H44/76 was modified by expression of the pagL gene encoding lipid A 3-O-deacylase from Bordetella bronchiseptica and by inactivation of the lgtB gene encoding the terminal oligosaccharide galactosyltransferase. Mass spectrometry analysis of purified mutant LPS was used for detailed compositional analysis of all present molecular species. This determined that the modified LPS was mainly pentaacylated, demonstrating high efficiency of conversion from the hexaacyl to the 3-O-deacylated form by heterologous lipid A 3-O-deacylase (PagL) expression. MS analyses also provided evidence for expression of only one major oligosaccharide glycoform, which lacked the terminal galactose residue as expected from inactivation of the lgtB gene. The immunomodulatory properties of PagL-deacylated LPS were compared with another pentaacyl form obtained from an lpxL1(-) mutant, which lacks the 2' secondary acyl chain. Although both LPS mutants displayed impaired capacity to induce production of the pro-inflammatory cytokine IL-6 in the monocytic cell line Mono Mac 6, induction of the Toll-interleukin-1 receptor domain-containing adaptor-inducing interferon-β-dependent chemokine interferon-γ-induced protein 10 was largely retained only for the lgtB(-)/pagL(+) mutant. Removal of remaining hexaacyl species exclusively present in lgtB(-)/pagL(+) LPS demonstrated that these minor species potentiate but do not determine the activity of this LPS. These results are the first to indicate a qualitatively different response of human innate cells to pentaacyl lpxL1(-) and pagL(+) LPS and show the importance of detailed structure-function analysis when working with modified lipid A structures. The pagL(+) LPS has significant potential as immune modulator in humans.

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.

Fcγ receptor I alpha chain (CD64) expression in macrophages is critical for the onset of meningitis by Escherichia coli K1

Neonatal meningitis due to Escherichia coli K1 is a serious illness with unchanged morbidity and mortality rates for the last few decades. The lack of a comprehensive understanding of the mechanisms involved in the development of meningitis contributes to this poor outcome. Here, we demonstrate that depletion of macrophages in newborn mice renders the animals resistant to E. coli K1 induced meningitis. The entry of E. coli K1 into macrophages requires the interaction of outer membrane protein A (OmpA) of E. coli K1 with the alpha chain of Fcγ receptor I (FcγRIa, CD64) for which IgG opsonization is not necessary. Overexpression of full-length but not C-terminal truncated FcγRIa in COS-1 cells permits E. coli K1 to enter the cells. Moreover, OmpA binding to FcγRIa prevents the recruitment of the γ-chain and induces a different pattern of tyrosine phosphorylation of macrophage proteins compared to IgG2a induced phosphorylation. Of note, FcγRIa^−/− mice are resistant to E. coli infection due to accelerated clearance of bacteria from circulation, which in turn was the result of increased expression of CR3 on macrophages. Reintroduction of human FcγRIa in mouse FcγRIa^−/− macrophages in vitro increased bacterial survival by suppressing the expression of CR3. Adoptive transfer of wild type macrophages into FcγRIa^−/− mice restored susceptibility to E. coli infection. Together, these results show that the interaction of FcγRI alpha chain with OmpA plays a key role in the development of neonatal meningitis by E. coli K1.

Escherichia coli K1 is the most common cause of meningitis in premature infants; the mortality rate of this disease ranges from 5% to 30%. A better understanding of the pathogenesis of E. coli K1 meningitis is needed to develop new preventative strategies. We have shown that outer membrane protein A (OmpA) of E. coli K1, independent of antibody opsonization, is critical for bacterial entrance and survival within macrophages. Using a newborn mouse model, we found that depletion of macrophages renders the animals resistant to E. coli K1 induced meningitis. OmpA binds to α-chain of Fcγ-receptor I (FcγRIa) in macrophages, but does not induce expected gamma chain association and signaling. FcγRIa knockout mice are resistant to E. coli K1 infection because their macrophages express more CR3 and are thus able to kill bacteria with greater efficiency, preventing the development of high-grade bacteremia, a pre-requisite for the onset of meningitis. These novel observations demonstrate that inhibiting OmpA binding to FcγRIa is a promising therapeutic target for treatment or prevention of neonatal meningitis.

Novel insights for systemic inflammation in sepsis and hemorrhage

The inflammatory responses in sepsis and hemorrhage remain a major cause of death. Clinically, it is generally accepted that shock in sepsis or hemorrhage differs in its mechanisms. However, the recognition of inflammatory cytokines as a common lethal pathway has become consent. Proinflammatory cytokines such as tumor necrosis factor (TNF) or high-mobility group box1 (HMGB1) are fanatically released and cause lethal multiorgan dysfunction. Inhibition of these cytokines can prevent the inflammatory responses and organ damage. In seeking potential anti-inflammatory strategies, we reported that ethyl pyruvate and alpha7 nicotinic acetylcholine receptor (alpha7nAChR) agonists effectively restrained cytokine production to provide therapeutic benefits in both experimental sepsis and hemorrhage. Here, we review the inflammatory responses and the anti-inflammatory strategies in experimental models of sepsis and hemorrhage, as they may have a consistent inflammatory pathway in spite of their different pathophysiological processes.

Pathway analysis of GWAS provides new insights into genetic susceptibility to 3 inflammatory diseases

Although the introduction of genome-wide association studies (GWAS) have greatly increased the number of genes associated with common diseases, only a small proportion of the predicted genetic contribution has so far been elucidated. Studying the cumulative variation of polymorphisms in multiple genes acting in functional pathways may provide a complementary approach to the more common single SNP association approach in understanding genetic determinants of common disease. We developed a novel pathway-based method to assess the combined contribution of multiple genetic variants acting within canonical biological pathways and applied it to data from 14,000 UK individuals with 7 common diseases. We tested inflammatory pathways for association with Crohn's disease (CD), rheumatoid arthritis (RA) and type 1 diabetes (T1D) with 4 non-inflammatory diseases as controls. Using a variable selection algorithm, we identified variants responsible for the pathway association and evaluated their use for disease prediction using a 10 fold cross-validation framework in order to calculate out-of-sample area under the Receiver Operating Curve (AUC). The generalisability of these predictive models was tested on an independent birth cohort from Northern Finland. Multiple canonical inflammatory pathways showed highly significant associations (p 10(-3)-10(-20)) with CD, T1D and RA. Variable selection identified on average a set of 205 SNPs (149 genes) for T1D, 350 SNPs (189 genes) for RA and 493 SNPs (277 genes) for CD. The pattern of polymorphisms at these SNPS were found to be highly predictive of T1D (91% AUC) and RA (85% AUC), and weakly predictive of CD (60% AUC). The predictive ability of the T1D model (without any parameter refitting) had good predictive ability (79% AUC) in the Finnish cohort. Our analysis suggests that genetic contribution to common inflammatory diseases operates through multiple genes interacting in functional pathways.

The C-terminal domain is sufficient for endonuclease activity of Neisseria gonorrhoeae MutL

The mutL gene of Neisseria gonorrhoeae has been cloned and the gene product purified. We have found that the homodimeric N. gonorrhoeae MutL (NgoL) protein displays an endonuclease activity that incises covalently closed circular DNA in the presence of Mn(2+), Mg(2+) or Ca(2+) ions, unlike human MutLalpha which shows endonuclease activity only in the presence of Mn(2+). We report in the present paper that the C-terminal domain of N. gonorrhoeae MutL (NgoL-CTD) consisting of amino acids 460-658 exhibits Mn(2+)-dependent endonuclease activity. Sedimentation velocity, sedimentation equilibrium and dynamic light scattering experiments show NgoL-CTD to be a dimer. The probable endonucleolytic active site is localized to a metal-binding motif, DMHAX2EX4E, and the nicking endonuclease activity is dependent on the integrity of this motif. By in vitro comparison of wild-type and a mutant NgoL-CTD protein, we show that the latter protein exhibits highly reduced endonuclease activity. We therefore suggest that the mode of excision initiation in DNA mismatch repair may be different in organisms that lack MutH protein, but have MutL proteins that harbour the D[M/Q]HAX2EX4E motif.

Quest for a broad-range vaccine against Neisseria meningitidis serogroup B: implications of genetic variations of the surface-exposed proteins

Despite the development of new vaccine formulations using new biotechnology resources to combat emerging and re-emerging diseases, serogroup B meningococcal disease is still a worldwide burden, accounting for many deaths and disabilities every year. The successful approach of coupling a polysaccharide (PS) with a carrier protein in order to increase long-lasting immunity could not be exploited againstNeisseria meningitidisB because of the limitations of using the capsular PS of serogroup B meningococci. Tailor-made vaccines based on exposed proteins were shown to be a promising approach to overcome these flaws. However, the continuous adaptation of surface meningococcal structures to the external environment has led to genetic shifts of potential vaccine-target epitopes, hampering the quest for a broad-range vaccine that could be used against all serogroups, especially against serogroup B.

The meningococcal ABC-Type L-glutamate transporter GltT is necessary for the development of experimental meningitis in mice

Experimental animal models of bacterial meningitis are useful to study the host-pathogen interactions occurring at the cerebral level and to analyze the pathogenetic mechanisms behind this life-threatening disease. In this study, we have developed a mouse model of meningococcal meningitis based on the intracisternal inoculation of bacteria. Experiments were performed with mouse-passaged serogroup C Neisseria meningitidis. Survival and clinical parameters of infected mice and microbiological and histological analysis of the brain demonstrated the establishment of meningitis with features comparable to those of the disease in humans. When using low bacterial inocula, meningococcal replication in the brain was very efficient, with a 1,000-fold increase of viable counts in 18 h. Meningococci were also found in the blood, spleens, and livers of infected mice, and bacterial loads in different organs were dependent on the infectious dose. As glutamate uptake from the host has been implicated in meningococcal virulence, mice were infected intracisternally with an isogenic strain deficient in the ABC-type L-glutamate transporter GltT. Noticeably, the mutant was attenuated in virulence in mixed infections, indicating that wild-type bacteria outcompeted the GltT-deficient meningococci. The data show that the GltT transporter plays a role in meningitis and concomitant systemic infection, suggesting that meningococci may use L-glutamate as a nutrient source and as a precursor to synthesize the antioxidant glutathione.

Use of a new single multiplex PCR-based assay for direct simultaneous characterization of six Neisseria meningitidis serogroups

We developed a new Neisseria meningitidis multiplex PCR to determine six serogroups, including X-specific primers, and to allow direct W135/Y discrimination. This assay offers a simple and low-cost method for serogrouping N. meningitidis from cerebrospinal fluid that could be useful in Africa.

Genetically modified L3,7 and L2 lipooligosaccharides from Neisseria meningitidis serogroup B confer a broad cross-bactericidal response

Currently available Neisseria meningitidis serogroup B (MenB) vaccines are based on outer membrane vesicles (OMVs) that are obtained from wild-type strains. They are purified with the aim of decreasing the lipooligosaccharide (LOS) content and hence reduce the reactogenicity of the vaccine even though LOS is a potential protective antigen. In <2-year-old children, these MenB vaccines confer protection only against strains expressing homologous PorA, a major and variable outer membrane protein. Our objective was to develop a safe LOS-based vaccine against MenB. To this end, we used modified porA knockout strains expressing genetically detoxified (msbB gene-deleted) L2 and L3,7 LOSs, allowing the production of LOS-enriched OMVs. The vaccine-induced antibodies were found to be bactericidal against nearly all invasive strains, irrespective of capsular serogroup. In addition, we have also demonstrated that LOS lacking the terminal galactose (with a lgtB mutation; truncated L3 LOS), but not LOS produced without the galE gene, induced a bactericidal antibody response in mice similar to that seen for LOS containing the full lacto-N-neotetraose (L3,7 LOS). In conclusion, a bivalent detoxified LOS OMV-based vaccine demonstrated the potential to afford a broad cross-protection against meningococcal disease.

Cloning and characterisation of dihydrodipicolinate synthase from the pathogen Neisseria meningitidis

Neisseria meningitidis is an obligate commensal bacterium of humans, and also an important human pathogen. To facilitate future drug studies, we report here the biochemical and structural characterisation of a key enzyme in (S)-lysine biosynthesis, dihydrodipicolinate synthase (DHDPS), from N. meningitidis (NmeDHDPS). X-ray crystallography revealed only minor structural differences between NmeDHDPS and the enzyme from E. coli at the active and allosteric effector sites. The catalytic capabilities of NmeDHDPS are similar to those of the enzyme from E. coli, but intriguingly NmeDHDPS is subject to substrate inhibition by high concentrations of the second substrate, (S)-aspartate semialdehyde, and is also significantly more sensitive to feedback inhibition by (S)-lysine. This heightened sensitivity to inhibition at both active and allosteric sites suggests that it may be possible to target DHDPS from N. meningitidis for antibiotic development.

Two centuries of meningococcal infection: from Vieusseux to the cellular and molecular basis of disease

Scientific knowledge of meningococcal infection has increased greatly since the epidemic nature of the illness was first described by Vieusseux at the dawn of the nineteenth century. In fact, revolutionary advances have been made in public-health measures, antimicrobial therapy, diagnostic procedures, anti-inflammatory drugs and supportive care facilities. Based on the knowledge accumulated to date, it is generally accepted that the pathogenesis of meningococcal infection involves multiple links that interconnect in a complex web of phenomena from Neisseria meningitidis attachment to meningococcal sepsis or meningitis. In fact, a myriad of strongly interacting inflammatory molecules and cells have been implicated in neisserial infection, illustrating the complexity of meningococcal pathogenesis. In addition, many of these signallers are critically involved in outcomes in the human host. Deciphering the pathogenesis of meningococcal infection could expand our knowledge and provide important clues to the host-pathogen interaction, as well as leading to the development of new therapeutic tools. Herein, we review the history of the discovery and characterization of meningococcal disease, epidemiological features of the disease with an emphasis on recent developments in Brazil, the cellular and molecular basis of disease, and discuss diagnosis and therapy.

Genetics and evolution of Neisseria meningitidis: importance for the epidemiology of meningococcal disease

Meningococcal disease is a life-threatening illness occurring worldwide with incidence rates varying from 1 to 1000 cases per 100,000. The causative organism, Neisseria meningitidis, is a normal commensal of humans. While strains associated with asymptomatic carriage are highly diverse, a few hyper-invasive genetic clones of the species may spread rapidly through human populations, resulting in countrywide epidemics of meningococcal meningitis. N. meningitidis fitness for spread and colonization is directly linked to the capability of the bacterium to change its genome and adapt to its environment, by means of a variety of genetic mechanisms. This review addresses some of the impacts of the evolutionary potential of N. meningitidis on the occurrence of meningococcal disease.

Transgenic mice expressing human transferrin as a model for meningococcal infection

The pathogenesis of meningococcal disease is poorly understood due to the lack of a relevant animal model. Moreover, the use of animal models is not optimal as most meningococcal virulence determinants recognize receptors that are specifically expressed in human tissues. One major element of the host specificity is the system of meningococcal iron uptake by transferrin-binding proteins that bind specifically human transferrin but not murine transferrin. We developed a new mouse model for experimental meningococcal infection using transgenic mice expressing human transferrin. Intraperitoneal challenge of transgenic mice induced bacteremia for at least 48 h with an early stage of multiplication, whereas the initial inoculum was rapidly cleared from blood in wild-type mice. Inflammation in the subarachnoidal space with a high influx of polymorphonuclear cells was observed only in transgenic mice. Meningococcal mutants that were unable to use transferrin as a source of iron were rapidly cleared from both wild-type and transgenic mice. Thus, transgenic mice expressing human transferrin may represent an important advance as a new mouse model for in vivo studies of meningococcal virulence and immunogenicity factors.

Neisserial outer membrane vesicles bind the coinhibitory receptor carcinoembryonic antigen-related cellular adhesion molecule 1 and suppress CD4+ T lymphocyte function

Pathogenic Neisseria bacteria naturally liberate outer membrane "blebs," which are presumed to contribute to pathology, and the detergent-extracted outer membrane vesicles (OMVs) from Neisseria meningitidis are currently employed as meningococcal vaccines in humans. While the composition of these vesicles reflects the bacteria from which they are derived, the functions of many of their constituent proteins remain unexplored. The neisserial colony opacity-associated Opa proteins function as adhesins, the majority of which mediate bacterial attachment to human carcinoembryonic antigen-related cellular adhesion molecules (CEACAMs). Herein, we demonstrate that the Opa proteins within OMV preparations retain the capacity to bind the immunoreceptor tyrosine-based inhibitory motif-containing coinhibitory receptor CEACAM1. When CD4(+) T lymphocytes were exposed to OMVs from Opa-expressing bacteria, their activation and proliferation in response to a variety of stimuli were effectively halted. This potent immunosuppressive effect suggests that localized infection will generate a "zone of inhibition" resulting from the diffusion of membrane blebs into the surrounding tissues. Moreover, it demonstrates that OMV-based vaccines must be developed from strains that lack CEACAM1-binding Opa variants.

Microbial genome dynamics in CNS pathogenesis

The balancing act between microbes and their host in commensal and disease states needs to be deciphered in order to fully treat and combat infectious diseases. The elucidation of microbial genome dynamics in each instance is therefore required. In this context, the major bacterial meningitis pathogens are Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae. In prokaryotic CNS pathogenesis both the intact organism as well as its released components can elicit disease, often resulting in neurological sequelae, neurodegeneration or fatal outcome. The study of microbial virulence in CNS disease is expected to generate findings that yield new information on the general mechanisms of brain edema and excitatory neuronal disturbances due to meningitis, with significant potential for discoveries that can directly influence and inspire new strategies for prevention and treatment of this serious disease.

Lessons from meningococcal carriage studies

Neisseria meningitidis, an obligate commensal of humans, normally colonizes the mucosa of the upper respiratory tract without affecting the host, a phenomenon known as carriage. In Europe, as much as 35% of young adults are carriers at a given time. Recent studies using molecular methods for clone identification have demonstrated the extensive genetic diversity of the strains isolated from carriers, in comparison with a limited number of hypervirulent strains associated with invasive disease. Published studies and new data generated through the framework of the EU-MenNet clearly indicated significant differences in pathogenicity between meningococcal clones and in the distribution of multilocus sequence types among isolates from asymptomatic carriers among European countries; simultaneous carriage of more than one meningococcal strain in the throat is rare, but occasionally occurs; and the commensal association of particular clones with a host is a long-term relationship, often lasting several months. Further investigations of the carrier state are warranted to improve our understanding of the epidemiology and pathogenesis of meningococcal disease, as well as to support the introduction and to measure the impact of mass vaccination.

Differential role of lipooligosaccharide of Neisseria meningitidis in virulence and inflammatory response during respiratory infection in mice

Meningococcal lipooligosaccharide (LOS) induces a strong proinflammatory response in humans during meningococcal infection. We analyzed the role of LOS in the inflammatory response and virulence during the early infectious process in a mouse model of meningococcal respiratory challenge. An lpxA mutant strain (serogroup B) devoid of LOS (strain Z0204) could not persist in the lungs and did not invade the blood. The persistence in the lungs and invasion of the bloodstream by a rfaD mutant expressing truncated LOS with only lipid A and 3-deoxy-d-manno-2-octulosonic acid molecules (strain Z0401) was intermediate between those of the wild-type and Z0204 strains. Both LOS mutants induced acute pneumonia with the presence of infiltrating polymorphonuclear leukocytes in lungs. Although tumor necrosis factor alpha production was reduced in mice infected with the mutant of devoid LOS, both LOS mutants induced production of other proinflammatory cytokines, such as interleukin-1beta (IL-1beta), IL-6, and the murine IL-8 homolog KC. Together, these results suggest that meningococcal LOS plays a role during the early infectious and invasive process, and they further confirm that other, nonlipopolysaccharide components of Neisseria meningitidis may significantly contribute to the inflammatory reaction of the host.

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.

Elastase and granzymes during meningococcal disease in children: correlation to disease severity

OBJECTIVE

To investigate the levels of human neutrophil elastase and lymphocyte-derived granzymes A and B in relation to disease severity in children with meningococcal disease.

DESIGN

Clinical observational cohort study.

SETTING

Paediatric intensive care unit.

PATIENTS

All patients with meningococcal disease during the study period were included.

MEASUREMENTS AND RESULTS

Blood sampling was done on the day of admission and on days 3 and 7. Assays for elastase and granzymes were done with ELISA. Sixty-one patients were included: 19 having distinct meningitis; 17 meningitis and shock; and 25 fulminant septicaemia. On admission levels of elastase were increased in all patients, being highest in those with fulminant septicaemia and lowest in those with distinct meningitis. Granzyme A (although marginally) and granzyme B levels were only increased in patients with shock. In 20 of the 28 patients admitted for > or = 3 days elastase decreased from admission ("rapid-decrease" group). In the remaining 8 patients, elastase started to decrease after 2 days ("slow-decrease" group). Patients of the "slow-decrease" group had a higher temperature up to day 4, needed more respiratory support (mean airway pressure in cm H2O on days 3 and 4: p=0.02 and p<0.01, respectively), and more circulatory support (>2 inotropic agents on day 3; p=0.04) compared with the "rapid-decrease" group.

CONCLUSIONS

Human neutrophil elastase and granzyme B are related with disease severity during the initial phase of meningococcal disease and prolonged neutrophil activation is associated with the extent of organ dysfunction during the period thereafter.

The "cytokine profile": a code for sepsis

Sepsis--the most common cause of death in hospitalized patients--affects over 18 million people worldwide and has an expected 1% increase of incidence per year. Recent clinical trials indicate that therapeutic approaches effective in diseases with similar pathogenesis have a modest effect against sepsis. Although the reason for this failure remains controversial, recent studies provide new insights and promising experimental strategies. We propose that the current definition of sepsis is too broad and encompasses heterogeneous groups of patients suffering similar, but different, syndromes that are historically grouped under the general diagnosis of sepsis. Future clinical trials might define patient populations and therapeutic strategies according to the profile of expression of cytokines.

Bi-functional effects of ATP/P2 receptor activation on tumor necrosis factor-alpha release in lipopolysaccharide-stimulated astrocytes

Neuroinflammation is associated with a variety of CNS pathologies. Levels of tumor necrosis factor-alpha (TNF-alpha), a major proinflammatory cytokine, as well as extracellular ATP, are increased following various CNS insults. Here we report on the relationship between ATP/P2 purinergic receptor activation and lipopolysaccharide (LPS)-induced TNF-alpha release from primary cultures of rat cortical astrocytes. Using ELISA, we confirmed that treatment with LPS stimulated the release of TNF-alpha in a concentration and time dependent manner. ATP treatment alone had no effect on TNF-alpha release. LPS-induced TNF-alpha release was attenuated by 1 mm ATP, a concentration known to activate P2X7 receptors. Consistent with this, 3'-O-(4-Benzoyl)benzoyl-ATP (BzATP), a P2X7 receptor agonist, also attenuated LPS-induced TNF-alpha release. This reduction in TNF-alpha release was not due to loss of cell viability. Adenosine and 2-chloroadenosine were ineffective, suggesting that attenuation of LPS-induced TNF-alpha release by ATP was not due to ATP breakdown and subsequent activation of adenosine/P1 receptors. Interestingly, treatment of astrocyte cultures with 10 microm or 100 microm ATP potentiated TNF-alpha release induced by a submaximal concentration of LPS. UTP and 2methylthioADP (2-MeSADP), P2Y receptor agonists, also enhanced this LPS-induced TNF-alpha release. Our observations demonstrate opposing effects of ATP/P2 receptor activation on TNF-alpha release, i.e. P2X receptor activation attenuates, whereas P2Y receptor activation potentiates TNF-alpha release in LPS-stimulated astrocytes. These observations suggest a mechanism whereby astrocytes can sense the severity of damage in the CNS via ATP release from damaged cells and can modulate the TNF-alpha mediated inflammatory response depending on the extracellular ATP concentration and corresponding type of astrocyte ATP/P2 receptor activated.

Inner core assembly and structure of the lipooligosaccharide of Neisseria meningitidis: capacity of strain NMB to express all known immunotype epitopes

Neisseria meningitidis expresses a heterogeneous population of lipooligosaccharide (LOS) inner cores variously substituted with alpha1-3-linked glucose and O-3, O-6, and O-7 linked phosphoethanolamine (PEA), as well as glycine, attached to HepII. Combinations of these attachments to the LOS inner core represent immunodominant epitopes that are being exploited as future vaccine candidates. Historically, each LOS immunotype was structurally assessed and prescribed a certain unique inner core epitope. We report that a single isolate, strain NMB, possesses the capacity to produce all of the known neisserial LOS inner core immunotype structures. Analysis of the inner cores from parental LOS revealed the presence or absence of alpha1,3-linked glucose, O-6 and/or O-7 linked PEA, in addition to glycine attached at the 7 position of the HepII inner core. Identification and inactivation of lpt-6 in strain NMB resulted in the loss of both O-6 and O-7 linked PEA groups from the LOS inner core, suggesting that Lpt-6 of strain NMB may have bifunctional transferase activities or that the O-6 linked PEA groups once attached to the inner core undergo nonenzymatic transfer to the O-7 position of HepII. Although O-3 linked PEA was not detected in parental LOS inner cores devoid of alpha1-3-linked glucose residues, LOS glycoforms bearing O-3 PEA groups accumulated in a truncated mutant, NMBlgtK (Hep2Kdo2-lipid A). Because these structures disappeared upon inactivation of the lpt-3 locus, strain NMB expresses a functional O-3 PEA transferase. The LOS glycoforms expressed by NMBlgtK were also devoid of glycine attachments, indicating that glycine was added to the inner core after the completion of the gamma-chain by LgtK. In conclusion, strain NMB has the capability to express all known inner core structures, but in in vitro culture L2 and L4 immunotype structures are predominantly expressed.

Complement activation and complement-dependent inflammation by Neisseria meningitidis are independent of lipopolysaccharide

Fulminant meningococcal sepsis has been termed the prototypical lipopolysaccharide (LPS)-mediated gram-negative septic shock. Systemic inflammation by activated complement and cytokines is important in the pathogenesis of this disease. We investigated the involvement of meningococcal LPS in complement activation, complement-dependent inflammatory effects, and cytokine or chemokine production. Whole blood anticoagulated with lepirudin was stimulated with wild-type Neisseria meningitidis H44/76 (LPS+), LPS-deficient N. meningitidis H44/76lpxA (LPS-), or purified meningococcal LPS (NmLPS) at concentrations that were relevant to meningococcal sepsis. Complement activation products, chemokines, and cytokines were measured by enzyme-linked immunosorbent assays, and granulocyte CR3 (CD11b/CD18) upregulation and oxidative burst were measured by flow cytometry. The LPS+ and LPS- N. meningitidis strains both activated complement effectively and to comparable extents. Purified NmLPS, used at a concentration matched to the amount present in whole bacteria, did not induce any complement activation. Both CR3 upregulation and oxidative burst were also induced, independent of LPS. Interleukin-1beta (IL-1beta), tumor necrosis factor alpha, and macrophage inflammatory protein 1alpha production was predominantly dependent on LPS, in contrast to IL-8 production, which was also markedly induced by the LPS- meningococci. In this whole blood model of meningococcal sepsis, complement activation and the immediate complement-dependent inflammatory effects of CR3 upregulation and oxidative burst occurred independent of LPS.

Innate immunity and toll-like receptors: clinical implications of basic science research

Humans are constantly exposed to a wide variety of microorganisms that can cause infection. In self-defense, the human host has evolved complex protective mechanisms, and Toll-like receptors (TLRs) have emerged as a central point in defense. These receptors bind molecular structures that are expressed by microbes but are not expressed by the human host, eg, lipopolysaccharides (LPS) or double-stranded RNA (dsRNA). Activation of these receptors initiates an inflammatory cascade that attempts to clear the offending pathogen and set in motion a specific adaptive immune response. Defects in sensing of pathogens may predispose the host to recurrent infections. The relative rarity of these syndromes of defective innate immunity, however, speaks to the redundancy in sensing of pathogens by the innate immune system. More common, polymorphisms in TLR4 are associated with increased predisposition to severe and recurrent infections but protection against atherosclerotic disease due to diminished inflammation. Toll-like receptor signaling may also contribute to the pathophysiology of disease and injure the host by activating a deleterious immune response such as in sepsis or inflammatory bowel disease (IBD). The focus of this article is to describe the role of TLRs in the innate immune response in health and disease.

Human dendritic cell activation by Neisseria meningitidis: phagocytosis depends on expression of lipooligosaccharide (LOS) by the bacteria and is required for optimal cytokine production

Group B Neisseria meningitidis is a human pathogen, for which a universally effective vaccine is still not available. Immune responses to bacteria are initiated by dendritic cells (DC), which internalize and process bacterial antigens for presentation to T cells. We show here that optimal IL-12 and TNF-alpha production by human monocyte derived DC in response to killed serogroup B N. meningitidis depends on physical contact and internalization of the bacteria by DC. The majority of DC producing cytokines had internalized N. meningitidis while inhibition of bacterial internalization markedly impaired IL-12 and TNF-alpha, but not IL-6 production. Internalization of N. meningitidis was shown to depend on lipooligosaccharide (LOS) expressed by the bacteria with poor internalization of LOS deficient bacteria compared to wild-type bacteria. Restoration of LOS biosynthesis in a LOS regulatory strain also restored both internalization and cytokine production and was enhanced in the presence of LPS binding protein (LBP). These results suggest that DC phagocytosis depends on expression of LOS within the bacteria and that optimal cytokine production, particularly IL-12, requires internalization of the bacteria. These findings have important implications for designing vaccines that will induce protective immune responses to group B N. meningitidis.

High-level endothelial E-selectin (CD62E) cell adhesion molecule expression by a lipopolysaccharide-deficient strain of Neisseria meningitidis despite poor activation of NF-kappaB transcription factor

Binding of host inflammatory cells to the endothelium is a critical contributor to the vascular damage characteristic of severe meningococcal disease and is regulated by endothelial cell adhesion molecules such as ICAM-1, VCAM-1 and CD62E. Intact meningococci induce far higher levels of CD62E than lipopolysaccharide (LPS) alone, whereas LPS is at least as potent as meningococci at inducing both VCAM-1 and ICAM-1 expression. This suggests that meningococci possess additional factors other than LPS present in whole bacteria that result in differential adhesion molecule expression. To investigate this possibility, we studied the capacity of an LPS-deficient isogenic strain of serogroup B Neisseria meningitidis H44/76 (lpxA-) to induce endothelial cell adhesion molecule expression and translocation of the transcription factor NF-kappaB, and compared it to both parent and unencapsulated strains of both B1940 and H44/76 and purified LPS. Although the LPS-deficient isogenic mutant of strain H44/76 was found to be a poor inducer of NF-kappaB, it induced higher levels of CD62E expression than LPS alone. These data provide evidence that intact meningococci induce a range of signals in the endothelium that are distinct from those seen with purified LPS alone and that they occur in a LPS-dependent and LPS-independent manner. These signals may explain the potent effects of N. meningitidis on CD62E expression on vascular endothelium and provide a basis for the complex endothelial dysregulation seen in meningococcal sepsis.

Inhibition of C5a-induced inflammation with preserved C5b-9-mediated bactericidal activity in a human whole blood model of meningococcal sepsis

The complement system plays an important role in the initial defense against Neisseria meningitidis. In contrast, uncontrolled activation in meningococcal sepsis contributes to the development of tissue damage and shock. In a novel human whole blood model of meningococcal sepsis, we studied the effect of complement inhibition on inflammation and bacterial killing. Monoclonal antibodies (mAbs) blocking lectin and alternative pathways inhibited complement activation by N meningitidis and oxidative burst induced in granulocytes and monocytes. Oxidative burst was critically dependent on CD11b/CD18 (CR3) expression but not on Fc gamma-receptors. Specific inhibition of C5a using mAb 137-26 binding the C5a moiety of C5 before cleavage prohibited CR3 up-regulation, phagocytosis, and oxidative burst but had no effect on C5b-9 (TCC) formation, lysis, and bacterial killing. An mAb-blocking cleavage of C5, preventing C5a and TCC formation, showed the same effect on CR3, phagocytosis, and oxidative burst as the anti-C5a mAb but additionally inhibited TCC formation, lysis, and bacterial killing, consistent with a C5b-9-dependent killing mechanism. In conclusion, the anti-C5a mAb 137-26 inhibits the potentially harmful effects of N meningitidis-induced C5a formation while preserving complement-mediated bacterial killing. We suggest that this may be an attractive approach for the treatment of meningococcal sepsis.

Recombination, repair and replication in the pathogenic Neisseriae: the 3 R's of molecular genetics of two human-specific bacterial pathogens

Most of the detailed mechanisms that have been established for the molecular biological processes that mediate recombination, repair and replication of DNA have come from studies of the Escherichia coli paradigm. The human specific pathogens, Neisseria gonorrhoeae and N. meningitidis, are Gram-negative bacteria that have some molecular processes that are similar to E. coli and others that appear to be divergent. We propose that the pathogenic Neisseriae have evolved a specialized collection of molecular mechanisms to adapt to life limited to human hosts. In this MicroReview, we explore what is known about the basic processes of DNA repair, DNA recombination (genetic exchange and pilin variation) and DNA replication in these human specific pathogens.