Molecular mechanisms in the compartmentalized inflammatory response presenting as meningococcal meningitis or septic shock

Compartmentalization of the inflammatory response during bacterial sepsis and severe COVID-19

Acute infections cause local and systemic disorders which can lead in the most severe forms to multi-organ failure and eventually to death. The host response to infection encompasses a large spectrum of reactions with a concomitant activation of the so-called inflammatory response aimed at fighting the infectious agent and removing damaged tissues or cells, and the anti-inflammatory response aimed at controlling inflammation and initiating the healing process. Fine-tuning at the local and systemic levels is key to preventing local and remote injury due to immune system activation. Thus, during bacterial sepsis and Coronavirus disease 2019 (COVID-19), concomitant systemic and compartmentalized pro-inflammatory and compensatory anti-inflammatory responses are occurring. Immune cells (e.g., macrophages, neutrophils, natural killer cells, and T-lymphocytes), as well as endothelial cells, differ from one compartment to another and contribute to specific organ responses to sterile and microbial insult. Furthermore, tissue-specific microbiota influences the local and systemic response. A better understanding of the tissue-specific immune status, the organ immunity crosstalk, and the role of specific mediators during sepsis and COVID-19 can foster the development of more accurate biomarkers for better diagnosis and prognosis and help to define appropriate host-targeted treatments and vaccines in the context of precision medicine.

Invited review: Neisseria meningitidis lipopolysaccharides in human pathology

Neisseria meningitidis causes meningitis, fulminant septicemia or mild meningococcemia attacking mainly children and young adults. Lipopolysaccharides (LPS) consist of a symmetrical hexa-acyl lipid A and a short oligosaccharide chain and are classified in 11 immunotypes. Lipid A is the primary toxic component of N. meningitidis . LPS levels in plasma and cerebrospinal fluid as determined by Limulus amebocyte lysate (LAL) assay are quantitatively closely associated with inflammatory mediators, clinical symptoms, and outcome. Patients with persistent septic shock, multiple organ failure, and severe coagulopathy reveal extraordinarily high levels of LPS in plasma. The cytokine production is compartmentalized to either the circulation or to the subarachnoid space. Mortality related to shock increases from 0% to > 80% with a 10-fold increase of plasma LPS from 10 to 100 endotoxin units/ml. Hemorrhagic skin lesions and thrombosis are caused by up-regulation of tissue factor which induces coagulation, and by inhibition of fibrinolysis by plasminogen activator inhibitor 1 (PAI-1). Effective antibiotic treatment results in a rapid decline of plasma LPS (half-life 1—3 h) and cytokines, and reduced generation of thrombin, and PAI-1. Early antibiotic treatment is mandatory. Three intervention trials to block lipid A have not significantly reduced the mortality of meningococcal septicemia.

Meningococcal disease: clinical presentation and sequelae

The clinical spectrum of invasive meningococcal disease is diverse with meningitis and/or septicaemia being the commonest modes of presentation. The severity of manifestations of meningococcal infection ranges from bacteraemia, associated with mild non-specific symptoms, to fulminant sepsis with multiorgan failure and death in approximately 10-15% of cases. Localised infections (such as conjunctivitis or septic arthritis) as well as chronic disease may be the sole clinical manifestations but can also lead to disseminated fulminant disease. Among survivors, disabling long-term sequelae can complicate meningococcal disease and result in potentially devastating effects on the quality of life of survivors, most of whom are infants, children and adolescents. The only rational approach to the prevention of meningococcal disease and the associated human suffering is through vaccination.

Toll-like receptor 9 polymorphisms are associated with severity variables in a cohort of meningococcal meningitis survivors

BACKGROUND

Genetic variation in immune response genes is associated with susceptibility and severity of infectious diseases. Toll-like receptor (TLR) 9 polymorphisms are associated with susceptibility to develop meningococcal meningitis (MM). The aim of this study is to compare genotype distributions of two TLR9 polymorphisms between clinical severity variables in MM survivors.

METHODS

We used DNA samples of a cohort of 390 children who survived MM. Next, we determined the genotype frequencies of TLR9 -1237 and TLR9 +2848 polymorphisms and compared these between thirteen clinical variables associated with prognostic factors predicting adverse outcome of bacterial meningitis in children.

RESULTS

The TLR9 -1237 TC and CC genotypes were associated with a decreased incidence of a positive blood culture for Neisseria (N.) meningitidis (p = 0.014, odds ratio (OR) 0.5. 95% confidence interval (CI) 0.3 - 0.9). The TLR9 +2848 AA mutant was associated with a decreased incidence of a positive blood culture for N. meningitidis (p = 0.017, OR 0.6, 95% CI 0.3 - 0.9). Cerebrospinal fluid (CSF) leukocytes per μL were higher in patients carrying the TLR9 -1237 TC or CC genotypes compared to carriers of the TT wild type (WT) (p = 0.024, medians: 2117, interquartile range (IQR) 4987 versus 955, IQR 3938). CSF blood/glucose ratios were lower in TLR9 -1237 TC or CC carriers than in carriers of the TT WT (p = 0.017, medians: 0.20, IQR 0.4 versus 0.35, IQR 0.5). CSF leukocytes/μL were higher in patients carrying the TLR9 +2848 AA mutant compared to carriers of GG or GA (p = 0.0067, medians: 1907, IQR 5221 versus 891, IQR 3952).

CONCLUSIONS

We identified TLR9 genotypes associated with protection against meningococcemia and enhanced local inflammatory responses inside the central nervous system, important steps in MM pathogenesis and defense.

Coadministration of the cyanobacterial lipopolysaccharide antagonist CyP with antibiotic inhibits cytokine production by an in vitro meningitis model infected with Neisseria meningitidis

OBJECTIVES

In this study, the objective was to determine the anti-inflammatory properties of CyP, a cyanobacterial lipopolysaccharide (LPS) antagonist, used in combination with antibiotic chemotherapy during infection of an in vitro meningitis model infected with Neisseria meningitidis (meningococcus).

METHODS

Monocultures of human meningioma cells and meningioma-primary human macrophage co-cultures were infected with meningococci (10(2)-10(8) cfu/monolayer) or treated with isolated outer membranes or purified LPS (0.1-100 ng/monolayer) from N. meningitidis. CyP (1-20 μg/monolayer) was added at intervals from t = 0 to 4 h, with and without benzylpenicillin (1-20 μg/monolayer). The antagonistic effect of CyP and its adjunctive properties to benzylpenicillin administration was determined by measuring cytokine levels in culture supernatants after 24 h.

RESULTS

CyP significantly inhibited (P < 0.05) the secretion of interleukin (IL)-6, IL-8, monocyte chemoattractant protein (MCP)-1 and RANTES ('regulated upon activation, normal T cell expressed and secreted') (overall reduction levels from 50% to >95%) by meningioma cell lines and meningioma-macrophage co-cultures challenged with either live meningococci or bacterial components. Inhibition was effective when CyP was added within 2 h of challenge (P < 0.05) and was still pronounced by 4 h. In the co-culture model, CyP alone partially inhibited IL-1β secretion, but did not prevent tumour necrosis factor (TNF)-α secretion, whereas penicillin alone inhibited IL-1β and TNF-α but conversely did not reduce MCP-1 and RANTES secretion. However, coadministration of CyP and penicillin in both models had an additive effect and restored the overall inhibitory profile.

CONCLUSIONS

CyP inhibits cytokine production in an in vitro meningitis model and augments the anti-inflammatory response when combined with benzylpenicillin. Administration of an LPS antagonist with antibiotic merits consideration in the emergency treatment of patients presenting with meningococcal infection.

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.

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.

High pneumococcal DNA loads are associated with mortality in Malawian children with invasive pneumococcal disease

BACKGROUND

In bacteremia owing to Streptococcus pneumoniae, high bacterial counts at presentation have been shown to be predictive of the development of serious invasive disease. Using real-time PCR, we aimed to determine pneumococcal DNA loads in blood and CSF, and their relationship to cytokine concentrations, clinical presentation and outcome.

METHODS

Children with confirmed meningitis (n = 82) or pneumonia (n = 13) were prospectively recruited, and blood and CSF samples taken for pneumococcal bacterial DNA loads and cytokine determination.

RESULTS

At the time of admission, the median bacterial load in blood was 1.6 x 10 DNA copies/mL (range 0.00-1.54 x 10) and in CSF it was 5.77 x 10 DNA copies/mL (range 4.42 x 10 to 6.15 x 10). Median blood and CSF bacterial loads (log DNA copies/mL) were significantly higher in nonsurvivors than in survivors; blood (3.80 vs. 2.97, P = 0.003), CSF (8.17 vs. 7.50, P = 0.03). In HIV-infected children (n = 59), blood and CSF loads and plasma tumor necrosis factor-alpha, interleukin-1beta (IL-1beta), IL-6 and IL-10 were all significantly higher in nonsurvivors than in survivors, but in HIV-uninfected children (n = 36) this difference was not significant. Blood bacterial loads and plasma cytokine concentrations were significantly associated, and were all significantly higher in children with meningitis than in those with pneumonia. In children with meningitis, median CSF cytokine concentrations were significantly higher than median plasma cytokine concentrations (P < 0.001) and CSF bacterial loads were significantly associated with CSF IL-1beta (P = 0.002) and IL-10 (P = 0.001) concentrations.

CONCLUSIONS

Pneumococcal DNA loads are associated with plasma cytokine concentrations, and are higher in meningitis than in pneumonia. High blood and CSF pneumococcal DNA loads are associated with a fatal outcome.

Systemic inflammation alters the inflammatory response in experimental lipopolysaccharide-induced meningitis

Experiments to evaluate the effect of the level and duration of endotoxaemia on the meningeal inflammatory response were performed in order to determine if systemic inflammation alters meningitis. Rabbits received either saline or Escherichia coli O111:B4 lipopolysacharide (LPS) intravenously at various doses (1, 3 or 10 microg) and times (-8, -2 or 0 h) before an intracisternal injection of 20 ng LPS. An intracisternal LPS injection together with saline intravenously produced a peak cerebrospinal fluid (CSF) tumour necrosis factor (TNF) level (95 +/- 26 ng/ml) at 2 h and peak leucocyte level (5413 +/- 764 cells/microl) at 4 h post-injection. Blood leucocytes were slightly elevated (12 000 +/- 500/microl at 0 h; 16 900 +/- 280/microl at 8 h) but plasma TNF was always undetectable (< 0.05 ng/ml). Conversely, intravenous injection of 3 or 10 microg LPS 2 h prior to intracisternal LPS injection impaired pleocytosis (peak < 220 cells/microl) and delayed ( approximately 4 h) and reduced peak CSF TNF levels (3 microg LPS 5.0 +/- 1.2 ng/ml; 10 microg LPS 6.9 +/- 1.9; P < 0.05). Intravenous administration of 1 microg LPS was less inhibitory to CSF inflammation, but delayed onset (peak 1100 +/- 60 leucocytes/microl CSF at 8 h; 6.3 +/- 0.3 ng TNF/ml CSF at 4 h; both P < 0.05). Neutropenia nadirs were dependent on LPS dose (1 microg, 4500 +/- 1700; 3 microg, 1900 +/- 60; 10 microg, 1100 +/- 100 all at 4 h post-intravenous dose). Peak plasma TNF levels were not dose-dependent (> 8 ng/ml), but plasma TNF was always detectable (> 0.2 ng/ml at 10 h post-intravenous dose). Intravenous LPS administration at 0 h also blocked pleocytosis, but the inhibitory effect was lost when administration at -8 h. In conclusion, the degree and duration of endotoxaemia affect the meningeal inflammatory response to LPS in experimental meningitis.

The MisR/MisS two-component regulatory system influences inner core structure and immunotype of lipooligosaccharide in Neisseria meningitidis

Lipooligosaccharide (LOS) of Neisseria meningitidis is the major inflammatory mediator that contributes to meningococcal pathogenesis. Variable attachments to the HepII residue of the LOS inner core together with the alpha-chain heterogeneity result in immunologically distinct LOS structures, which may be selected for during human infection. Lpt-3, a phosphoethanolamine (PEA) transferase, and LgtG, a glucosyltransferase, mediate the substitution of PEA or glucose at the O-3 position of HepII in L3 or L2 LOS immunotypes, respectively. Inactivation of a two-component response regulator, encoded by NMB0595, in N. meningitidis strain NMB resulted in the loss of all PEA decorations on the LOS inner core expressed by the NMB0595 mutant. When compared with the parental strain NMB that predominantly expresses L2 immunotype LOS and other minor LOS structures, the NMB0595 mutant expresses a pure population of a novel LOS structure completely substituted at the HepII O-3 position with glucose, but lacking other PEA decorations on the inner core. Quantitative real time PCR experiments showed increased transcription of lgtG in the NMB0595 mutant, and no significant change in lpt-3 transcription. Inactivation of lgtG resulted in LOS inner cores without glucose, but these structures, even though the lpt-3 transcription was unaffected, also lacked the O-3-linked PEA. Consistently, a double mutation of lgtG and misR in strain NMB yielded a LOS structure without PEA or Glc substitution of HepII. These data indicated a new pathway for the regulation of LOS inner core structure in N. meningitidis through an environmental sensing two-component regulatory system, named misR(NMB0595)/misS(NMB0594) for regulator and sensor of the meningococcal inner core structure.

Activation of human dendritic cells is modulated by components of the outer membranes of Neisseria meningitidis

Neisseria meningitidis serogroup B is a major cause of life-threatening meningitis and septicemia worldwide, and no effective vaccine is available. Initiation of innate and acquired immune responses to N. meningitidis is likely to be dependent on cellular responses of dendritic cells (DC) to antigens present in the outer membrane (OM) of the meningococcus. In this study, the responses of human monocyte-derived DC (mo-DC) to OM isolated from parent (lipopolysaccharide [LPS]-replete) meningococci and from a mutant deficient in LPS were investigated. Parent OM selectively up-regulated Toll-like receptor 4 (TLR4) mRNA expression and induced mo-DC maturation, as reflected by increased production of chemokines, proinflammatory cytokines, and CD83, CD80, CD86, CD40, and major histocompatibility complex (MHC) class II molecules. In contrast, LPS-deficient OM selectively up-regulated TLR2 mRNA expression and induced moderate increases in both cytokine production and expression of CD86 and MHC class II molecules. Preexposure to OM, with or without LPS, augmented the allostimulatory properties of mo-DC, which induced proliferation of naive CD4+ CD45RA+ T cells. In addition, LPS-replete OM induced a greater gamma interferon/interleukin-13 ratio in naive T cells, whereas LPS-deficient OM induced the reverse profile. These data demonstrate that components of the OM, other than LPS, are also likely to be involved in determining the levels of DC activation and the nature of the T-helper immune response.

Outer membrane vesicles from Neisseria meningitidis: effects on cytokine production in human whole blood

The Norwegian group B meningococcal outer membrane vesicle (OMV) vaccine consists of outer membrane proteins (OMPs) as main antigens with significant amounts of lipopolysaccharide (LPS; 5-9% relative to protein). We have studied the ability of this OMV vaccine preparation to induce secretion of pro-inflammatory cytokines, tumour necrosis factor alpha (TNF-alpha), interleukin 1beta (IL-1beta), interleukin 6 (IL-6), interleukin 8 (IL-8) and anti-inflammatory cytokines, interleukin 4 (IL-4), interleukin 10 (IL-10) and interleukin 13 (IL-13) in a human whole blood model. Plasma levels of TNF-alpha, IL-1beta, IL-6 and IL-8 were massively increased; mean peak levels of TNF-alpha 44 696+/-7764, IL-1beta 38 043+/-5411, IL-6 10 057+/-1619 and IL-8 30 449+/-5397 pg/ml were obtained with an OMV-LPS concentration of 1 microg/ml; corresponding levels in control plasmas were below the detection limit of the assay. Mean maximal level of IL-10 (2540+/-144 pg/ml) was obtained at OMV-LPS concentration of 10 microg/ml, after 24 h; while the level in control plasma was below detection limit. OMV-LPS did not induce release of IL-4 and IL-13 in doses from 0.001-10 microg/ml. The present results show that OMVs from meningococci have potent pro-inflammatory properties and are likely to contribute to the observed local and systemic inflammatory effects.

Meningococcemia as a model for testing the hypothesis of antisepsis therapies

OBJECTIVE

To critically review the advantages and disadvantages of pediatric meningococcemia as a model for testing antisepsis therapies.

DATA SOURCES

Research and review articles on the pathogenesis and treatment of human meningococcemia, as well as editorial commentaries discussing the failure of clinical trials for adult sepsis or Systemic Inflammatory Response Syndrome. Data from these sources are presented in the context of the author's experience as principal investigator in a large, randomized trial on children with invasive meningococcal disease.

STUDY SELECTION AND DATA EXTRACTION

Studies were selected to include aspects of epidemiology, pathophysiology, outcome prediction, and therapeutic trials.

DATA SYNTHESIS

Compared with an adult sepsis population, meningococcemia is a single disease, diagnosed clinically with high reliability. Patients are previously healthy, without underlying medical or surgical conditions. In contrast to sepsis trials, nearly all patients with meningococcal disease receive effective antibiotics. Finally, meningococcemia most closely resembles animal models of endotoxin infusion, in which most antisepsis therapies have been highly effective. However, the meningococcal model carries major disadvantages, among them that meningococcemia is rare and rapidly progressive and patients are widely dispersed geographically. In addition, a wide range of experimental therapies is routinely provided in an attempt to preserve life or limbs.

CONCLUSIONS

Meningococcemia is an ideal model of a rapidly progressive bacterial infection associated with marked endotoxemia. Problems with the model can be overcome by extensive pretrial logistic planning, as well as close coordination and cooperation with national regulatory agencies.

Epidemiology and pathogenesis of Neisseria meningitidis

Neisseria meningitidis, an exclusive pathogen of humans, remains the leading worldwide cause of meningitis and fatal sepsis, usually in otherwise healthy individuals. In recent years, significant advances have improved our understanding of the epidemiology and genetic basis of meningococcal disease and led to progress in the development of the next generation of meningococcal vaccines. This review summarizes current knowledge of the human susceptibility to and the epidemiology and molecular pathogenesis of meningococcal disease.

Update on meningococcal disease with emphasis on pathogenesis and clinical management

The only natural reservoir of Neisseria meningitidis is the human nasopharyngeal mucosa. Depending on age, climate, country, socioeconomic status, and other factors, approximately 10% of the human population harbors meningococci in the nose. However, invasive disease is relatively rare, as it occurs only when the following conditions are fulfilled: (i) contact with a virulent strain, (ii) colonization by that strain, (iii) penetration of the bacterium through the mucosa, and (iv) survival and eventually outgrowth of the meningococcus in the bloodstream. When the meningococcus has reached the bloodstream and specific antibodies are absent, as is the case for young children or after introduction of a new strain in a population, the ultimate outgrowth depends on the efficacy of the innate immune response. Massive outgrowth leads within 12 h to fulminant meningococcal sepsis (FMS), characterized by high intravascular concentrations of endotoxin that set free high concentrations of proinflammatory mediators. These mediators belonging to the complement system, the contact system, the fibrinolytic system, and the cytokine system induce shock and diffuse intravascular coagulation. FMS can be fatal within 24 h, often before signs of meningitis have developed. In spite of the increasing possibilities for treatment in intensive care units, the mortality rate of FMS is still 30%. When the outgrowth of meningococci in the bloodstream is impeded, seeding of bacteria in the subarachnoidal compartment may lead to overt meningitis within 24 to 36 h. With appropriate antibiotics and good clinical surveillance, the mortality rate of this form of invasive disease is 1 to 2%. The overall mortality rate of meningococcal disease can only be reduced when patients without meningitis, i.e., those who may develop FMS, are recognized early. This means that the fundamental nature of the disease as a meningococcus septicemia deserves more attention.

Update on meningococcal disease with emphasis on pathogenesis and clinical management

The only natural reservoir of Neisseria meningitidis is the human nasopharyngeal mucosa. Depending on age, climate, country, socioeconomic status, and other factors, approximately 10% of the human population harbors meningococci in the nose. However, invasive disease is relatively rare, as it occurs only when the following conditions are fulfilled: (i) contact with a virulent strain, (ii) colonization by that strain, (iii) penetration of the bacterium through the mucosa, and (iv) survival and eventually outgrowth of the meningococcus in the bloodstream. When the meningococcus has reached the bloodstream and specific antibodies are absent, as is the case for young children or after introduction of a new strain in a population, the ultimate outgrowth depends on the efficacy of the innate immune response. Massive outgrowth leads within 12 h to fulminant meningococcal sepsis (FMS), characterized by high intravascular concentrations of endotoxin that set free high concentrations of proinflammatory mediators. These mediators belonging to the complement system, the contact system, the fibrinolytic system, and the cytokine system induce shock and diffuse intravascular coagulation. FMS can be fatal within 24 h, often before signs of meningitis have developed. In spite of the increasing possibilities for treatment in intensive care units, the mortality rate of FMS is still 30%. When the outgrowth of meningococci in the bloodstream is impeded, seeding of bacteria in the subarachnoidal compartment may lead to overt meningitis within 24 to 36 h. With appropriate antibiotics and good clinical surveillance, the mortality rate of this form of invasive disease is 1 to 2%. The overall mortality rate of meningococcal disease can only be reduced when patients without meningitis, i.e., those who may develop FMS, are recognized early. This means that the fundamental nature of the disease as a meningococcus septicemia deserves more attention.

Genetic basis for biosynthesis, structure, and function of meningococcal lipooligosaccharide (endotoxin)

The exclusive human pathogen Neisseria meningitidis expresses lipooligosaccharide (LOS), an endotoxin that is structurally distinct from the lipopolysaccharides (LPS) of enteric Gram-negative bacilli. Differences that appear to be biologically important occur in the composition and attachment of acyl chains to lipid A, phosphorylation patterns of lipid A, and the incorporation and phosphorylation of sugar residues in the LOS inner core. Further, unlike most enteric LPS, only two to five sugar residues are attached to the meningococcal LOS inner core, and there are no multiple repeating units of O-antigens. In contrast to Escherichia coli, where the LPS biosynthesis genes are organized as large operons, the meningococcal LOS biosynthesis genes are organized into small operons or are located individually in the chromosome. Some of these genetic loci in meningococci and gonococci display polymorphisms caused by localized chromosomal rearrangements. One mechanism of antigenic variation of meningococci LOS is the regulation of glycosyltransferase activity by slipped strand mispairing of homopolymeric tracts within the 5' end of the genes encoding these enzymes, resulting in the addition of different sugar residues to the LOS molecule. Meningococcal LOS is a critical virulence factor in N. meningitidis infections and is involved in many aspects of pathogenesis, including the colonization of the human nasopharynx, survival after bloodstream invasion, and the inflammation associated with the morbidity and mortality of meningococcemia and meningitis. Meningococcal LOS, which is a component of serogroup B meningococcal vaccines currently in clinical trials, has been proposed as a candidate for a new generation of meningococcal vaccines. The rapidly expanding knowledge of the genetic basis for biosynthesis, structure, and regulation of meningococcal LOS provides insights into unique endotoxin structures and the precise role of LOS in the pathogenesis of meningococcal disease.

The lipooligosaccharide (LOS) of Neisseria meningitidis serogroup B strain NMB contains L2, L3, and novel oligosaccharides, and lacks the lipid-A 4'-phosphate substituent

The complete structure of the lipooligosaccharide (LOS) from Neisseria meningitidis strain NMB (serotype 2b:P1.2,5), a serogroup B cerebrospinal fluid isolate, was determined. Two oligosaccharide (OS) fractions and lipid-A were obtained following mild acid hydrolysis of the LOS. The structures in these fractions were determined using glycosyl composition and linkage analyses, N spectroscopy and mass spectrometry. One oligosaccharide fraction (OS1) consists of a molecule having a glycosyl sequence identical to that previously reported for the LOS from immunotype L2 N. meningitidis [A. Gamain, M. Beurret, F. Michon, J.-R. Brisson, and H.J. Jennings, J. Biol. Chem.,267,(112) 922-925] i.e., a lacto-N-neotetraose is attached to heptose I (Hep I), with terminally linked N-acetylglucosaminosyl and glucosyl residues attached to Hep II of the inner core. Approximately 70% of this structure is acetylated at O-6 of the terminally linked alpha-N-acetyl-glucosaminosyl residue. As with the L2 structure, the NMB LOS contained phosphoethanolamine (PEA) at O-6 or O-7 of the Hep II residue. The second oligosaccharide fraction (OS2) contains a a mixture of three different molecules, all of which vary from one another in their glycosyl substitution patterns of the Hep II residue. The most abundant molecule in OS2 has a structure identical to that of OSI, i.e., it has the L2 glycosyl sequence. A second molecule (OS2a) lacks the terminal glucosyl residue at O-3 of Hep II; i.e., it has a glycosyl sequence identical to that of the mild acid released oligosaccharide of N. meningitidis immunotype L3, L4, or L7 LOSs. The third molecule (OS2b) is a novel structure that lacks the terminal N-acetylglucosaminosyl residue linked to O-2 of Hep II. Overall, 76% of OS released from NMB LOS has the L2 structure, 15% is OS2a (L3), and 9% is OS2b. A portion (20%) of the molecules in the NMB LOS preparation also contained terminally linked sialic acid attached to O-3 of the lacto-N-neotetraose galactosyl residue, which is also consistent with the L3, or L4 LOS structures. In contrast to the previously reported structure of N. meningitidis lipid-A [V. A. Kulshin, U. Zähringer, B. Linder, C.E. Frasch, C-M. Tsai, B.A. Dmitriev, and E.T Rietschel, J. Bacteriol., 174, (1992)1793-1800], only 30% of the lipid-A from NMB LOS possesses 4'-phosphate. Comparison with the lipid-A of LOS purified from an isogenic acapsulate mutant, M7, revealed that the 4'-position was almost completely occupied with phosphate. These data emphasize the structural heterogeneity of the OS and phosphate substituents of Hep II, and 4'-phosphorylation of lipid-A of meningococcal LOS.

The Pattern of Interleukin-1β (IL-1β) and Its Modulating Agents IL-1 Receptor Antagonist and IL-1 Soluble Receptor Type II in Acute Meningococcal Infections

Interleukin-1β (IL-1β) is considered an important mediator in the pathogenesis of septic shock or bacterial meningitis. Its activity is specifically modulated by IL-1 receptor antagonist (IL-1Ra) and IL-1 soluble receptor type II (IL-1sRII). We now describe the time-course of IL-1β and these modulating agents in 59 patients with acute meningococcal infections, the prototype human disease of acute endotoxin exposure. Plasma IL-1β was increased only in severe shock and normalized within 12 to 24 hours, indicating that patients were admitted in an early stage of cytokine activation. Increased IL-1β values in cerebrospinal fluid (CSF ) were confined to patients with meningitis. Plasma IL-1Ra was elevated in both shock and nonshock patients, extremely high values being measured in severe shock. High concentrations of IL-1Ra in CSF were found in meningitis. Plasma IL-1Ra peaked shortly after IL-1β and decreased steeply in 1 to 2 days, followed by sustained moderately elevated levels in shock patients. Interestingly, IL-1sRII showed a completely different pattern. At admission, both nonshock and shock patients manifested a similar moderate increase of plasma IL-1sRII. However, during recovery plasma IL-1sRII further increased reaching maximal concentrations 3 to 5 days after admission, 1 to 2 days after normalization of IL-1Ra. In shock patients this increase was more prominent than in nonshock patients. It is hypothesized that this increase in plasma IL-1sRII can be explained by a synergistic effect of dexamethasone and endotoxin. A second interesting observation was that, unlike the pattern in plasma, IL-1sRII levels in CSF paralleled those of IL-1β and IL-1Ra. This suggests different modulation of IL-1β activity in the subarachnoid space and the plasma compartment. We conclude that: (1) During the early stage of meningococcal infections IL-1Ra modulates IL-1 activity, whereas during recovery IL-1sRII may be more important. (2) Modulation in CSF and in the plasma compartment are differentially regulated.

The Pattern of Interleukin-1β (IL-1β) and Its Modulating Agents IL-1 Receptor Antagonist and IL-1 Soluble Receptor Type II in Acute Meningococcal Infections

Interleukin-1β (IL-1β) is considered an important mediator in the pathogenesis of septic shock or bacterial meningitis. Its activity is specifically modulated by IL-1 receptor antagonist (IL-1Ra) and IL-1 soluble receptor type II (IL-1sRII). We now describe the time-course of IL-1β and these modulating agents in 59 patients with acute meningococcal infections, the prototype human disease of acute endotoxin exposure. Plasma IL-1β was increased only in severe shock and normalized within 12 to 24 hours, indicating that patients were admitted in an early stage of cytokine activation. Increased IL-1β values in cerebrospinal fluid (CSF ) were confined to patients with meningitis. Plasma IL-1Ra was elevated in both shock and nonshock patients, extremely high values being measured in severe shock. High concentrations of IL-1Ra in CSF were found in meningitis. Plasma IL-1Ra peaked shortly after IL-1β and decreased steeply in 1 to 2 days, followed by sustained moderately elevated levels in shock patients. Interestingly, IL-1sRII showed a completely different pattern. At admission, both nonshock and shock patients manifested a similar moderate increase of plasma IL-1sRII. However, during recovery plasma IL-1sRII further increased reaching maximal concentrations 3 to 5 days after admission, 1 to 2 days after normalization of IL-1Ra. In shock patients this increase was more prominent than in nonshock patients. It is hypothesized that this increase in plasma IL-1sRII can be explained by a synergistic effect of dexamethasone and endotoxin. A second interesting observation was that, unlike the pattern in plasma, IL-1sRII levels in CSF paralleled those of IL-1β and IL-1Ra. This suggests different modulation of IL-1β activity in the subarachnoid space and the plasma compartment. We conclude that: (1) During the early stage of meningococcal infections IL-1Ra modulates IL-1 activity, whereas during recovery IL-1sRII may be more important. (2) Modulation in CSF and in the plasma compartment are differentially regulated.

Net inflammatory capacity of human septic shock plasma evaluated by a monocyte-based target cell assay: identification of interleukin-10 as a major functional deactivator of human monocytes

We have developed a functional assay to study the inflammatory capacity of plasma collected from patients with severe gram-negative septic shock. In this assay, elutriation-purified, cryo-preserved human monocytes from one healthy donor are combined with plasma from patients with severe persistent septic shock for 5 h. Subsequently, the plasma is removed, medium added, and procoagulant activity (PCA) and secretion of tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) measured after 18-h incubation. Plasma from 10 patients (6 died) infected with Neisseria meningitidis previously shown to contain high levels of native lipopolysaccharide (LPS) (median 2,700 pg/ml), TNF-alpha, IL-6, IL-8, and complement activation products, had a low net spontaneous inflammatory capacity on the monocytes. The median levels of PCA, TNF-alpha, and IL-6 were 5, 0, and 4%, respectively, of the monocyte activities induced by normal plasma boosted with purified N. meningitidis (Nm)-LPS (2,500 pg/ml; net LPS-boosted capacity, 100%). The levels of PCA, TNF-alpha, and IL-6 obtained with plasma from shock patients were not different from those induced by plasma from 10 meningococcal patients without shock or with plasma from healthy persons. Boosting shock plasma with 2,500 pg/ml Nm-LPS had little effect on the monocyte activities since the median values of PCA, TNF-alpha, and IL-6 revealed a minimal increase from 5, 0, and 4% to 9, 2, and 6%, respectively. The shock plasmas revealed a strong LPS-inhibitory capacity that was largely absent in plasmas from 10 meningococcal patients without shock since the median levels of PCA, TNF-alpha, and IL-6 increased from 5, 0, and 0% to 135, 51, and 73%, respectively, after boosting with 2,500 pg/ml Nm-LPS. The LPS-inhibitory capacity was closely associated with the levels of IL-10. The median levels of IL-10 were 19,000 pg/ml in nine shock patients vs. 22 pg/ml in nine nonshock patients with systemic meningococcal disease. Removal of native IL-10 by immunoprecipitation restored the capacity of plasmas to induce monocyte activation either by native LPS or by boosting with Nm-LPS. IL-4 and TGF-beta were not detected in shock plasmas. In 24 patients with detectable meningococcal LPS ( > 10 pg/ml, 0.1 endotoxin units/ml), the levels of IL-10 were correlated to the levels of LPS (r = 0.79, P < 0.001). IL-10 declined from initiation of antibiotic therapy and paralleled the levels of native LPS. Decreasing levels of IL-10 in serially collected shock plasmas were directly related to increasing monocyte responsiveness after Nm-LPS boosting. These results suggest that IL-10 plays a major role in containing activation of monocytes and possibly other LPS-responsive cells during overwhelming meningococcemia.

Assessment of the effect of candidate anti-inflammatory treatments on the interaction between meningococci and inflammatory cells in vitro in a whole blood model

A wide range of immunomodulating agents are now available which may be of benefit in reducing inflammatory cell activation in meningococcal sepsis. In order to facilitate selection of candidate anti-inflammatory agents for clinical trials, we have used an in vitro whole blood model to evaluate the effects on meningococcal induced neutrophil and monocyte activation, of dexamethasone, prostacyclin, pentoxifylline and a human IgM anti-lipid A monoclonal antibody (HA-1A). Known concentrations of heat and penicillin killed meningococci were added to whole blood and the time course of cellular activation was determined. Using elastase alpha 1-antitrypsin (elastase-alpha 1-AT) and TNF alpha production as markers of neutrophil and monocyte activation respectively, plasma levels of elastase-alpha 1-AT and TNF alpha were found to increase in a dose-dependent manner. Elastase-alpha 1-AT was detected early, with most release occurring between 15-30 min whereas TNF alpha was detected later, between 120-180 min. Dexamethasone, prostacyclin and pentoxifylline caused a dose-dependent inhibition of TNF alpha release but had no effect on elastase release. HA-1A had no effect on either TNF alpha or elastase release. This model may be useful in determining the sequence of inflammatory cell activation and in selecting candidate anti-inflammatory agents for evaluation in clinical trials.

Endotoxemia: methods of detection and clinical correlates

As an assay for endotoxin, the Limulus amebocyte lysate assay has several desirable properties: sensitivity, specificity, and potential for adaptation to a quantitative format. Several modifications have been developed to enhance its potential for clinical application. The modifications that allow quantitative measurement of endotoxin and also improve its application to blood samples are described in this review. In fluids other than blood, the detection of endotoxin with the Limulus amebocyte lysate assay can be used as an aid to identify the presence of gram-negative bacteria, and the assay has established utility. With blood, however, there are a range of factors that interfere with the detection of endotoxemia and there are disparate views with respect to the diagnostic and prognostic significance of the test results. In general, the clinical significance of the finding of endotoxemia broadly parallels the frequency and importance of gram-negative sepsis in the patient groups studied and a decline in endotoxin levels accompanies clinical improvement. However, with therapies designed to reduce levels of endotoxin, or to antagonize its effects, it is unclear whether clinical improvement occurs as a consequence of changes in the levels of endotoxemia.

Kinetics of tumour necrosis factor-alpha, soluble tumour necrosis factor receptors, interleukin 1-beta and its receptor antagonist during serious infections

Tumour necrosis factor-alpha (TNF) and interleukin-1 beta (IL-1 beta) are the central mediators in the genesis of sepsis. The proinflammatory effects of these cytokines are counteracted in vivo by natural inhibitors. Soluble TNF receptors (sTNFR) are shed upon inflammatory stimuli such as IL-1 beta and TNF itself. Circulating TNF can be complexed by these receptors, thus preventing TNF from binding to effector cells. The binding of IL-1 beta to its receptor can be blocked by high concentrations of interleukin-1 receptor antagonist (IL-1Ra), which is produced and released upon nearly the same stimuli as IL-1 beta. This review presents some aspects of the kinetic behaviour of native sTNFR and of the production of native IL-1Ra during severe infections. It appears that in fulminant septicaemia, the plasma concentration of TNF is increased only transiently, during the very early stage of the infection. The concentration of sTNFR, in contrast, remains elevated much longer, probably due to a slower clearance. During the acute stage of severe infectious diseases, peripheral blood cells cannot be stimulated to produce IL-1 beta. The production of IL-1 Ra, in contrast, is not affected. Thus, the kinetic behaviour and regulation of TNF and IL-1 beta, is different from that of their antiinflammatory counterparts.