Mechanisms of injury in bacterial meningitis

Meningitis caused by Aeromonas hydrophila in Oreochromis niloticus: Proteomics and druggability of virulence factors

Meningitis caused by Gram-negative bacteria is a serious public health problem, causing morbidity and mortality in both children and adults. Here, we propose a novel experimental model using Nile tilapia (Oreochromis niloticus) to study neuroinflammation. The fish were infected with Aeromonas hydrophila, and the course of infection was monitored in the peripheral blood. Septicemia was obvious in the blood, while in the brain tissue, infection of the meninges was present. The histopathological examination showed suppurative meningitis, and the cellular immune response in the brain tissue during infection was mediated by microglia. These cells were morphologically characterized and phenotyped by MHC class II markers and CD68. The increased production of TNF-α, IL-1β and iNOS supported the infiltration of these cells during the neuroinflammatory process. In the proteomic analysis of A. hydrophila isolated from brain tissue, we found chemotactic and transport proteins, proteolytic enzymes and enzymes associated with the dismutation of nitric oxide (NO), as well as motor proteins and those responsible for cell division. After characterizing the most abundant proteins during the course of infection, we investigated the druggability index of these proteins and identified promising peptide sequences as molecular targets that are similar among bacteria. Thus, these findings deepened the understanding of the pathophysiology of meningitis caused by A. hydrophila. Moreover, through the proteomics analysis, important mechanisms and pathways used by the pathogen to subvert the host response were revealed, providing insights for the development of novel antibiotics and vaccines.

Self-Reported Executive Functioning in Young Adult Survivors of Childhood Bacterial Meningitis

OBJECTIVE

This study investigated executive functions (EFs) in young adult survivors of childhood bacterial meningitis (BM). These skills are important for normal development, and their potential vulnerability in early years suggests that childhood BM could affect executive functions in the longer term.

METHOD

The adult self-report Behavior Rating Inventory of Executive Function was administered to 474 young adult survivors of childhood BM who participated in the 20|30 Dutch Postmeningitis study. Average scores were compared to population-norm group scores. Subgroup scores were compared according to causative pathogen and age at onset.

RESULTS

Young adult survivors of childhood BM scored lower on overall metacognition than the age-matched population norm group. Young adult survivors of childhood BM caused by Streptococcus pneumoniae, S. agalactiae, or Escherichia coli had lower scores than cases caused by Neisseria meningitidis. Survivors with age-at-onset below 12 months had a higher (worse) overall EF score than survivors with age-at-onset above 12 months.

CONCLUSIONS

Young adult survivors of childhood BM experience difficulties in EF. However, most of the self-reported EF scores were within the norm. Future studies need to additionally assess EF in adult survivors of childhood BM using performance-based tests.

Diagnostic accuracy of interleukin-6 in multiple diseases: An umbrella review of meta-analyses

Objective

This review aims to conduct a comprehensive study of the diagnostic accuracy of interleukin-6 (IL-6) for multiple diseases by utilizing existing systematic reviews and meta-analyses.

Methods

We performed a thorough search of Embase, Web of Science, PubMed, and Cochrane Database of Systematic Reviews up to April 2023 to gather meta-analyses that investigate the diagnostic accuracy of IL-6. To assess the methodological quality of the studies, we employed the Assessing the Methodological Quality of Systematic Reviews-2 and Grading of Recommendations, Assessment, Development and Evaluation criteria.

Results

We included 34 meta-analyses out of the 3024 articles retrieved from the search. These meta-analyses covered 9 categories of diseases of the International Classification of Diseases-11. Studies rated as "Critically Low" or "Very Low" in the quality assessment process were excluded, resulting in a total of 6 meta-analyses that encompassed sepsis, colorectal cancer, tuberculous pleural effusion (TPE), endometriosis, among others. Among these diseases, IL-6 demonstrated a relatively high diagnostic potential in accurately identifying TPE and endometriosis.

Conclusions

IL-6 exhibited favorable diagnostic accuracy across multiple diseases, suggesting its potential as a reliable diagnostic biomarker in the near future. Substantial evidence supported its high diagnostic accuracy, particularly in the cases of TPE and endometriosis.

Understanding immune microenvironment alterations in the brain to improve the diagnosis and treatment of diverse brain diseases

Abnormal inflammatory states in the brain are associated with a variety of brain diseases. The dynamic changes in the number and function of immune cells in cerebrospinal fluid (CSF) are advantageous for the early prediction and diagnosis of immune diseases affecting the brain. The aggregated factors and cells in inflamed CSF may represent candidate targets for therapy. The physiological barriers in the brain, such as the blood‒brain barrier (BBB), establish a stable environment for the distribution of resident immune cells. However, the underlying mechanism by which peripheral immune cells migrate into the brain and their role in maintaining immune homeostasis in CSF are still unclear. To advance our understanding of the causal link between brain diseases and immune cell status, we investigated the characteristics of immune cell changes in CSF and the molecular mechanisms involved in common brain diseases. Furthermore, we summarized the diagnostic and treatment methods for brain diseases in which immune cells and related cytokines in CSF are used as targets. Further investigations of the new immune cell subtypes and their contributions to the development of brain diseases are needed to improve diagnostic specificity and therapy.

Application of metabolomics in diagnostics and differentiation of meningitis: A narrative review with a critical approach to the literature

Due to its high mortality rate associated with various life-threatening sequelae, meningitis poses a vital problem in contemporary medicine. Numerous algorithms, many of which were derived with the aid of artificial intelligence, were brought up in a strive for perfection in predicting the status of sepsis-related survival or exacerbation. This review aims to provide key insights on the contextual utilization of metabolomics. The aim of this the metabolomic approach set of methods can be used to investigate both bacterial and host metabolite sets from both the host and its microbes in several types of specimens - even in one's breath, mainly with use of two methods - Mass Spectrometry (MS) and Nuclear Magnetic Resonance (NMR). Metabolomics, and has been used to elucidate the mechanisms underlying disease development and metabolic identification changes in a wide range of metabolite contents, leading to improved methods of diagnosis, treatment, and prognosis of meningitis. Mass spectrometry (MS) and Nuclear Magnetic Resonance (NMR) are the main analytical platforms used in metabolomics. Its high sensitivity accounts for the usefulness of metabolomics in studies into meningitis, its sequelae, and concomitant comorbidities. Metabolomics approaches are a double-edged sword, due to not only their flexibility, but also - high complexity, as even minor changes in the multi-step methods can have a massive impact on the results. Information on the differential diagnosis of meningitis act as a background in presenting the merits and drawbacks of the use of metabolomics in context of meningeal infections.

Cerebral vasculitis as a complication of pneumococcal meningitis: A cohort study

OBJECTIVE

Cerebral vasculitis (CV) is a severe complication of pneumococcal meningitis (PM); whether dexamethasone use can reduce its occurrence remains to be determined.

METHODS

This is a retrospective observational bicentric study analyzing all adults with proven PM hospitalized between January 2002 and December 2020 in two tertiary hospitals. Extrapolating from a standardized definition of primary angiitis of the central nervous system, we defined CV as worsened neurological symptoms associated with compatible imaging. All images were analyzed by a radiologist, and two neurologists reviewed all inconclusive cases of suspected CV for adjudication. Factors associated with CV were analyzed, including dexamethasone use. A subgroup analysis was limited to patients with a lumbar puncture at PM diagnosis.

RESULTS

Among 168 patients with PM, 49 (29.2%) had CV, occurring after a median of 8 days (IQR 5-13) of PM diagnosis. In multivariate analysis (N = 151), initial CRP was associated with CV (OR 1.28 per 50-unit increase, p = 0.003), which was marginally linked with delayed hospital admission more than 48 hours after first symptoms (OR 2.39, p = 0.06) and prior NSAID intake (OR 2.94, p = 0.05). Dexamethasone administration did not impact CV occurrence. In 133 patients having undergone lumbar puncture, CSF protein level > 4.4 g/L (OR 4.50, p = 0.006) was associated with CV.

CONCLUSIONS

In our cohort, CV was a frequent and severe complication of PM, often occurring in association with unduly delayed medical care, high CRP at admission, and high levels of protein in CSF.

An Integrative Approach to Investigate the Mode of Action of (-)-Dendroparishiol in Bacterial Meningitis: Computer-Aided Estimation of Biological Activity and Network Pharmacology

Bacterial meningitis remains one of the most prevalent infectious diseases worldwide. Although advances in medical care have improved mortality and morbidity, neurological complications remain high. Therefore, aside from antibiotics, therapeutic adjuvants targeting neuroinflammation are essential to combat the long-term neuronal sequelae of bacterial meningitis. In the present study, we propose (-)-dendroparishiol as a potential add-on therapy to improve neuroinflammation associated with bacterial meningitis. The biological activity of (-)-dendroparishiol was first predicted by computational analysis and further confirmed in vitro using a cell-based assay with LPS-induced BV-2 microglial cells. Biological pathways involved with (-)-dendroparishiol were identified by applying network pharmacology. Computational predictions of biological activity indicated possible attenuation of several inflammatory processes by (-)-dendroparishiol. In LPS-induced BV-2 microglial cells, (-)-dendroparishiol significantly reduced the expression of inflammatory mediators: iNOS, NO, COX-2, IL-6, and TNF-α. Molecular docking results demonstrated the potential iNOS and COX-2 inhibitory activity of (-)-dendroparishiol. Network pharmacological analysis indicated the plausible role of (-)-dendroparishiol in biological processes involved in oxidative stress and neuroinflammation with enrichment in neuroinflammatory pathways. Overall, this study provides scientific evidence for the potential application of (-)-dendroparishiol in the management of bacterial meningitis-associated neuroinflammation.

Bacterial meningitis in Africa

Bacterial meningitis differs globally, and the incidence and case fatality rates vary by region, country, pathogen, and age group; being a life-threatening disease with a high case fatality rate and long-term complications in low-income countries. Africa has the most significant prevalence of bacterial meningitis illness, and the outbreaks typically vary with the season and the geographic location, with a high incidence in the meningitis belt of the sub-Saharan area from Senegal to Ethiopia. Streptococcus pneumoniae (pneumococcus) and Neisseria meningitidis (meningococcus) are the main etiological agents of bacterial meningitis in adults and children above the age of one. Streptococcus agalactiae (group B Streptococcus), Escherichia coli, and Staphylococcus aureus are neonatal meningitis's most common causal agents. Despite efforts to vaccinate against the most common causes of bacterial neuro-infections, bacterial meningitis remains a significant cause of mortality and morbidity in Africa, with children below 5 years bearing the heaviest disease burden. The factors attributed to this continued high disease burden include poor infrastructure, continued war, instability, and difficulty in diagnosis of bacterial neuro-infections leading to delay in treatment and hence high morbidity. Despite having the highest disease burden, there is a paucity of African data on bacterial meningitis. In this article, we discuss the common etiologies of bacterial neuroinfectious diseases, diagnosis and the interplay between microorganisms and the immune system, and the value of neuroimmune changes in diagnostics and therapeutics.

Progressive cognitive impairment after recovery from neuroinvasive and non-neuroinvasive Listeria monocytogenes infection

Background

Neuro-cognitive impairment is a deleterious complication of bacterial infections that is difficult to treat or prevent. Listeria monocytogenes (Lm) is a neuroinvasive bacterial pathogen and commonly used model organism for studying immune responses to infection. Antibiotic-treated mice that survive systemic Lm infection have increased numbers of CD8⁺ and CD4⁺ T-lymphocytes in the brain that include tissue resident memory (T_RM) T cells, but post-infectious cognitive decline has not been demonstrated. We hypothesized that Lm infection would trigger cognitive decline in accord with increased numbers of recruited leukocytes.

Methods

Male C57BL/6J mice (age 8 wks) were injected with neuroinvasive Lm 10403s, non-neuroinvasive Δhly mutants, or sterile saline. All mice received antibiotics 2-16d post-injection (p.i.) and underwent cognitive testing 1 month (mo) or 4 mo p.i. using the Noldus PhenoTyper with Cognition Wall, a food reward-based discrimination procedure using automated home cage based observation and monitoring. After cognitive testing, brain leukocytes were quantified by flow cytometry.

Results

Changes suggesting cognitive decline were observed 1 mo p.i. in both groups of infected mice compared with uninfected controls, but were more widespread and significantly worse 4 mo p.i. and most notably after Lm 10403s. Impairments were observed in learning, extinction of prior learning and distance moved. Infection with Lm 10403s, but not Δhly Lm, significantly increased numbers of CD8⁺ and CD4⁺ T-lymphocytes, including populations expressing CD69 and T_RM cells, 1 mo p.i. Numbers of CD8⁺, CD69⁺CD8⁺ T-lymphocytes and CD8⁺ T_RM remained elevated at 4 mo p.i. but numbers of CD4⁺ cells returned to homeostatic levels. Higher numbers of brain CD8⁺ T-lymphocytes showed the strongest correlations with reduced cognitive performance.

Conclusions

Systemic infection by neuroinvasive as well as non-neuroinvasive Lm triggers a progressive decline in cognitive impairment. Notably, the deficits are more profound after neuroinvasive infection that triggers long-term retention of CD8⁺ T-lymphocytes in the brain, than after non-neuroinvasive infection, which does not lead to retained cells in the brain. These results support the conclusion that systemic infections, particularly those that lead to brain leukocytosis trigger a progressive decline in cognitive function and implicate CD8⁺ T-lymphocytes, including CD8⁺T_RM in the etiology of this impairment.

Bovine neutrophil chemotaxis to Listeria monocytogenes in neurolisteriosis depends on microglia-released rather than bacterial factors

BACKGROUND

Listeria monocytogenes (Lm) is a bacterial pathogen of major concern for humans and ruminants due to its neuroinvasive potential and its ability to cause deadly encephalitis (neurolisteriosis). On one hand, polymorphonuclear neutrophils (PMN) are key players in the defense against Lm, but on the other hand intracerebral infiltration with PMN is associated with significant neural tissue damage. Lm-PMN interactions in neurolisteriosis are poorly investigated, and factors inducing PMN chemotaxis to infectious foci containing Lm in the central nervous system (CNS) remain unidentified.

METHODS

In this study, we assessed bovine PMN chemotaxis towards Lm and supernatants of infected endogenous brain cell populations in ex vivo chemotaxis assays, to identify chemotactic stimuli for PMN chemotaxis towards Lm in the brain. In addition, microglial secretion of IL-8 was assessed both ex vivo and in situ.

RESULTS

Our data show that neither Lm cell wall components nor intact bacteria elicit chemotaxis of bovine PMN ex vivo. Moreover, astrocytes and neural cells fail to induce bovine PMN chemotaxis upon infection. In contrast, supernatant from Lm infected microglia readily induced chemotaxis of bovine PMN. Microglial expression and secretion of IL-8 was identified during early Lm infection in vitro and in situ, although IL-8 blocking with a specific antibody could not abrogate PMN chemotaxis towards Lm infected microglial supernatant.

CONCLUSIONS

These data provide evidence that host-derived rather than bacterial factors trigger PMN chemotaxis to bacterial foci in the CNS, that microglia have a primary role as initiators of bovine PMN chemotaxis into the brain during neurolisteriosis and that blockade of these factors could be a therapeutic target to limit intrathecal PMN chemotaxis and PMN associated damage in neurolisteriosis.

Tp47 promoted the phagocytosis of HMC3 cells through autophagy induced by endoplasmic reticulum stress

BACKGROUND

Central nervous system damage is an essential clinical feature that occurs in the early or late stages of syphilis infection. The abnormal enhancement of microglial phagocytosis can cause damage to the nervous system. However, the contribution of abnormally enhanced microglial phagocytosis to the pathogenesis of Treponema pallidum subsp. pallidum (T. pallidum) infection remains unknown.

OBJECTIVES

In this study, we sought to determine the role of recombinant T. pallidum Tp47 in promoting microglia phagocytosis and its associated mechanisms.

METHODS

Microglial HMC3 cells were used to investigate the effect of the Tp47 on phagocytosis and the roles of autophagy and endoplasmic reticulum stress in Tp47-induced phagocytosis.

RESULTS

HMC3 cells exhibited obvious phagocytosis when stimulated with Tp47. The levels of P62 degradation, Beclin1 expression and the LC3II/LC3I ratio were significantly elevated, and the fusion of autophagosomes and lysosomes was promoted in Tp47-stimulated HMC3 cells. Treatment with the autophagy inhibitors 3-MA and Baf A1 inhibited Tp47-induced phagocytosis. Meanwhile, the endoplasmic reticulum stress markers PERK, IRE1α, GRP78, ATF4 and XBP1s were upregulated in Tp47-stimulated HMC3 cells. In addition, we found that TUDCA could inhibit Tp47-induced expression of IRE1α but not PERK or ATF4. 4-PBA inhibited TP47-induced PERK and ATF4 protein expression but did not inhibit IRE1α expression. Attenuation of endoplasmic reticulum stress by administration of TUDCA and 4-PBA abrogated Tp47-mediated autophagy.

CONCLUSIONS

These results suggested that Tp47 activated autophagy through two key pathways associated with endoplasmic reticulum stress, PERK/ATF4 and IRE1/XBP1, to promote phagocytosis in HMC3 cells. These findings provided a basis for the understanding of the pathophysiology of neurological disorders that occur during the course of syphilis.

Psychomotor Speed Predicts Outcome in Patients with Acute Meningitis and Encephalitis: A Prospective Observational Study

Background and Purpose. Although acute meningitis and encephalitis are known to cause cognitive dysfunction, the prognostic values of neuropsychological and neurophysiological tests in predicting clinical outcomes are seldom studied. We investigated specific neurocognitive dysfunction and event-related potentials (ERPs), which can predict functional outcomes in patients with acute meningitis and encephalitis. Methods. We enrolled consecutive adult patients with acute meningitis and encephalitis and performed neuropsychological tests and ERP studies using a passive auditory oddball paradigm at enrollment. Patient functional outcomes were assessed using the Glasgow Outcome Scale at 6 (GOS6) months after discharge. Results. Twenty-two patients were included in the study. Among 21 patients who performed neuropsychological tests, Korean-Trail Making Test-Elderly's version, Part A time (TMT-A time) correlated with GOS6, which remained significant even after controlling for age. We identified a significant association between TMT-A time and P3a latency. Post-hoc analysis showed that patients with longer TMT-A time (≥23 s) tended to have longer P3a latency than those with shorter TMT-A time. Conclusions. Decreased psychomotor speed predicted poor clinical outcomes. Because TMT-A time can be performed at the bedside in a relatively short time, this might be a useful neuropsychological biomarker to predict or monitor clinical outcomes. Furthermore, passive oddball P3a may be useful in patients with more severe disease who are unable to perform the TMT task.

Deciphering the TLR transcriptome and downstream signaling pathway in cerebrospinal fluid in pediatric meningitis

OBJECTIVE/DESIGN

Pediatric meningitis is characterized by a colossal inflammatory response to the pathogen in the central nervous system (CNS). This unabated inflammatory response persists even after the removal of the pathogen by antibiotics/steroids causing collateral damage to CNS tissue. Toll-like receptors (TLRs) are the key players in the recognition and elicitation of innate-immune response against bacterial/viral components in cerebrospinal fluid (CSF). Till date, the precise understanding of TLR-triggered inflammatory response in pediatric meningitis is lacking. The present study was designed to delineate the role of TLR transcriptome and downstream signaling pathways in CSF of pediatric meningitis.

METHODS

Children in the age group of > 3 months to 12 years with pediatric meningitis were included. A total of 249 cases of pediatric meningitis (bacterial = 89, viral = 160) were included. In addition, 71 children who tested negative to the pathogen in CSF tap and did not have signs of infection clinically constituted the controls. RNA was extracted from the CSF samples of both cases and controls. The relative gene expression profile of 42 TLR signaling pathway genes was performed. For the analysis of secretory cytokines and chemokines in CSF, Luminex assay was performed.

RESULTS

We report global upregulation of TLR genes in patients with acute bacterial meningitis (ABM). The downstream signaling molecules were upregulated as well. The CSF of pediatric ABM patients revealed a predominant pro-inflammatory milieu marked by increased levels of pro-inflammatory cytokines. A significant correlation between poor clinical outcomes of patients and an increased expression of TLR/pro-inflammatory cytokine genes was observed.

CONCLUSION

Our findings provide support for future studies exploring TLR-based adjunct therapy to limit the neurological sequelae, owing to persistent inflammation in pediatric ABM patients.

The Role of Formyl Peptide Receptors in Neurological Diseases via Regulating Inflammation

Formyl peptide receptors (FPRs) are a group of G protein-coupled cell surface receptors that play important roles in host defense and inflammation. Owing to the ubiquitous expression of FPRs throughout different cell types and since they interact with structurally diverse chemotactic agonists, they have a dual function in inflammatory processes, depending on binding with different ligands so that accelerate or inhibit key intracellular kinase-based regulatory pathways. Neuroinflammation is closely associated with the pathogenesis of neurodegenerative diseases, neurogenic tumors and cerebrovascular diseases. From recent studies, it is clear that FPRs are important biomarkers for neurological diseases as they regulate inflammatory responses by monitoring glial activation, accelerating neural differentiation, regulating angiogenesis, and controlling blood brain barrier (BBB) permeability, thereby affecting neurological disease progression. Given the complex mechanisms of neurological diseases and the difficulty of healing, we are eager to find new and effective therapeutic targets. Here, we review recent research about various mechanisms of the effects generated after FPR binding to different ligands, role of FPRs in neuroinflammation as well as the development and prognosis of neurological diseases. We summarize that the FPR family has dual inflammatory functional properties in central nervous system. Emphasizing that FPR2 acts as a key molecule that mediates the active resolution of inflammation, which binds with corresponding receptors to reduce the expression and activation of pro-inflammatory composition, govern the transport of immune cells to inflammatory tissues, and restore the integrity of the BBB. Concurrently, FPR1 is essentially related to angiogenesis, cell proliferation and neurogenesis. Thus, treatment with FPRs-modulation may be effective for neurological diseases.

Septic shock due to Escherichia coli meningoencephalitis treated with immunoglobulin-M-enriched immunoglobulin preparation as adjuvant therapy: a case report

BACKGROUND

Gram-negative bacteria are an uncommon etiology of spontaneous community-acquired adult meningitis and meningoencephalitis. Escherichia coli is a Gram-negative bacterium that is normally present in the intestinal microbial pool. Some Escherichia coli strains can cause diseases in humans and animals, with both intestinal and extraintestinal manifestations (extraintestinal pathogenic Escherichia coli) such as urinary tract infections, bacteremia with sepsis, and, more rarely, meningitis. Meningitis continues to be an important cause of mortality throughout the world, despite progress in antimicrobial chemotherapy and supportive therapy. The mortality rate fluctuates between 15% and 40%, and about 50% of the survivors report neurological sequelae. The majority of Escherichia coli meningitis cases develop as a result of hematogenous spread, with higher degrees of bacteremia also being related to worse prognosis. Cases presenting with impaired consciousness (that is, coma) are also reported to have poorer outcomes.

CASE PRESENTATION

We describe the case of a 48-year-old caucasian woman with meningoencephalitis, with a marked alteration of consciousness on admission, and septic shock secondary to pyelonephritis caused by Escherichia coli, treated with targeted antimicrobial therapy and immunoglobulin-M-enriched immunoglobulin (Pentaglobin) preparation as adjuvant therapy.

CONCLUSION

Despite the dramatic presentation of the patient on admission, the conflicting data on the use of immunoglobulins in septic shock, and the lack of evidence regarding their use in adult Escherichia coli meningoencephalitis, we obtained a remarkable improvement of her clinical condition, accompanied by partial resolution of her neurological deficits.

The Potentials of Melatonin in the Prevention and Treatment of Bacterial Meningitis Disease

Bacterial meningitis (BM) is an acute infectious central nervous system (CNS) disease worldwide, occurring with 50% of the survivors left with a long-term serious sequela. Acute bacterial meningitis is more prevalent in resource-poor than resource-rich areas. The pathogenesis of BM involves complex mechanisms that are related to bacterial survival and multiplication in the bloodstream, increased permeability of blood-brain barrier (BBB), oxidative stress, and excessive inflammatory response in CNS. Considering drug-resistant bacteria increases the difficulty of meningitis treatment and the vaccine also has been limited to several serotypes, and the morbidity rate of BM still is very high. With recent development in neurology, there is promising progress for drug supplements of effectively preventing and treating BM. Several in vivo and in vitro studies have elaborated on understanding the significant mechanism of melatonin on BM. Melatonin is mainly secreted in the pineal gland and can cross the BBB. Melatonin and its metabolite have been reported as effective antioxidants and anti-inflammation, which are potentially useful as prevention and treatment therapy of BM. In bacterial meningitis, melatonin can play multiple protection effects in BM through various mechanisms, including immune response, antibacterial ability, the protection of BBB integrity, free radical scavenging, anti-inflammation, signaling pathways, and gut microbiome. This manuscript summarizes the major neuroprotective mechanisms of melatonin and explores the potential prevention and treatment approaches aimed at reducing morbidity and alleviating nerve injury of BM.

Serum levels of neurofilament light chain, neuron-specific enolase and S100 calcium-binding protein B during acute bacterial meningitis: a prospective cohort study

PURPOSE

Acute bacterial meningitis (ABM) is a severe disease with an overall poor outcome. Neurofilament (NFL) has shown to be a promising biomarker of neuroaxonal injury in various neurological disorders but has not been investigated in ABM. The aims of this study were (i) to obtain a temporal profile of NFL, neuron-specific enolase (NSE) and S100B in serum during ABM, and (ii) to evaluate their use as biomarkers of severity (Glasgow coma score) and prognosis (Glasgow Outcome Score, GOS and death) in severe ABM.

METHODS

Fifteen adults with severe community-acquired ABM who were admitted to the intensive care unit (ICU) and fulfilled the inclusion criteria were included. Lumbar puncture and blood tests were performed on admission, and blood tests were performed three times daily during the ICU stay. GOS was obtained day 30.

RESULTS

Serum NFL was significantly elevated in ABM patients compared to healthy controls, both at admission and throughout the observation period (p < .01). NFL increased significantly from day 1 up to day 3-6 (p < .0001), peaking day 6. NSE increased significantly from admission up to day 3 (p < .01). At day 5-6, the serum values were not significantly different from values at admission. The highest median serum value of S100B was observed at admission (0.10 µg/L, IQR 0.06-0.14), significantly decreasing day 4-6 (p < .05). None of the investigated biomarkers revealed significant correlation with severity and prognosis.

CONCLUSION

This study represents a first clinical observation of the temporal profile of NFL in serum, in severe ABM. No correlation with severity or prognosis.

The formyl peptide receptor agonist Ac2-26 alleviates neuroinflammation in a mouse model of pneumococcal meningitis

Background

Bacterial meningitis is still a cause of severe neurological disability. The brain is protected from penetrating pathogens by the blood-brain barrier and the innate immune system. The invading pathogens are recognized by pattern recognition receptors including the G-protein-coupled formyl peptide receptors (FPRs), which are expressed by immune cells of the central nervous system. FPRs show a broad spectrum of ligands, including pro- and anti-inflammatory ones. Here, we investigated the effects of the annexin A1 mimetic peptide Ac2-26 in a mouse model of pneumococcal meningitis.

Methods

Wildtype (WT) and Fpr1- and Fpr2-deficient mice were intrathecally infected with Streptococcus pneumoniae D39 (type 2). Subsequently, the different mice groups were treated by intraperitoneal injections of Ac2-26 (1 mg/kg body weight) 2, 8, and 24 h post-infection. The extent of inflammation was analyzed in various brain regions by means of immunohistochemistry and real-time reverse transcription polymerase chain reaction (RT-PCR) 30 h post-infection.

Results

Ac2-26-treated WT mice showed less severe neutrophil infiltration, paralleled by a reduced induction of pro-inflammatory glial cell responses in the hippocampal formation and cortex. While meningitis was ameliorated in Ac2-26-treated Fpr1-deficient mice, this protective effect was not observed in Fpr2-deficient mice. Irrespective of Ac2-26 treatment, inflammation was more severe in Fpr2-deficient compared to Fpr1-deficient mice.

Conclusions

In summary, this study demonstrates anti-inflammatory properties of Ac2-26 in a model of bacterial meningitis, which are mediated via FPR2, but not FPR1. Ac2-26 and other FPR2 modulators might be promising targets for the development of novel therapies for Streptococcus pneumoniae-induced meningitis.

Combined therapy with ceftriaxone and doxycycline does not improve the outcome of meningococcal meningitis in mice compared to ceftriaxone monotherapy

BACKGROUND

Meningococcal meningitis (MM) is a life-threatening disease associated with approximately 10% case fatality rates and neurological sequelae in 10-20% of the cases. Recently, we have shown that the matrix metalloproteinase (MMP) inhibitor BB-94 reduced brain injury in a mouse model of MM. The present study aimed to assess whether doxycycline (DOX), a tetracycline that showed a neuroprotective effect as adjuvant therapy in experimental pneumococcal meningitis (PM), would also exert a beneficial effect when given as adjunctive therapy to ceftriaxone (CRO) in experimental MM.

METHODS

BALB/c mice were infected by the intracisternal route with a group C Neisseria meningitidis strain. Eighteen h post infection (hpi), animals were randomised for treatment with CRO [100 mg/kg subcutaneously (s.c.)], CRO plus DOX (30 mg/kg s.c.) or saline (control s.c.). Antibiotic treatment was repeated 24 and 40 hpi. Mouse survival and clinical signs, bacterial counts in cerebella, brain damage, MMP-9 and cyto/chemokine levels were assessed 48 hpi.

RESULTS

Analysis of bacterial load in cerebella indicated that CRO and CRO + DOX were equally effective at controlling meningococcal replication. No differences in survival were observed between mice treated with CRO (94.4%) or CRO + DOX (95.5%), (p > 0.05). Treatment with CRO + DOX significantly diminished both the number of cerebral hemorrhages (p = 0.029) and the amount of MMP-9 in the brain (p = 0.046) compared to untreated controls, but not to CRO-treated animals (p > 0.05). Levels of inflammatory markers in the brain of mice that received CRO or CRO + DOX were not significantly different (p > 0.05). Overall, there were no significant differences in the parameters assessed between the groups treated with CRO alone or CRO + DOX.

CONCLUSIONS

Treatment with CRO + DOX showed similar bactericidal activity to CRO in vivo, suggesting no antagonist effect of DOX on CRO. Combined therapy significantly improved mouse survival and disease severity compared to untreated animals, but addition of DOX to CRO did not offer significant benefits over CRO monotherapy. In contrast to experimental PM, DOX has no adjunctive activity in experimental MM.

The role of commensal microflora-induced T cell responses in glaucoma neurodegeneration

Over the last decade, new evidence has become increasingly more compelling that commensal microflora profoundly influences the maturation and function of resident immune cells in host physiology. The concept of gut-retina axis is actively being explored. Studies have revealed a critical role of commensal microbes linked with neuronal stress, immune responses, and neurodegeneration in the retina. Microbial dysbiosis changes the blood-retina barrier permeability and modulates T cell-mediated autoimmunity to contribute to the pathogenesis of retinal diseases, such as glaucoma. Heat shock proteins (HSPs), which are evolutionarily conserved, are thought to function both as neuroprotectant and pathogenic antigens of T cells contributing to cell protection and tissue damage, respectively. Activated microglia recruit and interact with T cells during this process. Glaucoma, characterized by the progressive loss of retinal ganglion cells, is the leading cause of irreversible blindness. With nearly 70 million people suffering glaucoma worldwide, which doubles the number of patients with Alzheimer's disease, it represents the most frequent neurodegenerative disease of the central nervous system (CNS). Thus, understanding the mechanism of neurodegeneration in glaucoma and its association with the function of commensal microflora may help unveil the secrets of many neurodegenerative disorders in the CNS and develop novel therapeutic interventions.

Selective Loss of Brain-Derived Neurotrophic Factor Exacerbates Brain Injury by Enhancing Neuroinflammation in Experimental Streptococcus pneumoniae Meningitis

Streptococcus pneumoniae meningitis is a life-threatening bacterial infection of the central nervous system (CNS), and its unfavorable prognosis usually results from an intense inflammatory response. Recent studies have shown that brain-derived neurotrophic factor (BDNF) mediates anti-inflammatory and neuroprotective effects in CNS diseases; however, the distinct contribution of BDNF to pneumococcal meningitis (PM) remains unknown. In this study, we sought to investigate the effects of endogenous BDNF on the inflammatory response and brain damage in experimental PM. We used Camk2a-CreERT2 mice to delete Bdnf from the cerebral cortex and hippocampus, and meningitis was induced by intracisternal infection with S. pneumoniae. Clinical parameters were assessed during acute meningitis. At 24 h post-infection, histopathology, neutrophil granulocytes infiltration, and microglia/macrophage proliferation of brain tissues were evaluated. Additionally, cortical damage and hippocampal apoptosis were assessed using Nissl staining and terminal deoxynucleotidyl transferase dUTP-nick-end labeling (TUNEL), respectively. Pro-inflammatory cytokine levels were determined using real-time polymerase chain reaction (RT-PCR). Key molecules associated with the related signaling pathways were analyzed by RT-PCR and western blot. To investigate the role of microglia/macrophage in infected BDNF conditional knockout mice, GW2580 was used for microglia/macrophage depletion. Here, we, for the first time, found that BDNF conditional knockouts exhibited more profound clinical impairment, pathological severity, and neuron injury and enhanced microglia/macrophage proliferation than were observed in their littermate controls. Furthermore, the BDNF conditional knockouts showed an obviously increase in the expression of pro-inflammatory factors (Tnf-α, Il-1β, and Il-6). Mechanistically, loss of BDNF activated TLR2- and NOD2-mediated downstream nuclear factor kappa B (NF-κB) p65 and p38 mitogen-activated protein kinase (MAPK) pathways associated with S. pneumoniae infection. Furthermore, targeted depletion of microglia/macrophage population decreased the resistance of mice to PM with diminishing neuroinflammation in BDNF conditional knockouts. Our findings suggest that loss of BDNF may enhance the inflammatory response and contribute to brain injury during PM at least partially by modulating TLR2- and NOD2-mediated signaling pathways, thereby providing a potential therapeutic target for future interventions in bacterial meningitis pathologies.

Pre-treatment with the viral Toll-like receptor 3 agonist poly(I:C) modulates innate immunity and protects neutropenic mice infected intracerebrally with Escherichia coli

BACKGROUND

Individuals with impaired immunity are more susceptible to infections than immunocompetent subjects. No vaccines are currently available to induce protection against E. coli meningoencephalitis. This study evaluated the potential of poly(I:C) pre-treatment to induce trained immunity. Poly(I:C) was administered as a non-specific stimulus of innate immune responses to protect immunocompetent and neutropenic wild-type mice from a subsequent challenge by the intracranial injection of E. coli K1.

METHODS

Three days prior to infection, mice received an intraperitoneal injection of poly(I:C) or vehicle. Kaplan-Meier survival curves were analyzed. In short-term experiments, bacterial titers and the inflammatory response were characterized in the blood, cerebellum, and spleen homogenates. NK cell subpopulations in the brain and spleen were analyzed by flow cytometry. Numbers of microglia and activation scores were evaluated by histopathology.

RESULTS

Pre-treatment with 200 μg poly(I:C) increased survival time, reduced mortality, and enhanced bacterial clearance in the blood, cerebellum, and spleen at early infection in neutropenic mice. Poly(I:C)-mediated protection correlated with an augmented number of NK cells (CD45⁺NK1.1⁺CD3^-) and Iba-1⁺ microglial cells and a higher production of IFN-γ in the brain. In the spleen, levels of CCL5/RANTES and IFN-γ were increased and sustained in surviving poly(I:C)-treated animals for 14 days after infection. In immunocompetent animals, survival time was not significantly prolonged in poly(I:C)-treated animals although poly(I:C) priming reduced brain bacterial concentrations compared with vehicle-injected animals at early infection.

CONCLUSIONS

Pre-treatment with the viral TLR3 agonist poly(I:C) modulated innate immune responses and strengthened the resistance of neutropenic mice against E. coli K1 meningoencephalitis.

Complement factor H contributes to mortality in humans and mice with bacterial meningitis

Background

The complement system is a vital component of the inflammatory response occurring during bacterial meningitis. Blocking the complement system was shown to improve the outcome of experimental pneumococcal meningitis. Complement factor H (FH) is a complement regulatory protein inhibiting alternative pathway activation but is also exploited by the pneumococcus to prevent complement activation on its surface conferring serum resistance.

Methods

In a nationwide prospective cohort study of 1009 episodes with community-acquired bacterial meningitis, we analyzed whether genetic variations in CFH influenced FH cerebrospinal fluid levels and/or disease severity. Subsequently, we analyzed the role of FH in our pneumococcal meningitis mouse model using FH knock-out (Cfh^−/−) mice and wild-type (wt) mice. Finally, we tested whether adjuvant treatment with human FH (hFH) improved outcome in a randomized investigator blinded trial in a pneumococcal meningitis mouse model.

Results

We found the major allele (G) of single nucleotide polymorphism in CFH (rs6677604) to be associated with low FH cerebrospinal fluid concentration and increased mortality. In patients and mice with bacterial meningitis, FH concentrations were elevated during disease and Cfh^−/− mice with pneumococcal meningitis had increased mortality compared to wild-type mice due to C3 depletion. Adjuvant treatment of wild-type mice with purified human FH led to complement inhibition but also increased bacterial outgrowth which resulted in similar disease outcomes.

Conclusion

Low FH levels contribute to mortality in pneumococcal meningitis but adjuvant treatment with FH at a clinically relevant time point is not beneficial.

Bacterial meningitis: new treatment options to reduce the risk of brain damage

Introduction: Bacterial meningitis (BM) is a medical emergency and its etiology varies according to the age group and geographic area. Studies have shown that brain damage, sequelae and neuropsychological deficits depend not only on the direct deleterious action of the pathogens, but also on the host defenses themselves.Areas covered: Corticosteroids (CS) were the first drugs used with the intent to limit the exaggerated host response. However, as steroid addition to antibiotics is frequently unsatisfactory, other measures have been suggested. In this study, the most important adjuvant therapies that are potentially useful to limit the neuropsychological damage of BM are discussed.Expert opinion: The pathophysiological mechanisms leading to the development of brain damage are not completely defined. Moreover, the efficacy of adjuvant therapies can vary according to the aetiologic cause of BM, and differences in immune system function of the host can play a relevant role in the expression of inflammation and related problems. It is likely that none of the measures with demonstrated efficacy in animal models can be translated into clinical practice in the next few years, suggesting that to reduce the total burden of BM, the increased use of vaccines seems to be the best solution.

Cerebral Metabolic Changes Related to Oxidative Metabolism in a Model of Bacterial Meningitis Induced by Lipopolysaccharide

BACKGROUND

Cerebral mitochondrial dysfunction is prominent in the pathophysiology of severe bacterial meningitis. In the present study, we hypothesize that the metabolic changes seen after intracisternal lipopolysaccharide (LPS) injection in a piglet model of meningitis is compatible with mitochondrial dysfunction and resembles the metabolic patterns seen in patients with bacterial meningitis.

METHODS

Eight pigs received LPS injection in cisterna magna, and four pigs received NaCl in cisterna magna as a control. Biochemical variables related to energy metabolism were monitored by intracerebral microdialysis technique and included interstitial glucose, lactate, pyruvate, glutamate, and glycerol. The intracranial pressure (ICP) and brain tissue oxygen tension (PbtO₂) were also monitored along with physiological variables including mean arterial pressure, blood glucose, lactate, and partial pressure of O₂ and CO₂. Pigs were monitored for 60 min at baseline and 240 min after LPS/NaCl injection.

RESULTS

After LPS injection, a significant increase in cerebral lactate/pyruvate ratio (LPR) compared to control group was registered (p = 0.01). This increase was due to a significant increased lactate with stable and normal values of pyruvate. No significant change in PbtO₂ or ICP was registered. No changes in physiological variables were observed.

CONCLUSIONS

The metabolic changes after intracisternal LPS injection is compatible with disturbance in the oxidative metabolism and partly due to mitochondrial dysfunction with increasing cerebral LPR due to increased lactate and normal pyruvate, PbtO₂, and ICP. The metabolic pattern resembles the one observed in patients with bacterial meningitis. Metabolic monitoring in these patients is feasible to monitor for cerebral metabolic derangements otherwise missed by conventional intensive care monitoring.

Protein Oxidation Biomarkers and Myeloperoxidase Activation in Cerebrospinal Fluid in Childhood Bacterial Meningitis

The immunological response in bacterial meningitis (BM) causes the formation of reactive oxygen and nitrogen species (ROS, RNS) and activates myeloperoxidase (MPO), an inflammatory enzyme. Thus, structural oxidative and nitrosative damage to proteins and DNA occurs. We aimed to asses these events in the cerebrospinal fluid (CSF) of pediatric BM patients. Phenylalanine (Phe), para-tyrosine (p-Tyr), nucleoside 2'-deoxiguanosine (2dG), and biomarkers of ROS/RNS-induced protein and DNA oxidation: ortho-tyrosine (o-Tyr), 3-chlorotyrosine (3Cl-Tyr), 3-nitrotyrosine (3NO₂-Tyr) and 8-oxo-2'-deoxyguanosine (8OHdG), concentrations were measured by liquid chromatography coupled to tandem mass spectrometry in the initial CSF of 79 children with BM and 10 without BM. All biomarkers, normalized with their corresponding precursors, showed higher median concentrations (p < 0.0001) in BM compared with controls, except 8OHdG/2dG. The ratios o-Tyr/Phe, 3Cl-Tyr/p-Tyr and 3NO₂-Tyr/p-Tyr were 570, 20 and 4.5 times as high, respectively. A significantly higher 3Cl-Tyr/p-Tyr ratio was found in BM caused by Streptococcus pneumoniae, than by Haemophilus influenzae type b, or Neisseria meningitidis (p = 0.002 for both). In conclusion, biomarkers indicating oxidative damage to proteins distinguished BM patients from non-BM, most clearly the o-Tyr/Phe ratio. The high 3Cl-Tyr/p-Tyr ratio in pneumococcal meningitis suggests robust inflammation because 3Cl-Tyr is a marker of MPO activation and, indirectly, of inflammation.

Community-acquired acute bacterial meningitis in adults: a clinical update

BACKGROUND

Acute bacterial meningitis (ABM) in adults is associated with a mortality that may exceed 30%. Immunization programs have reduced the global burden; in the UK, declining incidence but persistently high mortality and morbidity mean that clinicians must remain vigilant.

SOURCES OF DATA

A systematic electronic literature search of PubMed was performed to identify all ABM literature published within the past 5 years.

AREAS OF AGREEMENT AND CONTROVERSY

Clinical features cannot reliably distinguish between ABM and other important infectious and non-infectious aetiologies. Prompt investigation and empirical treatment are imperative. Lumbar puncture (LP) and cerebrospinal fluid microscopy, biochemistry and culture remain the mainstay of diagnosis, but molecular techniques are increasingly useful. The 2016 UK joint specialist societies' guideline provides expert recommendations for the management of ABM, yet published data suggest clinical care delivered in the UK is frequently not adherent. Anxiety regarding risk of cerebral herniation following LP, unnecessary neuroimaging, underutilization of molecular diagnostics and suboptimal uptake of adjunctive corticosteroids compromise management.

GROWING POINTS

There is increasing recognition that current antibiotic regimens and adjunctive therapies alone are insufficient to reduce the mortality and morbidity associated with ABM.

AREAS TIMELY FOR DEVELOPING RESEARCH

Research should be focused on optimization of vaccines (e.g. pneumococcal conjugate vaccines with extended serotype coverage), targeting groups at risk for disease and reservoirs for transmission; improving adherence to management guidelines; development of new faster, more accurate diagnostic platforms (e.g. novel point-of-care molecular diagnostics); and development of new adjunctive therapies (aimed at the host-inflammatory response and bacterial virulence factors).

MMPs and ADAMs in neurological infectious diseases and multiple sclerosis

Metalloproteinases-such as matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinases (ADAMs)-are involved in various diseases of the nervous system but also contribute to nervous system development, synaptic plasticity and neuroregeneration upon injury. MMPs and ADAMs proteolytically cleave many substrates including extracellular matrix components but also signaling molecules and receptors. During neuroinfectious disease with associated neuroinflammation, MMPs and ADAMs regulate blood-brain barrier breakdown, bacterial invasion, neutrophil infiltration and cytokine signaling. Specific and broad-spectrum inhibitors for MMPs and ADAMs have experimentally been shown to decrease neuroinflammation and brain damage in diseases with excessive neuroinflammation as a common denominator, such as pneumococcal meningitis and multiple sclerosis, thereby improving the disease outcome. Timing of metalloproteinase inhibition appears to be critical to effectively target the cascade of pathophysiological processes leading to brain damage without inhibiting the neuroregenerative effects of metalloproteinases. As the critical role of metalloproteinases in neuronal repair mechanisms and regeneration was only lately recognized, the original idea of chronic MMP inhibition needs to be conceptually revised. Recently accumulated research urges for a second chance of metalloproteinase inhibitors, which-when correctly applied and dosed-harbor the potential to improve the outcome of different neuroinflammatory diseases.

The Role of Microglia in Bacterial Meningitis: Inflammatory Response, Experimental Models and New Neuroprotective Therapeutic Strategies

Microglia have a pivotal role in the pathophysiology of bacterial meningitis. The goal of this review is to provide an overview on how microglia respond to bacterial pathogens targeting the brain, how the interplay between microglia and bacteria can be studied experimentally, and possible ways to use gained knowledge to identify novel preventive and therapeutic strategies. We discuss the dual role of microglia in disease development, the beneficial functions crucial for bacterial clearing, and the destructive properties through triggering neuroinflammation, characterized by cytokine and chemokine release which leads to leukocyte trafficking through the brain vascular endothelium and breakdown of the blood-brain barrier integrity. Due to intrinsic complexity of microglia and up until recently lack of specific markers, the study of microglial response to bacterial pathogens is challenging. New experimental models and techniques open up possibilities to accelerate progress in the field. We review existing models and discuss possibilities and limitations. Finally, we summarize recent findings where bacterial virulence factors are identified to be important for the microglial response, and how manipulation of evoked responses could be used for therapeutic or preventive purposes. Among promising approaches are: modulations of microglia phenotype switching toward anti-inflammatory and phagocytic functions, the use of non-bacterolytic antimicrobials, preventing release of bacterial components into the neural milieu and consequential amplification of immune activation, and protection of the blood-brain barrier integrity.

The role of CNS macrophages in streptococcal meningoencephalitis

In the healthy brain, microglia and other CNS macrophages are the most abundant immune cell type. Thus, they form the natural immune cell interface with streptococci, which are the leading cause of bacterial meningitis and encephalitis in infants and young children. In homeostasis, the blood-brain barrier allows for very limited access of immune cells circulating in the periphery. During bacterial meningoencephalitis, however, origin and fate of CNS macrophages are massively altered. This review summarizes the emerging knowledge on the sequence of reciprocal events between streptococci and CNS macrophages leading to host resistance, acute inflammation, changes in resident innate immune cells of the brain, and long-term neuronal damage.

Lack of chemokine (C-C motif) ligand 3 leads to decreased survival and reduced immune response after bacterial meningitis

Pneumococcal meningitis, caused by Streptococcus pneumoniae, is the most common type of bacterial meningitis. The clinical management of this disease has been challenged by the emergence of multidrug-resistant Streptococcus pneumoniae, requiring the urgent development of new therapeutic alternatives. Over the course of bacterial meningitis, pathogen invasion is accompanied by a massive recruitment of peripheral immune cells, especially neutrophil granulocytes, which are recruited under the coordination of several cytokines and chemokines. Here, we used chemokine (C-C motif) ligand 3 (Ccl3)-deficient mice to investigate the functional role of CCL3 in a mouse model of pneumococcal meningitis. Following intrathecal infection with Streptococcus pneumoniae Ccl3-deficient mice presented a significantly shorter survival and higher bacterial load than wildtype mice, paralleled by an ameliorated infiltration of neutrophil granulocytes into the CNS. Blood sample analysis revealed that infected Ccl3-deficient mice showed a significant decrease in erythrocytes, hemoglobin and hematocrit as well as in the number of banded neutrophils. Moreover, infected Ccl3-deficient mice showed an altered cytokine expression profile. Glial cell activation remained unchanged in both genotypes. In summary, this study demonstrates that CCL3 is beneficial in Streptococcus pneumoniae-induced meningitis. Pharmacological modulation of the CCL3 pathways might, therefore, represent a future therapeutic option to manage Streptococcus pneumoniae meningitis.

Combined effect of non-bacteriolytic antibiotic and inhibition of matrix metalloproteinases prevents brain injury and preserves learning, memory and hearing function in experimental paediatric pneumococcal meningitis

BACKGROUND

Pneumococcal meningitis is associated with high mortality and morbidity rates. Up to 50% of survivors show neurologic sequelae including hearing loss, cognitive impairments and learning disabilities, being particularly detrimental in affected infants and children where adjuvant therapy with dexamethasone has no proven beneficial effect. We evaluated the effect of concomitantly targeting specific pathophysiological mechanisms responsible for brain damage-i.e. matrix-metalloproteinase (MMP) activity and the exacerbated cerebral inflammation provoked through antibiotic-induced bacterial lysis. Here, we combined adjunctive therapies previously shown to be neuroprotective when used as single adjuvant therapies.

METHODS

Eleven-day-old Wistar rats were infected intracisternally with 6.44 ± 2.17 × 103 CFU Streptococcus pneumoniae and randomised for treatment with ceftriaxone combined with (a) single adjuvant therapy with daptomycin (n = 24), (b) single adjuvant therapy with Trocade (n = 24), (c) combined adjuvant therapy (n = 66) consisting of daptomycin and Trocade, or (d) ceftriaxone monotherapy (n = 42). Clinical parameters and inflammatory CSF cytokine levels were determined during acute meningitis. Cortical damage and hippocampal apoptosis were assessed 42 h after infection. Morris water maze and auditory brainstem responses were used to assess neurofunctional outcome 3 weeks after infection.

RESULTS

We found significantly reduced apoptosis in the hippocampal subgranular zone in infant rats receiving adjuvant Trocade (p < 0.01) or combined adjuvant therapy (p < 0.001). Cortical necrosis was significantly reduced in rats treated with adjuvant daptomycin (p < 0.05) or combined adjuvant therapy (p < 0.05) compared to ceftriaxone monotherapy. Six hours after treatment initiation, CSF cytokine levels were significantly reduced for TNF-α (p < 0.01), IL-1β (p < 0.01), IL-6 (p < 0.001) and IL-10 (p < 0.01) in animals receiving combined adjuvant intervention compared to ceftriaxone monotherapy. Importantly, combined adjuvant therapy significantly improved learning and memory performance in infected animals and reduced hearing loss (77.14 dB vs 60.92 dB, p < 0.05) by preserving low frequency hearing capacity, compared to ceftriaxone monotherapy.

CONCLUSION

Combined adjuvant therapy with the non-bacteriolytic antibiotic daptomycin and the MMP inhibitor Trocade integrates the neuroprotective effects of both single adjuvants in experimental paediatric pneumococcal meningitis by reducing neuroinflammation and brain damage, thereby improving neurofunctional outcome. This strategy represents a promising therapeutic option to improve the outcome of paediatric patients suffering from pneumococcal meningitis.

The Role of Procalcitonin in the Diagnosis of Meningitis: A Literature Review

OBJECTIVE

To review the current published literature on the use of procalcitonin as a diagnostic and prognostic marker in adult patients with meningitis.

METHODS

We conducted a PubMed search to identify all relevant publications regarding the diagnostic and prognostic value of serum procalcitonin in patients with a known or suspected central nervous system infection. We also reviewed the bibliographies of all identified manuscripts in an attempt to identify additional relevant references.

RESULTS

A significant body of evidence suggests that serum procalcitonin has a promising role and can be a useful biomarker in the assessment of patients with meningitis.

CONCLUSIONS

Our literature review suggests that data on the role of Cerebrospinal Fluid (CSF) procalcitonin are limited, whereas serum procalcitonin (S⁻PCT) is probably a useful tool in the evaluation of patients with a known or suspected central nervous system infection and can help distinguish between bacterial and viral meningitis.

Advances in Biomarker-Guided Therapy for Pediatric- and Adult-Onset Neuroinflammatory Disorders: Targeting Chemokines/Cytokines

The concept and recognized components of “neuroinflammation” are expanding at the intersection of neurobiology and immunobiology. Chemokines (CKs), no longer merely necessary for immune cell trafficking and positioning, have multiple physiologic, developmental, and modulatory functionalities in the central nervous system (CNS) through neuron–glia interactions and other mechanisms affecting neurotransmission. They issue the “help me” cry of neurons and astrocytes in response to CNS injury, engaging invading lymphoid cells (T cells and B cells) and myeloid cells (dendritic cells, monocytes, and neutrophils) (adaptive immunity), as well as microglia and macrophages (innate immunity), in a cascade of events, some beneficial (reparative), others destructive (excitotoxic). Human cerebrospinal fluid (CSF) studies have been instrumental in revealing soluble immunobiomarkers involved in immune dysregulation, their dichotomous effects, and the cells—often subtype specific—that produce them. CKs/cytokines continue to be attractive targets for the pharmaceutical industry with varying therapeutic success. This review summarizes the developing armamentarium, complexities of not compromising surveillance/physiologic functions, and insights on applicable strategies for neuroinflammatory disorders. The main approach has been using a designer monoclonal antibody to bind directly to the chemo/cytokine. Another approach is soluble receptors to bind the chemo/cytokine molecule (receptor ligand). Recombinant fusion proteins combine a key component of the receptor with IgG1. An additional approach is small molecule antagonists (protein therapeutics, binding proteins, and protein antagonists). CK neutralizing molecules (“neutraligands”) that are not receptor antagonists, high-affinity neuroligands (“decoy molecules”), as well as neutralizing “nanobodies” (single-domain camelid antibody fragment) are being developed. Simultaneous, more precise targeting of more than one cytokine is possible using bispecific agents (fusion antibodies). It is also possible to inhibit part of a signaling cascade to spare protective cytokine effects. “Fusokines” (fusion of two cytokines or a cytokine and CK) allow greater synergistic bioactivity than individual cytokines. Another promising approach is experimental targeting of the NLRP3 inflammasome, amply expressed in the CNS and a key contributor to neuroinflammation. Serendipitous discovery is not to be discounted. Filling in knowledge gaps between pediatric- and adult-onset neuroinflammation by systematic collection of CSF data on CKs/cytokines in temporal and clinical contexts and incorporating immunobiomarkers in clinical trials is a challenge hereby set forth for clinicians and researchers.

Response of Vancomycin according to Steroid Dosage in Pediatric Patients with Culture-Proven Bacterial Meningitis

BACKGROUND

This study aimed to evaluate the efficacy of combined vancomycin and steroid therapy for the treatment of culture-proven bacterial meningitis in pediatric patients.

MATERIALS AND METHODS

We identified a total of 86 pediatric patients with culture-positive cerebrospinal fluid who were treated at our facility between 2005 and 2015. Ten of these patients (5 boys and 5 girls) received first-line treatment with vancomycin as the initial form of therapy. All cultured bacteria were sensitive to vancomycin. We retrospectively analyzed these cases to examine the relationship between concomitant steroid dosage and antibiotic treatment effectiveness.

RESULTS

Nine of the 10 patients included in our analysis received steroid treatment. Of these, 3 received high-dose steroid therapy and 6 received low-dose steroid therapy. Five patients did not respond to vancomycin, including all 3 patients in the high-dose steroid group and 2 patients in the low-dose steroid group. Our analysis confirmed that the response rate to vancomycin treatment was significantly reduced in accordance with steroid dosage (P = 0.035). Patients who did not to respond to vancomycin with concomitant high-dose steroid administration improved clinically after the substitution of vancomycin with teicoplanin.

CONCLUSION

The use of steroids, especially in high doses, may impair the effectiveness of vancomycin for treating bacterial meningitis in pediatric patients. Physicians should be cautious when administering concomitant steroid therapy and should carefully monitor the steroid dosage.

Brain-derived neurotrophic factor reduces inflammation and hippocampal apoptosis in experimental Streptococcus pneumoniae meningitis

BACKGROUND

Streptococcus pneumoniae meningitis is a serious inflammatory disease of the central nervous system (CNS) and is associated with high morbidity and mortality rates. The inflammatory processes initiated by recognition of bacterial components contribute to apoptosis in the hippocampal dentate gyrus. Brain-derived neurotrophic factor (BDNF) has long been recommended for the treatment of CNS diseases due to its powerful neuro-survival properties, as well as its recently reported anti-inflammatory and anti-apoptotic effects in vitro and in vivo.

METHODS

In this study, we investigated the effects of BDNF-related signaling on the inflammatory response and hippocampal apoptosis in experimental models of pneumococcal meningitis. Pretreatment with exogenous BDNF or the tropomyosin-receptor kinase B (TrkB) inhibitor k252a was performed to assess the activation or inhibition of the BDNF/TrkB-signaling axis prior to intracisternal infection with live S. pneumoniae. At 24 h post-infection, rats were assessed for clinical severity and sacrificed to harvest the brains. Paraffin-embedded brain sections underwent hematoxylin and eosin staining to evaluate pathological severity, and cytokine and chemokine levels in the hippocampus and cortex were evaluated by enzyme-linked immunosorbent assay. Additionally, apoptotic neurons were detected in the hippocampal dentate gyrus by terminal deoxynucleotidyl transferase dUTP-nick-end labeling, key molecules associated with the related signaling pathway were analyzed by real-time polymerase chain reaction and western blot, and the DNA-binding activity of nuclear factor kappa B (NF-κB) was measured by electrophoretic mobility shift assay.

RESULTS

Rats administered BDNF exhibited reduced clinical impairment, pathological severity, and hippocampal apoptosis. Furthermore, BDNF pretreatment suppressed the expression of inflammatory factors, including tumor necrosis factor α, interleukin (IL)-1β, and IL-6, and increased the expression of the anti-inflammatory factor IL-10. Moreover, BDNF pretreatment increased TrkB expression, activated downstream phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling, and inhibited the myeloid differentiation primary response gene 88 (MyD88)/NF-κB-signaling pathway.

CONCLUSIONS

These data suggested that BDNF administration exerted anti-inflammatory and anti-apoptotic effects on an experimental pneumococcal meningitis model via modulation of MyD88/NF-κB- and PI3K/AKT-signaling pathways. Our results indicated that treatment with exogenous BDNF might constitute a potential therapeutic strategy for the treatment of bacterial meningitis.

Brain-derived neurotrophic factor is regulated via MyD88/NF-κB signaling in experimental Streptococcus pneumoniae meningitis

Streptococcus pneumoniae meningitis is an intractable disease of the central nervous system (CNS). Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophic family and found to participate in the immune inflammatory response. In this study, we investigated if activation of the classical inflammatory signaling pathway, myeloid differentiation factor 88 (MyD88)/nuclear factor-kappa B (NF-κB), regulates BDNF expression in experimental S. pneumoniae meningitis. MyD88 knockout (myd88-/-) mice and wild-type littermates were infected intracisternally with S. pneumoniae suspension. Twenty-four hours after inoculation, histopathology of brains was evaluated. Cytokine and chemokine in brains and spleens was analyzed using ELISA. NF-κB activation was evaluated using EMSA. Cortical and hippocampal BDNF was assessed using RT-PCR and ELISA, respectively. BDNF promoter activity was evaluated using ChIP-PCR. myd88-/- mice showed an obviously weakened inflammatory host response. This diminished inflammation was consistent with worse clinical parameters, neuron injury, and apoptosis. Deficiency in MyD88 was associated with decreased BDNF expression. Furthermore, we identified a valid κB-binding site in the BDNF promoter, consistent with activation of NF-κB induced by inflammation. To sum up, MyD88/NF-κB signaling has a crucial role in up-regulating BDNF, which might provide potential therapeutic targets for S. pneumoniae meningitis.

Prediction of Outcome From Adult Bacterial Meningitis in a High-HIV-Seroprevalence, Resource-Poor Setting Using the Malawi Adult Meningitis Score (MAMS)

Background.

Acute bacterial meningitis (ABM) in adults residing in resource-poor countries is associated with mortality rates >50%. To improve outcome, interventional trials and standardized clinical algorithms are urgently required. To optimize these processes, we developed and validated an outcome prediction tool to identify ABM patients at greatest risk of death.

Methods.

We derived a nomogram using mortality predictors derived from a logistic regression model of a discovery database of adult Malawian patients with ABM (n = 523 [65%] cerebrospinal fluid [CSF] culture positive). We validated the nomogram internally using a bootstrap procedure and subsequently used the nomogram scores to further interpret the effects of adjunctive dexamethasone and glycerol using clinical trial data from Malawi.

Results.

ABM mortality at 6-week follow-up was 54%. Five of 15 variables tested were strongly associated with poor outcome (CSF culture positivity, CSF white blood cell count, hemoglobin, Glasgow Coma Scale, and pulse rate), and were used in the derivation of the Malawi Adult Meningitis Score (MAMS) nomogram. The C-index (area under the curve) was 0.76 (95% confidence interval, .71–.80) and calibration was good (Hosmer-Lemeshow C-statistic = 5.48, df = 8, P = .705). Harmful effects of adjunctive glycerol were observed in groups with relatively low predicted risk of poor outcome (25%–50% risk): Case Fatality Rate of 21% in the placebo group and 52% in the glycerol group (P < .001). This effect was not seen with adjunctive dexamethasone.

Conclusions.

MAMS provides a novel tool for predicting prognosis and improving interpretation of ABM clinical trials by risk stratification in resource-poor settings. Whether MAMS can be applied to non-HIV-endemic countries requires further evaluation.

Diagnostic Accuracy of Cerebrospinal Fluid Procalcitonin in Bacterial Meningitis Patients with Empiric Antibiotic Pretreatment

Accurate diagnosis of bacterial meningitis (BM) relies on cerebrospinal fluid (CSF) Gram staining and bacterial culture, which often present high false-negative rates because of antibiotic abuse. Thus, a novel and reliable diagnostic biomarker is required. Procalcitonin (PCT) has been well demonstrated to be specifically produced from peripheral tissues by bacterial infection, which makes it a potential diagnostic biomarker candidate. Here, we performed a prospective clinical study comprising a total of 143 patients to investigate the diagnostic value of CSF PCT, serum PCT, and other conventional biomarkers for BM. Patients were assigned to the BM (n = 49), tuberculous meningitis (TBM) (n = 25), viral meningitis/encephalitis (VM/E) (n = 34), autoimmune encephalitis (AIE) (n = 15), or noninflammatory nervous system diseases (NINSD) group (n = 20). Empirical antibiotic pretreatment was not an exclusion criterion. Our results show that the CSF PCT level was significantly (P < 0.01) higher in patients with BM (median, 0.22 ng/ml; range, 0.13 to 0.54 ng/ml) than in those with TBM (median, 0.12 ng/ml; range, 0.07 to 0.16 ng/ml), VM/E (median, 0.09 ng/ml; range, 0.07 to 0.11 ng/ml), AIE (median, 0.06 ng/ml; range, 0.05 to 0.10 ng/ml), or NINSD (median, 0.07 ng/ml; range, 0.06 to 0.08 ng/ml). Among the assessed biomarkers, CSF PCT exhibited the largest area under the receiver operating characteristic curve (0.881; 95% confidence interval, 0.810 to 0.932; cutoff value, 0.15 ng/ml; sensitivity, 69.39%; specificity, 91.49%). Our study sheds light upon the diagnostic dilemma of BM due to antibiotic abuse. (This study has been registered at ClinicalTrials.gov under registration no. NCT02278016.).

Role of neural barriers in the pathogenesis and outcome of Streptococcus pneumoniae meningitis

Bacterial meningitis is an inflammatory disease of the meninges of the central nervous system (CNS). Streptococcus pneumoniae (S. pneumoniae), Neisseria meningitidis, and Haemophilus influenzae are the major bacterial pathogens causing meningitis with S. pneumoniae being responsible for two thirds of meningitis cases in the developed world. To reach the CNS following nasopharyngeal colonization and bacteraemia, the bacteria traverse from the circulation across the blood brain barrier (BBB) and choroid plexus. While the BBB has a protective role in healthy individuals by shielding the CNS from neurotoxic substances circulating in the blood and maintaining the homeostasis within the brain environment, dysfunction of the BBB is associated with the pathophysiology of numerous neurologic disorders, including bacterial meningitis. Inflammatory processes, including release of a broad range of cytokines and free radicals, further increase vascular permeability and contribute to the excessive neural damage observed. Injury to the cerebral microvasculature and loss of blood flow auto-regulation promote increased intracranial pressure and may lead to vascular occlusion. Other common complications commonly associated with meningitis include abnormal neuronal hyper-excitability (e.g., seizures) and loss of hearing. Despite the existence of antibiotic treatment and adjuvant therapy, the relatively high mortality rate and the severe outcomes among survivors of pneumococcal meningitis in developing and developed countries increase the urgency in the requirement of discovering novel biomarkers for the early diagnosis as well as novel treatment approaches. The present review aimed to explore the changes in the brain vascular barriers, which allow S. pneumoniae to invade the CNS, and describe the resultant brain injuries following bacterial meningitis.

Infectious immunity in the central nervous system and brain function

Inflammation is emerging as a critical mechanism underlying neurological disorders of various etiologies, yet its role in altering brain function as a consequence of neuroinfectious disease remains unclear. Although acute alterations in mental status due to inflammation are a hallmark of central nervous system (CNS) infections with neurotropic pathogens, post-infectious neurologic dysfunction has traditionally been attributed to irreversible damage caused by the pathogens themselves. More recently, studies indicate that pathogen eradication within the CNS may require immune responses that interfere with neural cell function and communication without affecting their survival. In this Review we explore inflammatory processes underlying neurological impairments caused by CNS infection and discuss their potential links to established mechanisms of psychiatric and neurodegenerative diseases.

Community-acquired bacterial meningitis

Meningitis is an inflammation of the meninges and subarachnoid space that can also involve the brain cortex and parenchyma. It can be acquired spontaneously in the community - community-acquired bacterial meningitis - or in the hospital as a complication of invasive procedures or head trauma (nosocomial bacterial meningitis). Despite advances in treatment and vaccinations, community-acquired bacterial meningitis remains one of the most important infectious diseases worldwide. Streptococcus pneumoniae and Neisseria meningitidis are the most common causative bacteria and are associated with high mortality and morbidity; vaccines targeting these organisms, which have designs similar to the successful vaccine that targets Haemophilus influenzae type b meningitis, are now being used in many routine vaccination programmes. Experimental and genetic association studies have increased our knowledge about the pathogenesis of bacterial meningitis. Early antibiotic treatment improves the outcome, but the growing emergence of drug resistance as well as shifts in the distribution of serotypes and groups are fuelling further development of new vaccines and treatment strategies. Corticosteroids were found to be beneficial in high-income countries depending on the bacterial species. Further improvements in the outcome are likely to come from dampening the host inflammatory response and implementing preventive measures, especially the development of new vaccines.

Lack of Toll-like receptor 2 results in higher mortality of bacterial meningitis by impaired host resistance

Bacterial meningitis is - despite therapeutical progress during the last decades - still characterized by high mortality and severe permanent neurogical sequelae. The brain is protected from penetrating pathogens by both the blood-brain barrier and the innate immune system. Invading pathogens are recognized by so-called pattern recognition receptors including the Toll-like receptors (TLR) which are expressed by glial immune cells in the central nervous system. Among these, TLR2 is responsible for the detection of Gram-positive bacteria such as the meningitis-causing pathogen Streptococcus pneumoniae. Here, we used TLR2-deficient mice to investigate the effects on mortality, bacterial growth and inflammation in a mouse model of pneumococcal meningitis. Our results revealed a significantly increased mortality rate and higher bacterial burden in TLR2-deficient mice with pneumococcal meningitis. Furthermore, infected TLR2-deficient mice suffered from a significantly increased pro-inflammatory cytokine tumor necrosis factor-α (TNF-α) and Chemokine (C-C motif) ligand 2 (CCL2) or CCL3 chemokine expression and decreased expression of anti-inflammatory cytokines and antimicrobial peptides. In contrast, glial cell activation assessed by glial cell marker expression was comparable to wildtype mice. Taken together, the results suggest that TLR2 is essential for an efficient immune response against Streptococcus pneumoniae meningitis since lack of the receptor led to a worse outcome by higher mortality due to increased bacterial burden, weakened innate immune response and reduced expression of antimicrobial peptides.

Infection of zebrafish embryos with live fluorescent Streptococcus pneumoniae as a real-time pneumococcal meningitis model

BACKGROUND

Streptococcus pneumoniae is one of the most important causes of bacterial meningitis, an infection where unfavourable outcome is driven by bacterial and host-derived toxins. In this study, we developed and characterized a pneumococcal meningitis model in zebrafish embryos that allows for real-time investigation of early host-microbe interaction.

METHODS

Zebrafish embryos were infected in the caudal vein or hindbrain ventricle with green fluorescent wild-type S. pneumoniae D39 or a pneumolysin-deficient mutant. The kdrl:mCherry transgenic zebrafish line was used to visualize the blood vessels, whereas phagocytic cells were visualized by staining with far red anti-L-plastin or in mpx:GFP/mpeg1:mCherry zebrafish, that have green fluorescent neutrophils and red fluorescent macrophages. Imaging was performed by fluorescence confocal and time-lapse microscopy.

RESULTS

After infection by caudal vein, we saw focal clogging of the pneumococci in the blood vessels and migration of bacteria through the blood-brain barrier into the subarachnoid space and brain tissue. Infection with pneumolysin-deficient S. pneumoniae in the hindbrain ventricle showed attenuated growth and migration through the brain as compared to the wild-type strain. Time-lapse and confocal imaging revealed that the initial innate immune response to S. pneumoniae in the subarachnoid space mainly consisted of neutrophils and that pneumolysin-mediated cytolytic activity caused a marked reduction of phagocytes.

CONCLUSIONS

This new meningitis model permits detailed analysis and visualization of host-microbe interaction in pneumococcal meningitis in real time and is a very promising tool to further our insights in the pathogenesis of pneumococcal meningitis.

Antibody-induced neutrophil depletion prior to the onset of pneumococcal meningitis influences long-term neurological complications in mice

During pneumococcal meningitis, clearance of bacteria by recruited neutrophils is crucial for host protection. However, these innate immune mechanisms are often insufficient and treatment with antibiotics is necessary to prevent death. Despite this antibiotic treatment, approximately half of all survivors suffer lifelong neurological problems. There is growing evidence indicating the harmful effects of neutrophils on CNS integrity. Therefore, the present study investigated the roles of neutrophils in the acute inflammatory response and the resulting long-term neuropsychological effects in murine pneumococcal meningitis. Long-term behavioural and cognitive functions in mice were measured using an automated IntelliCage system. Neutrophil depletion with antibody 1A8 as adjunctive therapy was shown to remarkably impair survival in meningitic C57BL/6J mice despite antibiotic (ceftriaxone) treatment. This was accompanied by increased bacterial load in the cerebrospinal fluid (CSF) and an increase in IL-1β, but decrease in TNF, within the CSF at 20h after bacterial inoculation. In the longer term, the surviving neutrophil-depleted post-meningitic (PM) mice displayed reduced diurnal hypolocomotion compared to PM mice treated with an isotype antibody. However, they showed nocturnal hyperactivity, and greater learning impairment in a patrolling task that is believed to depend upon an intact hippocampus. The data thus demonstrate two important mechanisms: 1. Neutrophil extravasation into the CNS during pneumococcal meningitis influences the pro-inflammatory response and is central to control of the bacterial load, an increase in which may lead to death. 2. Neutrophil-mediated changes in the acute inflammatory response modulate the neuropsychological sequelae in mice that survive pneumococcal meningitis.

Exogenous BDNF increases neurogenesis in the hippocampus in experimental Streptococcus pneumoniae meningitis

BACKGROUND

Despite the effective use of antibiotics, occurrences of mortality and neurological sequelae following Streptococcus pneumoniae meningitis remain high.

METHODS

We investigated the neurogenesis of endogenous neural stem cells (NSCs) after inoculation with exogenous brain-derived neurotrophic factor (BDNF) in the hippocampus dentate gyrus following experimental S. pneumoniae meningitis using a double-labeling immunofluorescence analysis with 5-bromo-2'-deoxyuridine (BrdU), Nestin, DCX and NeuN.

RESULTS

Our results showed that 7days after inoculation, the number of BrdU & Nestin co-labeled cells increased in the hippocampus in meningitis rats compared with control rats (p<0.05). But the number of DCX-positive cells decreased in the dentate gyrus of infected rats treated with saline (p<0.05). However, these cell numbers returned to close to normal-control levels in infected rats treated with BDNF (p>0.05). After treatment with exogenous BDNF, the number of BrdU & Nestin co-labeled cells increased in the hippocampus in both the meningitis rats and normal control rats (p<0.05), but this increase was more significant in the former (p<0.05). We found that the percentage of BrdU & DCX/BrdU co-labeled cells increased in infected rats treated with BDNF both 7days and 14days after inoculation in a greater proportion compared to other groups (p<0.05). No significant differences were found in the percentage of BrdU & NeuN/BrdU 28days after inoculation among all of the groups (p>0.05).

CONCLUSION

Our findings suggest that S. pneumoniae meningitis activates the proliferation of endogenous NSCs, but impairs their early differentiation. Administration of exogenous BDNF might improve the neurogenesis of endogenous NSCs in the hippocampus and may provide a promising therapy after bacterial meningitis.

Lack of Proinflammatory Cytokine Interleukin-6 or Tumor Necrosis Factor Receptor-1 Results in a Failure of the Innate Immune Response after Bacterial Meningitis

The most frequent pathogen that causes bacterial meningitis is the Gram-positive bacterium Streptococcus pneumoniae. By entering the brain, host cells will be activated and proinflammatory cytokines like interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) are released. The goal of the current study was to examine the interaction between IL-6 and TNFR1 as receptor for TNF-α and the innate immune response in vivo in a model of Streptococcus pneumoniae-induced meningitis. For the experiments IL-6(-/-), TNFR1(-/-), and TNFR1-IL-6(-/-) KO mice were used. Our results revealed higher mortality rates and bacterial burden after infection in TNFR1(-/-), IL-6(-/-), and TNFR1-IL-6(-/-) mice and a decreased immune response including lower neutrophil infiltration in the meninges of TNFR1(-/-) and TNFR1-IL-6(-/-) mice in contrast to IL-6(-/-) and wild type mice. Furthermore, the increased mortality of TNFR1(-/-) and TNFR1-IL-6(-/-) mice correlated with decreased glial cell activation compared to IL-6(-/-) or wild type mice after pneumococcal meningitis. Altogether, the results show the importance of TNFR1 and IL-6 in the regulation of the innate immune response. The lack of TNFR1 and IL-6 results in higher mortality by weakened immune defence, whereas the lack of TNFR1 results in more severe impairment of the innate immune response than the lack of IL-6 alone.

Streptococcus pneumoniae infection regulates expression of neurotrophic factors in the olfactory bulb and cultured olfactory ensheathing cells

Streptococcus pneumoniae is the causative agent of numerous diseases including severe invasive infections such as bacteremia and meningitis. It has been previously shown that strains of S. pneumoniae that are unable to survive in the bloodstream may colonize the CNS. However, information on cellular components and pathways involved in the neurotropism of these strains is still scarce. The olfactory system is a specialized tissue in which olfactory receptor neurons (ORNs) are interfacing with the external environment through several microvilli. Olfactory ensheathing cells (OECs) which also form the glial limiting membrane at the surface of the olfactory bulb (OB) are the only cells that ensheathe the ORNs axons. Since previous data from our group showed that OECs may harbor S. pneumoniae, we decided to test whether infection of the OB or OEC cultures modulates the expression levels of neurotrophic factor's mRNA and its putative effects on the activation and viability of microglia. We observed that neurotrophin-3 (NT-3) and glial cell-line-derived neurotrophic factor (GDNF) expression was significantly higher in the OB from uninfected mice than in infected mice. A similar result was observed when we infected OEC cultures. Brain-derived neurotrophic factor (BNDF) expression was significantly lower in the OB from infected mice than in uninfected mice. In contrast, in vitro infection of OECs resulted in a significant increase of BDNF mRNA expression. An upregulation of high-mobility group box 1 (HMGB1) expression was observed in both OB and OEC cultures infected with S. pneumoniae. Moreover, we found that conditioned medium from infected OEC cultures induced the expression of the pro-apoptotic protein cleaved-caspase-3 and an apparently continuous nuclear factor-kappa B (NF-κB) p65 activation in the N13 microglia. Altogether, our data suggest the possible existence of an OEC-pathogen molecular interface, through which the OECs could interfere on the activation and viability of microglia, favoring the access of non-hematogenous S. pneumoniae strains to the CNS in the absence of bacteremia.