Combining antibiotic with anti-TLR2/TLR13 therapy prevents brain pathology in pneumococcal meningitis.

Despite effective antibiotic therapy, brain-destructive inflammation often cannot be avoided in pneumococcal meningitis. The causative signals are mediated predominantly through TLR-recruited myeloid differentiation primary response adaptor 88 (MyD88), as indicated by a dramatic pneumococcal meningitis phenotype of Myd88-/- mice. Because lipoproteins and single-stranded RNA are crucial for recognition of Gram-positive bacteria such as Streptococcus pneumoniae by the host immune system, we comparatively analyzed the disease courses of Myd88-/- and Tlr2-/- Tlr13-/- mice. Their phenotypic resemblance indicated TLR2 and -13 as master sensors of S. pneumoniae in the cerebrospinal fluid. A neutralizing anti-TLR2 antibody (T2.5) and chloroquine (CQ) - the latter applied here as an inhibitor of murine TLR13 and its human ortholog TLR8 - abrogated activation of murine and human primary immune cells exposed to antibiotic-treated S. pneumoniae. The inhibitory effect of the T2.5/CQ cocktail was stronger than that of dexamethasone, the current standard adjunctive drug for pneumococcal meningitis. Accordingly, TLR2/TLR13 blockade concomitant with ceftriaxone application significantly improved the clinical course of pneumococcal meningitis compared with treatment with ceftriaxone alone or in combination with dexamethasone. Our study indicates the importance of murine TLR13 and human TLR8, besides TLR2, in pneumococcal meningitis pathology, and suggests their blockade as a promising antibiotic therapy adjunct.

Quantitative proteomic analysis of cerebrospinal fluid from patients with idiopathic facial nerve palsy.

BACKGROUND AND PURPOSE: Idiopathic facial palsy (IFP) accounts for over 60% of peripheral facial palsy (FP) cases. The cause of IFP remains to be determined. Possible etiologies are nerve swelling due to inflammation and/or viral infection. In this study, we applied an integrative mass spectrometry approach to identify possibly altered protein patterns in the cerebrospinal fluid (CSF) of IFP patients. METHODS: We obtained CSF samples from 34 patients with FP. In four patients, varicella-zoster virus was the cause (VZV-FP). Among the 30 patients diagnosed with IFP, 17 had normal CSF parameters, five had slightly elevated CSF cell counts and normal or elevated CSF protein, and eight had normal CSF cell counts but elevated CSF protein. Five patients with primary headache served as controls. All samples were tested for viral pathogens by PCR and subjected to liquid chromatography tandem mass spectrometry and bioinformatics analysis and multiplex cytokine/chemokine arrays. RESULTS: All CSF samples, except those from VZV-FP patients, were negative for all tested pathogens. The protein composition of CSF samples from IFP patients with normal CSF was comparable to controls. IFP patients with elevated CSF protein showed dysregulated proteins involved in inflammatory pathways, findings which were similar to those in VZV-FP patients. Multiplex analysis revealed similarly elevated cytokine levels in the CSF of IFP patients with elevated CSF protein and VZV-FP. CONCLUSIONS: Our study revealed a subgroup of IFP patients with elevated CSF protein that showed upregulated inflammatory pathways, suggesting an inflammatory/infectious cause. However, no evidence for an inflammatory cause was found in IFP patients with normal CSF.

CXCL13 and CXCL9 CSF Levels in Central Nervous System Lymphoma-Diagnostic, Therapeutic, and Prognostic Relevance.

Background: Diagnostic delay and neurologic deterioration are still a problem for the treatment of rapidly progressing CNS lymphoma (CNSL); there is an unmet need for a diagnostic test with a high diagnostic yield and limited risk, minimizing the time to the initiation of effective treatment. Methods: In this prospective monocentric study, we analyzed the utility of CXCL13 and CXCL9 as diagnostic, therapeutic and prognostic biomarkers for CNSL. Cerebrospinal fluid (CSF) from 155 consecutive patients admitted with brain lesions of various origins was collected. Levels of CXCL13 and CXCL9 were analyzed by ELISA. Additionally, CSF was analyzed during CNSL disease course (relapse, remission, progress) in 17 patients. Results: CXCL13 and CXCL9 CSF levels were significantly increased in patients with CNSL compared to control patients with lesions of other origin. Using logistic regression and a minimal-p-value approach, a cut-off value of 80 pg/ml for CXCL13 shows high sensitivity (90.7%) and specificity (90.1%) for the diagnosis of active CNSL. CXCL9 at a cut-off value of 84 pg/ml is less sensitive (61.5%) and specific (87.1%). Both cytokines correlate with the clinical course and response to therapy. Conclusions: Our results confirm the excellent diagnostic potential of CXCL13 and introduce CXCL9 as a novel albeit less powerful marker for PCNSL.

APRIL and BAFF: novel biomarkers for central nervous system lymphoma.

BACKGROUND: Early diagnosis of CNS lymphoma (CNSL) is essential for successful therapy of this rapidly progressing brain tumor. However, in patients presenting with focal brain lesions, fast and reliable diagnosis of PCNSL remains a challenge. A proliferation-inducing ligand (APRIL) and B cell activating factor (BAFF) are important factors in the pathophysiology, diagnosis, and prognosis of systemic B cell malignancies. However, their utility as biomarkers for the diagnosis of CNSL and their effects on CNSL cells remain unclear. METHODS: In this prospective study, we analyzed the levels of APRIL and BAFF in the cerebrospinal fluid (CSF) of 116 patients with suspected focal brain lesions, including 53 CNSL patients. Additionally, we serially measured their levels during chemotherapy and relapse. Furthermore, we analyzed the effect of APRIL and BAFF on two B cell lymphoma cell lines using proliferation, viability, and chemotaxis assays. RESULTS: CSF levels of APRIL and BAFF reliably differentiated CNSL from other focal brain lesions (including primary and metastatic brain tumors, autoimmune-inflammatory lesions, and neuroinfectious lesions) with a specificity of 93.7% (APRIL, BAFF) and a sensitivity of 62.3% (APRIL) and 47.1% (BAFF). Serial CSF analysis of CNSL patients during chemotherapy and relapse demonstrates a close correlation of APRIL CSF levels and the course of this disease. In vitro, APRIL and BAFF showed anti-apoptotic effects during MTX treatment and mediated chemotaxis of malignant B cells. CONCLUSION: This study extends the spectrum of valuable diagnostic biomarkers in CNSL. In patients with focal brain lesions, measurement of APRIL in CSF could help accelerating the diagnosis of CNSL. Moreover, our results highlight an important role of APRIL and BAFF in the pathophysiology of CNSL.

Inhibition of DAMP signaling as an effective adjunctive treatment strategy in pneumococcal meningitis.

BACKGROUND: Pneumococcal meningitis remains a potentially lethal and debilitating disease, mainly due to brain damage from sustained inflammation. The release of danger-associated molecular patterns (DAMPs), like myeloid-related protein 14 (MRP14) and high mobility group box 1 protein (HMGB1), plays a major role in persistence of inflammation. In this study, we evaluated if paquinimod, an MRP14-inhibitor, and an anti-HMGB1 antibody can improve clinical outcome as adjunctive therapeutics in pneumococcal meningitis. METHODS: We tested the adjuvant administration of paquinimod and the anti-HMGB1 antibody in our pneumococcal meningitis mouse model assessing clinical (clinical score, open-field-test, temperature) and pathophysiological parameters (intracranial pressure, white blood cell count in CSF, bleeding area) as well as bacterial titers in blood and brain 24 h after administration and 48 h after infection. Furthermore, we explored the interactions of these two agents with dexamethasone, the standard adjuvant treatment in pneumococcal meningitis (PM), and daptomycin, a non-bacteriolytic antibiotic preventing pathogen-associated molecular pattern (PAMP) release. RESULTS: Adjunctive inhibition of MRP14 or HMGB1 reduced mortality in mice with PM. This effect was lost when the two anti-DAMP agents were given simultaneously, possibly due to excessive immunosuppression. Combining anti-PAMP (daptomycin) and anti-DAMP treatments did not produce synergistic results; instead, the anti-DAMP treatment alone was sufficient and superior. The combination of anti-HMGB1 with dexamethasone did not diminish the effect of the former. CONCLUSIONS: DAMP inhibition possesses good potential as an adjuvant treatment approach in PM, as it improves clinical outcome and can be given together with the standard adjuvant dexamethasone without drug effect loss in experimental PM.

Myeloid-related protein 14 promotes inflammation and injury in meningitis.

BACKGROUND: Neutrophilic inflammation often persists for days despite effective antibiotic treatment and contributes to brain damage in bacterial meningitis. We propose here that myeloid-related protein 14 (MRP14), an abundant cytosolic protein in myeloid cells, acts as an endogenous danger signal, driving inflammation and aggravating tissue injury. METHODS: The release pattern of MRP14 was analyzed in human and murine cerebrospinal fluid (CSF), as well as in isolated neutrophils. Its functional role was assessed in a mouse meningitis model, using MRP14-deficient mice. RESULTS: We detected large quantities of MRP14 in CSF specimens from patients and mice with pneumococcal meningitis. Immunohistochemical analyses and a cell-depletion approach indicated neutrophils as the major source of MRP14. In a meningitis model, MRP14-deficient mice showed a better resolution of inflammation during antibiotic therapy, which was accompanied by reduced disease severity. Intrathecal administration of MRP14 before infection reverted the phenotype of MRP14-deficient mice back to wild type. Moreover, intrathecal injection of MRP14 alone was sufficient to induce meningitis in a Toll-like receptor 4 (TLR4)-CXCL2-dependent manner. Finally, treatment with the MRP14 antagonist paquinimod reduced inflammation and disease severity significantly, reaching levels comparable to those achieved after genetic depletion of MRP14. CONCLUSIONS: The present study implicates MRP14 as an essential propagator of inflammation and potential therapeutic target in pneumococcal meningitis.

Leukocyte attraction by CCL20 and its receptor CCR6 in humans and mice with pneumococcal meningitis.

We previously identified CCL20 as an early chemokine in the cerebrospinal fluid (CSF) of patients with pneumococcal meningitis but its functional relevance was unknown. Here we studied the role of CCL20 and its receptor CCR6 in pneumococcal meningitis. In a prospective nationwide study, CCL20 levels were significantly elevated in the CSF of patients with pneumococcal meningitis and correlated with CSF leukocyte counts. CCR6-deficient mice with pneumococcal meningitis and WT mice with pneumococcal meningitis treated with anti-CCL20 antibodies both had reduced CSF white blood cell counts. The reduction in CSF pleocytosis was also accompanied by an increase in brain bacterial titers. Additional in vitro experiments showed direct chemoattractant activity of CCL20 for granulocytes. In summary, our results identify the CCL20-CCR6 axis as an essential component of the innate immune defense against pneumococcal meningitis, controlling granulocyte recruitment.

Adjunctive N-acetyl-L-cysteine in treatment of murine pneumococcal meningitis.

Despite antibiotic therapy, acute and long-term complications are still frequent in pneumococcal meningitis. One important trigger of these complications is oxidative stress, and adjunctive antioxidant treatment with N-acetyl-l-cysteine was suggested to be protective in experimental pneumococcal meningitis. However, studies of effects on neurological long-term sequelae are limited. Here, we investigated the impact of adjunctive N-acetyl-l-cysteine on long-term neurological deficits in a mouse model of meningitis. C57BL/6 mice were intracisternally infected with Streptococcus pneumoniae. Eighteen hours after infection, mice were treated with a combination of ceftriaxone and placebo or ceftriaxone and N-acetyl-l-cysteine, respectively. Two weeks after infection, neurologic deficits were assessed using a clinical score, an open field test (explorative activity), a t-maze test (memory function), and auditory brain stem responses (hearing loss). Furthermore, cochlear histomorphological correlates of hearing loss were assessed. Adjunctive N-acetyl-l-cysteine reduced hearing loss after pneumococcal meningitis, but the effect was minor. There was no significant benefit of adjunctive N-acetyl-l-cysteine treatment in regard to other long-term complications of pneumococcal meningitis. Cochlear morphological correlates of meningitis-associated hearing loss were not reduced by adjunctive N-acetyl-l-cysteine. In conclusion, adjunctive therapy with N-acetyl-l-cysteine at a dosage of 300 mg/kg of body weight intraperitoneally for 4 days reduced hearing loss but not other neurologic deficits after pneumococcal meningitis in mice. These results make a clinical therapeutic benefit of N-acetyl-l-cysteine in the treatment of patients with pneumococcal meningitis questionable.

High mobility group box 1 prolongs inflammation and worsens disease in pneumococcal meningitis.

Neutrophilic inflammation, which often persists over days despite appropriate antibiotic therapy, contributes substantially to brain damage in bacterial meningitis. We hypothesized that persistent inflammation is the consequence of a vicious cycle in which inflammation-induced cell injury leads to the release of endogenous danger molecules (e.g. high mobility group box 1) that drive the inflammatory response, causing further damage. The present study aimed to assess the mechanisms of high mobility group box 1 protein release and its functional relevance for the development and progression of pneumococcal meningitis. High mobility group box 1 was found in large quantities in cerebrospinal fluid samples of patients and mice with pneumococcal meningitis (predominantly in advanced stages of the disease). By using macrophages, we demonstrated that the release of high mobility group box 1 from macrophages following pneumococcal challenge is passive in nature and probably not connected with inflammasome- and oxidative stress-dependent inflammatory cell death forms. In a mouse meningitis model, treatment with the high mobility group box 1 antagonists ethyl pyruvate or Box A protein had no effect on the development of meningitis, but led to better resolution of inflammation during antibiotic therapy, which was accompanied by reduced brain pathology and better disease outcome. Additional experiments using gene-deficient mice and murine neutrophils provided evidence that high mobility group box 1 acts as a chemoattractant for neutrophils in a receptor for advanced glycosylation end products-dependent fashion. In conclusion, the present study implicated high mobility group box 1, likely released from dying cells, as a central propagator of inflammation in pneumococcal meningitis. Because persistent inflammation contributes to meningitis-associated brain damage, high mobility group box 1 may represent a promising target for adjunctive therapy of this disease.

The NLRP3 inflammasome contributes to brain injury in pneumococcal meningitis and is activated through ATP-dependent lysosomal cathepsin B release.

Streptococcus pneumoniae meningitis causes brain damage through inflammation-related pathways whose identity and mechanisms of action are yet unclear. We previously identified caspase-1, which activates precursor IL-1 type cytokines, as a central mediator of inflammation in pneumococcal meningitis. In this study, we demonstrate that lack of the inflammasome components ASC or NLRP3 that are centrally involved in caspase-1 activation decreases scores of clinical and histological disease severity as well as brain inflammation in murine pneumococcal meningitis. Using specific inhibitors (anakinra and rIL-18-binding protein), we further show that ASC- and NLRP3-dependent pathologic alterations are solely related to secretion of both IL-1ß and IL-18. Moreover, using differentiated human THP-1 cells, we demonstrate that the pneumococcal pore-forming toxin pneumolysin is a key inducer of IL-1ß expression and inflammasome activation upon pneumococcal challenge. The latter depends on the release of ATP, lysosomal destabilization (but not disruption), and cathepsin B activation. The in vivo importance of this pathway is supported by our observation that the lack of pneumolysin and cathepsin B inhibition is associated with a better clinical course and less brain inflammation in murine pneumococcal meningitis. Collectively, our study indicates a central role of the NLRP3 inflammasome in the pathology of pneumococcal meningitis. Thus, interference with inflammasome activation might be a promising target for adjunctive therapy of this disease.

Reduced spiral ganglion neuronal loss by adjunctive neurotrophin-3 in experimental pneumococcal meningitis.

BACKGROUND: Hearing loss is a frequent long-term complication of pneumococcal meningitis (PM). Its main pathological correlate is damage to the organ of Corti and loss of spiral ganglion neurons. The only current treatment option is cochlear implants which require surviving neurons. Here, we investigated the impact of systemically applied neurotrophin-3 (NT-3) on long-term hearing loss and the survival of neurons. METHODS: Eighteen hours after infection with S. pneumoniae, C57BL/6 mice were treated with a combination of ceftriaxone with NT-3 or dexamethasone or placebo. Hearing, cochlear damage, and brain damage were assessed by audiometry and histology. RESULTS: The main findings from immunohistochemical visualization of neurotrophins (NT-3, BDNF) and their receptors (TrkB, TrkC, and p75) in the cochlea were (i) enhanced staining for the cell survival-promoting receptor TrkB and (ii) increased NT-3 staining in NT-3 treated mice, showing that systemically applied NT-3 reaches the cochlea. The major effects of adjunctive NT-3 treatment were (i) a reduction of meningitis-induced hearing impairment and (ii) a reduction of spiral ganglion neuronal loss. The efficacy of NT-3 therapy was comparable to that of dexamethasone. CONCLUSION: Systemically applied NT-3 might be an interesting candidate to improve hearing outcome after pneumococcal meningitis.

CXCL16 contributes to neutrophil recruitment to cerebrospinal fluid in pneumococcal meningitis.

In this study, we analyzed the expression and function of CXCL16 in pneumococcal meningitis. CXCL16 was found to be up‐regulated in RAW264.7 macrophages (but not in neutrophils and endothelial cells) upon pneumococcal stimulation, in the cerebrospinal fluid of patients, and in the brains as well as the cerebrospinal fluid of mice with pneumococcal meningitis. CXCL16 up‐regulation in vivo was dependent on Toll‐like receptor (TLR) 2/TLR4 and MyD88 signaling. Neutralization of CXCL16 in animals before intracisternal pneumococcal infection (using anti‐CXCL16 antibodies) resulted in reduced cerebrospinal fluid pleocytosis. In vitro, murine neutrophils expressed the CXCL16 receptor CXCR6 and showed dose‐dependant migration toward a CXCL16 gradient. Thus, this study implicates CXCL16 as an additional neutrophil chemoattractant in cerebrospinal fluid in early pneumococcal meningitis.

Simvastatin attenuates leukocyte recruitment in experimental bacterial meningitis.

Statins exert multiple effects besides lowering the serum cholesterol level, which might be beneficial for patients with sepsis and infections. We designed this study to assess the therapeutic potential of simvastatin in an established animal model of pneumococcal meningitis, a disease characterized by high morbidity and mortality despite effective antibiotic treatment. 24 h after injection of live pneumococci into the cisterna magna of mice, animals were clinically evaluated, cerebrospinal fluid (CSF) leukocyte counts and intracranial pressure were determined, and brains were removed for assessment of bacterial titer and blood-brain barrier breakdown. The following experimental groups were investigated: (I) no infection and treatment with vehicle; (II) infection and treatment with vehicle; infection and treatment with (III) 20 mg/kg or (IV) 40 mg/kg simvastatin s.c. 18 h before and just prior to infection. Treatment with simvastatin dose-dependently decreased CSF leukocyte counts, a marker for CNS inflammation. In addition, hypothermia was completely abolished in the 40 mg/kg simvastatin group. In contrast, a neurological clinical score, and intracranial complications like increase in intracranial pressure and blood-brain barrier breakdown were not altered by the treatment. In conclusion, simvastatin attenuates CNS leukocyte recruitment and systemic complications of experimental pneumococcal meningitis.

Innate immunity to pneumococcal infection of the central nervous system depends on toll-like receptor (TLR) 2 and TLR4.

BACKGROUND: Recent studies have suggested that, in addition to Toll-like receptor (TLR) 2, other pattern recognition receptors mediate activation of the immune response after infection of the central nervous system (CNS) with Streptococcus pneumoniae (SP). METHODS: Using a mouse meningitis model, we investigated the influence of TLR4 single deficiency (TLR4(-/-)), TLR2/TLR4 double deficiency (TLR2/4(-/-)), and TLR2/TLR4/TLR9 triple deficiency (TLR2/4/9(-/-)) on the immune response of the CNS to SP infection. To identify the cell populations that mediate the responses to SP, we generated TLR2/4(-/-)-wild-type (wt) bone marrow (BM) chimeras. RESULTS: Compared with infected wt mice, infected TLR2/4(-/-) and TLR2/4/9(-/-) mice had similar reductions in brain cytokine levels, pleocytosis, and cerebral pathologic findings, whereas no such effect was noted in infected TLR4(-/-) mice. The attenuated immune response was paralleled by an impaired host defense that resulted in worsening of disease. Analysis of the chimeric mice after infection showed that mere TLR2/4 deficiency, either of radioresistant cells or of transplanted BM-derived cells, was sufficient to mount a substantial cerebral immune response, such as that noted in wt mice. CONCLUSION: In murine SP meningitis, TLR2 and TLR4 expressed on radioresistant and transplanted BM-derived cells were major cellular sensors of invading SP inducing inflammatory responses.

Myeloid Src kinases regulate phagocytosis and oxidative burst in pneumococcal meningitis by activating NADPH oxidase.

Myeloid cells, including neutrophils and macrophages, play important roles in innate immune defense against acute bacterial infections. Myeloid Src family kinases (SFKs) p59/61(hck) (Hck), p58(c-fgr) (Fgr), and p53/56(lyn) (Lyn) are known to control integrin beta(2) signal transduction and FcgammaR-mediated phagocytosis in leukocytes. In this study, we show that leukocyte recruitment into the cerebrospinal fluid space and bacterial clearance is hampered in mice deficient in all three myeloid SFKs (hck(-/-)fgr(-/-)lyn(-/-)) during pneumococcal meningitis. As a result, the hck(-/-)fgr(-/-)lyn(-/-) mice developed increased intracranial pressure and a worse clinical outcome (increased neurologic deficits and mortality) compared with wild-type mice. Impaired bacterial killing was associated with a lack of phagocytosis and superoxide production in triple knockout neutrophils. Moreover, in hck(-/-)fgr(-/-)lyn(-/-) neutrophils, phosphorylation of p40(phox) was absent in response to pneumococcal stimulation, indicating a defect in NAPDH oxidase activation. Mice lacking the complement receptor 3 (CR3; CD11b/CD18), which belongs to the beta(2)-integrin family, also displayed impaired host defense against pneumococci, along with defective neutrophil superoxide production, but cerebrospinal fluid pleocytosis was normal. Cerebral expression of cytokines and chemokines was not decreased in both mouse strains, indicating that CR3 and myeloid SFKs are dispensable for the production of inflammatory mediators. Thus, our study demonstrates the pivotal role of myeloid SFKs and CR3 in mounting an effective defense against CNS infection with Streptococcus pneumonia by regulating phagocytosis and NADPH oxidase-dependent superoxide production. These data support the role of SFKs as critical mediators of CR3 signal transduction in host defense.

Acute brain injury triggers MyD88-dependent, TLR2/4-independent inflammatory responses.

Endogenous molecules released from disrupted cells and extracellular matrix degradation products activate Toll-like receptors (TLRs) and, thus, might contribute to immune activation after tissue injury. Here, we show that aseptic, cold-induced cortical injury triggered an acute immune response that involves increased production of multiple cytokines/chemokines accompanied by neutrophil recruitment to the lesion site. We observed selective reductions in injury-induced cytokine/chemokine expression as well as in neutrophil accumulation in mice lacking the common TLR signaling adaptor MyD88 compared with wild-type mice. Notably, attenuation of the immune response was paralleled by a reduction in lesion size. Neutrophil depletion of wild-type mice and transplantation of MyD88-deficient bone marrow into lethally irradiated wild-type recipients had no substantial impact on injury-induced expression of cytokines/chemokines and on lesion development. In contrast to MyD88 deficiency, double deficiency of TLR2 and TLR4 -- despite the two receptors being activated by specific endogenous molecules associated to danger and signal through MyD88 -- altered neither immune response nor extent of tissue lesion size on injury. Our data indicate modulation of the neuroinflammatory response and lesion development after aseptic cortical injury through MyD88-dependent but TLR2/4-independent signaling by central nervous system resident nonmyeloid cells.

Complement C1q and C3 are critical for the innate immune response to Streptococcus pneumoniae in the central nervous system.

Previous studies suggest that the complement system can contribute to limiting pneumococcal outgrowth within the CNS. In this study, we evaluated the role of the complement system in the activation of the innate immune response and the development of the prognosis-relevant intracranial complications in a murine model of pneumococcal meningitis. Thereby, we used mice deficient in C1q, lacking only the classical pathway, and C3, lacking all three complement activation pathways. At 24 h after intracisternal infection, bacterial titers in the CNS were almost 12- and 20-fold higher in C1q- and C3-deficient-mice, respectively, than in wild-type mice. Mean CSF leukocyte counts were reduced by 47 and 73% in C1q- and C3-deficient-mice, respectively. Intrathecal reconstitution with wild-type serum in C3-deficient mice restored both the ability of mice to combat pneumococcal infection of the CSF and the ability of leukocytes to egress into the CSF. The altered recruitment of leukocytes into the CSF of C3-deficient mice was paralleled by a strong reduction of the brain expression of cytokines and chemokines. The dampened immune response in C3-deficient mice was accompanied by a reduction of meningitis-induced intracranial complications, but, surprisingly, also with a worsening of short-term outcome. The latter seems to be due to more severe bacteremia (12- and 120-fold higher in C1q- and C3-deficient-mice, respectively) and, consecutively, more severe systemic complications. Thus, our study demonstrated for the first time that the complement system plays an integral role in mounting the intense host immune response to Streptococcus pneumoniae infection of the CNS.

Differential regulation of blood-brain barrier permeability in brain trauma and pneumococcal meningitis-role of Src kinases.

Increased vascular permeability causing vasogenic brain edema is characteristic for many acute neurological diseases such as stroke, brain trauma, and meningitis. Src family kinases, especially c-Src, play an important role in regulating blood-brain barrier permeability in response to VEGF, but also mediate leukocyte function and cytokine signalling. Here we demonstrate that pharmacological inhibition of Src or c-Src deficiency does not influence cerebrospinal fluid (CSF) pleocytosis, brain edema formation, and bacterial outgrowth during experimental pneumococcal meningitis despite the increased cerebral expression of inflammatory chemokines, such as IL-6, CCL-9, CXCL-1, CXCL-2 and G-CSF as determined by protein array analysis. In contrast, inhibition of Src significantly reduced brain edema formation, lesion volume, and clinical worsening in cold-induced brain injury without decreasing cytokine/chemokine expression. While brain trauma was associated with increased cerebral VEGF formation, VEGF levels significantly declined during pneumococcal meningitis. Therefore, we conclude that in brain trauma blood-brain barrier tightness is regulated by the VEGF/Src pathway whereas c-Src does not influence brain edema formation and leukocyte function during bacterial meningitis.

Protein expression pattern in experimental pneumococcal meningitis.

In this study, we investigated cytokine expression during experimental pneumococcal meningitis. Mice were intracisternally infected with Streptococcus pneumoniae and treated with ceftriaxone starting at 24 h after infection. At different time points before and after antibiotic therapy, the cytokine expression pattern was determined in mouse brains using protein arrays. Underlining the power of this method, the meningitis-relevant cytokines interleukin-1beta (IL-1beta), IL-6, KC, macrophage inflammatory protein-2 (MIP-2), and monocyte chemoattractant protein-1 (MCP-1/CCL2) were markedly elevated in infected animals. Newly identified proteins during the acute stage of the disease (until 30 h after infection) included lymphotactin (XCL-1), MIP-1gamma (CCL9) and MCP-5 (CCL12), cytokine responsive gene- 2 (CRG-2/CXCL10) and CXCL16, and insulin-like growth factor binding protein 3 (IGFBP3). During later stages, an induction of T-cell activation-3 (TCA-3/CCL1), platelet factor-4 (PF-4/CXCL4) and stromal derived factor-1alpha (SDF-1alpha/CXCL13), and IL-4 was observed. The validity of this method was supported by an additional ELISA analysis of the expression profile of CXCL16 and IGFBP3, which was identical to that observed by protein array. In conclusion, the use of protein array technology led to an extension of the current picture of protein expression in pneumococcal meningitis. Most important, new factors that might play a role in pneumococcal meningitis were identified.

Patterns of protein expression in infectious meningitis: a cerebrospinal fluid protein array analysis.

Seventy-nine cytokines, chemokines, and growth factors were measured by protein array analysis in the cerebrospinal fluid of patients with meningitis and controls. Several factors were found to be regulated, which have not been studied in the CNS before, e.g., macrophage inflammatory protein-1delta (CCL15) and neutrophil-activating peptide-2 (CXCL7). In pneumococcal meningitis, other new observations were an increase of macrophage migration inhibitory factor, monocyte chemoattractant protein-2 (CCL8), pulmonary and activation-regulated chemokine (CCL18), and macrophage inflammatory protein-3alpha (CCL20), and a sustained upregulation of several growth factors. In viral meningitis, new findings were an elevation of CCL8, thrombopoietin, and vascular endothelial growth factor.