Cytokine mRNA profiles during the course of experimental Haemophilus influenzae bacterial meningitis

Invited review: Compartmentalization of the inflammatory response in sepsis and SIRS

Sepsis and systemic inflammatory response syndrome (SIRS) are associated with an exacerbated production of both pro- and anti-inflammatory mediators that are mainly produced within tissues. Although a systemic process, the pathophysiological events differ from organ to organ, and from organ to peripheral blood, leading to the concept of compartmentalization. The nature of the insult ( e.g. burn, hemorrhage, trauma, peritonitis), the cellular composition of each compartment ( e.g . nature of phagocytes, nature of endothelial cells), and its micro-environment ( e.g. local presence of granulocyte-macrophage colony stimulating factor [GM-CSF] in the lungs, low levels of arginine in the liver, release of endotoxin from the gut), and leukocyte recruitment, have a great influence on local inflammation and on tissue injury. High levels of pro-inflammatory mediators ( e.g. interleukin-1 [IL-1], tumor necrosis factor [TNF], gamma interferon [IFN-γ], high mobility group protein-1 [HMGB1], macrophage migration inhibitory factor [MIF]) produced locally and released into the blood stream initiate remote organ injury as a consequence of an organ cross-talk. The inflammatory response within the tissues is greatly influenced by the local delivery of neuromediators by the cholinergic and sympathetic neurons. Acetylcholine and epinephrine contribute with IL-10 and other mediators to the anti-inflammatory compensatory response initiated to dampen the inflammatory process. Unfortunately, this regulatory response leads to an altered immune status of leukocytes that can increase the susceptibility to further infection. Again, the nature of the insult, the nature of the leukocytes, the presence of circulating microbial components, and the nature of the triggering agent employed to trigger cells, greatly influence the immune status of the leukocytes that may differ from one compartment to another. While anti-inflammatory mediators predominate within the blood stream to avoid igniting new inflammatory foci, their presence within tissues may not always be sufficient to prevent the initiation of a deleterious inflammatory response in the different compartments.

Interferon-γ-Induced Nitric Oxide Synthase-2 Contributes to Blood/Brain Barrier Dysfunction and Acute Mortality in Experimental Streptococcus pneumoniae Meningitis

The proinflammatory cytokine interferon-gamma (IFNγ) recently was shown to play a crucial role in experimental pneumococcal meningitis (PM) pathogenesis, and we aimed in this study to investigate IFNγ-driven nitric oxide synthase-2 (NOS2)-mediated pathogenesis of murine PM. We demonstrate that costimulation of toll-like receptors and IFNγ receptors was synergistic for NOS2 expression in cultured murine microglia. Using an experimental PM model, wild-type mice treated with anti-IFNγ antibody, as well as IFNγ and NOS2 gene knockout (GKO) mice, were inoculated intracerebroventricularly with 10(3) colony-forming units of Streptococcus pneumoniae (WU2 strain). Mice were monitored daily during a 200-h disease course to assess survival rate and blood-brain barrier (BBB) permeability measured at 48 h. IFNγ deficiency was protective in PM, with an approximate 3-fold increase in survival rates in both antibody-treated and IFNγ GKO mice compared to controls (P < 0.01). At 48 h postinoculation, brain NOS2 mRNA expression was significantly increased in an IFNγ-dependent manner. Mortality was significantly delayed in NOS2 GKO mice compared to controls (P < 0.01), and BBB dysfunction was reduced by 54% in IFNγ GKO mice and abolished in NOS2 GKO. These data suggest that IFNγ-dependent expression of NOS2 in the brain contributes to BBB breakdown and early mortality in murine PM.

Interactions of Haemophilus parasuis and its LOS with porcine brain microvascular endothelial cells

Haemophilus parasuis is a swine pathogen that causes Glässer's disease, which is characterized by polyserositis and meningitis. The pathogenesis of the H. parasuis infection is poorly understood. To cause meningitis, H. parasuis has to cross the blood-brain barrier (BBB) to gain access to the central nervous system (CNS). We recently showed that H. parasuis adheres to and invades porcine brain microvascular endothelial cells (PBMEC). The aim of this study was to evaluate the role of H. parasuis lipooligosaccharide (LOS) in the adhesion to PBMEC and to determine if H. parasuis (and/or its LOS) is able to induce apoptosis and activation of PBMEC. Results showed that adhesion of H. parasuis to PBMEC was partially mediated by LOS. Moreover, H. parasuis induces caspase-3-mediated apoptosis of PBMEC in a time--and dose--dependent manner, but its LOS did not seem to be involved in such a process. Furthermore, H. parasuis and, to a lesser extent, its LOS, was able to induce the release of IL-8 and IL-6 by PBMEC. Field strains of H. parasuis serotypes 4 and 5 induced similar levels of these inflammatory mediators. Our data suggest that H. parasuis uses cellular adhesion, induction of apoptosis and up-regulation of inflammatory mediators as mechanisms to invade the CNS via the BBB, and that LOS would play a certain but limited role in such pathological process.

Kinetic Th1/Th2 responses of transgenic mice with bacterial meningitis induced by Haemophilus influenzae

To investigate the kinetic Th1/Th2 immunopathogenic mechanisms of Haemophilus influenzae meningitis, we established a murine experimental model of meningitis and elucidated the Th1/Th2 immune responses in T1/T2 doubly transgenic mice based on a BALB/c background under the control of the IFN-gamma (interferon-gamma)/IL-4 (interleukin-4) promoters respectively. NTHi (non-typeable Haemophilus influenzae) meningitis was induced in these mice by inoculation with either a colonized (CNTHi) or invasive (INTHi) strain of NTHi. Mice inoculated with CNTHi displayed a less severe degree of disease in terms of clinical symptoms, mortality rate and brain histopathology. Conversely, INTHi-inoculated mice had more severe clinical symptoms. CNTHi-inoculated mice had a more significant Th1 response in terms of a higher percentage and longer maintenance of Th1 cells, and more production of IFN-gamma from strain-specific antigen-stimulated splenocytes than INTHi-inoculated mice. In contrast, INTHi-inoculated mice had a more significant Th2 response. This was due to a significant increase in IL-4-producing CD4(+) T-cells (Th2 cells) and more production of IL-4 from strain-specific antigen-stimulated splenocytes accompanied by a rapid decline of Th1 cells in INTHi-inoculated mice. In conclusion, the preferential Th1/Th2 trend in this murine model of NTHi meningitis is correlated with clinical severity as well as isolated characteristics of the pathogens themselves.

Haemophilus influenzae porin induces Toll-like receptor 2-mediated cytokine production in human monocytes and mouse macrophages

The production of proinflammatory cytokines is likely to play a major pathophysiological role in meningitis and other infections caused by Haemophilus influenzae type b (Hib). Previous studies have shown that Hib porin contributes to signaling of the inflammatory cascade. We examined here the role of Toll-like receptors (TLRs) and the TLR-associated adaptor protein MyD88 in Hib porin-induced production of tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6). Hib porin-induced TNF-alpha and IL-6 production was virtually eliminated in macrophages from TLR2- or MyD88-deficient mice. In contrast, macrophages from lipopolysaccharide (LPS)-hyporesponsive C3H/HeJ mice, which are defective in TLR4 function, responded normally to Hib porin. Moreover anti-TLR2 antibodies but not anti-TLR4 antibodies significantly reduced Hib porin-stimulated TNF-alpha and IL-6 release from the human monocytic cell line THP-1. These data indicate that the TLR2/MyD88 pathway plays an essential role in Hib porin-mediated cytokine production. These findings may be useful in the development of alternative therapies aimed at reducing excessive inflammatory responses during Hib infections.

NF-kappaB activation in cerebrospinal fluid cells from patients with meningitis

We examined whether or not NF-kappaB, a factor that regulates expression of the genes that code for pro-inflammatory cytokines, is activated in cerebrospinal fluid (CSF) cells to investigate the production of pro-inflammatory cytokines by CSF cells in patients with meningitis. Western blotting demonstrated that NF-kappaB was more activated in CSF cells of patients with bacterial meningitis than in those of patients with aseptic meningitis. NF-kappaB was hardly activated in carcinomatous meningitis. The NF-kappaB activation in CSF cells of patients with meningitis tended to be correlated with the CSF interleukin-6 concentration. Our data suggested that CSF cells produce pro-inflammatory cytokines through NF-kappaB activation in meningitis, and that increased NF-kappaB activation in CSF cells indicate infectious meningitis rather than carcinomatous meningitis.

Regulatory role of interleukin-10 in experimental group B streptococcal arthritis

Intravenous inoculation of CD-1 mice with 10(7) CFU of type IV group B Streptococcus (GBS) results in a high incidence of diffuse septic arthritis, associated with high levels of systemic and local production of interleukin-1beta (IL-1beta) and IL-6. In this study, the role of the anti-inflammatory cytokine IL-10 in the evolution of GBS systemic infection and arthritis was evaluated. IL-10 production was evident in sera and joints of GBS-infected mice. Neutralization of endogenous IL-10 by administration of anti-IL-10 antibodies (1 mg/mouse) at the time of infection resulted in worsening of articular lesions and 60% mortality associated with early sustained production of IL-6, IL-1beta, and tumor necrosis factor alpha (TNF-alpha). The effect of IL-10 supplementation was assessed by administering IL-10 (100, 200, or 400 ng/mouse) once a day for 5 days, starting 1 h after infection. Treatment with IL-10 had a beneficial effect on GBS arthritis, and there was a clear-cut dose dependence. The decrease in pathology was associated with a significant reduction in IL-6, IL-1beta, and TNF-alpha production. Histological findings showed limited periarticular inflammation and a few-cell influx in the articular cavity of IL-10-treated mice, confirming clinical observations. In conclusion, this study provides further information concerning the role of IL-10 in regulating the immune response and inflammation and calls attention to the potential therapeutic use of IL-10 in GBS arthritis.

From farm to table to brain: foodborne pathogen infection and the potential role of the neuro-immune-endocrine system in neurotoxic sequelae

The American diet is among the safest in the world; however, diseases transmitted by foodborne pathogens (FBPs) still pose a public health hazard. FBPs are the second most frequent cause of all infectious illnesses in the United States. Numerous anecdotal and clinical reports have demonstrated that central nervous system inflammation, infection, and adverse neurological effects occur as complications of foodborne gastroenteritis. Only a few well-controlled clinical or experimental studies, however, have investigated the neuropathogenesis. The full nature and extent of neurological involvement in foodborne illness is therefore unclear. To our knowledge, this review and commentary is the first effort to comprehensively discuss the issue of FBP induced neurotoxicity. We suggest that much of this information supports the role of a theoretical model, the neuro-immune-endocrine system, in organizing and helping to explain the complex pathogenesis of FBP neurotoxicity.

Inflammatory cytokine cascade released by leukocytes in cerebrospinal fluid after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) elicits an inflammatory response in the subarachnoid space, which is mediated by the release of various cytokines. To assess their involvement in post-hemorrhagic complications, we determined the source and time-course of the release of inflammatory cytokines and acute-phase proteins in cerebrospinal fluid (CSF) following SAH. Concentrations of interleukin (IL)- 1beta, IL-6, transforming growth factor-beta1 (TGF-beta1) and C-reactive protein (CRP) in CSF of 36 patients with SAH were measured by enzyme-linked immunoabsorbent assay (ELISA). Floating cells collected from the CSF were centrifuged four to six days after SAH, and examined immunohistochemically. Intracellular IL-1beta and IL-6 were examined by flow cytometric analysis. The molecular weight of TGF-beta1 in CSF of 30 patients was examined by Western blot analysis. The TGF-beta1 levels of patients who had undergone ventriculoperitoneal (VP) shunt (n = 19) was significantly higher than nonshunt group (n = 16). The CRP levels of VP shunt group was significantly higher than nonshunt group. IL-6 concentration was maximal within day 0-1 and it was secreted by neutrophils and monocytes. ELISA showed consistently low levels of IL-1beta, whereas a proportion of monocytes and lymphcytes were IL- 1beta-positive by flow cytometric analysis. TGF-beta1 levels were also maximal on day 0-1 according to ELISA, although it tended to be in the inactive form derived from platelets. A 25 kDa band of TGF-1 was detectable for at least 13 days after SAH, which may have been secreted in part by neutrophils and monocytes. CRP levels in CSF peaked on day 2-3. The present results suggest that leukocytes induced by SAH play an important role in post-hemorrhagic inflammation in the subarachnoid space by releasing IL-6 and TGF-beta1. The CRP and TGF-beta1 levels in CSF are strongly concerned with communicating hydrocephalus after SAH.

Suppression of macrophage activation with CNI-1493 increases survival in infant rats with systemic Haemophilus influenzae infection

CNI-1493, a potent macrophage deactivator, was used to treat infant rats systemically infected with Haemophilus influenzae type b (Hib). CNI-1493 was injected 1 h prior to bacterial inoculation and 24 h later and resulted in a 75 percent increased rate of survival compared to that for untreated controls. The effect of CNI-1493 on the inflammatory response was studied by immunohistochemical detection of individual tumor necrosis factor alpha (TNF-alpha)-, interleukin 1 beta (IL-1beta)-, and gamma interferon (IFN-gamma)-producing cells in the spleen. A significant reduction of the incidence of TNF-alpha- and IL-1beta-expressing cells was found for CNI-1493-treated animals. IFN-gamma expression was not suppressed by CNI-1493, indicating that cytokine inhibition was specific in macrophages. CNI-1493 significantly reduced the number of infiltrating granulocytes in the brain from that for controls. This study provides evidence that CNI-1493 protects against lethal Hib infection by deactivating the inflammatory cascade in infant rats.

Neutralization of macrophage inflammatory protein 2 (MIP-2) and MIP-1alpha attenuates neutrophil recruitment in the central nervous system during experimental bacterial meningitis

Chemokines are low-molecular-weight chemotactic cytokines that have been shown to play a central role in the perivascular transmigration and accumulation of specific subsets of leukocytes at sites of tissue damage. Using in situ hybridization (ISH), we investigated the mRNA induction of macrophage inflammatory protein 2 (MIP-2), MIP-1alpha, monocyte chemoattractant protein 1 (MCP-1), and RANTES. Challenge of infant rats' brains with Haemophilus influenzae type b intraperitoneally resulted in the time-dependent expression of MIP-2, MIP-1alpha, MCP-1, and RANTES, which was maximal 24 to 48 h postinoculation. Immunohistochemistry showed significant increases in neutrophils and macrophages infiltrating the meninges, the ventricular system, and the periventricular area. The kinetics of MIP-2, MIP-1alpha, MCP-1, and RANTES mRNA expression paralleled those of the recruitment of inflammatory cells and disease severity. Administration of anti-MIP-2 or anti-MIP-1alpha antibodies (Abs) resulted in significant reduction of neutrophils. Administration of anti-MCP-1 Abs significantly decreased macrophage infiltration. Combined studies of ISH and immunohistochemistry showed that MIP-2- and MIP-1alpha-positive cells were neutrophils and macrophages. MCP-1-positive cells were neutrophils, macrophages, and astrocytes. Expression of RANTES was localized predominantly to resident astrocytes and microglia. The present study indicates that blocking of MIP-2 or MIP-1alpha bioactivity in vivo results in decreased neutrophil influx. These data are also the first demonstration that the C-C chemokine MIP-1alpha is involved in neutrophil recruitment in vivo.

A novel mechanism for cytokine regulation: screening, selection, and characterization of anticytokine monoclonal and polyclonal autoantibodies

We have recently described an immunoregulatory mechanism involving release of neutralizing autoantibodies (Aab) to cytokines during bacterial infections. Intraperitoneal inoculation of Haemophilus influenzae type b (Hib) into Sprague-Dawley rats resulted in high levels of inflammatory mediators early after infection. Increased titers of cytokine Aab were observed, with a peak at day 7. We cloned Aab-producing B cells. Screening of the clones with five different cytokines resulted in detection of Aab-producing clones reactive with each cytokine. After repeated subcloning, monoclonal Aab (mAab) were selected and characterized for their specificity, isotypes, and affinities. To elucidate regulatory importance, mAab to interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) dose-dependently inhibited IFN-gamma-induced MHC expression by peritoneal macrophages and TNF-alpha-induced thymocyte proliferation, respectively. Fab fragments exhibited binding and neutralizing effects, confirming specificities. Cross-reactivity with other rat cytokines was excluded. Pools of clones containing several mAab to each cytokine were obtained and served as polyclonal Aab. The relative affinity of the Aab was determined and found to be of high index. The characterized Aab were tested in methodologic assays for cytokine detection, revealing that some Aab were useful in a cell release capturing (CRC) ELISA.

Interleukin-4 and interleukin-10 regulate IL1-beta induced mouse primary astrocyte activation: a comparative study

The pro-inflammatory cytokine interleukin-1beta (IL-1beta) is strongly expressed during brain injury and is able to induce severe cellular brain damage via the production of soluble factors. Different processes regulate IL-1 biological activities, like the production of anti-inflammatory cytokines such as interleukin-4 (IL-4) and interleukin-10 (IL-10). In this report, we describe the sequential effects of IL-4 and IL-10 on the production of interleukin-6 (IL-6) induced by IL-1beta in mouse primary astrocytes and compare these effects to those of the synthetic glucocorticoid agonist, dexamethasone. IL-6 secretion and IL-6 mRNA expression were determined by ELISA assay and a comparative RT-PCR method, respectively. Incubation of mouse astrocytes in primary culture simultaneously with IL-1beta (10 ng/ml) + IL-10 (10 ng/ml) or IL-1beta + dexamethasone (10(-6) M) markedly reduced IL-1beta induced IL-6 secretion and IL-6 mRNA expression, respectively, whereas simultaneous addition of IL-4 (10 ng/ml) did not alter the induction of IL-6 by IL-1beta. In contrast, after 24 h of IL-1beta treatment, the level of IL-6 was decreased below constitutive levels, and this change was reversed by addition of IL-4. IL-6 production in IL-1beta pretreated cells was also increased by addition of IL-4, whereas IL-10 and dexamethasone had no effects. The delayed time dependent effect of IL-4 might be partially explained by the induction of IL-4 receptor alpha-chain mRNA expression by IL-1beta. Therefore, we conclude that IL-10 and dexamethasone have rapid immunosuppressive effects on the astrocyte response to IL-1beta stimulation, whereas IL-4, which has a delayed action, acts as an immune inducer.

Induction of cytokines and anti-cytokine autoantibodies in cerebrospinal fluid (CSF) during experimental bacterial meningitis

We have recently described the induction of anti-cytokine autoantibodies (Aabs) in the serum as a novel mechanism for cytokine regulation during bacterial infections. Here we use the infant rat-model of Haemophilus influenzae type b (Hib) meningitis to examine the induction of five potentially important cytokines and their autoantibody responses in the CSF. Protein levels of the cytokines interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), transforming growth factor-beta (TGF-beta), IL-4 and IL-10 were detected at day 3 post-inoculation (p.i.) with maximum induction at day 8. Thereafter, these levels of cytokines had become undetectable. Increased Aab titres to these cytokines, except IL-4, were registered with peak levels between days 7 and 9. Upon re-inoculation with Hib at day 30, regeneration of Aabs was recorded 7 days later (i.e. at day 37). To control the specificity of these Aabs, preincubation of the CSF with a cytokine inhibited the binding effects of that particular cytokine, but not those of any other cytokine. Aabs dose-dependently inhibited IFN-gamma-induced MHC expression by peritoneal macrophages and TNF-alpha-mediated L929 cytotoxicity. Our data demonstrate for the first time the existence of the anti-cytokine antibodies in the CSF of the meningitis Hib model. Furthermore, the data present a role for the Aabs in cytokine regulation, which is consistent with the previously demonstrated effects of the Aabs in the serum.