Cytokine appearance and effects of anti-tumor necrosis factor alpha antibodies in a neonatal rat model of group B streptococcal infection

Caspase-8 inhibition improves the outcome of bacterial infections in mice by promoting neutrophil activation

During differentiation, neutrophils undergo a spontaneous pro-inflammatory program that is hypothesized here to be under caspase-8 control. In mice, intraperitoneal administration of the caspase-8 inhibitor z-IETD-fmk is sufficient to unleash the production of pro-inflammatory cytokines and neutrophil influx in the absence of cell death. These effects are due to selective inhibition of caspase-8 and require tonic interferon-β (IFN-β) production and RIPK3 but not MLKL, the essential downstream executioner of necroptotic cell death. In vitro, stimulation with z-IETD-fmk is sufficient to induce significant cytokine production in murine neutrophils but not in macrophages. Therapeutic administration of z-IETD-fmk improves clinical outcome in models of lethal bacterial peritonitis and pneumonia by augmenting cytokine release, neutrophil influx, and bacterial clearance. Moreover, the inhibitor protects mice against high-dose endotoxin shock. Collectively, our data unveil a RIPK3- and IFN-β-dependent pathway that is constitutively activated in neutrophils and can be harnessed therapeutically using caspase-8 inhibition.

IL-17A Secreted by Th17 Cells Is Essential for the Host against Streptococcus agalactiae Infections

Streptococcus agalactiae is an important bacterial pathogen and causative agent of diseases including neonatal sepsis and meningitis, as well as infections in healthy adults and pregnant women. Although antibiotic treatments effectively relieve symptoms, the emergence and transmission of multidrug-resistant strains indicate the need for an effective immunotherapy. Effector T helper (Th) 17 cells are a relatively newly discovered subpopulation of helper CD4⁺ T lymphocytes, and which, by expressing interleukin (IL)-17A, play crucial roles in host defenses against a variety of pathogens, including bacteria and viruses. However, whether S. agalactiae infection can induce the differentiation of CD4⁺ T cells into Th17 cells, and whether IL-17A can play an effective role against S. agalactiae infections, are still unclear. In this study, we analyzed the responses of CD4⁺ T cells and their defensive effects after S. agalactiae infection. The results showed that S. agalactiae infection induces not only the formation of Th1 cells expressing interferon (IFN)-γ, but also the differentiation of mouse splenic CD4⁺ T cells into Th17 cells, which highly express IL-17A. In addition, the bacterial load of S. agalactiae was significantly increased and decreased in organs as determined by antibody neutralization and IL-17A addition experiments, respectively. The results confirmed that IL-17A is required by the host to defend against S. agalactiae and that it plays an important role in effectively eliminating S. agalactiae. Our findings therefore prompt us to adopt effective methods to regulate the expression of IL-17A as a potent strategy for the prevention and treatment of S. agalactiae infection.

Progressive Control of Streptococcus agalactiae-Induced Innate Inflammatory Response Is Associated with Time Course Expression of MicroRNA-223 by Neutrophils

Group B streptococcus (GBS) is a human-pathogenic bacterium inducing a strong inflammatory response that may be detrimental for host tissues if not finely regulated. The inflammatory response can be modulated by different molecular mechanisms, among which growing evidence points toward the crucial role of microRNAs (miRNAs). Regarding innate inflammatory response, studies have reported that miR-223 is essential for the control of granulocyte proliferation and activation. Moreover, a number of investigations on miRNA expression profiling performed in various inflammatory settings have revealed that miR-223 is among the top differentially expressed miRNAs. Yet the dynamic pattern of expression of miR-223 in vivo with respect to the evolution of the inflammatory process, especially in microbial infection, remains elusive. In this study, we analyzed the kinetic expression of miR-223 in an inflammatory model of GBS-induced murine pneumonia and looked for correlates with inflammatory markers, including innate cell infiltrates. We found that miR-223 expression is rapidly induced at very early time points (3 to 6 h postinfection [p.i.]) mainly by lung-infiltrating neutrophils. Interestingly, the level of miR-223 accumulating in the lungs remains higher at later stages of infection (24 h and 48 h p.i.), and this correlates with reduced expression of primary inflammatory cytokines and chemokines and with a shift in infiltrating monocyte and macrophage subtypes toward a regulatory phenotype. Transient inhibition of miR-223 by an antagomir resulted in significant increase of CXCL2 expression and partial enhancement of infiltrating neutrophils in GBS-infected lung tissues. This suggests the potential contribution of miR-223 to the resolution phase of GBS-induced acute inflammation.

Neutrophils Enhance Their Own Influx to Sites of Bacterial Infection via Endosomal TLR-Dependent Cxcl2 Production

The influx of neutrophils to infection sites is a fundamental step in host defenses against the frequent human pathogen group B Streptococcus (GBS) and other extracellular bacteria. Using a mouse model of GBS-induced peritonitis, we show in this study that the chemokines Cxcl1 and Cxcl2 play distinctive roles in enhancing the recruitment and the antibacterial activities of neutrophils in a manner that is linked to differences in the cellular sources of these mediators. Cell depletion experiments demonstrated that neutrophils make a significant contribution to the in vivo production of Cxcl2 but not Cxcl1. In vitro, neutrophils responded weakly to LPS but released high levels of Cxcl2 after stimulation with GBS or other bacteria. Neutrophil-derived Cxcl2 acted in an autocrinous manner to increase its own production and to enhance antibacterial activities, including the release of oxygen radicals. In both neutrophils and macrophages, the production of Cxcl1/2 largely required the presence of functional UNC93B1, a chaperone protein involved in signaling by endosomal TLRs. Moreover, the phenotype of UNC93B1-defective phagocytes could be recapitulated by the simultaneous absence of TLR7, 9, and 13 but not by the absence of individual TLRs. Collectively, our data show that neutrophils recognize Gram-positive and Gram-negative bacteria by means of multiple phagosomal TLRs, resulting in de novo synthesis of Cxcl2, amplification of neutrophil recruitment, and potentiation of their antibacterial activities. These data may be useful to devise alternative therapeutic strategies aimed at enhancing the recruitment and the functional activities of polymorphonuclear leukocytes during infections caused by antibiotic-resistant bacteria.

Group B Streptococcal Maternal Colonization and Neonatal Disease: Molecular Mechanisms and Preventative Approaches

Group B Streptococcus (GBS) colonizes the gastrointestinal and vaginal epithelium of a significant percentage of healthy women, with potential for ascending intrauterine infection or transmission during parturition, creating a risk of serious disease in the vulnerable newborn. This review highlights new insights on the bacterial virulence determinants, host immune responses, and microbiome interactions that underpin GBS vaginal colonization, the proximal step in newborn infectious disease pathogenesis. From the pathogen perspective, the function GBS adhesins and biofilms, β-hemolysin/cytolysin toxin, immune resistance factors, sialic acid mimicry, and two-component transcriptional regulatory systems are reviewed. From the host standpoint, pathogen recognition, cytokine responses, and the vaginal mucosal and placental immunity to the pathogen are detailed. Finally, the rationale, efficacy, and potential unintended consequences of current universal recommended intrapartum antibiotic prophylaxis are considered, with updates on new developments toward a GBS vaccine or alternative approaches to reducing vaginal colonization.

Natural Killer Cell Functions during the Innate Immune Response to Pathogenic Streptococci

Dendritic cells (DCs) and NK cells play a crucial role in the first phase of host defense against infections. Group B Streptococcus (GBS) and Streptococcus suis are encapsulated streptococci causing severe systemic inflammation, leading to septicemia and meningitis. Yet, the involvement of NK cells in the innate immune response to encapsulated bacterial infection is poorly characterized. Here, it was observed that these two streptococcal species rapidly induce the release of IFN-γ and that NK cells are the major cell type responsible for this production during the acute phase of the infection. Albeit S. suis capacity to activate NK cells was lower than that of GBS, these cells partially contribute to S. suis systemic infection; mainly through amplification of the inflammatory loop. In contrast, such a role was not observed during GBS systemic infection. IFN-γ release by NK cells required the presence of DCs, which in turn had a synergistic effect on DC cytokine production. These responses were mainly mediated by direct DC-NK cell contact and partially dependent on soluble factors. Though IL-12 and LFA-1 were shown to be critical in S. suis-mediated activation of the DC-NK cell crosstalk, different or redundant molecular pathways modulate DC-NK interactions during GBS infection. The bacterial capsular polysaccharides also differently modulated NK cell activation. Together, these results demonstrated a role of NK cells in the innate immune response against encapsulated streptococcal infections; yet the molecular pathways governing NK activation seem to differ upon the pathogen and should not be generalized when studying bacterial infections.

Group B Streptococci Induce Proinflammatory Responses via a Protein Kinase D1-Dependent Pathway

Group B streptococci (GBS) are one of the leading causes of life-threatening illness in neonates. Proinflammatory responses to GBS mediated through host innate immune receptors play a critical role in the disease manifestation. However, the mechanisms involved in proinflammatory responses against GBS, as well as the contribution of signaling modulators involved in host immune defense, have not been fully elucidated. In the present study, we investigated the role of protein kinase D (PKD)1 in the proinflammatory responses to GBS. We found that both live and antibiotic-killed GBS induce activation of PKD1 through a pathway that is dependent on the TLR signaling adaptor MyD88 and its downstream kinase IL-1R-associated kinase 1, but independent of TNFR-associated factor 6. Our studies using pharmacological PKD inhibitors and PKD1-knockdown macrophages revealed that PKD1 is indispensable for GBS-mediated activation of MAPKs and NF-κB and subsequent expression of proinflammatory mediators. Furthermore, systemic administration of a PKD inhibitor protects d-galactosamine-sensitized mice from shock-mediated death caused by antibiotic-killed GBS. These findings imply that PKD1 plays a critical regulatory role in GBS-induced proinflammatory reactions and sepsis, and inhibition of PKD1 activation together with antibiotic treatment in GBS-infected neonates could be an effective way to control GBS diseases.

Neonatal Group B Streptococcal Disease in Otherwise Healthy Infants: Failure of Specific Neonatal Immune Responses

Only a small proportion of newborn infants exposed to a pathogenic microorganism develop overt infection. Susceptibility to infection in preterm infants and infants with known comorbidities has a likely multifactorial origin and can be often attributed to the concurrence of iatrogenic factors, environmental determinants, underlying pathogenic processes, and probably genetic predisposition. Conversely, infection occurring in otherwise healthy full-term newborn infants is unexplained in most cases. Microbial virulence factors and the unique characteristics of the neonatal immune system only partially account for the interindividual variability in the neonatal immune responses to pathogens. We here suggest that neonatal infection occurring in otherwise healthy infants is caused by a failure of the specific protective immunity to the microorganism. To explain infection in term and preterm infants, we propose an extension of the previously proposed model of the genetic architecture of infectious diseases in humans. We then focus on group B streptococcus (GBS) disease, the best characterized neonatal infection, and outline the potential molecular mechanisms underlying the selective failure of the immune responses against GBS. In light of the recent discoveries of pathogen-specific primary immunodeficiencies and of the role of anticytokine autoantibodies in increasing susceptibility to specific infections, we hypothesize that GBS disease occurring in otherwise healthy infants could reflect an immunodeficiency caused either by rare genetic defects in the infant or by transmitted maternal neutralizing antibodies. These hypotheses are consistent with available epidemiological data, with clinical and epidemiological observations, and with the state of the art of neonatal physiology and disease. Studies should now be designed to comprehensively search for genetic or immunological factors involved in susceptibility to severe neonatal infections.

Cross-tolerance between bacterial endotoxin and group B Streptococcus in neonatal rats

Although endotoxin tolerance can be induced in newborns, potential cross-tolerance to group B Streptococcus (GBS), a common Gram-positive neonatal pathogen has not been investigated. In the present study we tested the hypothesis that endotoxin or recombinant tumor necrosis factor (rTNFα) can induce tolerance to lethal injection of heat-killed GBS in rat newborn pups and vice versa. The effect of such cross-tolerance on endogenous generation of plasma TNFα was subsequently evaluated. Rat pups (18-24 h old) were pretreated intracardially (i.c.) with either phosphate buffered saline (PBS), Salmonella enteritidis endotoxin (30 μg/kg) or rTNFα (35, 70 or 140 μg/kg). The pups were pretreated for either 4, 24, 48, 96 or 240 h prior to a lethal heat-killed GBS challenge. The susceptibility of the neonates to GBS-induced mortality was dependent on the duration of the pretreatment period. At 4 h of pretreatment with endotoxin or TNF, GBS-induced mortality was augmented relative to the PBS group. However, by 24-48 h the endotoxin and TNF pretreated neonates became more resistant to GBS-induced mortality. In a converse of the above experiment, neonates were pretreated with heat killed GBS (0.7 mg/kg) or rTNFα (70 μg/kg) and sensitivity to endotoxin was determined at 4-240 h after pretreatment. The data were qualitatively similar to endotoxin pretreatment. The 4 h GBS or TNF pretreatment rendered the neonates more susceptible to endotoxin-induced mortality. However, by 24-48 h the pretreatment groups were more resistant (P < 0.05) to endotoxin than the PBS controls. Plasma TNFα levels were increased (P < 0.05) 2 h after challenge i.c. with lethal heat-killed GBS or S. enteritidis endotoxin. In the 4 h pretreatment groups that received either GBS or endotoxin and then challenged with endotoxin or GBS, respectively, the plasma TNFα response was markedly augmented (P < 0.05). By 48 h of pretreatment, however, the plasma TNFα response in these groups to the stimuli was significantly reduced (P < 0.05) compared to the PBS pretreated groups. Therefore, plasma TNFα parallels lethality induced by GBS or endotoxin pretreatment. The ability of GBS and endotoxin to induce cross tolerance suggests that common pathophysiological pathways are involved in these syndromes.

Neutrophils Directly Recognize Group B Streptococci and Contribute to Interleukin-1β Production during Infection

Previous studies have shown that the pro-inflammatory cytokine IL-1β has a crucial role in host defenses against group B streptococcus (GBS), a frequent human pathogen, by recruiting neutrophils to infection sites. We examined here the cell types and mechanisms involved in IL-1β production during infection. Using a GBS-induced peritonitis model in mice, we first found that a large proportion of exudate cells contain intracellular IL-1β by immunofluorescence. Of the IL-1β positive cells, 82 and 7% were neutrophils and macrophages, respectively, suggesting that the former cell type might significantly contribute to IL-1β production. Accordingly, depletion of neutrophils with anti-Ly6G antibodies resulted in a significant reduction in the levels of IL-1β, but not of TNF-α or IL-6. We next found that neutrophils are capable of releasing mature IL-1β and TNF-α directly in response to in vitro stimulation with GBS. The production of pro-IL-1β and TNF-α in these cells required the Toll-like receptor (TLR) adaptor MyD88 and the chaperone protein UNC93B1, which is involved in mobilization of a subfamily of TLRs to the endosomes. Moreover, pro-IL-1β processing and IL-1β release was triggered by GBS hemolysin and required components of the canonical inflammasome, including caspase-1, ASC and NLRP3. Collectively our findings indicate that neutrophils make a significant contribution to IL-1β production during GBS infection, thereby amplifying their own recruitment. These cells directly recognize GBS by means of endosomal TLRs and cytosolic sensors, leading to activation of the caspase-1 inflammasome.

Group B Streptococcus Induces a Robust IFN-γ Response by CD4(+) T Cells in an In Vitro and In Vivo Model

Group B Streptococcus (GBS) serotype III causes life-threatening infections. Cytokines have emerged as important players for the control of disease, particularly IFN-γ. Although potential sources of this cytokine have been proposed, no specific cell line has ever been described as a leading contributor. In this study, CD4⁺ T cell activation profiles in response to GBS were evaluated through in vivo, ex vivo, and in vitro approaches. Total splenocytes readily produce a type 1 proinflammatory response by releasing IFN-γ, TNF-α, and IL-6 and actively recruit T cells via chemokines like CXCL9, CXCL10, and CCL3. Responding CD4⁺ T cells differentiate into Th1 cells producing large amounts of IFN-γ, TNF-α, and IL-2. In vitro studies using dendritic cell and CD4⁺ T cell cocultures infected with wild-type GBS or a nonencapsulated mutant suggested that GBS capsular polysaccharide, one of the major bacterial virulence factors, differentially modulates surface expression of CD69 and IFN-γ production. Overall, CD4⁺ T cells are important producers of IFN-γ and might thus influence the course of GBS infection through the expression balance of this cytokine.

Role of Toll-like receptor 13 in innate immune recognition of group B streptococci

Murine Toll-like receptor 13 (TLR13), an endosomal receptor that is not present in humans, is activated by an unmethylated motif present in the large ribosomal subunit of bacterial RNA (23S rRNA). Little is known, however, of the impact of TLR13 on antibacterial host defenses. Here we examined the role of this receptor in the context of infection induced by the model pathogen group B streptococcus (GBS). To this end, we used bacterial strains masked from TLR13 recognition by virtue of constitutive expression of the ErmC methyltransferase, which results in dimethylation of the 23S rRNA motif at a critical adenine residue. We found that TLR13-mediated rRNA recognition was required for optimal induction of tumor necrosis factor alpha and nitrous oxide in dendritic cell and macrophage cultures stimulated with heat-killed bacteria or purified bacterial RNA. However, TLR13-dependent recognition was redundant when live bacteria were used as a stimulus. Moreover, masking bacterial rRNA from TLR13 recognition did not increase the ability of GBS to avoid host defenses and replicate in vivo. In contrast, increased susceptibility to infection was observed under conditions in which signaling by all endosomal TLRs was abolished, i.e., in mice with a loss-of-function mutation in the chaperone protein UNC93B1. Our data lend support to the conclusion that TLR13 participates in GBS recognition, although blockade of the function of this receptor can be compensated for by other endosomal TLRs. Lack of selective pressure by bacterial infections might explain the evolutionary loss of TLR13 in humans. However, further studies using different bacterial species are needed to prove this hypothesis.

Essential role of interleukin-1 signaling in host defenses against group B streptococcus

Signal transduction via MyD88, an adaptor protein engaged by the Toll-like receptor (TLR) and interleukin-1 receptor (IL-1R) family receptors, has a crucial role in host defenses against group B streptococcus (GBS). To examine the contribution of IL-1R signaling to MyD88-dependent host defenses, we analyzed GBS infection in type I IL-1R (IL-1RI)-deficient mice. Most of these animals displayed clinical signs of sepsis and neurological disease and died after a challenge with a bacterial dose that did not cause illness or death in any of the wild-type animals. Moreover, bacterial numbers in the blood and brains of the immunodefective mice were considerably increased. The ability of blood leukocytes or bone marrow-derived macrophages to kill GBS in vitro was not affected by a lack of IL-1RI. However, it was found in a newly developed model of GBS-induced peritoneal inflammation that IL-1 signaling selectively promoted the production of the chemokines KC and MIP-1α and neutrophil recruitment. Moreover, the secretion of KC and MIP-1α, but not tumor necrosis factor alpha, by peritoneal macrophages stimulated with GBS was significantly decreased in the absence of IL-1RI. Accordingly, the number of neutrophils in the blood and the concentration of myeloperoxidase, a neutrophil marker, in infected organs were severely reduced in the immunodefective mice during GBS disease, concomitantly with a reduction in tissue KC and MIP-1α levels. In conclusion, IL-1RI plays a crucial role in host defenses against GBS by inducing the high-level production of chemokines and the subsequent recruitment of neutrophilic polymorphonuclear leukocytes to infection sites.

Group B streptococcus (GBS) is a serious and frequent human pathogen. Experimental infection with this bacterium has been widely used to understand the mechanism whereby the body’s first line of defense, represented by cells and molecules of the innate immune system, fights infections. In both humans and mice, defective function of the adaptor molecule MyD88 has been associated with extreme susceptibility to infection by GBS and other extracellular bacteria. We show here that lack of signaling by interleukin-1 (IL-1) cytokines can largely, although not completely, explain the increased susceptibility to infection observed in the absence of MyD88 function. We show, in particular, that IL-1 signaling through the IL-1 receptor promotes the production of the leukocyte attractant chemokines KC and MIP-1α and recruitment of neutrophils to GBS infection sites, thereby enabling these leukocytes to clear the infection. Our findings indicate that stimulation of IL-1 signaling may be useful as an alternative therapeutic strategy to treat GBS infections.

Computational approach to characterize causative factors and molecular indicators of chronic wound inflammation

Chronic inflammation is rapidly becoming recognized as a key contributor to numerous pathologies. Despite detailed investigations, understanding of the molecular mechanisms regulating inflammation is incomplete. Knowledge of such critical regulatory processes and informative indicators of chronic inflammation is necessary for efficacious therapeutic interventions and diagnostic support to clinicians. We used a computational modeling approach to elucidate the critical factors responsible for chronic inflammation and to identify robust molecular indicators of chronic inflammatory conditions. Our kinetic model successfully captured experimentally observed cell and cytokine dynamics for both acute and chronic inflammatory responses. Using sensitivity analysis, we identified macrophage influx and efflux rate modulation as the strongest inducing factor of chronic inflammation for a wide range of scenarios. Moreover, our model predicted that, among all major inflammatory mediators, IL-6, TGF-β, and PDGF may generally be considered the most sensitive and robust indicators of chronic inflammation, which is supported by existing, but limited, experimental evidence.

Significance, management and prevention of Streptococcus agalactiae infection during the perinatal period

The highest annual death rate during the first five decades of life occurs in the first year, particularly during the perinatal period between the onset of labor and 72 h after birth. Invasive bacterial disease evoking the severe inflammatory response syndrome is a leading cause of perinatal morbidity and mortality. Group B streptococcus (Streptococcus agalactiae) is the most important pathogen in this period of life, although the concept of intrapartum antimicrobial prophylaxis has impressively reduced the rate of culture-proven invasive infection in neonates. This strategy, however, has considerable limitations since group B streptococcus-related stillbirths or prematurity and late-onset sepsis cannot be prevented. Moreover, the use of intrapartum antimicrobial prophylaxis has significantly increased the use of antibiotics during labor and therefore may select for intrapartum infections caused by other bacteria, including those resistant to antibiotics. Several advances in the development of vaccines and research on virulence factors and pathways involved in the immune response to group B streptococcus have been accomplished within the last years, including complete sequencing of the group B streptococcus genome. Development of effective vaccines and implementation of vaccination strategies will be one of the key challenges in the future for prevention of neonatal group B Streptococcus infections.

Aflatoxin B1 modulates the expression of phenotypic markers and cytokines by splenic lymphocytes of male F344 rats

Aflatoxin B1 (AFB1) is immunotoxic to animals and a suspected immunosuppressant in humans. In this study, we investigated the effects of AFB1 on splenic lymphocyte phenotypes and the inflammatory cytokine expression in male F344 rats. Exposure of animals to AFB1 [5-75 µg kg(-1) body weight (BW)] for 1 week showed dose-dependent decreases in the percentage of splenic CD8(+) T cells and CD3(-) CD8a(+) NK cells. A general inhibition of the expression of interleukin (IL)-4 and interferon (IFN)-γ by CD4(+) T cells, IL-4 and IFN-γ by CD8a(+) cells, and tumor necrosis factor (TNF)-α expression by natural killer (NK) cells was also found; however, no concurrent histological changes in spleen tissue were present, suggesting acute immunosuppression without overt toxicity. Five-week exposure with AFB1 significantly increased the percentages of CD3(+) and CD8(+) T cells, especially at low doses (≤ 25 µg kg(-1)). AFB1 treatment significantly decreased the anti-inflammatory cytokine IL-4 expression by CD4(+) T cells and significantly increased the pro-inflammatory cytokine IFN-γ expression by CD4(+) T cells and TNF-α expression by NK cells. These results indicated that repeated AFB1 exposure promotes inflammatory responses by regulating cytokine expression. Our data provides novel insights into the mechanisms by which AFB1 exposure differentially modulates the cell-mediated immune responses and suggests the involvement of an inflammatory response upon repeated exposure.

Activation of the NLRP3 inflammasome by group B streptococci

Group B Streptococcus (GBS) is a frequent agent of life-threatening sepsis and meningitis in neonates and adults with predisposing conditions. We tested the hypothesis that activation of the inflammasome, an inflammatory signaling complex, is involved in host defenses against this pathogen. We show in this study that murine bone marrow-derived conventional dendritic cells responded to GBS by secreting IL-1β and IL-18. IL-1β release required both pro-IL-1β transcription and caspase-1-dependent proteolytic cleavage of intracellular pro-IL-1β. Dendritic cells lacking the TLR adaptor MyD88, but not those lacking TLR2, were unable to produce pro-IL-1β mRNA in response to GBS. Pro-IL-1β cleavage and secretion of the mature IL-1β form depended on the NOD-like receptor family, pyrin domain containing 3 (NLRP3) sensor and the apoptosis-associated speck-like protein containing a caspase activation and recruitment domain adaptor. Moreover, activation of the NLRP3 inflammasome required GBS expression of β-hemolysin, an important virulence factor. We further found that mice lacking NLRP3, apoptosis-associated speck-like protein, or caspase-1 were considerably more susceptible to infection than wild-type mice. Our data link the production of a major virulence factor by GBS with the activation of a highly effective anti-GBS response triggered by the NLRP3 inflammasome.

The Tpl2 mutation Sluggish impairs type I IFN production and increases susceptibility to group B streptococcal disease

Sluggish was identified in a population of third generation mice descended from N-ethyl-N-nitrosourea-mutagenized sires. Macrophages from homozygotes exhibited impaired TNF-alpha production in response to all TLR ligands tested and displayed impaired type I IFN production in response to TLR7 and TLR9 stimulations. The phenotype was confined to a critical region on mouse chromosome 18 and then ascribed to a T to A transversion in the acceptor splice site of intron 4 at position 13346 of the Map3k8 gene, resulting in defective splicing. The Map3k8(Sluggish) mutation does not result in susceptibility to viral infections, but Sluggish mice displayed high susceptibility to group B streptococcus infection, with impaired TNF-alpha and type I IFN production in infected macrophages. Our data demonstrate that the encoded protein kinase Tpl2 plays an essential role in cell signaling in the immune response to certain pathogens.

Characterization of tumour necrosis factor-alpha genetic variants and mRNA expression in patients with severe sepsis

Tumour necrosis factor-alpha (TNFalpha) has been implicated in the pathogenicity of severe sepsis by both genetic association studies and animal models. Conflicting functional data have emerged in relation to genetic variants and TNFalpha protein production. Therefore, we assessed the functionality of TNFalpha genetic variants in terms of mRNA production and their potential influence on outcome in the setting of severe sepsis. Sixty-two Irish Caucasian patients presenting with severe sepsis were recruited and TNFalpha mRNA and protein levels were quantified. Patient DNA was analysed for the presence of common promoter polymorphisms and haplotypes were inferred. An A allele at position -863 was associated with more TNFalpha mRNA on day 1 compared to C homozygotes (P = 0.037). There was a trend for G homozygotes at position -308 to produce more TNFalpha mRNA on day 1 than those carrying an A allele (P = 0.059). The presence of an A allele at -863 was associated with greater levels of TNFalpha mRNA in comparison with patients carrying the A allele at -308 on day 1 (P = 0.02). Patients homozygous for the A allele at position -308 had a higher mortality than those carrying the G allele (P = 0.01). Our data are consistent with recent reports suggesting that a deficient proinflammatory response may be harmful in human sepsis. This deficient inflammatory response may be mediated in part by polymorphisms in the TNFalpha promoter.

Comparison of the susceptibilities of C57BL/6 and A/J mouse strains to Streptococcus suis serotype 2 infection

Streptococcus suis is an important swine and human pathogen. Assessment of susceptibility to S. suis using animal models has been limited to monitoring mortality rates. We recently developed a hematogenous model of S. suis infection in adult CD1 outbred mice to study the in vivo development of an early septic shock-like syndrome that leads to death and a late phase that clearly induces central nervous system damage, including meningitis. In the present study, we compared the severities of septic shock-like syndrome caused by S. suis between adult C57BL/6J (B6) and A/J inbred mice. Clinical parameters, proinflammatory mediators, and bacterial clearance were measured to dissect potential immune factors associated with genetic susceptibility to S. suis infection. Results showed that A/J mice were significantly more susceptible than B6 mice to S. suis infection, especially during the acute septic phase of infection (100% of A/J and 16% of B6 mice died before 24 h postinfection). The greater susceptibility of A/J mice was associated with an exaggerated inflammatory response, as indicated by their higher production of tumor necrosis factor alpha, interleukin-12p40/p70 (IL-12p40/p70), gamma interferon, and IL-1beta, but not with different bacterial loads in the blood. In addition, IL-10 was shown to be responsible, at least in part, for the higher survival in B6 mice. Our findings demonstrate that A/J mice are very susceptible to S. suis infection and provide evidence that the balance between pro- and anti-inflammatory mediators is crucial for host survival during the septic phase.

Streptococcus suisSerotype 2, an Important Swine and Human Pathogen, Induces Strong Systemic and Cerebral Inflammatory Responses in a Mouse Model of Infection

Streptococcus suis, an important swine and human pathogen, causes septic shock and meningitis. The pathogenesis of both systemic and CNS infections caused by S. suis is poorly understood. A hematogenous model of infection in CD1 mice was developed to study the systemic release of cytokines during the septic shock phase and the proinflammatory events in the CNS associated with this pathogen. Using a liquid array system, high levels of systemic TNF-alpha, IL-6, IL-12, IFN-gamma, CCL2, CXCL1, and CCL5 were observed 24 h after infection and might be responsible for the sudden death of 20% of animals. Infected mice that survived the early sepsis later developed clinical signs of meningitis and exhibited lesions in the meninges and in numerous regions of the brain, such as the cortex, hippocampus, thalamus, hypothalamus, and corpus callosum. Bacterial Ags were found in association with microglia residing only in the affected zones. In situ hybridization combined with immunocytochemistry showed transcriptional activation of TLR2 and TLR3 as well as CD14, NF-kappaB, IL-1beta, CCL2, and TNF-alpha, mainly in myeloid cells located in affected cerebral structures. Early transcriptional activation of TLR2, CD14, and inflammatory cytokines in the choroid plexus and cells lining the brain endothelium suggests that these structures are potential entry sites for the bacteria into the CNS. Our data indicate an important role of the inflammatory response in the pathogenesis of S. suis infection in mice. This experimental model may be useful for studying the mechanisms underlying sepsis and meningitis during bacterial infection.

Increased levels of tumor necrosis factor-alpha and decreased levels of interleukin-12 p 70 in tracheal aspirates, within 2 hrs after birth, are associated with mortality among ventilated preterm infants

OBJECTIVE

To determine the association of antibacterial interleukin (IL)-12 p 70 levels as well as the pathogen-induced proinflammatory cytokine response in tracheal aspirate (TA) to respiratory failure and mortality among ventilated preterm infants.

DESIGN

A prospective observational clinical cohort study with measurements of cytokine levels and microbial cultures of TA from ventilated preterm neonates. Interleukin (IL)-1 beta, IL-8, IL-6, IL-10, IL-12 p 70, and tumor necrosis factor (TNF)-alpha were measured in TA within 2 hrs of birth, and comorbidity characteristics were recorded prospectively. The association between cytokine levels in TA and neonatal mortality was determined, with correction for comorbidity factors by means of multivariate stepwise logistic regression.

SETTING

A single tertiary neonatal intensive care unit at the University Hospital of Antwerp, Belgium.

PATIENTS

One hundred forty-one neonates born before a gestational age of 31 wks and who required ventilation were enrolled in the study; 31 (22%) died and 37 (26%) had airway colonization.

MEASUREMENTS AND MAIN RESULTS

The airway colonization rate was significantly greater among deceased neonates (45% vs. 21%; chi-square, 7.4; p=.007). Neonates who died had a significantly lower IL-12 p 70 cytokine level (6 pg/mL vs. 11 pg/mL; p<.05) in their TA. Neonates with a low IL-12 p 70 cytokine level had more pronounced respiratory failure (significantly higher oxygenation index, higher degree of radiologic respiratory distress syndrome, higher critical index for babies score, and more surfactant use). Multivariate analysis revealed that, after correction for severity of disease by critical index for babies score, the degree of intraventricular hemorrhage (odds ratio, 5.0 [95% confidence interval, 2.6-9.7]), low IL-12 p 70 levels (odds ratio, 4.9 [95% confidence interval, 2.1-11.7]), and high TNF-alpha levels in TA (odds ratio, 3.5 [95% confidence interval, 1.6-7.5]) were significantly associated with neonatal mortality.

CONCLUSIONS

Pathogen-induced excessive production of the proinflammatory cytokine TNF-alpha and lack of antibacterial IL-12 p 70 response in the TA are associated with increased neonatal mortality among ventilated preterm infants.

Recombinant rat IL-1beta and IL-6 synergistically enhance C3 mRNA levels and complement component C3 secretion by H-35 rat hepatoma cells

Hepatic synthesis of complement component C3 is regulated in part by inflammatory cytokines. Rat models are frequently employed to investigate pathogenic roles of complement and cytokines. However, cytokines obtained from species other than the rat were used in previous studies of cytokine regulation of C3 synthesis in rat hepatocytes or hepatoma cells. It is not known whether these prior reports predict hepatocellular responses evoked by rat cytokines. Therefore, H-35 rat hepatoma cells were employed to measure the effect of recombinant rat IL-1beta, IL-6, IFN-gamma, and TNF-alpha on C3 protein secretion and C3 mRNA levels quantified by ELISA and quantitative RT-PCR. Compared to untreated control cells, H-35 cells treated with IL-1beta, IL-6, and IFN-gamma increased C3 secretion approximately 10-, 4-, and 2-fold, respectively. TNF-alpha was toxic, precluding further analysis. IL-1beta and IL-6 demonstrated synergy with respect to the quantity and rate of increase of C3 mRNA measured and the magnitude of C3 protein secretion. Previous reports using non-rat cytokines did not consistently predict H-35 responses to rat cytokines. Consequently, we recommend the use of rat cytokines in rat models that include analysis of cytokine-mediated events.

Dual role of TLR2 and myeloid differentiation factor 88 in a mouse model of invasive group B streptococcal disease

Toll-like receptors (TLRs) are involved in pathogen recognition by the innate immune system. Different TLRs and the adaptor molecule myeloid differentiation factor 88 (MyD88) were previously shown to mediate in vitro cell activation induced by group B streptococcus (GBS). The present study examined the potential in vivo roles of TLR2 and MyD88 during infection with GBS. When pups were infected locally with a low bacterial dose, none of the TLR2- or MyD88-deficient mice, but all of the wild-type ones, were able to prevent systemic spread of GBS from the initial focus. Bacterial burden was higher in MyD88- than in TLR2-deficient mice, indicating a more profound defect of host defense in the former animals. In contrast, a high bacterial dose induced high level bacteremia in both mutant and wild-type mice. Under these conditions, however, TLR2 or MyD88 deficiency significantly protected mice from lethality, concomitantly with decreased circulating levels of TNF-alpha and IL-6. Administration of anti-TNF-alpha Abs to wild-type mice could mimic the effects of TLR2 or MyD88 deficiency and was detrimental in the low dose model, but protective in the high dose model. In conclusion, these data highlight a dual role of TLR2 and MyD88 in the host defense against GBS sepsis and strongly suggest TNF-alpha as the molecular mediator of bacterial clearance and septic shock.

Adherence to, invasion by, and cytokine production in response to serotype VIII group B Streptococci

The adherence to and invasion of the human epithelial cell line A549 by group B streptococcus (GBS) serotype VIII strains were compared with those of serotype III strains by a conventional method and the dynamic in vitro attachment and invasion system. Twenty GBS strains, including nine vaginal isolates and one invasive isolate each of serotypes III and VIII, were used in the conventional attachment and invasion assay. Adherence to and invasion of A549 cells by serotype VIII GBS strains were significantly greater (P < 0.0001) than those by serotype III strains for both the invasive strain and vaginal isolates. Cytokine production by A549 cells following stimulation with GBS serotypes III and VIII or their purified capsular polysaccharides (CPS) was measured. Serotype III strains stimulated significantly greater tumor necrosis factor alpha (TNF-alpha) (P < 0.0001) and interleukin-10 (IL-10) (P < 0.05) production than did serotype VIII strains. IL-8 production in response to serotype VIII was significantly higher (P < 0.001) than that in response to serotype III. TNF-alpha, IL-8, and IL-10 production was greater in A549 cells infected with GBS than in the untreated control cells. TNF-alpha production was significantly greater (P < 0.005) after stimulation with purified GBS serotype III CPS than after stimulation with serotype VIII CPS, a result similar to that after stimulation with whole GBS. IL-12 production by A549 cells was observed only in response to infection with GBS serotype III, resulting in the possibility of a greater TH1 response in serotype III GBS. These results suggest differences in immune responses to infection with GBS serotypes III and VIII.

Interleukin-18 is an essential element in host resistance to experimental group B streptococcal disease in neonates

Previous studies demonstrated that interleukin-12 (IL-12)-dependent gamma interferon (IFN-gamma) responses have a major role in restricting in vivo bacterial growth during infection of mice with group B streptococci (GBS), important human pathogens. Like IL-12, IL-18 is a potent IFN-gamma inducer. The role of IL-18 in experimental GBS infection was investigated here. Significant elevations of IL-18 levels over baseline values were detected in plasma samples from neonatal mice rendered septic with GBS. Neutralization of IL-18 significantly increased mortality and bacterial burden (P < 0.05). In contrast, administration of recombinant IL-18 (rIL-18) before or after GBS challenge remarkably improved survival and decreased blood colony counts, in association with increased IFN-gamma production by spleen cells. The beneficial effects of rIL-18 were counteracted by administration of neutralizing anti-IFN-gamma monoclonal antibodies, indicating that the effects of IL-18 were mediated by IFN-gamma. Finally, low rIL-18 doses that had no effect of their own on bacterial burden could act in synergy with rIL-12 to protect neonatal mice during GBS infection. Collectively, our data indicate that IL-18 responses have an important role in host defenses against GBS and that rIL-18 may be useful in alternative strategies to treat neonatal GBS disease.

Critical role of the complement system in group B streptococcus-induced tumor necrosis factor alpha release

Group B Streptococcus (GBS) is a major cause of newborn sepsis and meningitis and induces systemic release of tumor necrosis factor alpha (TNF-alpha), believed to play a role in morbidity and mortality. While previous studies have shown that GBS can induce TNF-alpha release from monocytes and macrophages, little is known about the potential modulating effect of plasma or serum on GBS-induced TNF-alpha release, and there are conflicting reports as to the host receptors involved. In a human whole-blood assay system, GBS type III COH-1 potently induced substantial monocyte TNF-alpha release in adult peripheral blood and, due to a higher concentration of monocytes, 10-fold-greater TNF-alpha release in newborn cord blood. Remarkably, GBS-induced TNF-alpha release from human monocytes was enhanced approximately 1000-fold by heat-labile serum components. Experiments employing C2-, C3-, or C7-depleted serum demonstrated that C3 activation via the alternative pathway is crucial for potent GBS-induced TNF-alpha release. Accordingly, whole blood from C3-deficient mice demonstrated significantly reduced GBS-induced TNF-alpha release. Preincubation with human serum enhanced the TNF-alpha-inducing activity of GBS in a C3- and factor B-dependent manner, implying deposition of complement components via the alternative pathway. GBS-induced TNF-alpha release was inhibited by monoclonal antibodies directed against each of the components of CR3 and CR4: the common integrin beta subunit CD18 and the alpha subunits CD11b (of CR3) and CD11c (of CR4). Blood derived from CR3 (CD11b/CD18)-deficient mice demonstrated a markedly diminished TNF-alpha response to GBS. We conclude that the ability of plasma and serum to greatly amplify GBS-induced TNF-alpha release reflects the activity of the alternative complement pathway that deposits fragments on GBS and thereby enhances CR3- and CR4-mediated monocyte activation.

Mitogen-activated protein kinases and NF-kappa B are involved in TNF-alpha responses to group B streptococci

TNF-alpha is a mediator of lethality in experimental infections by group B streptococcus (GBS), an important human pathogen. Little is known of signal transduction pathways involved in GBS-induced TNF-alpha production. Here we investigate the role of mitogen-activated protein kinases (MAPKs) and NF-kappa B in TNF-alpha production by human monocytes stimulated with GBS or LPS, used as a positive control. Western blot analysis of cell lysates indicates that extracellular signal-regulated kinase 1/2 (ERK 1/2), p38, and c-Jun N-terminal kinase MAPKs, as well as I kappa B alpha, became phosphorylated, and hence activated, in both LPS- and GBS-stimulated monocytes. The kinetics of these phosphorylation events, as well as those of TNF-alpha production, were delayed by 30-60 min in GBS-stimulated, relative to LPS-stimulated, monocytes. Selective inhibitors of ERK 1/2 (PD98059 or U0126), p38 (SB203580), or NF-kappa B (caffeic acid phenetyl ester (CAPE)) could all significantly reduce TNF-alpha production, although none of the inhibitors used alone was able to completely prevent TNF-alpha release. However, this was completely blocked by combinations of the inhibitors, including PD98059-SB203580, PD98059-CAPE, or SB203580-CAPE combinations, in both LPS- and GBS-stimulated monocytes. In conclusion, our data indicate that the simultaneous activation of multiple pathways, including NF-kappa B, ERK 1/2, and p38 MAPKs, is required to induce maximal TNF-alpha production. Accordingly, in septic shock caused by either GBS or Gram-negative bacteria, complete inhibition of TNF-alpha release may require treatment with drugs or drug combinations capable of inhibiting multiple activation pathways.

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.

Anti-idiotypic vaccination against group B streptococci

We describe the antigenic properties of an anti-idiotypic single chain fragment variable (scFv) recombinant antibody mimicking the type III capsular polysaccharide of group B streptococci (GBS), an important cause of neonatal sepsis. This scFv could compete with the nominal antigen for binding to specific mouse or rabbit antibodies. Moreover, the scFv elicited, in mice, the production of antibodies which reacted against the type IlI polysaccharide and passively protected neonatal pups from GBS disease. Maternal immunization with the scFv also protected neonatal mice against GBS infection. Next, the scFv was expressed on the surface of the commensal bacterium Streptococcus gordonii. Intravaginal inoculation of mice with these recombinant bacteria induced significant elevations in serum titers of anti-GBS type III antibodies. Therefore, the expression scFv in commensal bacteria may be a convenient and effective way of delivering anti-idiotypic vaccines.

Pneumococcal virulence factors: structure and function

The overall goal for this review is to summarize the current body of knowledge about the structure and function of major known antigens of Streptococcus pneumoniae, a major gram-positive bacterial pathogen of humans. This information is then related to the role of these proteins in pneumococcal pathogenesis and in the development of new vaccines and/or other antimicrobial agents. S. pneumoniae is the most common cause of fatal community-acquired pneumonia in the elderly and is also one of the most common causes of middle ear infections and meningitis in children. The present vaccine for the pneumococcus consists of a mixture of 23 different capsular polysaccharides. While this vaccine is very effective in young adults, who are normally at low risk of serious disease, it is only about 60% effective in the elderly. In children younger than 2 years the vaccine is ineffective and is not recommended due to the inability of this age group to mount an antibody response to the pneumococcal polysaccharides. Antimicrobial drugs such as penicillin have diminished the risk from pneumococcal disease. Several pneumococcal proteins including pneumococcal surface proteins A and C, hyaluronate lyase, pneumolysin, autolysin, pneumococcal surface antigen A, choline binding protein A, and two neuraminidase enzymes are being investigated as potential vaccine or drug targets. Essentially all of these antigens have been or are being investigated on a structural level in addition to being characterized biochemically. Recently, three-dimensional structures for hyaluronate lyase and pneumococcal surface antigen A became available from X-ray crystallography determinations. Also, modeling studies based on biophysical measurements provided more information about the structures of pneumolysin and pneumococcal surface protein A. Structural and biochemical studies of these pneumococcal virulence factors have facilitated the development of novel antibiotics or protein antigen-based vaccines as an alternative to polysaccharide-based vaccines for the treatment of pneumococcal disease.

The involvement of cytokines in the second window of ischaemic preconditioning

We utilized a rat model of myocardial infarction to investigate whether manganese superoxide dismutase (Mn-SOD), an intrinsic radical scavenger, and tumour necrosis factor- alpha (TNF-alpha) and/or interleukin-1beta (IL-1beta) are involved in the late phase of ischaemic preconditioning (IP). IP was induced in anaesthetized rats by four 3-min left coronary artery (LCA) occlusions, each separated by 10 min of reperfusion. Twenty-four hours after the repetitive brief ischaemia, the LCA was occluded for 20 min followed by reperfusion for 48 h. IP reduced the infarct size by approximately 46% as determined after 48 h of reperfusion. Antisense oligodeoxynucleotides to Mn-SOD inhibited the increases in Mn-SOD content and activity, and abolished the expected decrease in myocardial infarct size. Sense or scrambled oligodeoxynucleotides did not abolish either Mn-SOD induction or tolerance to ischaemia/reperfusion. The simultaneous administration of the antibodies to TNF-alpha (0.5 ml) and IL-1beta (0.5 mg) prior to IP abolished the cardioprotection and the increase in Mn-SOD activity induced by IP. We conclude that the induction and activation of Mn-SOD, mediated by TNF-alpha and IL-1beta after IP, plays an important role in the acquisition of late-phase cardioprotection against ischaemia/reperfusion injury in rats.

Involvement of cytokines in the mechanism of whole-body hyperthermia-induced cardioprotection

BACKGROUND

Hyperthermia increases cardiac tolerance to ischemia/reperfusion injury and activates manganese superoxide dismutase (Mn-SOD), an intrinsic radical scavenger, in myocardium in a biphasic manner. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) induced a biphasic cardioprotection that corresponded to the activation of Mn-SOD. However, a direct association between Mn-SOD activation in myocardium and the acquisition of tolerance to ischemia/reperfusion injury induced by hyperthermia and the involvement of the cytokines in the signal transduction pathway for the hyperthermia-induced cardioprotection have not yet been elucidated.

METHODS AND RESULTS

Hyperthermia was induced in anesthetized rats by placement in a temperature-controlled water bath. At 0.5 and 72 hours after hyperthermia, ischemia was induced by occlusion of the left coronary artery for 20 minutes, followed by reperfusion for 48 hours. Inhibition of the increases in Mn-SOD content and activity 72 hours after hyperthermia by the administration of antisense oligodeoxynucleotides to Mn-SOD abolished the expected decrease in myocardial infarct size. The simultaneous administration of neutralizing antibodies to TNF-alpha and IL-1beta before hyperthermia abolished the biphasic cardioprotection and increase in Mn-SOD activity.

CONCLUSIONS

The increase in Mn-SOD activity mediated through the production of TNF-alpha and IL-1beta by whole-body hyperthermia is important in the acquisition of early- and late-phase cardioprotection against ischemia/reperfusion injury in rats.

Group B Streptococcus induces TNF-alpha gene expression and activation of the transcription factors NF-kappa B and activator protein-1 in human cord blood monocytes

It has been postulated that production of TNF-alpha is central to the pathogenesis of septic shock induced by group B Streptococcus (GBS). In vitro studies using human cord blood monocytes have demonstrated that GBS induces TNF-alpha secretion, but little is known about the intracellular signaling pathways of TNF-alpha induction. In this report we show that heat-killed serotype III GBS induces host cell signal transduction pathways that lead to activation of the transcription factors NF-kappaB and AP-1. Using adenoviral transfer of IkappaBalpha (IkappaBalpha overexpression), the production of TNF-alpha induced by whole GBS was inhibited by only 20%. We also show that the p38 mitogen-activated protein kinase (MAPK) pathway is involved in GBS-induced TNF-alpha secretion, because TNF-alpha protein and mRNA levels in the presence of a specific inhibitor of p38 MAPK, SB 202190, were dramatically diminished. EMSAs showed that SB 202190 inhibited GBS-induced AP-1 activation, but had no effect on NF-kappaB-DNA binding activity. These results indicate that both NF-kappaB and AP-1 (via p38 MAPK) are involved in the regulation of TNF-alpha production in GBS-stimulated neonatal monocytes. Therefore, disrupting the signal transduction pathways induced by GBS has the potential to attenuate the production of immune response mediators, thereby halting or possibly reversing the course of this potentially fatal disease.

Beta 2 integrins are involved in cytokine responses to whole Gram-positive bacteria

Proinflammatory cytokines have an important pathophysiologic role in septic shock. CD14 is involved in cytokine responses to a number of purified bacterial products, including LPS. However, little is known of monocyte receptors involved in cytokine responses to whole bacteria. To identify these receptors, human monocytes were pretreated with different mAbs and TNF-alpha was measured in culture supernatants after stimulation with whole heat-killed bacteria. Human serum and anti-CD14 Abs significantly increased and decreased, respectively, TNF-alpha responses to the Gram-negative Escherichia coli. However, neither treatment influenced responses to any of the Gram-positive bacteria tested, including group A and B streptococci, Listeria monocytogenes, and Staphylococcus aureus. Complement receptor type III (CR3 or CD18/CD11b) Abs prevented TNF-alpha release induced by heat-killed group A or B streptococci. In contrast, the same Abs had no effects when monocytes were stimulated with L. monocytogenes or S. aureus. Using either of the latter bacteria, significant inhibition of TNF-alpha release was produced by Abs to CD11c, one of the subunits of CR4. To confirm these blocking Ab data, IL-6 release was measured in CR3-, CR4-, or CD14-transfected Chinese hamster ovary cells after bacterial stimulation. Accordingly, streptococci triggered moderate IL-6 production (p < 0.05) in CR3 but not CD14 or CR4 transfectants. In contrast, L. monocytogenes and S. aureus induced IL-6 release in CR4 but not CR3 or CD14 transfectants. Collectively our data indicate that beta 2 integrins, such as CR3 and CR4, may be involved in cytokine responses to Gram-positive bacteria. Moreover, CD14 may play a more important role in responses to whole Gram-negative bacteria relative to Gram-positive ones.

Differential effects of hemorrhage and LPS on tissue TNF-alpha, IL-1 and associate neuro-hormonal and opioid alterations

LPS administration and hemorrhage are frequently used models for the in vivo study of the stress response. Both challenges stimulate cytokine production as well as activate opiate and neuro-endocrine pathways; which in turn modulate the inflammatory process. Differences in the magnitude and tissue specificity of the proinflammatory cytokine and neuro-hormonal responses to these stressors are not well established. We contrasted the tissue specificity and magnitude of the increase in circulating and tissue cytokine (TNF-alpha, IL-1alpha and IL-1beta) content in response to either fixed-pressure hemorrhage (approximately 40 mm Hg) followed by fluid resuscitation (HEM) or lipopolysaccharide (LPS; 100 microg/100 g BW) administration. LPS and HEM elevated circulating levels of TNF-alpha, while neither stress altered circulating IL-1-alpha and IL-beta. LPS-induced increases in TNF-alpha content were greater than those elicited by HEM in all tissues studied except for the lung, where both stressors produced similar increases. Tissue (lung, spleen and heart) content of IL-1alpha was increased by HEM but was not affected by LPS. Tissue (lung, spleen, and heart) content of IL-1beta was increased by LPS but was not affected by HEM. HEM produced greater increases than LPS in epinephrine (16- vs. 4-fold) and norepinephrine (4-fold vs. 60%) levels and similar elevations in beta-endorphin. LPS produced greater elevation in corticosterone levels (2-fold) than HEM (50%). These results suggest differential tissue cytokine modulation to HEM and LPS, both with respect to target tissue and cytokine type. The hormonal milieu to HEM is characterized by marked catecholaminergic and moderate glucocorticoid while that of LPS is characterized by marked glucocorticoid with moderate catecholaminergic influence.

Human monocyte receptors involved in tumor necrosis factor responses to group B streptococcal products

Several group B streptococcal products have been previously found to stimulate human monocytes to produce tumor necrosis factor alpha. In order to identify the receptors involved in these responses, monocytes were stimulated with purified group- or type-specific carbohydrates or lipoteichoic acid in the presence of anti-receptor monoclonal antibodies, soluble CD14, or lipopolysaccharide-binding protein. Results indicate that CD14 plays an important role in tumor necrosis factor alpha responses to all of the stimuli tested. Moreover, both CD14 and complement receptor type 3 may be involved in responses to the group-antigen.

Intracellular and extracellular cytokine production by human mixed mononuclear cells in response to group B streptococci

Group B streptococci (GBS) are a major cause of severe infection in newborns, pregnant females, and other immunocompromised hosts. Infection often includes septicemia, shock, pneumonia, and respiratory failure. In previous studies, we have reported that GBS induce marked production of tumor necrosis factor alpha (TNF-alpha) by human mononuclear cells. The present study was designed to measure the production of TNF-alpha as well as additional cytokines, including interleukin 1beta (IL-1beta), IL-6, IL-8, IL-12, and gamma interferon (IFN-gamma) but also to determine from what cells and at what time point during incubation with GBS that these cytokines are produced. Mixed mononuclear cells were incubated with heat-killed GBS, media alone, or 1 microg of Escherichia coli lipopolysaccharide (LPS). Brefeldin A was added to each sample prior to staining, which prevented the export of cytokines by the Golgi apparatus. The cells were then stained with the appropriate conjugated antibodies and analyzed by using a flow cytometer. Results indicate that intracellular cytokines appear, in almost all cases, simultaneous to or before secreted proteins are detected. In contrast to the response to LPS, where TNF-alpha, IL-1beta, IL-6, and IL-8 appear almost simultaneously, the human monocyte response to GBS results in the production of TNF-alpha but delayed appearance of IL-1beta, IL-6, and IL-8. The lymphocyte response to GBS was also strikingly different from that to LPS in that both secreted IFN-gamma and IL-12 was detected, while LPS failed to induce production of these critical cytokines. This suggests an important role for TNF-alpha, IFN-gamma, and IL-12 in GBS pathogenesis and/or immunity.

Role of IL-10 in a Neonatal Mouse Listeriosis Model

This study was undertaken to test the hypothesis that altered IL-10 production plays a role in the increased susceptibility of neonates to listeriosis. Plasma IL-10 levels were measured in neonatal and adult mice at various times after infection with Listeria monocytogenes. Relative to adults, neonatal mice had markedly increased IL-10 levels early in the course of infection with Listeria using a 90% lethal dose. Higher neonatal IL-10 responses were also observed after injecting adults and pups with equal doses of killed organisms. Splenic macrophages from neonates produced higher IL-10 levels than those of adults after in vitro stimulation with killed bacteria, confirming in vivo observations. Moreover, IL-10 blockade had differential effects in neonates and adults infected with live Listeria. In adult mice, anti-IL-10 Abs decreased bacterial burden early in the course of infection, but were no longer effective at 6 days or later after challenge. In the pups, however, the same treatment had beneficial effects both early and late during infection and resulted in increased survival. Collectively, our data suggest that an overproduction of IL-10 by macrophages may at least partially explain the increased susceptibility of neonates to listeriosis, and provide further evidence that cytokine production is different in adults and neonates.

Role of tumor necrosis factor alpha, interleukin-1beta, and interleukin-6 in a mouse model of group B streptococcal arthritis

Intravenous inoculation of CD1 mice with 10(7) CFU of type IV group B Streptococcus (GBS IV) results in a high incidence of diffuse septic arthritis. In this study the roles of tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6 in articular pathology were evaluated. Cytokine levels were quantified in the serum and joints by enzyme-linked immunosorbent assay in mice injected with GBS IV and tested or not tested with pentoxifylline (PTF), a methylxanthine that affects cytokine production. PTF was administered intraperitoneally at a dose of 1 mg/mouse (50 mg/kg of body weight) 1 h after GBS infection and then at 24-h intervals for 4 days. High levels of IL-1beta and IL-6, but not TNF-alpha, were detected in the joints of mice injected with GBS IV from 5 to 15 days after infection, when articular lesions were most frequent and severe. IL-1beta and IL-6 concentrations in the joints significantly (P < 0.001) exceeded those detected in the serum, confirming a strong local production. PTF treatment resulted in a strong reduction of cytokine production and in a marked decrease in both the incidence and severity of arthritis. Inoculation of exogenous murine recombinant IL-1beta or IL-6 in mice treated with GBS IV plus PTF resulted in an incidence and severity of articular lesions similar to those obtained with inoculation of GBS IV alone. No significant effect was obtained with TNF-alpha administration. These data show a strong involvement of IL-1beta and IL-6, but not TNF-alpha, in the pathogenesis of GBS arthritis.

Early neuronal expression of tumor necrosis factor-alpha after experimental brain injury contributes to neurological impairment

Tumor necrosis factor-alpha (TNF alpha) is a pleiotropic cytokine involved in inflammatory cascades associated with CNS injury. To examine the role of TNF alpha in the acute pathophysiology of traumatic brain injury (TBI), we studied its expression, localization and modulation in a clinically relevant rat model of non-penetrating head trauma. TNF alpha levels increased significantly in the injured cortex at 1 and 4, but not at 12, 24 or 72 h after severe lateral fluid-percussion trauma (2.6-2.7 atm). TNF alpha was not elevated after mild injury. At 1 and 4 h after severe TBI, marked increases of TNF alpha were localized immunocytochemically to neurons of the injured cerebral cortex. A small population of astrocytes, ventricular cells and microvessels, also showed positive TNF alpha staining, but this expression was not injury-dependent. Macrophages that were present in a hemorrhagic zone along the external capsule, corpus callosum and alveus hippocampus at 4 h after TBI did not express TNF alpha. Intracerebroventricular administration of a selective TNF alpha antagonist--soluble TNF alpha receptor fusion protein (sTNFR:Fc) (37.5 microg)--at 15 min before and 1 h after TBI, improved performance in a series of standardized motor tasks after injury. In contrast, intravenous administration of sTNFR:Fc (0.2, 1 or 5 mg/kg) at 15 min after trauma did not improve motor outcome. Collectively, this evidence suggests that enhanced early neuronal expression of TNF alpha after TBI contributes to subsequent neurological dysfunction.

Neonatal mouse immunity against group B streptococcal infection by maternal vaccination with recombinant anti-idiotypes

We investigated whether immunization with recombinant anti-idiotypic antibody fragments mimicking the conformation of the capsular antigen can protect against infection by group B streptococcus, an important neonatal pathogen. Single-chain fragment-variable anti-idiotypes competed with the type III carbohydrate for binding to type-specific antibodies and elicited, in mice, the production of protective immunoglobulins reacting against the type III polysaccharide. Moreover, maternal immunization with soluble or phage-displayed fragments protected neonatal mice against streptococcal infection. These data indicate that recombinant anti-idiotypic antibodies may be useful in developing protein images of relevant carbohydrate epitopes and, ultimately, in preventing infections by encapsulated bacteria.

Cytokine response to group B streptococcus infection in mice

This study was undertaken to better understand the complex relationship between specific and non-specific host defence mechanisms and group B streptococci (GBS). A comprehensive kinetics analysis of cytokine mRNA expression was performed, by Northern blot assay, in peritoneal exudate cells (PEC) and spleen cells (SC) recovered from CD-1 mice at various times during the course of an intraperitoneal infection with a lethal dose (5 x 10(3) microorganisms/mouse) of type Ia GBS, reference strain 090 (GBS-Ia). Analysis of cytokines involved in the development of a specific TH response shows that GBS-Ia in PEC induce only a weak increase of IL-2 mRNA expression and in SC a cytokine pattern characterized by IL-2, IFN-gamma and IL-12 in the absence of IL-4, IL-5 and IL-10. This selected cytokine pattern could provide appropriate conditions for the development of a TH1 response. Analysis of inflammatory cytokines, which are usually induced early during an in vivo infection, shows that there is a significant expression of mRNA specific for IL-1beta, TNFalpha and IL-6, both in PEC and SC only at 24 h which persists at a high level until 36 h. This delayed cytokine induction, accompanied by the contemporary activation of splenic phagocytic cells, occurs only when the number of GBS-Ia is extremely high. In fact, at 24 h GBS-Ia have heavily colonized all organs. In vitro infection of thioglycollate-elicited peritoneal macrophages confirms that the ability of GBS-Ia to induce a strong inflammatory cytokine response depends strictly on the number of infecting microorganisms. Indeed, macrophages respond to GBS-Ia with a very rapid induction of IL-1beta and TNFalpha mRNA when infected at a ratio of 1:10, but not at 100:1. Two major observations emerged from this study: (1) GBS-Ia, by inducing a cytokine pattern which seems to favour development of a TH1 response, could evade antibody production essential for resistance to GBS; and (2) inflammatory cytokine response is induced when a heavy microbial invasion of the host has already occurred. These novel features of GBS-Ia could contribute to the development and progression of lethal infection in mice.

Circulating antibody against tumor necrosis factor-alpha protects rat brain from reperfusion injury

The role of tumor necrosis factor-alpha (TNF alpha) in brain injury is controversial. We studied the effect of anti-TNF-alpha antibody in a rat model of reversible middle cerebral artery occlusion. During focal ischemia and early reperfusion, TNF-alpha was rapidly and transiently released into circulation. Pretreatment with intravenous anti-TNF-alpha antibody reduced cortical (71%, P < 0.015) and subcortical (58%, P < 0.007) injury, enhanced the cerebral blood flow during reperfusion, and improved the neurologic outcome. This further supports the contention that TNF-alpha is a deleterious cytokine in stroke, whereas circulating antibody against TNF-alpha may protect brain from reperfusion injury.

Lipopolysaccharide-induced cytokine cascade and lethality in LT alpha/TNF alpha-deficient mice

BACKGROUND

Tumor necrosis factor alpha (TNF-alpha) is often considered the main proinflammatory cytokine induced by lipopolysaccharide (LPS) and consequently the critical mediator of the lethality associated with septic shock.

MATERIALS AND METHODS

We used mice carrying a deletion of both the lymphotoxin alpha (LT-alpha) and TNF-alpha genes to assess the role of TNF in the cytokine cascade and lethality induced by LPS.

RESULTS

Initial production of IL-1 alpha, IL-1 beta, IL-6, and IL-10 is comparable in wild-type and mutant mice. However, at later times, expression of IL-1 alpha, IL-1 beta, and IL-10 is prolonged, whereas that of IL-6 decreases in mutant mice. Expression of IFN-gamma is almost completely abrogated in mutants, which is in agreement with a more significant alteration of the late phase of the cytokine cascade. We measured similar LD50 (600 micrograms) for the intravenous injection of LPS in mice of the three genotypes (+/+, +/-, -/-), demonstrating that the absence of TNF does not confer long-term protection from lethality. However, death occurred much more slowly in mutant mice, who were protected more efficiently from death by CNI 1493, an inhibitor of proinflammatory cytokine production, than were wild-type mice.

DISCUSSION

Thus, while TNF-alpha is not required for the induction of these cytokines by LPS, it modulates the kinetics of their expression. The lethality studies simultaneously confirm a role for TNF as a mediator of early lethality and establish that, in the absence of these cytokines, other mediators take over, resulting in the absence of long-term protection from LPS toxicity.

Extracellular superoxide dismutase is upregulated with inducible nitric oxide synthase after NF-kappa B activation

Inflammatory cytokines have been shown to upregulate secretion of the antioxidant enzyme extracellular superoxide dismutase (EC-SOD) in dermal fibroblasts and, in other cells, to stimulate production of nitric oxide (.NO). Because superoxide rapidly scavenges .NO, forming the injurious peroxynitrite anion (OONO-), we hypothesize that stimulated cells upregulate EC-SOD expression concurrently with .NO release. To test for coregulation of EC-SOD and .NO within the same cell, the timing of inducible nitric oxide synthase (iNOS) and EC-SOD transcription was measured after exposure of a rate type II pneumocyte analog, the L2 cell line, to a combination of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). Upregulation of iNOS and EC-SOD transcription occurred after 6 h of exposure, and transcription of both genes was linked by activation of the transcription factor nuclear factor-kappa B. Both EC-SOD and iNOS were elevated in rat lung homogenates 24 h after intratracheal instillation with IFN-gamma and TNF-alpha. The observation that EC-SOD and iNOS are temporally coregulated after cytokine exposure suggests the possibility of a critical mechanism by which cells might protect .NO and avoid the formation of OONO- during inflammation.