Divergent effects of tumor necrosis factor (TNF) in sepsis: a meta-analysis of experimental studies

INTRODUCTION

Experimental studies in animals have yielded conflicting results on the role of Tumor Necrosis Factor (TNF) in sepsis and endotoxemia, with some reporting adaptive and others inappropriate effects. A meta-analysis of the available literature was performed to determine the factors explaining this discrepancy.

METHODS

The study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The protocol was registered with PROSPERO (CRD42020167384) prior to data collection. PubMed and Embase were the databases queried. Risk of bias was evaluated using the SYRCLE Risk of Bias Tool. All animal studies investigating sepsis-related mortality and modified TNF signaling were considered eligible. The exclusion criteria were: lack of mortality data, 7-day mortality rates below 10% in both wild type and TNF-altered pathway animals, and absence of an English abstract. To determine the role of TNF according to the experimental protocol, three approaches were used: first an approach based on the statistical significance of each experiment, then the pooled mortality was calculated, and finally the weighted risk ratio for mortality was assessed.

RESULTS

A total of 175 studies were included in the analysis, comprising a total of 760 experiments and involving 19,899 animals. The main species used were mice (77%) and rats (21%). The most common method of TNF pathway modulation was TNF pathway inactivation that was primarily associated with an inappropriate secretion of TNF. At the opposite, TNF injection was associated with an adaptive role of TNF. Lipopolysaccharide (LPS) injection was the most used stimulus to establish an infectious model (42%) and was strongly associated with an inappropriate role of TNF. Conversely, live bacterial models, especially the cecal ligation and puncture (CLP) model, pneumonia, meningitis, and gastrointestinal infection, were associated with an adaptive role. This was particularly evident for Listeria monocytogenes, Streptococcus pneumoniae.

CONCLUSION

The role of TNF during infection varies depending on the experimental model used. Models that mimic clinical conditions, based on virulent bacteria that cause high mortality even at low inocula, demonstrated an adaptive role of TNF. Conversely, models based on LPS or low-pathogenic live bacteria, administered at doses well above physiological thresholds and combined with early antibiotic therapy, were associated with an inappropriate role.

FGD5 in basal cells induces CXCL14 secretion that initiates a feedback loop to promote murine mammary epithelial growth and differentiation

The interactions of environmental compartments with epithelial cells are essential for mammary gland development and homeostasis. Currently, the direct crosstalk between the endothelial niche and mammary epithelial cells remains poorly understood. Here, we show that faciogenital dysplasia 5 (FGD5) is enriched in mammary basal cells (BCs) and mediates critical interactions between basal and endothelial cells (ECs) in the mammary gland. Conditional deletion of Fgd5 reduced, whereas conditional knockin of Fgd5 increased, the engraftment and expansion of BCs, regulating ductal morphogenesis in the mammary gland. Mechanistically, murine mammary BC-expressed FGD5 inhibited the transcriptional activity of activating transcription factor 3 (ATF3), leading to subsequent transcriptional activation and secretion of CXCL14. Furthermore, activation of CXCL14/CXCR4/ERK signaling in primary murine mammary stromal ECs enhanced the expression of HIF-1α-regulated hedgehog ligands, which initiated a positive feedback loop to promote the function of BCs. Collectively, these findings identify functionally important interactions between BCs and the endothelial niche that occur through the FGD5/CXCL14/hedgehog axis.

Prolonged Inhibition of the MEK1/2-ERK Signaling Axis Primes Interleukin-1 Beta Expression through Histone 3 Lysine 9 Demethylation in Murine Macrophages

Macrophages undergo different cellular states upon activation that can be hyporesponsive (tolerated) or hyperresponsive (primed or trained) to subsequent stimuli. Epigenetic modifications are known to play key roles in determining these cellular states. However, little is known about the role of signaling pathways that lead to these epigenetic modifications. Here, we examined the effects of various inhibitors targeting key signaling pathways induced by lipopolysaccharide (LPS) on tolerance and priming in murine macrophages. We found that a prolonged inhibition (>18 h) of the mitogen-activated protein kinase (MEK)1/2-extracellular signal-regulated kinase (ERK)1/2 signaling axis reversed tolerance and primed cells in expressing interleukin (IL)-1β and other inflammatory cytokines such as IL-6, tumor necrosis factor (TNF)α, and CXCL10. The ectopic expression of catalytically active and inactive MEK1 mutants suppressed and enhanced IL-1β expression, respectively. A transcriptomic analysis showed that cells primed by the MEK1/2 inhibitor U0126 expressed higher levels of gene sets associated with immune responses and cytokine/chemokine production, but expressed lower levels of genes with cell cycle progression, chromosome organization, and heterochromatin formation than non-primed cells. Of interest, the mRNA expressions of the histone 3 lysine 9 (H3K9) methyltransferase Suv39h1 and the H3K9 methylation reader Cbx5 were substantially suppressed, whereas the H3K9 demethylase Kdm7a was enhanced, suggesting a role of the MEK1/2-ERK signaling axis in H3K9 demethylation. The H3K9 trimethylation levels in the genomic regions of IL-1β, TNFα, and CXCL10 were decreased by U0126. Also, the H3K9 methyltransferase inhibitor BIX01294 mimicked the U0126 training effects and the overexpression of chromobox homolog (CBX)5 prevented the U0126 training effects in both RAW264.7 cells and bone-marrow-derived macrophages. Collectively, these data suggest that the prolonged inhibition of the MEK1/2-ERK signaling axis reverses tolerance and primed macrophages likely through decreasing the H3K9 methylation levels.

Necroptosis in apical periodontitis: A programmed cell death with multiple roles

Programmed cell death (PCD) has been a research focus for decades and different mechanisms of cell death, such as necroptosis, pyroptosis, ferroptosis, and cuproptosis have been discovered. Necroptosis, a form of inflammatory PCD, has gained increasing attention in recent years due to its critical role in disease progression and development. Unlike apoptosis, which is mediated by caspases and characterized by cell shrinkage and membrane blebbing, necroptosis is mediated by mixed lineage kinase domain-like protein (MLKL) and characterized by cell enlargement and plasma membrane rupture. Necroptosis can be triggered by bacterial infection, which on the one hand represents a host defense mechanism against the infection, but on the other hand can facilitate bacterial escape and worsen inflammation. Despite its importance in various diseases, a comprehensive review on the involvement and roles of necroptosis in apical periodontitis is still lacking. In this review, we tried to provide an overview of recent progresses in necroptosis research, summarized the pathways involved in apical periodontitis (AP) activation, and discussed how bacterial pathogens induce and regulated necroptosis and how necroptosis would inhibit bacteria. Furthermore, the interplay between various types of cell death in AP and the potential treatment strategy for AP by targeting necroptosis were also discussed.

Role of Streptococcus pneumoniae extracellular glycosidases in immune evasion

Streptococcus pneumoniae (pneumococcus) typically colonizes the human upper airway asymptomatically but upon reaching other sites of the host body can cause an array of diseases such as pneumonia, bacteremia, otitis media, and meningitis. Be it colonization or progression to disease state, pneumococcus faces multiple challenges posed by host immunity ranging from complement mediated killing to inflammation driven recruitment of bactericidal cells for the containment of the pathogen. Pneumococcus has evolved several mechanisms to evade the host inflicted immune attack. The major pneumococcal virulence factor, the polysaccharide capsule helps protect the bacteria from complement mediated opsonophagocytic killing. Another important group of pneumococcal proteins which help bacteria to establish and thrive in the host environment is surface associated glycosidases. These enzymes can hydrolyze host glycans on glycoproteins, glycolipids, and glycosaminoglycans and consequently help bacteria acquire carbohydrates for growth. Many of these glycosidases directly or indirectly facilitate bacterial adherence and are known to modulate the function of host defense/immune proteins likely by removing glycans and thereby affecting their stability and/or function. Furthermore, these enzymes are known to contribute the formation of biofilms, the bacterial communities inherently resilient to antimicrobials and host immune attack. In this review, we summarize the role of these enzymes in host immune evasion.

Naturally-occurring serotype 3 Streptococcus pneumoniae strains that lack functional pneumolysin and autolysin have attenuated virulence but induce localized protective immune responses

Streptococcus pneumoniae is an important cause of fatal pneumonia in humans. These bacteria express virulence factors, such as the toxins pneumolysin and autolysin, that drive host inflammatory responses. In this study we confirm loss of pneumolysin and autolysin function in a group of clonal pneumococci that have a chromosomal deletion resulting in a pneumolysin-autolysin fusion gene Δ(lytA'-ply')593. The Δ(lytA'-ply')593 pneumococci strains naturally occur in horses and infection is associated with mild clinical signs. Here we use immortalized and primary macrophage in vitro models, which include pattern recognition receptor knock-out cells, and a murine acute pneumonia model to show that a Δ(lytA'-ply')593 strain induces cytokine production by cultured macrophages, however, unlike the serotype-matched ply+lytA+ strain, it induces less tumour necrosis factor α (TNFα) and no interleukin-1β production. The TNFα induced by the Δ(lytA'-ply')593 strain requires MyD88 but, in contrast to the ply+lytA+ strain, is not reduced in cells lacking TLR2, 4 or 9. In comparison to the ply+lytA+ strain in a mouse model of acute pneumonia, infection with the Δ(lytA'-ply')593 strain resulted in less severe lung pathology, comparable levels of interleukin-1α, but minimal release of other pro-inflammatory cytokines, including interferon-γ, interleukin-6 and TNFα. These results suggest a mechanism by which a naturally occurring Δ(lytA'-ply')593 mutant strain of S. pneumoniae that resides in a non-human host has reduced inflammatory and invasive capacity compared to a human S. pneumoniae strain. These data probably explain the relatively mild clinical disease in response to S. pneumoniae infection seen in horses in comparison to humans.

NETosis is critical in patients with severe community-acquired pneumonia

Pneumonia is the fourth leading cause of death globally, and the reason for the high mortality rate of patients with severe community-acquired pneumonia (SCAP) remains elusive. Corticosteroid treatment reduces mortality in adults with SCAP but can cause numerous adverse events. Therefore, novel therapeutic targets need to be explored and new adjunctive immune drugs are urgently required. We analyzed the transcriptome data of peripheral blood leukocytes from patients with SCAP and healthy controls from three perspectives: differentially expressed genes, predicted functions of differentially expressed long non-coding RNAs, and transcriptional read-through. We discovered that the NETosis pathway was top-ranked in patients with SCAP caused by diverse kinds of pathogens. This provides a potential therapeutic strategy for treating patients. Furthermore, we calculated the correlation between the expression of genes involved in NETosis and the ratio of arterial oxygen partial pressure to fractional inspired oxygen. We identified four novel potential therapeutic targets for NETosis in patients with SCAP, including H4C15, H3-5, DNASE1, and PRKCB. In addition, a higher occurrence of transcriptional read-through is associated with a worse outcome in patients with SCAP, which probably can explain the high mortality rate of patients with SCAP.

Interleukin-6, infection and cardiovascular outcomes in acute heart failure: Findings from the EDIFICA registry

AIMS

Interleukin-6 (IL-6) is upregulated in response to infectious and inflammatory triggers and independently predicts all-cause mortality in acute heart failure (AHF). However, the association of IL-6 with cardiovascular outcomes and its interplay with C-reactive protein and infection, a major precipitating factor in AHF, remains poorly understood.

METHODS AND RESULTS

The association between IL-6 and clinical outcomes (180 days) in AHF was evaluated using a cohort of 164 patients from the EDIFICA registry. Median IL-6 levels at admission were 17.4 pg/mL. Patients in the higher admission IL-6 tertile presented with lower blood pressure and more congestion, were diagnosed more frequently with infection, and had a longer hospital stay. Higher IL-6 levels were associated with increased risk of HF rehospitalization (hazard ratio per log₂ 3.69, 95% confidence interval (CI) 1.26-10.8, p =.017) and the composite of HF rehospitalization or cardiovascular death (hazard ratio per log₂ 3.50; 95% CI 1.28-9.57; p =.014), independently of major AHF prognosticators, including B-type natriuretic peptide and renal function. However, no independent associations were found for all-cause rehospitalization or mortality. Despite a moderate correlation of IL-6 with C-reactive protein (CRP) levels (R = .51), the latter were not associated with clinical outcomes in this population.

CONCLUSIONS

IL-6 levels associate with higher rate of cardiovascular events in AHF, independently of classical prognosticators and evidence of infection, outperforming CRP as an inflammatory outcome biomarker.

Neutrophil Recruitment in Pneumococcal Pneumonia

Streptococcus pneumoniae (Spn) is the primary agent of community-acquired pneumonia. Neutrophils are innate immune cells that are essential for bacterial clearance during pneumococcal pneumonia but can also do harm to host tissue. Neutrophil migration in pneumococcal pneumonia is therefore a major determinant of host disease outcomes. During Spn infection, detection of the bacterium leads to an increase in proinflammatory signals and subsequent expression of integrins and ligands on both the neutrophil as well as endothelial and epithelial cells. These integrins and ligands mediate the tethering and migration of the neutrophil from the bloodstream to the site of infection. A gradient of host-derived and bacterial-derived chemoattractants contribute to targeted movement of neutrophils. During pneumococcal pneumonia, neutrophils are rapidly recruited to the pulmonary space, but studies show that some of the canonical neutrophil migratory machinery is dispensable. Investigation of neutrophil migration is necessary for us to understand the dynamics of pneumococcal infection. Here, we summarize what is known about the pathways that lead to migration of the neutrophil from the capillaries to the lung during pneumococcal infection.

Lobar (croupous) pneumonia: old and new data

Background and aim

Pneumonia remains one of the most frequent death causes worldwide. Among the etiological factors S. pneumoniae-causing lobar pneumonia plays a leading role. According to current textbook knowledge at least three sequential stages of lobar pneumonia are distinguished: congestion, red hepatization and gray hepatization. However, there are no detailed data supporting this stage concept. There are also controversial views on its etiology. In this study, the lung changes in lobar pneumonia were related to the cause and duration of the disease. In addition, the complications of the disease were evaluated. PCR studies verified the etiology of pneumonia.

Material and methods

Lobar pneumonia was analyzed in 252 post mortem cases examined in a large hospital in Irkutsk. The pathology, etiology of pneumonia, course of disease and cause of death were recorded and correlated to its clinical course and duration. In the second part of the study, the results in 95 patients were analyzed in detail and related to PCR findings.

Results

Most patients were adult men of low social status who showed signs of severe alcoholism. Lobar pneumonia was observed in 85% of the patients, while the remaining patients showed sublobar (“lobular”, focal) lung involvement. Histologically, three patterns of inflammation were observed, which in most patients occurred concurrently in different parts of the involved lobe: “congestion”, characterized by serous exudation with multiple cocci (41% of cases), “red hepatization” (41% of cases) and “gray hepatization” (100% of cases). The latter pattern was subdivided into three subgroups according to the ratio of fibrin—neutrophils and the presence of macrophages. The mean number of different histological patterns observed per patient was 3.8. There was no correlation between the inflammatory patterns and the duration of the disease. In 23% of the patients, the cause of death was of pulmonary origin, while the remaining patients died of extrapulmonary complications (i.e. acute heart failure 26%, acute vascular insufficiency 15% purulent meningitis 11–24.3%. In 29/95 patients (20 with lobar and 9 with focal pneumonia) pneumococcal etiology of pneumonia was established by PCR.

Conclusion

Lobar pneumonia is a distinct clinico-pathological entity caused by S. pneumoniae, demonstrated by PCR testing and/or cytological examinations. Bacteriologic studies frequently give falsenegative results. Lobar pneumonia is characterized by three main histopathological patterns (congestion or microbeous edema, and red and gray hepatization) which usually occur side by side and not in chronological order. Early death is often related to heart failure and septic shock, while meningitis is a frequent complication later in the course.

RIPK3 Activates MLKL-mediated Necroptosis and Inflammasome Signaling during Streptococcus Infection

Community-acquired pneumonia is the most common type of pneumonia and remains a leading cause of morbidity and mortality worldwide. Although many different pathogens can contribute to pneumonia, Streptococcus pneumoniae is one of the common bacterial pathogens that underlie community-acquired pneumonia. RIPK3 (receptor-interacting protein kinase 3) is widely recognized as a key modulator of inflammation and cell death. To elucidate a potential role of RIPK3 in pneumonia, we examined plasma from healthy control subjects and patients positive for streptococcal pneumonia. In human studies, RIPK3 protein concentrations were significantly elevated and were identified as a potential plasma marker of pneumococcal pneumonia. To expand these findings, we used an in vivo murine model of pneumococcal pneumonia to demonstrate that RIPK3 deficiency leads to reduced bacterial clearance, severe pathological damage, and high mortality. Our results illustrated that RIPK3 forms a complex with RIPK1, MLKL (mixed-lineage kinase domain-like protein), and MCU (mitochondrial calcium uniporter) to induce mitochondrial calcium uptake and mitochondrial reactive oxygen species(mROS) production during S. pneumoniae infection. In macrophages, RIPK3 initiated necroptosis via the mROS-mediated mitochondrial permeability transition pore opening and NLRP3 inflammasome activation via the mROS-AKT pathway to protect against S. pneumoniae. In conclusion, our study demonstrated a mechanism by which RIPK3-initiated necroptosis is essential for host defense against S. pneumoniae.

Knockout of MAPK Phosphatase-1 Exaggerates Type I IFN Response during Systemic Escherichia coli Infection

We have previously shown that Mkp-1-deficient mice produce elevated TNF-α, IL-6, and IL-10 following systemic Escherichia coli infection, and they exhibited increased mortality, elevated bacterial burden, and profound metabolic alterations. To understand the function of Mkp-1 during bacterial infection, we performed RNA-sequencing analysis to compare the global gene expression between E. coli-infected wild-type and Mkp-1 ^-/- mice. A large number of IFN-stimulated genes were more robustly expressed in E. coli-infected Mkp-1 ^-/- mice than in wild-type mice. Multiplex analysis of the serum cytokine levels revealed profound increases in IFN-β, IFN-γ, TNF-α, IL-1α and β, IL-6, IL-10, IL-17A, IL-27, and GMSF levels in E. coli-infected Mkp-1 ^-/- mice relative to wild-type mice. Administration of a neutralizing Ab against the receptor for type I IFN to Mkp-1 ^-/- mice prior to E. coli infection augmented mortality and disease severity. Mkp-1 ^-/- bone marrow-derived macrophages (BMDM) produced higher levels of IFN-β mRNA and protein than did wild-type BMDM upon treatment with LPS, E. coli, polyinosinic:polycytidylic acid, and herring sperm DNA. Augmented IFN-β induction in Mkp-1 ^-/- BMDM was blocked by a p38 inhibitor but not by an JNK inhibitor. Enhanced Mkp-1 expression abolished IFN-β induction by both LPS and E. coli but had little effect on the IFN-β promoter activity in LPS-stimulated RAW264.7 cells. Mkp-1 deficiency did not have an overt effect on IRF3/7 phosphorylation or IKK activation but modestly enhanced IFN-β mRNA stability in LPS-stimulated BMDM. Our results suggest that Mkp-1 regulates IFN-β production primarily through a p38-mediated mechanism and that IFN-β plays a beneficial role in E. coli-induced sepsis.

The Relevance of IL-1-Signaling in the Protection against Gram-Positive Bacteria

Previous studies performed using a model of group B streptococcus (GBS)-induced peritoneal inflammation indicate that the interleukin-1 receptor (IL-1R) family plays an important role in the innate host defense against this encapsulated Gram-positive bacteria. Since the role of IL-1-dependent signaling in peritoneal infections induced by other Gram-positive bacteria is unknown, in the present study we sought to investigate the contribution of IL-1R signaling in host defenses against Streptococcus pyogenes (group A streptococcus or GAS) or Staphylococcus aureus, two frequent and global human Gram-positive extracellular pathogens. We analyzed here the outcome of GAS or S. aureus infection in IL-1R-deficient mice. After inoculated intraperitoneal (i.p.) inoculation with group A Streptococcus or S. aureus, all the wild-type (WT) control mice survived the challenge, while, respectively, 63% or 50% of IL-1-defective mice died. Lethality was due to the ability of both bacterial species to replicate and disseminate to the target organs of IL-1R-deficient mice. Moreover, the experimental results indicate that IL-1 signaling promotes the production of leukocyte attractant chemokines CXCL-1 and CXCL-2 and recruitment of neutrophils to bacterial infection sites. Accordingly, the reduced neutrophil recruitment in IL-1R-deficient mice was linked with decreased production of neutrophil chemokines. Collectively, our findings indicate that IL-1 signaling, as previously showed in host defense against GBS, plays a fundamental role also in controlling the progression and outcome of GAS or S. aureus disease.

Macrophage LC3-associated phagocytosis is an immune defense against Streptococcus pneumoniae that diminishes with host aging

Streptococcus pneumoniae is a leading cause of pneumonia and invasive disease, particularly, in the elderly. S. pneumoniae lung infection of aged mice is associated with high bacterial burdens and detrimental inflammatory responses. Macrophages can clear microorganisms and modulate inflammation through two distinct lysosomal trafficking pathways that involve 1A/1B-light chain 3 (LC3)-marked organelles, canonical autophagy, and LC3-associated phagocytosis (LAP). The S. pneumoniae pore-forming toxin pneumolysin (PLY) triggers an autophagic response in nonphagocytic cells, but the role of LAP in macrophage defense against S. pneumoniae or in age-related susceptibility to infection is unexplored. We found that infection of murine bone-marrow-derived macrophages (BMDMs) by PLY-producing S. pneumoniae triggered Atg5- and Atg7-dependent recruitment of LC3 to S. pneumoniae-containing vesicles. The association of LC3 with S. pneumoniae-containing phagosomes required components specific for LAP, such as Rubicon and the NADPH oxidase, but not factors, such as Ulk1, FIP200, or Atg14, required specifically for canonical autophagy. In addition, S. pneumoniae was sequestered within single-membrane compartments indicative of LAP. Importantly, compared to BMDMs from young (2-mo-old) mice, BMDMs from aged (20- to 22-mo-old) mice infected with S. pneumoniae were not only deficient in LAP and bacterial killing, but also produced higher levels of proinflammatory cytokines. Inhibition of LAP enhanced S. pneumoniae survival and cytokine responses in BMDMs from young but not aged mice. Thus, LAP is an important innate immune defense employed by BMDMs to control S. pneumoniae infection and concomitant inflammation, one that diminishes with age and may contribute to age-related susceptibility to this important pathogen.

Interaction of Macrophages and Cholesterol-Dependent Cytolysins: The Impact on Immune Response and Cellular Survival

Cholesterol-dependent cytolysins (CDCs) are key virulence factors involved in many lethal bacterial infections, including pneumonia, necrotizing soft tissue infections, bacterial meningitis, and miscarriage. Host responses to these diseases involve myeloid cells, especially macrophages. Macrophages use several systems to detect and respond to cholesterol-dependent cytolysins, including membrane repair, mitogen-activated protein (MAP) kinase signaling, phagocytosis, cytokine production, and activation of the adaptive immune system. However, CDCs also promote immune evasion by silencing and/or destroying myeloid cells. While there are many common themes between the various CDCs, each CDC also possesses specific features to optimally benefit the pathogen producing it. This review highlights host responses to CDC pathogenesis with a focus on macrophages. Due to their robust plasticity, macrophages play key roles in the outcome of bacterial infections. Understanding the unique features and differences within the common theme of CDCs bolsters new tools for research and therapy.

Current Therapeutic Options for the Main Monogenic Autoinflammatory Diseases and PFAPA Syndrome: Evidence-Based Approach and Proposal of a Practical Guide

Monogenic autoinflammatory diseases are rare conditions caused by genetic abnormalities affecting the innate immunity. Previous therapeutic strategies had been mainly based on results from retrospective studies and physicians' experience. However, during the last years, the significant improvement in their genetic and pathogenic knowledge has been accompanied by a remarkable progress in their management. The relatively recent identification of the inflammasome as the crucial pathogenic mechanism causing an aberrant production of interleukin 1β (IL-1β) in the most frequent monogenic autoinflammatory diseases led to the introduction of anti-IL-1 agents and other biologic drugs as part of the previously limited therapeutic armamentarium available. Advances in the treatment of autoinflammatory diseases have been favored by the use of new biologic agents and the performance of a notable number of randomized clinical trials exploring the efficacy and safety of these agents. Clinical trials have contributed to increase the level of evidence and provided more robust therapeutic recommendations. This review analyzes the treatment of the most frequent monogenic autoinflammatory diseases, namely, familial Mediterranean fever, tumor necrosis factor receptor-associated periodic fever syndrome, hyperimmunoglobulin D syndrome/mevalonate kinase deficiency, and cryopyrin-associated periodic syndromes, together with periodic fever with aphthous stomatitis, pharyngitis, and cervical adenitis syndrome, which is the most common polygenic autoinflammatory disease in children, also occurring in adult patients. Finally, based on the available expert consensus recommendations and the highest level of evidence of the published studies, a practical evidence-based guideline for the treatment of these autoinflammatory diseases is proposed.

Early or Late Bacterial Lung Infection Increases Mortality After Traumatic Brain Injury in Male Mice and Chronically Impairs Monocyte Innate Immune Function

OBJECTIVES

Respiratory infections in the postacute phase of traumatic brain injury impede optimal recovery and contribute substantially to overall morbidity and mortality. This study investigated bidirectional innate immune responses between the injured brain and lung, using a controlled cortical impact model followed by secondary Streptococcus pneumoniae infection in mice.

DESIGN

Experimental study.

SETTING

Research laboratory.

SUBJECTS

Adult male C57BL/6J mice.

INTERVENTIONS

C57BL/6J mice were subjected to sham surgery or moderate-level controlled cortical impact and infected intranasally with S. pneumoniae (1,500 colony-forming units) or vehicle (phosphate-buffered saline) at 3 or 60 days post-injury.

MAIN RESULTS

At 3 days post-injury, S. pneumoniae-infected traumatic brain injury mice (TBI + Sp) had a 25% mortality rate, in contrast to no mortality in S. pneumoniae-infected sham (Sham + Sp) animals. TBI + Sp mice infected 60 days post-injury had a 60% mortality compared with 5% mortality in Sham + Sp mice. In both studies, TBI + Sp mice had poorer motor function recovery compared with TBI + PBS mice. There was increased expression of pro-inflammatory markers in cortex of TBI + Sp compared with TBI + PBS mice after both early and late infection, indicating enhanced post-traumatic neuroinflammation. In addition, monocytes from lungs of TBI + Sp mice were immunosuppressed acutely after traumatic brain injury and could not produce interleukin-1β, tumor necrosis factor-α, or reactive oxygen species. In contrast, after delayed infection monocytes from TBI + Sp mice had higher levels of interleukin-1β, tumor necrosis factor-α, and reactive oxygen species when compared with Sham + Sp mice. Increased bacterial burden and pathology was also found in lungs of TBI + Sp mice.

CONCLUSIONS

Traumatic brain injury causes monocyte functional impairments that may affect the host's susceptibility to respiratory infections. Chronically injured mice had greater mortality following S. pneumoniae infection, which suggests that respiratory infections even late after traumatic brain injury may pose a more serious threat than is currently appreciated.

Recognition of Lipoproteins by Toll-like Receptor 2 and DNA by the AIM2 Inflammasome Is Responsible for Production of Interleukin-1β by Virulent Suilysin-negative Streptococcus suis Serotype 2

Streptococcus suis serotype 2 is an important porcine bacterial pathogen and zoonotic agent causing sudden death, septic shock and meningitis. These pathologies are the consequence of an exacerbated inflammatory response composed of various mediators including interleukin (IL)-1β. Elevated levels of the toxin suilysin (SLY) were demonstrated to play a key role in S. suis-induced IL-1β production. However, 95% of serotype 2 strains isolated from diseased pigs in North America, many of which are virulent, do not produce SLY. In this study, we demonstrated that SLY-negative S. suis induces elevated levels of IL-1β in systemic organs, with dendritic cells contributing to this production. SLY-negative S. suis-induced IL-1β production requires MyD88 and TLR2 following recognition of lipoproteins. However, the higher internalization rate of the SLY-negative strain results in intracellularly located DNA being recognized by the AIM2 inflammasome, which promotes IL-1β production. Finally, the role of IL-1 in host survival during the S. suis systemic infection is beneficial and conserved, regardless of SLY production, via modulation of the inflammation required to control bacterial burden. In conclusion, this study demonstrates that SLY is not required for S. suis-induced IL-1β production.

Relative Contributions of Extracellular and Internalized Bacteria to Early Macrophage Proinflammatory Responses to Streptococcus pneumoniae

Both intracellular immune sensing and extracellular innate immune sensing have been implicated in initiating macrophage proinflammatory cytokine responses to Streptococcus pneumoniae The S. pneumoniae capsule, a major virulence determinant, prevents phagocytosis, and we hypothesized that this would reduce activation of host innate inflammatory responses by preventing activation of intracellular proinflammatory signaling pathways. We investigated this hypothesis in human monocyte-derived macrophages stimulated with encapsulated or isogenic unencapsulated mutant S. pneumoniae Unexpectedly, despite strongly inhibiting bacterial internalization, the capsule resulted in enhanced inflammatory cytokine production by macrophages infected with S. pneumoniae Experiments using purified capsule material and a Streptococcus mitis mutant expressing an S. pneumoniae serotype 4 capsule indicated these differences required whole bacteria and were not due to proinflammatory effects of the capsule itself. Transcriptional profiling demonstrated relatively few differences in macrophage gene expression profiles between infections with encapsulated S. pneumoniae and those with unencapsulated S. pneumoniae, largely limited to reduced expression of proinflammatory genes in response to unencapsulated bacteria, predicted to be due to reduced activation of the NF-κB family of transcription factors. Blocking S. pneumoniae internalization using cytochalasin D had minimal effects on the inflammatory response to S. pneumoniae Experiments using murine macrophages indicated that the affected genes were dependent on Toll-like receptor 2 (TLR2) activation, although not through direct stimulation of TLR2 by capsule polysaccharide. Our data demonstrate that the early macrophage proinflammatory response to S. pneumoniae is mainly dependent on extracellular bacteria and reveal an unexpected proinflammatory effect of encapsulated S. pneumoniae that could contribute to disease pathogenesis.IMPORTANCE Multiple extra- and intracellular innate immune receptors have been identified that recognize Streptococcus pneumoniae, but the relative contributions of intra- versus extracellular bacteria to the inflammatory response were unknown. We have shown that intracellular S. pneumoniae contributes surprisingly little to the inflammatory responses, with production of important proinflammatory cytokines largely dependent on extracellular bacteria. Furthermore, although we expected the S. pneumoniae polysaccharide capsule to block activation of the host immune system by reducing bacterial internalization and therefore activation of intracellular innate immune receptors, there was an increased inflammatory response to encapsulated compared to unencapsulated bacteria, which is likely to contribute to disease pathogenesis.

ASC and NLRP3 maintain innate immune homeostasis in the airway through an inflammasome-independent mechanism

It is widely accepted that inflammasomes protect the host from microbial pathogens by inducing inflammatory responses through caspase-1 activation. Here, we show that the inflammasome components ASC and NLRP3 are required for resistance to pneumococcal pneumonia, whereas caspase-1 and caspase-11 are dispensable. In the lung of S. pneumoniae-infected mice, ASC and NLRP3, but not caspase-1/11, were required for optimal expression of several mucosal innate immune proteins. Among them, TFF2 and intelectin-1 appeared to be protective against pneumococcal pneumonia. During infection, ASC and NLRP3 maintained the expression of the transcription factor SPDEF, which can facilitate the expression of the mucosal defense factor genes. Moreover, activation of STAT6, a key regulator of Spdef expression, depended on ASC and NLRP3. Overexpression of these inflammasome proteins sustained STAT6 phosphorylation induced by type 2 cytokines. Collectively, this study suggests that ASC and NLRP3 promote airway mucosal innate immunity by an inflammasome-independent mechanism involving the STAT6-SPDEF pathway.

Dietary zinc and the control of Streptococcus pneumoniae infection

Human zinc deficiency increases susceptibility to bacterial infection. Although zinc supplementation therapies can reduce the impact of disease, the molecular basis for protection remains unclear. Streptococcus pneumoniae is a major cause of bacterial pneumonia, which is prevalent in regions of zinc deficiency. We report that dietary zinc levels dictate the outcome of S. pneumoniae infection in a murine model. Dietary zinc restriction impacts murine tissue zinc levels with distribution post-infection altered, and S. pneumoniae virulence and infection enhanced. Although the activation and infiltration of murine phagocytic cells was not affected by zinc restriction, their efficacy of bacterial control was compromised. S. pneumoniae was shown to be highly sensitive to zinc intoxication, with this process impaired in zinc restricted mice and isolated phagocytic cells. Collectively, these data show how dietary zinc deficiency increases sensitivity to S. pneumoniae infection while revealing a role for zinc as a component of host antimicrobial defences.

Zinc deficiency affects one-third of the world’s population and is associated with an increased susceptibility to bacterial infection. Despite this, the molecular basis for how zinc deficiency compromises host control of infection remains to be understood. We show that dietary zinc deficiency impacts host tissue zinc abundances and its mobilization during infection by the major respiratory pathogen Streptococcus pneumoniae. Zinc acts as a direct antimicrobial against the pathogen, mobilized by phagocytic cells as a component of the innate immune response. Although immune activation and infiltration of phagocytic cells is unaffected by host zinc status, the lack of antimicrobial zinc compromises bacterial control in zinc deficient hosts. These findings highlight the importance of zinc sufficiency in resisting bacterial infection.

Interleukin-1 signaling induced by Streptococcus suis serotype 2 is strain-dependent and contributes to bacterial clearance and inflammation during systemic disease in a mouse model of infection

Streptococcus suis serotype 2 is an important porcine pathogen and zoonotic agent causing sudden death, septic shock and meningitis, with exacerbated inflammation being a hallmark of the infection. A rapid, effective and balanced innate immune response against S. suis is critical to control bacterial growth without causing excessive inflammation. Even though interleukin (IL)-1 is one of the most potent and earliest pro-inflammatory mediators produced, its role in the S. suis pathogenesis has not been studied. We demonstrated that a classical virulent European sequence type (ST) 1 strain and the highly virulent ST7 strain induce important levels of IL-1 in systemic organs. Moreover, bone marrow-derived dendritic cells and macrophages contribute to its production, with the ST7 strain inducing higher levels. To better understand the underlying mechanisms involved, different cellular pathways were studied. Independently of the strain, IL-1β production required MyD88 and involved recognition via TLR2 and possibly TLR7 and TLR9. This suggests that the recognized bacterial components are similar and conserved between strains. However, very high levels of the pore-forming toxin suilysin, produced only by the ST7 strain, are required for efficient maturation of pro-IL-1β via activation of different inflammasomes resulting from pore formation and ion efflux. Using IL-1R^−/− mice, we demonstrated that IL-1 signaling plays a beneficial role during S. suis systemic infection by modulating the inflammation required to control and clear bacterial burden, thus promoting host survival. Beyond a certain threshold, however, S. suis-induced inflammation cannot be counterbalanced by this signaling, making it difficult to discriminate its role.

NLRP3/ASC/Caspase-1 axis and serine protease activity are involved in neutrophil IL-1β processing during Streptococcus pneumoniae infection

Streptococcus pneumoniae is a pathogenic bacterium that can cause severe invasive diseases, such as pneumonia, otitis media and meningitis. The pro-inflammatory cytokine, IL-1β, has been reported to play important role in host defense against S. pneumoniae. The mechanism of IL-1β maturation and secretion in macrophages has been well studied. However, the precise mechanism of IL-1β processing within neutrophils upon S. pneumoniae infection remains unclear. In this study, mouse peritoneal neutrophils from C57BL/6 WT and inflammasome components knockout mice were infected by S. pneumoniae in vitro. The results showed that NLRP3 inflammasome is critically involved in neutrophil IL-1β secretion, while the AIM2 and NLRC4 inflammasomes were dispensable. Moreover, the upstream kinase, JNK, modulates ASC oligomerization and consequent caspase-1 activation and IL-1β secretion. Additionally, neutrophil serine proteases also participate in IL-1β secretion by mediating ASC oligomerization and caspase-1 activation. Taken together, these findings indicated that both the NLRP3 inflammasome-related pathway and neutrophil serine protease mediate IL-1β processing upon S. pneumoniae infection.

Necroptotic Cell Death Promotes Adaptive Immunity Against Colonizing Pneumococci

Pore-forming toxin (PFT) induced necroptosis exacerbates pulmonary injury during bacterial pneumonia. However, its role during asymptomatic nasopharyngeal colonization and toward the development of protective immunity was unknown. Using a mouse model of Streptococcus pneumoniae (Spn) asymptomatic colonization, we determined that nasopharyngeal epithelial cells (nEC) died of pneumolysin (Ply)-dependent necroptosis. Mice deficient in MLKL, the necroptosis effector, or challenged with Ply-deficient Spn showed less nEC sloughing, increased neutrophil infiltration, and altered IL-1α, IL-33, CXCL2, IL-17, and IL-6 levels in nasal lavage fluid (NALF). Activated MLKL correlated with increased presence of CD11c⁺ antigen presenting cells in Spn-associated submucosa. Colonized MLKL KO mice and wildtype mice colonized with Ply-deficient Spn produced less antibody against the bacterial surface protein PspA, were delayed in bacterial clearance, and were more susceptible to a lethal secondary Spn challenge. We conclude that PFT-induced necroptosis is instrumental in the natural development of protective immunity against opportunistic PFT-producing bacterial pathogens.

TLR4 deficiency reduces pulmonary resistance to Streptococcus pneumoniae in gut microbiota-disrupted mice

Streptococcus pneumoniae is a clinically important pathogen responsible for significant morbidity and mortality worldwide. Disruption of the host gut microbiota by antibiotics reduces the pulmonary resistance to S. pneumoniae. The aim of our study was to determine the potential role of TLR4 in the reduced pulmonary resistance to S. pneumoniae following gut microbiota disruption. Wild-type and TLR4-deficient mice were given broad-spectrum antibiotics for 3 weeks by oral gavage to disrupt the gut microbiota, and subsequently inoculated intra-nasally with S. pneumoniae. The extent of the decline in pulmonary resistance in both animal groups was evaluated in terms of the overall survival and pulmonary bacterial clearance. Both survival and pulmonary clearance of S. pneumoniae were lower in the TLR4-deficient mice with disrupted gut microbiota, compared to their intestinally healthy counterparts after pneumococcal infection. However, the degree of decline was much lower in the TLR4-deficient mice compared to the wild-type mice. Our findings indicate that impaired TLR4 function might be the basis of the reduced pulmonary resistance to S. pneumoniae caused by gut microbiota disruption.

Syk and JNK signaling pathways are involved in inflammasome activation in macrophages infected with Streptococcus pneumoniae

Streptococcus pneumoniae is a pathogen of significant clinical importance worldwide that can cause severe invasive diseases, such as pneumonia, otitis media and meningitis. Inflammsomes has been reported to participate in host defense against S. pneumoniae infection. S. pneumoniae could induce the assembly of the nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3)/absent in melanoma 2 (AIM2) inflammasome, which mediates the activation of caspase-1 and the subsequent maturation of Interleukin-1β (IL-1β). However, the precise signals that activate inflammasomes during pneumococcal infection remain to be fully elucidated. In the present study, primary mouse macrophages were selected as a cell model, and the effects of kinases on inflammasome activity induced by S. pneumoniae infection were examined by ELISA and western blotting after pretreatment with a kinase inhibitor. Here, we show that Syk and JNK signaling are required for S. pneumoniae-induced activation of the inflammasome. Inhibitors of Syk and JNK almost abolished the oligomerization of apoptosis-associated speck-like protein containing a caspase-activating and recruitment domain (ASC) and subsequent caspase-1 activation and IL-1β secretion. Moreover, pneumolysin (PLY) participated in this process and was critical for Syk/JNK activation. These results suggested that the Syk/JNK signaling pathway may play a vital role in the inflammasome activation and modulate host immune responses against S. pneumoniae.

NLRP3 inflammasome activation in aged macrophages is diminished during Streptococcus pneumoniae infection

Pneumococcal infections are the eigth leading cause of death in the United States, and it is estimated that older patients (≥65 yr of age) account for the most serious cases. The goal of our current study is to understand the impact of biological aging on innate immune responses to Streptococcus pneumoniae, a causative agent of bacterial pneumonia. With the use of in vitro and in vivo aged murine models, our findings demonstrate that age-enhanced unfolded protein responses (UPRs) contribute to diminished inflammasome assembly and activation during S. pneumoniae infection. Pretreatment of aged mice with endoplasmic reticulum chaperone and the stress-reducing agent tauroursodeoxycholic acid (TUDCA) decreased mortality in aged hosts that was associated with increased NLRP3 inflammasome activation, improved pathogen clearance, and decreased pneumonitis during infection. Taken together, our data provide new evidence as to why older persons are more susceptible to S. pneumoniae and provide a possible therapeutic target to decrease morbidity and mortality in this population.

Function and regulation of IL-1α in inflammatory diseases and cancer

The interleukin (IL)-1 family of cytokines is currently comprised of 11 members that have pleiotropic functions in inflammation and cancer. IL-1α and IL-1β were the first members of the IL-1 family to be described, and both signal via the same receptor, IL-1R. Over the last decade, much progress has been made in our understanding of biogenesis of IL-1β and its functions in human diseases. Studies from our laboratory and others have highlighted the critical role of nod-like receptors (NLRs) and multi-protein complexes known as inflammasomes in the regulation of IL-1β maturation. Recent studies have increased our appreciation of the role played by IL-1α in inflammatory diseases and cancer. However, the mechanisms that regulate the production of IL-1α and its bioavailability are relatively understudied. In this review, we summarize the distinctive roles played by IL-1α in inflammatory diseases and cancer. We also discuss our current knowledge about the mechanisms that control IL-1α biogenesis and activity, and the major unanswered questions in its biology.

ASC and NLRP3 impair host defense during lethal pneumonia caused by serotype 3 Streptococcus pneumoniae in mice

Streptococcus (S.) pneumoniae is the most common cause of community-acquired pneumonia. The Nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, consisting of NLRP3, ASC (the adaptor apoptosis-associated speck-like protein containing a CARD) and caspase-1, has been implicated in protective immunity during pneumonia induced by high doses of S. pneumoniae serotype 2. Here we investigated the role of the NLRP3 inflammasome in the host response during lethal airway infection with a low dose of serotype 3 S. pneumoniae. Mice were euthanized at predefined endpoints for analysis or observed in survival studies. In additional studies, Tlr2^-/- /Tlr4^-/- mice and Myd88^-/- mice incapable of Toll-like receptor signaling were studied. In stark contrast with existing literature, both Nlrp3^-/- and Asc^-/- mice showed a strongly improved host defense, as reflected by a markedly reduced mortality rate accompanied by diminished bacterial growth and dissemination. Host defense was unaltered in Tlr2^-/- /Tlr4^-/- mice and Myd88^-/- mice. These results show that the NLRP3 inflammasome impairs host defense during lethal pneumonia caused by serotype 3 S. pneumoniae. Our findings challenge the current paradigm that proximal innate detection systems are indispensable for an adequate host immune response against bacteria.

Pneumolysin-Dependent Calpain Activation and Interleukin-1α Secretion in Macrophages Infected with Streptococcus pneumoniae

Pneumolysin (PLY), a major virulence factor of Streptococcus pneumoniae, is a pore-forming cytolysin that modulates host innate responses contributing to host defense against and pathogenesis of pneumococcal infections. Interleukin-1α (IL-1α) has been shown to be involved in tissue damage in a pneumococcal pneumonia model; however, the mechanism by which this cytokine is produced during S. pneumoniae infection remains unclear. In this study, we examined the role of PLY in IL-1α production. Although the strains induced similar levels of pro-IL-1α expression, wild-type S. pneumoniae D39, but not a deletion mutant of the ply gene (Δply), induced the secretion of mature IL-1α from host macrophages, suggesting that PLY is critical for the maturation and secretion of IL-1α during S. pneumoniae infection. Further experiments with calcium chelators and calpain inhibitors indicated that extracellular calcium ions and calpains (calcium-dependent proteases) facilitated the maturation and secretion of IL-1α from D39-infected macrophages. Moreover, we found that PLY plays a critical role in calcium influx and calpain activation, as elevated intracellular calcium levels and the degradation of the calpain substrate α-fodrin were detected in macrophages infected with D39 but not the Δply strain. These results suggested that PLY induces the influx of calcium in S. pneumoniae-infected macrophages, followed by calpain activation and subsequent IL-1α maturation and secretion.

Tyk2 as a target for immune regulation in human viral/bacterial pneumonia

The severity and lethality of influenza A virus (IAV) infections is frequently aggravated by secondary bacterial pneumonia. However, the mechanisms in human lung tissue that provoke this increase in fatality are unknown and therapeutic immune modulatory options are lacking.We established a human lung ex vivo co-infection model to investigate innate immune related mechanisms contributing to the susceptibility of secondary pneumococcal pneumonia.We revealed that type I and III interferon (IFN) inhibits Streptococcus pneumoniae-induced interleukin (IL)-1β release. The lack of IL-1β resulted in the repression of bacterially induced granulocyte-macrophage colony-stimulating factor (GM-CSF) liberation. Specific inhibition of IFN receptor I and III-associated tyrosine kinase 2 (Tyk2) completely restored the S. pneumoniae-induced IL-1β-GM-CSF axis, leading to a reduction of bacterial growth. A preceding IAV infection of the human alveolus leads to a type I and III IFN-dependent blockade of the early cytokines IL-1β and GM-CSF, which are key for orchestrating an adequate innate immune response against bacteria. Their virally induced suppression may result in impaired bacterial clearance and alveolar repair.Pharmacological inhibition of Tyk2 might be a new treatment option to sustain beneficial endogenous GM-CSF levels in IAV-associated secondary bacterial pneumonia.

Inflammasomes in Pneumococcal Infection: Innate Immune Sensing and Bacterial Evasion Strategies

Streptococcus pneumoniae frequently colonizes the upper respiratory tract of healthy individuals, but also commonly causes severe invasive infections such as community-acquired pneumonia and meningitis. One of the key virulence factors of pneumococci is the pore-forming toxin pneumolysin which stimulates cell death and is involved in the evasion of some defense mechanisms. The immune system, however, employs different inflammasomes to sense pneumolysin-induced pore formation, cellular membrane damage, and/or subsequent leakage of bacterial nucleic acid into the host cell cytosol. Canonical inflammasomes are cytosolic multiprotein complexes consisting of a receptor molecule such as NLRP3 or AIM2, the adapter ASC, and caspase-1. NLRP3 and AIM2 inflammasomes mediate cell death and production of important IL-1 family cytokines to recruit leukocytes and defend against S. pneumoniae. Here, we review recent evidence that highlights inflammasomes as critical sensors of S. pneumoniae-induced cellular perturbations, summarize their role in pneumococcal infections, and discuss potential evasion strategies of some emerging pneumococcal strains.

Clash of the Cytokine Titans: counter-regulation of interleukin-1 and type I interferon-mediated inflammatory responses

Over the past decades the notion of 'inflammation' has been extended beyond the original hallmarks of rubor (redness), calor (heat), tumor (swelling) and dolor (pain) described by Celsus. We have gained a more detailed understanding of the cellular players and molecular mediators of inflammation which is now being applied and extended to areas of biomedical research such as cancer, obesity, heart disease, metabolism, auto-inflammatory disorders, autoimmunity and infectious diseases. Innate cytokines are often central components of inflammatory responses. Here, we discuss how the type I interferon and interleukin-1 cytokine pathways represent distinct and specialized categories of inflammatory responses and how these key mediators of inflammation counter-regulate each other.

IL-17A attracts inflammatory cells in murine lung infection with P. aeruginosa

IL-17A-dependent immunity is of importance in the protection against extracellular bacterial pathogens. However, IL-17A is also suggested to mediate the pathogenesis of lung diseases, such as acute respiratory distress syndrome. Here, we studied the role of IL-17A in a mouse model of acute pneumonia. IL-17A mediated the expression of keratinocyte-derived chemokine (KC) and the recruitment of inflammatory cells in mice infected with a sub-lethal dose of Pseudomonas aeruginosa. IL-17A deficiency protected mice from lethal P. aeruginosa lung infection. A sub-lethal infection with Streptococcus pneumoniae resulted in increased bacterial burden associated with increased pulmonary inflammation. Thus, the type of infectious bacteria seemed to influence the way in which IL-17A functions during pulmonary infection. Reducing pulmonary inflammation by targeting IL-17A may be a therapeutic option in acute P. aeruginosa pneumonia.

Cinobufagin Modulates Human Innate Immune Responses and Triggers Antibacterial Activity

The traditional Chinese medicine Chan-Su is widely used for treatment of cancer and cardiovascular diseases, but also as a remedy for infections such as furunculosis, tonsillitis and acute pharyngitis. The clinical use of Chan-Su suggests that it has anti-infective effects, however, the mechanism of action is incompletely understood. In particular, the effect on the human immune system is poorly defined. Here, we describe previously unrecognized immunomodulatory activities of cinobufagin (CBG), a major bioactive component of Chan-Su. Using human monocyte-derived dendritic cells (DCs), we show that LPS-induced maturation and production of a number of cytokines was potently inhibited by CBG, which also had a pro-apoptotic effect, associated with activation of caspase-3. Interestingly, CBG triggered caspase-1 activation and significantly enhanced IL-1β production in LPS-stimulated cells. Finally, we demonstrate that CBG upregulates gene expression of the antimicrobial peptides (AMPs) hBD-2 and hBD-3 in DCs, and induces secretion of HNP1-3 and hCAP-18/LL-37 from neutrophils, potentiating neutrophil antibacterial activity. Taken together, our data indicate that CBG modulates the inflammatory phenotype of DCs in response to LPS, and triggers an antibacterial innate immune response, thus proposing possible mechanisms for the clinical effects of Chan-Su in anti-infective therapy.

MicroRNAs Constitute a Negative Feedback Loop in Streptococcus pneumoniae-Induced Macrophage Activation

Streptococcus pneumoniae causes high mortality as a major pneumonia-inducing pathogen. In pneumonia, control of innate immunity is necessary to prevent organ damage. We assessed the role of microRNAs (miRNAs) as regulators in pneumococcal infection of human macrophages. Exposure of primary blood-derived human macrophages with pneumococci resulted in transcriptional changes in several gene clusters and a significant deregulation of 10 microRNAs. Computational network analysis retrieved miRNA-146a as one putatively important regulator of pneumococci-induced host cell activation. Its induction depended on bacterial structural integrity and was completely inhibited by blocking Toll-like receptor 2 (TLR-2) or depleting its mediator MyD88. Furthermore, induction of miRNA-146a release did not require the autocrine feedback of interleukin 1β and tumor necrosis factor α released from infected macrophages, and it repressed the TLR-2 downstream mediators IRAK-1 and TRAF-6, as well as the inflammatory factors cyclooxygenase 2 and interleukin 1β. In summary, pneumococci recognition induces a negative feedback loop, preventing excessive inflammation via miR-146a and potentially other miRNAs.

Inflammasome/IL-1β Responses to Streptococcal Pathogens

Inflammation mediated by the inflammasome and the cytokine IL-1β are some of the earliest and most important alarms to infection. These pathways are responsive to the virulence factors that pathogens use to subvert immune processes, and thus are typically activated only by microbes with potential to cause severe disease. Among the most serious human infections are those caused by the pathogenic streptococci, in part because these species numerous strategies for immune evasion. Since the virulence factor armament of each pathogen is unique, the role of IL-1β and the pathways leading to its activation varies for each infection. This review summarizes the role of IL-1β during infections caused by streptococcal pathogens, with emphasis on emergent mechanisms and concepts countering paradigms determined for other organisms.

Chitosan-based mucosal adjuvants: Sunrise on the ocean

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Metabolism and safety profile of chitosan and its derivatives on mucosal application.

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Mechanisms of chitosan as potent mucosal adjuvant.

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Different types and forms of chitosan in pre-clinical applications.

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Clinical perspectives.

Mucosal vaccination, which is shown to elicit systemic and mucosal immune responses, serves as a non-invasive and convenient alternative to parenteral administration, with stronger capability in combatting diseases at the site of entry. The exploration of potent mucosal adjuvants is emerging as a significant area, based on the continued necessity to amplify the immune responses to a wide array of antigens that are poorly immunogenic at the mucosal sites. As one of the inspirations from the ocean, chitosan-based mucosal adjuvants have been developed with unique advantages, such as, ability of mucosal adhesion, distinct trait of opening the junctions to allow the paracellular transport of antigen, good tolerability and biocompatibility, which guaranteed the great potential in capitalizing on their application in human clinical trials. In this review, the state of art of chitosan and its derivatives as mucosal adjuvants, including thermo-sensitive chitosan system as mucosal adjuvant that were newly developed by author's group, was described, as well as the clinical application perspective. After a brief introduction of mucosal adjuvants, chitosan and its derivatives as robust immune potentiator were discussed in detail and depth, in regard to the metabolism, safety profile, mode of actions and preclinical and clinical applications, which may shed light on the massive clinical application of chitosan as mucosal adjuvant.

The lung communication network

The different types of cells in the lung, from the conducting airway epithelium to the alveolar epithelium and the pulmonary vasculature, are interconnected by gap junctions. The specific profile of gap junction proteins, the connexins, expressed in these different cell types forms compartments of intercellular communication that can be further shaped by the release of extracellular nucleotides via pannexin1 channels. In this review, we focus on the physiology of connexins and pannexins and describe how this lung communication network modulates lung function and host defenses in conductive and respiratory airways.

Loss of Interleukin 1 Receptor Antagonist Enhances Susceptibility to Ebola Virus Infection

The current outbreak of Ebola virus (EBOV) infection in West Africa is unprecedented, with nearly 26 000 confirmed cases and >10 000 deaths. Comprehensive data on the pathogenesis of EBOV infection are lacking; however, recent studies suggested that fatal EBOV infections are characterized by dysregulation of the innate immune response and a subsequent cytokine storm. Specifically, several studies suggested that hypersecretion of interleukin 1 receptor antagonist (IL-1Ra) correlates with lethal EBOV infections. To examine the significance of IL-1Ra in EBOV infections, we infected mice that lack the gene encoding IL-1Ra, Il1rn (IL-1RN-KO), and mice with wild-type Il1rn (IL-1RN-WT) with a mouse-adapted EBOV (MA-EBOV). Infected IL-1RN-KO mice lost more weight and had a lower survival rate than IL-1RN-WT mice infected with MA-EBOV. In addition, IL-1RN-KO mice infected with wild-type EBOV, which does not cause lethal infection in adult immunocompetent mice, such as C57BL/6 mice, experienced greater weight loss than IL-1RN-WT mice infected with wild-type EBOV. Further studies revealed that the levels of 6 cytokines in spleens-IL-1α, IL-1β, interleukin 12p40, interleukin 17, granulocyte colony-stimulating factor, and regulated on activation, normal T-cell expressed and secreted-were significantly different between IL-1RN-KO mice and IL-1RN-WT mice infected with MA-EBOV. Collectively, our data suggest that IL-1Ra may have a protective effect upon EBOV infection, likely by damping an overactive proinflammatory immune response.

Sensing of interleukin-1 cytokines during Streptococcus pneumoniae colonization contributes to macrophage recruitment and bacterial clearance

Streptococcus pneumoniae (the pneumococcus), a leading cause of bacterial disease, is most commonly carried in the human nasopharynx. Colonization induces inflammation that promotes the organism's growth and transmission. This inflammatory response is dependent on intracellular sensing of bacterial components that access the cytosolic compartment via the pneumococcal pore-forming toxin pneumolysin. In vitro, cytosolic access results in cell death that includes release of the proinflammatory cytokine interleukin-1β (IL-1β). IL-1 family cytokines, including IL-1β, are secreted upon activation of inflammasomes, although the role of this activation in the host immune response to pneumococcal carriage is unknown. Using a murine model of pneumococcal nasopharyngeal colonization, we show that mice deficient in the interleukin-1 receptor type 1 (Il1r1(-/-)) have reduced numbers of neutrophils early after infection, fewer macrophages later in carriage, and prolonged bacterial colonization. Moreover, intranasal administration of Il-1β promoted clearance. Macrophages are the effectors of clearance, and characterization of macrophage chemokines in colonized mice revealed that Il1r1(-/-) mice have lower expression of the C-C motif chemokine ligand 6 (CCL6), correlating with reduced macrophage recruitment to the nasopharynx. IL-1 family cytokines are known to promote adaptive immunity; however, we observed no difference in the development of humoral or cellular immunity to pneumococcal colonization between wild-type and Il1r1(-/-) mice. Our findings show that sensing of IL-1 cytokines during colonization promotes inflammation without immunity, which may ultimately benefit the pneumococcus.

Degradation products of the extracellular pathogen Streptococcus pneumoniae access the cytosol via its pore-forming toxin

Streptococcus pneumoniae is a leading pathogen with an extracellular lifestyle; however, it is detected by cytosolic surveillance systems of macrophages. The innate immune response that follows cytosolic sensing of cell wall components results in recruitment of additional macrophages, which subsequently clear colonizing organisms from host airways. In this study, we monitored cytosolic access by following the transit of the abundant bacterial surface component capsular polysaccharide, which is linked to the cell wall. Confocal and electron microscopy visually characterized the location of cell wall components in murine macrophages outside membrane-bound organelles. Quantification of capsular polysaccharide through cellular fractionation demonstrated that cytosolic access of bacterial cell wall components is dependent on phagocytosis, bacterial sensitivity to the host’s degradative enzyme lysozyme, and release of the pore-forming toxin pneumolysin. Activation of p38 mitogen-activated protein kinase (MAPK) signaling is important for limiting access to the cytosol; however, ultimately, these are catastrophic events for both the bacteria and the macrophage, which undergoes cell death. Our results show how expression of a pore-forming toxin ensures the death of phagocytes that take up the organism, although cytosolic sensing results in innate immune detection that eventually allows for successful host defense. These findings provide an example of how cytosolic access applies to an extracellular microbe and contributes to its pathogenesis.

Importance Streptococcus pneumoniae (the pneumococcus) is a bacterial pathogen that is a leading cause of pneumonia. Pneumococcal disease is preceded by colonization of the nasopharynx, which lasts several weeks before being cleared by the host’s immune system. Although S. pneumoniae is an extracellular microbe, intracellular detection of pneumococcal components is critical for bacterial clearance. In this study, we show that following bacterial uptake and degradation by phagocytes, pneumococcal products access the host cell cytosol via its pore-forming toxin. This phenomenon of cytosolic access results in phagocyte death and may serve to combat the host cells responsible for clearing the organism. Our results provide an example of how intracellular access and subsequent immune detection occurs during infection with an extracellular pathogen.

Streptococcus pneumoniae (the pneumococcus) is a bacterial pathogen that is a leading cause of pneumonia. Pneumococcal disease is preceded by colonization of the nasopharynx, which lasts several weeks before being cleared by the host’s immune system. Although S. pneumoniae is an extracellular microbe, intracellular detection of pneumococcal components is critical for bacterial clearance. In this study, we show that following bacterial uptake and degradation by phagocytes, pneumococcal products access the host cell cytosol via its pore-forming toxin. This phenomenon of cytosolic access results in phagocyte death and may serve to combat the host cells responsible for clearing the organism. Our results provide an example of how intracellular access and subsequent immune detection occurs during infection with an extracellular pathogen.

Increased expression of interleukin (IL)-35 and IL-17, but not IL-27, in gingival tissues with chronic periodontitis

BACKGROUND

Interleukin (IL)-35 plays an important role in immune regulation through the suppression of effector T-cell populations, including T-helper 17 (Th17) cells. Although Th17 cells and IL-17 are involved in the pathogenesis of periodontitis, the level of IL-35 in inflamed periodontal tissues is unclear. Here, IL-35, IL-17, and IL-27 production/expression in gingival crevicular fluid (GCF) and human gingival tissue were investigated.

METHODS

GCF samples were collected from buccal (mesial, center, and distal) sites of teeth from patients with chronic periodontitis (CP) and healthy controls and were analyzed by enzyme-linked immunosorbent assay for IL-35 (periodontitis, n = 36; healthy, n = 30) and IL-17 (periodontitis, n = 16; healthy, n = 13). Gingival tissue, including sulcus/pocket epithelium and underlying connective tissue, was collected from an additional 10 healthy participants and 10 patients with CP and were analyzed by quantitative polymerase chain reaction (qPCR) for Epstein Barr virus-induced gene 3 (EBI3), IL12A, and IL17A. IL27p28 was also tested by qPCR.

RESULTS

IL-35 and IL-17 were significantly higher in GCF from patients with periodontitis than healthy participants (P <0.01, P <0.05, respectively). In both healthy participants and those with periodontitis, positive correlations were found among IL-35 and probing depth and clinical attachment level (CAL) as well as between IL-17 and CAL. EBI3, IL12A (components of IL-35), and IL17A messenger RNA expression levels were significantly higher in inflamed gingival tissue than in healthy control tissues (P <0.05). IL27p28 was not detected in any sample, suggesting that IL-27 is not produced in large quantities in periodontal tissue.

CONCLUSION

IL-35 and IL-17, but not IL-27, may play important roles in the pathogenesis of periodontitis.

MicroRNA-155 is required for clearance of Streptococcus pneumoniae from the nasopharynx

Pneumonia caused by Streptococcus pneumoniae is a major cause of death and an economic burden worldwide. S. pneumoniae is an intermittent colonizer of the human upper respiratory tract, and the ability to control asymptomatic colonization determines the likelihood of developing invasive disease. Recognition of S. pneumoniae by resident macrophages via Toll-like receptor 2 (TLR-2) and the macrophage receptor with collagenous structure (MARCO) and the presence of interleukin-17 (IL-17)-secreting CD4(+) T cells are required for macrophage recruitment and bacterial clearance. Despite the fact that the primary cellular effectors needed for bacterial clearance have been identified, much of the underlying regulatory mechanisms are unknown. Herein, we demonstrate that the small, noncoding RNA microRNA-155 (mir-155) is critical for the effective clearance of S. pneumoniae. Our studies show that mir-155-deficient mice maintain the ability to prevent acute invasive pneumococcal infection but have significantly higher bacterial burdens following colonization, independently of macrophage recognition by TLR-2, MARCO expression, or bactericidal capacity. The observed defects in bacterial clearance parallel reduced IL-17A and gamma interferon CD4(+) T-cell responses in vivo, lower IL-17A mRNA levels in the nasopharynx, and a reduced capacity to induce Th17 cell polarization. Given that knockout mice are also limited in the capacity to generate high-titer S. pneumoniae-specific antibodies, we conclude that mir-155 is a critical mediator of the cellular effectors needed to clear primary and secondary S. pneumoniae colonizations.

The interleukin-1β/CXCL1/2/neutrophil axis mediates host protection against group B streptococcal infection

Previous studies have indicated that group B streptococcus (GBS), a frequent human pathogen, potently induces the release of interleukin-1β (IL-1β), an important mediator of inflammatory responses. Since little is known about the role of this cytokine in GBS disease, we analyzed the outcome of infection in IL-1β-deficient mice. These animals were markedly sensitive to GBS infection, with most of them dying under challenge conditions that caused no deaths in wild-type control mice. Lethality was due to the inability of the IL-1β-deficient mice to control local GBS replication and dissemination to target organs, such as the brain and the kidneys. Moreover, in a model of inflammation induced by the intraperitoneal injection of killed GBS, a lack of IL-1β was associated with selective impairment in the production of the neutrophil chemokines CXCL1 and CXCL2 and in neutrophil recruitment to the peritoneal cavity. Decreased blood neutrophil counts and impaired neutrophil recruitment to the brain and kidneys were also observed during GBS infection in IL-1β-deficient mice concomitantly with a reduction in CXCL1 and CXCL2 tissue levels. Notably, the hypersusceptibility to GBS infection observed in the immune-deficient animals was recapitulated by neutrophil depletion with anti-Gr1 antibodies. Collectively, our data identify a cytokine circuit that involves IL-1β-induced production of CXCL1 and CXCL2 and leads the recruitment of neutrophils to GBS infection sites. Moreover, our data point to an essential role of these cells in controlling the progression and outcome of GBS disease.

Probenecid reduces infection and inflammation in acute Pseudomonas aeruginosa pneumonia

The activation of inflammasome signaling mediates pathology of acute Pseudomonas aeruginosa pneumonia. This suggests that the inflammasome might represent a target to limit the pathological consequences of acute P. aeruginosa lung infection. Pannexin-1 (Px1) channels mediate the activation of caspase-1 and release of IL-1β induced by P2X7 receptor activation. The approved drug probenecid is an inhibitor of Px1 and ATP release. In this study, we demonstrate that probenecid reduces infection and inflammation in acute P. aeruginosa pneumonia. Treatment of mice prior to infection with P. aeruginosa resulted in an enhanced clearance of P. aeruginosa and reduced levels of inflammatory mediators, such as IL-1β. In addition, probenecid inhibited the release of inflammatory mediators in murine alveolar macrophages and human U937 cell-derived macrophages upon bacterial infection but not in human bronchial epithelial cells. Thus, Px1 blockade via probenecid treatment may be a therapeutic option in P. aeruginosa pneumonia by improving bacterial clearance and reducing negative consequences of inflammation.

Type I interferon signaling regulates activation of the absent in melanoma 2 inflammasome during Streptococcus pneumoniae infection

Streptococcus pneumoniae, a Gram-positive bacterial pathogen, causes pneumonia, meningitis, and septicemia. Innate immune responses are critical for the control and pathology of pneumococcal infections. It has been demonstrated that S. pneumoniae induces the production of type I interferons (IFNs) by host cells and that type I IFNs regulate resistance and chemokine responses to S. pneumoniae infection in an autocrine/paracrine manner. In this study, we examined the effects of type I IFNs on macrophage proinflammatory cytokine production in response to S. pneumoniae. The production of interleukin-18 (IL-18), but not other cytokines tested, was significantly decreased by the absence or blockade of the IFN-α/β receptor, suggesting that type I IFN signaling is necessary for IL-18 production. Type I IFN signaling was also required for S. pneumoniae-induced activation of caspase-1, a cysteine protease that plays a central role in maturation and secretion of IL-18. Earlier studies proposed that the AIM2 and NLRP3 inflammasomes mediate caspase-1 activation in response to S. pneumoniae. From our results, the AIM2 inflammasome rather than the NLRP3 inflammasome seemed to require type I IFN signaling for its optimal activation. Consistently, AIM2, but not NLRP3, was upregulated in S. pneumoniae-infected macrophages in a manner dependent on the IFN-α/β receptor. Furthermore, type I IFN signaling was found to contribute to IL-18 production in pneumococcal pneumonia in vivo. Taken together, these results suggest that type I IFNs regulate S. pneumoniae-induced activation of the AIM2 inflammasome by upregulating AIM2 expression. This study revealed a novel role for type I IFNs in innate responses to S. pneumoniae.