Caspase-1 dependent IL-1β secretion is critical for host defense in a mouse model of Chlamydia pneumoniae lung infection

TLR4-mediated endoplasmic reticulum stress regulates pyroptosis in macrophages infected with the Bacillus Calmette-Guérin mycobacterial

Tuberculosis results from Mycobacterium tuberculosis (Mtb) infection. Immune responses controlled by Toll-like receptor 4 (TLR4) are closely associated with the host response to pathogens, including Mtb. NLRP3 inflammasome-mediated pyroptosis forms a significant part of the inflammatory response during Mtb infection, and endoplasmic reticulum stress (ERS) is implicated in the activation of the NLRP3 inflammasome. Here, the function of TLR4 in macrophage pyroptosis induced by infection with the Bacillus Calmette-Guérin (BCG) mycobacterial strain was investigated. It was found that infection with BCG activated TLR4 signaling, induced ERS and subsequent NLRP3 inflammasome activation, leading to pyroptosis in mouse lung tissues. The TLR4 inhibitor TAK 242 inhibited the ERS onset, NLRP3 inflammasome stimulation, and pyroptosis, while the ERS inhibitor TUDCA blocked both inflammasome activation and pyroptosis, and the NLRP3 inhibitor MCC950 specifically inhibited pyroptosis. Furthermore, TAK 242, TUDCA, and MCC950 all exacerbated lung injury caused by BCG infection and promoted BCG survival. Similarly, after in BCG-infected THP-1 macrophages, TLR4 signaling was found to mediate NLRP3 inflammasome activation through ERS, thereby inducing pyroptosis. In summary, BCG infection leads to macrophage pyroptosis via the TLR4/ERS/NLRP3 inflammasome signaling axis, providing new insights for further research into the pathogenesis and treatment of tuberculosis.

Chlamydia pneumoniae in Alzheimer's disease pathology

While recent advances in diagnostics and therapeutics offer promising new approaches for Alzheimer's disease (AD) diagnosis and treatment, there is still an unmet need for an effective remedy, suggesting new avenues of research are required. Besides many plausible etiologies for AD pathogenesis, mounting evidence supports a possible role for microbial infections. Various microbes have been identified in the postmortem brain tissues of human AD patients. Among bacterial pathogens in AD, Chlamydia pneumoniae (Cp) has been well characterized in human AD brains and is a leading candidate for an infectious involvement. However, no definitive studies have been performed proving or disproving Cp's role as a causative or accelerating agent in AD pathology and cognitive decline. In this review, we discuss recent updates for the role of Cp in human AD brains as well as experimental models of AD. Furthermore, based on the current literature, we have compiled a list of potential mechanistic pathways which may connect Cp with AD pathology.

Sex-dependent vulnerability for Wistar rats model following intranasal instillation with Klebsiella pneumoniae ATCC 43816 causing lobar pneumonia

BACKGROUND

Klebsiella pneumoniae has become one of the major threats to public health as it causes nosocomial and community-acquired infections like lobar pneumonia. This infection causes acute inflammation in the lung, characterized by the recruitment of polymorphonuclear cells, generating free radicals, and decreasing the endogenous antioxidant balance system. Many experimental studies have focused on the induction, progression and resolution of infection up to its peak, but these documented processes remain highly random and their sex dependence un-elicited. These fluctuations of physiopathological parameters would impact disease progression depending on the animal's model and bacterial strain used. The present study investigated the sex-dependent vulnerability of Wistar rats to K. pneumoniae ATCC 43816 lobar pneumonia induced by the intranasal instillation method.

METHODS

Experimental pneumonia was induced by K. pneumoniae ATCC 43816 in male and female Wistar rats following intranasal instillation. The physiopathogenesis of the disease was studied by bacteriological and histopathological exams, histomorphometric analysis of the blood and/or lung tissue, and body weight loss in infected animals. In addition, the overall severity of lesions was determined by the total score obtained by averaging the individual scores from the same group of animals.

RESULTS

The K. pneumoniae ATCC 43816 strain showed inoculation dose-, incubation time of the disease- and sex-dependent- differences in its ability to induce lobar pneumonia. Evaluation of different parameters showed that the disease peaked on day 15 post-inoculation, with more pathogenic effects on female rats. This observed sex-dependence difference in Wistar rats was mainly highlighted by the determined lethal dose 50 (LD50), bacterial load count in whole blood and lung tissues, body weight loss, inflammatory granulomas forming and diffuse alveolar damages. The pathogenicity was confirmed by scoring the severity of pathologic lesions of lung tissues.

CONCLUSIONS

The results obtained highlighted the gender-dependency in the physiopathogenesis processes of K. pneumoniae ATCC 43816 induced-lobar pneumonia, in Wistar rats. Female Wistar rats' susceptibility is useful in studying pathology and in preclinical trial investigations of new treatments for infectious pneumonia.

Two-pore potassium channel TREK-1 (K2P2.1) regulates NLRP3 inflammasome activity in macrophages

Because of the importance of potassium efflux in inflammasome activation, we investigated the role of the two-pore potassium (K2P) channel TREK-1 in macrophage inflammasome activity. Using primary alveolar macrophages (AMs) and bone marrow-derived macrophages (BMDMs) from wild-type (wt) and TREK-1-/- mice, we measured responses to inflammasome priming [using lipopolysaccharide (LPS)] and activation (LPS + ATP). We measured IL-1β, caspase-1, and NLRP3 via ELISA and Western blot. A membrane-permeable potassium indicator was used to measure potassium efflux during ATP exposure, and a fluorescence-based assay was used to assess changes in membrane potential. Inflammasome activation induced by LPS + ATP increased IL-1β secretion in wt AMs, whereas activation was significantly reduced in TREK-1-/- AMs. Priming of BMDMs using LPS was not affected by either genetic deficiency or pharmacological inhibition of TREK-1 with Spadin. Cleavage of caspase-1 following LPS + ATP treatment was significantly reduced in TREK-1-/- BMDMs. The intracellular potassium concentration in LPS-primed wt BMDMs was significantly lower compared with TREK-1-/- BMDMs or wt BMDMs treated with Spadin. Conversely, activation of TREK-1 with BL1249 caused a decrease in intracellular potassium in wt BMDMs. Treatment of LPS-primed BMDMs with ATP caused a rapid reduction in intracellular potassium levels, with the largest change observed in TREK-1-/- BMDMs. Intracellular K+ changes were associated with changes in the plasma membrane potential (Em), as evidenced by a more depolarized Em in TREK-1-/- BMDMs compared with wt, and Em hyperpolarization upon TREK-1 channel opening with BL1249. These results suggest that TREK-1 is an important regulator of NLRP3 inflammasome activation in macrophages.NEW & NOTEWORTHY Because of the importance of potassium efflux in inflammasome activation, we investigated the role of the two-pore potassium (K2P) channel TREK-1 in macrophage inflammasome activity. Using primary alveolar macrophages and bone marrow-derived macrophages from wild-type and TREK-1-/- mice, we measured responses to inflammasome priming (using LPS) and activation (LPS + ATP). Our results suggest that TREK-1 is an important regulator of NLRP3 inflammasome activation in macrophages.

The pathogenicity and immune effects of different generations of Mycoplasma synoviae on chicken embryos

1. Mycoplasma synoviae (MS) is the primary causative agent of synovitis in avian species. In order to investigate the pathogenicity and immunological responses associated with MS in specific pathogen-free chicken embryos, a series of generations (F1, F95, F120, F160 and F200) of MS were introduced into 7-day-old SPF chicken embryos and subsequent mortality rates were recorded and analysed2. Reverse transcription-quantitative polymerase chain reaction was performed to detect expression of heat shock proteins HSP27, HSP40, HSP60, HSP70 and HSP90 and inflammatory factors interleukin (IL)-1β, caspase-1 and IL-18 in the tracheal tissue.3. The results showed that the mortality rate of SPF chicken embryos decreased with an increase in the number of passages, with the highest being 80% (8/10) for F1 generation and the lowest being 10% (1/10) for F200. The expression of HSP27, IL-1β, HSP40, caspase-1, HSP70 and HSP90 showed a significant downregulation trend with an increase in the generation (except IL-18; P < 0.05). The HSP60 expression was significantly upregulated with increasing generations (P < 0.05).4. A relationship between pathogenicity and the number of passages was observed and the decrease in pathogenicity appeared to be associated with HSP and genes related to inflammatory factors. The present work offers a scientific foundation for screening potential MS strains that might be employed to develop attenuated vaccines.

Roles of pattern recognition receptors in response to fungal keratitis

Fungal keratitis is one of the leading causes of blindness worldwide, which has become an increasingly serious threat to public ocular health, but no effective treatment strategies are available now. Pattern recognition receptors (PRRs) of the innate immune system are the first line of host defense against fungal infections. They could recognize pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) and trigger an array of inflammatory responses. Over the last decades, research has resulted in significant progress regarding the roles of PRRs in fungal keratitis. This review will highlight the importance of several pattern recognition receptors (C-type lectin-like receptors, Toll-like receptors, and NOD-like receptors) in regulating the innate immunity under fungal keratitis and describe the crosstalk and collaboration in PRRs contributing to disease pathology. Meanwhile, some potential therapy-based PRRs against corneal fungal infections are discussed.

Past Exposure to Cigarette Smoke Aggravates Cognitive Impairment in a Rat Model of Vascular Dementia via Neuroinflammation

Smoking is a risk factor for dementia. Cognitive function can be partially restored after quitting smoking, but still lower than never smoked group. The underlying mechanisms still remain unclear. The effects of smoking cessation combined with cerebral chronic hypoperfusion (CCH) on cognitive function have never been described. Here, we established a cigarette smoking cessation model, a CCH model, and a cigarette smoking cessation plus CCH model. We investigated cognitive function in these models and the mechanisms of the neuroinflammation, nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3(NLRP3)/cysteine aspartate-specific proteinase (caspase-1)/interleukin- 1β (IL-1β) pathway, and eucaryotic initiation factor 2α (eIF2α) /autophagy pathway. We used morris water maze (MWM) and novel object recognition (NOR) test to evaluate cognitive function in rats. Nissl staining was performed to observe cell morphology in the hippocampal CA1 area. A neuroinflammatory marker (glial fibrillary acidic protein, GFAP) was assessed by Western blot analysis and immunohistochemistry staining. IL-1β levels were detected by ELISA. The protein levels of NLRP3/caspase-1/ IL-1β and eIF2α/autophagy pathway were evaluated by Western blot analysis. LC3 was assessed by immunofluorescence staining. CCH can affect cognitive function by influencing neuroinflammation, NLRP3/caspase-1/IL-1β pathway, and eIF2α/autophagy pathway. Past exposure to cigarette smoke can also affect cognitive function by influencing neuroinflammation and NLRP3/caspase-1/IL-1β pathway, which may be induced by smoking and may not be alleviated after smoking cessation. Past exposure to cigarette smoke does not influence autophagy, which may be increased by smoking and then decrease to normal levels after smoking cessation. Past exposure to smoking can further aggravate cognitive impairment and neuroinflammation in VaD animals: cognitive impairment induced by CCH via neuroinflammation, NLRP3/caspase-1/IL-1β, and eIF2α/autophagy pathway and cognitive impairment induced by past exposure to cigarette smoke via neuroinflammation and NLRP3/caspase-1/IL-1β pathway. The combined group had the worst cognitive impairment because of harmful reasons.

Traditional Medicinal Plants—A Possible Source of Antibacterial Activity on Respiratory Diseases Induced by Chlamydia pneumoniae, Haemophilus influenzae, Klebsiella pneumoniae and Moraxella catarrhalis

Background. Nowadays, phytotherapy offers viable solutions in managing respiratory infections, disorders known for considerable incidence in both children and adults. In a context in which more and more people are turning to phytotherapy, finding new remedies is a topical goal of researchers in health and related fields. This paper aims to identify those traditional medicinal plants that show potentially antibacterial effects against four Gram-negative germs (Chlamydia pneumoniae, Haemophilus influenzae, Klebsiella pneumoniae, and Moraxella catarrhalis), which are considered to have high involvement in respiratory infections. Furthermore, a comparison with Romanian folk medicines was performed. Methods. An extensive review of books and databases was undertaken to identify vegetal species of interest in the context of the topic. Results. Some traditional Romanian species (such as Mentha × piperita, Thymus vulgaris, Pinus sylvestris, Allium sativum, Allium cepa, Ocimum basilicum, and Lavandulaangustifolia) were identified and compared with the plants and preparations confirmed as having antibacterial effects against specific germs. Conclusions. The antibacterial effects of some traditionally used Romanian medicinal plants are poorly investigated, and deserve further attention.

Chlamydia pneumoniae and Helicobacter pylori infections and immunological profile of community-dwelling older adults

Chronic bacterial infections are associated with changes in the immunosenescence process and immunological biomarkers can assist in monitoring these changes. The identification of this immunological profile is important because Chlamydia pneumoniae (C. pneumoniae) and Helicobacter pylori (H. pylori) infections are important factors of morbidity and mortality among the older adults. This study aimed to identify changes in the immunological profile in the presence of C. pneumoniae and H. pylori infections among community-dwelling older adults. This is a cross-sectional study that used data from 1432 participants from the Bambuí Cohort Study of Aging, Minas Gerais, Brazil. The presence of immunoglobulin G (IgG) for C. pneumoniae and H. pylori was considered a dependent variable and assessed in the participants' serum using the enzyme-linked immunosorbent assay (ELISA). In assessing the immunological profile, the following inflammatory markers were considered: CXCL8, CXCL9, CXCL10, CCL2, CCL5, IL-1β, IL-6, IL-10, IL-12, TNF, and CRP. Associations were assessed by logistic regression, estimating odds ratios and confidence intervals (95%) using the Stata® V.13.1 software. The seroprevalence of anti-C. pneumoniae and anti-H. pylori antibodies was 55.9% and 70.3%, respectively. While high levels of anti-C. pneumoniae antibodies were associated with higher concentrations of CXCL10 and IL-10, higher levels of IL-1β and IL-6 were inversely associated with the titration of anti-H. pylori antibodies. The results characterize immunological profiles associated with these chronic infections and reinforce the potential effects of biomarkers on infections by these bacteria and on the immunosenescence process.

Chlamydia evasion of neutrophil host defense results in NLRP3 dependent myeloid-mediated sterile inflammation through the purinergic P2X7 receptor

Chlamydia trachomatis infection causes severe inflammatory disease resulting in blindness and infertility. The pathophysiology of these diseases remains elusive but myeloid cell-associated inflammation has been implicated. Here we show NLRP3 inflammasome activation is essential for driving a macrophage-associated endometritis resulting in infertility by using a female mouse genital tract chlamydial infection model. We find the chlamydial parasitophorous vacuole protein CT135 triggers NLRP3 inflammasome activation via TLR2/MyD88 signaling as a pathogenic strategy to evade neutrophil host defense. Paradoxically, a consequence of CT135 mediated neutrophil killing results in a submucosal macrophage-associated endometritis driven by ATP/P2X7R induced NLRP3 inflammasome activation. Importantly, macrophage-associated immunopathology occurs independent of macrophage infection. We show chlamydial infection of neutrophils and epithelial cells produce elevated levels of extracellular ATP. We propose this source of ATP serves as a DAMP to activate submucosal macrophage NLRP3 inflammasome that drive damaging immunopathology. These findings offer a paradigm of sterile inflammation in infectious disease pathogenesis.

Host cell death during infection with Chlamydia: a double-edged sword

The phylum Chlamydiae constitutes a group of obligate intracellular bacteria that infect a remarkably diverse range of host species. Some representatives are significant pathogens of clinical or veterinary importance. For instance, Chlamydia trachomatis is the leading infectious cause of blindness and the most common bacterial agent of sexually transmitted diseases. Chlamydiae are exceptionally dependent on their eukaryotic host cells as a consequence of their developmental biology. At the same time, host cell death is an integral part of the chlamydial infection cycle. It is therefore not surprising that the bacteria have evolved exquisite and versatile strategies to modulate host cell survival and death programs to their advantage. The recent introduction of tools for genetic modification of Chlamydia spp., in combination with our increasing awareness of the complexity of regulated cell death in eukaryotic cells, and in particular of its connections to cell-intrinsic immunity, has revived the interest in this virulence trait. However, recent advances also challenged long-standing assumptions and highlighted major knowledge gaps. This review summarizes current knowledge in the field and discusses possible directions for future research, which could lead us to a deeper understanding of Chlamydia's virulence strategies and may even inspire novel therapeutic approaches.

Avoidance of the NLRP3 Inflammasome by the Stealth Pathogen, Coxiella burnetii

Coxiella burnetii, a highly adapted obligate intracellular bacterial pathogen and the cause of the zoonosis Q fever, is a reemerging public health threat. C. burnetii employs a Type IV secretion system (T4SS) to establish and maintain its intracellular niche and modulate host immune responses including the inhibition of apoptosis. Interactions between C. burnetii and caspase-1-mediated inflammasomes are not fully elucidated. This study confirms that C. burnetii does not activate caspase-1 during infection of mouse macrophages in vitro. C. burnetii-infected cells did not develop NLRP3 and ASC foci indicating its ability to avoid cytosolic detection. C. burnetii is unable to inhibit the pyroptosis and IL-1β secretion that is induced by potent inflammasome stimuli but rather enhances these caspase-1-mediated effects. We found that C. burnetii upregulates pro-IL-1β and robustly primes NLRP3 inflammasomes via TLR2 and MyD88 signaling. As for wildtype C. burnetii, T4SS-deficient mutants primed and potentiated NLRP3 inflammasomes. An in vivo model of pulmonary infection in C57BL/6 mice was developed. Mice deficient in NLRP3 or caspase-1 were like wildtype mice in the development and resolution of splenomegaly due to red pulp hyperplasia, and histologic lesions and macrophage kinetics, but had slightly higher pulmonary bacterial burdens at the greatest measured time point. Together these findings indicate that C. burnetii primes but avoids cytosolic detection by NLRP3 inflammasomes, which are not required for the clinical resistance of C57BL/6 mice. Determining mechanisms employed by C. burnetii to avoid cytosolic detection via NLRP3 inflammasomes will be beneficial to the development of preventative and interventional therapies for Q fever.

FXR/TGR5 mediates inflammasome activation and host resistance to bacterial infection

Bacterial infections are a major cause of chronic infections and mortality. Innate immune control is crucial for protection against bacterial pathogens. Bile acids facilitate intestinal absorption of lipid-soluble nutrients and modulate various metabolic pathways through the farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5 (TGR5). Here, we identified a new role of FXR and TGR5 in promoting inflammasome activation during bacterial infection. Caspase-1/11 activation and release of cleaved interleukin (IL)-1β in FXR- and TGR5-deficient mouse bone marrow-derived macrophages upon Listeria monocytogenes or Escherichia coli infection was significantly reduced. In contrast, FXR- or TGR5-deficiency did not affect the transcription of caspase-1/11 and IL-1β. Inflammasome activation is critical for host immune defense against bacterial infections. Consistent with this, the deletion of FXR or TGR5 impaired effective clearance of L. monocytogenes or E. coli in vitro and in vivo, which was associated with greater mortality and bacterial burden than that of wild-type mice. Pretreatment with an FXR agonist decreased bacterial burden in vitro and increased survival in vivo. Thus, FXR and TGR5 promote inflammasome-mediated antimicrobial responses and may represent novel antibacterial therapeutic targets.

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FXR- or TGR5-deficiency decreases inflammasome activation upon Listeria monocytogenes or Escherichia coli infection.

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FXR- or TGR5-deficiency impaired effective clearance of L. monocytogenes or E. coli.

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FXR and TGR5 promote inflammasome-mediated antimicrobial responses.

Oxidative Stress and Inflammation in SARS-CoV-2- and Chlamydia pneumoniae-Associated Cardiovascular Diseases

Throughout the years, a growing number of studies have provided evidence that oxidative stress and inflammation may be involved in the pathogenesis of infectious agent-related cardiovascular diseases. Amongst the numerous respiratory pathogens, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel coronavirus responsible for the global ongoing pandemic, and Chlamydia pneumoniae, a widely known intracellular obligate bacteria, seem to have an essential role in promoting reactive oxygen species and cytokine production. The present review highlights the common oxidative and inflammatory molecular pathways underlying the cardiovascular diseases associated with SARS-CoV-2 or C. pneumoniae infections. The main therapeutic and preventive approaches using natural antioxidant compounds will be also discussed.

Insights Into Host Cell Cytokines in Chlamydia Infection

Chlamydial infection causes a number of clinically relevant diseases and induces significant morbidity in humans. Immune and inflammatory responses contribute to both the clearance of Chlamydia infection and pathology in host tissues. Chlamydia infection stimulates host cells to produce a large number of cytokines that trigger and regulate host immune responses against Chlamydia. However, inappropriate responses can occur with excessive production of cytokines, resulting in overreactive inflammatory responses and alterations in host or Chlamydia metabolism. As a result, Chlamydia persists and causes wound healing delays, leading to more severe tissue damage and triggering long-lasting fibrotic sequelae. Here, we summarize the roles of cytokines in Chlamydia infection and pathogenesis, thus advancing our understanding chlamydial infection biology and the pathogenic mechanisms involved.

The Purinergic P2X7 Receptor-NLRP3 Inflammasome Pathway: A New Target in Alcoholic Liver Disease?

The World Health Organization has estimated that approximately 3 million deaths are attributable to alcohol consumption each year. Alcohol consumption is notably associated with the development and/or progression of many non-communicable inflammatory diseases-particularly in the liver. Although these alcoholic liver diseases were initially thought to be caused by the toxicity of ethanol on hepatocytes, the latest research indicates Kupffer cells (the liver macrophages) are at the heart of this "inflammatory shift". Purinergic signaling (notably through P2X7 receptors and the NLRP3 inflammasome) by Kupffer cells appears to be a decisive factor in the pathophysiology of alcoholic liver disease. Hence, the modulation of purinergic signaling might represent a new means of treating alcoholic liver disease. Here, we review current knowledge on the pathophysiology of alcoholic liver diseases and therapeutic perspectives for targeting these inflammatory pathways.

Purinergic signalling in host innate immune defence against intracellular pathogens

Purinergic signalling is an evolutionarily conserved signalling pathway mediated by extracellular nucleotides and nucleosides. Tri- and diphosphonucleotides released from host cells during intracellular pathogen infections activate plasma membrane purinergic type 2 receptors (P2 receptors) that stimulate microbicidal mechanisms in host innate immune cells. P2X ion channels and P2Y G protein-coupled receptors are involved in activating host innate immune defence mechanisms, phagocytosis, phagolysosomal fusion, production of reactive species, acidification of parasitophorous vacuoles, inflammasome activation, and the release of cytokines, chemokines, and other inflammatory mediators. In this review, as part of a special issue in tribute to Geoffrey Burnstock, we discuss advances in understanding the importance of P2 receptors in the host antimicrobial innate mechanisms against intracellular pathogen infections.

The effects of maternal separation stress experienced by parents on male reproductive potential in the next generation

There is little information available about the effects of early-life parental stress on the reproductive potential of the next generation. The aim of this study is to examine the reproductive potential of male mice whose parents experienced maternal separation stress. In the present study, male first-generation offspring from parents were undergone of maternal separation (MS) were examined. Sperm characteristics, histological changes in testis, reactive oxygen species (ROS) production, expression of apoptotic and inflammatory genes and proteins were assessed. Findings showed that MS experienced by parents significantly decreased the morphology and viability of spermatozoa. Furthermore, significant changes in testicular tissue histology were observed. Increased production of ROS, decreased glutathione peroxidase (GPX) and adenosine triphosphate (ATP) concentrations, and affected the expression of genes and cytokines involved in inflammation. Finally, the mean percentage of caspase-1 and NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) positive cells was significantly higher in first-generation group. MS experienced by parents may negatively affect the reproduction of first generation offspring.

Insights into the toll-like receptors in sexually transmitted infections

Toll-like receptors (TLRs) are like soldiers of an innate immune system, which protects vital biological processes against invading pathogens. TLR signalling pathways help in the removal of pathogens and mediate well-established inflammatory processes. However, these processes may also aid in the development or augmentation of an infection or an autoimmune disease. Recent studies have delineated TLR polymorphism's role in the loss of function, making hosts more resistant or vulnerable to the development of an infection. In this review, we have discussed the association of TLRs with sexually transmitted infections (STIs), especially to the pathogen-specific ligands. We have also assessed the impact on TLR downstream signalling and the maintenance of cellular homeostasis during immune responses. Besides, we have discussed the role of TLRs single nucleotide polymorphisms in various STIs. Since TLRs are known to play a part in defence mechanisms and in aiding infections therefore, a thorough understanding of TLRs structure and molecular mechanisms is required to explain how they can influence the outcome of an STI. Such a strategy may lead to the development of novel and useful immunotherapeutic approaches to control pathogen progression and prevent transmission.

Oxidative stress, inflammatory reactions and apoptosis mediated the negative effect of chronic stress induced by maternal separation on the reproductive system in male mice

Exposure to severe and long-lasting stressors during early postnatal life negatively affects development of the brain and associated biological networks. Maternal separation (MS) is a valid stressful experience in early life that adversely affects neurobiological circuits. In the present study, we aimed to evaluate the effects of MS on sperm quality and histology of the testis in adult male mice. In this study, male mice were subjected to MS during post-natal days (PND) 2-14. Sperm parameters, histological alterations in the testicular tissue, ROS production (using DCFH-DA assay), gene expression of TLR4, NLRP3, TNFα, BAX, ASC, caspase-1 and BCL-2 (using RT-PCR), protein levels of caspase-3 and caspase-8 (using western blotting), and protein levels of IL-1β, IL-18, GPx and ATP (using ELISA) as well as protein expression of caspase-1 and NLRP3 (using immunocytochemistry) were evaluated. Findings showed that MS decreased count, morphology and viability of spermatozoa. MS decreased the diameter of seminiferous tubules and decreased the thickness of seminiferous epithelium. Furthermore, MS increased the level of ROS production and decreased the concentrations of GPx and ATP. MS led to increased expression of TLR4, NlRP3, TNFα, caspase-1, ASC, IL-1β and IL-18. In addition, MS induced apoptosis as evidenced by increased BAX, caspase-3 and caspase-8 as well as decreased BCL-2 expression. We concluded that early life stress induced by MS has detrimental effects on sperm parameters and testicular tissue. Our results suggest that these effects are mediated by activation of ROS production, and alterations in mitochondrial function, inflammatory processes and apoptosis pathways.

Antibiotic treatment of Chlamydia-induced cystitis in the koala is linked to expression of key inflammatory genes in reactive oxygen pathways

Chlamydial-induced cystitis in the koala (Phascolarctos cinereus) is currently treated by antibiotics. However, while reducing the chlamydial load, this treatment can also lead to gastrointestinal complications and death. Development of alternative treatments, such as a therapeutic chlamydial vaccine, are hindered by the lack of detailed understanding of the innate immune response to chlamydial clearance and disease regression during antibiotic treatment. Through clinical, microbiological and transcriptomic approaches, disease regression, bacterial clearance and innate immune responses were mapped in koalas with signs of chlamydial-induced cystitis while receiving anti-chlamydial antibiotics. Significant reduction in the signs of cystitis were observed during and post antibiotic treatment. This was observed as a thinning of the bladder wall and complete reversal of urinary incontinence. Transcriptomic analysis before treatment, at the end of treatment and prior to release identified significant down-regulation of specific genes involved in 21 biological pathways. Of these, the chemokine receptor signalling and NOD-like receptor signalling pathways where identified as important markers of inflammation. Specific genes within these pathways (NCF1 and NOX2) were significantly down-regulated, suggesting a decrease in reactive oxygen species production. Through the monitoring of specific clinical and transcriptomic markers, these findings allow detailed profiling of the clinical response to therapeutic vaccination in koalas with current signs of disease. This also adds to our understanding of innate immune responses to chlamydial infections and indicates that chlamydial-induced cystitis in the koala is linked to the regulation of reactive oxygen pathways.

Chlamydia and Lipids Engage a Common Signaling Pathway That Promotes Atherogenesis

BACKGROUND

Recent studies indicate that Toll-like receptor 4 (TLR4) and myeloid differentiation factor 88 (MyD88) signaling promote the development of high fat diet-induced atherosclerosis in hypercholesterolemic mice.

OBJECTIVES

The authors investigated the role of TLR4/MyD88 signaling in hematopoietic and stromal cells in the development and infection-mediated acceleration of atherosclerosis.

METHODS

The authors generated bone marrow chimeras between wild-type and Tlr4^-/- mice, as well as wild-type and Myd88^-/- mice. All mice were on the Apoe^-/- background and fed high fat diet. The authors infected the chimeric mice with C. pneumoniae (CP) and fed them high fat diet.

RESULTS

Aortic sinus plaques and lipid content were significantly reduced in Apoe^-/- mice that received Tlr4^-/-or Myd88^-/- bone marrow compared with control animals despite similar cholesterol levels. Similarly, Tlr4 or Myd88 deficiency in stromal cells also led to a reduction in the lesion area and lipid in aortic sinus plaques. MyD88 expression only in CD11c+ dendritic cells (myeloid cells) in cells was sufficient in otherwise MyD88-deficient mice to induce CP infection-mediated acceleration of atherosclerosis, underlining the key role of MyD88 in CD11c+ dendritic cells (myeloid cells). Whereas CP infection markedly accelerated atherosclerosis in TLR4- or MyD88-positive chimeras, CP infection had a minimal effect on atherosclerosis in TLR4- or MyD88-deficient mice (either in the hematopoietic or stromal cell compartments).

CONCLUSIONS

The authors show that both CP infection and metabolic stress associated with dyslipidemia use the same innate immune response pathway, utilizing TLR4/MyD88 signaling, with similar relative contributions in bone marrow-derived hematopoietic cells and in stromal cells. Further studies are required to understand this intricate and complex cross talk among innate and adaptive immune systems in various conditions to more effectively design dendritic cell-mediated atheroprotective vaccines and other therapeutic strategies.

Autophagy Limits Inflammasome During Chlamydia pneumoniae Infection

Autophagy can either antagonize or promote intracellular bacterial growth, depending on the pathogen. Here, we investigated the role of autophagy during a pulmonary infection with the obligate intracellular pathogen, Chlamydia pneumoniae (CP). In mouse embryonic fibroblasts (MEFs) or macrophages, deficiency of autophagy pathway components led to enhanced CP replication, suggesting that autophagy exerts a bactericidal role. However, in vivo, mice with myeloid-specific deletion of the autophagic protein ATG16L1 suffered increased mortality during CP infection, neutrophilia, and increased inflammasome activation despite no change in bacterial burden. Induction of autophagy led to reduced CP replication in vitro, but impaired survival in CP-infected mice, associated with an initial reduction in IL-1β production, followed by enhanced neutrophil recruitment, defective CP clearance, and later inflammasome activation and IL-1β production, which drove the resulting mortality. Taken together, our data suggest that a delicate interplay exists between autophagy and inflammasome activation in determining the outcome of CP infection, perturbation of which can result in inflammatory pathology or unrestricted bacterial growth.

Chlamydia pneumoniae is present in the dental plaque of periodontitis patients and stimulates an inflammatory response in gingival epithelial cells

Chlamydia pneumoniae is an airborne, Gram-negative, obligate intracellular bacterium which causes human respiratory infections and has been associated with atherosclerosis. Because individuals with periodontitis are at greater risk for atherosclerosis as well as respiratory infections, we in-vestigated the role of C. pneumoniae in inflammation and periodontal dis-ease. We found that C. pneumoniae was more frequently found in subgingival dental plaque obtained from periodontally diseased sites of the mouth versus healthy sites. The known periodontal pathogens, Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, were also found in the plaque. In addition, C. pneumoniae could efficiently invade human gingival epithelial cells (GECs) in vitro, causing translocation of NF-κB to the nucleus along with increased secretion of mature IL-1β cytokine. Supernatants collected from C. pneumoniae-infected GECs showed increased activation of caspase-1 protein, which was significantly reduced when nlrp3 gene expression was silenced using shRNA lentiviral vectors. Our results demonstrate that C. pneumoniae was found in higher levels in periodontitis patients compared to control pa-tients. Additionally, C. pneumoniae could infect GECs, leading to inflammation caused by activation of NF-κB and the NLRP3 inflammasome. We propose that the presence of C. pneumoniae in subgingival dental plaque may contribute to periodontal disease and could be used as a potential risk indicator of perio-dontal disease.

Differential role of the NLRP3 inflammasome in infection and tumorigenesis

Dysregulated inflammation is one of the hallmarks of cancer initiation and progression. Emerging evidence indicates that inflammasomes play a central role in regulating immune cell functions in various infections and cancer. Inflammasomes are multimeric complexes consisting of nucleotide-binding oligomerization domain (NOD) -like receptors (NLRs). Among the NLRs, NOD1, NOD2 and NLRP3 respond to a variety of endogenous (i.e. damage-associated molecular patterns) and exogenous (i.e. pathogen-associated molecular patterns) stimuli. The NLRP3 inflammasome is associated with the onset and progression of autoinflammatory and autoimmune diseases, including metabolic disorders, multiple sclerosis, inflammatory bowel disease, and cryopyrin-associated periodic fever syndrome. NLRP3 is also associated with a wide variety of infections and tumorigenesis that are closely correlated with chemotherapy response and prognosis. In this review, we explore the rapidly expanding body of research on the expression and functions of NLRP3 in infections and cancers and outline novel inhibitors targeting the NLRP3 inflammasome that could be developed as therapeutic alternatives to current anticancer treatment.

Pharmacological Effects and Mechanisms of Chinese Medicines Modulating NLRP3 Inflammasomes in Ischemic Cardio/Cerebral Vascular Disease

Cardio/cerebral-vascular diseases seriously threaten human health and are the leading cause of death. As such, there is great interest in identifying a potential mechanism that controls the development process of cardio/cerebral vascular diseases. Present studies demonstrate that inflammasomes play an important role in the process of ischemic cardio/cerebral vascular diseases (ICCVDs). Among the pathological process of ICCVDs, inflammasomes activated the sterile inflammatory response that accelerated the development of diseases and aggravated the acute lesion of tissue. As the most thoroughly studied inflammasome, the NLRP3 inflammasome has been proven to be a potential therapeutic target for ICCVDs. In this review, we summarized the mechanisms of Chinese herbal medicine which can affect ICCVDs via the regulation of the NLRP3 inflammasome. Our study discovers that active compounds of Chinese medicines have a negative effect on NLRP3 in different ICCVDs models. Astragaloside IV may influence the receptor of the cell membrane to inhibit NLRP3 activation. Resveratrol, colchicinesis, salvianolic acid B, chrysophanol and sulforaphane may directly damage the formation of NLRP3 by inhibiting ASC or Caspase-1. Most of the active natural compounds can negatively regulate the downstream products of NLRP3 inflammasome such as IL-18 and IL1 β . In addition, Chinese medicines such as sinomenine, ruscogenin, resveratrol, arctigenin and cepharanthineas may downregulate NLRP3 inflammasome by inducing autophagy activation. Due to the advantages of multi-target effects, Chinese herbal medicine can be treated as a splendid therapy for ICCVDs by inhibiting NLRP3 inflammasome.

T-Cell-Intrinsic Receptor Interacting Protein 2 Regulates Pathogenic T Helper 17 Cell Differentiation

Receptor interacting protein 2 (RIP2) plays a role in sensing intracellular pathogens, but its function in T cells is unclear. We show that RIP2 deficiency in CD4+ T cells resulted in chronic and severe interleukin-17A-mediated inflammation during Chlamydia pneumoniae lung infection, increased T helper 17 (Th17) cell formation in lungs of infected mice, accelerated atherosclerosis, and more severe experimental autoimmune encephalomyelitis. While RIP2 deficiency resulted in reduced conventional Th17 cell differentiation, it led to significantly enhanced differentiation of pathogenic (p)Th17 cells, which was dependent on RORα transcription factor and interleukin-1 but independent of nucleotide oligomerization domain (NOD) 1 and 2. Overexpression of RIP2 resulted in suppression of pTh17 cell differentiation, an effect mediated by its CARD domain, and phenocopied by a cell-permeable RIP2 CARD peptide. Our data suggest that RIP2 has a T cell-intrinsic role in determining the balance between homeostatic and pathogenic Th17 cell responses.

Cytosolic Recognition of Microbes and Pathogens: Inflammasomes in Action

Infection is a dynamic biological process underpinned by a complex interplay between the pathogen and the host. Microbes from all domains of life, including bacteria, viruses, fungi, and protozoan parasites, have the capacity to cause infection. Infection is sensed by the host, which often leads to activation of the inflammasome, a cytosolic macromolecular signaling platform that mediates the release of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18 and cleavage of the pore-forming protein gasdermin D, leading to pyroptosis. Host-mediated sensing of the infection occurs when pathogens inject or carry pathogen-associated molecular patterns (PAMPs) into the cytoplasm or induce damage that causes cytosolic liberation of danger-associated molecular patterns (DAMPs) in the host cell. Recognition of PAMPs and DAMPs by inflammasome sensors, including NLRP1, NLRP3, NLRC4, NAIP, AIM2, and Pyrin, initiates a cascade of events that culminate in inflammation and cell death. However, pathogens can deploy virulence factors capable of minimizing or evading host detection. This review presents a comprehensive overview of the mechanisms of microbe-induced activation of the inflammasome and the functional consequences of inflammasome activation in infectious diseases. We also explore the microbial strategies used in the evasion of inflammasome sensing at the host-microbe interaction interface.

Chlamydia pneumoniae Hijacks a Host Autoregulatory IL-1β Loop to Drive Foam Cell Formation and Accelerate Atherosclerosis

Pathogen burden accelerates atherosclerosis, but the mechanisms remain unresolved. Activation of the NLRP3 inflammasome is linked to atherogenesis. Here we investigated whether Chlamydia pneumoniae (C.pn) infection engages NLRP3 in promoting atherosclerosis. C.pn potentiated hyperlipidemia-induced inflammasome activity in cultured macrophages and in foam cells in atherosclerotic lesions of Ldlr^-/- mice. C.pn-induced acceleration of atherosclerosis was significantly dependent on NLRP3 and caspase-1. We discovered that C.pn-induced extracellular IL-1β triggers a negative feedback loop to inhibit GPR109a and ABCA1 expression and cholesterol efflux, leading to accumulation of intracellular cholesterol and foam cell formation. Gpr109a and Abca1 were both upregulated in plaque lesions in Nlrp3^-/- mice in both hyperlipidemic and C.pn infection models. Mature IL-1β and cholesterol may compete for access to the ABCA1 transporter to be exported from macrophages. C.pn exploits this metabolic-immune crosstalk, which can be modulated by NLRP3 inhibitors to alleviate atherosclerosis.

Multiple inflammasomes may regulate the interleukin-1-driven inflammation in protracted bacterial bronchitis

Protracted bacterial bronchitis (PBB) in young children is characterised by prolonged wet cough, prominent airway interleukin (IL)-1β expression and infection, often with nontypeable Haemophilus influenzae (NTHi). The mechanisms responsible for IL-1-driven inflammation in PBB are poorly understood.

We hypothesised that the inflammation in PBB involves the NLRP3 and/or AIM2 inflammasome/IL-1β axis. Lung macrophages obtained from bronchoalveolar lavage (BAL), peripheral blood mononuclear cells (PBMCs), blood monocytes and monocyte-derived macrophages from patients with PBB and age-matched healthy controls were cultured in control medium or exposed to live NTHi.

In healthy adult PBMCs, CD14⁺ monocytes contributed to 95% of total IL-1β-producing cells upon NTHi stimulation. Stimulation of PBB PBMCs with NTHi significantly increased IL-1β expression (p<0.001), but decreased NLRC4 expression (p<0.01). NTHi induced IL-1β secretion in PBMCs from both healthy controls and patients with recurrent PBB. This was inhibited by Z-YVAD-FMK (a caspase-1 selective inhibitor) and by MCC950 (a NLRP3 selective inhibitor). In PBB BAL macrophages inflammasome complexes were visualised as fluorescence specks of NLRP3 or AIM2 colocalised with cleaved caspase-1 and cleaved IL-1β. NTHi stimulation induced formation of specks of cleaved IL-1β, NLRP3 and AIM2 in PBMCs, blood monocytes and monocyte-derived macrophages.

We conclude that both the NLRP3 and AIM2 inflammasomes probably drive the IL-1β-dominated inflammation in PBB.

Airway IL-1β activation in protracted bacterial bronchitishttp://ow.ly/ut9r30iqim2

The P2X7 Receptor in Inflammatory Diseases: Angel or Demon?

Under physiological conditions, adenosine triphosphate (ATP) is present at low levels in the extracellular milieu, being massively released by stressed or dying cells. Once outside the cells, ATP and related nucleotides/nucleoside generated by ectonucleotidases mediate a high evolutionary conserved signaling system: the purinergic signaling, which is involved in a variety of pathological conditions, including inflammatory diseases. Extracellular ATP has been considered an endogenous adjuvant that can initiate inflammation by acting as a danger signal through the activation of purinergic type 2 receptors-P2 receptors (P2Y G-protein coupled receptors and P2X ligand-gated ion channels). Among the P2 receptors, the P2X7 receptor is the most extensively studied from an immunological perspective, being involved in both innate and adaptive immune responses. P2X7 receptor activation induces large-scale ATP release via its intrinsic ability to form a membrane pore or in association with pannexin hemichannels, boosting purinergic signaling. ATP acting via P2X7 receptor is the second signal to the inflammasome activation, inducing both maturation and release of pro-inflammatory cytokines, such as IL-1β and IL-18, and the production of reactive nitrogen and oxygen species. Furthermore, the P2X7 receptor is involved in caspases activation, as well as in apoptosis induction. During adaptive immune response, P2X7 receptor modulates the balance between the generation of T helper type 17 (Th17) and T regulatory (Treg) lymphocytes. Therefore, this receptor is involved in several inflammatory pathological conditions. In infectious diseases and cancer, P2X7 receptor can have different and contrasting effects, being an angel or a demon depending on its level of activation, cell studied, type of pathogen, and severity of infection. In neuroinflammatory and neurodegenerative diseases, P2X7 upregulation and function appears to contribute to disease progression. In this review, we deeply discuss P2X7 receptor dual function and its pharmacological modulation in the context of different pathologies, and we also highlight the P2X7 receptor as a potential target to treat inflammatory related diseases.

Inhibitors of Apoptosis Protein Antagonists (Smac Mimetic Compounds) Control Polarization of Macrophages during Microbial Challenge and Sterile Inflammatory Responses

Apoptosis is a physiological cell death process essential for development, tissue homeostasis, and for immune defense of multicellular animals. Inhibitors of apoptosis proteins (IAPs) regulate apoptosis in response to various cellular assaults. Using both genetic and pharmacological approaches we demonstrate here that the IAPs not only support opportunistic survival of intracellular human pathogens like Chlamydia pneumoniae but also control plasticity of iNOS+ M1 macrophage during the course of infection and render them refractory for immune stimulation. Treatment of Th1 primed macrophages with birinapant (IAP-specific antagonist) inhibited NO generation and relevant proteins involved in innate immune signaling. Accordingly, birinapant promoted hypoxia, angiogenesis, and tumor-induced M2 polarization of iNOS+ M1 macrophages. Interestingly, birinapant-driven changes in immune signaling were accompanied with changes in the expression of various proteins involved in the metabolism, and thus revealing the new role of IAPs in immune metabolic reprogramming in committed macrophages. Taken together, our study reveals the significance of IAP targeting approaches (Smac mimetic compounds) for the management of infectious and inflammatory diseases relying on macrophage plasticity.

Inflammasome in the Pathogenesis of Pulmonary Diseases

Lung diseases are common and significant causes of illness and death around the world. Inflammasomes have emerged as an important regulator of lung diseases. The important role of IL-1 beta and IL-18 in the inflammatory response of many lung diseases has been elucidated. The cleavage to turn IL-1 beta and IL-18 from their precursors into the active forms is tightly regulated by inflammasomes. In this chapter, we structurally review current evidence of inflammasome-related components in the pathogenesis of acute and chronic lung diseases, focusing on the "inflammasome-caspase-1-IL-1 beta/IL-18" axis.

New concepts in Chlamydia induced inflammasome responses

Since the concept of the inflammasome was introduced by Martinon, Burns and Tschopp in 2002, there has been an exponential increase in our understanding of how inflammasomes (caspase activating molecular platforms) regulate innate inflammatory responses to infectious microorganisms. Advances in understanding inflammasome biology have been developed using a range of bacterial pathogens. Recent studies investigating inflammasome responses during Chlamydia infection have provided interesting mechanistic insights in to inflammasome activation during intracellular bacterial infection. This review highlights new concepts regulating inflammasome activation to bacterial infections including: interferon-regulated loss of compartmentalisation, mechanisms of canonical and non-canonical inflammasome activation and their relevance to Chlamydia infections are discussed.

The emerging role of ASC in dendritic cell metabolism during Chlamydia infection

Chlamydia trachomatis is a bacterial agent that causes sexually transmitted infections worldwide. The regulatory functions of dendritic cells (DCs) play a major role in protective immunity against Chlamydia infections. Here, we investigated the role of ASC in DCs metabolism and the regulation of DCs activation and function during Chlamydia infection. Following Chlamydia stimulation, maturation and antigen presenting functions were impaired in ASC^-/- DCs compared to wild type (WT) DCs, in addition, ASC deficiency induced a tolerant phenotype in Chlamydia stimulated DCs. Using real-time extracellular flux analysis, we showed that activation in Chlamydia stimulated WT DCs is associated with a metabolic change in which mitochondrial oxidative phosphorylation (OXPHOS) is inhibited and the cells become committed to utilizing glucose through aerobic glycolysis for differentiation and antigen presenting functions. However, in ASC^-/- DCs Chlamydia-induced metabolic change was prevented and there was a significant effect on mitochondrial morphology. The mitochondria of Chlamydia stimulated ASC^-/- DCs had disrupted cristae compared to the normal narrow pleomorphic cristae found in stimulated WT DCs. In conclusion, our results suggest that Chlamydia-mediated activation of DCs is associated with a metabolic transition in which OXPHOS is inhibited, thereby dedicating the DCs to aerobic glycolysis, while ASC deficiency disrupts DCs function by inhibiting the reprogramming of DCs metabolism within the mitochondria, from glycolysis to electron transport chain.

Growth of Chlamydia pneumoniae Is Enhanced in Cells with Impaired Mitochondrial Function

Effective growth and replication of obligate intracellular pathogens depend on host cell metabolism. How this is connected to host cell mitochondrial function has not been studied so far. Recent studies suggest that growth of intracellular bacteria such as Chlamydia pneumoniae is enhanced in a low oxygen environment, arguing for a particular mechanistic role of the mitochondrial respiration in controlling intracellular progeny. Metabolic changes in C. pneumoniae infected epithelial cells were analyzed under normoxic (O₂ ≈ 20%) and hypoxic conditions (O₂ < 3%). We observed that infection of epithelial cells with C. pneumoniae under normoxia impaired mitochondrial function characterized by an enhanced mitochondrial membrane potential and ROS generation. Knockdown and mutation of the host cell ATP synthase resulted in an increased chlamydial replication already under normoxic conditions. As expected, mitochondrial hyperpolarization was observed in non-infected control cells cultured under hypoxic conditions, which was beneficial for C. pneumoniae growth. Taken together, functional and genetically encoded mitochondrial dysfunction strongly promotes intracellular growth of C. pneumoniae.

Inflammasomes, the eye and anti-inflammasome therapy

Inflammasomes, key molecular regulators that play an important role in inflammation, consist of a central protein, an adaptor protein ASC (apoptosis speck-like protein) and a caspase-1 protein. Upon activation, caspase-1 induces maturation of cytokines such as interleukin-1β (IL-1β) and interleukin-18 (IL-18). The release of these cytokines can result in inflammation. Inflammasomes are activated by a variety of factors and their activation involves complex signalling leading to resolution of infection, but can also contribute to the pathology of inflammatory, autoimmune, and infectious diseases. The role of NLRP1, NLRP3, NLRC4 and AIM2 inflammasomes in the pathogenesis of ocular diseases such as glaucoma, age related macular degeneration (AMD), diabetic retinopathy, dry eye and infections of the eye has been established over the past decade. In experimental studies and models, inhibition of inflammasomes generally helps to reduce the inflammation associated with these eye diseases, but as yet the role of these inflammasomes in many human eye diseases is unknown. Therefore, a need exists to study and understand various aspects of inflammasomes and their contribution to the pathology of human eye diseases. The goal of this review is to discuss the role of inflammasomes in the pathology of eye diseases, scope for anti-inflammasome therapy, and current research gaps in inflammasome-related eye disease.

Detection of a microbial metabolite by STING regulates inflammasome activation in response to Chlamydia trachomatis infection

The innate immune system is a critical component of host defence against microbial pathogens, but effective responses require an ability to distinguish between infectious and non-infectious insult to prevent inappropriate inflammation. Using the important obligate intracellular human pathogen Chlamydia trachomatis; an organism that causes significant immunopathology, we sought to determine critical host and pathogen factors that contribute to the induction of inflammasome activation. We assayed inflammasome activation by immunoblotting and ELISA to detect IL-1β processing and LDH release to determine pyroptosis. Using primary murine bone marrow derived macrophages or human monocyte derived dendritic cells, infected with live or attenuated Chlamydia trachomatis we report that the live organism activates both canonical and non-canonical inflammasomes, but only canonical inflammasomes controlled IL-1β processing which preceded pyroptosis. NADPH oxidase deficient macrophages were permissive to Chlamydia trachomatis replication and displayed elevated type-1 interferon and inflammasome activation. Conversely, attenuated, non-replicating Chlamydia trachomatis, primed but did not activate inflammasomes and stimulated reduced type-1 interferon responses. This suggested bacterial replication or metabolism as important factors that determine interferon responses and inflammasome activation. We identified STING but not cGAS as a central mediator of interferon regulated inflammasome activation. Interestingly, exogenous delivery of a Chlamydia trachomatis metabolite and STING ligand—cyclic di-AMP, recovered inflammasome activation to attenuated bacteria in a STING dependent manner thus indicating that a bacterial metabolite is a key factor initiating inflammasome activation through STING, independent of cGAS. These data suggest a potential mechanism of how the innate immune system can distinguish between infectious and non-infectious insult and instigate appropriate immune responses that could be therapeutically targeted.

Innate responses to bacterial infection such as Chlamydia trachomatis activate inflammasomes to enable the processing of IL-1β, IL-18 and the induction of an inflammatory form of cell death termed pyroptosis. Inflammasomes are crucial to host defence but require tight regulation in order to prevent inappropriate inflammation and immunopathology. Here, we demonstrate that the pro-inflammatory potential of an attenuated strain of Chlamydia trachomatis, that fails to activate the inflammasome, can be rescued by the addition of a bacterial metabolite. The requirement for this metabolite, highlights a novel mechanism of inflammasome regulation and reveals a crucial role for STING mediated interferon signalling independent of cGAS. These findings further our understanding of how the innate immune system can differentiate between potential infectious and non-infectious threats and mount appropriate immune responses.

Quercetin Inhibits Inflammasome Activation by Interfering with ASC Oligomerization and Prevents Interleukin-1 Mediated Mouse Vasculitis

Interleukin-1β (IL-1β) is a highly inflammatory cytokine that significantly contributes to both acute and chronic inflammatory diseases. The secretion of IL-1β requires a unique protease, caspase-1, which is activated by various protein platforms called inflammasomes. Data suggests a key role for mitochondrial reactive oxygen species for inflammasome activation. Flavonoids constitute a group of naturally occurring polyphenolic molecules with many biological activities, including antioxidant effects. In this study, we investigated the effect of three flavonoids, quercetin (QUC), naringenin, and silymarim on inflammasome activation. We found that QUC inhibits IL-1β secretion by both the NLRP3 and AIM2 inflammasome in a dose dependent manner, but not the NLRC4 inflammasome. QUC inhibition of the inflammasome was still observed in Atg16l1 knockout macrophages, indicating that QUC’s effect was autophagy independent. Since QUC inhibited both NLRP3 and AIM2 inflammasomes but not NLRC4, we assessed ASC speck formation. QUC reduced ASC speck formation and ASC oligomerization compared with controls. Additionally, QUC inhibited IL-1β in Cryopyrin-Associated Periodic Syndromes (CAPS) macrophages, where NLRP3 inflammasome is constitutively activated. In conclusion, QUC inhibits both the NLRP3 and AIM2 inflammasome by preventing ASC oligomerization and may be a potential therapeutic candidate for Kawasaki disease vasculitis and other IL-1 mediated inflammatory diseases.

NLRP3 inflammasome mediates interleukin-1β production in immune cells in response to Acinetobacter baumannii and contributes to pulmonary inflammation in mice

Acinetobacter baumannii is a multi-drug resistant, Gram-negative bacteria and infection with this organism is one of the major causes of mortality in intensive care units. Inflammasomes are multiprotein oligomers that include caspase-1, and their activation is required for maturation of interleukin-1β (IL-1β). Inflammasome signalling is involved in host defences against various microbial infections, but the precise mechanism by which A. baumannii activates inflammasomes and the roles of relevant signals in host defence against pulmonary A. baumannii infection are unknown. Our results showed that NLRP3, ASC and caspase-1, but not NLRC4, are required for A. baumannii-induced production of IL-1β in macrophages. An inhibitor assay revealed that various pathways, including P2X7R, K⁺ efflux, reactive oxygen species production and release of cathepsins, are involved in IL-1β production in macrophages in response to A. baumannii. Interleukin-1β production in bronchoalveolar lavage (BAL) fluid was impaired in NLRP3-deficient and caspase-1/11-deficient mice infected with A. baumannii, compared with that in wild-type (WT) mice. However, the bacterial loads in BAL fluid and lungs were comparable between WT and NLRP3-deficient or caspase-1/11-deficient mice. The severity of lung pathology was reduced in NLRP3- deficient, caspase-1/11- deficient and IL-1-receptor-deficient mice, although the recruitment of immune cells and production of inflammatory cytokines and chemokines were not altered in these mice. These findings indicate that A. baumannii leads to the activation of NLRP3 inflammasome, which mediates IL-1β production and lung pathology.

Ugonin U stimulates NLRP3 inflammasome activation and enhances inflammasome-mediated pathogen clearance

The NOD-like receptor pyrin domain 3 (NLRP3) inflammasome contains Nod-like receptors, a subclass of pattern recognition receptors, suggesting that this complex has a prominent role in host defenses. Various structurally diverse stimulators activate the NLRP3 inflammasome through different signaling pathways. We previously reported that ugonin U (UgU), a natural flavonoid isolated from Helminthostachys zeylanica (L) Hook, directly stimulates phospholipase C (PLC) and triggers superoxide release in human neutrophils. In the present study, we showed that UgU induced NLRP3 inflammasome assembly and subsequent caspase-1 and interleukin (IL)-1β processing in lipopolysaccharide-primed human monocytes. Moreover, UgU elicited mitochondrial superoxide generation in a dose-dependent manner, and a specific scavenger of mitochondrial reactive oxygen species (ROS) diminished UgU-induced IL-1β and caspase-1 activation. UgU induced Ca²⁺ mobilization, which was inhibited by treatment with inhibitors of PLC or inositol triphosphate receptor (IP₃R). Blocking Ca²⁺ mobilization, PLC, or IP₃R diminished UgU-induced IL-1β release, caspase-1 activation, and mitochondrial ROS generation. These data demonstrated that UgU activated the NLPR3 inflammasome activation through Ca²⁺ mobilization and the production of mitochondrial ROS. We also demonstrated that UgU-dependent NLRP3 inflammasome activation enhanced the bactericidal function of human monocytes. The ability of UgU to stimulate human neutrophils and monocytes, both of which are professional phagocytes, and its capacity to activate the NLRP3 inflammasome, which is a promising molecular target for developing anti-infective medicine, indicate that UgU treatment should be considered as a possible novel therapy for treating infectious diseases.

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The immuno-stimulatory effects UgU in human monocytes were evaluated.

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UgU induces Ca²⁺ mobilization and eventually activates the NLRP3 inflammasome.

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UgU facilitates the bactericidal function of human monocytes.

Inflammasomes and Their Role in Innate Immunity of Sexually Transmitted Infections

Inflammasomes are multiprotein complexes present in the cytosol as pattern recognition receptors or as sensors of damage-associated molecular patterns. After recognition of microbe-associated molecular patterns or host-derived danger signals, nucleotide oligomerization domain-like receptors oligomerize to form inflammasomes. The activation of inflammasomes results in an alarm, which is raised to alert adjacent cells through the processing and release of a number of other substrates present in the cytosol. A wide array of inflammasomes and their adapter molecules have been identified in the host’s innate immune system in response to various pathogens. Components of specific pathogens activate different inflammasomes, which once activated in response to pathogen-induced infection, induce the activation of caspases, and the release of mature forms of interleukin-1β (IL-1β) and IL-18. Identifying the mechanisms underlying pathogen-induced inflammasome activation is important if we are to develop novel therapeutic strategies to target sexually transmitted infections (STIs) related pathogens. This information is currently lacking in literature. In this review, we have discussed the role of various inflammasomes in sensing different STIs, as well as the beneficial or detrimental effects of inflammasome signaling in host resistance. Additionally, we have discussed both canonical and non-canonical processing of IL-1β induced with respect to particular infections. Overall, these findings transform our understanding of both the basic biology and clinical relevance of inflammasomes.

The inflammasome: Friend or foe in Chlamydia infection?

In this issue of the Biomedical Journal, we take a look at the still somewhat perplexing role of the inflammasome in Chlamydia infection. We also highlight findings suggesting a link between structural changes to arteries in the brain and the onset of depression. Finally, we learn about some of the implications of co-morbidity between diabetes and infectious diseases.

Danger signals, inflammasomes, and the intricate intracellular lives of chlamydiae

Chlamydiae are obligate intracellular bacterial pathogens, and as such are sensitive to alterations in the cellular physiology of their hosts. Chlamydial infections often cause pathologic consequences due to prolonged localized inflammation. Considerable advances have been made in the last few years regarding our understanding of how two key inflammation-associated signaling pathways influence the biology of Chlamydia infections: inflammation regulating purinergic signaling pathways significantly impact intracellular chlamydial development, and inflammasome activation modulates both chlamydial growth and infection mediated pro-inflammatory cytokine production. We review here elements of both pathways, presenting the latest developments contributing to our understanding of how chlamydial infections are influenced by inflammasomes and purinergic signaling.

Impact of micro-environmental changes on respiratory tract infections with intracellular bacteria

Community-acquired pneumonia is caused by intra- and extracellular bacteria, with some of these bacteria also being linked to the pathogenesis of chronic lung diseases, including asthma and chronic obstructive pulmonary disease. Chlamydia pneumoniae is an obligate intracellular pathogen that is highly sensitive to micro-environmental conditions controlling both pathogen growth and host immune responses. The availability of nutrients, as well as changes in oxygen, pH and interferon-γ levels, have been shown to directly influence the chlamydial life cycle and clearance. Although the lung has been traditionally regarded as a sterile environment, sequencing approaches have enabled the identification of a large number of bacteria in healthy and diseased lungs. The influence of the lung microbiota on respiratory infections has not been extensively studied so far and data on chlamydial infections are currently unavailable. In the present study, we speculate on how lung microbiota might interfere with acute and chronic infections by focusing exemplarily on the obligate intracellular C. pneumoniae. Furthermore, we consider changes in the gut microbiota as an additional player in the control of lung infections, especially in view the increasing evidence suggesting the involvement of the gut microbiota in various immunological processes throughout the human body.

Integrating Inflammasome Signaling in Sexually Transmitted Infections

Inflammasomes are cytosolic multiprotein platforms with pivotal roles in infectious diseases. Activation of inflammasomes results in proinflammatory cytokine signaling and pyroptosis. Sexually transmitted infections (STIs) are a major health problem worldwide, yet few studies have probed the impact of inflammasome signaling during these infections. Due to the dearth of appropriate infection models, our current understanding of inflammasomes in STIs is mostly drawn from results obtained in vitro, from distant infection sites, or from related microbial strains that are not sexually transmitted. Understanding how inflammasomes influence the outcome of STIs may lead to the development of novel and effective strategies to control disease and prevent transmission. Here we discuss and highlight the recent progress in this field.

Neutrophils mediate Salmonella Typhimurium clearance through the GBP4 inflammasome-dependent production of prostaglandins

Inflammasomes are cytosolic molecular platforms that alert the immune system about the presence of infection. Here we report that zebrafish guanylate-binding protein 4 (Gbp4), an IFNγ-inducible GTPase protein harbouring a C-terminal CARD domain, is required for the inflammasome-dependent clearance of Salmonella Typhimurium (ST) by neutrophils in vivo. Despite the presence of the CARD domain, Gbp4 requires the universal inflammasome adaptor Asc for mediating its antibacterial function. In addition, the GTPase activity of Gbp4 is indispensable for inflammasome activation and ST clearance. Mechanistically, neutrophils are recruited to the infection site through the inflammasome-independent production of the chemokine (CXC motif) ligand 8 and leukotriene B4, and then mediate bacterial clearance through the Gbp4 inflammasome-dependent biosynthesis of prostaglandin D2. Our results point to GBPs as key inflammasome adaptors required for prostaglandin biosynthesis and bacterial clearance by neutrophils and suggest that transient activation of the inflammasome may be used to treat bacterial infections.

The role of guanylate-binding proteins (GBPs) in innate immunity is increasingly recognized. Here the authors show that GBP4 activates inflammasome in zebrafish neutrophils, and that this process is critical for the clearance of Salmonella infection via prostaglandin D2.

Regulation and Function of the Nucleotide Binding Domain Leucine-Rich Repeat-Containing Receptor, Pyrin Domain-Containing-3 Inflammasome in Lung Disease

Inflammasomes are specialized inflammatory signaling platforms that govern the maturation and secretion of proinflammatory cytokines, such as IL-1β and IL-18, through the regulation of caspase-1-dependent proteolytic processing. Several nucleotide binding domain leucine-rich repeat-containing receptor (NLR) family members (i.e., NLR family, pyrin domain containing [NLRP] 1, NLRP3, and NLR family, caspase recruitment domain containing-4 [NLRC4]) as well as the pyrin and hemopoietic expression, interferon-inducibility, nuclear localization domain-containing family member, absent in melanoma 2, can form inflammasome complexes in human cells. In particular, the NLRP3 inflammasome is activated in response to cellular stresses through a two-component pathway, involving Toll-like receptor 4-ligand interaction (priming) followed by a second signal, such as ATP-dependent P2X purinoreceptor 7 receptor activation. Emerging studies suggest that the NLRP3 inflammasome can exert pleiotropic effects in human diseases with potentially both pro- and antipathogenic sequelae. Whereas NLRP3 inflammasome activation can serve as a vital component of host defense against invading bacteria and pathogens, excessive activation of the inflammasome can lead to inflammation-associated tissue injury in the setting of chronic disease. In addition, pyroptosis, an inflammasome-associated mode of cell death, contributes to host defense. Recent research has described the regulation and function of the NLRP3 inflammasome in various pulmonary diseases, including acute lung injury and acute respiratory distress syndrome, sepsis, respiratory infections, chronic obstructive pulmonary disease, asthma, pulmonary hypertension, cystic fibrosis, and idiopathic pulmonary fibrosis. The NLRP3 and related inflammasomes, and their regulated cytokines or receptors, may represent novel diagnostic or therapeutic targets in pulmonary diseases and other diseases in which inflammation contributes to pathogenesis.