Microinvasion by Streptococcus pneumoniae induces epithelial innate immunity during colonisation at the human mucosal surface

The STING signaling pathways and bacterial infection

As antibiotic-resistant bacteria continue to emerge frequently, bacterial infections have become a significant and pressing challenge to global public health. Innate immunity triggers the activation of host responses by sensing "non-self" components through various pattern recognition receptors (PRRs), serving as the first line of antibacterial defense. Stimulator of interferon genes (STING) is a PRR that binds with cyclic dinucleotides (CDN) to exert effects against bacteria, viruses, and cancer by inducing the production of type I interferon and inflammatory cytokines, and facilitating regulated cell death. Currently, drugs targeting the STING signaling pathway are predominantly applied in the fields of modulating host immune defense against cancer and viral infections, with relatively limited application in treating bacterial infections. Given the significant immunomodulatory functions of STING in the interaction between bacteria and hosts, this review summarizes the research progress on STING signaling pathways and their roles in bacterial infection, as well as the novel functions of STING modulators, aiming to offer insights for the development of antibacterial drugs.

GOLPH3 knockdown alleviates the inflammation and apoptosis in lipopolysaccharide-induced acute lung injury by inhibiting Golgi stress mediated autophagy

Pneumonia, an acute inflammatory lesion of the lung, is the leading cause of death in children aged < 5 years. We aimed to study the function and mechanism of Golgi phosphoprotein 3 (GOLPH3) in infantile pneumonia. Lipopolysaccharide (LPS)-induced acute lung injury (ALI) mice and injury of MLE-12 cells were used as the pneumonia model in vitro. After GOLPH3 was knocked down, the histopathological changes of lung tissues were assessed by hematoxylin-eosin (H&E) staining. The Wet/Dry ratio of lung tissues was calculated. The enzyme-linked immunosorbent assay (ELISA) method was used to detecte the contents of inflammatory factors in bronchoalveolar lavage fluid (BALF). The damaged DNA in apoptotic cells in lung tissues was tested by Terminal deoxynucleotidyl transferase-mediated dUTP Nick end labeling (TUNEL) staining. Immunofluorescence staining analyzed LC3II and Golgi matrix protein 130 (GM130) expression in lung tissues and MLE-12 cells. The apoptosis of MLE-12 cells was measured by flow cytometry analysis. Additionally, the expression of proteins related to apoptosis, autophagy and Golgi stress was examined with immunoblotting. Results indicated that GOLPH3 knockdown alleviated lung tissue pathological changes in LPS-triggered ALI mice. LPS-induced inflammation and apoptosis in lung tissues and MLE-12 cells were remarkably alleviated by GOLPH3 deficiency. Besides, GOLPH3 depletion suppressed autophagy and Golgi stress in lung tissues and MLE-12 cells challenged with LPS. Moreover, Rapamycin (Rap), an autophagy inhibitor, counteracted inflammation and apoptosis inhibited by GOLPH3 silencing in LPS-induced MLE-12 cells. Furthermore, brefeldin A (BFA) pretreatment apparently abrogated the inhibitory effect of GOLPH3 knockdown on autophagy in MLE-12 cells exposed to LPS. To be concluded, GOLPH3 knockdown exerted lung protective effect against LPS-triggered inflammation and apoptosis by inhibiting Golgi stress mediated autophagy.

Inflammation of the nasal mucosa is associated with susceptibility to experimental pneumococcal challenge in older adults

Streptococcus pneumoniae colonization in the upper respiratory tract is linked to pneumococcal disease development, predominantly affecting young children and older adults. As the global population ages and comorbidities increase, there is a heightened concern about this infection. We investigated the immunological responses of older adults to pneumococcal-controlled human infection by analyzing the cellular composition and gene expression in the nasal mucosa. Our comparative analysis with data from a concurrent study in younger adults revealed distinct gene expression patterns in older individuals susceptible to colonization, highlighted by neutrophil activation and elevated levels of CXCL9 and CXCL10. Unlike younger adults challenged with pneumococcus, older adults did not show recruitment of monocytes into the nasal mucosa following nasal colonization. However, older adults who were protected from colonization showed increased degranulation of cluster of differentiation 8+ T cells, both before and after pneumococcal challenge. These findings suggest age-associated cellular changes, in particular enhanced mucosal inflammation, that may predispose older adults to pneumococcal colonization.

Blocking HXA3-mediated neutrophil elastase release during S. pneumoniae lung infection limits pulmonary epithelial barrier disruption and bacteremia

Streptococcus pneumoniae (Sp), a leading cause of community-acquired pneumonia, can spread from the lung into the bloodstream to cause septicemia and meningitis, with a concomitant threefold increase in mortality. Limitations in vaccine efficacy and a rise in antimicrobial resistance have spurred searches for host-directed therapies that target pathogenic immune processes. Polymorphonuclear leukocytes (PMNs) are essential for infection control but can also promote tissue damage and pathogen spread. The major Sp virulence factor, pneumolysin, triggers acute inflammation by stimulating the 12-lipoxygenase (12-LOX) eicosanoid synthesis pathway in epithelial cells. This pathway is required for systemic spread in a mouse pneumonia model and produces a number of bioactive lipids, including hepoxilin A3 (HXA3), a hydroxy epoxide PMN chemoattractant that has been hypothesized to facilitate breach of mucosal barriers. To understand how 12-LOX-dependent inflammation promotes dissemination during Sp lung infection and dissemination, we utilized bronchial stem cell-derived air-liquid interface cultures that lack this enzyme to show that HXA3 methyl ester (HXA3-ME) is sufficient to promote basolateral-to-apical PMN transmigration, monolayer disruption, and concomitant Sp barrier breach. In contrast, PMN transmigration in response to the non-eicosanoid chemoattractant N-formyl-L-methionyl-L-leucyl-phenylalanine (fMLP) did not lead to epithelial disruption or bacterial translocation. Correspondingly, HXA3-ME but not fMLP increased the release of neutrophil elastase (NE) from Sp-infected PMNs. Pharmacologic blockade of NE secretion or activity diminished epithelial barrier disruption and bacteremia after pulmonary challenge of mice. Thus, HXA3 promotes barrier-disrupting PMN transmigration and NE release, pathological events that can be targeted to curtail systemic disease following pneumococcal pneumonia.IMPORTANCEStreptococcus pneumoniae (Sp), a leading cause of pneumonia, can spread from the lung into the bloodstream to cause systemic disease. Limitations in vaccine efficacy and a rise in antimicrobial resistance have spurred searches for host-directed therapies that limit pathologic host immune responses to Sp. Excessive polymorphonuclear leukocyte (PMN) infiltration into Sp-infected airways promotes systemic disease. Using stem cell-derived respiratory cultures that reflect bona fide lung epithelium, we identified eicosanoid hepoxilin A3 as a critical pulmonary PMN chemoattractant that is sufficient to drive PMN-mediated epithelial damage by inducing the release of neutrophil elastase. Inhibition of the release or activity of this protease in mice limited epithelial barrier disruption and bacterial dissemination, suggesting a new host-directed treatment for Sp lung infection.

Blocking HXA3-mediated neutrophil elastase release during S. pneumoniae lung infection limits pulmonary epithelial barrier disruption and bacteremia

Streptococcus pneumoniae (Sp), a leading cause of community-acquired pneumonia, can spread from the lung into the bloodstream to cause septicemia and meningitis, with a concomitant three-fold increase in mortality. Limitations in vaccine efficacy and a rise in antimicrobial resistance have spurred searches for host-directed therapies that target pathogenic immune processes. Polymorphonuclear leukocytes (PMNs) are essential for infection control but can also promote tissue damage and pathogen spread. The major Sp virulence factor, pneumolysin (PLY), triggers acute inflammation by stimulating the 12-lipoxygenase (12-LOX) eicosanoid synthesis pathway in epithelial cells. This pathway is required for systemic spread in a mouse pneumonia model and produces a number of bioactive lipids, including hepoxilin A3 (HXA3), a hydroxy epoxide PMN chemoattractant that has been hypothesized to facilitate breach of mucosal barriers. To understand how 12-LOX-dependent inflammation promotes dissemination during Sp lung infection and dissemination, we utilized bronchial stem cell-derived air-liquid interface (ALI) cultures that lack this enzyme to show that HXA3 methyl ester (HXA3-ME) is sufficient to promote basolateral-to-apical PMN transmigration, monolayer disruption, and concomitant Sp barrier breach. In contrast, PMN transmigration in response to the non-eicosanoid chemoattractant fMLP did not lead to epithelial disruption or bacterial translocation. Correspondingly, HXA3-ME but not fMLP increased release of neutrophil elastase (NE) from Sp-infected PMNs. Pharmacologic blockade of NE secretion or activity diminished epithelial barrier disruption and bacteremia after pulmonary challenge of mice. Thus, HXA3 promotes barrier disrupting PMN transmigration and NE release, pathological events that can be targeted to curtail systemic disease following pneumococcal pneumonia.

Bacterial surface lipoproteins mediate epithelial microinvasion by Streptococcus pneumoniae

Streptococcus pneumoniae, a common colonizer of the upper respiratory tract, invades nasopharyngeal epithelial cells without causing disease in healthy participants of controlled human infection studies. We hypothesized that surface expression of pneumococcal lipoproteins, recognized by the innate immune receptor TLR2, mediates epithelial microinvasion. Mutation of lgt in serotype 4 (TIGR4) and serotype 6B (BHN418) pneumococcal strains abolishes the ability of the mutants to activate TLR2 signaling. Loss of lgt also led to the concomitant decrease in interferon signaling triggered by the bacterium. However, only BHN418 lgt::cm but not TIGR4 lgt::cm was significantly attenuated in epithelial adherence and microinvasion compared to their respective wild-type strains. To test the hypothesis that differential lipoprotein repertoires in TIGR4 and BHN418 lead to the intraspecies variation in epithelial microinvasion, we employed a motif-based genome analysis and identified an additional 525 a.a. lipoprotein (pneumococcal accessory lipoprotein A; palA) encoded by BHN418 that is absent in TIGR4. The gene encoding palA sits within a putative genetic island present in ~10% of global pneumococcal isolates. While palA was enriched in the carriage and otitis media pneumococcal strains, neither mutation nor overexpression of the gene encoding this lipoprotein significantly changed microinvasion patterns. In conclusion, mutation of lgt attenuates epithelial inflammatory responses during pneumococcal-epithelial interactions, with intraspecies variation in the effect on microinvasion. Differential lipoprotein repertoires encoded by the different strains do not explain these differences in microinvasion. Rather, we postulate that post-translational modifications of lipoproteins may account for the differences in microinvasion.IMPORTANCEStreptococcus pneumoniae (pneumococcus) is an important mucosal pathogen, estimated to cause over 500,000 deaths annually. Nasopharyngeal colonization is considered a necessary prerequisite for disease, yet many people are transiently and asymptomatically colonized by pneumococci without becoming unwell. It is therefore important to better understand how the colonization process is controlled at the epithelial surface. Controlled human infection studies revealed the presence of pneumococci within the epithelium of healthy volunteers (microinvasion). In this study, we focused on the regulation of epithelial microinvasion by pneumococcal lipoproteins. We found that pneumococcal lipoproteins induce epithelial inflammation but that differing lipoprotein repertoires do not significantly impact the magnitude of microinvasion. Targeting mucosal innate immunity and epithelial microinvasion alongside the induction of an adaptive immune response may be effective in preventing pneumococcal colonization and disease.

Impaired upper respiratory tract barrier function during postnatal development predisposes to invasive pneumococcal disease

Infants are highly susceptible to invasive respiratory and gastrointestinal infections. To elucidate the age-dependent mechanism(s) that drive bacterial spread from the mucosa, we developed an infant mouse model using the prevalent pediatric respiratory pathogen, Streptococcus pneumoniae (Spn). Despite similar upper respiratory tract (URT) colonization levels, the survival rate of Spn-infected infant mice was significantly decreased compared to adults and corresponded with Spn dissemination to the bloodstream. An increased rate of pneumococcal bacteremia in early life beyond the newborn period was attributed to increased bacterial translocation across the URT barrier. Bacterial dissemination in infant mice was independent of URT monocyte or neutrophil infiltration, phagocyte-derived ROS or RNS, inflammation mediated by toll-like receptor 2 or interleukin 1 receptor signaling, or the pore-forming toxin pneumolysin. Using molecular barcoding of Spn, we found that only a minority of bacterial clones in the nasopharynx disseminated to the blood in infant mice, indicating the absence of robust URT barrier breakdown. Rather, transcriptional profiling of the URT epithelium revealed a failure of infant mice to upregulate genes involved in the tight junction pathway. Expression of many such genes was also decreased in early life in humans. Infant mice also showed increased URT barrier permeability and delayed mucociliary clearance during the first two weeks of life, which corresponded with tighter attachment of bacteria to the respiratory epithelium. Together, these results demonstrate a window of vulnerability during postnatal development when altered mucosal barrier function facilitates bacterial dissemination.

The pharmacokinetics/pharmacodynamics of ceftazidime/avibactam for central nervous system infections caused by carbapenem-resistant Gram-negatives: a prospective study

OBJECTIVES

To describe the pharmacokinetics/pharmacodynamics (PK/PD) of ceftazidime/avibactam in critically ill patients with CNS infections.

METHODS

A prospective study of critically ill patients with CNS infections who were treated with ceftazidime/avibactam and the steady-state concentration (Css) of ceftazidime/avibactam in serum and/or CSF was conducted between August 2020 and May 2023. The relationship between PK/PD goal achievement, microbial eradication and the clinical efficacy of ceftazidime/avibactam was evaluated.

RESULTS

Seven patients were finally included. The ceftazidime/avibactam target attainment in plasma was optimal for three, quasi-optimal for one and suboptimal for three. In three patients with CSF drug concentrations measured, ceftazidime/avibactam target attainment in CSF was 100% (3/3), which was optimal. The AUCCSF/serum values were 0.59, 0.44 and 0.35 for ceftazidime and 0.57, 0.53 and 0.51 for avibactam. Of the seven patients, 100% (7/7) were treated effectively, 71.4% (5/7) achieved microbiological eradication, 85.7% (6/7) survived and 14.3% (1/7) did not survive.

CONCLUSIONS

The limited clinical data suggest that ceftazidime/avibactam is effective in the treatment of CNS infections caused by MDR Gram-negative bacilli (MDR-GNB), can achieve the ideal drug concentration of CSF, and has good blood-brain barrier penetration.

Knockdown of Slfn5 alleviates lipopolysaccharide-induced pneumonia by regulating Janus kinase/signal transduction and activator of transcription pathway

Background

In recent years, the incidence of pneumonia has been increasing, which is the main cause of death and morbidity of children and the elderly in the world. Slfn5 is implicated in multiple cancers, and Slfn5 promotes epithelial-mesenchymal transition and metastasis in lung cancer. However, the influences of Slfn5 in pneumonia have not yet been completely cleared. Herein, we aimed to explore the underlying effects and regulatory mechanisms of Slfn5 in lipopolysaccharide (LPS)-induced pneumonia in mice and A549 cells.

Methods

Mice were intratracheally administered 5 mg/kg LPS to construct pneumonia model. In vitro, A549 cells were treated with 10 µg/mL LPS to construct cellular pneumonia model. Slfn5 expression was detected using immunohistochemistry and western blotting. Haematoxylin and eosin staining, TUNEL (terminal deoxynucleotidyl transferasemediated deoxyuridine triphosphate‑biotin nick end‑labelling), and western blotting were performed to assess pathological injury and inflammation. MTT [3(4,5‑dimethyl‑2‑thiazolyl)‑2,5‑diphenyl‑2‑H‑tetrazolium bromide], flow cytometry, and enzyme-linked immunosorbent assay analysis were performed to analyze cell viability, apoptosis, and inflammation. Gene set enrichment analysis was performed to explore the mechanism of Slfn5 in pneumonia.

Results

Slfn5 expression was upregulated in LPS-induced pneumonia in mice and A549 cells. In mice, knockdown of Slfn5 weakened LPS-induced lung injury and inflammation and decreased the expression of p-JAK2, p-JAK3, and p-STAT3. In LPS-stimulated A549 cells, downregulation of Slfn5 expression increased and Slfn5 overexpression decreased cell viability. Downregulation of Slfn5 expression decreased and Slfn5 overexpression increased cell apoptosis, inflammation and the expression of p-JAK2, p-JAK3, and p-STAT3. AG490, an inhibitor of the JAK/STAT pathway, reversed the damaging effects of Slfn5 overexpression.

Conclusions

In the LPS-induced pneumonia model, Slfn5 knockdown alleviated LPS-induced lung injury by regulating the JAK/STAT pathway.

Host Transcriptional Regulatory Genes and Microbiome Networks Crosstalk through Immune Receptors Establishing Normal and Tumor Multiomics Metafirm of the Oral-Gut-Lung Axis

The microbiome has shown a correlation with the diet and lifestyle of each population in health and disease, the ability to communicate at the cellular level with the host through innate and adaptative immune receptors, and therefore an important role in modulating inflammatory process related to the establishment and progression of cancer. The oral cavity is one of the most important interaction windows between the human body and the environment, allowing the entry of an important number of microorganisms and their passage across the gastrointestinal tract and lungs. In this review, the contribution of the microbiome network to the establishment of systemic diseases like cancer is analyzed through their synergistic interactions and bidirectional crosstalk in the oral-gut-lung axis as well as its communication with the host cells. Moreover, the impact of the characteristic microbiota of each population in the formation of the multiomics molecular metafirm of the oral-gut-lung axis is also analyzed through state-of-the-art sequencing techniques, which allow a global study of the molecular processes involved of the flow of the microbiota environmental signals through cancer-related cells and its relationship with the establishment of the transcription factor network responsible for the control of regulatory processes involved with tumorigenesis.

The metabolic, virulence and antimicrobial resistance profiles of colonising Streptococcus pneumoniae shift after PCV13 introduction in urban Malawi

Streptococcus pneumoniae causes substantial mortality among children under 5-years-old worldwide. Polysaccharide conjugate vaccines (PCVs) are highly effective at reducing vaccine serotype disease, but emergence of non-vaccine serotypes and persistent nasopharyngeal carriage threaten this success. We investigated the hypothesis that following vaccine, adapted pneumococcal genotypes emerge with the potential for vaccine escape. We genome sequenced 2804 penumococcal isolates, collected 4-8 years after introduction of PCV13 in Blantyre, Malawi. We developed a pipeline to cluster the pneumococcal population based on metabolic core genes into "Metabolic genotypes" (MTs). We show that S. pneumoniae population genetics are characterised by emergence of MTs with distinct virulence and antimicrobial resistance (AMR) profiles. Preliminary in vitro and murine experiments revealed that representative isolates from emerging MTs differed in growth, haemolytic, epithelial infection, and murine colonisation characteristics. Our results suggest that in the context of PCV13 introduction, pneumococcal population dynamics had shifted, a phenomenon that could further undermine vaccine control and promote spread of AMR.

The quorum sensing com system regulates pneumococcal colonisation and invasive disease in a pseudo-stratified airway tissue model

BACKGROUND

The effects of the com quorum sensing system during colonisation and invasion of Streptococcus pneumoniae (Spn) are poorly understood.

METHODS

We developed an ex vivo model of differentiated human airway epithelial (HAE) cells with beating ciliae, mucus production and tight junctions to study Spn colonisation and translocation. HAE cells were inoculated with Spn wild-type TIGR4 (wtSpn) or its isogenic ΔcomC quorum sensing-deficient mutant.

RESULTS

Colonisation density of ΔcomC mutant was lower after 6 h but higher at 19 h and 30 h compared to wtSpn. Translocation correlated inversely with colonisation density. Transepithelial electric resistance (TEER) decreased after pneumococcal inoculation and correlated with increased translocation. Confocal imaging illustrated prominent microcolony formation with wtSpn but disintegration of microcolony structures with ΔcomC mutant. ΔcomC mutant showed greater cytotoxicity than wtSpn, suggesting that cytotoxicity was likely not the mechanism leading to translocation. There was greater density- and time-dependent increase of inflammatory cytokines including NLRP3 inflammasome-related IL-18 after infection with ΔcomC compared with wtSpn. ComC inactivation was associated with increased pneumolysin expression.

CONCLUSIONS

ComC system allows a higher organisational level of population structure resulting in microcolony formation, increased early colonisation and subsequent translocation. We propose that ComC inactivation unleashes a very different and possibly more virulent phenotype that merits further investigation.

Mathematical modeling of pneumococcal transmission dynamics in response to PCV13 infant vaccination in Germany predicts increasing IPD burden due to serotypes included in next-generation PCVs

INTRODUCTION

Two next-generation pneumococcal conjugate vaccines (PCVs), a 15- and a 20-valent PCV (PCV15 and PCV20), have recently been licensed for use in adults, and PCV15 has also been licensed in children. We developed a dynamic transmission model specific for Germany, with the aim to predict carriage prevalence and invasive pneumococcal disease (IPD) burden for serotypes included in these vaccines.

METHODS

The model allows to follow serotype distributions longitudinally both in the absence and presence of PCV vaccinations. We considered eight age cohorts and seven serotype groups according to the composition of different pneumococcal vaccines. This comprises the additional serotypes contained in PCV15 and PCV20 but not in PCV13.

RESULTS

The model predicted that by continuing the current vaccine policy (standard vaccination with PCV13 in children and with PPSV23 in adults) until 2031, IPD case counts due to any serotype in children <2 years of age will remain unchanged. There will be a continuous decrease of IPD cases in adults aged 16-59y, but a 20% increase in adults ≥60y. Furthermore, there will be a steady decrease of the proportion of carriage and IPD due to serotypes included in PCV7 and PCV13 over the model horizon and a steady rise of non-PCV13 serotypes in carriage and IPD. The highest increase for both pneumococcal carriage and absolute IPD case counts was predicted for serotypes 22F and 33F (included in both PCV15 and PCV20) and serotypes 8, 10A, 11A, 12F, and 15B (included in PCV20 only), particularly in older adults. Between 2022 and 2031, serotypes included in PCV20 only are expected to cause 19.7-25.3% of IPD cases in adults ≥60y.

CONCLUSIONS

We conclude that introduction of next-generation PCVs for adults may prevent a substantial and increasing proportion of adult IPDs, with PCV20 having the potential to provide the broadest protection against pneumococcal disease.

The development of a 3D-printed in vitro integrated oro-pharyngeal air-liquid interface cellular throat model for drug transport

To simulate the deposition of drugs in the oro-pharynx region, several in vitro models are available such as the United States Pharmacopeia-Induction Port (USP-IP) throat and the Virginia Commonwealth University (VCU) models. However, currently, there is no such in vitro model that incorporates a biological barrier to elucidate drug transport across the pharyngeal cells. Cellular models such as in vitro air-liquid interface (ALI) models of human respiratory epithelial cell lines are extensively used to study drug transport. To date, no studies have yet been performed to optimise the ALI culture conditions of the human pharyngeal cell line Detroit 562 and determine whether it could be used for drug transport. Therefore, this study aimed to develop a novel 3D-printed throat model integrated with an ALI cellular model of Detroit 562 cells and optimise the culture conditions to investigate whether the combined model could be used to study drug transport, using Lidocaine as a model drug. Differentiating characteristics specific to airway epithelia were assessed using 3 seeding densities (30,000, 60,000, and 80,000 cells/well (c/w), respectively) over 21 days. The results showed that Detroit 562 cells completely differentiates on day 18 of ALI for both 60,000 and 80,000 c/w with significant mucus production, showing response to bacterial and viral stimuli and development of functional tight junctions and Lidocaine transport with no significant differences observed between the ALI models with the 2 cell seeding densities. Results showed the suitability of the Low density (60,000 c/w or 1.8 × 10⁵ cells/cm²) ALI model to study drug transport. Importantly, the developed novel 3D-printed throat model integrated with our optimised in vitro Detroit 562 ALI model showed transport of Lidocaine throat spray. Overall, the study highlights the potential of the novel 3D-printed bio-throat integrated model as a promising in vitro system to investigate the transport of inhalable drug therapies targeted at the oro-pharyngeal region.

Integrated next-generation sequencing and comparative transcriptomic analysis of leaves provides novel insights into the ethylene pathway of Chrysanthemum morifolium in response to a Chinese isolate of chrysanthemum virus B

Background

Chrysanthemum virus B (CVB), a key member of the genus Carlavirus, family Betaflexiviridae, causes severe viral diseases in chrysanthemum (Chrysanthemum morifolium) plants worldwide. However, information on the mechanisms underlying the response of chrysanthemum plants to CVB is scant.

Methods

Here, an integrated next-generation sequencing and comparative transcriptomic analysis of chrysanthemum leaves was conducted to explore the molecular response mechanisms of plants to a Chinese isolate of CVB (CVB-CN) at the molecular level.

Results

In total, 4934 significant differentially expressed genes (SDEGs) were identified to respond to CVB-CN, of which 4097 were upregulated and 837 were downregulated. Gene ontology and functional classification showed that the majority of upregulated SDEGs were categorized into gene cohorts involved in plant hormone signal transduction, phenylpropanoid and flavonoid biosynthesis, and ribosome metabolism. Enrichment analysis demonstrated that ethylene pathway-related genes were significantly upregulated following CVB-CN infection, indicating a strong promotion of ethylene biosynthesis and signaling. Furthermore, disruption of the ethylene pathway in Nicotiana benthamiana, a model plant, using virus-induced gene silencing technology rendered them more susceptible to cysteine-rich protein of CVB-CN induced hypersensitive response, suggesting a crucial role of this pathway in response to CVB-CN infection.

Conclusion

This study provides evidence that ethylene pathway has an essential role of plant in response to CVB and offers valuable insights into the defense mechanisms of chrysanthemum against Carlavirus.

Intracellular survival of Streptococcus pneumoniae in human alveolar macrophages is augmented with HIV infection

People Living with HIV (PLHIV) are at an increased risk of pneumococcal pneumonia than HIV-uninfected adults, but the reasons for this are still not well understood. We investigated whether alveolar macrophages (AM) mediated control of pneumococcal infection is impaired in PLHIV compared to HIV-uninfected adults. We assessed anti-bactericidal activity against Streptococcus pneumoniae of primary human AM obtained from PLHIV and HIV-uninfected adults. We found that pneumococcus survived intracellularly in AMs at least 24 hours post ex vivo infection, and this was more frequent in PLHIV than HIV-uninfected adults. Corroborating these findings, in vivo evidence showed that PLHIV had a higher propensity for harboring S. pneumoniae within their AMs than HIV-uninfected adults. Moreover, bacterial intracellular survival in AMs was associated with extracellular propagation of pneumococcal infection. Our data suggest that failure of AMs to eliminate S. pneumoniae intracellularly could contribute to the increased risk of pneumococcal pneumonia in PLHIV.

Mycoplasma pneumoniae Compared to Streptococcus pneumoniae Avoids Induction of Proinflammatory Epithelial Cell Responses despite Robustly Inducing TLR2 Signaling

Mycoplasma pneumoniae and Streptococcus pneumoniae are the most common bacterial causes of pneumonia in children. The clinical characteristics of pneumonia differ significantly between the two bacteria. We aimed to elucidate the differences in pathogenesis between M. pneumoniae and S. pneumoniae by characterizing the respiratory epithelial cell immune response to both pathogens. Using primary human bronchial epithelial cells in air-liquid interface cultures, we observed lower production of the proinflammatory cytokines interleukin-6 (IL-6) and IL-8 in response to M. pneumoniae than to S. pneumoniae. In contrast to the differences in proinflammatory cytokine production, Toll-like receptor 2 (TLR2)-mediated signaling in response to M. pneumoniae was stronger than to S. pneumoniae. This difference largely depended on TLR1 and not TLR6. We found that M. pneumoniae, but not S. pneumoniae, also induced signaling of TLR10, a coreceptor of TLR2 that has inhibitory properties. M. pneumoniae-induced TLR10 signaling on airway epithelial cells was partially responsible for low IL-8 production, as blocking TLR10 by specific antibodies increased cytokine production. M. pneumoniae maintained Th2-associated cytokine production by epithelial cells, which concurs with the known association of M. pneumoniae infection with asthma. M. pneumoniae left IL-33 levels unchanged, whereas S. pneumoniae downregulated IL-33 production both under homeostatic and Th2-promoting conditions. By directly comparing M. pneumoniae and S. pneumoniae, we demonstrate that M. pneumoniae avoids induction of proinflammatory cytokine response despite its ability to induce robust TLR2 signaling. Our new findings suggest that this apparent paradox may be partially explained by M. pneumoniae-induced signaling of TLR2/TLR10.

Rapid synchronous type 1 IFN and virus-specific T cell responses characterize first wave non-severe SARS-CoV-2 infections

Effective control of SARS-CoV-2 infection on primary exposure may reveal correlates of protective immunity to future variants, but we lack insights into immune responses before or at the time virus is first detected. We use blood transcriptomics, multiparameter flow cytometry, and T cell receptor (TCR) sequencing spanning the time of incident non-severe infection in unvaccinated virus-naive individuals to identify rapid type 1 interferon (IFN) responses common to other acute respiratory viruses and cell proliferation responses that discriminate SARS-CoV-2 from other viruses. These peak by the time the virus is first detected and sometimes precede virus detection. Cell proliferation is most evident in CD8 T cells and associated with specific expansion of SARS-CoV-2-reactive TCRs, in contrast to virus-specific antibodies, which lag by 1-2 weeks. Our data support a protective role for early type 1 IFN and CD8 T cell responses, with implications for development of universal T cell vaccines.

A novel Streptococcus pneumoniae human challenge model demonstrates Treg lymphocyte recruitment to the infection site

To investigate local tissue responses to infection we have developed a human model of killed Streptococcus pneumoniae challenge by intradermal injection into the forearm. S. pneumoniae intradermal challenge caused an initial local influx of granulocytes and increases in TNF, IL6 and CXCL8. However, by 48 h lymphocytes were the dominant cell population, mainly consisting of CD4 and CD8 T cells. Increases in local levels of IL17 and IL22 and the high proportion of CD4 cells that were CCR6⁺ suggested a significant Th17 response. Furthermore, at 48 h the CD4 population contained a surprisingly high proportion of likely memory Treg cells (CCR6 positive and CD45RA negative CD4⁺CD25^highCD127^low cells) at 39%. These results demonstrate that the intradermal challenge model can provide novel insights into the human response to S. pneumoniae and that Tregs form a substantial contribution of the normal human lymphocyte response to infection with this important pathogen.

Betacoronavirus-specific alternate splicing

Viruses can subvert a number of cellular processes including splicing in order to block innate antiviral responses, and many viruses interact with cellular splicing machinery. SARS-CoV-2 infection was shown to suppress global mRNA splicing, and at least 10 SARS-CoV-2 proteins bind specifically to one or more human RNAs. Here, we investigate 17 published experimental and clinical datasets related to SARS-CoV-2 infection, datasets from the betacoronaviruses SARS-CoV and MERS, as well as Streptococcus pneumonia, HCV, Zika virus, Dengue virus, influenza H3N2, and RSV. We show that genes showing differential alternative splicing in SARS-CoV-2 have a similar functional profile to those of SARS-CoV and MERS and affect a diverse set of genes and biological functions, including many closely related to virus biology. Additionally, the differentially spliced transcripts of cells infected by coronaviruses were more likely to undergo intron-retention, contain a pseudouridine modification, and have a smaller number of exons as compared with differentially spliced transcripts in the control groups. Viral load in clinical COVID-19 samples was correlated with isoform distribution of differentially spliced genes. A significantly higher number of ribosomal genes are affected by differential alternative splicing and gene expression in betacoronavirus samples, and the betacoronavirus differentially spliced genes are depleted for binding sites of RNA-binding proteins. Our results demonstrate characteristic patterns of differential splicing in cells infected by SARS-CoV-2, SARS-CoV, and MERS. The alternative splicing changes observed in betacoronaviruses infection potentially modify a broad range of cellular functions, via changes in the functions of the products of a diverse set of genes involved in different biological processes.

Immune responses to bacterial lung infections and their implications for vaccination

The pulmonary immune system plays a vital role in protecting the delicate structures of gaseous exchange against invasion from bacterial pathogens. With antimicrobial resistance becoming an increasing concern, finding novel strategies to develop vaccines against bacterial lung diseases remains a top priority. In order to do so, a continued expansion of our understanding of the pulmonary immune response is warranted. Whilst some aspects are well characterised, emerging paradigms such as the importance of innate cells and inducible immune structures in mediating protection provide avenues of potential to rethink our approach to vaccine development. In this review, we aim to provide a broad overview of both the innate and adaptive immune mechanisms in place to protect the pulmonary tissue from invading bacterial organisms. We use specific examples from several infection models and human studies to depict the varying functions of the pulmonary immune system that may be manipulated in future vaccine development. Particular emphasis has been placed on emerging themes that are less reviewed and underappreciated in vaccine development studies.

Angulo-Zamudio U, McDevitt E, Jop Vidal AG, Alibayov B, Scasny A, Wong SM, Akerley BJ, McDaniel LS. Prophylactic Inhibition of Colonization by Streptococcus pneumoniae with the Secondary Bile Acid Metabolite Deoxycholic Acid

Streptococcus pneumoniae colonizes the nasopharynx of children and the elderly but also kills millions worldwide yearly. The secondary bile acid metabolite deoxycholic acid (DoC) affects the viability of human pathogens but also plays multiple roles in host physiology. We assessed in vitro the antimicrobial activity of DoC and investigated its potential to eradicate S. pneumoniae colonization using a model of human nasopharyngeal colonization and an in vivo mouse model of colonization. At a physiological concentration, DoC (0.5 mg/ml; 1.27 mM) killed all tested S. pneumoniae strains (n = 48) 2 h postinoculation. The model of nasopharyngeal colonization showed that DoC eradicated colonization by S. pneumoniae strains as soon as 10 min postexposure. The mechanism of action did not involve activation of autolysis, since the autolysis-defective double mutants ΔlytAΔlytC and ΔspxBΔlctO were as susceptible to DoC as was the wild type (WT). Oral streptococcal species (n = 20), however, were not susceptible to DoC (0.5 mg/ml). Unlike trimethoprim, whose spontaneous resistance frequency (srF) for TIGR4 or EF3030 was ≥1 × 10-9, no spontaneous resistance was observed with DoC (srF, ≥1 × 10-12). Finally, the efficacy of DoC to eradicate S. pneumoniae colonization was assessed in vivo using a topical route via intranasal (i.n.) administration and as a prophylactic treatment. Mice challenged with S. pneumoniae EF3030 carried a median of 4.05 × 105 CFU/ml 4 days postinoculation compared to 6.67 × 104 CFU/ml for mice treated with DoC. Mice in the prophylactic group had an ∼99% reduction of the pneumococcal density (median, 2.61 × 103 CFU/ml). Thus, DoC, an endogenous human bile salt, has therapeutic potential against S. pneumoniae.

Mycoplasma pneumoniae carriage evades induction of protective mucosal antibodies

Background

Mycoplasma pneumoniae is the most common bacterial cause of pneumonia in children hospitalised for community-acquired pneumonia (CAP). Prevention of infection by vaccines may be an important strategy in the presence of emerging macrolide-resistant M. pneumoniae. However, knowledge of immune responses to M. pneumoniae is limited, complicating vaccine design.

Methods

We studied the antibody response during M. pneumoniae respiratory tract infection and asymptomatic carriage in two different cohorts.

Results

In a nested case–control study (n=80) of M. pneumoniae carriers and matched controls we observed that carriage by M. pneumoniae does not lead to a rise in either mucosal or systemic M. pneumoniae-specific antibodies, even after months of persistent carriage. We replicated this finding in a second cohort (n=69) and also found that during M. pneumoniae CAP, mucosal levels of M. pneumoniae-specific IgA and IgG did increase significantly. In vitro adhesion assays revealed that high levels of M. pneumoniae-specific antibodies in nasal secretions of paediatric patients prevented the adhesion of M. pneumoniae to respiratory epithelial cells.

Conclusions

Our study demonstrates that M. pneumoniae-specific mucosal antibodies protect against bacterial adhesion to respiratory epithelial cells, and are induced only during M. pneumoniae infection and not during asymptomatic carriage. This is strikingly different from carriage with bacteria such as Streptococcus pneumoniae where mucosal antibodies are induced by bacterial carriage.

Antibodies against M. pneumoniae, the most common bacterial cause of pneumonia in children, are able to prevent adhesion of M. pneumoniae to epithelial cells, but are only induced during infection and not during asymptomatic carriagehttps://bit.ly/3CNdAhM

Preprocessing of Public RNA-Sequencing Datasets to Facilitate Downstream Analyses of Human Diseases

Publicly available RNA-sequencing (RNA-seq) data are a rich resource for elucidating the mechanisms of human disease; however, preprocessing these data requires considerable bioinformatic expertise and computational infrastructure. Analyzing multiple datasets with a consistent computational workflow increases the accuracy of downstream meta-analyses. This collection of datasets represents the human intracellular transcriptional response to disorders and diseases such as acute lymphoblastic leukemia (ALL), B-cell lymphomas, chronic obstructive pulmonary disease (COPD), colorectal cancer, lupus erythematosus; as well as infection with pathogens including Borrelia burgdorferi, hantavirus, influenza A virus, Middle East respiratory syndrome coronavirus (MERS-CoV), Streptococcus pneumoniae, respiratory syncytial virus (RSV), severe acute respiratory syndrome coronavirus (SARS-CoV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We calculated the statistically significant differentially expressed genes and Gene Ontology terms for all datasets. In addition, a subset of the datasets also includes results from splice variant analyses, intracellular signaling pathway enrichments as well as read mapping and quantification. All analyses were performed using well-established algorithms and are provided to facilitate future data mining activities, wet lab studies, and to accelerate collaboration and discovery.

Betacoronavirus-specific alternate splicing

Viruses can subvert a number of cellular processes in order to block innate antiviral responses, and many viruses interact with cellular splicing machinery. SARS-CoV-2 infection was shown to suppress global mRNA splicing, and at least 10 SARS-CoV-2 proteins bind specifically to one or more human RNAs. Here, we investigate 17 published experimental and clinical datasets related to SARS-CoV-2 infection as well as datasets from the betacoronaviruses SARS-CoV and MERS as well as Streptococcus pneumonia, HCV, Zika virus, Dengue virus, influenza H3N2, and RSV. We show that genes showing differential alternative splicing in SARS-CoV-2 have a similar functional profile to those of SARS-CoV and MERS and affect a diverse set of genes and biological functions, including many closely related to virus biology. Additionally, the differentially spliced transcripts of cells infected by coronaviruses were more likely to undergo intron-retention, contain a pseudouridine modification and a smaller number of exons than differentially spliced transcripts in the control groups. Viral load in clinical COVID-19 samples was correlated with isoform distribution of differentially spliced genes. A significantly higher number of ribosomal genes are affected by DAS and DGE in betacoronavirus samples, and the betacoronavirus differentially spliced genes are depleted for binding sites of RNA-binding proteins. Our results demonstrate characteristic patterns of differential splicing in cells infected by SARS-CoV-2, SARS-CoV, and MERS, potentially modifying a broad range of cellular functions and affecting a diverse set of genes and biological functions.

Upper Respiratory Tract Co-detection of Human Endemic Coronaviruses and High-density Pneumococcus Associated With Increased Severity Among HIV-Uninfected Children Under 5 Years Old in the PERCH Study

BACKGROUND

Severity of viral respiratory illnesses can be increased with bacterial coinfection and can vary by sex, but influence of coinfection and sex on human endemic coronavirus (CoV) species, which generally cause mild to moderate respiratory illness, is unknown. We evaluated CoV and pneumococcal co-detection by sex in childhood pneumonia.

METHODS

In the 2011-2014 Pneumonia Etiology Research for Child Health study, nasopharyngeal and oropharyngeal (NP/OP) swabs and other samples were collected from 3981 children <5 years hospitalized with severe or very severe pneumonia in 7 countries. Severity by NP/OP detection status of CoV (NL63, 229E, OC43 or HKU1) and high-density (≥6.9 log10 copies/mL) pneumococcus (HDSpn) by real-time polymerase chain reaction was assessed by sex using logistic regression adjusted for age and site.

RESULTS

There were 43 (1.1%) CoV+/HDSpn+, 247 CoV+/HDSpn-, 449 CoV-/HDSpn+ and 3149 CoV-/HDSpn- cases with no significant difference in co-detection frequency by sex (range 51.2%-64.0% male, P = 0.06). More CoV+/HDSpn+ pneumonia was very severe compared with other groups for both males (13/22, 59.1% versus range 29.1%-34.7%, P = 0.04) and females (10/21, 47.6% versus 32.5%-43.5%, P = 0.009), but only male CoV+/HDSpn+ required supplemental oxygen more frequently (45.0% versus 20.6%-28.6%, P < 0.001) and had higher mortality (35.0% versus 5.3%-7.1%, P = 0.004) than other groups. For females with CoV+/HDSpn+, supplemental oxygen was 25.0% versus 24.8%-33.3% (P = 0.58) and mortality was 10.0% versus 9.2%-12.9% (P = 0.69).

CONCLUSIONS

Co-detection of endemic CoV and HDSpn was rare in children hospitalized with pneumonia, but associated with higher severity and mortality in males. Findings may warrant investigation of differences in severity by sex with co-detection of HDSpn and SARS-CoV-2.

Insights Into the Effects of Mucosal Epithelial and Innate Immune Dysfunction in Older People on Host Interactions With Streptococcus pneumoniae

In humans, nasopharyngeal carriage of Streptococcus pneumoniae is common and although primarily asymptomatic, is a pre-requisite for pneumonia and invasive pneumococcal disease (IPD). Together, these kill over 500,000 people over the age of 70 years worldwide every year. Pneumococcal conjugate vaccines have been largely successful in reducing IPD in young children and have had considerable indirect impact in protection of older people in industrialized country settings (herd immunity). However, serotype replacement continues to threaten vulnerable populations, particularly older people in whom direct vaccine efficacy is reduced. The early control of pneumococcal colonization at the mucosal surface is mediated through a complex array of epithelial and innate immune cell interactions. Older people often display a state of chronic inflammation, which is associated with an increased mortality risk and has been termed 'Inflammageing'. In this review, we discuss the contribution of an altered microbiome, the impact of inflammageing on human epithelial and innate immunity to S. pneumoniae, and how the resulting dysregulation may affect the outcome of pneumococcal infection in older individuals. We describe the impact of the pneumococcal vaccine and highlight potential research approaches which may improve our understanding of respiratory mucosal immunity during pneumococcal colonization in older individuals.

Streptococcus pneumoniae Infection Promotes Histone H3 Dephosphorylation by Modulating Host PP1 Phosphatase

Pathogenic bacteria can alter host gene expression through post-translational modifications of histones. We show that a natural colonizer, Streptococcus pneumoniae, induces specific histone modifications, including robust dephosphorylation of histone H3 on serine 10 (H3S10), during infection of respiratory epithelial cells. The bacterial pore-forming toxin pneumolysin (PLY), along with the pyruvate oxidase SpxB responsible for H₂O₂ production, play important roles in the induction of this modification. The combined effects of PLY and H₂O₂ trigger host signaling that culminates in H3S10 dephosphorylation, which is mediated by the host cell phosphatase PP1. Strikingly, S. pneumoniae infection induces dephosphorylation and subsequent activation of PP1 catalytic activity. Colonization of PP1 catalytically deficient cells results in impaired intracellular S. pneumoniae survival and infection. Interestingly, PP1 activation and H3S10 dephosphorylation are not restricted to S. pneumoniae and appear to be general epigenomic mechanisms favoring intracellular survival of pathogenic bacteria.

Acute bacterial meningitis

Purpose of review

Community-acquired bacterial meningitis is a continually changing disease. This review summarises both dynamic epidemiology and emerging data on pathogenesis. Updated clinical guidelines are discussed, new agents undergoing clinical trials intended to reduce secondary brain damage are presented.

Recent findings

Conjugate vaccines are effective against serotype/serogroup-specific meningitis but vaccine escape variants are rising in prevalence. Meningitis occurs when bacteria evade mucosal and circulating immune responses and invade the brain: directly, or across the blood–brain barrier. Tissue damage is caused when host genetic susceptibility is exploited by bacterial virulence. The classical clinical triad of fever, neck stiffness and headache has poor diagnostic sensitivity, all guidelines reflect the necessity for a low index of suspicion and early Lumbar puncture. Unnecessary cranial imaging causes diagnostic delays. cerebrospinal fluid (CSF) culture and PCR are diagnostic, direct next-generation sequencing of CSF may revolutionise diagnostics. Administration of early antibiotics is essential to improve survival. Dexamethasone partially mitigates central nervous system inflammation in high-income settings. New agents in clinical trials include C5 inhibitors and daptomycin, data are expected in 2025.

Summary

Clinicians must remain vigilant for bacterial meningitis. Constantly changing epidemiology and emerging pathogenesis data are increasing the understanding of meningitis. Prospects for better treatments are forthcoming.

Imaging host-pathogen interactions using epithelial and bacterial cell infection models

The age-old saying, seeing is believing, could not be truer when we think about the value of imaging interactions between epithelial cells and bacterial pathogens. Imaging and culturing techniques have vastly improved over the years, and the breadth and depth of these methods is ever increasing. These technical advances have benefited researchers greatly; however, due to the large number of potential model systems and microscopy techniques to choose from, it can be overwhelming to select the most appropriate tools for your research question. This Review discusses a variety of available epithelial culturing methods and quality control experiments that can be performed, and outlines various options commonly used to fluorescently label bacterial and mammalian cell components. Both light- and electron-microscopy techniques are reviewed, with descriptions of both technical aspects and common applications. Several examples of imaging bacterial pathogens and their interactions with epithelial cells are discussed to provide researchers with an idea of the types of biological questions that can be successfully answered by using microscopy.

Experimental Human Challenge Defines Distinct Pneumococcal Kinetic Profiles and Mucosal Responses between Colonized and Non-Colonized Adults

Colonization of the upper respiratory tract with Streptococcus pneumoniae is the precursor of pneumococcal pneumonia and invasive disease. Following exposure, however, it is unclear which human immune mechanisms determine whether a pathogen will colonize. We used a human challenge model to investigate host-pathogen interactions in the first hours and days following intranasal exposure to Streptococcus pneumoniae Using a novel home sampling method, we measured early immune responses and bacterial density dynamics in the nose and saliva after volunteers were experimentally exposed to pneumococcus. Here, we show that nasal colonization can take up to 24 h to become established. Also, the following two distinct bacterial clearance profiles were associated with protection: nasal clearers with immediate clearance of bacteria in the nose by the activity of pre-existent mucosal neutrophils and saliva clearers with detectable pneumococcus in saliva at 1 h post challenge and delayed clearance mediated by an inflammatory response and increased neutrophil activity 24 h post bacterial encounter. This study describes, for the first time, how colonization with a bacterium is established in humans, signifying that the correlates of protection against pneumococcal colonization, which can be used to inform design and testing of novel vaccine candidates, could be valid for subsets of protected individuals.IMPORTANCE Occurrence of lower respiratory tract infections requires prior colonization of the upper respiratory tract with a pathogen. Most bacterial infection and colonization studies have been performed in murine and in vitro models due to the current invasive sampling methodology of the upper respiratory tract, both of which poorly reflect the complexity of host-pathogen interactions in the human nose. Self-collecting saliva and nasal lining fluid at home is a fast, low-cost, noninvasive, high-frequency sampling platform for continuous monitoring of bacterial encounter at defined time points relative to exposure. Our study demonstrates for the first time that, in humans, there are distinct profiles of pneumococcal colonization kinetics, distinguished by speed of appearance in saliva, local phagocytic function, and acute mucosal inflammatory responses, which may either recruit or activate neutrophils. These data are important for the design and testing of novel vaccine candidates.

The histone demethylase KDM6B fine-tunes the host response to Streptococcus pneumoniae

Streptococcus pneumoniae is a natural colonizer of the human respiratory tract and an opportunistic pathogen. Although epithelial cells are among the first to encounter pneumococci, the cellular processes and contribution of epithelial cells to the host response are poorly understood. Here, we show that a S. pneumoniae serotype 6B ST90 strain, which does not cause disease in a murine infection model, induces a unique NF-κB signature response distinct from an invasive-disease-causing isolate of serotype 4 (TIGR4). This signature is characterized by activation of p65 and requires a histone demethylase KDM6B. We show, molecularly, that the interaction of the 6B strain with epithelial cells leads to chromatin remodelling within the IL-11 promoter in a KDM6B-dependent manner, where KDM6B specifically demethylates histone H3 lysine 27 dimethyl. Remodelling of the IL-11 locus facilitates p65 access to three NF-κB sites that are otherwise inaccessible when stimulated by IL-1β or TIGR4. Finally, we demonstrate through chemical inhibition of KDM6B with GSK-J4 inhibitor and through exogenous addition of IL-11 that the host responses to the 6B ST90 and TIGR4 strains can be interchanged both in vitro and in a murine model of infection in vivo. Our studies therefore reveal how a chromatin modifier governs cellular responses during infection.

Silencing of lncRNA MIAT alleviates LPS-induced pneumonia via regulating miR-147a/NKAP/NF-κB axis

Purpose: Pneumonia is a respiratory disease with an increasing incidence in recent years. More and more studies have revealed that lncRNAs can regulate the transcriptional expression of target genes at different stage. Herein, we aimed to explore the effect of lncRNA MIAT in LPS-induced pneumonia, and further illuminate the possible underlying mechanisms.

Method and results: Mice were intraperitoneally injected with LPS, and the lung inflammation was evaluated. Microarray showed lncRNA MIAT was up-regulated in LPS-induced pulmonary inflammation. And qRT-PCR and FISH assay indicated that MIAT was increased in mice with LPS injection. Functional analysis showed sh-MIAT inhibited LPS-induced inflammation response, inhibited apoptosis level and protected lung function. As well, si-MIAT removed the injury of LPS on mouse lung epithelial TC-1 cells, and inhibited the activation of NF-κB signaling. Furthermore, MIAT acted as a sponge of miR-147a, and miR-147a directly targeted NKAP. Functionally, AMO-147a or NKAP remitted the beneficial effects of si-MIAT on LPS-induced inflammation response of TC-1 cells.

Conclusion: Deletion of MIAT protected against LPS-induced lung inflammation via regulating miR-147a/NKAP, which might provide new insight for pneumonia treatment.

Structural insights into loss of function of a pore forming toxin and its role in pneumococcal adaptation to an intracellular lifestyle

The opportunistic pathogen Streptococcus pneumoniae has dual lifestyles: one of an asymptomatic colonizer in the human nasopharynx and the other of a deadly pathogen invading sterile host compartments. The latter triggers an overwhelming inflammatory response, partly driven via pore forming activity of the cholesterol dependent cytolysin (CDC), pneumolysin. Although pneumolysin-induced inflammation drives person-to-person transmission from nasopharynx, the primary reservoir for pneumococcus, it also contributes to high mortality rates, creating a bottleneck that hampers widespread bacterial dissemination, thus acting as a double-edged sword. Serotype 1 ST306, a widespread pneumococcal clone, harbours a non-hemolytic variant of pneumolysin (Ply-NH). Performing crystal structure analysis of Ply-NH, we identified Y150H and T172I as key substitutions responsible for loss of its pore forming activity. We uncovered a novel inter-molecular cation-π interaction, governing formation of the transmembrane β-hairpins (TMH) in the pore state of Ply, which can be extended to other CDCs. H150 in Ply-NH disrupts this interaction, while I172 provides structural rigidity to domain-3, through hydrophobic interactions, inhibiting TMH formation. Loss of pore forming activity enabled improved cellular invasion and autophagy evasion, promoting an atypical intracellular lifestyle for pneumococcus, a finding that was corroborated in in vivo infection models. Attenuation of inflammatory responses and tissue damage promoted tolerance of Ply-NH-expressing pneumococcus in the lower respiratory tract. Adoption of this altered lifestyle may be necessary for ST306 due to its limited nasopharyngeal carriage, with Ply-NH, aided partly by loss of its pore forming ability, facilitating a benign association of SPN in an alternative, intracellular host niche.

Bacterial Interference With Lactate Dehydrogenase Assay Leads to an Underestimation of Cytotoxicity

Models to study host-pathogen interactions in vitro are an important tool for investigating the infectious disease process and evaluating the efficacy of antimicrobial compounds. In these models, the viability of mammalian cells is often determined using the lactate dehydrogenase (LDH) cytotoxicity assay. In the present study we evaluated whether bacteria could interfere with the LDH assay. As a model for host-pathogen interactions, we co-cultured lung epithelial cells with eight bacteria encountered in the lower respiratory tract. We show that LDH activity is affected by Pseudomonas aeruginosa, Klebsiella pneumoniae, Stenotrophomonas maltophilia, and Streptococcus pneumoniae, and that this depends on the density of the start inoculum and the duration of infection. Two different mechanisms were discovered through which bacteria interfered with LDH activity, i.e., acidification of the cell culture medium (by K. pneumoniae and S. pneumoniae) and protease production (by P. aeruginosa and S. maltophilia). In addition, we developed and validated a modified protocol to evaluate cytotoxicity using the LDH assay, where bacterial interference with LDH quantification is avoided.

Influenza-like illness is associated with high pneumococcal carriage density in Malawian children

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Influenza-like illness (ILI) in children is associated with high pneumococcal carriage density.

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Children with ILI harboured more viral organisms than asymptomatic healthy children.

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Children with ILI patients had higher IL-8 levels in nasal aspirates than asymptomatic healthy children.

Background

High pneumococcal carriage density is a risk factor for invasive pneumococcal disease (IPD) and transmission, but factors that increase pneumococcal carriage density are still unclear.

Methods

We undertook a cross-sectional study to evaluate the microbial composition, cytokine levels and pneumococcal carriage densities in samples from children presenting with an influenza-like illness (ILI) and asymptomatic healthy controls (HC).

Results

The proportion of children harbouring viral organisms (Relative risk (RR) 1.4, p = 0.0222) or ≥ 4 microbes at a time (RR 1.9, p < 0.0001), was higher in ILI patients than HC. ILI patients had higher IL-8 levels in nasal aspirates than HC (median [IQR], 265.7 [0 – 452.3] vs. 0 [0 – 127.3] pg/ml; p = 0.0154). Having an ILI was associated with higher pneumococcal carriage densities compared to HC (RR 4.2, p < 0.0001).

Conclusion

These findings suggest that children with an ILI have an increased propensity for high pneumococcal carriage density. This could in part contribute to increased susceptibility to IPD and transmission in the community.

Time-resolved mRNA and miRNA expression profiling reveals crucial coregulation of molecular pathways involved in epithelial-pneumococcal interactions

Streptococcus pneumoniae is a major causative agent of pneumonia worldwide and its complex interaction with the lung epithelium has not been thoroughly characterized. In this study, we exploited both RNA‐sequencing and microRNA (miRNA)‐sequencing approaches to monitor the transcriptional changes in human lung alveolar epithelial cells infected by S. pneumoniae in a time‐resolved manner. A total of 1330 differentially expressed (DE) genes and 45 DE miRNAs were identified in all comparisons during the infection process. Clustering analysis showed that all DE genes were grouped into six clusters, several of which were primarily involved in inflammatory or immune responses. In addition, target gene enrichment analyses identified 11 transcription factors that were predicted to link at least one of four clusters, revealing transcriptional coregulation of multiple processes or pathways by common transcription factors. Notably, pharmacological treatment suggested that phosphorylation of p65 is important for optimal transcriptional regulation of target genes in epithelial cells exposed to pathogens. Furthermore, network‐based clustering analysis separated the DE genes negatively regulated by DE miRNAs into two functional modules (M1 and M2), with an enrichment in immune responses and apoptotic signaling pathways for M1. Integrated network analyses of potential regulatory interactions in M1 revealed that multiple DE genes related to immunity and apoptosis were regulated by multiple miRNAs, indicating the coordinated regulation of multiple genes by multiple miRNAs. In conclusion, time‐series expression profiling of messenger RNA and miRNA provides a wealth of information for global transcriptional changes, and offers comprehensive insight into the molecular mechanisms underlying host–pathogen interactions.

Respiratory Barrier as a Safeguard and Regulator of Defense Against Influenza A Virus and Streptococcus pneumoniae

The primary function of the respiratory system of gas exchange renders it vulnerable to environmental pathogens that circulate in the air. Physical and cellular barriers of the respiratory tract mucosal surface utilize a variety of strategies to obstruct microbe entry. Physical barrier defenses including the surface fluid replete with antimicrobials, neutralizing immunoglobulins, mucus, and the epithelial cell layer with rapidly beating cilia form a near impenetrable wall that separates the external environment from the internal soft tissue of the host. Resident leukocytes, primarily of the innate immune branch, also maintain airway integrity by constant surveillance and the maintenance of homeostasis through the release of cytokines and growth factors. Unfortunately, pathogens such as influenza virus and Streptococcus pneumoniae require hosts for their replication and dissemination, and prey on the respiratory tract as an ideal environment causing severe damage to the host during their invasion. In this review, we outline the host-pathogen interactions during influenza and post-influenza bacterial pneumonia with a focus on inter- and intra-cellular crosstalk important in pulmonary immune responses.

Pneumolysin Induces 12-Lipoxygenase-Dependent Neutrophil Migration during Streptococcus pneumoniae Infection

Streptococcus pneumoniae is a major cause of pneumonia, wherein infection of respiratory mucosa drives a robust influx of neutrophils. We have previously shown that S. pneumoniae infection of the respiratory epithelium induces the production of the 12-lipoxygenase (12-LOX)-dependent lipid inflammatory mediator hepoxilin A3, which promotes recruitment of neutrophils into the airways, tissue damage, and lethal septicemia. Pneumolysin (PLY), a member of the cholesterol-dependent cytolysin (CDC) family, is a major S. pneumoniae virulence factor that generates ∼25-nm diameter pores in eukaryotic membranes and promotes acute inflammation, tissue damage, and bacteremia. We show that a PLY-deficient S. pneumoniae mutant was impaired in triggering human neutrophil transepithelial migration in vitro. Ectopic production of PLY endowed the nonpathogenic Bacillus subtilis with the ability to trigger neutrophil recruitment across human-cultured monolayers. Purified PLY, several other CDC family members, and the α-toxin of Clostridium septicum, which generates pores with cross-sectional areas nearly 300 times smaller than CDCs, reproduced this robust neutrophil transmigration. PLY non-pore-forming point mutants that are trapped at various stages of pore assembly did not recruit neutrophils. PLY triggered neutrophil recruitment in a 12-LOX-dependent manner in vitro. Instillation of wild-type PLY but not inactive derivatives into the lungs of mice induced robust 12-LOX-dependent neutrophil migration into the airways, although residual inflammation induced by PLY in 12-LOX-deficient mice indicates that 12-LOX-independent pathways also contribute to PLY-triggered pulmonary inflammation. These data indicate that PLY is an important factor in promoting hepoxilin A3-dependent neutrophil recruitment across pulmonary epithelium in a pore-dependent fashion.