Infection Model Research Articles

Zebrafish use conserved CLR and TLR signaling pathways to respond to fungal PAMPs in zymosan.

Pattern recognition receptors (PRRs) such as C-type lectin receptors (CLRs) and Toll-like receptors (TLRs) are used by hosts to recognize pathogen-associated molecular patterns (PAMPs) in microorganisms and to initiate innate immune responses. While PRRs exist across invertebrate and vertebrate species, the functional homology of many of these receptors is still unclear. In this study, we investigate the innate immune response of zebrafish larvae to zymosan, a β-glucan-containing particle derived from fungal cell walls. Macrophages and neutrophils robustly respond to zymosan and are required for zymosan-induced activation of the NF-κB transcription factor. Full activation of NF-κB in response to zymosan depends on Card9/Syk and Myd88, conserved CLR and TLR adaptor proteins, respectively. Two putative CLRs, Clec4c and Sclra, are both required for maximal sensing of zymosan and NF-κB activation. Altogether, we identify conserved PRRs and PRR signaling pathways in larval zebrafish that promote recognition of fungal PAMPs. These results inform modeling of human fungal infections in zebrafish and increase our knowledge of the evolution and conservation of PRR pathways in vertebrates.

Immune correlates of protection of the four-segmented Rift Valley fever virus candidate vaccine in mice

ABSTRACT Rift Valley fever (RVF) is a mosquito-borne zoonotic disease caused by RVF virus (RVFV). RVFV infections in humans are usually asymptomatic or associated with mild febrile illness, although more severe cases of haemorrhagic disease and encephalitis with high mortality also occur. Currently, there are no licensed human vaccines available. The safety and efficacy of a genetically engineered four-segmented RVFV variant (hRVFV-4s) as a potential live-attenuated human vaccine has been tested successfully in mice, ruminants, and marmosets though the correlates of protection of this vaccine are still largely unknown. In the present study, we have assessed hRVFV-4s-induced humoral and cellular immunity in a mouse model of RVFV infection. Our results confirm that a single dose of hRVFV-4s is highly efficient in protecting naïve mice from developing severe disease following intraperitoneal challenge with a highly virulent RVFV strain and data show that virus neutralizing (VN) serum antibody titres in a prime-boost regimen are significantly higher compared to the single dose. Subsequently, VN antibodies from prime-boost-vaccinated recipients were shown to be protective when transferred to naïve mice. In addition, hRVFV-4s vaccination induced a significant virus-specific T cell response as shown by IFN-γ ELISpot assay, though these T cells did not provide significant protection upon passive transfer to naïve recipient mice. Collectively, this study highlights hRVFV-4s-induced VN antibodies as a major correlate of protection against lethal RVFV infection.

Staphylococcus pseudintermedius and Pseudomonas aeruginosa Lubbock Chronic Wound Biofilm (LCWB): a suitable dual-species model for in vitro studies

Antimicrobial treatment of methicillin-resistant Staphylococcus pseudintermedius associated with canine wounds represents an important challenge. The aim of this study was to create a canine wound infection model, Lubbock Chronic Wound Biofilm (LCWB), with a focus on S. pseudintermedius, drawing inspiration from the established human model involving Staphylococcus aureus. Methicillin-resistant S. pseudintermedius 115 (MRSP) and Pseudomonas aeruginosa 700 strains, isolated from dog wounds, were used to set up the LCWB at 24, 48 and 72 h. The LCWBs were evaluated in terms of volume, weight, and microbial CFU/mg. The microbial spatial distribution in the LCWBs was assessed by SEM and CLSM imaging. The best incubation time for the LCWB production in terms of volume (3.38 cm3 ± 0.13), weight (0.86 gr ± 0.02) and CFU/mg (up to 7.05 × 106 CFU/mg ± 2.89 × 105) was 48 h. The SEM and CLSM images showed a major viable microbial colonization at 48 h with non-mixed bacteria with a prevalence of MRSP on the surface and P. aeruginosa 700 in the depth of the wound. The obtained findings demonstrate the capability of S. pseudintermedius to grow together P. aeruginosa in the LCWB model, representing the suitable model to reproduce the animal chronic wound in vitro.

The Microbiological Characteristics of Acinetobacter Baumannii Associated With Early Mortality in Patients With Bloodstream Infection.

Despite rapid deaths resulting from Acinetobacter baumannii bacteremia, the clinical impact of the microbiological characteristics of A baumannii strains on early mortality (EM) is unclear. We aimed to identify the microbiological characteristics of A baumannii strains associated with EM. Clinical information and isolates from patients with A baumannii bacteremia from January 2015 to December 2021 were collected. EM was defined as death within 3 days of the initial positive blood culture, whereas late mortality meant death within 5-30 days. The microbiological characteristics of A baumannii were analyzed using multilocus sequence typing, polymerase chain reactions, and a Galleria mellonella in vivo infection model. Among 130 patients, 69 (53.1%) died within 30 days and EM occurred in 38 (55.1% of 30-day deaths). Sequence type 191 (ST191) strain was more prevalent in patients with EM than in 30-day survivors (31.6% vs 6.6%). Regarding virulence genes, bfmS was more frequent (92.1% vs 47.5%), whereas bauA was less frequent (13.2% vs 52.5%) in patients with EM than in 30-day survivors. Higher clinical severity, pneumonia, and ST191 infection were identified as independent risk factors for EM. In the G mellonella infection model, ST191, bfmS+, and bauA- isolates showed higher virulence than non-ST191, bfmS-, and bauA+ isolates, respectively. ST191 and bfmS were more frequently found in the EM group. ST191 infection was also an independent risk factor for EM and highly virulent in the in vivo model. Tailored infection control measures based on these characteristics are necessary for A baumannii bacteremia management.

PhosphoLipidome Alteration Induced by Clostridioides difficile Toxin B in Enteric Glial Cells.

Clostridioides difficile (C. difficile) is responsible for a spectrum of nosocomial/antibiotic-associated gastrointestinal diseases that are increasing in global incidence and mortality rates. The C. difficile pathogenesis is due to toxin A and B (TcdA/TcdB), both causing cytopathic and cytotoxic effects and inflammation. Recently, we demonstrated that TcdB induces cytopathic and cytotoxic (apoptosis and necrosis) effects in enteric glial cells (EGCs) in a dose/time-dependent manner and described the underlying signaling. Despite the role played by lipids in host processes activated by pathogens, to counter infection and/or induce cell death, to date no studies have investigated lipid changes induced by TcdB/TcdA. Here, we evaluated the modification of lipid composition in our in vitro model of TcdB infection. Apoptosis, cell cycle, cell viability, and lipidomic profiles were evaluated in EGCs treated for 24 h with two concentrations of TcdB (0.1 ng/mL; 10 ng/mL). In EGCs treated with the highest concentration of TcdB, not only an increased content of total lipids was observed, but also lipidome changes, allowing the separation of TcdB-treated cells and controls into different clusters. The statistical analyses also allowed us to ascertain which lipid classes and lipid molecular species determine the clusterization. Changes in lipid species containing inositol as polar head and plasmalogen phosphatidylethanolamine emerged as key indicators of altered lipid metabolism in TcdB-treated EGCs. These results not only provide a picture of the phospholipid profile changes but also give information regarding the lipid metabolism pathways altered by TcdB, and this might represent an important step for developing strategies against C. difficile infection.

Recent advances in the therapeutic potential of cathelicidins.

The alarming increase in antimicrobial resistance in the last decades has prompted the search for alternatives to control infectious diseases. Antimicrobial peptides (AMPs) represent a heterogeneous class of molecules with ample antibacterial, antiviral, and antifungal effects. They can be found in many organisms, including all classes of vertebrates, providing a valuable source of new antimicrobial agents. The unique properties of AMPs make it harder for microbes develop resistance, while their immunomodulatory properties and target diversity reinforce their translational use in multiple diseases, from autoimmune disorders to different types of cancer. The latest years have witnessed a vast number of studies evaluating the use of AMPs in therapy, with many progressing to clinical trials. The present review explores the recent developments in the medicinal properties of cathelicidins, a vast family of AMPs with potent antimicrobial and immunomodulatory effects. Cathelicidins from several organisms have been tested in disease models of viral and bacterial infections, inflammatory diseases, and tumors, with encouraging results. Combining nanomaterials with active, natural antimicrobial peptides, including LL-37 and synthetic analogs like ceragenins, leads to the creation of innovative nanoagents with significant clinical promise. However, there are still important limitations, such as the toxicity of many cathelicidins to healthy host cells and low stability in vivo. The recent advances in nanomaterials and synthetic biology may help overcome the current limitations, enabling the use of cathelicidins in future therapeutics. Furthermore, a better understanding of the mechanisms of cathelicidin action in vivo and their synergy with other host molecules will contribute to the development of safer, highly effective therapies.

Helminth infection induces a distinct subset of CD101hi lung tissue-infiltrating eosinophils that are differentially regulated by type 2 cytokines.

Eosinophils play divergent roles in health and disease, contributing to both immunoregulatory and proinflammatory responses. Helminth infection is strongly associated with eosinophilia and the induction of the type 2 cytokines interleukin (IL)-5, IL-4 and IL-13. This study aimed to elucidate the heterogeneity of pulmonary eosinophils in response to helminth infection and the roles of IL-5, IL-4 and IL-13 in driving pulmonary eosinophil responses. Using the murine helminth model Nippostrongylus brasiliensis (Nb), we characterize a subtype of eosinophils, defined by high expression of CD101, that is induced in the lungs of Nb-infected mice and are phenotypically distinct from lung eosinophils that express low levels of CD101. Strikingly, we show that the two eosinophil subtypes have distinct anatomical localization within the lung: CD101low eosinophils are predominantly localized in the lung vasculature, whereas Nb-induced CD101hi eosinophils are predominantly localized in the extravascular lung niche. We show that CD101hi eosinophils are also induced across other models of pulmonary infection and inflammation, including a nonlung-migrating helminth infection, house dust mite-induced allergic inflammation and influenza infection. Furthermore, we demonstrate that the induction of CD101hi tissue eosinophils is independent of IL-5 and IL-4 signaling, but is dependent on intact IL-13 signaling. These results suggest that IL-13 produced during helminth infection and other disease states promotes a pulmonary tissue-infiltrating program in eosinophils defined by high expression of CD101.

Antibacterial activity of t-cinnamaldehyde: An approach to its mechanistic principle towards enterohemorrhagic Escherichia coli (EHEC)

BackgroundCompounds of natural origin are potent source of drugs with unique mechanisms of action. Among phytochemicals, trans-cinnamaldehyde (t-CA) exhibits a wide range of biological activity, thus has been used for centuries to fight bacterial and fungal infections. However, the molecular basis of these properties has not been fully covered. Considering that difficult-to-control infections are becoming a rising global problem, there is a need to elucidate the molecular potential of t-CA. PurposeTo evaluate the antibacterial activity of t-CA against Shiga-toxigenic E. coli strains and elucidate its mechanism of action based on the inhibition of the virulence factor expression. MethodsThe antimicrobial potential of t-CA was assessed with two-fold microdilution and time-kill assays. Further evaluation included bioluminescence suppression assays, quantification of reactive oxygen species (ROS) and assessment of NAD+/NADH ratios. Morphological changes post t-CA exposure were examined using transmission electron microscopy. RNA sequencing and radiolabeling of nucleotides elucidated the metabolic alterations induced by t-CA. Toxin expression level was monitored through the application of fusion proteins, monitoring of bacteriophage development, and fluorescence microscopy studies. Lastly, the therapeutic efficacy in vivo was assessed using Galleria mellonella infection model. ResultsA comprehensive study of t-CA's bioactivity showed unique properties affecting bacterial metabolism and morphology, resulting in significant bacterial cell deformation and effective virulence inhibition. Elucidation of the underlying mechanisms indicated that t-CA activates the global regulatory system, the stringent response, manifested by its alarmone, (p)ppGpp, overproduction mediated by the RelA enzyme, thereby inhibiting bacterial proliferation. Intriguingly, t-CA effectively downregulates Shiga toxin gene expression via alarmone molecules, indicating its potential for therapeutic effect. In vivo validation demonstrated a significant improvement in larval survival rates post- t-CA treatment with 50 mg/kg (p < 0.05), akin to the efficacy observed with azithromycin, thus indicating its effectiveness against EHEC infections (p < 0.05). ConclusionsCollectively, these results reveal the robust antibacterial capabilities of t-CA, warranting its further exploration as a viable anti-infective agent.

Adapting Real-Time Lung Function Measurements for SARS-CoV-2 Infection Studies in Syrian Hamsters.

Pulmonary function examinations are critical to assess respiratory disease severity in patients. In preclinical rodent models of viral respiratory infections, however, disease is frequently evaluated based on virological, pathological and/or surrogate clinical parameters, which are not directly associated with lung function. To bridge the gap between preclinical and clinical readouts, we aimed to apply unrestrained whole-body plethysmography (WBP) measurements in a SARS-CoV-2 Syrian hamster challenge model. While WBP measurements are frequently used for preclinical research in mice and rats, results from studies in hamsters are still limited. During unrestrained WBP measurements, we obtained highly variable breathing frequency values outside of the normal physiological range for hamsters. Importantly, we observed that animal movements were recorded as breaths during WBP measurements. By limiting animal movement through either mechanical or chemical restraint, we improved the reliability of the lung function readout and obtained breathing frequencies that correlated with clinical signs when comparing two different variants of SARS-CoV-2 post-inoculation. Simultaneously, however, new sources of experimental variation were introduced by the method of restraint, which demands further optimalization of WBP measurements in Syrian hamsters. We concluded that WBP measurements are a valuable refinement either in combination with video recordings or if average values of measurements lasting several hours are analyzed.

A Mycobacterium ulcerans vaccine pilot trial using an accurate low-dose challenge.

In preparation for its proposed use in a controlled human infection model (CHIM), this study reports the successful infection of BALB/c mice using a carefully characterized, low-dose inoculum of Mycobacterium ulcerans JKD8049 (our proposed CHIM strain). We also demonstrate that Mycobacterium bovis bacille Calmette-Guérin delays the onset of disease but cannot alter the course of illness once a lesion becomes apparent. We also validate the findings of previous low-dose challenges that used less accurate methods to determine the inoculum, but our presented methodology is practical, accurate, and anticipated to be reproducible.

The osmoregulated metabolism of trehalose contributes to production of type 1 fimbriae and bladder colonization by extraintestinal Escherichia coli strain BEN2908.

In Escherichia coli, the disaccharide trehalose can be metabolized as a carbon source or be accumulated as an osmoprotectant under osmotic stress. In hypertonic environments, E. coli accumulates trehalose in the cell by synthesis from glucose mediated by the cytosolic enzymes OtsA and OtsB. Trehalose in the periplasm can be hydrolyzed into glucose by the periplasmic trehalase TreA. We have previously shown that a treA mutant of extraintestinal E. coli strain BEN2908 displayed increased resistance to osmotic stress by 0.6 M urea, and reduced production of type 1 fimbriae, reduced invasion of avian fibroblasts, and decreased bladder colonization in a murine model of urinary tract infection. Since loss of TreA likely results in higher periplasmic trehalose concentrations, we wondered if deletion of otsA and otsB genes, which would lead to decreased internal trehalose concentrations, would reduce resistance to stress by 0.6 M urea and promote type 1 fimbriae production. The BEN2908ΔotsBA mutant was sensitive to osmotic stress by urea, but displayed an even more pronounced reduction in production of type 1 fimbriae, with the consequent reduction in adhesion/invasion of avian fibroblasts and reduced bladder colonization in the murine urinary tract. The BEN2908ΔtreAotsBA mutant also showed a reduction in production of type 1 fimbriae, but in contrast to the ΔotsBA mutant, resisted better than the wild type in the presence of urea. We hypothesize that, in BEN2908, resistance to stress by urea would depend on the levels of periplasmic trehalose, but type 1 fimbriae production would be influenced by the levels of cytosolic trehalose.

Research Note: Synergistic effect of isopropoxy benzene guanidine and colistin against mcr-1-positive Escherichia coli in vitro and in duck intestine infection models

Colistin (CST) is considered as "agent of last resort" against gram-negative bacteria as feed additive. Its clinical effectiveness has reduced since the emergence of mcr-1 gene in ducks. Isopropoxy benzene guanidine (IBG), a new guanidine derivative, showed positive effects on improving animal weights and alleviating intestinal pathogens, therefore, the objective of this study was to evaluate the effect of this compound supplement with CST in ducks and explore the possibilities in feed additive. A total of fifteen duck-origin Escherichia coli carrying the mcr-1 gene were included in this study. A checkerboard microdilution assay was used to evaluate the in vitro antibacterial activity of IBG combined with CST against mcr-1-positive E. coli. A 3-by-2 time-kill array of IBG (16, 32, and 64 μg/mL) and CST (1/2 MIC and 1/4 MIC) over 24 hours was utilized to characterize the activity of the agents alone and in combination against E. coli strain 1 in vitro. The intestinal colonization model was used to evaluate the in vivo effect of IBG combined with CST. These results indicated that the combination of IBG plus CST showed a synergistic effect against all clinical isolates (FICI < 0.5). The bacterial burden was reduced by more than 2 log10 CFU/mL when E. coli strain 1 was tested with 1/2 MIC CST plus 64 μg/mL IBG for 24 h. Further experiments in vivo demonstrated that the CST combined with IBG was able to increase duck weights, reduced intestinal pathogenic E. coli and showed a synergistic antibacterial effect. Combination of CST (4 mg/kg b.w.) plus IBG (32 or 64 mg/kg b.w.) achieved 1.84 to 3.29 log10 CFU/g killing after 7 d of therapy, which was significantly different from that in the challenge control group (p<0.05). In summary, our study demonstrated the potential use of IBG as feed additive for veterinary purposes in ducks and provided new insights into overcoming resistance in the future.

Inhibition of the ATP synthase increases sensitivity of Escherichia coli carrying mcr-1 to polymyxin B.

Bacterial infections caused by multidrug-resistant (MDR) gram-negative strains carrying the mobile colistin resistance gene mcr-1 are serious threats to world public health due to the lack of effective treatments. Inhibition of the ATP synthase makes bacteria such as Staphylococcus aureus and Klebsiella pneumoniae more sensitive to polymyxin. This provides new strategies for treating infections caused by polymyxins-resistant bacteria carrying mcr-1. Six mcr-1-positive strains were isolated from clinical samples, and all were identified as Escherichia coli. Here we investigated several ATP synthase inhibitors, N,N'-dicyclohexylcarbodiimide (DCCD), resveratrol, and piceatannol, for their antibacterial effects against the mcr-1-positive strains combined with polymyxin B (POL). Checkerboard assay, time-kill assay, biofilm inhibition and eradication assay indicated the significant synergistic effect of ATP synthase inhibitors/POL combination in vitro. Meanwhile, mouse infection model experiment was also performed, showing a 5 log10 reduction of the pathogen after treatment with the resveratrol/POL combination. Moreover, adding adenosine disodium triphosphate (Na2ATP) could inhibit the antibacterial effect of the ATP synthase inhibitors/POL combination. In conclusion, our study confirmed that inhibition of ATP production could increase the susceptibility of bacteria carrying mcr-1 to polymyxins. This provides a new strategy against polymyxins-resistant bacteria infection.

A mathematical model of mobility-related infection and vaccination in an epidemiological case

In this study, we established a system of differential equations with piecewise constant arguments to explain the impact of epidemiological transmission between different locations. Our main goal is to look into the need for vaccines as well as the necessity of the lockdown period. We proved that keeping social distance was necessary during the pandemic spread to stop transmissions between different locations and that re-vaccinations, including screening tests, were crucial to avoid reinfections. Using the Routh-Hurwitz Criterion, we examined the model’s local stability and demonstrated that the system could experience Stationary and Neimark-Sacker bifurcations depending on certain circumstances.

A mathematical model of mobility-related infection and vaccination in an epidemiological case

In this study, we established a system of differential equations with piecewise constant arguments to explain the impact of epidemiological transmission between different locations. Our main goal is to look into the need for vaccines as well as the necessity of the lockdown period. We proved that keeping social distance was necessary during the pandemic spread to stop transmissions between different locations and that re-vaccinations, including screening tests, were crucial to avoid reinfections. Using the Routh-Hurwitz Criterion, we examined the model’s local stability and demonstrated that the system could experience Stationary and Neimark-Sacker bifurcations depending on certain circumstances.

Antibacterial activity of gallic acid and methyl gallate against emerging non-fermenting bacilli.

Stenotrophomonas maltophilia, Achromobacter xylosoxidans, and Burkholderia cenocepacia are considered emerging pathogens classified as a public health problem due to extensive antimicrobial resistance. Therefore, the discovery of new therapeutic strategies has become crucial. This study aimed to evaluate the antimicrobial activity of gallic acid and methyl gallate against non-fermenting bacteria. The study included five clinical isolates of Stenotrophomonas maltophilia, Achromobacter xylosoxidans, and Burkholderia cenocepacia. The minimum inhibitory concentrations of gallic acid and methyl gallate were determined by the broth microdilution method. Growth curves, metabolic activity, and biofilm formation of each bacterial strain in the presence or absence of phenolic compounds were performed. Finally, the therapeutic efficacy of the compounds was evaluated using an in vivo model. Gallic acid and methyl gallate showed antibacterial activity against bacterial strains in a concentration range of 64 to 256µg/mL, both compounds reduced bacterial growth and metabolic activity of the strains, even at subinhibitory concentrations. Only, methyl gallate exhibited activity to inhibit the formation of bacterial biofilms. Moreover, gallic acid and methyl gallate increased larval survival by up to 60% compared to 30% survival of untreated larvae in a bacterial infection model in Galleria mellonella. Our results highlight the potential of gallic acid and methyl gallate as therapeutic alternatives for infections by emerging non-fermentative bacteria.

The Influence of Body Fat Dynamics on Pulmonary Immune Responses in Murine Tuberculosis: Unraveling Sex-Specific Insights.

The World Health Organization (WHO) highlights a greater susceptibility of males to tuberculosis (TB), a vulnerability attributed to sex-specific variations in body fat and dietary factors. Our study delves into the unexplored terrain of how alterations in body fat influence Mycobacterium tuberculosis (Mtb) burden, lung pathology, immune responses, and gene expression, with a focus on sex-specific dynamics. Utilizing a low-dose Mtb-HN878 clinical strain infection model, we employ transgenic FAT-ATTAC mice with modulable body fat to explore the impact of fat loss (via fat ablation) and fat gain (via a medium-fat diet, MFD). Firstly, our investigation unveils that Mtb infection triggers severe pulmonary pathology in males, marked by shifts in metabolic signaling involving heightened lipid hydrolysis and proinflammatory signaling driven by IL-6 and localized pro-inflammatory CD8+ cells. This stands in stark contrast to females on a control regular diet (RD). Secondly, our findings indicate that both fat loss and fat gain in males lead to significantly elevated (1.6-fold (p ≤ 0.01) and 1.7-fold (p ≤ 0.001), respectively) Mtb burden in the lungs compared to females during Mtb infection (where fat loss and gain did not alter Mtb load in the lungs). This upsurge is associated with impaired lung lipid metabolism and intensified mitochondrial oxidative phosphorylation-regulated activity in lung CD8+ cells during Mtb infection. Additionally, our research brings to light that females exhibit a more robust systemic IFNγ (p ≤ 0.001) response than males during Mtb infection. This heightened response may either prevent active disease or contribute to latency in females during Mtb infection. In summary, our comprehensive analysis of the interplay between body fat changes and sex bias in Mtb infection reveals that alterations in body fat critically impact pulmonary pathology in males. Specifically, these changes significantly reduce the levels of pulmonary CD8+ T-cells and increase the Mtb burden in the lungs compared to females. The reduction in CD8+ cells in males is linked to an increase in mitochondrial oxidative phosphorylation and a decrease in TNFα, which are essential for CD8+ cell activation.

Inhibitory effect of 5-hydroxy-6,7-dimethoxyflavone on H1N1 influenza virus-induced ferroptosis and inflammation in A549 cells and its possible mechanisms

To investigate the protective effect of 5-hydroxy-6,7-dimethoxyflavone (5-HDF), a compound extracted from Elsholtzia blanda Benth., against lung injury induced by H1N1 influenza virus and explore its possible mechanism of action. 5-HDF was extracted from Elsholtzia blanda Benth. using ethanol reflux extraction and silica gel chromatography and characterized using NMR and MS analyses. In an A549 cell model of H1N1 influenza virus infection (MOI=0.1), the cytotoxicity of 5-HDF was assessed using MTT assay, and its effect on TRAIL and IL-8 expressions was examined using flow cytometry; Western blotting was used to detect the expression levels of inflammatory, apoptosis, and ferroptosis-related proteins. In a mouse model of H1N1 influenza virus infection established by nasal instillation of 50 μL H1N1 virus at the median lethal dose, the effects of 30 and 60 mg/kg 5-HDF by gavage on body weight, lung index, gross lung anatomy and lung histopathology were observed. 5-HDF exhibited no significant cytotoxicity in A549 cells within the concentration range of 0-200 μg/mL. In H1N1-infected A549 cells, treatment with 5-HDF effectively inhibited the activation of phospho-p38 MAPK and phospho-NF-κB p65, lowered the expressions of IL-8, enhanced the expression of anti-ferroptosis proteins (SLC7A11 and GPX4), and inhibited the expressions of apoptosis markers PARP and caspase-3 and the apoptotic factor TRAIL. In H1N1-infected mice, treatment with 5-HDF for 7 days significantly suppressed body weight loss and increment of lung index and obviously alleviated lung tissue pathologies. 5-HDF offers protection against H1N1 influenza virus infection in mice possibly by suppressing H1N1-induced ferroptosis, inflammatory responses, and apoptosis via upregulating SLC7A11 and GPX4, inhibiting the activation of phospho-NF-κB p65 and phospho-p38 MAPK, and decreasing the expression of cleaved caspase3 and cleaved PARP.

CD8+ T cell-derived Fgl2 regulates immunity in a cell-autonomous manner via ligation of FcγRIIB

The regulatory circuits dictating CD8+ T cell responsiveness versus exhaustion during anti-tumor immunity are incompletely understood. Here we report that tumor-infiltrating antigen-specific PD-1+ TCF-1− CD8+ T cells express the immunosuppressive cytokine Fgl2. Conditional deletion of Fgl2 specifically in mouse antigen-specific CD8+ T cells prolongs CD8+ T cell persistence, suppresses phenotypic and transcriptomic signatures of T cell exhaustion, and improves control of the tumor. In a mouse model of chronic viral infection, PD-1+ CD8+ T cell-derived Fgl2 also negatively regulates virus-specific T cell responses. In humans, CD8+ T cell-derived Fgl2 is associated with poorer survival in patients with melanoma. Mechanistically, the dampened responsiveness of WT Fgl2-expressing CD8+ T cells, when compared to Fgl2-deficient CD8+ T cells, is underpinned by the cell-intrinsic interaction of Fgl2 with CD8+ T cell-expressed FcγRIIB and concomitant caspase 3/7-mediated apoptosis. Our results thus illuminate a cell-autonomous regulatory axis by which PD-1+ CD8+ T cells both express the receptor and secrete its ligand in order to mediate suppression of anti-tumor and anti-viral immunity.

Tracking Chlamydia – Host interactions and antichlamydial activity in Caenorhabditis elegans

The fading efficacy of antibiotics is a growing global health concern due to its life-threatening consequences and increased healthcare costs. Non-genetic mechanisms of antimicrobial resistance, such as those employed by Chlamydia pneumoniae and Chlamydia trachomatis, complicate treatment as these bacteria can enter a non-replicative, persistent state under stress, evading antibiotics and linking to inflammatory conditions. Understanding chlamydial persistence at the molecular level is challenging, and new models for studying Chlamydia-host interactions in vivo are urgently needed. Caenorhabditis elegans offers an alternative given its immune system and numerous orthologues of human genes. This study established C. elegans as an in vivo model for chlamydial infection. Both Chlamydia species reduced the worm's lifespan, their DNA being detectable at three- and six-days post-infection. Azithromycin at its MIC (25 nM) failed to prevent the infection-induced lifespan reduction, indicating a persister phenotype. In contrast, the methanolic extract of Schisandra chinensis berries showed anti-chlamydial activity both in vitro (in THP-1 macrophages) and in vivo, significantly extending the lifespan of infected C. elegans and reducing the bacterial load. Moreover, S. chinensis increased the transcriptional activity of SKN-1 in the worms, but was unable to impact the bacterial load or lifespan in a sek-1 defective C. elegans strain. In summary, this study validated C. elegans as a chlamydial infection model and showcased S. chinensis berries' in vivo anti-chlamydial potential, possibly through SEK/SKN-1 signaling modulation.