Infection and Immunity最新文献

The stomach bacterium Helicobacter pylori is estimated to infect half of the world's population, and the health implications are affected by the age at infection. Neonatal H. pylori infection of mice is a relevant model to investigate metabolic and immunological effects. We performed an explorative study at the dynamic 1st month of life to compare the composition of the gastrointestinal tract microbiome and stomach gene expression of mice neonatally infected with H. pylori with that of uninfected mice. We found that H. pylori was present only in the stomach, and that H. pylori loads increase with age from 1 week after infection and onward, especially after weaning. Stomach and colon microbiome composition was strikingly similar between sites at the same sampling time but changed significantly over 1 week, with increased diversity at both sites. Despite the fact that the relative abundance of H. pylori in the stomach was low and never exceeded 3%, the composition and alpha diversity of the gastrointestinal microbiome was significantly affected by infection. In a pathway enrichment analysis, we found that stomach gene expression related to the extracellular matrix, muscle contraction, and metabolism was affected by infection. Expression of these key processes was, in infected mice, shifted away from that of control mice toward that of all mice sampled the subsequent week, which we speculate represents accelerated development in infected mice.

Cryptosporidium infects the intestine in a wide variety of vertebrates, and intestinal epithelial cells provide the first line of defense against Cryptosporidium infection. Interferon gamma (IFN-γ) from immune cells infiltrated at the site of infection plays a key role in the epithelial cell-intrinsic defense. Nevertheless, the success of the parasite is the result of its ability to evade the host immune responses. Increasing evidence suggests that long noncoding RNAs (lncRNA) participate in host-pathogen interactions, but the underlying mechanisms are not fully understood. We previously demonstrated that lncRNA U90926 is upregulated in response to infection but appears to be playing a pro-parasitic role given its ability to repress transcription of defense genes and aid the parasite during infection. We show here that inhibition of U90926 during Cryptosporidium infection increased expressions of Irgm2, Igtp, and Iigp1, which are known IFN-γ-stimulated genes, in a gene-specific manner. Depletion of U90926 results in an increase in histone modifications associated with gene transactivation in the promoter regions of Irgm2, Igtp, and Ilgp1, suggesting U90926 is regulating defense gene expression via epigenetic modifications. U90926 can interact with Ehmt2, a potent euchromatic methyltransferase, in the promoter region of these defense genes to alter histone modifications. Knockout of U90926 enhances IFN-γ-mediated inhibition of Cryptosporidium infection, suggesting that U90926 may modulate IFN-γ-induced gene expression to suppress cell-intrinsic antimicrobial defenses. The data highlight a strategy Cryptosporidium has evolved to hijack host cell lncRNA machinery to suppress the immune response and allow for a robust infection.

Chronic infections with Pseudomonas aeruginosa are a major contributor of lung decline in persons with cystic fibrosis (pwCF). P. aeruginosa establishes life-long infections in the CF airway by utilizing various adaptation strategies to persist, including altering the expression of metabolic genes to acquire nutrients that are abundant in the CF airway. Glycerol, which is readily available in the airway, is imported and metabolized by genes in the glp regulon, which is under the control of the GlpR repressor. Previously, it has been shown that the loss of GlpR results in increased biofilm development in a CF-adapted isolate of P. aeruginosa compared to a wound isolate. Based on the increased biofilm phenotype previously observed and because biofilms are associated with reduced antibiotic susceptibility, we questioned whether GlpR plays a role in mediating antibiotic susceptibility of P. aeruginosa. In this report, we show that loss of GlpR reduces tobramycin susceptibility of a CF-adapted isolate in synthetic sputum and in airway epithelial cell and Drosophila melanogaster colonization models. Furthermore, transcriptomics analysis revealed that CF-adapted mutants of glpR overexpress genes involved in multidrug resistance and chronic infection phenotypes such as alginate. In summary, our study illustrates that the activation of the glycerol (glp) regulon may promote P. aeruginosa persistence in the CF airway.

Clostridioides difficile is a spore-forming, Gram-positive bacterium that can cause infections in subjects with weakened immune system or following antibiotic treatment. These infections may lead to pseudomembranous colitis and antibiotic-associated diarrhea in humans. As such, C. difficile is a major cause of nosocomial illness worldwide. Major virulence factors of the bacterium are the large clostridium toxins A (TcdA) and B (TcdB)-high molecular mass proteins with intrinsic glucosyltransferase activity. Toxins bind to the intestinal epithelium and undergo endocytosis by the epithelial cells, followed by a conformational change triggered by the low pH of early endosomes. This conformational change leads to the exposure of hydrophobic segments, followed by membrane insertion, formation of pores, and translocation of the glucosyltransferase domain into the cellular cytoplasm. Once in the cytoplasm, the glucosyltransferase domain inactivates small GTPases of the Rho family of proteins, leading to the disruption of the cytoskeleton. In the current work, we describe the discovery and characterization of a panel of neutralizing mouse monoclonal antibodies capable of interfering with several steps of cellular intoxication by the toxins. The antibodies were produced using hybridoma technology. Neutralizing activity of the antibodies was confirmed using toxin neutralization assays, and functional assays were used to identify specific neutralization mechanisms. Binding epitopes of the antibodies were identified by hydrogen-deuterium exchange mass spectrometry and confirmed through negative-stain and cryo-electron microscopy. Together, our results show that full-length toxins and/or genetically- and chemically-modified toxoids can induce a wide spectrum of antibodies capable of neutralizing the toxins via a variety of mechanisms.

Chronic infections involving bacterial biofilms are a major clinical challenge due to the ability of biofilm to resist antimicrobial treatments and host immune responses. The resulting persistent infections are often accompanied by collateral damage mainly executed by activated components of the innate immune system in response to the infectious biofilm. The innate immune system responds to the recognition of pathogen-associated molecular patterns (PAMPs), which are broadly expressed by both planktonic and biofilm-forming bacteria. However, the expression of special PAMPs in association with biofilms remains poorly defined. Here, we review prior studies that provide experimental evidence of the existence of immune-activating molecular patterns that are expressed at immunostimulatory levels in biofilms but not in planktonic bacteria. Accordingly, we introduce the concept of biofilm-associated molecular patterns (BAMPs) as a subset of PAMPs that are expressed in biofilms. Identifying BAMPs and elucidating their role in innate immune activation may inform the development of targeted therapies to reduce collateral tissue damage in biofilm-associated infections.

Mobile genetic elements play an essential part in the infectious process of major pathogens, yet the role of prophage dynamics in Staphylococcus aureus pathogenesis is still not well understood. Here, we studied the impact of the Φ13 hlb-converting prophage, whose integration inactivates the hlb β-toxin gene, on staphylococcal pathogenesis. We showed that prophage Φ13 is lost in approximately half the bacterial population during the course of infection. Inactivation of the Φ13 int recombinase gene, essential for insertion/excision, locked the prophage in the bacterial chromosome, leading to a significant loss of virulence in a murine systemic infection model. In contrast, the non-lysogen strain (ΔΦ13), where the hlb beta-hemolysin gene is reconstituted, displayed strongly increased virulence. Accordingly, histopathological analyses revealed more severe nephritis in mice infected with bacteria lacking prophage Φ13 (ΔΦ13), compared to infection with the parental strain. Infection with the ∆int mutant, where beta-hemolysin production is abolished, led to the least severe renal lesions. Cytokine induction in a human neutrophil model showed significantly increased IL-6 expression following infection with the beta-hemolysin producing strain (ΔΦ13). Our results indicate that timely in vivo excision of the Φ13 prophage is essential for progression of the S. aureus infectious process: early excision leads to rapid host death, whereas the inability to excise the prophage significantly reduces staphylococcal virulence.IMPORTANCEThis study highlights prophage Φ13 excision as a critical factor in Staphylococcus aureus pathogenesis, influencing infection outcomes by balancing rapid host killing with reduced bacterial virulence. This mechanism may represent a bet-hedging strategy in genetic regulation, resulting in a mixed bacterial population capable of rapidly switching between two processes: bacterial colonization and host damage. Unraveling this dynamic opens new possibilities for developing targeted therapies to disrupt or modulate prophage activity, offering a novel approach to mitigating S. aureus infections.

Chlamydia trachomatis (CT) infection can lead to pelvic inflammatory disease, infertility, and other reproductive sequelae when it ascends to the upper genital tract. Factors including chlamydial burden, coinfection with other sexually transmitted bacterial pathogens, and oral contraceptive use influence risk for upper genital tract spread. Cervicovaginal microbiome composition influences CT susceptibility, and we investigated if it contributes to spread by analyzing amplicon sequence variants (ASVs) derived from the V4 region of 16S rRNA genes in vaginal samples collected from women at high risk for CT infection and for whom endometrial infection had been determined. Participants were classified as CT negative (CT-, n = 70), CT positive at the cervix (Endo-, n = 79), or CT positive at both cervix and endometrium (Endo+, n = 68). Although we were unable to identify many significant differences between CT-infected and -uninfected women, differences in abundance of ASVs representing Lactobacillus iners and Lactobacillus crispatus subspecies but not dominant lactobacilli were detected. Thirteen informative ASVs predicted endometrial chlamydial infection (area under the curve = 0.72), with CT ASV abundance emerging as a key predictor. We also observed a positive correlation between levels of cervically secreted cytokines previously associated with CT ascension and abundance of the informative ASVs. Our findings suggest that vaginal microbial community members may influence chlamydial spread directly by nutrient limitation and/or disrupting endocervical epithelial integrity and indirectly by modulating proinflammatory signaling and/or homeostasis of adaptive immunity. Further investigation of these predictive microbial factors may lead to cervicovaginal microbiome biomarkers useful for identifying women at increased risk for disease.

Preterm infants are highly susceptible to bacterial infections and inflammatory diseases. These vulnerabilities arise from disruptions in gut microbiome structure and function, immune system immaturity, and underdeveloped organ systems. In this review, we explore the role of the gut microbiome in neonatal health. With a specific focus on preterm infants, we outline how microbiome disruption contributes to negative clinical outcomes. First, we provide an overview of infant gut microbiome development, highlighting key factors that influence its trajectory. Next, we examine the interplay between the infant gut microbiome and the development of systemic and intestinal immune systems, with emphasis on how microbiome perturbations related to preterm birth alter host-microbiome interactions and the overall immune landscape. We then discuss the role of altered gut composition in disease states common to preterm infants, such as sepsis, bacterial infections, and necrotizing enterocolitis. Finally, we discuss current and future diagnostics and treatments and offer our perspective on future research to untangle the host-microbiome interface in early life.

Entamoeba histolytica is a major cause of diarrheal disease. E. histolytica trophozoites ("amoebae") can invade the intestine and disseminate via the bloodstream, resisting complement lysis through unknown mechanisms. Amoebae kill human cells by performing trogocytosis. After performing trogocytosis, amoebae display human proteins on their own surface and are resistant to lysis by human serum. In this study, we sought to further evaluate the mechanism by which amoebae resist complement lysis. To test if complement is responsible for lysis of amoebae, C3-depleted serum was compared to replete serum, and C3 was indeed required for lysis. Amoebae were allowed to perform trogocytosis of human cells and exposed to mouse serum. Although they had performed trogocytosis on a different species than the source of the serum, they were protected from lysis. To test if the protection from lysis by mouse serum was due to the functional interchangeability of human and mouse complement pathway proteins, human CD46 or CD55 (negative regulators of complement activation) were exogenously expressed. Amoebae that expressed human CD46 or CD55 were protected from lysis by mouse serum, indicating that display of human proteins was sufficient to inhibit mouse complement activation. Finally, amoebae were allowed to perform trogocytosis of a cell type in which the complement pathway is not conserved, and they did not become resistant to lysis. Overall, these findings are consistent with the model that trogocytosis enables amoebic acquisition and display of host proteins, including negative regulators of the complement pathway, that provide protection from complement lysis. Since other microbes can perform trogocytosis, this novel mechanism for complement resistance might apply to other infections.

Bloodstream infections caused by Pseudomonas aeruginosa are associated with high mortality rates. The complement system, a key component of the innate immune response, plays a major role in eliminating P. aeruginosa from human blood. However, the sensitivity of P. aeruginosa strains to plasma varies widely, ranging from highly sensitive to persistent or fully resistant. Although most studies use model strains, the species genomic and phenotypic diversities suggest more complex interactions with complement than previously appreciated. In this study, we characterized the plasma resistome of P. aeruginosa using Tn-seq in three strains with varying levels of plasma sensitivity. A gain-of-function screen in the plasma-sensitive strain PA14 revealed numerous bacterial factors influencing plasma resistance, including components of the RetS-LadS/Gac/Rsm regulatory pathway and outer membrane porins. In the plasma-resistant strains CHA and YIK, Tn-seq analysis indicated that each strain relies on a distinct, limited set of proteins to evade complement-mediated killing. Despite these differences, we identified common mechanisms across all three strains. These include the production of exopolysaccharides (EPSs), the presence of surface appendages, and modifications in the O-specific antigen. Notably, we identified Ssg and Crc as shared contributors to plasma resistance. Although deletion mutants lacking ssg and/or crc exhibited reduced survival in plasma, a subpopulation of these mutants was able to persist during prolonged exposure. Overall, this work provides new insights into the complex interplay between P. aeruginosa and the human complement system in the context of bloodstream infections and raises concerns regarding the efficacy of therapies that target individual virulence factors.