Infection and Immunity最新文献

Type I interferons (IFNs) play complex roles during bacterial infections. We previously found that type I IFNs were induced in Bordetella pertussis-infected adult mice but not in infant mice, a potentially relevant clinical dichotomy, since pertussis can be fatal in human infants. We investigated the role of type I IFNs and their cross-regulation with type III IFNs (IFN-λ) in B. pertussis infection across developmental stages. In contrast to global IFNAR1 knockout adult mice, in which lung inflammation was equivalent to that in wild-type mice, myeloid cell-specific deficiency of the type I IFN receptor protein IFNAR1 (LysM^CreIFNAR1^fl/fl) resulted in significantly reduced lung inflammation and pro-inflammatory cytokine production, despite elevated pulmonary IFN-λ levels. Mechanistically, we found that, in contrast to WT macrophages, IFNAR1-deficient macrophages produced IFN-λ in response to B. pertussis or pertussis toxin, a process dependent on the G protein-coupled receptor lysophosphatidic acid receptor 1 (LPAR1). IFNAR1 deficiency did not affect type I IFN expression or killing capacity by macrophages and neutrophils. In striking contrast to WT infant mice, which developed resistance to lethal B. pertussis infection by postnatal day 10 (P10), LysM^CreIFNAR1^fl/fl infant mice remained highly susceptible to lethal infection through P21, exhibiting increased lung bacterial burden and inflammation, as well as increased bacterial dissemination compared to WT infant mice. These findings reveal a critical age- and cell-specific interplay between type I and III IFNs during B. pertussis infection and highlight a novel LPAR1-dependent pathway for IFN-λ induction in the absence of type I IFN signaling.

Staphylococcus aureus is an important cause of human infections globally and ranks among the top causes of death by bacteria. In addition, the microbe is notorious for developing resistance to antibiotics. Methicillin-resistant S. aureus is endemic in healthcare facilities and the community in many regions of the world. Although our understanding of S. aureus as a human commensal organism and opportunistic pathogen remains incomplete, the use of genomics and transcriptomics approaches for S. aureus research has advanced this knowledge significantly over the past 20 years. This article reviews genomics approaches, with special emphasis on transcriptomics and single-cell sequencing, used to study S. aureus, past and present, and highlights selected discoveries made with these methods and new applications moving forward.

Listeria monocytogenes is a facultative intracellular pathogen that has garnered attention as a potential cancer therapeutic due to its ability to induce robust cell-mediated immunity. To ensure safe clinical administration, deletion of certain genes, such as actA, has been used to attenuate L. monocytogenes-based vaccine strains while preserving immunogenicity. Here we explored the potential inclusion of a purA gene deletion to enhance the development of L. monocytogenes-based immunotherapy. The purA gene encodes adenylosuccinate synthetase, which catalyzes the conversion of inosine monophosphate to adenosine monophosphate (AMP), a critical step in the de novo biosynthesis of purines. Since nucleotide biosynthesis is critical for the survival and pathogenesis of many bacterial pathogens, we examined the requirements of L. monocytogenes AMP synthesis in tissue culture and animal infection models. The purA mutants were able to escape from phagosomes of bone marrow-derived macrophages but were highly defective for subsequent growth in the host cell cytosol. In contrast to wild-type bacteria, the mutants did not grow in human serum or sheep blood. In intravenously infected mice, purA mutants were highly attenuated, similar to actA mutants, but displayed distinct growth kinetics during the course of infection. Remarkably, the purA mutants exhibited different localization patterns across splenic immune cells and elicited a more potent CD8⁺ T-cell response compared to actA mutants. These results underscore the essentiality of AMP biosynthesis for L. monocytogenes pathogenesis and provide new avenues for developing safe L. monocytogenes-based vaccines and therapeutics.

Klebsiella pneumoniae (Kp) is a major human pathogen causing hospital-acquired and community-acquired infections with emerging hypervirulent strains (hvKp) posing a significant threat due to its ability to cause severe invasive infections in healthy individuals. In addition to antimicrobial resistance, virulence factors including capsule production, biofilm formation, and iron acquisition systems are critical for hvKp pathogenesis. In this study, we investigated how resistance-nodulation-division (RND)-family efflux systems contribute to antimicrobial resistance and virulence in hvKp strain KPPR1 using the RND-specific inhibitor phenyl-arginine β-naphthylamide (PAβN). We found that PAβN treatment rendered KPPR1 more susceptible to multiple antibiotics while simultaneously attenuating virulence factor production. PAβN significantly reduced capsule biosynthetic gene expression, resulting in decreased uronic acid levels, hypermucoviscosity, and biofilm formation. PAβN also impaired growth under iron-limited conditions, suggesting RND-mediated efflux contributes to iron acquisition. PAβN-dependent virulence attenuation was demonstrated through reduced KPPR1 adherence to cultured intestinal enterocytes and decreased pathogenicity in the Galleria mellonella infection model compared to untreated controls. Collectively, these results demonstrate that RND-mediated efflux is critical for both antimicrobial resistance and virulence in hvKp strain KPPR1. Our findings establish RND efflux inhibitors as promising dual-target therapeutics that can simultaneously combat antibiotic resistance and attenuate virulence in hvKp infections.

Lymphotoxin β receptor (LTβR/TNFRSF3) signaling plays a crucial role in immune defense. Notably, LTβR-deficient (LTβR^-/-) mice exhibit severe defects in innate and adaptive immunity against various pathogens and succumb to Toxoplasma gondii infection. Here, we investigated the bone marrow (BM) and peritoneal cavity (PerC) compartments of LTβR^-/- mice during T. gondii infection, demonstrating perturbed B-cell and T-cell subpopulations in the absence of LTβR signaling. T. gondii infection disrupted BM lymphopoiesis, depleting early and mature B cells in WT mice, whereas mature B cells remained present in LTβR^-/- BM. LTβR^-/- BM also exhibited reduced MHCII⁺ monocytes and a plasma cell compartment skewed toward IgM⁺ rather than IgA⁺ cells. In addition, BM Tcell subsets were altered, exhibiting decreased double-negative (CD4^-/CD8^-) and increased CD4⁺ and CD8⁺ T-cell frequencies. Analysis of the BM transcriptome revealed diminished interferon responses but an upregulated TNFα-NF-κB signaling signature in uninfected and infected LTβR^-/- mice, potentially compensating for the absence of LTβR signaling. LTβR^-/- mice displayed an altered B-1a to B-1b ratio and a predominant presence of neutrophils in the PerC. In summary, we identified novel immunological alterations in the BM and PerC compartments of LTβR^-/- mice, which suggest new roles for LTβR signaling in B- and T-cell homeostasis, migration, and pathogen defense.

Contagious bovine pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides (Mmm), is a devastating cattle disease with high morbidity and mortality, threatening cattle productivity in Sub-Saharan Africa and potentially in parts of Asia. Cross-border livestock trade increases the risk of CBPP introduction or reintroduction. Current vaccines were developed from attenuated Mmm strains in the last century and face limitations regarding animal welfare, immunity duration, and adverse reactions, necessitating new vaccine strategies. Subunit vaccines offer a promising alternative, but identifying effective antigens is critical. Given the key role of cellular immunity in CBPP control, we focused on antigen identification that elicits a host cellular immune response. This study explores antigen candidates based on Ben-181, a vaccine that successfully eradicated CBPP in China. Ben-181 specifically induces interferon-γ (IFN-γ)-dependent IRG-47 expression, and IFN-γ correlates with cellular immune responses. We propose IRG-47 as a potential marker for Mmm antigen screening. Comparative genomic analysis between Ben-181 and the non-immunoprotective strain Ben-468 identified 35 proteins potentially linked to IRG-47 expression. Further screening revealed Mmm604, Mmm605, and Mmm606 as inducers of IRG-47 release. Intranasal immunization with these proteins in mice enhanced splenic lymphocyte proliferation, CD8 +T cell activation, a mixed Th1/Th2/Th17 response, and humoral antibody production. Mmm604 and Mmm606 also trigger mucosal antibody responses in mice. These proteins effectively stimulate cellular and humoral responses, making them promising candidates for Mmm subunit vaccine development. Our study highlights the potential of IRG-47 in Mmm antigen screening.

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.