Infection and Immunity最新文献

Canine and human anaplasmosis are tick-borne diseases caused by the obligate intracellular bacteria, Anaplasma phagocytophilum and Anaplasma platys, respectively. In veterinary medicine, peptides derived from the immunodominant P44 protein are used to detect antibodies in serological point-of-care tests for anaplasmosis. To inform efforts to develop improved chimeric diagnostic proteins for anaplasmosis, the structure of the predicted surface-exposed domain (residues 151-308) of P44 was determined at a resolution of 1.65 Å. This domain comprises six α-helices and six short β-strands connected by loop regions. A structural similarity search of the P44_151-308 domain using the Distance Matrix Alignment server against the AlphaFold Database revealed that the domain represents a previously uncharacterized protein fold. The determined structure is consistent with AlphaFold v2 predictions, which further predict the core of P44 to be an eight-stranded β-barrel. Using P44 fragments, immunodominant epitopes were mapped within residues 151-308. Four chimeric genes (ADC1, ADC2, ADC3, and ADC4) were designed that incorporate the analogous immunodominant P44 domains from A. phagocytophilum and A. platys. The recombinant ADC chimerics were assessed for sensitivity and specificity by screening with serum from dogs diagnosed with anaplasmosis, Lyme disease, or ehrlichiosis, with sera from specific pathogen-free dogs serving as negative controls. Accuracy was further demonstrated by screening characterized serum samples from coyotes (Canis latrans; wild canids). The ADC1 chimeric provided 100% sensitivity and 98.04% specificity. The sensitivity and specificity of ADC1 support its potential use as a diagnostic Ag for anaplasmosis.

The biosynthetic locus encoding the exopolysaccharide poly-N-acetyl-glucosamine (PNAG) is widely conserved across bacteria, including the World Health Organization critical-priority pathogen Klebsiella pneumoniae (Kp). In Kp, PNAG synthesis is mediated by the pgaABCD operon, yet its lineage-specific regulation remains incompletely understood. Using a comparative genomics approach to interrogate the pgaABCD locus across the high-risk clonal Kp complex 258 (CC258) lineage, we identified a previously uncharacterized positive transcriptional regulator located immediately upstream of pgaA, which we designate pgaR. Phylogenetic analysis revealed recurrent evolutionary events affecting this regulatory region, including repeated deletion or truncation of pgaR and a G > A substitution upstream of the pgaR start codon. Functional characterization demonstrated that loss of pgaR abolishes pgaABCD expression and PNAG production, whereas the upstream G > A substitution drives PNAG hyperproduction. Under in vitro growth conditions, Kp produce extensive extracellular PNAG networks. Using a prototype hypervirulent strain to model the role of PNAG in vivo indicated that it is dispensable for virulence in murine pneumonia and peritonitis models. In contrast, PNAG hyper-production significantly attenuated virulence and reduced disease severity. Collectively, these findings identify PgaR as a novel upstream gene regulator of the pgaABCD operon and reveal a previously unrecognized lineage-specific layer of PNAG regulation in Kp. This demonstrates that opposing PNAG phenotypes, loss and hyper-production, have independently and repeatedly emerged among clinical CC258 isolates, highlighting selective pressures acting on this locus.

Interferons (IFNs) coordinate host defense at the lung barrier by linking pathogen recognition to epithelial and immune-cell responses. Their effects are highly context-dependent and can be protective or pathological according to IFN class and ligand, cellular source and target, and the timing and duration of signaling. In this minireview, we compare the induction of type I, II, and III IFNs during respiratory viral infection and pulmonary Aspergillus fumigatus infection, highlighting epithelial-led antiviral sensing and predominantly myeloid-centered antifungal sensing. We then examine how receptor distribution, ligand identity, JAK-STAT complex assembly, and integration with inflammatory pathways generate cell type-specific transcriptional and functional programs. Finally, we discuss three interconnected consequences of IFN crosstalk at the respiratory barrier: regulation of epithelial permeability and repair, licensing or pathological reprogramming of immune effector cells during primary infection, and loss of coordination during viral-fungal coinfection, including influenza-associated and COVID-19-associated pulmonary aspergillosis. Collectively, the available evidence supports a model in which spatially restricted and appropriately timed IFN responses promote pathogen control and preserve barrier function, whereas excessive, prolonged, or mistimed signaling impairs epithelial recovery, disrupts phagocyte activity, and increases susceptibility to secondary fungal invasion. Defining these context-dependent circuits may guide therapeutic strategies that modulate IFN signaling with greater temporal and cell type specificity.

The ESKAPE group of pathogens comprises Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp., which are capable of developing profound biofilms while infecting host tissues and medical devices. In addition to acting as a barrier to antimicrobial treatments and as a niche for the transmission of antibiotic resistance genes, biofilm-associated extracellular polymeric substances and metabolites modulate innate and adaptive immune responses. With the rise of emerging resistance against last-resort antibiotics, divulging the cross-talk between ESKAPE biofilms and the host immune system is essential for designing therapies aimed at immunoactivation. Compared with their Gram-positive ESKAPE counterparts, limited therapeutics coupled with higher mortality-associated phenotypes make Gram-negative ESKAPE pathogens an urgent priority for immediate action. The ultimate goals for strategizing such interventions are to disrupt biofilm integrity, restore immune efficacy, and improve clinical outcomes against multi- or pan-drug-resistant pathogens. Against this backdrop, this review highlights the alteration of the host immune system and the modifications in innate and adaptive immune responses caused by Gram-negative ESKAPE pathogens. In addition, the possibility of success of immunomodulation-based strategies in combating bacterial biofilms and accentuating the activity of known antimicrobials is discussed objectively.

Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) are ESKAPE pathogens that are responsible for severe skin and soft tissue infections (SSTIs), particularly in the elderly and those with immunocompromising conditions. Rising rates of methicillin-resistant S. aureus (MRSA) and carbapenem-resistant PA have rendered standard antibiotics less effective. Unfortunately, there are currently no licensed vaccines for either pathogen. To address this need, we developed a bivalent intranasal (IN) vaccine formulation combining L-PaF, a fusion of PA T3SS proteins PcrV and PopB, with the mucosal adjuvant LTA1, NEAT2 (N2), the protective heme-transporting domain of SA IsdB protein, and a novel TLR-4 agonist, which is a detoxified lipid A analog designated Bacterial Enzymatic Combinatorial Chemistry 438 (BECC438b), formulated in an oil-in-water medImmune emulsion (ME). Mice immunized with L-PaF/ME/N2/BECC438b generated robust antigen-specific IgG and IgA responses, which correlated with strong opsonophagocytic killing of both MRSA and PA strains. Vaccination also induced interleukin IL-17A, IL-2, and IL-22 responses in spleen cells from both young and elderly mice, supporting Th1/Th17-mediated immunity. In stringent murine SSTI models, immunized animals exhibited significantly reduced dermonecrosis, abscess volume, and bacterial burden, with approximately a 10-fold reduction in abscess CFUs compared to non-immunized controls. Notably, significant protection was observed in both young and elderly mice despite age-related immunosenescence, with elderly vaccinated animals showing substantially reduced abscess formation and bacterial burden relative to non-immunized controls. These results suggest that the bivalent L-PaF/ME/N2/BECC438b formulation has potential as a broad-spectrum vaccine against both MRSA- and PA-mediated SSTIs across different age groups.

Dendritic cells (DCs) require substantial metabolic reprogramming to mount an immune response against parasites. In the context of Echinococcus granulosus infection, parasite antigens can modulate host immune responses; however, their specific impact on DC metabolism remains poorly defined. We measured mitochondrial membrane potential (ΔΨM), intracellular reactive oxygen species (ROS), and nitric oxide (NO) production in FMS-like tyrosine kinase 3 ligand (FLT3-L)-derived DC (FL-DCs) stimulated with hydatid fluid (HF) or purified laminar layer (pLL) from E. granulosus. Gene expression profiling of key metabolic enzymes involved in glycolysis and oxidative phosphorylation (OXPHOS) was performed using RT-qPCR. Functional metabolic flux was analyzed using the Seahorse glycolysis stress test, while key metabolites from both pathways were quantified by HPLC. Our results showed that HF-stimulated FL-DCs exhibited marked mitochondrial dysfunction, evidenced by reduced ΔΨM and diminished mitochondrial network complexity, in contrast to the preserved mitochondrial morphology in pLL-stimulated cells. Gene expression analysis revealed that both stimuli enhanced glycolytic enzyme transcripts; however, only pLL induced OXPHOS-related genes, suggesting divergent bioenergetic adaptations. HF-stimulated FL-DCs produced elevated levels of ROS and NO, indicative of oxidative stress and a glycolysis-favored metabolic state, whereas pLL maintained mitochondrial respiration without excessive ROS production. Metabolic flux assays corroborated these findings; HF-stimulated cells displayed an increased extracellular acidification rate and a decreased oxygen consumption rate, indicating a glycolytic shift. In contrast, pLL-stimulated FL-DCs preserved oxidative metabolism and aerobic glycolysis. Our findings demonstrate that HF and pLL from E. granulosus differentially modulate metabolic programs in FL-DCs and highlight potential targets for modulating DC function in echinococcosis pathogenesis.

Campylobacter jejuni is a microaerophilic, gram-negative bacterium and one of the leading causes of bacterial gastroenteritis worldwide, most commonly transmitted through contaminated poultry products. The organism exhibits striking host-specific behavior, persisting as a harmless commensal in the chicken intestine while causing inflammatory disease and rapid proliferation in the human gut. Despite its clinical importance, the mechanisms underlying nutrient acquisition, metabolic adaptation, and fitness during infection remain incompletely understood. The ferret model of campylobacteriosis closely reproduces the colonic pathology observed in humans and has provided important insights into how C. jejuni modifies and exploits the intestinal environment during infection. Inflammation induced by infection alters gut physiology, increasing luminal oxygen availability and concentrations of metabolites such as L-lactate. Elevated L-lactate serves as a key nutrient source that enhances C. jejuni growth in vivo, illustrating the broader concept of host-pathogen metabolic crosstalk in which immune-mediated inflammation unintentionally creates nutrient-rich conditions favorable for pathogen expansion. Within the altered redox landscape of the inflamed intestine, redox-responsive signaling pathways may further regulate genes involved in lactate utilization and metabolic adaptation. Although many enteric pathogens produce virulence factors that manipulate host physiology to promote colonization, similar mechanisms in C. jejuni remain poorly defined. This review explores the potential contribution of the cytolethal distending toxin in reshaping the host environment to support bacterial growth and persistence. Understanding these metabolic and regulatory adaptations provides new insight into C. jejuni pathogenesis and highlights potential targets for therapeutic intervention.

Curli fibers produced by Escherichia coli are functional amyloids that activate Toll-like receptor 2 (TLR2), initiating innate immune responses at mucosal surfaces. While microbiome-derived curli contribute to host-microbe interactions, their intrinsic immunostimulatory activity limits their utility as programmable scaffolds for engineered probiotic systems, and dysregulated TLR2 activation has been associated with inflammatory bowel disease, systemic lupus erythematosus, neurodegeneration, and sepsis. Here, we engineered E. coli Nissle 1917 to produce modified curli fibers designed to reduce TLR2 signaling through two mechanistically distinct strategies: steric shielding via silk-elastin-like protein sequences and direct receptor antagonism via a known TLR2 antagonist, staphylococcal superantigen-like protein 3 (SSL3). Both engineered variants assembled into structurally intact amyloid fibers and exhibited significantly reduced intrinsic TLR2-dependent NF-κB activation in reporter cells. In competitive inhibition assays against structurally diverse TLR2 agonists, the SSL3 fusion achieved near-complete attenuation of TLR2-dependent signaling, maintained under rising agonist load, while steric shielding provided moderate, agonist class-dependent inhibition. In primary human monocyte-derived dendritic cells, the SSL3 fusion robustly attenuated IL-8 secretion and transcriptional induction of IL-8, IL-6, and IL-1β, whereas steric shielding produced only partial attenuation that did not translate to broad inflammatory suppression. These results establish engineered curli as a tunable platform for receptor-specific modulation of innate immune signaling and highlight the broader potential of modular microbial amyloids as programmable interfaces for engineering host-microbe interactions at mucosal surfaces.

Glycosaminoglycans (GAGs) are negatively charged polysaccharides composed of repeating disaccharide units and are essential components of the extracellular matrix throughout numerous tissues. The bladder urothelium has a protective GAG layer that primarily consists of chondroitin sulfate (CS), heparan sulfate (HS), and hyaluronic acid (HA), and urinary tract pathogens must either degrade or otherwise circumvent this layer to infect the urothelium. In this study, we investigated GAG degradation by Proteus mirabilis, a common and persistent colonizer of the catheterized urinary tract. Almost all P. mirabilis urinary tract isolates harbor a putative chondroitin endolyase (PMI2127), exolyase (PMI2128), and sulfatase (PMI2124). By generating mutant and complemented strains of these genes, we determined that P. mirabilis strain HI4320 degrades multiple forms of CS under numerous culture conditions, including during growth in human urine, and can use CS degradation products as a carbon source. Sulfatase and endolyase activities were required for efficient degradation of all CS types, while the exolyase only contributed to using CS-B or CS-C as a carbon source. Interestingly, only endolyase activity contributed to colonization in a murine model of catheter-associated urinary tract infection (CAUTI), although the colonization defect was even more pronounced when both the endolyase and exolyase were disrupted. The colonization defect was specific to the CAUTI model, likely due to the impact of catheterization on the GAG landscape of the bladder. Limiting CS degradation by P. mirabilis may therefore reduce the risk of ascending infection in catheterized patients.

Successful gastrointestinal (GI) colonization by bacterial pathogens requires adaptation to nutrient competition and host-derived stresses in the gut, with adaptation via the bacterial stringent stress response playing a critical role. Epidemiological data suggest that the GI tract serves as a reservoir from which K. pneumoniae can spread and cause invasive disease or transmit to another host. DksA is a conserved stringent response transcriptional regulator that was identified in an in vivo transposon mutagenesis screen as an important K. pneumoniae gut determinant. However, its role in K. pneumoniae pathogenesis and gut colonization remain uncharacterized. Here, we demonstrate that DksA is required for survival against membrane-targeting antibiotics, consistent with a role in cell envelope stress tolerance. In addition, DksA positively influences capsule biosynthesis gene expression and hypermucoviscosity, and is essential for robust biofilm formation. Using a murine model, we establish that DksA functions as a determinant of GI colonization, despite disruption of the resident gut microbiota. Furthermore, we demonstrate that DksA is important for environmental survival and transmission by regulating RpoS, thereby providing a mechanistic link between the stringent stress response, environmental survival, and subsequent transmission. Together, these findings establish DksA as a central integrator of the stringent response, coordinating membrane stress resistance, virulence traits, and gastrointestinal colonization in K. pneumoniae.