Infection and Immunity最新文献

Cell death is an integral part of homeostasis, removing damaged and infected cells and replenishing healthy cells. It is a process well understood from a host perspective, with clearly delineated pathways and an expansive literature as to how it interacts with other immune and tissue mechanisms. However, the interaction between cell death and the microbial community is less well explored. There is an understanding of how bacterial pathogens are able to induce death and can have a detrimental impact on tissue resolution and repair but little on how bacteria respond to homeostatic cell death or death caused by non-bacterial stimuli. This review will cover recent advances in the understanding of host-microbe communication during cell death and will discuss how bacteria modulate/are modulated by cell death-related phenomena. The interplay between the microbiota and the fundamental processes involved in host cell death presents an exciting opportunity to discover how modulation of host mechanisms can beneficially modulate the microbiota, and therefore concurrently offer potential routes to control a number of conditions that have been linked to aberrant microbiota composition, including inflammatory bowel disease and cancer.

Biological metals are vital trace elements required by metalloproteins, which are involved in virtually every cellular, structural, and catalytic function of the bacterial cell. Bacterial pathogenesis involves a tug-of-war between the host's nutritional immunity sequestering essential metals and the invading pathogens that deploy adapted high-metal affinity uptake strategies, such as metallophores, in order to efficiently circumvent these defense mechanisms. Pseudopaline is a metallophore produced and secreted by Pseudomonas aeruginosa to acquire zinc when the bioavailability of this metal is severely restricted, as in the presence of a strong metal chelator such as EDTA, or during infections when the nutritional immunity of the host is active. We show that when facing strong metal chelation, the general Znu zinc uptake pathway becomes ineffective and only the pseudopaline pathway is capable of supplying the bacteria with the necessary zinc to maintain their growth, establishing that the pseudopaline pathway is the last-resort pathway for the bacteria to acquire zinc under such restricted growth conditions. Based on this statement, the present study explores the pleiotropic role of pseudopaline-mediated zinc acquisition on clinically relevant phenotypes such as biofilm formation and associated antibiotic tolerance, as well as its capacity to determine infection outcomes using cell-culture and murine models. The expression of pseudopaline-dependent phenotypes in such a diversity of biological contexts demonstrates the essentiality of this specific metal uptake system for P. aeruginosa pathogenicity during infection. We therefore identify this machinery as a promising therapeutic target for P. aeruginosa infections.

Mucosal DNA vaccination using a non-invasive Lactococcus lactis (LL) vector has been investigated. However, its immunogenicity and plasmid transfer mechanisms remain largely unknown. In this study, we investigated the intranasal delivery of LL carrying a mammalian enhanced green fluorescent protein (EGFP)-expressing plasmid and the cellular pathways underlying DNA transfer. Intranasally administered LL was primarily localized on the nasal epithelial surfaces, and a smaller fraction penetrated the subepithelial tissues. Intranasal administration of LL-carrying pLEC-EGFP plasmid induces antigen-specific serum IgG and mucosal IgA responses. In vitro co-culture analyses demonstrated that plasmid delivery and expression occurred in phagocytic cell lines but not in epithelial cell lines. This transfer was inhibited by compounds specific for phagocytosis, consistent with the observed time course of DNA transfer and localization of LL within Lamp-1⁺ phagolysosomes. In contrast, compounds for bactericidal mechanisms, including lysosomal acidification, reactive oxygen species, and reactive nitrogen species, did not affect DNA transfer. As our findings suggest that phagocytosis is the primary pathway for plasmid delivery by non-invasive LL vectors in cell culture assays, further studies to confirm these findings in animal models are warranted to develop new strategies for improved LL-based mucosal DNA vaccines.

The maternal-infant microbiome axis represents a dynamic interface that shapes neonatal immune and metabolic development from the earliest stages of life. Microbial communities from the maternal gut, vaginal tract, and breast milk seed the infant microbiome, influencing chromatin remodeling, transcriptional activity, and immunometabolic programming. Rather than functioning solely as a conduit of microbial inheritance, this axis operates as a regulatory network where microbial metabolites such as short-chain fatty acids and indole derivatives modulate histone acetylation, DNA methylation, and noncoding RNA pathways that calibrate immune tolerance and pathogen defense. Perturbations, including cesarean delivery, perinatal antibiotic exposure, or maternal metabolic disorders, disrupt these processes and are associated with altered immune set points, heightened infection susceptibility, and increased risk of inflammatory and metabolic disease. Multi-omics studies now provide mechanistic insights linking microbial signals to epigenetic regulation of neonatal immune responses, while also exposing important controversies, such as the debated presence of a placental microbiome and the variable efficacy of probiotic interventions. Emerging strategies, including maternal dietary modulation of the microbiome, perinatal microbiota restoration, and development of live biotherapeutics, show promise, but their translational potential remains constrained by limited sample sizes, heterogeneous outcomes, and safety concerns. Framing the maternal-infant microbiome axis as an epigenetic and immunometabolic orchestrator highlights both its therapeutic promise and the need for rigorous mechanistic and clinical evaluation to advance preventive strategies for women's and children's health.

Echinococcus granulosus sensu lato antigen B (EgAgB) is a major parasite lipoprotein, produced by the hydatid and released at the host-parasite interface. Accumulating evidence supports that EgAgB may exert immunomodulatory effects on myeloid cells; however, the underlying molecular mechanisms remain poorly understood. We examined the impact of native EgAgB (nEgAgB) and recombinant EgAgB8/1 (rEgAgB) on lipopolysaccharide (LPS)-induced activation of bone marrow-derived dendritic cells (BMDC) to help elucidate these mechanisms. Both immunoaffinity-purified nEgAgB or rEgAgB induced modest BMDC activation, indicated by the production of IL-6, IL-12p40, and nitric oxide, but not IFN-β. This activation was primarily attributed to LPS traces in EgAgB preparations since it was nearly abolished by a specific TLR4 inhibitor and in Tlr4^-/- BMDC, while EgAgB binding to BMDC was TLR4-independent. Notably, both nEgAgB and rEgAgB inhibited LPS-induced cytokine and nitric oxide production and disrupted TLR4 dimerization and endocytosis. Competitive binding assays showed that EgAgB and human high-density lipoprotein (hHDL) similarly inhibited LPS binding to macrophages and BMDC; however, EgAgB more effectively suppressed LPS-induced cytokine secretion. Contrastingly, EgAgB did not modulate BMDC responses to lipoteichoic acid, unlike hHDL. Using dynamic light scattering and an ELISA-like assay, we demonstrated a higher potential of EgAgB to bind LPS than hHDL. Additionally, docking analyzes suggest the presence of a defined LPS-binding interface in EgAgB8/1 subunit. Overall, these findings reveal a novel binding property of EgAgB, which enables it to act as an extracellular LPS scavenger, interfering with TLR4-mediated LPS recognition and downstream proinflammatory responses in myeloid cells.

Currently, no fungal vaccine exists for clinical use, while fungal infections are responsible for over 1.5 million deaths every year. Our previous studies identified a Cryptococcus neoformans mutant strain fbp1Δ as a potential vaccine candidate. This strain contains deletion of the F-box protein Fbp1, a key subunit of the SCF E3 ligase complex necessary for ubiquitin-mediated proteolysis. Vaccination with heat-killed fbp1Δ (HK-fbp1) can elicit an interferon gamma (IFN-γ)-dependent Type 1 immune response and provide protection against C. neoformans and its sibling species C. gattii. However, we have yet to decipher the immunogenic factor(s) expressed by the fbp1∆ mutant that are responsible for the induction of the protective immune response. In this study, we have identified that the capsule plays an important role in HK-fbp1 vaccine-mediated protection as acapsular HK-fbp1 cells showed diminished protection against wild-type challenge. Additionally, our studies have shown that Cytokine Inducing Glycoprotein 1 (Cig1), a GPI-anchored mannoprotein, is regulated by Fbp1 and contributes to the immunogenicity of HK-fbp1. Deletion of Cig1 in the fbp1Δ background resulted in decreased recruitment of antifungal effector T cells and diminished production of protective inflammatory cytokines by the host. Furthermore, loss of Cig1 in the fbp1Δ mutant resulted in reduced protection in vaccination survival studies at lower vaccine inoculum doses compared to HK-fbp1. In aggregate, these findings demonstrate Cig1 is an antigen contributing to the immunogenicity of HK-fbp1 that may be utilized to further optimize the HK-fbp1 fungal vaccine as a tool in the arsenal against invasive fungal infections.

Klebsiella pneumoniae infections are sharply on the rise among at-risk populations. K. pneumoniae has nine serogroups of O-antigens. Recently, additional O-antigen subtypes within these serogroups have been identified; the contributions of these subtypes to pathogenic fitness and their immunogenicity, functional antibody responses, and cross-reactivity are unknown. We investigated how the addition of the single-branched galactose in O-antigen subtype O2b compared to O2a alters its virulence and host immune responses. We deleted the gmlABC region of an O2b strain of K. pneumoniae, converting it to an otherwise isogenic O2a strain. Complementation of this mutant allowed us to identify the specific genes responsible for the addition of the single branched galactose of O2b. Experiments using the O2a mutant and its parent O2b strain confirmed similar phenotypic expression of virulence factors beyond the O-antigen. Well-established murine models of pneumonia were used to determine the pulmonary fitness of the strains and assess the host innate immune responses. Complement-mediated killing assays suggested differences in susceptibility to innate immune defenses, with the O2a mutant being more susceptible to serum killing. Lastly, using polysaccharide-protein bioconjugate vaccines against these specific O-antigen subtypes, we determined that only partial cross-reactivity and protection are elicited. These studies advance our understanding of the immune response to K. pneumoniae O-antigens by defining a fitness advantage of O2b compared to O2a and informing vaccine design to combat this drug-resistant pathogen.

Chronic wound infection is a major global public health issue, with Enterococcus faecalis among the most commonly isolated pathogens from such wounds. Neutrophils are short-lived immune cells critical for host defense, yet E. faecalis-neutrophil interactions are poorly understood. Here, we show that instead of eliminating E. faecalis, neutrophils provide a niche for intracellular persistence and replication, potentially prolonging infection and inflammation at the wound site. In murine wound beds and ex vivo wound cells, intracellular E. faecalis was detected in recruited neutrophils at 24 h post-infection (h p.i). Unexpectedly, extended infection did not induce neutrophil death. Rather, E. faecalis infection significantly prolonged the life spans of both murine and human neutrophils in vitro compared to uninfected controls. Quantification of intracellular CFU revealed that E. faecalis were phagocytosed regardless of opsonization and persisted intracellularly up to 24 h p.i. This finding was confirmed via transmission electron microscopy and confocal microscopy. Blinded quantification and fluorescent D-amino acid staining, which marks newly synthesized bacterial peptidoglycan, revealed active replication within murine neutrophils between 6 and 18 h p.i., followed by a predominately persistent phase between 18 and 24 h p.i. Infected murine neutrophils remained immunologically active, secreting pro-inflammatory and chemoattractant cytokines. These findings highlight an underappreciated intracellular lifestyle for E. faecalis that may contribute to its ability to persist in chronic wounds and contribute to biofilm-associated infections.

Avian Pathogenic Escherichia coli (APEC) is a major cause of economic loss in poultry, exacerbated by the rising prevalence of antibiotic resistance. While sulfur metabolism is essential for bacterial growth, its specific role and regulation in APEC virulence remain poorly understood. This study identifies the LsrR-cysN axis as a novel regulatory pathway that critically governs APEC virulence. We demonstrate that the quorum-sensing regulator LsrR directly binds to the cysN promoter, activating its transcription. Functional analysis revealed that cysN deletion drastically attenuated virulence, significantly reducing biofilm formation, serum resistance, adhesion, invasion, and motility. The APEC94∆cysN also exhibited altered antibiotic resistance profiles, which were linked to the upregulation of efflux pumps acrA and tolC. Crucially, in a murine model, the APEC94∆cysN showed a 75% reduction in mortality and severe impairment in colonization of blood, lungs, liver, spleen, and kidneys. This attenuation was associated with a skewed host immune response, characterized by reduced levels of IL-2 and IL-6 and elevated levels of IL-4 and TNF-α. Our findings establish the LsrR-cysN axis as a central regulator connecting quorum sensing to virulence in APEC, revealing a promising target for novel anti-virulence strategies.

The type VI secretion system (T6SS) is a major virulence factor in Vibrio parahaemolyticus, but its pathogenic mechanisms are poorly understood or still not fully understood. This study investigates how two critical T6SS1 structural components, VipA1 and Hcp1, contribute to bacterial virulence and host inflammatory responses. Comparative proteomics revealed 149 secreted proteins dependent on T6SS1, including 28 core proteins requiring both VipA1 and Hcp1 for secretion. These proteins were functionally linked to metabolic pathways such as folate-mediated one-carbon metabolism and lysine degradation, as well as structural processes like flagellar assembly. Phenotypic analysis revealed that the ΔvipA1-hcp1 double mutant showed markedly attenuated virulence: 52.7% reduction in antibacterial activity compared to the wild-type strain. Biofilm formation increased 2.1-fold at 30°C and 2.8-fold at 37°C in ΔvipA1-hcp1, while swimming and swarming motility decreased by 30.9% and 35.5%. In vivo, ΔvipA1-hcp1 caused only 50% mortality in mice, compared to 91.7% for the wild-type strain, and exhibited 3- to 15-fold lower bacterial loads in the blood, liver, and spleen. Histopathological analysis confirmed that the ΔvipA1-hcp1 failed to induce tissue damage, unlike the wild-type strain. At the host interface, deletion of vipA1 and hcp1 led to significantly elevated inflammatory cytokine (IL-1β, IL-8, and IL-6) mRNA levels. Mechanistically, T6SS1 inhibited NF-κB activation by stabilizing IκBα and reducing p65 nuclear translocation (40.0% in wild-type-infected cells vs 85.8% in double mutant-infected cells). These findings establish VipA1 and Hcp1 as critical regulators of T6SS1-mediated coordinating effector secretion, virulence, immune evasion, and lethality, providing novel mechanistic insights into V. parahaemolyticus pathogenesis.