Infection and Immunity最新文献

Streptococcus gordonii is a commensal bacterium in the oral cavity and has many surface adhesins that have been well characterized. SspA/B belongs to the Antigen I/II-like family of proteins, which are well known for their multifunctional adherence capabilities. Most AgI/II-like proteins adhere to salivary agglutinin (also known as glycoprotein 340, Gp340). In an effort to identify the putative binding site on the AgI/II-like family of proteins, we conducted structural studies to determine the V-domain of SspB. In this paper, we report the structure of SspB's V-domain in complex with a TEV-peptide that was inserted to cleave the histidine tag at the C-terminus after purification. This peptide shared sequence and structural homology with a helical region on the scavenger receptor cysteine-rich (SRCR) domain of Gp340. Our studies with the synthetic peptide PepCD1^SRCR show that it inhibits the Streptococcus mutans biofilm formation in a dose-dependent manner. A comprehensive comparative analysis of this site with the corresponding sites in the homologous V-domains of S. mutans AgI/II and GbpC established that most of these interface residues were conserved. Based on the structural data, mutational analysis was initiated to study the effect of binding-interface residues on the ability of each of these V-domains from S. mutans and S. gordonii to adhere to salivary agglutinin. Here, we report for the first time the binding site for the V-regions that are distinct among oral streptococci, which provides potential opportunities for therapeutic intervention of pathogenic species.

Emergomyces africanus is a thermal dimorphic fungus and a leading cause of emergomycosis, a neglected infection primarily affecting immunocompromised individuals. Despite its clinical relevance, little is known about how E. africanus adapts to the host environment. Recent studies suggest that fungal extracellular vesicles (EVs) may contribute to host adaptation by modulating immune responses and transporting virulence factors. Here, we report the production and characterization of E. africanus EVs obtained under nutrient-rich and nutrient-limited media, mimicking environmental and host-like conditions. We also evaluated the effect of E. africanus EVs released in nutrient-limited media on bone marrow-derived dendritic cells (BMDCs) and bone marrow-derived macrophages (BMDMs). Under nutrient limitation, E. africanus released EVs enriched in virulence-associated proteins, including catalase, HSP60, and chitinase, whereas EVs from rich media carried proteins linked to anabolic pathways. Chitin-like structures and β-1,3-glucans were also detected in EVs released in nutrient-limited conditions. EVs from nutrient-limited conditions activated BMDCs, increased MHC-II and CD40 expression, and promoted a pro-inflammatory cytokine profile (IL-6 and TNF-α). In contrast, BMDMs exhibited elevated IL-10 levels, suggesting an anti-inflammatory phenotype. Remarkably, EV pre-treatment enhanced BMDM antifungal activity, significantly reducing E. africanus viability post-infection. These findings show that E. africanus dynamically adjusts its EV cargo in response to environmental cues, directly influencing immune modulation and fungal survival. Indeed, pre-treatment of the insect Galleria mellonella with EVs induced a protective response against a lethal inoculum of Histoplasma capsulatum. This work provides new insights into fungal adaptation and highlights EVs as potential therapeutic and vaccine platforms.

Klebsiella pneumoniae is an opportunistic Gram-negative pathogen and a common cause of antibiotic-resistant infections including neonatal sepsis and hospital-acquired pneumonia. K. pneumoniae strains can be categorized into two pathotypes: classical K. pneumoniae (cKp), which often causes nosocomial infections, and hypervirulent K. pneumoniae (hvKp), which can cause severe disease in healthy hosts. New therapies are urgently needed for these infections, and caseinolytic proteins have emerged as promising therapeutic targets in other bacterial pathogens. ClpX and ClpP have been implicated in bacterial protein homeostasis, regulation of virulence, and antimicrobial susceptibility in other species, but their specific roles in K. pneumoniae pathogenesis have yet to be defined. Here, we investigate the contribution of K. pneumoniae ClpX and ClpP to lung infection, virulence factor regulation, and antibiotic susceptibility. In a murine pneumonia model, loss of ClpX impairs infection of both hvKp and cKp. Loss of ClpX results in decreased capsule production in hvKp and enhances type 1 pilus production in both pathotypes. In hvKp, loss of ClpX increases type 3 pili, while in cKp, increased type 3 piliation is observed with loss of ClpP. Across both pathotypes, loss of ClpX or ClpP increases susceptibility to a range of antibiotics. These data identify ClpX as critical to K. pneumoniae virulence and antimicrobial susceptibility. By connecting ClpX to capsule production, pili regulation, and in vivo virulence, this work highlights a conserved putative therapeutic target that may enable adjunctive strategies to enhance antibiotic efficacy or attenuate the severity of K. pneumoniae infection.IMPORTANCEKlebsiella pneumoniae is a leading cause of antibiotic-resistant and hospital-acquired infections. The emergence of highly virulent strains of K. pneumoniae capable of causing severe disease is of utmost concern. Here, we investigate two specific caseinolytic proteins, ClpX and ClpP, produced by both classical and hypervirulent strains of K. pneumoniae and their role in K. pneumoniae lung infection. We show that ClpX is a key regulator of virulence factors including bacterial pili and capsule; it is essential for murine pulmonary fitness across both classical and hypervirulent pathotypes. Furthermore, loss of ClpX increases susceptibility to multiple antibiotics, indicating a role in both protein homeostasis and pathogenicity. These findings suggest ClpX is a conserved virulence determinant in multiple strains of K. pneumoniae and highlight its potential as a therapeutic target to enhance antibiotic efficacy or mitigate disease severity.

More than half of the people with microbiologically cured tuberculosis (TB) present with post-TB lung disease (PTLD). PTLD compromises long-term respiratory health and adds to the global burden of chronic lung diseases. Despite its prevalence, the mechanisms driving tissue damage in TB are not well understood. In this review, we discuss the global burden of PTLD, evaluate host-directed therapies as promising interventions, and highlight the C3HeB/FeJ mouse model as a powerful tool for advancing pre-clinical PTLD research.

Chlamydia trachomatis is a leading cause of urogenital infections that can result in serious long-term complications. This obligate intracellular bacterium undergoes a biphasic developmental cycle alternating between the infectious elementary body and the replicative reticulate body and can enter a persistent state in response to adverse environmental conditions. Although transcriptomic reprogramming is central to chlamydial stress adaptation and persistence, how responses differ across biologically distinct stressors remains incompletely defined. Here, we performed a comparative reanalysis of five published, high-quality C. trachomatis RNA-Seq data sets generated under prolonged interferon-γ treatment, tryptophan starvation, iron starvation, penicillin exposure, or acute heat shock. Global transcriptomic analyses reveal stress-specific reprogramming and a clear separation between the transcriptome induced by heat shock and those induced by chronic stresses. Transcriptomic overlap observed among chronic stress conditions is substantially reduced when the heat shock transcriptome is included, indicating that shared transcriptional features are stressor-dependent. Consistent with prior findings, tryptophan starvation and iron starvation exhibit particularly close transcriptomic similarity, likely reflecting regulatory cross-talk mediated by the iron-dependent transcriptional repressor YtgR. Notably, this similarity exceeds that observed between tryptophan starvation and interferon-γ treatment, despite the well-established role of interferon-γ in inducing host-mediated tryptophan depletion. In contrast, interferon-γ induces a distinct but partially overlapping transcriptome, likely reflecting activation of additional host-mediated antimicrobial mechanisms beyond tryptophan deprivation. Together, these findings demonstrate that adaptation to different biological stressors in C. trachomatis is driven by distinct transcriptomic reprogramming, while consistently involving a subset of functions that may represent points of vulnerability for disrupting chlamydial persistence.

Non-receptor tyrosine kinase c-Abl is critical for host defense against bacterial and viral infections, yet its role in antifungal immunity remains elusive. Here, we report that inhibition of c-Abl with flumatinib mesylate significantly impairs the survival rate and exacerbates fungal burden in mice infected with Candida albicans. Our findings reveal that c-Abl inhibition reduces production of TNF-α, IL-10, and IL-12 in bone marrow-derived dendritic cells (BMDCs) after stimulation with fungal β-glucan or α-mannan. Mechanistically, c-Abl inhibition significantly blocks p38 and extracellular signal-regulated kinases 1/2 (ERK1/2) activation in BMDCs after α-mannan stimulation in a c-Cbl dependent manner. Collectively, our study uncovers a c-Abl/c-Cbl/MAPK signaling axis in dendritic cells that governs antifungal innate immunity, highlighting c-Cbl as a critical downstream mediator linking c-Abl to host defense against C. albicans. Our findings provide a mechanistic basis for fungal risk assessment in cancer patients treated with c-Abl inhibitors.

Multiple countries have observed an alarming increase in scarlet fever cases, and invasive infections often associated with a new sublineage of Streptococcus pyogenes known as M1_UK. M1_UK strains express increased levels of the streptococcal pyrogenic exotoxin A (SpeA) superantigen, and here we compare the virulence characteristics of this sublineage with the circulating M1_global strain. We obtained contemporary Canadian M1_UK isolates, and genome sequencing revealed that some M1_UK strains had acquired additional DNAse- and superantigen-encoding prophage elements, as well as an isolate with a mutation in covS. Five S. pyogenes strains were chosen for functional experiments, including 5448 (M1_global strain), M1_UK350 (a "typical" M1_UK strain), M1_UK162 (M1_UK strain containing a mutation in the covS gene), M1_UK362_ΦSP1380.vir (M1_UK strain containing a prophage element encoding the spd1, speC, and ssa genes), and M1_UK155_Φ370.1 (M1_UK strain containing a prophage element encoding the spd1 and speC genes). Exoprotein profiles demonstrated that all M1_UK background strains had enhanced production of the SpeA superantigen relative to S. pyogenes 5448. Furthermore, strains that had acquired the additional prophage elements showed enhanced activation for human T cells, although cytotoxic activity, adhesion capacity, and DNA degradation were not detectably different. Using a "humanized" superantigen-sensitive HLA-transgenic mouse infection model, the M1_UK162 covS mutant, and both M1_UK362_ΦSP1380.vir and M1_UK155_Φ370.1 strains each demonstrated increased severity during experimental skin infection compared to 5448 and M1_UK350. These findings indicate that circulating M1_UK background strains continue to acquire additional prophage-encoded virulence factors, or hypervirulent covS mutations, and that these genetic alterations may contribute to increase severity of human infections.

Cryptosporidium is a protozoan parasite that causes cryptosporidiosis, an enteric infection associated with diarrhea, malnutrition, and impaired childhood development in low- and middle-income countries. Both humoral and cell-mediated immune responses have been implicated in protection, but the durability and quality of human immune responses in immunocompetent adults remain poorly defined. We investigated the development of immunity in two healthy U.S. adults following primary cryptosporidiosis acquired during travel to Bangladesh. Longitudinal plasma samples were analyzed for antibody responses to Cryptosporidium antigens Cp17 and Cp23 and for circulating cytokine profiles. Circulating antibody peaked at 3 weeks post-infection but declined rapidly thereafter, approaching baseline within 16 weeks. In contrast, antibody avidity increased steadily over time, consistent with ongoing affinity maturation in germinal centers. While affinity maturation occurred, the composition of memory B cells specific to Cryptosporidium antigens was skewed toward IgM+ cells across time points, suggesting extrafollicular responses dominated and germinal center-derived, class-switched memory was limited. Cytokine profiling revealed an acute Th1-skewed response, with elevations in CXCL9, CXCL10, IL-27, IFNγ, IL-12, and IL-18 during early infection. These signatures mirrored protective pathways identified in murine models, underscoring the importance of type I immunity in parasite clearance. Together, these findings highlight that while antibody responses to Cryptosporidium are short-lived, avidity maturation persists, and Th1-driven cytokine responses dominate during acute infection. This work provides rare longitudinal data on immune responses in naïve adults following natural cryptosporidiosis and offers insight into mechanisms that may inform vaccine development and strategies to mitigate recurrent infection in vulnerable populations.

Metabolic adaptation to the host environment is a key determinant of bacterial pathogenesis, enabling both colonization and invasive disease. This is particularly true for Neisseria gonorrhoeae (Gc), the causative agent of gonorrhea, which lacks effector-injecting secretion systems or toxins. Gc infection triggers a rapid influx of neutrophils (polymorphonuclear cells [PMNs) that typically kill bacteria through multiple mechanisms, including a potent oxidative burst. Despite this, Gc exhibits remarkable resistance to reactive oxygen species and readily replicates in the presence of PMNs, which is in part due to the consumption of PMN-derived lactate. Previous studies demonstrated that the lactate permease, LctP, is required for oxidative stress resistance in Gc and host colonization in a murine model of gonorrhea, suggesting that lactate utilization contributes to virulence. Gc encodes four lactate dehydrogenases (LDHs) with distinct regulation and mechanisms, including two L-LDHs, LldD and LutACB. Although either enzyme alone supports L-lactate utilization, we found that both are required for full fitness during co-colonization with PMNs, indicating some non-redundant roles. Furthermore, LldD enhances oxidative stress resistance and is required for Gc colonization in a murine model of gonorrhea, whereas LutACB is dispensable. These findings identify LldD as a key factor promoting oxidative stress resistance, survival during PMN challenge, and host colonization.

Streptococcus pneumoniae (S. pneumoniae) infection induces pyroptosis in human pulmonary artery epithelial cells (HPAEpiCs), which contributes to pneumonia pathogenesis. We aimed to investigate the regulatory role of N6-methyladenosine (m⁶A) modification mediated by methyltransferase-like (METTL) 14 in this process and elucidate the underlying molecular mechanisms. HPAEpiCs were infected with S. pneumoniae. Cell viability was assessed using the cell counting kit-8 assay, while cytokine concentrations were measured by enzyme-linked immunosorbent assay. Pyroptosis levels were analyzed through flow cytometry and Western blot for pyroptotic protein expression. Gene expression profiles, protein-RNA interactions, and m⁶A methylation sites were characterized by quantitative reverse transcription-polymerase chain reaction, RNA immunoprecipitation, and dual-luciferase reporter assays. In vivo experiments involved intranasal administration of S. pneumoniae in mice to evaluate pulmonary pathological changes. S. pneumoniae D39-infected HPAEpiCs exhibited enhanced pyroptosis and adhesive/invasive capabilities, accompanied by elevated m⁶A modification mediated by METTL14. In addition, METTL14 inhibition suppressed pyroptosis and adhesive/invasive capabilities and ameliorated S. pneumoniae D39-induced lung injury. Notably, NEK7 overexpression reversed the pyroptosis reduction caused by METTL14 knockout. Mechanistically, the METTL14/insulin-like growth factor 2 mRNA-binding proteins (IGF2BP)1 m⁶A regulatory axis modulated NEK7 mRNA stability through m⁶A-dependent post-transcriptional regulation. The METTL14/IGF2BP1 m⁶A regulatory axis promoted S. pneumoniae D39-induced pyroptosis by stabilizing NEK7 mRNA transcripts. Targeting this m⁶A regulatory pathway represents a potential therapeutic strategy for managing S. pneumoniae D39-induced pneumonia.