Infection and Immunity最新文献

Leptospirosis is a neglected disease caused by pathogenic Leptospira spp., affecting an estimated 1 million people annually and resulting in approximately 60,000 deaths. The disease can lead to hepatic, renal, and pulmonary dysfunctions and may contribute to the development of chronic kidney disease. The Complement System plays an important role in eliminating bacteria by lysis, generating opsonins and anaphylatoxins, which degranulate mastocytes and basophils, and attracting immune cells to the site of infection, among other important functions. We aimed to investigate the role of C3 during chronic infection by L. interrogans strain FIOCRUZ L1-130 (LIC) in C57BL/6 wild-type (WT) and C3 knockout (C3KO) mice, monitored for 15, 30, 60, 90, or 180 days post-infection (d.p.i.). LIC-infected C3KO mice exhibited significantly higher leptospiral loads in the kidneys compared to WT counterparts. While both groups showed local inflammation at 15 and 30 d.p.i., LIC-infected C3KO showed a higher number of Leptospira DNA copies at 30 d.p.i. At this same time point, C3KO LIC-infected mice developed a larger fibrotic area than WT mice. Additionally, levels of specific IgG2b and IgG3 antibodies were significantly higher in LIC-infected C3KO mice compared to WT mice. The number of naïve T lymphocytes (both CD4⁺ and CD8⁺) was also increased in LIC-infected C3KO mice. This study demonstrates that during LIC infection, the absence of C3 does not impact mouse survival but results in increased renal leptospiral load and fibrosis. It also highlights the role of C3 in promoting the maturation and differentiation of T lymphocytes into pre-effector cells.

There are no licensed vaccines against enterotoxigenic Escherichia coli (ETEC), a group of E. coli strains that produce a heat-labile toxin and/or a heat-stable toxin (STa). ETEC is one of the top four leading causes of diarrhea in children in developing countries (children's diarrhea) and is the most common cause of diarrhea among international travelers (travelers' diarrhea). Remarkable progress has been achieved in understanding disease mechanisms and developing vaccines against ETEC-associated diarrhea. With an understanding of the disease mechanism and identification of virulence determinants, efforts have focused on developing vaccines that target these virulence determinants using either a cellular (whole-cell) vaccine expressing these antigens or an acellular (subunit) approach that primarily targets ETEC adhesins and/or enterotoxins. However, it remains challenging to develop either a cellular or an acellular ETEC vaccine that effectively protects against ETEC strains and associated diarrheal disease, as ETEC strains produce approximately 30 immunologically heterogeneous adhesins and two distinctive enterotoxins, including the potent and poorly immunogenic STa toxin. Additionally, the prevalence of these virulence factors, particularly adhesins, varies over time and across different geographical regions. In this review article, we summarize the ETEC vaccine candidates that have progressed in the last decade and further discuss the potential challenges associated with the leading candidates. We also highlight the novel epitope- and structure-based multiepitope fusion antigen platform and its application in developing cross-protective multivalent precision vaccines.

Infection induces unfavorable environments in the host that can be detrimental to the survival of commensal and pathogenic bacteria. Although the adaptive strategies employed by pathogenic bacteria to overcome harsh environments are characterized, similar capabilities of the commensal bacteria to survive in hostile host niches during infection remain understudied. The human oral pathogen group A streptococcus (GAS) encounters host-induced zinc (Zn) limitation at infection sites that limits bacterial proliferation. However, GAS employs the Zn-sensing transcription regulator AdcR to monitor Zn levels and evades host-imposed Zn scarcity by upregulating the AdcR regulon. To elucidate the adaptive responses of oropharyngeal commensal streptococci to Zn scarcity, we analyzed the oropharyngeal pathogenic and commensal streptococcal genomes for the presence of the AdcR regulon. GAS has the full repertoire of the AdcR regulon that includes adcR, Zn importer adcABC, extracellular Zn binding proteins adcAII and Pht, and Zn-free alternative ribosomal S14 subunit, rpsN.2. Contrarily, except for the conserved presence of adcR and adcABC, the oropharyngeal commensal streptococci varied in the composition of the AdcR regulon. Specifically, the gene encoding rpsN.2 was absent in the screened commensal streptococcal genomes. We further demonstrated that rpsN.2 is critical for the survival of GAS in Zn-limiting environments including human saliva, whereas the commensal Streptococcus vestibularis that lacks several components of the AdcR regulon, including rpsN.2, is defective in survival in Zn-deficient conditions. Together, we identified a pathogen-specific adaptive strategy that aids evasion of host-imposed Zn limitation and confers survival advantage over oropharyngeal commensal streptococci during Zn scarcity.

Mycobacterium marinum serves as an ideal model organism for studying tuberculosis due to its genetic similarity to Mycobacterium tuberculosis. However, there is a need for more suitable animal models to study M. marinum infections. In this study, we established a novel infection model using red-eared slider turtles (Trachemys scripta elegans). The turtles were infected with M. marinum via subcutaneous injection in the hind limb. Inoculation with >10⁶ CFU of M. marinum resulted in acute infection, causing mortality in at least 80% of turtles within five weeks, whereas 10⁵ CFU caused only 10% mortality. In subacute infections, M. marinum colonized and proliferated in various tissues for at least four weeks, with higher bacterial loads observed in the spleen and liver compared to the heart and lungs. Granuloma formation in the liver was correlated positively with bacterial load. Knockdown of adenylate kinase (ADK) in M. marinum reduced bacterial load by one order of magnitude in the liver and by half in the spleen, suggesting ADK as a potential drug target. Treatment with amikacin and moxifloxacin reduced bacterial load by approximately one order of magnitude in the liver and by half in the spleen. The red-eared slider turtle-M. marinum infection model developed in this study provides a robust tool for tuberculosis research.

Streptococcus pneumoniae is a leading cause of pneumonia. Importantly, the extent and impact of changes in the infected airway on bacterial nutrient availability and gene expression are not known. Utilizing untargeted UPLC-ESI-MS/MS metabolomics, we comprehensively characterized the metabolic landscape in the airway across early, mid, and severe stages of pneumococcal pneumonia. This revealed that dynamic shifts in metabolites occurred during pneumonia, with an initial influx of metabolites at the early stage, followed by declines as the disease progressed. Specific host metabolic perturbations were indicative of purine dysregulation, cellular stress, and outright tissue injury. Levels of glucose, a known modulator of pneumococcal capsule production, were highest at the early disease stage and then declined as the disease progressed, overlaying general metabolite trends. Concurrent bacterial transcriptome profiling was performed using a NanoString nCounter custom panel of 66 genes selected for their importance to metabolism, virulence, and stress response; 9% of which had disease-stage significant differences in gene expression. This analysis revealed remarkably high expression of spxB, the gene encoding pyruvate oxidase, at the severe stage of pneumonia compared to the mid-stage pneumonia, consistent with a drop in glucose levels and indicative of a shift toward mixed fermentation and the increased production of hydrogen peroxide. Our study improves our understanding of how pneumococcal infection alters the lung environment, driving profound metabolic shifts that, in turn, influence bacterial phenotypes. This detailed understanding of host-pathogen metabolic interactions offers valuable insights into novel therapeutic strategies.

Toxoplasma gondii is an obligate intracellular parasite capable of subverting host defenses to establish infection. Necroptosis, a lytic pro-inflammatory form of programed cell death, has emerged as a host defense mechanism against intracellular pathogens. However, its relevance in controlling T. gondii replication remains unclear. Here, we investigated the role of necroptosis in limiting T. gondii replication using bone marrow-derived macrophages (BMDMs) deficient in key necroptotic mediators, RIPK3 and MLKL. We demonstrate that under naïve conditions, T. gondii replication proceeds unimpeded in RIPK3^-/- and MLKL^-/- BMDMs. However, co-treatment with TNF-α and the pan-caspase inhibitor Z-VAD-FMK, conditions that promote necroptosis, significantly reduced parasite replication in wild-type BMDMs but not in those lacking RIPK3 or MLKL. This suppression was dependent on RIPK1 activity, as pharmacological inhibition with Necrostatin-1 abrogated the effect. We further confirmed that TNF-α and Z-VAD-FMK treatment induced necroptotic cell death characterized by loss of plasma membrane integrity, both of which were absent in RIPK3^-/- and MLKL^-/- cells. These findings establish that the activation of necroptosis can effectively limit T. gondii replication in BMDMs and underscore the importance of RIPK1-RIPK3-MLKL signaling in mounting a cell-intrinsic immune defense. Our study provides new insight into the functional capacity of necroptosis in restricting intracellular parasites and highlights its potential as a therapeutic target in toxoplasmosis.

Ehrlichia chaffeensis is an obligately intracellular bacterium that manipulates mononuclear phagocytes by hijacking host cell signaling pathways to promote infection. Previous studies from our laboratory have shown that multiple signal transducer and activator of transcription (STAT) family members interact with E. chaffeensis effector proteins. However, the functional role of STATs during infection remains poorly understood. Notably, STAT3, a highly immunomodulatory and pro-survival factor, interacts with the E. chaffeensis effector protein TRP75. In this study, we examined activation of STAT family members and transcription of STAT target genes during E. chaffeensis infection. We observed significant activation of multiple STATs (STAT1, STAT3, STAT5, and STAT6), with STAT3 showing the highest level of activation. Therefore, we further investigated STAT3 activation dynamics and effects of its inhibition on infection. STAT3 phosphorylation and nuclear translocation were detected beginning 48 h post-infection, coinciding with upregulation of STAT3 target genes, including the anti-apoptotic gene MCL-1. Pharmacological inhibition of STAT3 significantly reduced MCL-1 expression and increased caspase cleavage, implicating STAT3 as a regulator of anti-apoptotic signaling during infection. Furthermore, both pharmacological inhibition and genetic knockout of STAT3 significantly reduced bacterial load, highlighting its critical role in supporting infection. Ectopic expression of TRP75 in human embryonic kidney 293 cells induced STAT3 phosphorylation, demonstrating a specific role for TRP75 in STAT3 activation. Collectively, these findings support a model in which E. chaffeensis exploits STAT3 via the TRP75 effector to activate an anti-apoptotic program and other cellular pathways that promote infection.

The intracellular survival and replication of Chlamydia trachomatis rely on the precise manipulation of host signaling pathways. Host kinases are instrumental in the modulation of host signaling during C. trachomatis infection. However, the potential contribution of host phosphatases to chlamydial pathogenesis remains poorly understood. Here, we identified the host tyrosine phosphatase PTP1B as a positive regulator of C. trachomatis intracellular development. Gain-of-function approaches revealed that PTP1B promotes inclusion development and increases the production of infectious elementary bodies, whereas loss-of-function by chemical inhibition or silencing leads to a reduction in both inclusion size and bacterial infectivity. Interestingly, PTP1B inhibition did not affect Chlamydia trachomatis invasion efficiency, suggesting a specific role during the developmental phase of the chlamydial life cycle. To explore the functional relevance of PTP1B and its potential interaction with chlamydial effectors, we focused on the early-secreted effector Tarp, which undergoes tyrosine phosphorylation upon host cell entry. In vitro biochemical assays demonstrated that recombinant PTP1B can dephosphorylate both native and recombinant forms of Tarp. However, PTP1B inhibition during infection did not significantly alter Tarp phosphorylation levels, possibly owing to the overpowering influence of host tyrosine kinases. These findings suggest that while Tarp may not be a major physiological substrate, PTP1B is capable of interacting with phosphorylated chlamydial effectors. Together, these results establish PTP1B as a host factor that supports chlamydial development and underscore the underappreciated role of host phosphatases in bacterial pathogenesis. This study provides a foundation for future work exploring phosphatase-mediated regulation of infection and potential host-directed therapeutic strategies.

Visceral leishmaniasis (VL), caused by Leishmania donovani, is a neglected tropical disease with limited therapeutic options and increasing drug resistance. This study investigates the immunological mechanisms and antiparasitic efficacy of imidazoquinoline-based Toll-like receptor 7/8 (TLR7/8) agonists as host-directed agents in an in vitro VL model. Using RAW 264.7 macrophages and L. donovani promastigotes and amastigotes, we examined macrophage activation, nitric oxide (NO) induction, and cell cycle disruption in parasites. The lead compounds (5 and 10) significantly enhanced NO production in macrophages, both in unstimulated and LPS-stimulated conditions, indicating robust innate immune activation. Additionally, parasite-derived reactive oxygen species (ROS) levels were markedly elevated, suggesting oxidative stress as a mechanism of direct leishmanicidal action. Flow cytometric analysis revealed G₀/G₁ arrest in treated promastigotes, further supporting interference with parasite proliferation. Importantly, these compounds exhibited low cytotoxicity toward host cells and favorable selectivity indices. Notably, this is the first in vitro study to comprehensively demonstrate the ability of TLR7/8 agonists to exert direct parasiticidal effects along with immune modulation in the context of VL. The results underscore the potential of TLR-targeted immunomodulation to enhance host defense mechanisms against intracellular protozoan infections and contribute to the development of novel immunopharmacological interventions for VL.

Here, we report the identification of bacteriophage Mu contamination in a commonly used Citrobacter rodentium DBS100 ∆cpxRA mutant strain. After re-constructing a new Mu-free ∆cpxRA strain, we independently replicated the results of a recent study by A. Gilliland, C. Gavino, S. Gruenheid, and T. Raivio (Infect Immun 90:e00314-22, 2022, https://doi.org/10.1128/iai.00314-22). The only result from Gilliland et al. that was impacted by the presence of Mu was the outcome of interbacterial competition assays with the ∆cpxRA strain, as strains carrying Mu consistently outcompeted susceptible Mu-free competitors. These results are important for the field, as the contaminated DBS100 ∆cpxRA mutant strain has been used in six different studies. We believe that the Mu contamination occurred during the construction of the ∆cpxRA allele, during the conjugation of DBS100 with a popular Mu-containing donor strain. Our results highlight the importance of using Mu-free conjugal donor strains and how phage contamination can impact bacterial physiology and experimental results.