Infection and Immunity最新文献

Serotype M28 isolates of the bacterial pathogen the group A Streptococcus (GAS; Streptococcus pyogenes), but not isolates of other serotypes, have a nonrandom association with cases of puerperal sepsis, a life-threatening infection that can occur in women following childbirth. In prior studies, we established that RD2, a pathogenicity island present in all M28 GAS isolates but mostly absent from other serotypes, is a factor in the M28-puerperal sepsis association. Here, we identified a significant reduction in the RD2 conjugation frequency in inter-serotype conjugation assays relative to intra-serotype assays. As isolates of most GAS serotypes produce an antiphagocytic hyaluronic acid capsule, while M28 isolates do not, we tested whether the capsule served as a barrier to RD2 acquisition or maintenance. The data showed that capsule production had no impact on the RD2 conjugation frequency or on the ability of RD2 to enhance vaginal colonization by GAS, but did inhibit the ability of RD2 to enhance GAS adherence to vaginal epithelial cell lines. Further molecular explanations for the inter-serotype barrier to RD2 conjugative transfer were investigated, and a conserved, chromosomally encoded Type I restriction-modification system was identified as being key. We also identified that RD2 modifies the GAS transcriptome, including mRNAs encoding virulence factors with adherence and dissemination roles, following exposure to human plasma. Our data provide insights into factors that contribute to the restriction of the RD2 pathogenicity island to discrete subsets of the GAS population.

To control schistosomiasis mansoni, it is important to attempt preventing the worms' egg-induced pathology in the liver and limiting pathogen transmission following egg exit from the intestines to the exterior. Therefore, the present study aimed to clarify the reasons behind the decades-long riddle of periovular granulomas downmodulation in the liver, but not the small intestine, with the progression of murine schistosomiasis mansoni. Outbred female CD-1 mice were percutaneously exposed to 15 Schistosoma mansoni cercariae. The liver and small intestine were collected from mice harboring a minimum of a worm couple at 8, 12, 16, and 20 weeks post-infection, assessed for egg counts/g and histopathological changes, and used to prepare Triton X-100 extracts. Content of cytokines, saturated and unsaturated fatty acids, triglycerides, cholesterol, reactive oxygen species, and uric acid per mg tissue extract proteins were evaluated using capture enzyme-linked immunosorbent assays, gas chromatography-flame ionization detector, and standard commercially available reagents, respectively. Examination of hematoxylin-eosin-stained tissue sections confirmed the decrease in size and changes in cellular composition of periovular granulomas in the liver but not the small intestine, associated with wide differences in released cytokines types and amounts, and content of the bioactive lipids, arachidonic and docosahexaenoic acids, reactive oxygen species, and uric acid. The results together disclosed that the downmodulation of hepatic, but not the small intestine, circumoval granulomas with the progression of murine S. mansoni naturally results from site- and tissue- specific immunological and biochemical responses to the egg-derived antigens and molecules and suggested that the intestines appear to harbor immune-privileged sites.

C-di-AMP homeostasis is critical for bacterial stress response, cell wall integrity, and virulence. Except for osmotic stress response, the molecular mechanisms underlying other processes are not well defined. A Listeria monocytogenes mutant lacking both c-di-AMP phosphodiesterases, denoted as the ΔPDE mutant, is significantly attenuated in the mouse model of systemic infection. We utilized the ΔPDE mutant to define the molecular functions of c-di-AMP. RNAseq revealed that the ΔPDE mutant is significantly impaired for the expression of virulence genes regulated by the master transcription factor PrfA, which is activated by reduced glutathione (GSH) during infection. Subsequent quantitative gene expression analyses revealed that the ΔPDE strain is defective for PrfA-regulated gene expression both at the basal level and upon activation by GSH. We further found the ΔPDE strain to be significantly depleted for cytoplasmic GSH and impaired for GSH uptake. The ΔPDE strain was also deficient in GSH under conditions that activate GSH synthesis by the synthase GshF and upon constitutive expression of gshF, suggesting that c-di-AMP accumulation inhibits GSH synthesis activity or promotes GSH catabolism. A constitutively active PrfA* variant restored virulence gene expression in ΔPDE in broth cultures supplemented with GSH but did not rescue virulence defect in vivo. Therefore, virulence attenuation at high c-di-AMP is likely associated with defects outside of the PrfA regulon. For instance, the ΔPDE strain was sensitive to oxidative stress, a phenotype exacerbated in the absence of GshF. Our data reveal GSH metabolism as another pathway that is regulated by c-di-AMP.IMPORTANCEC-di-AMP regulates both bacterial pathogenesis and interactions with the host. Although c-di-AMP is essential in many bacteria, its accumulation also attenuates the virulence of many bacterial pathogens. Therefore, disrupting c-di-AMP homeostasis is a promising antibacterial treatment strategy and has inspired several studies that screened for chemical inhibitors of c-di-AMP phosphodiesterases. However, the molecular functions of c-di-AMP are still not fully defined, and the underlying mechanisms for attenuated virulence at high c-di-AMP levels are unclear. Our analyses in Listeria monocytogenes indicate that virulence-related defects are likely outside of the virulence gene regulon. We found c-di-AMP accumulation to impair L. monocytogenes virulence gene expression and disrupt GSH metabolism. Further studies are necessary to establish the relative contributions of these regulations to virulence and host adaptation.

Candida albicans is a fungal constituent of the human gastrointestinal microbiota that can tolerate acidic environments like the stomach, where it can be associated with ulcers and chronic gastritis. In mice, C. albicans induces gastritis without concurrent intestinal inflammation, suggesting that the stomach is particularly prone to fungal infection. We previously showed that C. albicans invasion in the limiting ridge does not extend to or elicit an inflammatory response in the adjacent glandular region, indicating regionalized gastritis in the murine stomach. However, the molecular pathways involved in the host response to C. albicans specifically in the limiting ridge have not been investigated. Here, we found that gastric dysbiosis was associated with C. albicans limiting ridge colonization and gastritis. We isolated the limiting ridge and evaluated the expression of over 90 genes involved in mucosal responses. C. albicans infection triggered a type 3 immune response marked by elevated Il17a, Il17f, Il1b, Tnf, and Il36g, as well as an upregulation of Il12a, Il4, Il10, and l13. Chemokine gene induction (including Ccl2, Ccl3, Ccl4, Ccl1l, Cxcl1, Cxcl2, Cxcl9, and Cxcl10) coincided with an influx of neutrophils, monocytes/macrophages, and eosinophils. Hyphal invasion caused tissue damage, epithelial remodeling, and upregulation of genes linked to epithelium signaling and antimicrobial responses in the limiting ridge. Our findings support a need for continued exploration into the interactions between the immunological milieu, the host microbiota, and clinical interventions such as the use of antibiotics and immunotherapeutic agents and their collective impact on invasive candidiasis risk.

Tail-specific proteases (Tsp) are members of a widely distributed family of serine proteases that commonly target and process periplasmic proteins in Gram-negative bacteria. The obligately intracellular, Gram-negative Chlamydia encode a highly conserved Tsp homolog whose target and function are unclear. We identified a Chlamydia muridarum mutant with a nonsense mutation in tsp. Differentiation of the tsp mutant elementary bodies into vegetative reticulate bodies was delayed at 37°C and completely blocked at 40°C. Tsp localized to C. muridarum cells but was not detected outside the inclusion, suggesting that it targets chlamydial rather than host proteins. The abundance of key chlamydia outer membrane complex and virulence-related proteins differed in wild-type and tsp mutant elementary bodies, consistent with the possibility that Tsp regulates developmental cycle progression. The altered abundances of chlamydial structural and virulence factors could explain why the mutant, but not an isogenic recombinant with wild-type tsp, was highly attenuated in a mouse intravaginal infection model. Thus, chlamydial Tsp is required for timely differentiation of elementary bodies into reticulate bodies in vitro and is an essential virulence factor in vivo.

Intracellular bacterial pathogens deploy secreted effector proteins that manipulate diverse host machinery and pathways to promote infection. Although many effectors carry out a single function or interaction, there are a growing number of secreted effectors capable of interacting with multiple host factors. However, few effectors secreted by arthropod-borne obligate intracellular Rickettsia species have been linked to multiple host targets. Here, we investigated the conserved rickettsial secreted effector Sca4, which was previously shown to interact with host vinculin in donor cells to promote cell-to-cell spread in the model Rickettsia species R. parkeri. We discovered that Sca4 also binds the host cell protein clathrin heavy chain (CHC, CLTC) via a conserved segment in the Sca4 N-terminus. In mammalian host cells, ablation of CLTC expression or chemical inhibition of endocytosis reduced R. parkeri cell-to-cell spread, indicating that clathrin promotes efficient spread. Unexpectedly, the contribution of CHC to spread was independent of Sca4 and appeared restricted to the recipient host cell, suggesting that the Sca4-clathrin interaction regulates another aspect of the infectious lifecycle. Indeed, R. parkeri lacking Sca4 or expressing a Sca4 truncation unable to bind clathrin had markedly reduced burdens in tick cells, hinting at a cell type-specific function for the Sca4-clathrin interaction. Sca4 homologs from diverse Rickettsia species also bound clathrin, suggesting that the function of this novel effector-host interaction may be broadly important for rickettsial infection. We conclude that Sca4 has multiple targets during infection and that rickettsiae may manipulate host endocytic machinery to facilitate several stages of their life cycles.