Evasion of host immune responses is a prerequisite for chronic bacterial diseases; however, the underlying mechanisms are not fully understood. Here, we show that the persistent intracellular ...pathogen Brucella abortus prevents immune activation of macrophages by inducing CD4(+)CD25(+) T cells to produce the anti-inflammatory cytokine interleukin-10 (IL-10) early during infection. IL-10 receptor (IL-10R) blockage in macrophages resulted in significantly higher NF-kB activation as well as decreased bacterial intracellular survival associated with an inability of B. abortus to escape the late endosome compartment in vitro. Moreover, either a lack of IL-10 production by T cells or a lack of macrophage responsiveness to this cytokine resulted in an increased ability of mice to control B. abortus infection, while inducing elevated production of pro-inflammatory cytokines, which led to severe pathology in liver and spleen of infected mice. Collectively, our results suggest that early IL-10 production by CD25(+)CD4(+) T cells modulates macrophage function and contributes to an initial balance between pro-inflammatory and anti-inflammatory cytokines that is beneficial to the pathogen, thereby promoting enhanced bacterial survival and persistent infection.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Brucellosis is a zoonotic infection caused primarily by the bacterial pathogens Brucella melitensis and B. abortus. It is acquired by consumption of unpasteurized dairy products or by contact with ...infected animals. Globally, it is one of the most widespread zoonoses, with 500,000 new cases reported each year. In endemic areas, Brucella infections represent a serious public health problem that results in significant morbidity and economic losses. An important feature of the disease is persistent bacterial colonization of the reticuloendothelial system. In this review we discuss recent insights into mechanisms of intracellular survival and immune evasion that contribute to systemic persistence by the pathogenic Brucella species.
Eradication of persistent intracellular bacterial pathogens with antibiotic therapy is often slow or incomplete. However, strategies to augment antibiotics are hampered by our poor understanding of ...the nutritional environment that sustains chronic infection. Here we show that the intracellular pathogen Brucella abortus survives and replicates preferentially in alternatively activated macrophages (AAMs), which are more abundant during chronic infection. A metabolic shift induced by peroxisome proliferator-activated receptor γ (PPARγ), which increases intracellular glucose availability, is identified as a causal mechanism promoting enhanced bacterial survival in AAMs. Glucose uptake was crucial for increased replication of B. abortus in AAMs, and for chronic infection, as inactivation of the bacterial glucose transporter gluP reduced both intracellular survival in AAMs and persistence in mice. Thus, a shift in intracellular nutrient availability induced by PPARγ promotes chronic persistence of B. abortus within AAMs, and targeting this pathway may aid in eradicating chronic infection.
•B. abortus is associated with AAMs during chronic infection in mice•AAMs support high levels of intracellular B. abortus replication•PPARγ activation contributes to increased persistence of B. abortus in vivo•Elevated glucose in AAMs promotes increased intracellular replication of B. abortus
Subversion of endoplasmic reticulum (ER) function is a feature shared by multiple intracellular bacteria and viruses, and in many cases this disruption of cellular function activates pathways of the ...unfolded protein response (UPR). In the case of infection with
, the etiologic agent of brucellosis, the unfolded protein response in the infected placenta contributes to placentitis and abortion, leading to pathogen transmission. Here we show that
infection of pregnant mice led to death of infected placental trophoblasts in a manner that depended on the VirB type IV secretion system (T4SS) and its effector VceC. The trophoblast death program required the ER stress-induced transcription factor CHOP. While NOD1/NOD2 expression in macrophages contributed to ER stress-induced inflammation, these receptors did not play a role in trophoblast death. Both placentitis and abortion were independent of apoptosis-associated Speck-like protein containing a caspase activation and recruitment domain (ASC). These studies show that
uses its T4SS to induce cell-type-specific responses to ER stress in trophoblasts that trigger placental inflammation and abortion. Our results suggest further that in
the T4SS and its effectors are under selection as bacterial transmission factors.
infects the placenta of pregnant cows, where it replicates to high levels and triggers abortion of the calf. The aborted material is highly infectious and transmits infection to both cows and humans, but very little is known about how
causes abortion. By studying this infection in pregnant mice, we discovered that
kills trophoblasts, which are important cells for maintaining pregnancy. This killing required an injected bacterial protein (VceC) that triggered an endoplasmic reticulum (ER) stress response in the trophoblast. By inhibiting ER stress or infecting mice that lack CHOP, a protein induced by ER stress, we could prevent death of trophoblasts, reduce inflammation, and increase the viability of the pups. Our results suggest that
injects VceC into placental trophoblasts to promote its transmission by abortion.
Background
Accurate diagnosis of coronavirus disease 2019 is essential to limiting transmission within healthcare settings. The aim of this study was to identify patient demographic and clinical ...characteristics that could impact the clinical sensitivity of the nasopharyngeal severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV2) reverse transcription polymerase chain reaction (RT‐PCR) test.
Methods
We conducted a retrospective, matched case‐control study of patients who underwent repeated nasopharyngeal SARS‐CoV2 RT‐PCR testing at a tertiary care academic medical center between March 1 and July 23, 2020. The primary endpoint was conversion from negative to positive PCR status within 14 days. We conducted conditional logistic regression modeling to assess the associations between demographic and clinical features and conversion to test positivity.
Results
Of 51,116 patients with conclusive SARS‐CoV2 nasopharyngeal RT‐PCR results, 97 patients converted from negative to positive within 14 days. We matched those patients 1:2 to 194 controls by initial test date. In multivariate analysis, clinical suspicion for a respiratory infection (adjusted odds ratio aOR 20.9, 95% confidence interval CI: 3.1–141.2) and lack of pulmonary imaging (aOR 4.7, 95% CI: 1.03–21.8) were associated with conversion, while a lower burden of comorbidities trended toward an increased odds of conversion (aOR 2.2, 95% CI: 0.9–5.3).
Conclusions
Symptoms consistent with a respiratory infection, especially in relatively healthy individuals, should raise concerns about a clinical false‐negative result. We have identified several characteristics that should be considered when creating institutional infection prevention guidelines in the absence of more definitive data and should be included in future studies.
Human brucellosis is most commonly diagnosed by serology based on agglutination of fixed Brucella abortus as antigen. Nucleic acid amplification techniques have not proven capable of reproducibly and ...sensitively demonstrating the presence of Brucella DNA in clinical specimens. We sought to optimize a monoclonal antibody-based assay to detect Brucella melitensis lipopolysaccharide in blood by conjugating B. melitensis LPS to keyhole limpet hemocyanin, an immunogenic protein carrier to maximize IgG affinity of monoclonal antibodies. A panel of specific of monoclonal antibodies was obtained that recognized both B. melitensis and B. abortus lipopolysaccharide epitopes. An antigen capture assay was developed that detected B. melitensis in the blood of experimentally infected mice and, in a pilot study, in naturally infected Peruvian subjects. As a proof of principle, a majority (7/10) of the patients with positive blood cultures had B. melitensis lipopolysaccharide detected in the initial blood specimen obtained. One of 10 patients with relapsed brucellosis and negative blood culture had a positive serum antigen test. No seronegative/blood culture negative patients had a positive serum antigen test. Analysis of the pair of monoclonal antibodies (2D1, 2E8) used in the capture ELISA for potential cross-reactivity in the detection of lipopolysaccharides of E. coli O157:H7 and Yersinia enterocolitica O9 showed specificity for Brucella lipopolysaccharide. This new approach to develop antigen-detection monoclonal antibodies against a T cell-independent polysaccharide antigen based on immunogenic protein conjugation may lead to the production of improved rapid point-of-care-deployable assays for the diagnosis of brucellosis and other infectious diseases.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
To discern virulent from innocuous microbes, the innate immune system senses events associated with bacterial access to immunoprivileged sites such as the host cell cytosol. One such pathway is ...triggered by the cytosolic delivery of flagellin, the major subunit of the flagellum, by bacterial secretion systems. This leads to inflammasome activation and subsequent proinflammatory cell death (pyroptosis) of the infected phagocyte. In this study, we demonstrate that the causative agent of typhoid fever, Salmonella enterica serovar Typhi, can partially subvert this critical innate immune recognition event. The transcriptional regulator TviA, which is absent from Salmonella serovars associated with human gastroenteritis, repressed the expression of flagellin during infection of human macrophage-like (THP-1) cells. This mechanism allowed S. Typhi to dampen inflammasome activation, leading to reduced interleukin-1β (IL-1β) secretion and diminished cell death. Likewise, the introduction of the tviA gene in nontyphoidal Salmonella enterica serovar Typhimurium reduced flagellin-induced pyroptosis. These data suggest that gene regulation of virulence factors enables S. Typhi to evade innate immune recognition by concealing a pathogen-induced process from being sensed by the inflammasome.
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