Display omitted
•The cytosolic domain of EscV forms a nonameric ring in solution.•The inter-protomer interface is primarily electrostatic.•A large electropositive surface may interact with the ...transmembrane domain.•Subdomains 2 and 4 take on a closed conformation.
The bacterial injectisome and flagella both rely on type III secretion systems for their assembly. The syringe-like injectisome creates a continuous channel between the bacterium and the host cell, through which signal-modulating effector proteins are secreted. The inner membrane pore protein SctV controls the hierarchy of substrate selection and may also be involved in energizing secretion. We present the 4.7 Å cryo-EM structure of the SctV cytosolic domain (SctVC) from the enteropathogenic Escherichia coli injectisome. SctVC forms a nonameric ring with primarily electrostatic interactions between its subunits. Molecular dynamics simulations show that monomeric SctVC maintains a closed conformation, in contrast with previous studies on flagellar homologue FlhA. Comparison with substrate-bound homologues suggest that a conformational change would be required to accommodate binding partners.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The type III secretion system (T3SS) is a virulence mechanism employed by Gram-negative pathogens. The T3SS forms a proteinaceous channel that projects a needle into the extracellular medium where it ...interacts with the host cell to deliver virulence factors. Enteropathogenic Escherichia coli (EPEC) is unique in adopting a needle extension to the T3SS—a filament formed by EspA—which is absolutely required for efficient colonization of the gut. Here, we describe the cryoelectron microscopy structure of native EspA filaments from EPEC at 3.6-Å resolution. Within the filament, positively charged residues adjacent to a hydrophobic groove line the lumen of the filament in a spiral manner, suggesting a mechanism of substrate translocation mediated via electrostatics. Using structure-guided mutagenesis, in vivo studies corroborate the role of these residues in secretion and translocation function. The high-resolution structure of the EspA filament could aid in structure-guided drug design of antivirulence therapeutics.
Display omitted
•Structure of native EspA adopts a unique fold compared with other T3SS tip proteins•Native EspA adopts a different conformation from the chaperone-bound state•The EspA structure reveals an electropositive pattern within its lumen•In vivo studies show that electrostatics play a crucial role in function
EPEC pathogenicity is dependent on a syringe-like nanomachine, the T3SS, including its long needle extension EspA. Lyons et al. characterize the cryo-EM-derived structure of the EspA filament purified from EPEC. Structure-guided mutagenesis and in vivo studies reveal a mechanism of substrate translocation through this essential extracellular conduit to the infected host.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Quantification of platelet activation can be important for patients suffering from prothrombotic states, bleeding diatheses, cardiovascular disease, and other diseases in which platelets play a role. ...The analysis of platelet activation ex vivo typically requires blood processing
immediately after venipuncture; this requirement can create problematic situations for both medical and research personnel. Flow cytometry is one method used to quantify platelet activation by measuring the expression of platelet surface markers with fluorescent antibodies. PAMFix is a fixative
that stabilizes platelet activation markers, including P-selectin (CD62P), in whole blood. PAMFix has already been validated for use in humans and canines for stabilization of whole blood, thus allowing flow cytometry to be performed up to 28 and 22 d, respectively, after venipuncture and
reducing the need for expensive equipment and highly trained personnel at the location of venipuncture. Pigtailed macaques (Macaca nemestrina) are frequently used in infectious disease research that may require containment conditions that preclude immediate processing of samples. In
this study, we tested the efficacy of PAMFix on whole blood from pigtailed macaques to determine the short- and long-term effects of PAMFix on platelet P-selectin expression as analyzed by flow cytometry.
Fifty-one specific pathogen-free (SPF) cats 10 weeks to 13 years of age were infected with a cat-to-cat fecal–oral passed strain of feline enteric coronavirus (FECV). Clinical signs ranged from ...unapparent to a mild and self-limiting diarrhea. Twenty-nine of these cats were FECV naïve before infection and followed sequentially for fecal virus shedding and antibody responses over a period of 8–48 months. Fecal shedding, as determined by real-time polymerase chain reaction (RT-PCR) from rectal swabs, appeared within a week and was significantly higher in kittens than older cats. FECV shedding remained at high levels for 2–10 months before eventually evolving into one of three excretion patterns. Eleven cats shed the virus persistently at varying levels over an observation period of 9–24 months. Eleven cats appeared to have periods of virus shedding interlaced with periods of non-shedding (intermittent or recurrent shedders), and seven cats ceased shedding after 5–19 months (average 12 months). There was no change in the patterns of virus shedding among cats that were excreting FECV at the time of a secondary challenge exposure. Four cats, which had ceased shedding, re-manifested a primary type infection when secondarily infected. Cats with higher feline coronavirus (FCoV) antibody titers were significantly more likely to shed virus, while cats with lower titers were significantly less likely to be shedding. Twenty-two kittens born to experimentally infected project queens began shedding virus spontaneously, but never before 9–10 weeks of age. Natural kittenhood infections appeared to be low grade and abortive. However, a characteristic primary type infection occurred following experimental infection with FECV at 12–15 weeks of age. Pregnancy, parturition and lactation had no influence on fecal shedding by queens. Methylprednisolone acetate treatment did not induce non-shedders to shed and shedders to increase shedding.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Background. Sensitive assays are needed for detection of residual human immunodeficiency virus (HIV) in patients with undetectable plasma viral loads to determine whether eradication strategies are ...effective. The gold standard quantitative viral outgrowth assay (QVOA) underestimates the magnitude of the viral reservoir. We sought to determine whether xenograft of leukocytes from HIV type 1 (HIV)-infected patients with undetectable plasma viral loads into immunocompromised mice would result in viral amplification. Methods. Peripheral blood mononuclear cells or purified CD4⁺ T cells from HIV or simian immunodeficiency virus (SIV)-infected subjects with undetectable plasma viral loads were adoptively transferred into NOD.Cg-PrkdcscidIl2rgtmlWjl/SzJ (NSG) mice. The mice were monitored for viremia following depletion of human CD8⁺ T cells to minimize antiviral activity. In some cases, humanized mice were also treated with activating anti-CD3 antibody. Results. With this murine viral outgrowth assay (MVOA), we successfully amplified replication-competent HIV or SIV from all subjects tested, including 5 HIV-positive patients receiving suppressive antiretroviral therapy (ART) and 6 elite controllers or suppressors who were maintaining undetectable viral loads without ART, including an elite suppressor from whom we were unable to recover virus by QVOA. Conclusions. Our results suggest that the MVOA has the potential to serve as a powerful tool to identify residual HIV in patients with undetectable viral loads.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Simian immunodeficiency virus (SIV) infection of macaques recapitulates many aspects of HIV pathogenesis and is similarly affected by both genetic and environmental factors. Psychosocial stress is ...associated with immune system dysregulation and worse clinical outcomes in people with HIV. This study assessed the impact of single housing, as a model of psychosocial stress, on innate immune responses of pigtailed macaques ( Macaca nemestrina ) during acute SIV infection.
A retrospective analysis of acute SIV infection of 2- to si6-year-old male pigtailed macaques was performed to compare the innate immune responses of socially ( n = 41) and singly ( n = 35) housed animals. Measures included absolute monocyte count and subsets, and in a subset ( n ≤ 18) platelet counts and activation data.
SIV infection resulted in the expected innate immune parameter changes with a modulating effect from housing condition. Monocyte number increased after infection for both groups, driven by classical monocytes (CD14 + CD16 - ), with a greater increase in socially housed animals (227%, p < .001, by day 14 compared with preinoculation time points). Platelet numbers recovered more quickly in the socially housed animals. Platelet activation (P-selectin) increased by 65% ( p = .004) and major histocompatibility complex class I surface expression by 40% ( p = .009) from preinoculation only in socially housed animals, whereas no change in these measures occurred in singly housed animals.
Chronic psychosocial stress produced by single housing may play an immunomodulatory role in the innate immune response to acute retroviral infection. Dysregulated innate immunity could be one of the pathways by which psychosocial stress contributes to immune suppression and increased disease severity in people with HIV.
In this chapter we outline a RNA extraction method for very low immune cell populations isolated from the central nervous system of mice undergoing experimental autoimmune encephalomyelitis. We ...compare various normalization and quantification techniques to examine miRNA expression. Our data highlight that employing a mean normalization procedure using a number of well-selected housekeeping miRNA genes, followed by absolute quantification with a standard curve generated from a commercial miRNA oligo, gave the most robust and reproducible miRNA expression results.
Platelets are key participants in innate immune responses to pathogens. As a decrease in circulating platelet count is one of the initial hematologic indicators of human immunodeficiency virus (HIV) ...infection, we sought to determine whether decline in platelet number during acute infection results from decreased production, increased antibody-mediated destruction, or increased platelet activation in a simian immunodeficiency virus (SIV)/macaque model. During acute SIV infection, circulating platelets were activated with increased surface expression of P-selectin, CD40L and major histocompatibility complex class I. Platelet production was maintained and platelet autoantibodies were not detected during acute infection. Concurrent with a decrease in platelet numbers and an increase in circulating monocytes, platelets were found sequestered in plateletmonocyte aggregates, thereby contributing to the decline in platelet counts. Because the majority of circulating CD16⁺ monocytes formed complexes with platelets during acute SIV infection, a decreased platelet count may represent platelet participation in the innate immune response to HIV.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
In this chapter, we describe simple methods to investigate microRNA (miRNA) induction in response to lipopolysaccharide, the ligand for Toll-Like Receptor-4 activation. In brief, we demonstrate how ...to investigate global miRNA induction and/or repression in bone marrow-derived macrophages using TaqMan MicroRNA Arrays, followed by methods to measure individual miRNAs and target mRNA expression. Moreover, we explain step-by-step instructions on how to modulate endogenous miRNA expression through the use of miRNA inhibitors and mimics as well as highlight how miRNA modulation can be used to confirm mRNA targeting via Luciferase reporter assay. Moreover, these methods can be applied to whichever cell type and cellular function under investigation.
Platelet decline is a feature of many acute viral infections, including cytomegalovirus (CMV) infection in humans and mice. Platelet sequestration in association with other cells, including ...endothelium and circulating leukocytes, can contribute to this decline and influence the immune response to and pathogenesis of viral infection. We sought to determine if platelet-endothelial associations (PEAs) contribute to platelet decline during acute murine CMV (mCMV) infection, and if these associations affect viral load and production. Male BALB/c mice were infected with mCMV (Smith strain), euthanized at timepoints throughout acute infection and compared to uninfected controls. An increase in PEA formation was confirmed in the salivary gland at all post-inoculation timepoints using immunohistochemistry for CD41+ platelets co-localizing with CD34+ vessels. Platelet depletion did not change amount of viral DNA or timecourse of infection, as measured by qPCR. However, platelet depletion reduced viral titer of mCMV in the salivary glands while undepleted controls demonstrated robust replication in the tissue by plaque assay. Thus, platelet associations with endothelium may enhance the ability of mCMV to replicate within the salivary gland. Further work is needed to determine the mechanisms behind this effect and if pharmacologic inhibition of PEAs may reduce CMV production in acutely infected patients.
Full text
Available for:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
PDF
