Many intracellular pathogens, including Toxoplasma gondii, survive within macrophages by residing in vacuoles that avoid fusion with lysosomes. It is important to determine whether cell-mediated immunity can trigger macrophage antimicrobial activity by rerouting these vacuoles to lysosomes. We report that CD40 stimulation of human and mouse macrophages infected with T. gondii resulted in fusion of parasitophorous vacuoles and late endosomes/lysosomes. Vacuole/lysosome fusion took place even when CD40 was ligated after the formation of parasitophorous vacuoles. Genetic and pharmacological approaches that impaired phosphoinositide-3-class 3 (PIK3C3), Rab7, vacuolar ATPase, and lysosomal enzymes revealed that vacuole/lysosome fusion mediated antimicrobial activity induced by CD40. Ligation of CD40 caused colocalization of parasitophorous vacuoles and LC3, a marker of autophagy, which is a process that controls lysosomal degradation. Vacuole/lysosome fusion and antimicrobial activity were shown to be dependent on autophagy. Thus, cell-mediated immunity through CD40 stimulation can reroute an intracellular pathogen to the lysosomal compartment, resulting in macrophage antimicrobial activity.
Rosa M. Andrade, Matthew Wessendarp, Marc-Jan Gubbels, Boris Striepen, Carlos S. Subauste
Whooping cough is considered a childhood disease, although there is growing evidence that children are infected by adult carriers. Additionally, increasing numbers of vaccinated adults are being diagnosed with Bordetella pertussis disease. Thus it is critical to understand how B. pertussis remains endemic even in highly vaccinated or immune populations. Here we used the mouse model to examine the nature of sterilizing immunity to B. pertussis. Antibodies were necessary to control infection but did not rapidly clear B. pertussis from the lungs. However, antibodies affected B. pertussis after a delay of at least a week by a mechanism that involved neutrophils and Fc receptors, suggesting that neutrophils phagocytose and clear antibody-opsonized bacteria via Fc receptors. B. pertussis blocked migration of neutrophils and inhibited their recruitment to the lungs during the first week of infection by a pertussis toxin–dependent (PTx-dependent) mechanism; a PTx mutant of B. pertussis induced rapid neutrophil recruitment and was rapidly cleared from the lungs by adoptively transferred antibodies. Depletion of neutrophils abrogated the defects of the PTx mutant. Together these results indicate that PTx inhibits neutrophil recruitment, which consequently allows B. pertussis to avoid rapid antibody-mediated clearance and therefore successfully infect immune hosts.
Girish S. Kirimanjeswara, Luis M. Agosto, Mary J. Kennett, Ottar N. Bjornstad, Eric T. Harvill
The tuberculosis vaccine Mycobacterium bovis bacille Calmette-Guérin (BCG) was equipped with the membrane-perforating listeriolysin (Hly) of Listeria monocytogenes, which was shown to improve protection against Mycobacterium tuberculosis. Following aerosol challenge, the Hly-secreting recombinant BCG (hly+ rBCG) vaccine was shown to protect significantly better against aerosol infection with M. tuberculosis than did the parental BCG strain. The isogenic, urease C–deficient hly+ rBCG (ΔureC hly+ rBCG) vaccine, providing an intraphagosomal pH closer to the acidic pH optimum for Hly activity, exhibited still higher vaccine efficacy than parental BCG. ΔureC hly+ rBCG also induced profound protection against a member of the M. tuberculosis Beijing/W genotype family while parental BCG failed to do so consistently. Hly not only promoted antigen translocation into the cytoplasm but also apoptosis of infected macrophages. We concluded that superior vaccine efficacy of ΔureC hly+ rBCG as compared with parental BCG is primarily based on improved cross-priming, which causes enhanced T cell–mediated immunity.
Leander Grode, Peter Seiler, Sven Baumann, Jürgen Hess, Volker Brinkmann, Ali Nasser Eddine, Peggy Mann, Christian Goosmann, Silke Bandermann, Debbie Smith, Gregory J. Bancroft, Jean-Marc Reyrat, Dick van Soolingen, Bärbel Raupach, Stefan H.E. Kaufmann
Group B streptococci (GBSs) are the leading cause of neonatal meningitis. GBSs enter the CNS by penetrating the blood-brain barrier (BBB), which consists of specialized human brain microvascular endothelial cells (hBMECs). To identify GBS factors required for BBB penetration, we generated random mutant libraries of a virulent strain and screened for loss of hBMEC invasion in vitro. Two independent hypo-invasive mutants possessed disruptions in the same gene, invasion associated gene (iagA), which encodes a glycosyltransferase homolog. Allelic replacement of iagA in the GBS chromosome produced a 4-fold decrease in hBMEC invasiveness. Mice challenged with the GBS ΔiagA mutant developed bacteremia comparably to WT mice, yet mortality was significantly lower (20% vs. 90%), as was the incidence of meningitis. The glycolipid diglucosyldiacylglycerol, a cell membrane anchor for lipoteichoic acid (LTA) and predicted product of the IagA glycosyltransferase, was absent in the ΔiagA mutant, which consequently shed LTA into the media. Attenuation of virulence of the ΔiagA mutant was found to be independent of TLR2-mediated signaling, but bacterial supernatants from the ΔiagA mutant containing released LTA inhibited hBMEC invasion by WT GBS. Our data suggest that LTA expression on the GBS surface plays a role in bacterial interaction with BBB endothelium and the pathogenesis of neonatal meningitis.
Kelly S. Doran, Erin J. Engelson, Arya Khosravi, Heather C. Maisey, Iris Fedtke, Ozlem Equils, Kathrin S. Michelsen, Moshe Arditi, Andreas Peschel, Victor Nizet
Hypoxia is a characteristic feature of the tissue microenvironment during bacterial infection. Here we report on our use of conditional gene targeting to examine the contribution of hypoxia-inducible factor 1, α subunit (HIF-1α) to myeloid cell innate immune function. HIF-1α was induced by bacterial infection, even under normoxia, and regulated the production of key immune effector molecules, including granule proteases, antimicrobial peptides, nitric oxide, and TNF-α. Mice lacking HIF-1α in their myeloid cell lineage showed decreased bactericidal activity and failed to restrict systemic spread of infection from an initial tissue focus. Conversely, activation of the HIF-1α pathway through deletion of von Hippel–Lindau tumor-suppressor protein or pharmacologic inducers supported myeloid cell production of defense factors and improved bactericidal capacity. HIF-1α control of myeloid cell activity in infected tissues could represent a novel therapeutic target for enhancing host defense.
Carole Peyssonnaux, Vivekanand Datta, Thorsten Cramer, Andrew Doedens, Emmanuel A. Theodorakis, Richard L. Gallo, Nancy Hurtado-Ziola, Victor Nizet, Randall S. Johnson
Inhibitors of HIV protease have been shown to have antiapoptotic effects in vitro, yet whether these effects are seen in vivo remains controversial. In this study, we have evaluated the impact of the HIV protease inhibitor (PI) nelfinavir, boosted with ritonavir, in models of nonviral disease associated with excessive apoptosis. In mice with Fas-induced fatal hepatitis, Staphylococcal enterotoxin B–induced shock, and middle cerebral artery occlusion–induced stroke, we demonstrate that PIs significantly reduce apoptosis and improve histology, function, and/or behavioral recovery in each of these models. Further, we demonstrate that both in vitro and in vivo, PIs block apoptosis through the preservation of mitochondrial integrity and that in vitro PIs act to prevent pore function of the adenine nucleotide translocator (ANT) subunit of the mitochondrial permeability transition pore complex.
Joel G.R. Weaver, Agathe Tarze, Tia C. Moffat, Morgane LeBras, Aurelien Deniaud, Catherine Brenner, Gary D. Bren, Mario Y. Morin, Barbara N. Phenix, Li Dong, Susan X. Jiang, Valerie L. Sim, Bogdan Zurakowski, Jessica Lallier, Heather Hardin, Peter Wettstein, Rolf P.G. van Heeswijk, Andre Douen, Romano T. Kroemer, Sheng T. Hou, Steffany A.L. Bennett, David H. Lynch, Guido Kroemer, Andrew D. Badley
Major barriers separating the blood from tissue compartments in the body are composed of endothelial cells. Interaction of bacteria with such barriers defines the course of invasive infections, and meningitis has served as a model system to study endothelial cell injury. Here we report the impressive ability of Streptococcus pneumoniae, clinically one of the most important pathogens, to induce 2 morphologically distinct forms of programmed cell death (PCD) in brain-derived endothelial cells. Pneumococci and the major cytotoxins H202 and pneumolysin induce apoptosis-like PCD independent of TLR2 and TLR4. On the other hand, pneumococcal cell wall, a major proinflammatory component, causes caspase-driven classical apoptosis that is mediated through TLR2. These findings broaden the scope of bacterial-induced PCD, link these effects to innate immune TLRs, and provide insight into the acute and persistent phases of damage during meningitis.
Daniela Bermpohl, Annett Halle, Dorette Freyer, Emilie Dagand, Johann S. Braun, Ingo Bechmann, Nicolas W.J. Schröder, Joerg R. Weber
The study of fungal regulatory networks is essential to the understanding of how these pathogens respond to host environmental signals with effective virulence-associated traits. In this study, a virulence-associated DEAD-box RNA helicase–encoding gene (VAD1) was isolated from a mutant defective in the virulence factor laccase. A Δvad1 mutant exhibited a profound reduction in virulence in a mouse model that was restored after reconstitution with WT VAD1. Loss of VAD1 resulted in upregulation of NOT1, a gene encoding a global repressor of transcription. NOT1 was found to act as an intermediary transcriptional repressor of laccase. Vad1 was located within macromolecular complexes that formed cytoplasmic granular bodies in mature cells and during infection of mouse brain. In addition, VAD1 was shown by in situ hybridization to be expressed in the brain of an AIDS patient coinfected with C. neoformans. To understand the role of VAD1 in virulence, a functional genomics approach was used to identify 3 additional virulence determinants dependent on VAD1: PCK1, TUF1, and MPF3, involved in gluconeogenesis, mitochondrial protein synthesis, and cell wall integrity, respectively. These data show that fungal virulence-associated genes are coordinately regulated and that an analysis of such transcriptomes allows for the identification of important new genes involved in the normal growth and virulence of fungal pathogens.
John Panepinto, Lide Liu, Jeanie Ramos, Xudong Zhu, Tibor Valyi-Nagy, Saliha Eksi, Jianmin Fu, H. Ari Jaffe, Brian Wickes, Peter R. Williamson
Coagulase-negative staphylococci, with the leading species Staphylococcus epidermidis, are the predominant cause of hospital-acquired infections. Treatment is especially difficult owing to biofilm formation and frequent antibiotic resistance. However, virulence mechanisms of these important opportunistic pathogens have remained poorly characterized. Here we demonstrate that S. epidermidis secretes poly-γ-DL-glutamic acid (PGA) to facilitate growth and survival in the human host. Importantly, PGA efficiently sheltered S. epidermidis from key components of innate host defense, namely antimicrobial peptides and neutrophil phagocytosis, and was indispensable for persistence during device-related infection. Furthermore, PGA protected S. epidermidis from high salt concentration, a key feature of its natural environment, the human skin. Notably, PGA was synthesized by all tested strains of S. epidermidis and a series of closely related coagulase-negative staphylococci, most of which are opportunistic pathogens. Our study presents important novel biological functions for PGA and indicates that PGA represents an excellent target for therapeutic maneuvers aimed at treating disease caused by S. epidermidis and related staphylococci.
Stanislava Kocianova, Cuong Vuong, Yufeng Yao, Jovanka M. Voyich, Elizabeth R. Fischer, Frank R. DeLeo, Michael Otto
Macrophages are critical effectors of bacterial clearance and must retain viability, despite exposure to toxic bacterial products, until key antimicrobial functions are performed. Subsequently, host-mediated macrophage apoptosis aids resolution of infection. The ability of macrophages to make this transition from resistance to susceptibility to apoptosis is important for effective host innate immune responses. We investigated the role of Mcl-1, an essential regulator of macrophage lifespan, in this switch from viability to apoptosis, using the model of pneumococcal-associated macrophage apoptosis. Upon exposure to pneumococci, macrophages initially upregulate Mcl-1 protein and maintain viability for up to 14 hours. Subsequently, macrophages reduce expression of full-length Mcl-1 and upregulate a 34-kDa isoform of Mcl-1 corresponding to a novel BH3-only splice variant, Mcl-1Exon-1. Change in expression of Mcl-1 protein is associated with mitochondrial membrane permeabilization, which is characterized by loss of mitochondrial inner transmembrane potential and translocation of cytochrome c and apoptosis-inducing factor. Following pneumococcal infection, macrophages expressing full-length human Mcl-1 as a transgene exhibit a delay in apoptosis and in bacterial killing. Mcl-1 transgenic mice clear pneumococci from the lung less efficiently than nontransgenic mice. Dynamic changes in Mcl-1 expression determine macrophage viability as well as antibacterial host defense.
Helen M. Marriott, Colin D. Bingle, Robert C. Read, Karen E. Braley, Guido Kroemer, Paul G. Hellewell, Ruth W. Craig, Moira K.B. Whyte, David H. Dockrell
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