Thursday, December 29, 2011

Targeted Disruption of Toxoplasma gondii Serine Protease Inhibitor 1 Increases Bradyzoite Cyst Formation In Vitro and Parasite Tissue Burden in Mice

Infect Immun. 2011 Dec 27. [Epub ahead of print]

Targeted Disruption of Toxoplasma gondii Serine Protease Inhibitor 1 Increases Bradyzoite Cyst Formation In Vitro and Parasite Tissue Burden in Mice.

Pszenny V, Davis PH, Zhou XW, Hunter CA, Carruthers VB, Roos DS.

Departments of Biology.

As an intracellular protozoan parasite, Toxoplasma gondii is likely to exploit proteases for host cell invasion, acquisition of nutrients, avoidance of host protective responses, escape from the parasitophorous vacuole, differentiation, and other activities. The serine protease inhibitor TgPI1 is the most abundantly expressed protease inhibitor in parasite tachyzoites. We show here that alternative splicing produces two TgPI1 isoforms, both of which are secreted via dense granules into the parasitophorous vacuole shortly after invasion, become progressively more abundant over the course of the infectious cycle, and can be detected in the infected host cell cytoplasm. To investigate TgPI1 function, the endogenous genomic locus was disrupted in the RH strain background. ΔTgPI1 parasites replicate normally as tachyzoites, but exhibit increased bradyzoite gene transcription and labeling of vacuoles with Dolichos biflorous lectin and under conditions promoting in vitro differentiation; both phenotypes can be partially complemented by either TgPI1 isoform. Mice infected with the ΔTgPI1 mutant display ∼3-fold increased parasite burden in the spleen and liver, and this in vivo phenotype is also complemented by either TgPI1 isoform. These results demonstrate that TgPI1 influences both parasite virulence and bradyzoite differentiation, presumably by inhibiting parasite and/or host serine proteases.

PMID: 22202120 [PubMed - as supplied by publisher]

Sunday, December 25, 2011

The Distribution of Toxoplasma gondii Cysts in the Brain of a Mouse with Latent Toxoplasmosis: Implications for the Behavioral Manipulation Hypothesis

PLoS One. 2011;6(12):e28925. Epub 2011 Dec 14.

The Distribution of Toxoplasma gondii Cysts in the Brain of a Mouse with Latent Toxoplasmosis: Implications for the Behavioral Manipulation Hypothesis

Berenreiterová M, Flegr J, Kuběna AA, Němec P.

Biology Section, Faculty of Science, Charles University in Prague, Praha, Czech Republic.

The highly prevalent parasite Toxoplasma gondii reportedly manipulates rodent behavior to enhance the likelihood of transmission to its definitive cat host. The proximate mechanisms underlying this adaptive manipulation remain largely unclear, though a growing body of evidence suggests that the parasite-entrained dysregulation of dopamine metabolism plays a central role. Paradoxically, the distribution of the parasite in the brain has received only scant attention.


The distributions of T. gondii cysts and histopathological lesions in the brains of CD1 mice with latent toxoplasmosis were analyzed using standard histological techniques. Mice were infected per orally with 10 tissue cysts of the avirulent HIF strain of T. gondii at six months of age and examined 18 weeks later. The cysts were distributed throughout the brain and selective tropism of the parasite toward a particular functional system was not observed. Importantly, the cysts were not preferentially associated with the dopaminergic system and absent from the hypothalamic defensive system. The striking interindividual differences in the total parasite load and cyst distribution indicate a probabilistic nature of brain infestation. Still, some brain regions were consistently more infected than others. These included the olfactory bulb, the entorhinal, somatosensory, motor and orbital, frontal association and visual cortices, and, importantly, the hippocampus and the amygdala. By contrast, a consistently low incidence of tissue cysts was recorded in the cerebellum, the pontine nuclei, the caudate putamen and virtually all compact masses of myelinated axons. Numerous perivascular and leptomeningeal infiltrations of inflammatory cells were observed, but they were not associated with intracellular cysts.


The observed pattern of T. gondii distribution stems from uneven brain colonization during acute infection and explains numerous behavioral abnormalities observed in the chronically infected rodents. Thus, the parasite can effectively change behavioral phenotype of infected hosts despite the absence of well targeted tropism.

PMID: 22194951 [PubMed - in process]

Iron-saturated lactoferrin and pathogenic protozoa: could this protein be an iron source for their parasitic style of life?

Future Microbiol. 2012 Jan;7:149-64.

Iron-saturated lactoferrin and pathogenic protozoa: could this protein be an iron source for their parasitic style of life?

Ortíz-Estrada G, Luna-Castro S, Piña-Vázquez C, Samaniego-Barrón L, León-Sicairos N, Serrano-Luna J, de la Garza M.


Departamento de Biología Celular, Centro de Investigación y de Estudios Avanzados del IPN, Apdo. 14-740, México DF 07000, México.


Iron is an essential nutrient for the survival of pathogens inside a host. As a general strategy against microbes, mammals have evolved complex iron-withholding systems for efficiently decreasing the iron accessible to invaders. Pathogens that inhabit the respiratory, intestinal and genitourinary tracts encounter an iron-deficient environment on the mucosal surface, where ferric iron is chelated by lactoferrin, an extracellular glycoprotein of the innate immune system. However, parasitic protozoa have developed several mechanisms to obtain iron from host holo-lactoferrin. Tritrichomonas fetus, Trichomonas vaginalis, Toxoplasma gondii and Entamoeba histolytica express lactoferrin-binding proteins and use holo-lactoferrin as an iron source for growth in vitro; in some species, these binding proteins are immunogenic and, therefore, may serve as potential vaccine targets. Another mechanism to acquire lactoferrin iron has been reported in Leishmania spp. promastigotes, which use a surface reductase to recognize and reduce ferric iron to the accessible ferrous form. Cysteine proteases that cleave lactoferrin have been reported in E. histolytica. This review summarizes the available information on how parasites uptake and use the iron from lactoferrin to survive in hostile host environments.

PMID: 22191452 [PubMed - in process]

IL-6 signaling SOCS critical for IL-12 host response to Toxoplasma gondii

Future Microbiol. 2012 Jan;7:13-6.

IL-6 signaling SOCS critical for IL-12 host response to Toxoplasma gondii.

Mirpuri J, Yarovinsky F.


Department of Immunology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390-9093, USA.


Evaluation of: Whitmarsh RJ, Gray CM, Gregg B et al. A critical role for SOCS3 in innate resistance to Toxoplasma gondii. Cell Host Microbe 10(3), 224-236 (2011). SOCS are a family of proteins that play an important role in the negative regulation of the cytokine-JAK-STAT pathway. Socs3 deletion results in prolonged IL-6 signaling measured by STAT3 phosphorylation. A role for STAT3 and SOCS3 in the context of Toxoplasma gondii infection is of particular importance, because STAT3 appears to be a key target of T. gondii virulence factors. By utilizing LysM-cre Socs3(fl/fl) mice, the Hunter laboratory recently established that macrophage-specific SOCS3 knockout mice have enhanced susceptibility to infection with T. gondii. The authors demonstrated that lack of SOCS3-mediated control of IL-6 signaling results in acute susceptibility to T. gondii due to impaired IL-12 production by inflammatory monocytes, macrophages and neutrophils. This article further explores these findings and their implications in the field of host resistance to microbial pathogens.

PMID: 22191442 [PubMed - in process]

Tuesday, December 20, 2011

The apicoplast and endoplasmic reticulum cooperate in fatty acid biosynthesis in the apicomplexan parasite Toxoplasma gondii

J Biol Chem. 2011 Dec 16. [Epub ahead of print]

The apicoplast and endoplasmic reticulum cooperate in fatty acid biosynthesis in the apicomplexan parasite Toxoplasma gondii.

Ramakrishnan S, Docampo MD, Macrae JI, Pujol FM, Brooks CF, van Dooren GG, Hiltunen JK, Kastaniotis AJ, McConville MJ, Striepen B.

University of Georgia, United States;

Apicomplexan parasites are responsible for high impact human diseases such as malaria, toxoplasmosis and cryptosporidiosis. These obligate intracellular pathogens are dependent on both de novo lipid biosynthesis as well as the uptake of host lipids for biogenesis of parasite membranes. Genome annotations and biochemical studies indicate that apicomplexan parasites can synthesize fatty acids via a number of different biosynthetic pathways that are differentially compartmentalized. However, the relative contribution of each of these biosynthetic pathways to total fatty acid composition of intracellular parasite stages remains poorly defined. Here we use a combination of genetic, biochemical and metabolomic approaches to delineate the contribution of fatty acid biosynthetic pathways in Toxoplasma gondii. Metabolic labeling studies with (13)Parasite fatty acid synthesis is an attractive drug target but complex and poorly understood.C-glucose showed that intracellular tachyzoites synthesized a range of long and very long chain fatty acids (C14:0-26:1). Genetic disruption of the apicoplast localized type II fatty acid synthase (FASII) resulted in greatly reduced synthesis of saturated fatty acids up to eighteen carbons long. Ablation of FASII activity resulted in reduced intracellular growth that was partially restored by addition of long chain fatty acids. In contrast, synthesis of very long chain fatty acids was primarily dependent on a fatty acid elongation system comprising three elongases, two reductases and a dehydratase that were localized to the endoplasmic reticulum. The function of these enzymes was confirmed by heterologous expression in yeast. This elongase pathway appears to have a unique role in generating very long unsaturated fatty acids (C26:1) that cannot be salvaged from the host.

PMID: 22179608 [PubMed - as supplied by publisher]

Independent Roles of Apical Membrane Antigen 1 and Rhoptry Neck Proteins during Host Cell Invasion by Apicomplexa

Cell Host Microbe. 2011 Dec 15;10(6):591-602.

Independent Roles of Apical Membrane Antigen 1 and Rhoptry Neck Proteins during Host Cell Invasion by Apicomplexa.

Giovannini D, Späth S, Lacroix C, Perazzi A, Bargieri D, Lagal V, Lebugle C, Combe A, Thiberge S, Baldacci P, Tardieux I, Ménard R.

Institut Pasteur, Unité de Biologie et Génétique du Paludisme, 75724 Paris, France.

During invasion, apicomplexan parasites form an intimate circumferential contact with the host cell, the tight junction (TJ), through which they actively glide. The TJ, which links the parasite motor to the host cell cytoskeleton, is thought to be composed of interacting apical membrane antigen 1 (AMA1) and rhoptry neck (RON) proteins. Here we find that, in Plasmodium berghei, while both AMA1 and RON4 are important for merozoite invasion of erythrocytes, only RON4 is required for sporozoite invasion of hepatocytes, indicating that RON4 acts independently of AMA1 in the sporozoite. Further, in the Toxoplasma gondii tachyzoite, AMA1 is dispensable for normal RON4 ring and functional TJ assembly but enhances tachyzoite apposition to the cell and internalization frequency. We propose that while the RON proteins act at the TJ, AMA1 mainly functions on the zoite surface to permit correct attachment to the cell, which may facilitate invasion depending on the zoite-cell combination.

Copyright © 2011 Elsevier Inc. All rights reserved.

PMID: 22177563 [PubMed - in process]

Secretion of multi-protein migratory complex induced by Toxoplasma gondii infection in macrophages involves the uPA/uPAR activation system

Vet Parasitol. 2011 Nov 20. [Epub ahead of print]

Secretion of multi-protein migratory complex induced by Toxoplasma gondii infection in macrophages involves the uPA/uPAR activation system.

Schuindt SH, Oliveira BC, Pimentel PM, Resende TL, Retamal CA, Damatta RA, Seipel D, Arnholdt AC.

Laboratório de Biologia do Reconhecer, Centro de Biociências e Biotecnologia, Universidade Estadual do Norte Fluminense, Campos dos Goytacazes, Rio de Janeiro, Brazil.

Toxoplasmosis is a world wide spread zoonosis caused by Toxoplasma gondii, an obligate intracellular parasite that is able to disseminate into deep tissues and cross biological barriers, reaching immunoprivileged sites such as the brain and retina. The parasite is able to infect macrophages and dendritic cells for dispersal throughout the body. However, the molecular mechanisms or outcomes of the subversion of the host cell are largely unknown. Recently our group established that metalloproteinases are involved in migration of infected macrophages. Herein, we evaluated the recruitment of host invasive machinery components in T. gondii infected murine macrophages. We showed by immunoprecipitation assays that MMP-9, CD44 TIMP-1 and uPAR were secreted as a multi-protein complex by infected macrophages. Zymographic analysis revealed that MMP-9 was present in its pro- and active form. Moreover, inhibition of uPA/uPAR pathway by PAI-1 decreased secretion of MMP-9 active forms, as well those associated to uPAR and TIMP-1, but not to CD44. Data presented here suggest that MMP-9 is secreted as a multiprotein complex by T. gondii infected macrophages, similar to that observed in metastatic cells. We further speculate that uPA/uPAR system is involved in the expression/secretion of complexes containing active MMP-9 forms.

Copyright © 2011 Elsevier B.V. All rights reserved.

PMID: 22177333 [PubMed - as supplied by publisher]

Monday, December 19, 2011

New insights into parasite rhomboid proteases

Mol Biochem Parasitol. 2011 Dec 7. [Epub ahead of print]

New insights into parasite rhomboid proteases.

Santos JM, Graindorge A, Soldati-Favre D.

Department of Microbiology, Faculty of Medicine, University of Geneva, 1 Rue-Michel Servet, 1211 Geneva 4, Switzerland.

The rhomboid-like proteins constitute a large family of intramembrane serine proteases that are present in all branches of life. First studied in Drosophila, these enzymes catalyse the release of the active forms of proteins from the membrane and hence trigger signalling events. In protozoan parasites, a limited number of rhomboid-like proteases have been investigated and some of them are associated to pathogenesis. In Apicomplexans, rhomboid-like protease activity is involved in shedding adhesins from the surface of the zoites during motility and host cell entry. Recently, a Toxoplasma gondii rhomboid was also implicated in an intracellular signalling mechanism leading to parasite proliferation. In Entamoeba histolytica, the capacity to adhere to host cells and to phagocytose cells is potentiated by a rhomboid-like protease. Survey of a small number of protozoan parasite genomes has uncovered species-specific rhomboid-like protease genes, many of which are predicted to encode inactive enzymes. Functional investigation of the rhomboid-like proteases in other protozoan parasites will likely uncover novel and unexpected implications for this family of proteases.

Copyright © 2011. Published by Elsevier B.V.

PMID: 22173057 [PubMed - as supplied by publisher]

Deficiency of a Niemann-Pick, Type C1-related Protein in Toxoplasma Is Associated with Multiple Lipidoses and Increased Pathogenicity

PLoS Pathog. 2011 Dec;7(12):e1002410. Epub 2011 Dec 8.

Deficiency of a Niemann-Pick, Type C1-related Protein in Toxoplasma Is Associated with Multiple Lipidoses and Increased Pathogenicity.

Lige B, Romano JD, Bandaru VV, Ehrenman K, Levitskaya J, Sampels V, Haughey NJ, Coppens I.

Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, United States of America.

Several proteins that play key roles in cholesterol synthesis, regulation, trafficking and signaling are united by sharing the phylogenetically conserved 'sterol-sensing domain' (SSD). The intracellular parasite Toxoplasma possesses at least one gene coding for a protein containing the canonical SSD. We investigated the role of this protein to provide information on lipid regulatory mechanisms in the parasite. The protein sequence predicts an uncharacterized Niemann-Pick, type C1-related protein (NPC1) with significant identity to human NPC1, and it contains many residues implicated in human NPC disease. We named this NPC1-related protein, TgNCR1. Mammalian NPC1 localizes to endo-lysosomes and promotes the movement of sterols and sphingolipids across the membranes of these organelles. Miscoding patient mutations in NPC1 cause overloading of these lipids in endo-lysosomes. TgNCR1, however, lacks endosomal targeting signals, and localizes to flattened vesicles beneath the plasma membrane of Toxoplasma. When expressed in mammalian NPC1 mutant cells and properly addressed to endo-lysosomes, TgNCR1 restores cholesterol and GM1 clearance from these organelles. To clarify the role of TgNCR1 in the parasite, we genetically disrupted NCR1; mutant parasites were viable. Quantitative lipidomic analyses on the ΔNCR1 strain reveal normal cholesterol levels but an overaccumulation of several species of cholesteryl esters, sphingomyelins and ceramides. ΔNCR1 parasites are also characterized by abundant storage lipid bodies and long membranous tubules derived from their parasitophorous vacuoles. Interestingly, these mutants can generate multiple daughters per single mother cell at high frequencies, allowing fast replication in vitro, and they are slightly more virulent in mice than the parental strain. These data suggest that the ΔNCR1 strain has lost the ability to control the intracellular levels of several lipids, which subsequently results in the stimulation of lipid storage, membrane biosynthesis and parasite division. Based on these observations, we ascribe a role for TgNCR1 in lipid homeostasis in Toxoplasma.

PMID: 22174676 [PubMed - in process]

Thursday, December 15, 2011

Dynamics and 3D organization of secretory organelles of Toxoplasma gondii

J Struct Biol. 2011 Dec 4. [Epub ahead of print]

Dynamics and 3D organization of secretory organelles of Toxoplasma gondii.

Paredes-Santos TC, de Souza W, Attias M.

SourceInstituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Brazil; Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Bioimagem, Brazil.

Micronemes, rhoptries and dense granules are secretory organelles of Toxoplasma gondii crucial for host cell invasion and formation of the parasitophorous vacuole (PV). We examined whether their relative volumes change during the intracellular cycle. Stereological analysis of random ultrathin sections taken at 5min of interaction, 7 and 24h post-infection demonstrated that the relative volume of each type of organelle decreases just after the respective peak of secretion. Micronemes are radially arranged below the polar ring, while rhoptries converge to but only a few reach the inside of the conoid. In contrast to the apical and polarized organelles, dense granules were found scattered throughout the cytoplasm, with no preferential location in the parasite cell body. Extensive observation of random sections indicated that each organelle probably secretes in a different region. Micronemes secrete just below the posterior ring and probably require that the conoid is extruded. The rhoptries passing through the conoid secrete at a porosome-like point at the most apical region. Dense granules secrete laterally, probably at fenestrations in the inner membrane complex. Immunocytochemistry showed that there are no subpopulations of rhoptries or dense granules, as a single organelle can contain more than one kind of its specific proteins. The vacuolar-like profiles observed at the apical portion of parasites just after invasion were confirmed to be empty rhoptries, as they were positively labeled for rhoptry proteins. These findings contribute for a better understanding of the essential behavior of secretory organelles.

Copyright © 2011. Published by Elsevier Inc.

PMID:22155668[PubMed - as supplied by publisher]

Toxoplasma and Plasmodium protein kinases: Roles in invasion and host cell remodelling

Int J Parasitol. 2011 Dec 4. [Epub ahead of print]

Toxoplasma and Plasmodium protein kinases: Roles in invasion and host cell remodelling.

Lim DC, Cooke BM, Doerig C, Saeij JP.

SourceDavid H. Koch Institute for Integrative Cancer Research, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Some apicomplexan parasites have evolved distinct protein kinase families to modulate host cell structure and function. Toxoplasma gondii rhoptry protein kinases and pseudokinases (ROPKs) are involved in virulence and modulation of host cell signalling. The proteome of Plasmodium falciparum contains a family of putative kinases called FIKKs, some of which are exported to the host red blood cell and might play a role in erythrocyte remodelling. In this review we will discuss kinases known to be critical for host cell invasion, intracellular growth and egress, focusing on (i) calcium-dependent protein kinases (CDPKs) and (ii) the secreted kinases that are unique to Toxoplasma (ROPKs) and Plasmodium (FIKKs).

Copyright © 2011. Published by Elsevier Ltd.

PMID:22154850[PubMed - as supplied by publisher]

Thursday, December 08, 2011

A systematic screen to discover and analyze apicoplast proteins identifies a conserved and essential protein import factor

PLoS Pathog. 2011 Dec;7(12):e1002392. Epub 2011 Dec 1.

A systematic screen to discover and analyze apicoplast proteins identifies a conserved and essential protein import factor.

Sheiner L, Demerly JL, Poulsen N, Beatty WL, Lucas O, Behnke MS, White MW, Striepen B.
SourceCenter for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia, United States of America.

Parasites of the phylum Apicomplexa cause diseases that impact global health and economy. These unicellular eukaryotes possess a relict plastid, the apicoplast, which is an essential organelle and a validated drug target. However, much of its biology remains poorly understood, in particular its elaborate compartmentalization: four membranes defining four different spaces. Only a small number of organellar proteins have been identified in particular few proteins are known for non-luminal apicoplast compartments. We hypothesized that enlarging the catalogue of apicoplast proteins will contribute toward identifying new organellar functions and expand the realm of targets beyond a limited set of characterized pathways. We developed a bioinformatic screen based on mRNA abundance over the cell cycle and on phyletic distribution. We experimentally assessed 57 genes, and of 30 successful epitope tagged candidates eleven novel apicoplast proteins were identified. Of those, seven appear to target to the lumen of the organelle, and four localize to peripheral compartments. To address their function we then developed a robust system for the construction of conditional mutants via a promoter replacement strategy. We confirm the feasibility of this system by establishing conditional mutants for two selected genes - a luminal and a peripheral apicoplast protein. The latter is particularly intriguing as it encodes a hypothetical protein that is conserved in and unique to Apicomplexan parasites and other related organisms that maintain a red algal endosymbiont. Our studies suggest that this peripheral plastid protein, PPP1, is likely localized to the periplastid compartment. Conditional disruption of PPP1 demonstrated that it is essential for parasite survival. Phenotypic analysis of this mutant is consistent with a role of the PPP1 protein in apicoplast biogenesis, specifically in import of nuclear-encoded proteins into the organelle.

PMID:22144892[PubMed - in process]

Autophagy Protein Atg3 is Essential for Maintaining Mitochondrial Integrity and for Normal Intracellular Development of Toxoplasma gondii Tachyzoites

PLoS Pathog. 2011 Dec;7(12):e1002416. Epub 2011 Dec 1.

Autophagy Protein Atg3 is Essential for Maintaining Mitochondrial Integrity and for Normal Intracellular Development of Toxoplasma gondii Tachyzoites.

Besteiro S, Brooks CF, Striepen B, Dubremetz JF.

SourceUMR 5235 CNRS, Universités de Montpellier 2 et 1, Dynamique des Interactions Membranaires Normales et Pathologiques, Montpellier, France.

Autophagy is a cellular process that is highly conserved among eukaryotes and permits the degradation of cellular material. Autophagy is involved in multiple survival-promoting processes. It not only facilitates the maintenance of cell homeostasis by degrading long-lived proteins and damaged organelles, but it also plays a role in cell differentiation and cell development. Equally important is its function for survival in stress-related conditions such as recycling of proteins and organelles during nutrient starvation. Protozoan parasites have complex life cycles and face dramatically changing environmental conditions; whether autophagy represents a critical coping mechanism throughout these changes remains poorly documented. To investigate this in Toxoplasma gondii, we have used TgAtg8 as an autophagosome marker and showed that autophagy and the associated cellular machinery are present and functional in the parasite. In extracellular T. gondii tachyzoites, autophagosomes were induced in response to amino acid starvation, but they could also be observed in culture during the normal intracellular development of the parasites. Moreover, we generated a conditional T. gondii mutant lacking the orthologue of Atg3, a key autophagy protein. TgAtg3-depleted parasites were unable to regulate the conjugation of TgAtg8 to the autophagosomal membrane. The mutant parasites also exhibited a pronounced fragmentation of their mitochondrion and a drastic growth phenotype. Overall, our results show that TgAtg3-dependent autophagy might be regulating mitochondrial homeostasis during cell division and is essential for the normal development of T. gondii tachyzoites.

PMID:22144900[PubMed - in process]

An atypical strain associated with congenital toxoplasmosis in Tunisia

New Microbiol. 2011 Oct;34(4):413-6. Epub 2011 Oct 31.

An atypical strain associated with congenital toxoplasmosis in Tunisia.

Boughattas S, Abdallah RB, Siala E, Aoun K, Bouratbine A.

SourceLaboratoire de Recherche 05SP03, Laboratoire de Parasitologie, Institut Pasteur de Tunis, Tunis Belvedère, Tunisia.

We report the identification and typing of a congenital toxoplasmosis case in a diabetic pregnant young woman living in Tunis. The Toxoplasma DNA extracted from amniotic fluid was detected by Real Time PCR and subjected to a multilocus genetic characterisation of the strain at markers: 3'SAG2, 5'SAG2, New SAG2, SAG3, GRA6, BTUB, APICO, PK1, KT850 and UPRT1. An atypical genotype of T.gondii with unusual genetic composition was revealed. It is the first time that an atypical strain has been associated with congenital toxoplasmosis in Africa. Atypical strains are associated with severe clinical manifestations so systematic genotyping should be investigated with the amniocentesis.

PMID:22143816[PubMed - in process]

Microbial Infection-Induced Expansion of Effector T Cells Overcomes the Suppressive Effects of Regulatory T Cells via an IL-2 Deprivation Mechanism

J Immunol. 2011 Dec 5. [Epub ahead of print]

Microbial Infection-Induced Expansion of Effector T Cells Overcomes the Suppressive Effects of Regulatory T Cells via an IL-2 Deprivation Mechanism.

Benson A, Murray S, Divakar P, Burnaevskiy N, Pifer R, Forman J, Yarovinsky F.

SourceDepartment of Immunology, University of Texas Southwestern Medical Center, Dallas, TX 75390.

Regulatory Foxp3(+) T cells are a critical cell population that suppresses T cell activation in response to microbial and viral pathogens. We identify a cell-intrinsic mechanism by which effector CD4(+) T cells overcome the suppressive effects of regulatory T (Treg) cells in the context of three distinct infections: Toxoplasma gondii, Listeria monocytogenes, and vaccinia virus. The acute responses to the parasitic, bacterial, and viral pathogens resulted in a transient reduction in frequency and absolute number of Treg cells. The infection-induced partial loss of Treg cells was essential for the initiation of potent Th1 responses and host protection against the pathogens. The observed disappearance of Treg cells was a result of insufficiency in IL-2 caused by the expansion of pathogen-specific CD4(+) T cells with a limited capacity of IL-2 production. Exogenous IL-2 treatment during the parasitic, bacterial, and viral infections completely prevented the loss of Treg cells, but restoration of Treg cells resulted in a greatly enhanced susceptibility to the pathogens. These results demonstrate that the transient reduction in Treg cells induced by pathogens via IL-2 deprivation is essential for optimal T cell responses and host resistance to microbial and viral pathogens.

PMID:22147768[PubMed - as supplied by publisher]

Differential Gene Expression in Mice Infected with Distinct Toxoplasma Strains

Infect Immun. 2011 Dec 5. [Epub ahead of print]

Differential Gene Expression in Mice Infected with Distinct Toxoplasma Strains.

Hill RD, Gouffon JS, Saxton AM, Su C.

SourceDepartment of Microbiology.

Toxoplasma gondii is the causative agent of toxoplasmosis in human and animals. In mouse model, T. gondii strains can be divided into three groups, including the virulent, intermediately virulent and non-virulent. The clonal Type I, II and III T. gondii strains belong to these three groups respectively. To better understand the basis of virulence phenotypes, we investigated mouse gene expression responses to the infection of different T. gondii strains at day 5 post intraperitoneal inoculation with 500 tachyzoites. The transcriptomes of mouse peritoneal cells showed that 1927, 1573, and 1009 transcripts were altered more than 2 fold by Type I, II and III infections, respectively, and majority of altered transcripts were shared. Overall transcription patterns were similar in Type I and Type II infections and both had greater changes than that of Type III. Quantification of parasite burden in mouse spleens showed that Type I was 1000 times higher than Type II, and Type II was 20 times higher than Type III. Fluorescence activated cell sorting revealed that Type I and II infections had comparable macrophage populations and both were higher than Type III infection. In addition, Type I infection had higher percentage of neutrophils than that of Type II and III. Taken together, these results suggested that there is a common gene expression response to T. gondii infection in mice. This response is further modified by parasite strain specific factors that determine their distinct virulence phenotypes.

PMID:22144491[PubMed - as supplied by publisher]

Saturday, December 03, 2011

Structural insight into the activation mechanism of Toxoplasma gondii nucleoside triphosphate diphosphohydrolases by disulfide reduction

J Biol Chem. 2011 Nov 30. [Epub ahead of print]

Structural insight into the activation mechanism of Toxoplasma gondii nucleoside triphosphate diphosphohydrolases by disulfide reduction.

Krug U, Zebisch M, Krauss M, Sträter N.

SourceUniversity of Leipzig, Germany;

The intracellular parasite Toxoplasma gondii produces two nucleoside triphosphate diphosphohydrolases (NTPDase1 and -3). These tetrameric, cysteine-rich enzymes require activation by reductive cleavage of a hitherto unknown disulfide bond. Despite a 97% sequence identity both isozymes differ largely in their ability to hydrolyze ATP and ADP. Here, we present crystal structures of inactive NTPDase3 as apo form and in complex with the product AMP to resolutions of 2.0 Ang. and 2.2 Ang., respectively. We find that the enzyme is present in an open conformation that precludes productive substrate binding and catalysis. The cysteine bridge 258-268 is identified to be responsible for locking of activity. Crystal structures of constitutively active variants of NTPDase1 and -3 generated by mutation of C258-C268 show that opening of the regulatory cysteine bridge induces a pronounced contraction of the whole tetramer. This is accompanied by a 12 deg domain closure motion resulting in the correct arrangement of all active site residues. A complex structure of activated NTPDase3 with a non-hydrolyzable ATP analog and the cofactor Mg2+ to a resolution of 2.85 Ang. indicates that catalytic differences between the NTPDases are primarily dictated by differences in positioning of the adenine base caused by substitution of R492 and E493 in NTPDase1 by glycines in NTPDase3.

PMID:22130673[PubMed - as supplied by publisher]