Tuesday, July 26, 2011

The IRG protein-based resistance mechanism in mice and its relation to virulence in Toxoplasma gondii

Curr Opin Microbiol. 2011 Jul 22. [Epub ahead of print]

The IRG protein-based resistance mechanism in mice and its relation to virulence in Toxoplasma gondii

Howard JC, Hunn JP, Steinfeldt T

SourceInstitute for Genetics, University of Cologne, Zülpicher Strasse 47a, 50674 Cologne, Germany; Stellenbosch Institute for Advanced Study (STIAS), Wallenberg Research Centre at Stellenbosch University, Marais Street, Stellenbosch 7600, South Africa.

IRG proteins (immunity-related GTPases) provide an early defense mechanism in mice against the protozoal pathogen, Toxoplasma gondii. This is a particularly suitable time to provide a brief review of this host-pathogen interaction because the nature of the IRG resistance system, and to some extent its mode of action, have become known in the past few years. Likewise, forward genetic screens have recently drawn attention to a number of loci contributing to the differential virulence of T. gondii strains in mice. It is now clear that at least some important virulence mechanisms exert their action against components of the IRG resistance system. Thus these two mechanisms form the two poles of a dynamic host-pathogen virulence-resistance relationship with interesting and accessible properties.

Copyright © 2011 Elsevier Ltd. All rights reserved.

PMID:21783405[PubMed - as supplied by publisher]

Saturday, July 23, 2011

Host cell invasion by apicomplexan parasites: insights from the co-structure of AMA1 with a RON2 peptide

Science. 2011 Jul 22;333(6041):463-7

Host cell invasion by apicomplexan parasites: insights from the co-structure of AMA1 with a RON2 peptide

Tonkin ML, Roques M, Lamarque MH, Pugnière M, Douguet D, Crawford J, Lebrun M, Boulanger MJ

SourceDepartment of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia V8W 3P6, Canada.

Apicomplexan parasites such as Toxoplasma gondii and Plasmodium species actively invade host cells through a moving junction (MJ) complex assembled at the parasite-host cell interface. MJ assembly is initiated by injection of parasite rhoptry neck proteins (RONs) into the host cell, where RON2 spans the membrane and functions as a receptor for apical membrane antigen 1 (AMA1) on the parasite. We have determined the structure of TgAMA1 complexed with a RON2 peptide at 1.95 angstrom resolution. A stepwise assembly mechanism results in an extensive buried surface area, enabling the MJ complex to resist the mechanical forces encountered during host cell invasion. Besides providing insights into host cell invasion by apicomplexan parasites, the structure offers a basis for designing therapeutics targeting these global pathogens.

Comment in
Science. 2011 Jul 22;333(6041):410-1.
PMID:21778402[PubMed - in process]

Thursday, July 21, 2011

The secreted kinase ROP18 defends Toxoplasma's border

Bioessays. 2011 Jul 20. doi: 10.1002/bies.201100054. [Epub ahead of print]

The secreted kinase ROP18 defends Toxoplasma's border

Fentress SJ, Sibley LD

SourceDepartment of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO, USA.

Toxoplasma gondii is a highly successful parasite capable of infecting virtually all warm-blooded animals by actively invading nucleated host cells and forming a modified compartment where it replicates within the cytosol. The parasite-containing vacuole provides a safe haven, even in professional phagocytes such as macrophages, which normally destroy foreign microbes. In an effort to eliminate the parasite, the host up-regulates a family of immunity-related p47 GTPases (IRGs), which are recruited to the parasite-containing vacuole, resulting in membrane rupture and digestion of the parasite. To avoid this fate, highly virulent strains of Toxoplasma coat the external surface of their vacuole with a secretory serine/threonine kinase, known as ROP18. At this host-pathogen interface, ROP18 phosphorylates and inactivates IRGs, thereby protecting the parasite from killing. These findings reveal a novel molecular mechanism by which the parasite disarms host innate immunity.

Copyright © 2011 Wiley Periodicals, Inc.

PMID:21773979[PubMed - as supplied by publisher]

Tuesday, July 12, 2011

Genotyping of the protozoan pathogen Toxoplasma gondii using high-resolution melting analysis of the repeated B1 gene

J Microbiol Methods. 2011 Jul 1. [Epub ahead of print]

Genotyping of the protozoan pathogen Toxoplasma gondii using high-resolution melting analysis of the repeated B1 gene.

Costa JM, Cabaret O, Moukoury S, Bretagne S.

SourceGroupe hospitalier Chenevier-Mondor, APHP, Laboratoire de Parasitologie-Mycologie, Créteil, France; Laboratoire Cerba, Cergy-Pontoise, France.

Genetic studies of the protozoan parasite Toxoplasma gondii have identified three main distinct types according to virulence in some hosts. Several methods have been developed to differentiate genotypes currently dominated by microsatellite markers targeting single-copy loci. We analyzed the possibility of using the 35-fold repetitive B1 gene via high-resolution melting (HRM) curve analysis. Sequencing of the B1 gene of 14 reference strains (four Type I, six Type II, and four Type III strains) identified 18 single nucleotide polymorphisms (SNP). Primers were designed to amplify eight of them for HRM analysis and for relative quantification of each nucleotide variation using SNaPshot mini-sequencing. Genotyping with five microsatellite markers was performed for comparison. Two to four HRM profiles were obtained depending on the SNP tested. The differences observed relied on the different ratios of nucleotides at the SNP locus as evidenced via SNaPshot mini-sequencing. The three main lineages could be distinguished by using several HRM profiles. Some HRM profiles proved more informative than the analysis based on five microsatellite markers, showing additional differences in Type I and Type II strains. Using HRM analysis, we obtained at least an equally good discrimination of the main lineages than that based on five microsatellite markers.

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

Monday, July 11, 2011

Parasite-Mediated Upregulation of NK Cell-Derived IFN{gamma} Protects Against Severe HPAI H5N1 Influenza Virus Infection

J Virol. 2011 Jul 6. [Epub ahead of print]

Parasite-Mediated Upregulation of NK Cell-Derived IFN{gamma} Protects Against Severe HPAI H5N1 Influenza Virus Infection.

O'Brien KB, Schultz-Cherry S, Knoll LJ.

SourceDepartment of Infectious Diseases, St Jude Children's Research Hospital, Memphis, TN 38105;

Outbreaks of influenza A viruses are associated with significant human morbidity worldwide. Given the increasing resistance to the available influenza drugs, new therapies for the treatment of influenza virus infection are needed. An alternative approach is to identify products that enhance a protective immune response. In these studies we demonstrate that infecting mice with the Th1-inducing parasite Toxoplasma gondii prior to highly pathogenic avian H5N1 influenza virus infection led to decreased lung viral titers and enhanced survival. A non-infectious fraction of T. gondii soluble antigens (STAg) elicits an immune response similar to live parasites and administration of STAg two days post-H5N1 influenza virus infection enhanced survival, lowered viral titers, and reduced clinical disease. STAg administration protected H5N1 virus infected mice lacking lymphocytes suggesting that while the adaptive immune response was not required for enhanced survival, it was necessary for STAg-mediated viral clearance. Mechanistically, we found that administration of STAg led to increased production of interferon gamma (IFNγ) from Natural Killer (NK) cells, which were both necessary and sufficient for survival. Further, administration of exogenous IFNγ alone enhanced survival from H5N1 influenza virus infection; although not to the same level as STAg treatment. These studies demonstrate that a non-infectious T. gondii extract enhances the protective immune response against severe H5N1 influenza virus infections even when a single dose is administered two days post-infection.

PMID:21734055[PubMed - as supplied by publisher]

Examination of a virulence mutant uncovers the ribosome biogenesis regulatory protein of Toxoplasma

J Parasitol. 2011 Jul 7. [Epub ahead of print]

Examination of a virulence mutant uncovers the ribosome biogenesis regulatory protein of Toxoplasma gondii

Milligan-Myhre KC, Rooney PJ, Knoll LJ

Sourcea Department of Molecular Biology, University of Oregon, Eugene, Oregon, 97403.

Abstract Several insertional mutants identified in a screen for Toxoplasma gondii that were defective in establishing a chronic infection had a common site of plasmid insertion. This insertion site was determined to be 43 bp upstream of the transcription initiation site of a gene whose predicted product has homology to ribosome biogenesis regulatory protein Rrs1p, an essential protein required for ribosome biogenesis in Saccharomyces cerevisiae. Northern blot analysis of this locus, termed TgRRS1, showed that in the C3 mutant, the full-length transcript is downregulated and at least one new smaller transcript is present. Restoration of the intact predicted promoter and locus to TgRRS1 insertional mutant strain C3 did not restore brain cyst formation to the levels of the parent strain. Epitope-tagged TgRRS1 was found to localize to the parasite nucleolus, in an area corresponding to the granular component region. TgRRS1 can serve as a marker for the subnucleolar granular component region of T. gondii.

PMID:21736491[PubMed - as supplied by publisher]

Tuesday, July 05, 2011

Beyond the genome: Recent advances in Toxoplasma gondii functional genomics

Parasite Immunol. 2011 Jul 1. doi: 10.1111/j.1365-3024.2011.01312.x. [Epub ahead of print]

Beyond the genome: Recent advances in Toxoplasma gondii functional genomics.

Adomako-Ankomah Y, Wier GM, Boyle JP.

SourceDepartment of Biological Sciences University of Pittsburgh.

Recent years have witnessed an explosion in the amount of genomic information available for Toxoplasma gondii and other closely related pathogens. These data, many of which have been made publicly available prior to publication, have facilitated a wide variety of functional genomics studies. In this review we provide a brief overview of existing database tools for querying the Toxoplasma genome and associated genome-wide data and review recent publications that have been facilitated by these data. Topics covered include strain comparisons and quantitative trait loci mapping, gene expression analyses during the cell cycle as well as during parasite differentiation, and proteomics.

Copyright © 2011 Blackwell Publishing Ltd.

PMID:21722143[PubMed - as supplied by publisher]

Friday, July 01, 2011

The Differential Effect of Toxoplasma Gondii Infection on the Stability of BCL2-Family Members Involves Multiple Activities

Front Microbiol. 2011;2:1. Epub 2011 Jan 24.

The Differential Effect of Toxoplasma Gondii Infection on the Stability of BCL2-Family Members Involves Multiple Activities.

Carmen JC, Sinai AP.

SourceDepartment of Microbiology, Immunology, and Molecular Genetics, University of Kentucky College of Medicine Lexington, KY, USA.

The regulation of mitochondrial permeability, a key event in the initiation of apoptosis is governed by the opposing actions of the pro- and anti-apoptotic members of the BCL2-family of proteins. The BCL2-family can be classified further based on the number of BCL-homology (BH) domains they encode. Pathogen mediated modulation of BCL2-family members play a significant role in their ability to affect the apoptotic pathways in the infected host cell. The protozoan parasite Toxoplasma gondii establishes a profound blockade of apoptosis noted by a requirement for host NFκB activity and correlating with the selective degradation of pro-apoptotic BCL2-family members. In this study, we explore the potential activities associated with the inherent stability of the anti-apoptotic BCL2 as well as the selective degradation of the pro-apoptotic proteins BAX, BAD, and BID. We find that multiple activities govern the relative stability of BCL2-family members suggesting a complex and balanced network of stability-enhancing and-destabilizing activities are perturbed by parasite infection. The data leave open the possibility for both parasite induced host activities as well as the direct consequence of parasite effectors in governing the relative levels of BCL2-proteins in the course of infection.

PMID:21716958[PubMed - in process]

Toxoplasma gondii Seropositivity and Suicide Rates in Women

J Nerv Ment Dis. 2011 Jul;199(7):440-4.

Toxoplasma gondii Seropositivity and Suicide Rates in Women.

Ling VJ, Lester D, Mortensen PB, Langenberg PW, Postolache TT.

Source*University of Hawaii at Manoa, Honolulu, HI; †Richard Stockton College, Pomona, NJ; ‡National Centre for Register-Based Research, University of Aarhus, Aarhus, Denmark; and §Department of Epidemiology and Preventive Medicine, and ∥Mood and Anxiety Program, Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MD.

Toxoplasma gondii (T. gondii) is an intracellular protozoan parasite that infects roughly a third of the world population. In an immunocompetent host, infection is generally chronic and asymptomatic, as the immune system keeps T. gondii confined to cysts and the intracellular space within the muscle and brain. Seropositivity has been linked to schizophrenia, car accidents, changes in personality, and more recently, suicidal attempts. Very recently, seroprevalence for 20 European countries was found to be associated with increased suicide rates. Although suicide rates were age-standardized, given that T. gondii seroprevalence increases with age and that the blood samples were drawn in women, we now retested in women only the association between suicide and T. gondii seropositivity, stratified by age. Simple correlations between ranked T. gondii seropositivity and suicide rate identified statistically significant relationships in women 60 years or older (p < 0.05); adjusting for GDP, the statistical significance expanded to include women 45 years and older. The strongest association was in the 60- to 74-year-old group where, after adjustment for GDP, the relationship (p = 0.007) resisted Bonferroni adjustment for multiple comparisons. In conclusion, the results suggest that a positive relationship between rates of infection with T. gondii and suicide is apparent in women of postmenopausal age. Prospective studies are necessary to further confirm this association predictively and to explore mechanisms mediating this relationship.

PMID:21716055[PubMed - in process]