We would like to thank Nichole Brinkman and Michael Ware for technical review of the manuscript and Dr. Abu Sayed and Linda Ransick for technical and administrative support. The United States Environmental Protection Agency through its Office of Research and Development partially funded and collaborated in the research described here under contract number EP-D-06-096 to Dynamac, Inc. and an interagency agreement number DW-12-92289801-0 to USDA. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. MJS current address: Dynamac, Inc. Cincinnati, OH.

1. General safety precautions when working with T. gondii oocysts
 <ol>
 <li>It is important to follow all safety precautions when working with T. gondii oocysts. In most healthy individuals, T. gondii infection is readily controlled by the immune system; however, a life-long infection results. Immunocompromised individuals are particularly susceptible to toxoplasmosis and should not handle T. gondii oocysts. Pregnant women should also not handle T. gondii oocysts, because infection can cause severe birth defects8. </li>
 <li>T. gondii oocysts should only be handled in a designated area and with trained personnel. Signs indicating T. gondii oocyst work is in progress must be posted to alert others entering the designated area. </li>
 <li>Wear appropriate personal protective equipment (PPE) such as a lab coat, disposable gown, disposable gloves, and proper eye protection or a face shield when handling T. gondii oocysts.</li>
 <li>Frequent glove changes are recommended. Do not handle any lab equipment with T. gondii oocyst contaminated gloves. </li>
 <li>Always use metal autoclavable trays lined with a disposable absorbent liners when working with T. gondii oocysts. Ensure all racks, tubes, etc. used are either disposable or autoclavable. </li>
 <li>All T. gondii waste must be autoclaved twice for at least one hour.</li>
 <li>All non-disposable equipment (racks, trays, etc.) must also be autoclaved twice for at least one hour.</li>
 <li>Vacuum lines used to aspirate liquids should be connected to a Vacushield&trade; filter to prevent contamination of the vacuum pump.</li>
 <li>All affected laboratory bench-tops must be disinfected after completing work with T. gondii oocysts. Freshly made 10% hypochlorite should be liberally applied to the work area and allowed dry. The area must then be rinsed well with water.</li>
 </ol>
2. Preparation of buffers and solutions
 <ol>
 <li>Prepare a 1 L 2.2 M solution of sucrose by dissolving 752.66 g of sucrose in 600 ml ddH2O. Stir and heat gently using a heated stir plate to dissolve the sucrose. Once completely dissolved, bring volume to 1 L with ddH2O. This should be followed by sterilization by autoclaving the solution for at least 20 minutes. </li>
 <li>Prepare a 1L TE buffer (50 mM Tris-HCl, 10 mM EDTA), pH 7.2 by adding 6.05 g of Tris-HCl and 3.7 g of EDTA in 700 ml of ddH2O, adjust pH to 7.2 then bring volume to 1 L with ddH2O.</li>
 <li>For the CsCl gradient, prepare a stock solution of CsCl with a specific gravity of 1.15 (1.15-CsCl) by adding 21.75 g of CsCl with 103.25 ml of TE Buffer. For Solution A, mix 30 ml of TE with 20 ml of 1.15-CsCl. For Solution B, mix 20 ml of TE with 30 ml of 1.15-CsCl and 12.5 &mu;l of phenol red solution. For Solution C, mix 10 ml of TE with 40 ml of 1.15-CsCl (Table 1).</li>
 <li>Prepare a 1L 1 N solution of sodium hydroxide (NaOH) by dissolving 40 g of NaOH, in 800 ml of ddH2O. Once dissolved, bring volume to 1 L with ddH2O.</li>
 <li> Prepare a 1 L 2% (by volume) solution of H2SO4 mixing 20 ml of H2SO4 with 980 ml of ddH2O. </li>
 </ol>
 3. Sucrose float
 <ol>
 <li>Add 10 ml of a fecal suspension of T. gondii oocysts, in 2% H2SO4, into a 50 ml conical centrifuge tube. It must be noted that fecal suspension refers to samples that have been pre-processed through a sucrose flotation procedure as previously described8. When the fecal samples are initially harvested from the infected cats they are processed through a sucrose float as described in reference 8. This additional sucrose float is necessary to further minimize fecal debris carried over to the CsCl purification process and obtain the purest T. gondii oocysts possible.</li>
 <li>Neutralize the 2% H2SO4 by adding 6 ml (3/5 volumes) of 1 N NaOH to the fecal suspension. Mix well by vortexing.</li>
 <li>Add an equal volume (16 ml) of 2.2 M sucrose creating a final concentration of 1.1 M to the fecal suspension and mix well by vortexing.</li>
 <li>Carefully overlay the sucrose/fecal suspension with 10 ml ddH2O using a 10 ml pipette. Centrifuge the suspension at 1,200 x g for 20 min at room temperature with no brake.</li>
 <li>Carefully collect the top water and interphase layers and transfer to a new 50 ml conical centrifuge tube by pipetting from the air-water interface without swirling the pipette. It is important to minimize sucrose carryover while collecting the interphase layer.</li>
 <li>Mix the remaining sucrose/fecal pellet solution by vortexing the tube.</li>
 <li>Repeat steps 3.4 and 3.5.</li>
 <li>Bring the volume of the two oocyst interphase solutions to 50 ml with ddH2O and centrifuge the tubes at 2,000 x g for 10 minutes at room temperature. </li>
 <li>Aspirate the supernatant from each tube and resuspend pellets with 5 ml TE buffer and pool the oocyst suspension together. The total pooled volume should be 10 ml. </li>
 </ol>
4. CsCl gradient
<ol>
 <li>Prepare a discontinuous CsCl gradient in a 50 ml polycarbonate Oak Ridge tube by carefully underlaying each layer using a 50 ml syringe with an 18 gauge blunt-ended, autoclavable, steel needle, and a 2 way stop cock. Note: Phenol red is added to Solution B to easily distinguish between the gradient layers (Table 1).</li>
 <li>Slowly add the following solutions to the tube in the order listed below. It should be noted that the flow rate should not exceed more than 0.5 ml/sec.
<ol>
 <li>10 ml of the TE/oocyst suspension sample</li>
 <li>8 ml Solution A</li>
 <li>8 ml Solution B</li>
 <li>8 ml Solution C</li>
</ol>
</li>
 <li>Centrifuge the Oak Ridge tube at 12,000 x g for 60 min at 4 &deg;C with no brake. Use of a fixed angle rotor is acceptable, but a high speed swinging bucket results in better separation of the oocysts from the suspension sample with minimal fecal debris smears along the side or the tube. The extent of the smears depends on the composition of the fecal suspension and thus it may be necessary to perform two CsCl gradients if the fecal suspension is extremely dirty. </li>
 <li>Following centrifugation, collect the opaque/white oocyst containing band between solutions A and B. To minimize contamination with fecal debris, go directly to the oocyst band without disturbing the gradient and collect the oocyst interphase using a 10 ml pipette. Transfer the oocyst interphase to a new 50 ml conical centrifuge tube. Try to minimize the amount of CsCl solution aspirated while collecting the oocyst interphase as it may pose a problem in pelleting the oocysts during the wash step.</li>
 <li>Wash oocysts with 30-40 ml of ddH2O. Centrifuge the tube at 2,000 x g at room temperature for 10 min with no brake. Carefully aspirate the supernatant without disturbing the oocyst pellet. Repeat the wash 2 additional times. </li>
 <li>At the end of the final wash, carefully aspirate the supernatant and resuspend the pellet in 10 ml 2% sulfuric acid and store at 4 &deg;C until use. Oocysts are now ready for further manipulation. Oocyst purity can be checked microscopically by the absence of fecal debris in the sample.</li>
</ol>

<ol>
	<li>Dubey, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prevalence+of+viable+Toxoplasma+gondii+in+beef,+chicken,+and+pork+from+retail+meat+stores+in+the+United+States:+risk+assessment+to+consumers.">Prevalence of viable Toxoplasma gondii in beef, chicken, and pork from retail meat stores in the United States: risk assessment to consumers.</a> J. Parasitol. 91, 1082-1093 (2005).</li><li>Tenter, A. M., Heckeroth, A. R., Weiss, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toxoplasma+gondii:+from+animals+to+humans.">Toxoplasma gondii: from animals to humans.</a> Int. J. Parasitol. 30, 1217-1258 (2000).</li><li>Bowie, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Outbreak+of+toxoplasmosis+associated+with+municipal+drinking+water.">Outbreak of toxoplasmosis associated with municipal drinking water.</a> Lancet. 350, 173-177 (1997).</li><li>Moura, L. d. e. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Waterborne+toxoplasmosis,+Brazil,+from+field+to+gene.">Waterborne toxoplasmosis, Brazil, from field to gene.</a> Emerg. Infect. Dis. 12, 326-329 (2006).</li><li>Jones, J. L., Dubey, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Waterborne+toxoplasmosis+-+Recent+developments.">Waterborne toxoplasmosis - Recent developments.</a> Exp. Parasitol. doi: 10.1016/j.exppara.2009.03.013, (2009).</li><li>Dumetre, A., Darde, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+to+detect+Toxoplasma+gondii+oocysts+in+environmental+samples.">How to detect Toxoplasma gondii oocysts in environmental samples.</a> FEMS Microbiol. Rev. 27, 651-661 (2003).</li><li>Dumetre, A., Darde, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Purification+of+Toxoplasma+gondii+oocysts+by+cesium+chloride+gradient.">Purification of Toxoplasma gondii oocysts by cesium chloride gradient.</a> J. Microbiol. Methods. 56, 427-4230 (2004).</li><li>Dubey, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toxoplasmosis+of+Animals+and+Man.">Toxoplasmosis of Animals and Man.</a> , (2009).</li></ol>

obtaining highly purified toxoplasma gondii oocysts by a discontinuous cesium chloride gradient

Toxoplasma gondii is an obligate intracellular protozoan pathogen that commonly infects humans. It is a well characterized apicomplexan associated with causing food- and water-borne disease outbreaks. The definitive host is the feline species where sexual replication occurs resulting in the development of the highly infectious and environmentally resistant oocyst. Infection occurs via ingestion of tissue cysts from contaminated meat or oocysts from soil or water. Infection is typically asymptomatic in healthy individuals, but results in a life-long latent infection that can reactivate causing toxoplasmic encephalitis and death if the individual becomes immunocompromised. Meat contaminated with T. gondii cysts have been the primary source of infection in Europe and the United States, but recent changes in animal management and husbandry practices and improved food handling and processing procedures have significantly reduced the prevalence of T. gondii cysts in meat1, 2. Nonetheless, seroprevalence in humans remains relatively high suggesting that exposure from oocyst contaminated soil or water is likely. Indeed, waterborne outbreaks of toxoplasmosis have been reported worldwide supporting the theory exposure to the environmental oocyst form poses a significant health risk3-5. To date, research on understanding the prevalence of T. gondii oocysts in the water and environment are limited due to the lack of tools to detect oocysts in the environment 5, 6. This is primarily due to the lack of efficient purification protocols for obtaining large numbers of highly purified T gondii oocysts from infected cats for research purposes. This study describes the development of a modified CsCl method that easily purifies T. gondii oocysts from feces of infected cats that are suitable for molecular biological and tissue culture manipulation7.

Watch this Scientific Journal Video about Obtaining Highly Purified Toxoplasma gondii Oocysts by a Discontinuous Cesium Chloride Gradient at JoVE.com

Obtaining Highly Purified Toxoplasma gondii Oocysts by a Discontinuous Cesium Chloride Gradient

This study describes the development of a modified CsCl method that easily purifies T. gondii oocysts from feces of infected cats that are suitable for molecular biological and tissue culture manipulation

Obtaining Highly Purified Toxoplasma gondii Oocysts by a Discontinuous Cesium Chloride Gradient

Toxoplasma gondii is an obligate intracellular protozoan pathogen that commonly infects humans. It is a well characterized apicomplexan associated with ...

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13.5K Views.  Dynamac, Inc.. This study describes the development of a modified CsCl method that easily purifies T. gondii oocysts from feces of infected cats that are suitable for molecular biological and tissue culture manipulation

Video: Obtaining Highly Purified Toxoplasma gondii Oocysts by a Discontinuous Cesium Chloride Gradient

Toxoplasma gondii Cyst Wall Formation in Activated Bone Marrow-derived Macrophages and Bradyzoite Conditions

Toxoplasma gondii is an obligate intracellular parasite that can invade any nucleated cell of warm-blooded animals. During infection, T. gondii disseminates as a fast replicating form called the tachyzoite. Tachyzoites convert into a slow-growing encysted form called the bradyzoite by a signaling process that is not well characterized. Within animals, bradyzoite cysts are found in the central nervous system and muscle tissue and represent the chronic stage of infection. Conversion to bradyzoites can be simulated in tissue culture by CO2 starvation, using medium with high a pH, or the addition of interferon gamma (IFN&gamma;). Bradyzoites are characterized by the presence of a cyst wall, to which the lectin Dolichos biflorus agglutinin (DBA) binds. Fluorescently labeled DBA is used to visualize the cyst wall in parasites grown in human foreskin fibroblasts (HFFs) that have been exposed to low CO2 and high pH medium. Similarly, parasites residing in murine bone marrow-derived macrophages (BMMs) display a cyst wall detectable by DBA after the BMMs are activated with IFN&gamma; and lipopolysaccharide (LPS). This protocol will demonstrate how to induce conversion of T. gondii to bradyzoites using a high pH growth medium with low CO2 and activation of BMMs. Host cells will be cultured on coverslips, infected with tachyzoites and either activated with addition of IFN&gamma; and LPS (BMMs) or exposed to a high pH growth medium (HFFs) for three days. Upon completion of infections, host cells will be fixed, permeabilized, and blocked. Cyst walls will be visualized using rhodamine DBA with fluorescence microscopy.

Toxoplasma gondii Cyst Wall Formation in Activated Bone Marrow-derived Macrophages and Bradyzoite Conditions

Toxoplasma gondii converts to a cyst form in response to environmental stresses, which can be mimicked in tissue culture models. This video demonstrates techniques to examine cyst wall formation by activating bone marrow-derived macrophages or changing growth medium pH in fibroblast cells.

Toxoplasma gondii is an obligate intracellular parasite that can invade any nucleated cell of warm-blooded animals. During infection, T. gondii ...

Transnuclear Mice with Pre-defined T Cell Receptor Specificities Against Toxoplasma gondii Obtained Via SCNT

Lymphocytes, such as T cells, undergo genetic V(D)J recombination, to generate a receptor with a certain specificity1. Mice transgenic for a rearranged antigen-specific T cell receptor (TCR) have been an indispensable tool to study T cell development and function. However, such TCRs are usually isolated from the relevant T cells after long-term culture often following repeated antigen stimulation, which unavoidably selects for T cells with high affinity. Random genomic integration of the TCR &alpha;- and &beta;-chain and expression from non-endogenous promoters can lead to variations in expression level and kinetics.
Epigenetic reprogramming via somatic cell nuclear transfer provides a tool to generate embryonic stem cells and mice from any cell of interest. Consequently, when SCNT is applied to T cells of known specificity, these genetic V(D)J rearrangements are transferred to the SCNT-embryonic stem cells (ESCs) and the mice derived from them, while epigenetic marks are reset. We have demonstrated that T cells with pre-defined specificities against Toxoplasma gondii can be used to generate mouse models that express the specific TCR from their endogenous loci, without experimentally introduced genetic modification. The relative ease and speed with which such transnuclear models can be obtained holds promise for the construction of other disease models.

Transnuclear Mice with Pre-defined T Cell Receptor Specificities Against Toxoplasma gondii Obtained Via SCNT

We demonstrate here that epigenetic reprogramming via Somatic Cell Nuclear Transfer (SCNT) can be used as a tool to generate mouse models with pre-defined T cell receptor (TCR) specificities. These transnuclear mice express the corresponding TCR from their endogenous locus under the control of the endogenous promoter.

Lymphocytes, such as T cells, undergo genetic V(D)J recombination, to generate a receptor with a certain specificity1. Mice transgenic for a rearranged ...

A Genetic Screen to Isolate Toxoplasma gondii Host-cell Egress Mutants

The widespread, obligate intracellular, protozoan parasite Toxoplasma gondii causes opportunistic disease in immuno-compromised patients and causes birth defects upon congenital infection. The lytic replication cycle is characterized by three stages: 1. active invasion of a nucleated host cell; 2. replication inside the host cell; 3. active egress from the host cell. The mechanism of egress is increasingly being appreciated as a unique, highly regulated process, which is still poorly understood at the molecular level. The signaling pathways underlying egress have been characterized through the use of pharmacological agents acting on different aspects of the pathways1-5. As such, several independent triggers of egress have been identified which all converge on the release of intracellular Ca2+, a signal that is also critical for host cell invasion6-8. This insight informed a candidate gene approach which led to the identification of plant like calcium dependent protein kinase (CDPK) involved in egress9. In addition, several recent breakthroughs in understanding egress have been made using (chemical) genetic approaches10-12. To combine the wealth of pharmacological information with the increasing genetic accessibility of Toxoplasma we recently established a screen permitting the enrichment for parasite mutants with a defect in host cell egress13. Although chemical mutagenesis using N-ethyl-N-nitrosourea (ENU) or ethyl methanesulfonate (EMS) has been used for decades in the study of Toxoplasma biology11,14,15, only recently has genetic mapping of mutations underlying the phenotypes become routine16-18. Furthermore, by generating temperature-sensitive mutants, essential processes can be dissected and the underlying genes directly identified. These mutants behave as wild-type under the permissive temperature (35 &deg;C), but fail to proliferate at the restrictive temperature (40 &deg;C) as a result of the mutation in question. Here we illustrate a new phenotypic screening method to isolate mutants with a temperature-sensitive egress phenotype13. The challenge for egress screens is to separate egressed from non-egressed parasites, which is complicated by fast re-invasion and general stickiness of the parasites to host cells. A previously established egress screen was based on a cumbersome series of biotinylation steps to separate intracellular from extracellular parasites11. This method also did not generate conditional mutants resulting in weak phenotypes. The method described here overcomes the strong attachment of egressing parasites by including a glycan competitor, dextran sulfate (DS), that prevents parasites from sticking to the host cell19. Moreover, extracellular parasites are specifically killed off by pyrrolidine dithiocarbamate (PDTC), which leaves intracellular parasites unharmed20. Therefore, with a new phenotypic screen to specifically isolate parasite mutants with defects in induced egress, the power of genetics can now be fully deployed to unravel the molecular mechanisms underlying host cell egress.

A Genetic Screen to Isolate Toxoplasma gondii Host-cell Egress Mutants

Forward genetics is a powerful method to unravel the molecular level of how Toxoplasma egresses from its host cell. Protocols are provided to chemically mutagenize parasites, enrich for mutants with defects in induced egress, and validate the phenotype of cloned mutants.

The widespread, obligate intracellular, protozoan parasite Toxoplasma gondii causes opportunistic disease in immuno-compromised patients and causes birth ...

Genetic Manipulation in &Delta;ku80 Strains for Functional Genomic Analysis of Toxoplasma gondii

Targeted genetic manipulation using homologous recombination is the method of choice for functional genomic analysis to obtain a detailed view of gene function and phenotype(s). The development of mutant strains with targeted gene deletions, targeted mutations, complemented gene function, and/or tagged genes provides powerful strategies to address gene function, particularly if these genetic manipulations can be efficiently targeted to the gene locus of interest using integration mediated by double cross over homologous recombination.
Due to very high rates of nonhomologous recombination, functional genomic analysis of Toxoplasma gondii has been previously limited by the absence of efficient methods for targeting gene deletions and gene replacements to specific genetic loci. Recently, we abolished the major pathway of nonhomologous recombination in type I and type II strains of T. gondii by deleting the gene encoding the KU80 protein1,2. The &Delta;ku80 strains behave normally during tachyzoite (acute) and bradyzoite (chronic) stages in vitro and in vivo and exhibit essentially a 100% frequency of homologous recombination. The &Delta;ku80 strains make functional genomic studies feasible on the single gene as well as on the genome scale1-4.
Here, we report methods for using type I and type II &Delta;ku80&Delta;hxgprt strains to advance gene targeting approaches in T. gondii. We outline efficient methods for generating gene deletions, gene replacements, and tagged genes by targeted insertion or deletion of the hypoxanthine-xanthine-guanine phosphoribosyltransferase (HXGPRT) selectable marker. The described gene targeting protocol can be used in a variety of ways in &Delta;ku80 strains to advance functional analysis of the parasite genome and to develop single strains that carry multiple targeted genetic manipulations. The application of this genetic method and subsequent phenotypic assays will reveal fundamental and unique aspects of the biology of T. gondii and related significant human pathogens that cause malaria (Plasmodium sp.) and cryptosporidiosis (Cryptosporidium).

Genetic Manipulation in &lt;em&gt;&amp;Delta;ku80&lt;/em&gt; Strains for Functional Genomic Analysis of &lt;em&gt;Toxoplasma gondii&lt;/em&gt;

Here we report a method for using type I and type II &Delta;ku80 strains of Toxoplasma gondii to efficiently generate targeted gene deletions and gene replacements for functional genomic analysis.

Targeted genetic manipulation using homologous recombination is the method of choice for functional genomic analysis to obtain a detailed view of gene ...

Identifying DNA Mutations in Purified Hematopoietic Stem/Progenitor Cells

In recent years, it has become apparent that genomic instability is tightly related to many developmental disorders, cancers, and aging. Given that stem cells are responsible for ensuring tissue homeostasis and repair throughout life, it is reasonable to hypothesize that the stem cell population is critical for preserving genomic integrity of tissues. Therefore, significant interest has arisen in assessing the impact of endogenous and environmental factors on genomic integrity in stem cells and their progeny, aiming to understand the etiology of stem-cell based diseases.
LacI transgenic mice carry a recoverable &#955;&#160;phage vector encoding the LacI reporter system, in which the LacI gene serves as the mutation reporter. The result of a mutated LacI gene is the production of &#946;-galactosidase that cleaves a chromogenic substrate, turning it blue. The LacI reporter system is carried in all cells, including stem/progenitor cells and can easily be recovered and used to subsequently infect E. coli. After incubating infected E. coli on agarose that contains the correct substrate, plaques can be scored; blue plaques indicate a mutant LacI gene, while clear plaques harbor wild-type. The frequency of blue (among clear) plaques indicates the mutant frequency in the original cell population the DNA was extracted from. Sequencing the mutant LacI gene will show the location of the mutations in the gene and the type of mutation.
The LacI transgenic mouse model is well-established as an in vivo mutagenesis assay. Moreover, the mice and the reagents for the assay are commercially available. Here we describe in detail how this model can be adapted to measure the frequency of spontaneously occurring DNA mutants in stem cell-enriched Lin-IL7R-Sca-1+cKit++(LSK) cells and other subpopulations of the hematopoietic system.

Here we describe an in vivo mutagenesis assay for small numbers of purified hematopoietic cells using the LacI transgenic mouse model.&#160;The LacI gene can be isolated to determine the frequency, location, and type of DNA mutants&#160;spontaneously arisen or after exposure to genotoxins.

In recent years, it has become apparent that genomic instability is tightly related to many developmental disorders, cancers, and aging. Given that stem ...

Highly Resolved Intravital Striped-illumination Microscopy of Germinal Centers

Monitoring cellular communication by intravital deep-tissue multi-photon microscopy is the key for understanding the fate of immune cells within thick tissue samples and organs in health and disease. By controlling the scanning pattern in multi-photon microscopy and applying appropriate numerical algorithms, we developed a striped-illumination approach, which enabled us to achieve 3-fold better axial resolution and improved signal-to-noise ratio, i.e. contrast, in more than 100 &#181;m tissue depth within highly scattering tissue of lymphoid organs as compared to standard multi-photon microscopy. The acquisition speed as well as photobleaching and photodamage effects were similar to standard photo-multiplier-based technique, whereas the imaging depth was slightly lower due to the use of field detectors. By using the striped-illumination approach, we are able to observe the dynamics of immune complex deposits on secondary follicular dendritic cells &#8211; on the level of a few protein molecules in germinal centers.

High-resolution intravital imaging with enhanced contrast up to 120 &#181;m depth in lymph nodes of adult mice is achieved by spatially modulating the excitation pattern of a multi-focal two-photon microscope. In 100 &#181;m depth we measured resolutions of 487 nm (lateral) and 551 nm (axial), thus circumventing scattering and diffraction limits.

Monitoring cellular communication by intravital deep-tissue multi-photon microscopy is the key for understanding the fate of immune cells within thick ...

Isolation of Human Monocytes by Double Gradient Centrifugation and Their Differentiation to Macrophages in Teflon-coated Cell Culture Bags

Human macrophages are involved in a plethora of pathologic processes ranging from infectious diseases to cancer. Thus they pose a valuable tool to understand the underlying mechanisms of these diseases. We therefore present a straightforward protocol for the isolation of human monocytes from buffy coats, followed by a differentiation procedure which results in high macrophage yields. The technique relies mostly on commonly available lab equipment and thus provides a cost and time effective way to obtain large quantities of human macrophages. Briefly, buffy coats from healthy blood donors are subjected to a double density gradient centrifugation to harvest monocytes from the peripheral blood. These monocytes are then cultured in fluorinated ethylene propylene (FEP) Teflon-coated cell culture bags in the presence of macrophage colony-stimulating factor (M-CSF). The differentiated macrophages can be easily harvested and used for subsequent studies and functional assays. Important methods for quality control and validation of the isolation and differentiation steps will be highlighted within the protocol. In summary, the protocol described here enables scientists to routinely and reproducibly isolate human macrophages without the need for cost intensive tools. Furthermore, disease models can be studied in a syngeneic human system circumventing the use of murine macrophages.

We present a simple and efficient protocol for the generation of human macrophages. Buffy coats are processed by double density gradient centrifugation and isolated monocytes are then differentiated to macrophages in Teflon-coated cell culture bags. This maximizes macrophage yields and facilitates cell harvesting for subsequent experiments.

Human macrophages are involved in a plethora of pathologic processes ranging from infectious diseases to cancer. Thus they pose a valuable tool to ...

Highly Efficient Transfection of Human THP-1 Macrophages by Nucleofection

Macrophages, as key players of the innate immune response, are at the focus of research dealing with tissue homeostasis or various pathologies. Transfection with siRNA and plasmid DNA is an efficient tool for studying their function, but transfection of macrophages is not a trivial matter. Although many different approaches for transfection of eukaryotic cells are available, only few allow reliable and efficient transfection of macrophages, but reduced cell vitality and severely altered cell behavior like diminished capability for differentiation or polarization are frequently observed. Therefore a transfection protocol is required that is capable of transferring siRNA and plasmid DNA into macrophages without causing serious side-effects thus allowing the investigation of the effect of the siRNA or plasmid in the context of normal cell behavior. The protocol presented here provides a method for reliably and efficiently transfecting human THP-1 macrophages and monocytes with high cell vitality, high transfection efficiency, and minimal effects on cell behavior. This approach is based on Nucleofection and the protocol has been optimized to maintain maximum capability for cell activation after transfection. The protocol is adequate for adherent cells after detachment as well as cells in suspension, and can be used for small to medium sample numbers. Thus, the method presented is useful for investigating gene regulatory effects during macrophage differentiation and polarization. Apart from presenting results characterizing macrophages transfected according to this protocol in comparison to an alternative chemical method, the impact of cell culture medium selection after transfection on cell behavior is also discussed. The presented data indicate the importance of validating the selection for different experimental settings.

This protocol presents an efficient and reliable method to transfect human THP-1 macrophages with siRNA or plasmid DNA by electroporation with high transfection efficiency while maintaining high cell vitality and full macrophage capacity for differentiation and polarization.

Macrophages, as key players of the innate immune response, are at the focus of research dealing with tissue homeostasis or various pathologies. ...

Forward Genetics Screens Using Macrophages to Identify Toxoplasma gondii Genes Important for Resistance to IFN-&#947;-Dependent Cell Autonomous Immunity

Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan pathogen. The parasite invades and replicates within virtually any warm blooded vertebrate cell type. During parasite invasion of a host cell, the parasite creates a parasitophorous vacuole (PV) that originates from the host cell membrane independent of phagocytosis within which the parasite replicates. While IFN-dependent-innate and cell mediated immunity is important for eventual control of infection, innate immune cells, including neutrophils, monocytes and dendritic cells, can also serve as vehicles for systemic dissemination of the parasite early in infection. An approach is described that utilizes the host innate immune response, in this case macrophages, in a forward genetic screen to identify parasite mutants with a fitness defect in infected macrophages following activation but normal invasion and replication in na&#239;ve macrophages. Thus, the screen isolates parasite mutants that have a specific defect in their ability to resist the effects of macrophage activation. The paper describes two broad phenotypes of mutant parasites following activation of infected macrophages: parasite stasis versus parasite degradation, often in amorphous vacuoles. The parasite mutants are then analyzed to identify the responsible parasite genes specifically important for resistance to induced mediators of cell autonomous immunity. The paper presents a general approach for the forward genetics screen that, in theory, can be modified to target parasite genes important for resistance to specific antimicrobial mediators. It also describes an approach to evaluate the specific macrophage antimicrobial mediators to which the parasite mutant is susceptible. Activation of infected macrophages can also promote parasite differentiation from the tachyzoite to bradyzoite stage that maintains chronic infection. Therefore, methodology is presented to evaluate the importance of the identified parasite gene to establishment of chronic infection.

Forward Genetics Screens Using Macrophages to Identify Toxoplasma gondii Genes Important for Resistance to IFN-&amp;#947;-Dependent Cell Autonomous Immunity

Forward genetics is a powerful approach to identify genes in intracellular pathogens important for resistance to cell autonomous immunity. The current approach uses innate immune cells, specifically macrophages, to identify novel Toxoplasma gondii genes important for immune evasion.

Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan pathogen. The parasite invades and replicates within ...

In Vitro Disassembly of Influenza A Virus Capsids by Gradient Centrifugation

Acid-triggered molecular processes closely control cell entry of many viruses that enter through the endocytic system. In the case of influenza A virus (IAV), virus fusion with the endosomal membrane as well as the subsequent disassembly of the viral capsid, called uncoating, is governed by the ionic conditions inside endocytic vesicles. The early steps in the virus life cycle are hard to study because endosomes cannot be directly accessed experimentally, creating the need for an in vitro approach. Here, we describe a method based on velocity gradient centrifugation of purified virions through a two-layer glycerol gradient, which enables analysis of the IAV core and its stability. The gradient contains a non-ionic detergent (NP-40) in its lower layer to remove the viral membrane by solubilization as the virus sediments toward the bottom. At neutral pH, viral cores are pelleted as stable structures. The major core components, matrix protein (M1) and the viral ribonucleoproteins (vRNPs), can be clearly identified in the pellet fraction by SDS-PAGE. Decreasing the pH to 6.0 or lower in the bottom layer selectively removes M1 from the pellet followed by release of vRNPs at more acidic conditions. Viral protein bands on Coomassie-stained gels can be subjected to densitometric quantification to monitor intermediate states of IAV disassembly. Besides pH, other factors that influence viral core stability can be assessed, such as salt concentration and putative viral uncoating factors, simply by modifying the detergent-containing glycerol layer accordingly. Taken together, the presented technique allows highly reproducible and quantitative analysis of viral uncoating in vitro. It can be applied to other enveloped viruses that undergo complex uncoating processes.

In Vitro Disassembly of Influenza A Virus Capsids by Gradient Centrifugation

Disassembly of influenza A virus cores during virus entry into host cells is a multistep process. We describe an in vitro method to analyze the early stages of viral uncoating. In this approach, velocity gradient centrifugation is used to biochemically dissect the steps that initiate uncoating under defined conditions.

Acid-triggered molecular processes closely control cell entry of many viruses that enter through the endocytic system. In the case of influenza A virus ...