Name: complementary use of microscopic techniques and fluorescence reading in studying cryptococcus-amoeba interactions
Uploaded: 2019-06-22T13:00:00
Description: Watch this Scientific Journal Video about Complementary Use of Microscopic Techniques and Fluorescence Reading in Studying Cryptococcus-Amoeba Interactions at JoVE.com

The work was supported by a grant from the National Research Foundation of South Africa (grant number: UID 87903) and the University of the Free State. We are also grateful to services and assistance offered by Pieter van Wyk and Hanlie Grobler during our microscopy studies.

Cryptococcus neoformans and some Acanthamoeba castellanii strains are regarded as biosafety level-2 (BSL-2) pathogens; thus, researchers must take proper precautions when working with these organisms. For example, laboratory personnel should have specific training and personal protective equipment (PPE) such as lab coats, gloves, and eye protection. A biological safety cabinet (level-2) should be used for procedures that can cause infection14.
1. Cultiva...

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In the paper, different techniques were successfully employed to reveal the possible outcome that may arise when amoeba interact with cryptococcal cells. Also, we were interested to show the effects of 3-hydroxy fatty acids on the outcome of Cryptococcus-amoeba interactions.
The first technique used was confocal microscopy, which rendered still images. The major drawback of this technique here was that it only gave us information that is limited to a particular timepoint. Any conclusi...

Microbes have evolved over time to occupy and thrive in different ecological niches such as the open physical boundaries of the soil and water, among others1. In these niches, microbes often engage in the direct competition for limited resources; importantly, for nutrients that they use for supporting their growth or space, which they need to accommodate the expanding population2,3. In certain instances, some holozoic organisms like amoeba may even predate on cryptococcal cells as a way of extracting nutrients from their biomass4,5. In turn, this allows such organisms to establish territorial dominance via controlling the population numbers of its prey. Because of this predatory pressure, some prey may be selected to produce microbial factors, such as the cryptococcal capsule6, to reconcile the negative effects of the pressure. However, as an unintended consequence of this pressure, some microbes acquire factors that allow them to cross the species barrier and seek out new niches to colonize7, like the confined spaces of the human body that are rich in nutrients and have ideal conditions. The latter may explain how a terrestrial microbe like Cryptococcus (C.) neoformans can transform to become pathogenic. 
To this end, it is important to study the initial contact that cryptococcal cells may have with amoeba and how this may select them to become pathogenic. More specifically, this may give clues on how cryptococcal cells behave when acted upon by macrophages during infection. It is for this reason that amoeba was chosen as a model for macrophages here, as it is relatively cheap and easy to maintain a culture of amoeba in a laboratory8. Of interest was to also examine how cryptococcal secondary metabolites viz. 3-hydroxy fatty acids9,10 influence the interaction between amoebae and cryptococcal cells.
A simple way of perceiving the interaction between amoeba and its prey with the naked eye is to create a lawn using its prey on the surface of an agar plate and spot amoeba. The visualization of plaques or clear zones on the agar plate depicts areas where amoeba may have fed on its prey. However, at this macro level, only the outcome of the process is noted, and the process of phagocytosis is mechanized cannot be observed. Therefore, to appreciate the process on a cell-to-cell basis, there are several microscopic methods that can be used11,12. For example, an inverted microscope with an incubation chamber can be used to video record a time-lapse of events between a phagocytic cell and its target13. Unfortunately, due to the cost of a microscope with a time-lapse functionality, it is not always possible for laboratories to purchase such a microscope, especially in resource poor-settings. 
To circumvent the above limitation, this study presents a sequential exploratory design that evaluates the interaction of C. neoformans viz C. neoformans UOFS Y-1378 and C. neoformans LMPE 046 with Acanthamoeba castellani. First, a qualitative method is used that precedes a quantitative method. Still images are captured using an inverted fluorescence microscope, as well as a transmission electron microscope to depict amoeba-Cryptococcus interactions. This was followed by quantifying fluorescence using a plate reader to estimate the efficiency of amoeba to internalize cryptococcal cells. When reconciling findings from these methods during the data-interpretation stage, this may equally reveal as much critical information as perusing a phagocytosis time-lapse video.

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			<td height="21" style="height:21px;width:312px;">1,4-Diazabicyclo-[2.2.2]-octane</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">D27802</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1.5-mL plastic tube&#160;</td>
			<td>Thermo Fisher Scientific</td>
			<td style="width:123px;">69715</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">15-mL Centrifuge tube&#160;</td>
			<td>Thermo Fisher Scientific</td>
			<td style="width:123px;">7252018</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">50-mL Centrifuge tube&#160;</td>
			<td>Thermo Fisher Scientific</td>
			<td style="width:123px;">1132017</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">8-Well chamber slide</td>
			<td style="width:176px;">Thermo Fisher Scientific</td>
			<td style="width:123px;">1109650</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Acetone</td>
			<td style="width:176px;">Merck</td>
			<td style="width:123px;">SAAR1022040LC</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:312px;">Amoeba strain</td>
			<td style="width:176px;">ATCC&#210;</td>
			<td style="width:123px;">30234TM</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:312px;">ATCC medium 712</td>
			<td style="width:176px;">ATCC&#210;</td>
			<td style="width:123px;">712TM</td>
			<td style="width:172px;">Amoeba medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Black 96-well microtiter plate</td>
			<td>Thermo Fisher Scientific</td>
			<td style="width:123px;">152089</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Centrifuge</td>
			<td style="width:176px;">Hermle</td>
			<td style="width:123px;">-</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Chloroform</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">C2432</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Confocal microscope</td>
			<td style="width:176px;">Nikon</td>
			<td>Nikon TE 2000</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td colspan="4" height="21" style="height:21px;width:783px;">Epoxy resin:</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">[1] NSA</td>
			<td style="width:176px;">[1] ALS</td>
			<td style="width:123px;">[1] R1054</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">[2] DER 736</td>
			<td style="width:176px;">[2] ALS</td>
			<td style="width:123px;">[2] R1073</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">[3] ERL Y221 resin</td>
			<td style="width:176px;">[3] ALS</td>
			<td style="width:123px;">[3] R1047R</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">[4] S1 (2-dimethylaminoethanol)</td>
			<td style="width:176px;">[4] ALS&#160;</td>
			<td style="width:123px;">[4] R1067</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Fluorescein isothiocyanate</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">F4274</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Formic Acid</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">489441</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fluoroskan Ascent FL</td>
			<td>Thermo Fisher Scientific</td>
			<td style="width:123px;">374-91038C</td>
			<td style="width:172px;">Microplate reader</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Glucose</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">G8270</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Glutaraldehyde</td>
			<td style="width:176px;">ALS</td>
			<td style="width:123px;">R1009</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Hemocytometer</td>
			<td style="width:176px;">Boeco</td>
			<td style="width:123px;">-</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Lead citrate</td>
			<td style="width:176px;">ALS</td>
			<td style="width:123px;">R1209</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Liquid Chromatography Mass Spectrometer</td>
			<td>Thermo Fisher Scientific</td>
			<td style="width:123px;"></td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Methanol</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">R 34,860</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Orbital shaker</td>
			<td style="width:176px;">Lasec&#160;</td>
			<td style="width:123px;">-</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Osmium tetroxide</td>
			<td style="width:176px;">ALS</td>
			<td style="width:123px;">R1015</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:312px;">pHrodo Green Zymosan A BioParticles</td>
			<td style="width:176px;">Life Technologies</td>
			<td style="width:123px;">P35365</td>
			<td style="width:172px;">This is the pH-sensitive dye</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Physiological buffer solution</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">P4417-50TAB</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Rotary shaker</td>
			<td style="width:176px;">Labcon</td>
			<td style="width:123px;">-</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td colspan="4" height="21" style="height:21px;width:783px;">Sodium phosphate buffer:</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:312px;">[1] di-sodium hydrogen orthophosphate dihydrate&#160;</td>
			<td style="width:176px;">[1] Merck</td>
			<td style="width:123px;">[1] 106580</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:312px;">[2] sodium di-hydrogen orthophosphate dihydrate</td>
			<td style="width:176px;">[2] Merck&#160;</td>
			<td style="width:123px;">[2] 106345</td>
			<td style="width:172px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Transmission electron microscope</td>
			<td style="width:176px;">Philips</td>
			<td>Philips EM 100&#160;</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Trypan blue&#160;</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">T8154</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Ultramicrotome</td>
			<td style="width:176px;">Leica</td>
			<td style="width:123px;">EM UC7</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Uranyl acetate</td>
			<td style="width:176px;">ALS</td>
			<td style="width:123px;">R1260A</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Vacuum dessicator</td>
			<td style="width:176px;">Lasec&#160;</td>
			<td style="width:123px;">-</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Vial</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">29651-U</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">YNB</td>
			<td style="width:176px;">Lasec&#160;</td>
			<td style="width:123px;">239210</td>
			<td style="width:172px;">-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">YPD agar</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">Y-1500</td>
			<td>-</td>
		</tr>
	</tbody>
</table>

complementary use of microscopic techniques and fluorescence reading in studying cryptococcus-amoeba interactions

To simulate Cryptococcus infection, amoeba, which is the natural predator of cryptococcal cells in the environment, can be used as a model for macrophages. This predatory organism, similar to macrophages, employs phagocytosis to kill internalized cells. With the aid of a confocal laser-scanning microscope, images depicting interactive moments between cryptococcal cells and amoeba are captured. The resolution power of the electron microscope also helps to reveal the ultrastructural detail of cryptococcal cells when trapped inside the amoeba food vacuole. Since phagocytosis is a continuous process, quantitative data is then integrated in the analysis to explain what happens at the timepoint when an image is captured. To be specific, relative fluorescence units are read in order to quantify the efficiency of amoeba in internalizing cryptococcal cells. For this purpose, cryptococcal cells are stained with a dye that makes them fluoresce once trapped inside the acidic environment of the food vacuole. When used together, information gathered through such techniques can provide critical information to help draw conclusions on the behavior and fate of cells when internalized by amoeba and, possibly, by other phagocytic cells.

Microbes are microscopic organisms that cannot be perceived with the naked eye. However, their impact may result in observable clinically evident illnesses, such as skin infections. When studying certain aspects of microbes, ranging from their morphology, byproducts, and interactions, being able to provide pictorial and video evidence is of the utmost importance.
We first sought to visualize the interaction between cryptococcal ...

Watch this Scientific Journal Video about Complementary Use of Microscopic Techniques and Fluorescence Reading in Studying Cryptococcus-Amoeba Interactions at JoVE.com

Complementary Use of Microscopic Techniques and Fluorescence Reading in Studying Cryptococcus-Amoeba Interactions

This paper details a protocol for preparing a co-culture of cryptococcal cells and amoebae that is studied using still, fluorescent images and high-resolution transmission electron microscope images. Illustrated here is how quantitative data can complement such qualitative information.

Complementary Use of Microscopic Techniques and Fluorescence Reading in Studying Cryptococcus-Amoeba Interactions

To simulate Cryptococcus infection, amoeba, which is the natural predator of cryptococcal cells in the environment, can be used as a model for ...

The overall purpose of this procedure is to use microscopy as a tool to study the phagocytosis of the pathogenic fungal species Cryptococcus neoformans by its environmental predator amoeba. This video details a protocol for preparing a co-culture of cryptococcal cells and amoebae which I will study using confocal laser-scanning microscopy and transmission electron microscopy. Information obtained from using these techniques could shed insights into the behavior of cryptococcal cells when internalized during infection.Streak out the test fungal strains on YPD agar plates. Incubate the plate for 48 hours at 30 degrees Celsius. Scrape off a loopful of cells from the 48-hour-old plate and inoculate them into a 250-milliliter conical flask containing 100 milliliters of YNB broth that is supplemented with 4%glucose.Incubate the flask at 30 degrees Celsius for 24 hours on a rotary shaker. After a 24-hour incubation period, count the fungal cells using a hemocytometer and adjust the cell number to one million cells per milliliter with physiological buffer solution. Cultivate amoeba cells in peptone yeast extract glucose broth for a week at 30 degrees Celsius.Count the amoeba cells using a hemocytometer and adjust the cell number to 10 million cells per milliliter with fresh sterile ATCC medium 712. Following this, perform a viability assay using a trypan blue stain. It is advisable to work with cells that show at least 80%viability.Dispense a 200-microliter suspension of standardized amoeba cells into chambers of an adherent slide. Allow two hours to pass for cells to adhere to the surface at 30 degrees Celsius. While amoeba cells are settling down, stain the standardized cryptococcal cells with fluorescein isothiocyanate.Gently agitate the fungal cells for two hours at room temperature and in the dark. Dispense 200-microliter suspension of stained cryptococcal cells after washing to appropriate chambers that already contain amoeba cells. Incubate the prepared co-culture at 30 degrees Celsius for an additional two-hour period.At the end of the coincubation period, wash the chambers twice with PBS to remove any unbound amoeba cells including non-internalized cryptococcal cells. Aspirate the glutaraldehyde that was used to fix the cells, and wash the chamber twice with PBS. Dismantle the chamber slide.View the co-cultured cells using a confocal laser-scanning microscope. To complement the above assay, stain the cryptococcal cells with pHrodo dye which selectively allows for the reading of cells trapped inside the food vacuole. Dispense these stained cells into the wells of a black adherent microtiter plate that already contains seeded amoeba cells.Measure fluorescence on a microplate reader that can convert logarithmic signals to relative fluorescence units. Add five milliliters of standardized cryptococcal cells to the same centrifuge tube that already contains five milliliters of standardized amoeba cells. Allow the tube to stand for two hours at 30 degrees Celsius.Aspirate the supernatant after centrifugation. Fix the pellet which represents the co-cultured cells with one molar of sodium phosphate buffered 3%glutaraldehyde at pH 7 for three hours. Wash the co-cultured cells once with sodium phosphate buffer.Fix again for 1 1/2 hours in similarly buffered 1%osmium tetroxide followed by washing. Dehydrate the TEM material also known as the co-cultured cells in a graded acetone series of 30%50%70%95%and 100%for 15 minutes each. Here, repeat the final dehydration step in two changes.Prepare the epoxy resin by weighing off epoxy of normal consistency. Embed material into the epoxy resin. Polymerize the TEM material for eight hours at 70 degrees Celsius.Cut 16-nanometer sections with glass knives mounted on the ultratome. Stain the sections with uranyl acetate for 10 minutes in the dark followed by lead citrate for 10 minutes, also in the dark. View the sections with a transmission electron microscope.For illustrative purposes, in the video, two isolates are examined, one that produces 3-hydroxy fatty acid and the other that does not. 3-hydroxy fatty acids are secondary metabolites that do not play role in the growth of cryptococcal cells. Here are snapshots that show interactive moments between Cryptococcus and amoebae.To the point, a cryptococcal cell before and after internalization can be observed. When studying phagocytosis, it is ideal to make use of live imaging. However, it is not always possible for researchers to have access to such a microscope in order to follow the process of phagocytosis continuously.A possible solution to compensate for this limitation may be to complement images with quantitative data through the reading of relative fluorescence units. The bar graph is an example of data that I used to complement the images. Importantly, both the qualitative data in the form of images and the quantitative data can be taken at different time points over the course of time.By piecing all the information, one can start to construct a bigger image of what transpires during the process of phagocytosis. From the quantitative data, it is clear to see that the cells with 3-hydroxy fatty acids are less susceptible to amoeba action when compared to cells that do not produce 3-hydroxy fatty acid as fewer cells are internalized. The TEM is particularly a powerful tool as it can give a bird's-eye view into the lumen of the food vacuole because of its high resolution power, and this is the kind of detail that is often missed when examining live imaging as well as still images.In this specific TEM micrograph, protuberances on the surface of cryptococcal cells can clearly be seen. Previously, it was theorized that these cell surface structures are channels by which 3-hydroxy fatty acids are released into the surrounding environment. To the point, these channels may help to deliver 3-hydroxy fatty acids into the lumen of the food vacuole of amoebae to alter the internal conditions, hence the promotion of cell survival.pHrodo or like FITC may be a much better stain to use as it only fluoresce at a low pH, like inside the food vacuole. To be specific, pHrodo only allows the researcher to obtain data concerning internalized cells. Towards this end, it is important that cells are suspended in phosphate buffer solution before staining and that amoeba media is of a neutral pH.Transmission electron microscope operators are to be well trained to section properly as this is often the point where the results could be distorted and micrograph damaged by electron bombardment. It is envisaged that researchers will be able to take enough information from the presented protocol and optimize them in their own studies. Moreover, researchers may also develop antibodies against targeted metabolite and apply them during their immunofluorescent microscopy study including immunogold labeling during TEM examination.

complementary-use-microscopic-techniques-fluorescence-reading

Research

JoVE Journal

Immunology and Infection

Use of an Optical Trap for Study of Host-Pathogen Interactions for Dynamic Live Cell Imaging

Dynamic live cell imaging allows direct visualization of real-time interactions between cells of the immune system1, 2; however, the lack of spatial and temporal control between the phagocytic cell and microbe has rendered focused observations into the initial interactions of host response to pathogens difficult. Historically, intercellular contact events such as phagocytosis3 have been imaged by mixing two cell types, and then continuously scanning the field-of-view to find serendipitous intercellular contacts at the appropriate stage of interaction. The stochastic nature of these events renders this process tedious, and it is difficult to observe early or fleeting events in cell-cell contact by this approach. This method requires finding cell pairs that are on the verge of contact, and observing them until they consummate their contact, or do not. To address these limitations, we use optical trapping as a non-invasive, non-destructive, but fast and effective method to position cells in culture.
Optical traps, or optical tweezers, are increasingly utilized in biological research to capture and physically manipulate cells and other micron-sized particles in three dimensions4. Radiation pressure was first observed and applied to optical tweezer systems in 19705, 6, and was first used to control biological specimens in 19877. Since then, optical tweezers have matured into a technology to probe a variety of biological phenomena8-13.
We describe a method14 that advances live cell imaging by integrating an optical trap with spinning disk confocal microscopy with temperature and humidity control to provide exquisite spatial and temporal control of pathogenic organisms in a physiological environment to facilitate interactions with host cells, as determined by the operator. Live, pathogenic organisms like Candida albicans and Aspergillus fumigatus, which can cause potentially lethal, invasive infections in immunocompromised individuals15, 16 (e.g. AIDS, chemotherapy, and organ transplantation patients), were optically trapped using non-destructive laser intensities and moved adjacent to macrophages, which can phagocytose the pathogen. High resolution, transmitted light and fluorescence-based movies established the ability to observe early events of phagocytosis in living cells. To demonstrate the broad applicability in immunology, primary T-cells were also trapped and manipulated to form synapses with anti-CD3 coated microspheres in vivo, and time-lapse imaging of synapse formation was also obtained. By providing a method to exert fine spatial control of live pathogens with respect to immune cells, cellular interactions can be captured by fluorescence microscopy with minimal perturbation to cells and can yield powerful insight into early responses of innate and adaptive immunity.

A method is described to individually select, manipulate, and image live pathogens using an optical trap coupled to a spinning disk microscope. The optical trap provides spatial and temporal control of organisms and places them adjacent to host cells. Fluorescence microscopy captures dynamic intercellular interactions with minimal perturbation to cells.

Dynamic live cell imaging allows direct visualization of real-time interactions between cells of the immune system1, 2; however, the lack of spatial and ...

Use of the EpiAirway Model for Characterizing Long-term Host-pathogen Interactions

Nontypeable Haemophilus influenzae (NTHi) are human-adapted Gram-negative bacteria that can cause recurrent and chronic infections of the respiratory mucosa 1; 2. To study the mechanisms by which these organisms survive on and inside respiratory tissues, a model in which successful long-term co-culture of bacteria and human cells can be performed is required. We use primary human respiratory epithelial tissues raised to the air-liquid interface, the EpiAirway model (MatTek, Ashland, MA). These are non-immortalized, well-differentiated, 3-dimensional tissues that contain tight junctions, ciliated and nonciliated cells, goblet cells that produce mucin, and retain the ability to produce cytokines in response to infection. 
This biologically relevant in vitro model of the human upper airway can be used in a number of ways; the overall goal of this method is to perform long-term co-culture of EpiAirway tissues with NTHi and quantitate cell-associated and internalized bacteria over time. As well, mucin production and the cytokine profile of the infected co-cultures can be determined. This approach improves upon existing methods in that many current protocols use submerged monolayer or Transwell cultures of human cells, which are not capable of supporting bacterial infections over extended periods3. For example, if an organism can replicate in the overlying media, this can result in unacceptable levels of cytotoxicity and loss of host cells, arresting the experiment. The EpiAirway model allows characterization of long-term host-pathogen interactions. Further, since the source for the EpiAirway is normal human tracheo-bronchial cells rather than an immortalized line, each is an excellent representation of actual human upper respiratory tract tissue, both in structure and in function4.
For this method, the EpiAirway tissues are weaned off of anti-microbial and anti-fungal compounds for 2 days prior to delivery, and all procedures are performed under antibiotic-free conditions. This necessitates special considerations, since both bacteria and primary human tissues are used in the same biosafety cabinet, and are co-cultured for extended periods.

This method allows characterization of extended bacterial co-culture with EpiAirways, primary human respiratory epithelial tissue grown at the air-liquid interface, a biologically relevant in vitro model. The approach can be used with any microbe that is amenable to long-term co-culture.

Nontypeable Haemophilus influenzae  (NTHi) are human-adapted Gram-negative bacteria that can cause recurrent and chronic infections of the respiratory ...

Assessing Hepatic Metabolic Changes During Progressive Colonization of Germ-free Mouse by 1H NMR Spectroscopy

It is well known that gut bacteria contribute significantly to the host homeostasis, providing a range of benefits such as immune protection and vitamin synthesis. They also supply the host with a considerable amount of nutrients, making this ecosystem an essential metabolic organ. In the context of increasing evidence of the link between the gut flora and the metabolic syndrome, understanding the metabolic interaction between the host and its gut microbiota is becoming an important challenge of modern biology.1-4
 Colonization (also referred to as normalization process) designates the establishment of micro-organisms in a former germ-free animal. While it is a natural process occurring at birth, it is also used in adult germ-free animals to control the gut floral ecosystem and further determine its impact on the host metabolism. A common procedure to control the colonization process is to use the gavage method with a single or a mixture of micro-organisms. This method results in a very quick colonization and presents the disadvantage of being extremely stressful5. It is therefore useful to minimize the stress and to obtain a slower colonization process to observe gradually the impact of bacterial establishment on the host metabolism.
 In this manuscript, we describe a procedure to assess the modification of hepatic metabolism during a gradual colonization process using a non-destructive metabolic profiling technique. We propose to monitor gut microbial colonization by assessing the gut microbial metabolic activity reflected by the urinary excretion of microbial co-metabolites by 1H NMR-based metabolic profiling. This allows an appreciation of the stability of gut microbial activity beyond the stable establishment of the gut microbial ecosystem usually assessed by monitoring fecal bacteria by DGGE (denaturing gradient gel electrophoresis).6 The colonization takes place in a conventional open environment and is initiated by a dirty litter soiled by conventional animals, which will serve as controls. Rodents being coprophagous animals, this ensures a homogenous colonization as previously described.7
 Hepatic metabolic profiling is measured directly from an intact liver biopsy using 1H High Resolution Magic Angle Spinning NMR spectroscopy. This semi-quantitative technique offers a quick way to assess, without damaging the cell structure, the major metabolites such as triglycerides, glucose and glycogen in order to further estimate the complex interaction between the colonization process and the hepatic metabolism7-10. This method can also be applied to any tissue biopsy11,12.

Assessing Hepatic Metabolic Changes During Progressive Colonization of Germ-free Mouse by 1H NMR Spectroscopy

A progressive colonization procedure is described to further assess its impact on the host hepatic metabolism. Colonization is monitored non invasively by evaluating the urinary excretion of microbial co-metabolites by NMR-based metabolic profiling while hepatic metabolism is assessed by High Resolution Magic Angle Spinning (HR MAS) NMR profiling of intact biopsy.

It is well known that gut bacteria contribute significantly to the host homeostasis, providing a range of benefits such as immune protection and vitamin ...

Use of Artificial Sputum Medium to Test Antibiotic Efficacy Against Pseudomonas aeruginosa in Conditions More Relevant to the Cystic Fibrosis Lung

There is growing concern about the relevance of in vitro antimicrobial susceptibility tests when applied to isolates of P. aeruginosa from cystic fibrosis (CF) patients. Existing methods rely on single or a few isolates grown aerobically and planktonically. Predetermined cut-offs are used to define whether the bacteria are sensitive or resistant to any given antibiotic1. However, during chronic lung infections in CF, P. aeruginosa populations exist in biofilms and there is evidence that the environment is largely microaerophilic2. The stark difference in conditions between bacteria in the lung and those during diagnostic testing has called into question the reliability and even relevance of these tests3.
 Artificial sputum medium (ASM) is a culture medium containing the components of CF patient sputum, including amino acids, mucin and free DNA. P. aeruginosa growth in ASM mimics growth during CF infections, with the formation of self-aggregating biofilm structures and population divergence4,5,6. The aim of this study was to develop a microtitre-plate assay to study antimicrobial susceptibility of P. aeruginosa based on growth in ASM, which is applicable to both microaerophilic and aerobic conditions.
 An ASM assay was developed in a microtitre plate format. P. aeruginosa biofilms were allowed to develop for 3 days prior to incubation with antimicrobial agents at different concentrations for 24 hours. After biofilm disruption, cell viability was measured by staining with resazurin. This assay was used to ascertain the sessile cell minimum inhibitory concentration (SMIC) of tobramycin for 15 different P. aeruginosa isolates under aerobic and microaerophilic conditions and SMIC values were compared to those obtained with standard broth growth. Whilst there was some evidence for increased MIC values for isolates grown in ASM when compared to their planktonic counterparts, the biggest differences were found with bacteria tested in microaerophilic conditions, which showed a much increased resistance up to a &gt;128 fold, towards tobramycin in the ASM system when compared to assays carried out in aerobic conditions.
 The lack of association between current susceptibility testing methods and clinical outcome has questioned the validity of current methods3. Several in vitro models have been used previously to study P. aeruginosa biofilms7, 8. However, these methods rely on surface attached biofilms, whereas the ASM biofilms resemble those observed in the CF lung9 . In addition, reduced oxygen concentration in the mucus has been shown to alter the behavior of P. aeruginosa2 and affect antibiotic susceptibility10. Therefore using ASM under microaerophilic conditions may provide a more realistic environment in which to study antimicrobial susceptibility.

Use of Artificial Sputum Medium to Test Antibiotic Efficacy Against Pseudomonas aeruginosa in Conditions More Relevant to the Cystic Fibrosis Lung

Current diagnostic antimicrobial susceptibility testing relies on the planktonic growth of isolates in nutrient rich, aerobic conditions. Here, we employ an alternative artificial sputum medium to study antimicrobial susceptibility of Pseudomonas aeruginosa biofilms under both aerobic and microaerophilic conditions more representative of the cystic fibrosis lung.

There  is growing concern about the relevance of in vitro antimicrobial  susceptibility tests when applied to isolates of P. aeruginosa from  cystic ...

Studying Interactions of Staphylococcus aureus with Neutrophils by Flow Cytometry and Time Lapse Microscopy

We present methods to study the effect of phenol soluble modulins (PSMs) and other toxins produced and secreted by Staphylococcus aureus on neutrophils. To study the effects of the PSMs on neutrophils we isolate fresh neutrophils using density gradient centrifugation. These neutrophils are loaded with a dye that fluoresces upon calcium mobilization. The activation of neutrophils by PSMs initiates a rapid and transient increase in the free intracellular calcium concentration. In a flow cytometry experiment this rapid mobilization can be measured by monitoring the fluorescence of a pre-loaded dye that reacts to the increased concentration of free Ca2+. Using this method we can determine the PSM concentration necessary to activate the neutrophil, and measure the effects of specific and general inhibitors of the neutrophil activation.	
	To investigate the expression of the PSMs in the intracellular space, we have constructed reporter fusions of the promoter of the PSM&alpha; operon to GFP. When these reporter strains of S. aureus are phagocytosed by neutrophils, the induction of expression can be observed using fluorescence microscopy.

Studying Interactions of Staphylococcus aureus with Neutrophils by Flow Cytometry and Time Lapse Microscopy

We present methods to study the effect of PSMs and other toxins secreted by Staphylococcus aureus on neutrophils using flow cytometry and fluorescence microscopy.

We present methods to study the effect of phenol soluble modulins (PSMs)  and other toxins produced and secreted by Staphylococcus  aureus on neutrophils. ...

Use of Shigella flexneri to Study Autophagy-Cytoskeleton Interactions

Shigella flexneri is an intracellular pathogen that can escape from phagosomes to reach the cytosol, and polymerize the host actin cytoskeleton to promote its motility and dissemination. New work has shown that proteins involved in actin-based motility are also linked to autophagy, an intracellular degradation process crucial for cell autonomous immunity. Strikingly, host cells may prevent actin-based motility of S. flexneri by compartmentalizing bacteria inside &#8216;septin cages&#8217; and targeting them to autophagy. These observations indicate that a more complete understanding of septins, a family of filamentous GTP-binding proteins, will provide new insights into the process of autophagy. This report describes protocols to monitor autophagy-cytoskeleton interactions caused by S. flexneri in vitro using tissue culture cells and in vivo using zebrafish larvae. These protocols enable investigation of intracellular mechanisms that control bacterial dissemination at the molecular, cellular, and whole organism level.

Use of Shigella flexneri to Study Autophagy-Cytoskeleton Interactions

To counteract pathogen dissemination, host cells reorganize their cytoskeleton to compartmentalize bacteria and induce autophagy. Using Shigella infection of tissue culture cells, host and pathogen determinants underlying this process are identified and characterized. Using zebrafish models of Shigella infection, the role of discovered molecules and mechanisms are investigated in vivo.

Shigella flexneri is an intracellular pathogen that can escape from phagosomes to reach the cytosol, and polymerize the host actin cytoskeleton to promote ...

A Novel In vitro Model for Studying the Interactions Between Human Whole Blood and Endothelium

The majority of all known diseases are accompanied by disorders of the cardiovascular system. Studies into the complexity of the interacting pathways activated during cardiovascular pathologies are, however, limited by the lack of robust and physiologically relevant methods. In order to model pathological vascular events we have developed an in vitro assay for studying the interaction between endothelium and whole blood. The assay consists of primary human endothelial cells, which are placed in contact with human whole blood. The method utilizes native blood with no or very little anticoagulant, enabling study of delicate interactions between molecular and cellular components present in a blood vessel.
We investigated functionality of the assay by comparing activation of coagulation by different blood volumes incubated with or without human umbilical vein endothelial cells (HUVEC). Whereas a larger blood volume contributed to an increase in the formation of thrombin antithrombin (TAT) complexes, presence of HUVEC resulted in reduced activation of coagulation. Furthermore, we applied image analysis of leukocyte attachment to HUVEC stimulated with tumor necrosis factor (TNF&#945;) and found the presence of CD16+ cells to be significantly higher on TNF&#945; stimulated cells as compared to unstimulated cells after blood contact. In conclusion, the assay may be applied to study vascular pathologies, where interactions between the endothelium and the blood compartment are perturbed.

A Novel In vitro Model for Studying the Interactions Between Human Whole Blood and Endothelium

The accessibility of reliable models to investigate vascular blood interactions in humans is lacking. We present an in vitro model of cultured primary human endothelial cells combined with human whole blood to investigate cellular interactions both in the blood (ELISA) and the vascular compartment (microscopy).

The majority of all known diseases are accompanied by disorders of the cardiovascular system. Studies into the complexity of the interacting pathways ...

Evaluation of the Efficacy And Toxicity of RNAs Targeting HIV-1 Production for Use in Gene or Drug Therapy

Small RNA therapies targeting post-integration steps in the HIV-1 replication cycle are among the top candidates for gene therapy and have the potential to be used as drug therapies for HIV-1 infection. Post-integration inhibitors include ribozymes, short hairpin (sh) RNAs, small interfering (si) RNAs, U1 interference (U1i) RNAs and RNA aptamers. Many of these have been identified using transient co-transfection assays with an HIV-1 expression plasmid and some have advanced to clinical trials. In addition to measures of efficacy, small RNAs have been evaluated for their potential to affect the expression of human RNAs, alter cell growth and/or differentiation, and elicit innate immune responses. In the protocols described here, a set of transient transfection assays designed to evaluate the efficacy and toxicity of RNA molecules targeting post-integration steps in the HIV-1 replication cycle are described. We have used these assays to identify new ribozymes and optimize the format of shRNAs and siRNAs targeting HIV-1 RNA. The methods provide a quick set of assays that are useful for screening new anti-HIV-1 RNAs and could be adapted to screen other post-integration inhibitors of HIV-1 replication.

Methods to evaluate the efficacy and toxicity of RNA molecules targeting post-integration steps of the HIV-1 replication cycle are described. These methods are useful for screening new molecules and optimizing the format of existing ones.

Small RNA therapies targeting post-integration steps in the HIV-1 replication cycle are among the top candidates for gene therapy and have the potential ...

Co-immunoprecipitation Assay for Studying Functional Interactions Between Receptors and Enzymes

Receptor-associated enzymes are the major mediators of cellular activation. These enzymes are regulated, at least in part, by physical interactions with cytoplasmic tails of the receptors. The interactions often occur through specific protein domains and result in activation of the enzymes. There are several methods to study interactions between proteins. While co-immunoprecipitation is commonly used to study domains that are required for protein-protein interactions, there are no assays that document the contribution of specific domains to activity of the recruited enzymes at the same time. Accordingly, the method described here combines co-immunoprecipitation and an on-bead enzymatic activity assay for simultaneous evaluation of interactions between proteins and associated enzymatic activation. The goal of this protocol is to identify the domains that are critical for physical interactions between a protein and enzyme and the domains that are obligatory for complete activation of the enzyme. The importance of this assay is demonstrated, as certain receptor protein domains contribute to the binding of the enzyme to the cytoplasmic tail of the receptor, while other domains are necessary to regulate the function of the same enzyme.

Here, we present a protocol for co-immunoprecipitation and an on-bead enzymatic activity assay to simultaneously study the contribution of specific protein domains of plasma membrane receptors to both enzyme recruitment and enzyme activity.

Receptor-associated enzymes are the major mediators of cellular activation. These enzymes are regulated, at least in part, by physical interactions with ...

Analysis of SAMHD1 Restriction by Flow Cytometry in Human Myeloid U937 Cells

Sterile &#945;-motif/histidine-aspartate domain-containing protein 1 (SAMHD1) inhibits replication of HIV-1 in quiescent myeloid cells. U937 cells are widely used as a convenient cell system for analyzing SAMHD1 activity due to a low level of SAMHD1 RNA expression, leading to undetectable endogenous protein expression. Based on similar assays developed in the Stoye laboratory to characterize other retroviral restriction factors, the Bishop lab developed a two-color restriction assay to analyze SAMHD1 in U937 cells. Murine Leukaemia Virus-like particles expressing SAMHD1, alongside YFP expressed from an IRES, are used to transduce U937 cells. Cells are then treated with phorbol myristate acetate to induce differentiation to a quiescent phenotype. Following differentiation, cells are infected with HIV-1 virus-like particles expressing a fluorescent reporter. After 48 h, cells are harvested and analyzed by flow cytometry. The proportion of HIV-infected cells in the SAMHD1-expressing population is compared to that in internal control cells lacking SAMHD1. This comparison reveals a restriction ratio. SAMHD1 expression leads to a five-fold reduction in HIV infection, corresponding to a restriction ratio of 0.2. Our recent substitution of RFP for the original GFP as the reporter gene for HIV infection has facilitated flow cytometry analysis.
This assay has been successfully used to characterize the effect of amino acid substitutions on SAMHD1 restriction by transducing with viruses encoding altered SAMHD1 proteins, derived from site-directed mutagenesis of the expression vector. For example, the catalytic site substitutions HD206-7AA show a restriction phenotype of 1, indicating a loss of restriction activity. Equally, the susceptibility of different tester viruses can be determined. The assay can be further adapted to incorporate the effect of differentiation status, metabolic status, and SAMHD1 modifiers to better understand the relationship between SAMHD1, cell metabolic state, and viral restriction.

Described here is an established method to determine the extent of HIV-1 restriction by the cellular inhibitory protein SAMHD1. Human myeloid lineage U937 cells are transduced with a SAMHD1 expression vector co-expressing YFP, differentiated and then challenged with HIV-RFP. The level of restriction is determined by flow cytometry analysis.

Sterile &#945;-motif/histidine-aspartate domain-containing protein 1 (SAMHD1) inhibits replication of HIV-1 in quiescent myeloid cells. U937 cells are ...