Name: opsono-adherence assay to evaluate functional antibodies in vaccine development against bacillus anthracis and other encapsulated pathogens
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Description: Watch this Scientific Journal Video about Opsono-Adherence Assay to Evaluate Functional Antibodies in Vaccine Development Against Bacillus anthracis and Other Encapsulated Pathogens at JoVE.com

J. Chua, D. Chabot and A. Friedlander designed the procedures described in the manuscript. J. Chua and T. Putmon-Taylor performed the experiments. D. Chabot performed data analysis. J. Chua wrote the manuscript.
The authors thank Kyle J. Fitts for excellent technical assistance.
The work was supported by the Defense Threat Reduction Agency grant CBM.VAXBT.03.10.RD.015, plan number 921175.
Opinions, interpretations, conclusions and recommendations are those of the authors and are not necessarily endorsed by the U. S. Army. The content of this publication does not necessarily reflect the views or policies of the Department of Defense, nor does mention of trade names, commercial products, or organizations imply endorsement by the U. S. Government.

In compliance with the Animal Welfare Act, Public Health Service policy, and other federal statutes and regulations pertaining to animals and experiments involving animals, the research described here was conducted under an Institutional Animal Care and Use Committee&#8211;approved protocol. The facility where this research was conducted is accredited by the Association for Assessment and Accreditation of Laboratory Animal Care, International and adheres to principles stated in the Guide for the Care and Use of Laborator...

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Capsule based vaccines have been shown to be efficacious against numerous bacterial pathogens, and many are licensed for use in humans25,26,27. These vaccines work by generating antibodies targeting the capsule and many of these studies use the OPKA to show the opsono-phagocytic functions of the antibodies13,14,16,<sup class=...

Recognition, adherence, internalization, and degradation of a pathogen are integral to phagocytosis1, a salient pathway in the host innate immune response first described by Ilya Metchnikoff in 18832,3. Phagocytic leukocytes, as well as other cells of the immune system, are highly discriminatory in their selection of targets; they are able to distinguish between &#8220;infectious non-self&#8221; and &#8220;non-infectious self&#8221; through pathogen associated molecular patterns by their repertoire of pattern recognition receptors (PRRs)4,5. Host recognition of a pathogen may also occur with the binding of host&#160;opsonins, such as complement and antibodies6. This process, called opsonization, coats the pathogen with these molecules, enhancing internalization upon binding to opsonic receptors (e.g., complement and Fc receptors) on phagocytic cells6. For a pathogen to adhere to a phagocyte, collective binding of multiple receptors with their cognate ligands is necessary. Only then can adherence trigger and sustain signaling cascades inside the host cell to initiate internalization6.
Due to the importance of phagocytosis in the clearance of pathogens and prevention of infection, extracellular pathogens have developed numerous ways to subvert this process to prolong their survival. One strategy of importance is the production of an anionic polymeric (e.g., polysaccharide or polyamino acid) capsule which is anti-phagocytic by virtue of its charge, is poorly immunogenic, and shields molecules on the bacterial envelope from PRRs6,7. Pathogens such as Cryptococcus neoformans and Streptococcus pneumoniae have capsules composed of saccharide polymers, whereas Staphylococcus epidermidis and some Bacillus species produce poly-&#611;-glutamic acid (PGGA)7,8. Yet other pathogens produce capsules that resemble the non-infectious self. For example, Streptococcus pyogenes and a pathogenic strain of B. cereus have a hyaluronic acid capsule that is not only anti-phagocytic but which also may not be recognized as foreign by the immune system9,10.
Conjugation of capsule to carrier proteins converts them from poor, T-independent antigens into highly immunogenic T-dependent antigens that can induce high serum anti-capsule antibody titers11,12. This strategy is employed for licensed vaccines against S. pneumoniae, Haemophilus influenzae, and Neisseria meningitides11. The opsonic activities of anti-capsule antibodies have commonly been evaluated by&#160;opsono-phagocytic killing assays (OPKA)13,14,15,16. These&#160;assays test&#160;whether functional antibodies can trigger phagocytosis and killing14. However, the use of OPKA with infectious pathogens, such as Tier 1 Biological Select Agents and Toxins (BSAT), including B. anthracis17, is hazardous and presents security risks; these assays necessitate extensive handling of a select agent. Select agent handling can only be done in restricted biosafety level 3 (BSL-3) laboratories; work in these areas demands protracted operating procedures due to the numerous safety and security precautions that must be followed. BSL-3 laboratories are also typically not equipped with the specialized equipment used for OPKA work, such as microscopes and cytometers. Thus, we developed an alternative assay based on the use of inactivated bacteria18,19. We refer to this as an opsono-adherence assay (OAA) that is not dependent on internalization and killing as assay outputs; instead, adherence of opsonized inactivated pathogens is used as an index of phagocytosis. Mechanistically, OAA is a suitable substitute because adherence occurs a priori and is intimately intertwined with internalization and intracellular killing. From a biosafety perspective, OAA is preferred because it requires minimal handling of an infectious agent, is experimentally of shorter duration than OPKA, and can be performed in BSL-2 laboratories after a stock of the inactivated pathogen has been produced and transferred.
We demonstrate the utilization of OAA to examine the opsonic function of anti-capsule antibodies found in sera of non-human primates (NHPs) vaccinated with a capsule conjugate [i.e. PGGA from B. anthracis conjugated to the outer membrane protein complex (OMPC) of Neisseria meningitides]20. Serum opsonized bacilli were incubated with an adherent mouse macrophage cell line, RAW 264.7. After fixation, the cell monolayer and adherent bacilli were imaged by fluorescence microscopy. Bacterial adherence increased when the bacilli were incubated with serum from NHPs vaccinated with the capsule conjugate compared to control serum20. Adherence correlated with survival of the anthrax challenge20,21. Thus, the use of OAA characterized the function of anti-capsule antibodies and greatly facilitated testing of our vaccine candidate.&#160;&#160; &#160;

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			<td height="20" style="height:20px;width:380px;">0.20 &#181;m syringe filter (25mm, regenerated cellulose)</td>
			<td style="width:483px;">Corning, Corning, NY</td>
			<td style="width:267px;">431222</td>
			<td style="width:391px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">10 mL syringe (Luer-Lok tip)</td>
			<td>BD, Franklin Lakes, NJ</td>
			<td>302995</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">15&#181; 96 well black plates (plate #1 for imaging)</td>
			<td>In Vitro Scientific, Sunnyvale, CA</td>
			<td>P96-1-N</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">16% paraformaldehyde</td>
			<td>Electron Microscopy Science, Hatfield, PA</td>
			<td>15710</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">75 cm sq. tissue culture treated flask</td>
			<td>Corning, Corning, NY</td>
			<td>430641</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Agar (powder)</td>
			<td>Sigma-Aldrich, St. Louis, MO</td>
			<td>A1296</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Baby Rabbit Complement</td>
			<td>Cedarlane Labs, Burlington, NC</td>
			<td>CL3441</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Bacto Yeast Extract</td>
			<td>BD, Sparks, MD</td>
			<td>288620</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">BBL Brain Heart Infusion (BHI)</td>
			<td>BD, Sparks, MD</td>
			<td>211059</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Blood Agar (TSA with Sheep Blood) plates</td>
			<td>Remel, Lenexa, KS</td>
			<td>R01198</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Cell scraper</td>
			<td>Sarstedt, Newton, NC</td>
			<td>83.183</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Costar 96 well cell culture plates (plates #2 &#38; 3 for dilutions)</td>
			<td>Corning, Corning, NY</td>
			<td>3596</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Cover glass</td>
			<td>Electron Microscopy Science, Hatfield, PA</td>
			<td>72200-10</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Difco Nutrient Broth</td>
			<td>BD, Sparks, MD</td>
			<td>234000</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Dulbecco&#39;s Modified Eagle Medium (DMEM), high glucose</td>
			<td>Gibco, Thermo Fisher Scientific, Waltham, MA</td>
			<td>11965-092</td>
			<td>contains 4500 mg/L glucose, 4 mM L-glutamine, Phenol Red</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">EVOS FL Auto Cell Imaging System (fluorescence microscope)</td>
			<td>Life Technologies, Thermo Fisher Scientific, Waltham, MA</td>
			<td>AMAFD1000</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Fetal Bovine Serum</td>
			<td>Hyclone, GE Healthcare Life Sciences, South Logan, UT</td>
			<td>SH30071.03</td>
			<td>not gamma irradiated, not heat inactivated</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Fluorescein isothiocyanate</td>
			<td>Invitrogen, Thermo Fisher Scientific, Waltham, MA</td>
			<td>F143</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HCS Cell Mask Orange Cell Stain</td>
			<td>Invitrogen, Thermo Fisher Scientific, Waltham, MA</td>
			<td>H32713</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">hemocytometer (Improved Neubauer)</td>
			<td>Hausser Scientific, Horsham, PA</td>
			<td>3900</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">India Ink solution</td>
			<td>BD, Sparks, MD</td>
			<td>261194</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">L- glutamine (200 mM)</td>
			<td>Gibco, Thermo Fisher Scientific, Waltham MA</td>
			<td>25030081</td>
			<td>supplement medium with additional 2mM L-glutamine</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Nikon Eclipse TE2000-U (inverted compound microscope)</td>
			<td>Nikon Instruments, Melville, NY</td>
			<td>TE2000</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">PBS without Calcium or Magnesium</td>
			<td>Lonza, Walkersville, MD</td>
			<td>17-516F</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Penicillin-Streptomycin Solution, 100x</td>
			<td>Hyclone, GE Healthcare Life Sciences, South Logan, UT</td>
			<td>SV30010</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">petri dishes (100 x 15 mm)</td>
			<td>Falcon, Corning, Durham, NC</td>
			<td>351029</td>
			<td>for agar plates</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">RAW 264.7 macrophage cell line (Tib47)</td>
			<td>ATCC, Manassas, VA</td>
			<td>ATCC TIB-71</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Slides</td>
			<td>VWR, Radnor, PA</td>
			<td>16004-422</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sodium Bicarbonate</td>
			<td>Sigma-Aldrich, St. Louis, MO</td>
			<td>S5761</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Trypan Blue Solution (0.4%)</td>
			<td>Sigma-Aldrich, St. Louis, MO</td>
			<td>T8154</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Zeiss 700 Laser Scanning Microscopy (confocal microscope)</td>
			<td>Carl Zeiss Microimaging, Thornwood, NY</td>
			<td>4109001865956000</td>
			<td></td>
		</tr>
	</tbody>
</table>

opsono-adherence assay to evaluate functional antibodies in vaccine development against bacillus anthracis and other encapsulated pathogens

The opsono-adherence assay is a functional assay that enumerates the attachment of bacterial pathogens to professional phagocytes. Because adherence is requisite to phagocytosis and killing, the assay is an alternative method to&#160;opsono-phagocytic killing assays. An advantage of the opsono-adherence&#160;assay is the option of using inactivated pathogens and mammalian cell lines, which allows standardization across multiple experiments. The use of an inactivated pathogen in the assay also facilitates work with biosafety level 3 infectious agents and other virulent pathogens. In our work, the opsono-adherence assay was used to assess the functional ability of antibodies, from sera of animals immunized with an anthrax capsule-based vaccine, to induce adherence of fixed Bacillus anthracis to a mouse macrophage cell line, RAW 264.7. Automated fluorescence microscopy was used to capture images of bacilli adhering to macrophages. Increased adherence was correlated with the presence of anti-capsule antibodies in the serum. Non-human primates that exhibited high serum anti-capsule antibody concentrations were protected from anthrax challenge. Thus, the opsono-adherence assay can be used to elucidate the biological functions of antigen specific antibodies in sera, to evaluate the efficacy of vaccine candidates and other therapeutics, and to serve as a possible correlate of immunity.&#160;&#160;&#160;&#160;&#160;&#160;

This section shows representative micrographs collected during an OAA experiment along with results&#160;showing that the OAA can be used to examine the biological function of antibodies. Here, the assay was successfully used to evaluate the efficacy of an anthrax vaccine candidate. It is critical to verify the state of encapsulation on the bacilli as little to no encapsulation causes them to adhere to host cells, producing a high background. Figure 1 is an image of B. anthracis Ame...

Watch this Scientific Journal Video about Opsono-Adherence Assay to Evaluate Functional Antibodies in Vaccine Development Against Bacillus anthracis and Other Encapsulated Pathogens at JoVE.com

Opsono-Adherence Assay to Evaluate Functional Antibodies in Vaccine Development Against Bacillus anthracis and Other Encapsulated Pathogens

The opsono-adherence assay is an alternative method to the opsono-phagocytic killing assay to evaluate the opsonic functions of antibodies in vaccine development.

Opsono-Adherence Assay to Evaluate Functional Antibodies in Vaccine Development Against Bacillus anthracis and Other Encapsulated Pathogens

The opsono-adherence assay is a functional assay that enumerates the attachment of bacterial pathogens to professional phagocytes. Because adherence is ...

The Opsono-Adherence Assay analyzes the presence of functional oposonic antibodies produced in animals after vaccination, which have been shown to correlate with the efficacy of several licensed human vaccines. This assay is preferred for use with biological select agents and other infectious pathogens and can be performed in a BSL-1 or BSL-2 lab after the inactivated BSL-3 agent is transferred. Antibodies against bacterial capsules, including the Bacillus anthracis capsule, have been demonstrated to be efficacious in animal models of infection.Opsono-Adherence assays functionally evaluate antibodies without infecting animals. Follow all institutional safety and security procedures when working with encapsulated virulent strains of Bacillus anthracis. For this video, we're using an inactivated strain under biosafety level two conditions.Begin this procedure with preparation of RAW 264.7 cells, as described in the text protocol. To plate the cells for the opsono-adherence assay, replace the flask with fresh medium and use a cell scraper to gently scrape cells off the flask. Pipette up and down to break up the cell clumps for easier cell counting.Plate 14, 000 cells per well in a 96-well 0.15 micron thick glass flat bottom plate. Allow cells to grow for three days, replacing spent medium one day before performing the OAA. After three days of incubation, the number of cells should be approximately 50, 000 cells per well.To begin the assay, prepare a master plate of Bacillus anthracis from a spore stock by streaking it for isolation on an NBY agar plate. For demonstration purposes, a sheep blood agar plate was used. Incubate at 37 degrees Celsius for one day before culturing in broth.Then, inoculate 30 milliliters of culture broth in a vented 250 milliliter flask with several colonies of the bacilli. Shake the broth culture at 125 RPM, 37 degrees Celsius, with 20%CO2 and humidity for 18 to 24 hours. Use negative staining with India ink to ensure sufficient encapsulation, and that Bacilli are in short chains prior to fixation.To do so, mix five microliters of bacterial suspension with two microliters of India ink on a microscope slide. Then, place a one or 1.5 micron thick cover glass on top of the suspension without creating bubbles. Observe the bacterial suspension using a 40 times to 100 times oil objective lens on a light microscope.A thick capsule excludes India ink. Ensure that the Bacilli are encapsulated by observing a zone of clearance surrounding each bacterium. Also ensure that the Bacilli chains are short.To determine Colony Forming Units, or CFUs, serially dilute 100 microliters of culture one to 10 in PBS solution, and plate culture dilutions on sheep blood agar plates. Incubate for 12 to 18 hours at 37 degrees Celsius. Count CFUs, and determine the number of bacteria per milliliter of culture.After ensuring that the Bacilli are sufficiently encapsulated, diluted, and plated, fix the remaining bacterial culture by adding 10 milliliters of 16%paraformaldehyde to the 30 milliliters of culture at a final concentration of 4%paraformaldehyde. Transfer the volume to a 50 milliliter conical tube. Then, slowly agitate on a shaker at ambient temperature for seven days.To test for sterility, transfer four milliliters, or 10%volume, of fixed bacterial suspension to a 50 milliliter conical tube. Wash the suspension by adding PBS, and pelleting at a minimum of 3000 G for 45 minutes. Then remove the supernatant, ensuring that the fluffy pellet is not disturbed.After repeating this wash at least two times, resuspend the fixed sample in four milliliters PBS. It's necessary to remove all fixative during the washes so that the fixative does not interfere with the viability testing. If necessary, increase the number of washes.For viability testing, inoculate 40 milliliters of a bacterial growth medium with four milliliters of washed suspension and incubate at 37 degrees Celsius for seven days. Check optical density at 600 nanometers in a spectrophotometer before and after seven days to measure turbidity. After seven days of incubation in broth culture, plate at least 100 microliters of broth onto an agar plate and incubate for another seven days.If no increase in turbidity and no growth on plates are seen, the original culture is considered sterile, and maybe transferred to a BSL-2 laboratory. Follow institutional guidelines for transfer approval. Wash the inactivated bacterial stock three times in PBS to remove fixative.Add FITC solution at a final concentration of 75 micrograms per milliliter. Slowly agitate the mixture for 18 to 24 hours at four degrees Celsius. Wash the bacteria as before to remove excess FITC.After the final wash, resuspend the Bacilli in PBS in the same start volume. and store Bacilli in minus 20 degrees Celsius until use. Heat-inactivate a small volume of test sera from non-human primates at 56 degrees Celsius for 30 minutes in a heat block or PCR machine.Fall and wash FITC-labeled bacteria with PBS two times by pelleting at 15, 000 times G for three to five minutes. Resuspend in PBS in the same start volume. In a 96-well round-bottom plate, serially dilute the test sera in cell medium.In another 96-well round-bottom plate, add 10 microliters of diluted test sera into each well. Then, add 10 microliters of freshly reconstituted baby rabbit compliment. To plate number three, add the appropriate volume of FITC-labeled Bacilli for a multiplicity of infection of 20.For example, at a volume containing 50, 000 times 20 Bacilli per 50, 000 cells. Top off each well in plate number three with the appropriate volume of cell medium to a total of 105 microliters. Incubate plate number three at 37 degrees Celsius for 30 minutes in the presence of 5%CO2 with humidity to opsonize Bacilli.Place plate number one, which contains adherence cells, on a 37 degrees Celsius heat block. Use a multi-channel pipetter to remove spent medium from wells, and quickly replace with 100 microliters of opsonize bacteria from plate number three, ensuring no bubbles are generated in the wells during pipetting. To not disturb the cell monolayer, add volume to the sides of the wells.Incubate plate number one at 37 degrees Celsius with 5%CO2 and humidity for 30 minutes for adherence. Wash each well five times with 150 microliters of PBS, on top of the 37 degrees Celsius heat block, to remove unattached Bacilli. Pipette to the side of the wells to ensure that the cells are not accidentally dispersed during washing.Add 150 microliters of 4%paraformaldehyde to each well, and fix the cells for one hour. After washing the cells twice with PBS, mix two microliters of high-content screening orange cells stain in 10 milliliters of PBS. Then, add 150 microliters of this staining solution to fix cells, and incubate for 30 minutes at ambient temperature.Place plate number one on the stage and focus on the cells using brightfield or phase contrast. In the Acquisition tab, select 96-well format as the plate setting. Then, select Channel settings.Next, select setting to Tile mode. Indicate the number of images to be acquired. Change the Acquisition mode to black and white or monochrome, and set the Binning to at least two by two.Turn on the Autofocus or focusing module. Indicate how often the autofocusing function is to be performed. Next, turn on the Z-Stack function, if available.Indicate the number of Z-Stacks that will capture the thickness of the cell monolayer and adherent Bacilli. Designate a file folder to save the images to. Now, run the automated imaging program.Perform data collection and analysis as described in the text protocol. The Ames strain of bacillus anthracis was negatively stained with India ink to examine encapsulation. The state of encapsulation must be verified, as little to no encapsulation causes them to adhere to host cells without antibodies, producing a high background.Fluorescence intensity and photo bleaching characteristics of the Bacilli was examined using Confocal Microscopy. It is critical to verify that the fluorescence of the Bacilli do not significantly fade over time, because the Bacilli will undergo long exposures to light during imaging. The maximum projection images of Bacillus anthracis attach to the cell monolayers are shown here.These are representative fields of view that were counted and scored for the opsono-adherence assay. The increase in attachment of Bacilli incubated with capsule conjugate antiserum is due to the presence of anti-capsule antibodies that opsonized the Bacilli. The serum titers of non-human primates vaccinated with 10 and 50 micrograms of capsule conjugate are significantly higher than the titers for conjugate and capsule alone.We are developing a similar assay that uses flow cytometry and human neutrophils, which are nonadherent cells, to measure opsonic activity and also to quantitate capsule on the surface of bacteria. After watching this video, you should have a good understanding of the opsono-adherence assay. Don't forget that working with BSL-3 pathogens is extremely hazardous.Institutional guidelines and safety precautions must be strictly followed.

opsono-adherence-assay-to-evaluate-functional-antibodies-vaccine

Research

JoVE Journal

Immunology and Infection

Passive Administration of Monoclonal Antibodies Against H. capsulatum and Others Fungal Pathogens

The purpose of the use of this methodology is 1) to advance our capacity to protect individuals with antibody or vaccine for preventing or treating histoplasmosis caused by the fungus Histoplasma capsulatum and 2) to examine the role of virulence factors as target for therapy. To generate mAbs, mice are immunized, the immune responses are assessed using a solid phase ELISA system developed in our laboratory, and the best responder mice are selected for isolation of splenocytes for fusion with hybridoma cells. C57BL/6 mice have been extensively used to study H. capsulatum pathogenesis and provide the best model for obtaining the data required. In order to assess the role of the mAbs in infection, mice are intraperitoneally administered with either mAb to H. capsulatum or isotype matched control mAb and then infected by either intravenous (i.v.), intraperitoneal (i.p.), or intranasal (i.n.) routes. In the scientific literature, efficacy of mAbs for fungal infections in mice relies on mortality as an end point, in conjunction with colony formin units (CFU) assessments at earlier time points. Survival (time to death) studies are necessary as they best represent human disease. Thus, efficacy of our intervention would not adequately be established without survival curves. This is also true for establishing efficacy of vaccine or testing of mutants for virulence. With histoplasmosis, the mice often go from being energetic to dead over several hours. The capacity of an intervention such as the administration of a mAb may initially protect an animal from disease, but the disease can relapse which would not be realized in short CFU experiments. In addition to survival and fungal burden assays, we examine the inflammatory responses to infection (histology, cellular recruitment, cytokine responses). For survival/time to death experiments, the mice are infected and monitored at least twice daily for signs of morbidity. To assess fungal burden, histopathology, and cytokine responses, the mice are euthanized at various times after infection. Animal experiments are performed according to the guidelines of the Institute for Animal Studies of the Albert Einstein College of Medicine.

Passive Administration of Monoclonal Antibodies Against H. capsulatum and Others Fungal Pathogens

C57BL/6 mice have been used to study Hc pathogenesis and provide the best model. We are exploring the potential benefits of humoral immunity against this fungus and generated several mAbs [to histone H2B and a heat shock protein 60kDa] that we tested for their protective efficacy after intraperitoneal administration.

The purpose of the use of this methodology is 1) to advance our capacity to protect individuals with antibody or vaccine for preventing or treating ...

Generation of Recombinant Arenavirus for Vaccine Development in FDA-Approved Vero Cells

The development and implementation of arenavirus reverse genetics represents a significant breakthrough in the arenavirus field 4. The use of cell-based arenavirus minigenome systems together with the ability to generate recombinant infectious arenaviruses with predetermined mutations in their genomes has facilitated the investigation of the contribution of viral determinants to the different steps of the arenavirus life cycle, as well as virus-host interactions and mechanisms of arenavirus pathogenesis 1, 3, 11 . In addition, the development of trisegmented arenaviruses has permitted the use of the arenavirus genome to express additional foreign genes of interest, thus opening the possibility of arenavirus-based vaccine vector applications 5 . Likewise, the development of single-cycle infectious arenaviruses capable of expressing reporter genes provides a new experimental tool to improve the safety of research involving highly pathogenic human arenaviruses 16 . The generation of recombinant arenaviruses using plasmid-based reverse genetics techniques has so far relied on the use of rodent cell lines 7,19 , which poses some barriers for the development of Food and Drug Administration (FDA)-licensed vaccine or vaccine vectors. To overcome this obstacle, we describe here the efficient generation of recombinant arenaviruses in FDA-approved Vero cells.

Rescue of recombinant arenaviruses from cloned cDNAs, an approach referred to as reverse genetics, allows researchers to investigate the role of specific viral gene products, as well as the contribution of their different specific domains and residues, to many different aspects of the biology of arenavirus. Likewise, reverse genetics techniques in FDA-approved cell lines (Vero) for vaccine development provides novel possibilities for the generation of effective and safe vaccines to combat human pathogenic arenaviruses.

The development and implementation of arenavirus reverse genetics represents a significant breakthrough in the arenavirus field  4. The use of cell-based ...

Cell-based Flow Cytometry Assay to Measure Cytotoxic Activity

Cytolytic activity of CD8+ T cells is rarely evaluated. We describe here a new cell-based assay to measure the capacity of antigen-specific CD8+ T cells to kill CD4+ T cells loaded with their cognate peptide. Target CD4+ T cells are divided into two populations, labeled with two different concentrations of CFSE. One population is pulsed with the peptide of interest (CFSE-low) while the other remains un-pulsed (CFSE-high). Pulsed and un-pulsed CD4+ T cells are mixed at an equal ratio and incubated with an increasing number of purified CD8+ T cells. The specific killing of autologous target CD4+ T cells is analyzed by flow cytometry after coculture with CD8+ T cells containing the antigen-specific effector CD8+ T cells detected by peptide/MHCI tetramer staining. The specific lysis of target CD4+ T cells measured at different effector versus target ratios, allows for the calculation of lytic units, LU30/106 cells. This simple and straightforward assay allows for the accurate measurement of the intrinsic capacity of CD8+ T cells to kill target CD4+ T cells.

This protocol describes a sensitive, cell-based cytotoxicity assay. By enumerating the decrease in frequency of live target CD4+ T cells in the presence of an increasing number of effector CD8+ T cells, this assay allows for the direct assessment of cytolytic activity of antigen-specific CD8+ T cells.

Cytolytic activity of CD8+ T cells is rarely evaluated. We describe here a new cell-based assay to measure the capacity of antigen-specific CD8+ T cells ...

A High-throughput Compatible Assay to Evaluate Drug Efficacy against Macrophage Passaged Mycobacterium tuberculosis

The early drug development process for anti-tuberculosis drugs is hindered by the inefficient translation of compounds with in vitro activity to effectiveness in the clinical setting. This is likely due to a lack of consideration for the physiologically relevant cellular penetration barriers that exist in the infected host. We recently established an alternative infection model that generates large macrophage aggregate structures containing densely packed M. tuberculosis (Mtb) at its core, which was suitable for drug susceptibility testing. This infection model is inexpensive, rapid, and most importantly BSL-2 compatible. Here, we describe the experimental procedures to generate Mtb/macrophage aggregate structures that would produce macrophage-passaged Mtb for drug susceptibility testing. In particular, we demonstrate how this infection system could be directly adapted to the 96-well plate format showing throughput capability for the screening of compound libraries against Mtb. Overall, this assay is a valuable addition to the currently available Mtb drug discovery toolbox due to its simplicity, cost effectiveness, and scalability.

A High-throughput Compatible Assay to Evaluate Drug Efficacy against Macrophage Passaged Mycobacterium tuberculosis

New models and assays that would improve the early drug development process for next-generation anti-tuberculosis drugs are highly desirable. Here, we describe a quick, inexpensive, and BSL-2 compatible assay to evaluate drug efficacy against Mycobacterium tuberculosis that can be easily adapted for high-throughput screening.

The early drug development process for anti-tuberculosis drugs is hindered by the inefficient translation of compounds with in vitro activity to ...

Generation of Monoclonal Antibodies Against Natural Products

The analysis of the bioactive components present in foods and natural products has become a popular area of study in many fields, including traditional Chinese medicine and food safety/toxicology. Many of the classical analysis techniques require expensive equipment and/or expertise. Notably, enzyme-linked immunosorbent assays (ELISAs) have become an emerging method for the analysis of foods and natural products. This method is based on antibody-mediated detection of the target components. However, as many of the bioactive components in natural products are small (&lt;1,000 Da) and do not induce an immune response, creating monoclonal antibodies (mAbs) against them is often difficult. In this protocol, we provide a detailed explanation of the steps required to generate mAbs against target molecules as well as those needed to create the associated indirect competitive (ic)ELISA for the rapid analysis of the compound in multiple samples. The procedure describes the synthesis of the artificial antigen (i.e., the hapten-carrier conjugate), immunization, cell fusion, monoclonal hybridoma preparation, characterization of the mAb, and the ELISA-based application of the mAb. The hapten-carrier conjugate was synthesized by the sodium periodate method and evaluated by MALDI-TOF-MS. After immunization, splenocytes were isolated from the immunized mouse with the highest antibody titer and fused with the hypoxanthine-aminopterin-thymidine (HAT)-sensitive mouse myeloma cell line Sp2/0 -Ag14 using a polyethylene glycol (PEG)-based method. The hybridomas secreting mAbs reactive to the target antigen were screened by icELISA for specificity and cross-reactivity. Furthermore, the limiting dilution method was applied to prepare monoclonal hybridomas. The final mAbs were further characterized by icELISA and then utilized in an ELISA-based application for the rapid and convenient detection of the example hapten (naringin (NAR)) in natural products.

This article provides a detailed protocol for the preparation and evaluation of monoclonal antibodies against natural products for use in various immunoassays. This procedure includes immunization, cell fusion, indirect competitive ELISA for positive clone screening, and monoclonal hybridoma preparation. The specifications for antibody characterization using MALDI-TOF-MS and ELISA analyses are also provided.

The analysis of the bioactive components present in foods and natural products has become a popular area of study in many fields, including traditional ...

Opsonophagocytic Killing Assay to Assess Immunological Responses Against Bacterial Pathogens

A key aspect of the immune response to bacterial colonization of the host is phagocytosis. An opsonophagocytic killing assay (OPKA) is an experimental procedure in which phagocytic cells are co-cultured with bacterial units. The immune cells will phagocytose and kill the bacterial cultures in a complement-dependent manner. The efficiency of the immune-mediated cell killing is dependent on a number of factors and can be used to determine how different bacterial cultures compare with regard to resistance to cell death. In this way, the efficacy of potential immune-based therapeutics can be assessed against specific bacterial strains and/or serotypes. In this protocol, we describe a simplified OPKA that utilizes basic culture conditions and cell counting to determine bacterial cell viability after co-culture with treatment conditions and HL-60 immune cells. This method has been successfully utilized with a number of different pneumococcal serotypes, capsular and acapsular strains, and other bacterial species. The advantages of this OPKA protocol are its simplicity, versatility (as this assay is not limited to antibody treatments as opsonins), and minimization of time and reagents to assess basic experimental groups.

This opsonophagocytic killing assay is used to compare the ability of phagocytic immune cells to respond to and kill bacteria based on different treatments and/or conditions. Classically, this assay serves as the gold&#160;standard for assessing effector functions of antibodies raised against a bacterium as opsonin.

A key aspect of the immune response to bacterial colonization of the host is phagocytosis. An opsonophagocytic killing assay (OPKA) is an experimental ...

Using Human Induced Pluripotent Stem Cell-derived Intestinal Organoids to Study and Modify Epithelial Cell Protection Against Salmonella and Other Pathogens

The intestinal &#8216;organoid&#8217; (iHO) system, wherein 3-D structures representative of the epithelial lining of the human gut can be produced from human induced pluripotent stem cells (hiPSCs) and maintained in culture, provides an exciting opportunity to facilitate the modeling of the epithelial response to enteric infections. In vivo, intestinal epithelial cells (IECs) play a key role in regulating intestinal homeostasis and may directly inhibit pathogens, although the mechanisms by which this occurs are not fully elucidated. The cytokine interleukin-22 (IL-22) has been shown to play a role in the maintenance and defense of the gut epithelial barrier, including inducing a release of antimicrobial peptides and chemokines in response to infection.
We describe the differentiation of healthy control hiPSCs into iHOs via the addition of specific cytokine combinations to their culture medium before embedding them into a basement membrane matrix-based prointestinal culture system. Once embedded, the iHOs are grown in media supplemented with Noggin, R-spondin-1, epidermal growth factor (EGF), CHIR99021, prostaglandin E2, and Y-27632 dihydrochloride monohydrate. Weekly passages by manual disruption of the iHO ultrastructure lead to the formation of budded iHOs, with some exhibiting a crypt/villus structure. All iHOs demonstrate a differentiated epithelium consisting of goblet cells, enteroendocrine cells, Paneth cells, and polarized enterocytes, which can be confirmed via immunostaining for specific markers of each cell subset, transmission electron microscopy (TEM), and quantitative PCR (qPCR). To model infection, Salmonella enterica serovar Typhimurium SL1344 are microinjected into the lumen of the iHOs and incubated for 90 min at 37 &#176;C, and a modified gentamicin protection assay is performed to identify the levels of intracellular bacterial invasion. Some iHOs are also pretreated with recombinant human IL-22 (rhIL-22) prior to infection to establish whether this cytokine is protective against Salmonella infection.

Using Human Induced Pluripotent Stem Cell-derived Intestinal Organoids to Study and Modify Epithelial Cell Protection Against Salmonella and Other Pathogens

Human induced pluripotent stem cell (hiPSC)-derived intestinal organoids offer exciting opportunities to model enteric diseases in vitro. We demonstrate the differentiation of hiPSCs into intestinal organoids (iHOs), the stimulation of these iHOs with cytokines, and the microinjection of Salmonella Typhimurium into the iHO lumen, enabling the study of an epithelial invasion by this pathogen.

The intestinal &#8216;organoid&#8217; (iHO) system, wherein 3-D structures representative of the epithelial lining of the human gut can be produced from ...

In Vitro ELISA Test to Evaluate Rabies Vaccine Potency

The growing global concern for the animal welfare is encouraging manufacturers and the National Control Laboratories (OMCLs) to follow the 3Rs strategy for the Replacement, Reduction, and Refinement of the laboratory animal testing. The development of in vitro approaches is recommended at the WHO and European levels as alternatives to the NIH test for evaluating the rabies vaccine potency. At the surface of the rabies virus (RABV) particle, trimers of glycoprotein constitute the major immunogen to induce Viral Neutralizing Antibodies (VNAbs). An ELISA test, where Neutralizing Monoclonal Antibodies (mAb-D1) recognize the trimeric form of the glycoprotein, has been developed to determine the contents of the native folded trimeric glycoprotein along with the production of the vaccine batches. This in vitro potency test demonstrated a good concordance with the NIH test and has been found suitable in collaborative trials by RABV vaccine manufacturers and OMCLs. Avoidance of animal use is an achievable objective in the near future.
The method presented is based on an indirect ELISA sandwich immunocapture using the mAb-D1 which recognizes the antigenic sites III (aa 330 to 338) of the trimeric RABV glycoprotein, i.e., the immunogenic RABV antigen. mAb-D1 is used for both coating and detection of glycoprotein trimers present in the vaccine batch. Since the epitope is recognized because of its conformational properties, the potentially denatured glycoprotein (less immunogenic) cannot be captured and detected by the mAb-D1. The vaccine to be tested is incubated in a plate sensitized with the mAb-D1. Bound trimeric RABV glycoproteins are identified by adding the mAb-D1 again, labeled with peroxidase and then revealed in the presence of substrate and chromogen. Comparison of the absorbance measured for the tested vaccine and the reference vaccine allows for the determination of the immunogenic glycoprotein content.

Here we describe an indirect ELISA sandwich immunocapture to determine the immunogenic glycoprotein contents in rabies vaccines. This test uses a neutralizing Monoclonal Antibody (mAb-D1) recognizing glycoprotein trimers. It is an alternative to the in vivo NIH test to follow the consistency of vaccine potency during production.

The growing global concern for the animal welfare is encouraging manufacturers and the National Control Laboratories (OMCLs) to follow the 3Rs strategy ...

Use of an Influenza Antigen Microarray to Measure the Breadth of Serum Antibodies Across Virus Subtypes

The influenza virus remains a significant cause of mortality worldwide due to the limited effectiveness of currently available vaccines. A key challenge to the development of universal influenza vaccines is high antigenic diversity resulting from antigenic drift. Overcoming this challenge requires novel research tools to measure the breadth of serum antibodies directed against many virus strains across different antigenic subtypes. Here, we present a protocol for analyzing the breadth of serum antibodies against diverse influenza virus strains using a protein microarray of influenza antigens.
This influenza antigen microarray is constructed by printing purified hemagglutinin and neuraminidase antigens onto a nitrocellulose-coated membrane using a microarray printer. Human sera are incubated on the microarray to bind antibodies against the influenza antigens. Quantum-dot-conjugated secondary antibodies are used to simultaneously detect IgG and IgA antibodies binding to each antigen on the microarray. Quantitative antibody binding is measured as fluorescence intensity using a portable imager. Representative results are shown to demonstrate assay reproducibility in measuring subtype-specific and cross-reactive influenza antibodies in human sera.
Compared to traditional methods such as ELISA, the influenza antigen microarray provides a high throughput multiplexed approach capable of testing hundreds of sera for multiple antibody isotypes against hundreds of antigens in a short time frame, and thus has applications in sero-surveillance and vaccine development. A limitation is the inability to distinguish binding antibodies from neutralizing antibodies.

We present a protocol for using a protein microarray constructed by printing influenza antigens onto nitrocellulose-coated slides to simultaneously probe serum for multiple antibody isotypes against over 250 antigens from different virus strains, thus allowing measurement of the breadth of serum antibodies across virus subtypes.

The influenza virus remains a significant cause of mortality worldwide due to the limited effectiveness of currently available vaccines. A key challenge ...

Determination of Chemical Inhibitor Efficiency against Intracellular Toxoplasma Gondii Growth Using a Luciferase-Based Growth Assay

Toxoplasma gondii is a protozoan pathogen that widely affects the human population. The current antibiotics used for treating clinical toxoplasmosis are limited. In addition, they exhibit adverse side effects in certain groups of people. Therefore, discovery of novel therapeutics for clinical toxoplasmosis is imperative. The first step of novel antibiotic development is to identify chemical compounds showing high efficacy in inhibition of parasite growth using a high throughput screening strategy. As an obligate intracellular pathogen, Toxoplasma can only replicate within host cells, which prohibits the use of optical absorbance measurements as a quick indicator of growth. Presented here is a detailed protocol for a luciferase-based growth assay. As an example, this method is used to calculate the doubling time of wild-type Toxoplasma parasites and measure the efficacy of morpholinurea-leucyl-homophenyl-vinyl sulfone phenyl (LHVS, a cysteine protease-targeting compound) regarding inhibition of parasite intracellular growth. Also described, is a CRISPR-Cas9-based gene deletion protocol in Toxoplasma using 50 bp homologous regions for homology-dependent recombination (HDR). By quantifying the inhibition efficacies of LHVS in wild-type and TgCPL (Toxoplasma cathepsin L-like protease)-deficient parasites, it is shown that LHVS inhibits wild-type parasite growth more efficiently than &#916;cpl growth, suggesting that TgCPL is a target that LHVS binds to in Toxoplasma. The high sensitivity and easy operation of this luciferase-based growth assay make it suitable for monitoring Toxoplasma proliferation and evaluating drug efficacy in a high throughput manner.

Determination of Chemical Inhibitor Efficiency against Intracellular Toxoplasma Gondii Growth Using a Luciferase-Based Growth Assay

Presented here is a protocol to evaluate the inhibition efficacy of chemical compounds against in vitro intracellular growth of Toxoplasma gondii using a luciferase-based growth assay. The technique is used to confirm inhibition specificity by genetic deletion of the corresponding target gene. The inhibition of LHVS against TgCPL protease is evaluated as an example.

Toxoplasma gondii is a protozoan pathogen that widely affects the human population. The current antibiotics used for treating clinical toxoplasmosis are ...