Name: opsonophagocytic killing assay to assess immunological responses against bacterial pathogens
Uploaded: 2019-04-05T14:00:00
Description: Watch this Scientific Journal Video about Opsonophagocytic Killing Assay to Assess Immunological Responses Against Bacterial Pathogens at JoVE.com

We thank Dr. Moon Nahm (University of Alabama Birmingham) for his invaluable assistance in establishing OPKA assays in our laboratory. This work was supported by National Institutes of Health Grant 1R01AI123383-01A1 to FYA.

1. Culture, Differentiation, and Validation of HL-60 Cells

<ol>
	<li>Prepare HL-60 cell culture media composed of 500 mL RPMI with L-glutamine and 50 mL heat-inactivated fetal bovine serum. Do not add antibiotics as this may affect the differentiation of the HL-60 cells.</li>
	<li>For propagation/maintenance of HL-60 cells, culture 5 x 106 cells in 10 mL of HL-60 cell culture media in 75 cm2 vented flasks at 37 &#176;C and 5% CO2. Passage cells every 3&#8722;4 days to maintain o...

<ol>
	<li>Romero-Steiner, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Standardization+of+an+opsonophagocytic+assay+for+the+measurement+of+functional+antibody+activity+against+Streptococcus+pneumoniae+using+differentiated+HL-60+cells.">Standardization of an opsonophagocytic assay for the measurement of functional antibody activity against Streptococcus pneumoniae using differentiated HL-60 cells.</a> Clinical and Diagnostic Laboratory Immunology. 4 (4), 415-422 (1997).</li><li>Nanra, J. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capsular+polysaccharides+are+an+important+immune+evasion+mechanism+for+Staphylococcus+aureus.">Capsular polysaccharides are an important immune evasion mechanism for Staphylococcus aureus.</a> Human Vaccines and Immunotherapeutics. 9 (3), 480-487 (2013).</li><li>Ishibashi, K., Yamaguchi, O., Shiraiwa, Y., Ogihara, M., Shigeta, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combination+therapy+of+Pseudomonas+aeruginosa+pyelonephritis+in+neutropenic+mice+with+human+antilipopolysaccharide+monoclonal+antibody+and+cefsulodin.">Combination therapy of Pseudomonas aeruginosa pyelonephritis in neutropenic mice with human antilipopolysaccharide monoclonal antibody and cefsulodin.</a> Journal of Urology. 155 (6), 2094-2097 (1996).</li><li>Middleton, D. R., Paschall, A. V., Duke, J. A., Avci, F. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enzymatic+Hydrolysis+of+Pneumococcal+Capsular+Polysaccharide+Renders+the+Bacterium+Vulnerable+to+Host+Defense.">Enzymatic Hydrolysis of Pneumococcal Capsular Polysaccharide Renders the Bacterium Vulnerable to Host Defense.</a> Infection and Immunity. , (2018).</li><li>Baker, C. J., Noya, F. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Potential+use+of+intravenous+immune+globulin+for+group+B+streptococcal+infection.">Potential use of intravenous immune globulin for group B streptococcal infection.</a> Reviews of Infectious Diseases. 12, 476-482 (1990).</li><li>Tian, H., Weber, S., Thorkildson, P., Kozel, T. R., Pirofski, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficacy+of+opsonic+and+nonopsonic+serotype+3+pneumococcal+capsular+polysaccharide-specific+monoclonal+antibodies+against+intranasal+challenge+with+Streptococcus+pneumoniae+in+mice.">Efficacy of opsonic and nonopsonic serotype 3 pneumococcal capsular polysaccharide-specific monoclonal antibodies against intranasal challenge with Streptococcus pneumoniae in mice.</a> Infection and Immunity. 77 (4), 1502-1513 (2009).</li><li>Parameswarappa, S. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Semi-synthetic+Oligosaccharide+Conjugate+Vaccine+Candidate+Confers+Protection+against+Streptococcus+pneumoniae+Serotype+3+Infection.">A Semi-synthetic Oligosaccharide Conjugate Vaccine Candidate Confers Protection against Streptococcus pneumoniae Serotype 3 Infection.</a> Cell Chemical Biology. 23 (11), 1407-1416 (2016).</li><li>Jackson, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Randomized+clinical+trial+of+a+single+versus+a+double+dose+of+13-valent+pneumococcal+conjugate+vaccine+in+adults+55+through+74+years+of+age+previously+vaccinated+with+23-valent+pneumococcal+polysaccharide+vaccine.">Randomized clinical trial of a single versus a double dose of 13-valent pneumococcal conjugate vaccine in adults 55 through 74 years of age previously vaccinated with 23-valent pneumococcal polysaccharide vaccine.</a> Vaccine. 36 (5), 606-614 (2018).</li><li>Cywes-Bentley, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antibody+to+a+conserved+antigenic+target+is+protective+against+diverse+prokaryotic+and+eukaryotic+pathogens.">Antibody to a conserved antigenic target is protective against diverse prokaryotic and eukaryotic pathogens.</a> Proceedings of the National Academy of Sciences of the USA. 110 (24), 2209-2218 (2013).</li><li>Fleck, R. A., Romero-Steiner, S., Nahm, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+HL-60+cell+line+to+measure+opsonic+capacity+of+pneumococcal+antibodies.">Use of HL-60 cell line to measure opsonic capacity of pneumococcal antibodies.</a> Clinical and Diagnostic Laboratory Immunology. 12 (1), 19-27 (2005).</li><li>Collins, S. J., Ruscetti, F. W., Gallagher, R. E., Gallo, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Terminal+differentiation+of+human+promyelocytic+leukemia+cells+induced+by+dimethyl+sulfoxide+and+other+polar+compounds.">Terminal differentiation of human promyelocytic leukemia cells induced by dimethyl sulfoxide and other polar compounds.</a> Proceedings of the National Academy of Sciences of the USA. 75 (5), 2458-2462 (1978).</li><li>Melnick, N., Rajam, G., Carlone, G. M., Sampson, J. S., Ades, E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+a+novel+therapeutic+approach+to+treating+severe+pneumococcal+infection+using+a+mouse+model.">Evaluation of a novel therapeutic approach to treating severe pneumococcal infection using a mouse model.</a> Clinical and Vaccine Immunology. 16 (6), 806-810 (2009).</li><li>Dwyer, M., Gadjeva, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Opsonophagocytic+assay.">Opsonophagocytic assay.</a> Methods in Molecular Biology. 1100, 373-379 (2014).</li><li>Burton, R. L., Nahm, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+fourfold+multiplexed+opsonophagocytosis+assay+for+pneumococcal+antibodies+against+additional+serotypes+and+discovery+of+serological+subtypes+in+Streptococcus+pneumoniae+serotype+20.">Development of a fourfold multiplexed opsonophagocytosis assay for pneumococcal antibodies against additional serotypes and discovery of serological subtypes in Streptococcus pneumoniae serotype 20.</a> Clinical and Vaccine Immunololgy. 19 (6), 835-841 (2012).</li><li>Clarke, M. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-cost,+high-throughput,+automated+counting+of+bacterial+colonies.">Low-cost, high-throughput, automated counting of bacterial colonies.</a> Cytometry Part A. 77 (8), 790-797 (2010).</li><li>Aanei, C. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Database-guided+Flow-cytometry+for+Evaluation+of+Bone+Marrow+Myeloid+Cell+Maturation.">Database-guided Flow-cytometry for Evaluation of Bone Marrow Myeloid Cell Maturation.</a> Journal of Visualized Experiments. (141), e57867 (2018).</li><li>Hirz, T., Dumontet, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil+Isolation+and+Analysis+to+Determine+their+Role+in+Lymphoma+Cell+Sensitivity+to+Therapeutic+Agents.">Neutrophil Isolation and Analysis to Determine their Role in Lymphoma Cell Sensitivity to Therapeutic Agents.</a> Journal of Visulaized Experiments. (109), e53846 (2016).</li><li>Rieger, A. M., Nelson, K. L., Konowalchuk, J. D., Barreda, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modified+annexin+V/propidium+iodide+apoptosis+assay+for+accurate+assessment+of+cell+death.">Modified annexin V/propidium iodide apoptosis assay for accurate assessment of cell death.</a> Journal of Visualized Experiments. (50), 2597 (2011).</li><li>Blair, O. C., Carbone, R., Sartorelli, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differentiation+of+HL-60+promyelocytic+leukemia+cells:+simultaneous+determination+of+phagocytic+activity+and+cell+cycle+distribution+by+flow+cytometry.">Differentiation of HL-60 promyelocytic leukemia cells: simultaneous determination of phagocytic activity and cell cycle distribution by flow cytometry.</a> Cytometry. 7 (2), 171-177 (1986).</li><li>Middleton, D. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+characterization+of+the+Streptococcus+pneumoniae+type+3+capsule-specific+glycoside+hydrolase+of+Paenibacillus+species+32352.">Identification and characterization of the Streptococcus pneumoniae type 3 capsule-specific glycoside hydrolase of Paenibacillus species 32352.</a> Glycobiology. 28 (2), 90-99 (2018).</li></ol>

OPKAs serve essential roles in assessing antibody mediated immune responses induced by vaccinations6,8. The main significance of this simplified OPKA is the adaptability in the conditions to be tested (i.e., antibodies, enzyme treatments, etc.). In this sense, while this assay can be used to test the contribution of opsonins (i.e., antibodies) in phagocytosis, it can also be used to assess ways to overcome virulence factors (i.e., capsular polysaccharides) that n...

The opsonophagocytic killing assay (OPKA) is a critical tool for linking alterations in bacterial structure or function to subsequent changes in immune response and function. As such, it is frequently used as a complementary assay to determine immune-based efficacy of antibody treatments, vaccine candidates, enzyme optimization, etc. While in vivo assays are necessary to determine effective clearance or protection in a bacterial infection model, the OPKA can be used to assess immune contribution to bacterial cell death at the most basic components: bacteria, immune cells, and experimental treatments. Previous studies have shown that OPKAs can be modified and used for a variety of bacteria and serotypes, including Streptococcus pneumoniae1, Staphylococcus aureus2, Pseudomonas aeruginosa3. Furthermore, these optimized assays can be used to assess different experimental treatments, including the ability of an enzyme to make the bacterium more accessible to complement-mediated immune cells4 and antibody treatments to improve opsonization5. Classically, OPKA assay has been successfully used in basic and clinical research settings as a powerful indicator for protection induced by pathogen-specific antibodies6,7,8,9.
Different types of immune cells may be used for assessment of opsonophagocytic killing. One commonly used phagocytic population is the HL-60 human leukemic cell line. This cell line can be kept as inactivated promyelocytes in culture; however, they can be differentiated into various activated states via different drug treatments10,11. Treatment of HL60 with N,N-dimethylformamide differentiates the cell line into activated neutrophils with strong phagocytic activity11. While HL-60 cells have been optimized and are frequently used for these phagocytosis assays10, other primary polymorphonuclear leukocytes can be used as the immune arm of the experiment12.
Additionally, these assays can be simplified13 or multiplexed14 to look at multiple antibiotic-resistant strains of the bacteria to be tested. The multiplexed method has been made more feasible through the development of software that can efficiently count bacterial colony forming units (CFUs) per spot on an agar plate15. Here, we describe a streamlined method using one bacterial strain, HL-60 cells, baby rabbit complement, and blood agar plates. With this method, multiple treatments can be assessed quickly to address specific research questions on how the innate immune response to bacterial infection can be modulated.

<table border="0" cellpadding="0" cellspacing="0" style="width:636px;" width="637">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:204px;">Annexin V (APC conjugated)</td>
			<td style="width:147px;">BioLegend</td>
			<td style="width:119px;">640919</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:204px;">anti-CD35, human (PE conjugated)</td>
			<td style="width:147px;">BioLegend</td>
			<td style="width:119px;">333405</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:204px;">anti-CD71, human (PE conjugated)</td>
			<td style="width:147px;">BioLegend</td>
			<td style="width:119px;">334105</td>
			<td></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:204px;">bacterial strain to be used (ie, Streptococcus pneumoniae, WU2)</td>
			<td style="width:147px;">Bacterial Respiratory Reference Laboratory (Dr. Moon Nahm)&#160;</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:204px;">blood agar plates</td>
			<td>Hardy Diagnostic</td>
			<td>A10</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:204px;">Fetal Clone serum</td>
			<td>HyClone</td>
			<td>SH30080.03</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:204px;">glycerol</td>
			<td>Sigma</td>
			<td>G9012-1L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:204px;">HL-60 cells</td>
			<td>ATCC</td>
			<td>CCL-240</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:204px;">IgG Isotype Control (PE conjugated)</td>
			<td style="width:147px;">BioLegend</td>
			<td style="width:119px;">400907</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:204px;">N,N-dimethylformamide (DMF)</td>
			<td>Fisher Chemical</td>
			<td>UN2265</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:204px;">propidium iodide</td>
			<td style="width:147px;">Sigma</td>
			<td style="width:119px;">P4864</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:204px;">RPMI media with L-glutamine</td>
			<td>Corning</td>
			<td>10-040-CV</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Validation of HL-60 differentiation should be performed before starting the OPKA. This can be accomplished using flow cytometry to determine the extracellular expression of CD11b, CD35, CD71, and annexin V (Figure 1). Propidium iodide can also be used as a viability marker. After being treated with DMF for 3 days, expression of CD35 should be increased (&#8805;55% of all cells) and expression of CD71 should be decreased (&#8804;20% of all cells). The percentage of annexin V+ and propidium io...

Watch this Scientific Journal Video about Opsonophagocytic Killing Assay to Assess Immunological Responses Against Bacterial Pathogens at JoVE.com

Opsonophagocytic Killing Assay to Assess Immunological Responses Against Bacterial Pathogens

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 ...

This assay links modulation of bacterial structure and function to immune cell based antibacterial activity. As such, a key immunotherapeutic of a potential treatment can be assessed in determining the likelihood of improved bacterial clearance. Opsonophagocytic killing assay traditionally serves as the gold standard for assessing effective functions of antibodies raised against the bacterium as obsonant.This protocol offers simplicity and versatility over existing high throughput standardized assays. In this protocol, we investigate the effects of a drug treatment on streptococcus pneumonia and how these effects translate to improved phagocytosis of the bacterium. Here, we apply the OPKA to streptococcus pneumonia cells.However this protocol can be adopted to assess phagocytic killing of other pathogens by immune cells. Dedicate time to optimize the bacterial stocks and ensure the final CFUs to be counted fall within the optimum range. We strongly recommend using flow cytometry to ensure HL60 cells are viable and active and trying different culture conditions to ensure functionally active cells.Visual demonstration will give a better understanding of how the sample should be plated and how to achieve countable samples. To begin, prepare HL60 cell culture media composed of 500 milliliters RPMI supplemented with L-glutamine and 15 milliliters heat inactivated fetal bovine serum. For propagation and maintenance of HL60 cells, culture five million cells in 10 milliliters of HL60 cell culture media in 75 square centimeter vented flasks at 37 degrees celsius and five percent carbon dioxide.To generate working stocks of HL60 cells, add approximately one million cells per milliliter in HL60 culture media supplemented with 10%dimethyl sulfoxide into one milliliter cryogenic tubes. To differentiate HL60 cells, culture 1.5 times 10 to the seven cells in 15 milliliters of HL60 cell culture media supplemented with 0.6%DMF in sterile filter capped 75 square centimeter flasks at 37 degrees celsius and 5%carbon dioxide for three days prior to OPKA. To prepare the bacterial stock samples, grow the WU2 bacterial strain in an appropriate broth for approximately two to four hours at 37 degrees celsius.Next, pellet the bacteria by centrifugation at six thousand times G for two minutes and resuspend the cells in 10 to 30 milliliters of 15%glycerol in the appropriate broth. Aliquot the bacteria culture into sterile 1.5 milliliter centrifuge tubes and store at 80 degrees celsius. Next, thaw out one vial of bacterial stock in a 37 degree celsius water bath.Pellet the bacterial cells and resuspend in 500 microliters of OBB under sterile conditions. Plate dilutions of the untreated bacterial stock on blood agar plates and culture the plates overnight at 30 degrees celsius. After the incubation step, count the colonies for each dilution of untreated bacterial stock co-cultured with HL60 cells.Record which dilution of bacteria yields the optimal number of countable colonies for future OPKAs with this bacterial stock. Thaw one tube of bacterial stock. Pellet bacteria at six thousand times G for two minutes and resuspend the cell pellet in OBB at the optimal dilution obtained in the previous step.Pipette 10 microliters of the resuspended bacterial dilution per well in a round bottom 96 well cell culture plate. Then, add 20 microliters of an appropriate antibody or a drug treatment to each experimental well in duplicate. For control wells, use 1XPBS or OBB depending on the buffer used for the treatment wells.Shake the sample plate at approximately 90 rpm at room temperature for one hour. To harvest the HL60 differentiated cells that are treated with DMF three days prior, pellet the cells at 500 times G for three minutes. Discard the supernatant and wash the pellet with at least 10 milliliters of 1XPBS.Pellet the washed cells at 500 times G for three minutes. Discard the supernatant and resuspend the cells in OBB. Add sterile undiluted baby rabbit serum at a one to five final volume.After a one hour bacterial culture, divide each sample into duplicate wells for two groups. Next, add 50 microliters of the HL60 complement mixture to each experimental set of wells and 50 microliters of OBB to the wells of bacteria only. Shake the 96 well plate at 37 degrees celsius for one hour.To plate samples, dilute each well with OBB at a one to five final volume so that each sample has a volume of at least 50 microliters. Next, pipette 50 microliters of each sample directly onto a designated area of a bacterial culture plate, ensuring adequate spacing between samples. Cover and allow samples to dry for approximately 15 minutes at room temperature.Invert the plates and culture overnight at 30 degrees celsius. Alternatively, culture plates in anaerobic jars to test whether anoxic conditions affect the bacterial growth or to control for morphology. After overnight culture, count the colonies in each designated sample area and proceed to analyzing data by comparing the number of live cells in each set to the corresponding controls.The most difficult aspects of establishing this technique for the first time will likely be optimizing the starting CFUs of the bacterial stock, as well as ensuring the HL60 cells are effectively differentiated. Before starting the OPKA, HL60 differentiation was validated using flow cytometry with propidium iodide as a viability marker. After being treated with DMF for three days, expression of CD35 was increased and expression of CD71 was decreased.The average percentages of bacterial CFUs in the HL60 treated groups compared to the corresponding non-HL60 treated groups was used to compare the bacterial cell survival of different treatments. Results showed that with an effective treatment, the numbers of colonies were different between HL60 co-culture and no HL60 cells, indicative of more efficient phagocytosis. Results showed that when the bacterial dilution was not optimized or the colony growth was not carefully observed after plating, overgrowth of the colonies could prevent accurate counting of colonies.The most important thing to remember when attempting this procedure is to monitor the bacterial incubation carefully so as to avoid overgrowth of the CFUs. In vivo assays can be used to asses effective bacterial clearance within a host. These assays can be used to confirm the immune efficacy observed with the OPKA are translatable to human or animal models.The opsonophagocytic killing assay has been used to great effect in previous significant research studies to link antibacterial therapies to phagostic immune responses. Working with bacterial pathogens can be hazardous. Please wear protective personal equipment at all times during this assay.

opsonophagocytic-killing-assay-to-assess-immunological-responses

Research

JoVE Journal

Immunology and Infection

Enzyme-linked Immunospot Assay (ELISPOT):  Quantification of Th-1 Cellular Immune Responses Against Microbial Antigens

Adaptive immunity is an important component to clearance of intracellular pathogens. The ability to detect and quantify these responses in humans is an important diagnostic tool. The enzyme-linked immunospot assay (ELISPOT) is gaining popularity for its ability to identify cellular immune responses against microbial antigens, including immunosuppressed populations such as those with HIV infection, transplantation, and steroid use. This assay has the capacity to quantify the immune responses against specific microbial antigens, as well as distinguish if these responses are Th1 or Th2 in character. ELISPOT is not limited to the site of inflammation. It is versatile in its ability to assess for immune responses within peripheral blood, as well as sites of active involvement such as bronchoalveolar lavage, cerebral spinal fluid, and ascites. Detection of immune responses against a single or multiple antigens is possible, as well as specific epitopes within microbial proteins. This assay facilitates detection of immune responses over time, as well as distinctions in antigens recognized by host T cells. Dual color ELISPOT assays are available for detection of simultaneous expression of two cytokines. Recent applications for this technique include diagnosis of extrapulmonary tuberculosis, as well as investigation of the contribution of infectious antigens to autoimmune diseases.

Enzyme-linked Immunospot Assay ELISPOT:  Quantification of Th-1 Cellular Immune Responses Against Microbial Antigens

Identification of microbial targets of adaptive immunity in idiopathic diseases can be accomplished by the use of the enzyme-linked immunospot assay.

Adaptive immunity is an important component to clearance of intracellular pathogens.  The ability to detect and quantify these responses in humans is an ...

Antigen Specific In Vivo Killing Assay using CFSE Labeled Target Cells

Carboxyfluorescein diacetate succinimidyl ester (CFSE) can be used to easily and quickly label a cell population of interest for in vivo investigation. This labeling has classically been used to study proliferation and migration. In the method presented here, we have shortened the timeline after adoptive transfer to look at survival and killing of epitope specific CFSE labeled target cells4-6. The level of specific killing of a CD8 + T cell clone can indicate the quality of the response, as their quantity may be misleading. Specific CD8+ T cells can become functionally exhausted over time with a decline in cytokine production and killing7,8. Also, certain CD8 + T cell clones may not kill as well as others with differing TCR specificities9. For effective Cell Mediated Immunity (CMI), antigens must be identified that produce not only adequate numbers of responding T cells, but also functionally robust responding T cells. Here we assess the percent cell specific killing of two peptide specific T cell clones in BALB/c mice.

Antigen Specific In Vivo Killing Assay using CFSE Labeled Target Cells

Many infections elicit a strong CTL response, but occasionally, the quantity of responding cells does not correlate to control of the pathogen1. One measure of CTL quality is their ability to kill specifically2. CFSE labeling of target cells can be used to investigate this CTL response quality in vivo3,4.

Carboxyfluorescein diacetate succinimidyl ester (CFSE) can be used to easily and quickly label a cell population of interest for in vivo investigation.  ...

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 ...

'Bioluminescent' Reporter Phage for the Detection of Category A Bacterial Pathogens

Yersinia pestis and Bacillus anthracis are Category A bacterial pathogens that are the causative agents of the plague and anthrax, respectively 1. Although the natural occurrence of both diseases&#39; is now relatively rare, the possibility of terrorist groups using these pathogens as a bioweapon is real. Because of the disease&#39;s inherent communicability, rapid clinical course, and high mortality rate, it is critical that an outbreak be detected quickly. Therefore methodologies that provide rapid detection and diagnosis are essential to ensure immediate implementation of public health measures and activation of crisis management.
Recombinant reporter phage may provide a rapid and specific approach for the detection of Y. pestis and B. anthracis. The Centers for Disease Control and Prevention currently use the classical phage lysis assays for the confirmed identification of these bacterial pathogens 2-4. These assays take advantage of naturally occurring phage which are specific and lytic for their bacterial hosts. After overnight growth of the cultivated bacterium in the presence of the specific phage, the formation of plaques (bacterial lysis) provides a positive identification of the bacterial target. Although these assays are robust, they suffer from three shortcomings: 1) they are laboratory based; 2) they require bacterial isolation and cultivation from the suspected sample, and 3) they take 24-36 h to complete. To address these issues, recombinant &#34;light-tagged&#34; reporter phage were genetically engineered by integrating the Vibrio harveyi luxAB genes into the genome of Y. pestis and B. anthracis specific phage 5-8. The resulting luxAB reporter phage were able to detect their specific target by rapidly (within minutes) and sensitively conferring a bioluminescent phenotype to recipient cells. Importantly, detection was obtained either with cultivated recipient cells or with mock-infected clinical specimens 7.
For demonstration purposes, here we describe the method for the phage-mediated detection of a known Y. pestis isolate using a luxAB reporter phage constructed from the CDC plague diagnostic phage &#934;A1122 6,7 (Figure 1). A similar method, with minor modifications (e.g. change in growth temperature and media), may be used for the detection of B. anthracis isolates using the B. anthracis reporter phage W&#946;::luxAB 8. The method describes the phage-mediated transduction of a biolumescent phenotype to cultivated Y. pestis cells which are subsequently measured using a microplate luminometer. The major advantages of this method over the traditional phage lysis assays is the ease of use, the rapid results, and the ability to test multiple samples simultaneously in a 96-well microtiter plate format.
<img alt="Figure 1" src="/files/ftp_upload/2740/2740fig1.jpg" /> 
Figure 1. Detection schematic. The phage are mixed with the sample, the phage infects the cell, luxAB are expressed, and the cell bioluminesces. Sample processing is not necessary; the phage and cells are mixed and subsequently measured for light.

A simple method for the identification of priority bacterial pathogens is to use genetically engineered reporter phage. These reporter phage, which are specific to their particular host species, are capable of rapidly transducing a bioluminescent signal response to host cells. Herein, we describe the use of reporter phage for the detection of Yersinia pestis.

Yersinia pestis and Bacillus anthracis are Category A bacterial pathogens that are the causative agents of the plague and anthrax, respectively 1. ...

Infection of Zebrafish Embryos with Intracellular Bacterial Pathogens

Zebrafish (Danio rerio) embryos are increasingly used as a model for studying the function of the vertebrate innate immune system in host-pathogen interactions 1. The major cell types of the innate immune system, macrophages and neutrophils, develop during the first days of embryogenesis prior to the maturation of lymphocytes that are required for adaptive immune responses. The ease of obtaining large numbers of embryos, their accessibility due to external development, the optical transparency of embryonic and larval stages, a wide range of genetic tools, extensive mutant resources and collections of transgenic reporter lines, all add to the versatility of the zebrafish model. Salmonella enterica serovar Typhimurium (S. typhimurium) and Mycobacterium marinum can reside intracellularly in macrophages and are frequently used to study host-pathogen interactions in zebrafish embryos. The infection processes of these two bacterial pathogens are interesting to compare because S. typhimurium infection is acute and lethal within one day, whereas M. marinum infection is chronic and can be imaged up to the larval stage 2, 3. The site of micro-injection of bacteria into the embryo (Figure 1) determines whether the infection will rapidly become systemic or will initially remain localized. A rapid systemic infection can be established by micro-injecting bacteria directly into the blood circulation via the caudal vein at the posterior blood island or via the Duct of Cuvier, a wide circulation channel on the yolk sac connecting the heart to the trunk vasculature. At 1 dpf, when embryos at this stage have phagocytically active macrophages but neutrophils have not yet matured, injecting into the blood island is preferred. For injections at 2-3 dpf, when embryos also have developed functional (myeloperoxidase-producing) neutrophils, the Duct of Cuvier is preferred as the injection site. To study directed migration of myeloid cells towards local infections, bacteria can be injected into the tail muscle, otic vesicle, or hindbrain ventricle 4-6. In addition, the notochord, a structure that appears to be normally inaccessible to myeloid cells, is highly susceptible to local infection 7. A useful alternative for high-throughput applications is the injection of bacteria into the yolk of embryos within the first hours after fertilization 8. Combining fluorescent bacteria and transgenic zebrafish lines with fluorescent macrophages or neutrophils creates ideal circumstances for multi-color imaging of host-pathogen interactions. This video article will describe detailed protocols for intravenous and local infection of zebrafish embryos with S. typhimurium or M. marinum bacteria and for subsequent fluorescence imaging of the interaction with cells of the innate immune system.

Transparent zebrafish embryos have proved useful model hosts to visualize and functionally study interactions between innate immune cells and intracellular bacterial pathogens, such as Salmonella typhimurium and Mycobacterium marinum. Micro-injection of bacteria and multi-color fluorescence imaging are essential techniques involved in the application of zebrafish embryo infection models.

Zebrafish (Danio rerio) embryos are increasingly used as a model for studying the function of the vertebrate innate immune system in host-pathogen ...

Rearing and Injection of Manduca sexta Larvae to Assess Bacterial Virulence

Manduca sexta, commonly known as the tobacco hornworm, is considered a significant agricultural pest, feeding on solanaceous plants including tobacco and tomato. The susceptibility of M. sexta larvae to a variety of entomopathogenic bacterial species1-5, as well as the wealth of information available regarding the insect's immune system6-8, and the pending genome sequence9 make it a good model organism for use in studying host-microbe interactions during pathogenesis. In addition, M. sexta larvae are relatively large and easy to manipulate and maintain in the laboratory relative to other susceptible insect species. Their large size also facilitates efficient tissue/hemolymph extraction for analysis of the host response to infection.
The method presented here describes the direct injection of bacteria into the hemocoel (blood cavity) of M. sexta larvae. This approach can be used to analyze and compare the virulence characteristics of various bacterial species, strains, or mutants by simply monitoring the time to insect death after injection. This method was developed to study the pathogenicity of Xenorhabdus and Photorhabdus species, which typically associate with nematode vectors as a means to gain entry into the insect. Entomopathogenic nematodes typically infect larvae via natural digestive or respiratory openings, and release their symbiotic bacterial contents into the insect hemolymph (blood) shortly thereafter10. The injection method described here bypasses the need for a nematode vector, thus uncoupling the effects of bacteria and nematode on the insect. This method allows for accurate enumeration of infectious material (cells or protein) within the inoculum, which is not possible using other existing methods for analyzing entomopathogenesis, including nicking11 and oral toxicity assays12. Also, oral toxicity assays address the virulence of secreted toxins introduced into the digestive system of larvae, whereas the direct injection method addresses the virulence of whole-cell inocula.
The utility of the direct injection method as described here is to analyze bacterial pathogenesis by monitoring insect mortality. However, this method can easily be expanded for use in studying the effects of infection on the M. sexta immune system. The insect responds to infection via both humoral and cellular responses. The humoral response includes recognition of bacterial-associated patterns and subsequent production of various antimicrobial peptides7; the expression of genes encoding these peptides can be monitored subsequent to direct infection via RNA extraction and quantitative PCR13. The cellular response to infection involves nodulation, encapsulation, and phagocytosis of infectious agents by hemocytes6. To analyze these responses, injected insects can be dissected and visualized by microscopy13, 14.

Rearing and Injection of Manduca sexta Larvae to Assess Bacterial Virulence

The method described here utilizes direct injection of entomopathogenic bacteria into the hemocoel of Manduca sexta insect larvae. M. sexta is a commercially available and well-studied insect. Thus, this method represents a simple approach to analyzing host-bacterial interactions from the perspective of one or both partners.

Manduca sexta, commonly known as the tobacco hornworm, is considered a significant agricultural pest, feeding on solanaceous plants including tobacco and ...

A Visual Assay to Monitor T6SS-mediated Bacterial Competition

Type VI secretion systems (T6SSs) are molecular nanomachines allowing Gram-negative bacteria to transport and inject proteins into a wide variety of target cells1,2. The T6SS is composed of 13 core components and displays structural similarities with the tail-tube of bacteriophages3. The phage uses a tube and a puncturing device to penetrate the cell envelope of target bacteria and inject DNA. It is proposed that the T6SS is an inverted bacteriophage device creating a specific path in the bacterial cell envelope to drive effectors and toxins to the surface. The process could be taken further and the T6SS device could perforate other cells with which the bacterium is in contact, thus injecting the effectors into these targets. The tail tube and puncturing device parts of the T6SS are made with Hcp and VgrG proteins, respectively4,5.
The versatility of the T6SS has been demonstrated through studies using various bacterial pathogens. The Vibrio cholerae T6SS can remodel the cytoskeleton of eukaryotic host cells by injecting an "evolved" VgrG carrying a C-terminal actin cross-linking domain6,7. Another striking example was recently documented using Pseudomonas aeruginosa which is able to target and kill bacteria in a T6SS-dependent manner, therefore promoting the establishment of bacteria in specific microbial niches and competitive environment8,9,10.
In the latter case, three T6SS-secreted proteins, namely Tse1, Tse2 and Tse3 have been identified as the toxins injected in the target bacteria (Figure 1). The donor cell is protected from the deleterious effect of these effectors via an anti-toxin mechanism, mediated by the Tsi1, Tsi2 and Tsi3 immunity proteins8,9,10. This antimicrobial activity can be monitored when T6SS-proficient bacteria are co-cultivated on solid surfaces in competition with other bacterial species or with T6SS-inactive bacteria of the same species8,11,12,13.
The data available emphasized a numerical approach to the bacterial competition assay, including time-consuming CFU counting that depends greatly on antibiotic makers. In the case of antibiotic resistant strains like P. aeruginosa, these methods can be inappropriate. Moreover, with the identification of about 200 different T6SS loci in more than 100 bacterial genomes14, a convenient screening tool is highly desirable. We developed an assay that is easy to use and requires standard laboratory material and reagents. The method offers a rapid and qualitative technique to monitor the T6SS-dependent bactericidal/bacteriostasis activity by using a reporter strain as a prey (in this case Escherichia coli DH5&alpha;) allowing a-complementation of the lacZ gene. Overall, this method is graphic and allows rapid identification of T6SS-related phenotypes on agar plates. This experimental protocol may be adapted to other strains or bacterial species taking into account specific conditions such as growth media, temperature or time of contact.

We describe a qualitative assay to monitor bacterial competition mediated by the Pseudomonas aeruginosa type VI secretion system (T6SS). The assay relies on the survival/killing of Escherichia coli target cells carrying a lacZ-reporter. This technique is adjustable to assess the bactericidal/bacteriostasis activity of T6SS-proficient microorganisms.

Type VI secretion systems (T6SSs) are molecular  nanomachines allowing Gram-negative bacteria to transport and inject proteins  into a wide variety of ...

Application of Long-term cultured Interferon-&#947; Enzyme-linked Immunospot Assay for Assessing Effector and Memory T Cell Responses in Cattle

Effector and memory T cells are generated through developmental programing of na&#239;ve cells following antigen recognition. If the infection is controlled up to 95 % of the T cells generated during the expansion phase are eliminated (i.e., contraction phase) and memory T cells remain, sometimes for a lifetime. In humans, two functionally distinct subsets of memory T cells have been described based on the expression of lymph node homing receptors. Central memory T cells express C-C chemokine receptor 7 and CD45RO and are mainly located in T-cell areas of secondary lymphoid organs. Effector memory T cells express CD45RO, lack CCR7 and display receptors associated with lymphocyte homing to peripheral or inflamed tissues. Effector T cells do not express either CCR7 or CD45RO but upon encounter with antigen produce effector cytokines, such as interferon-&#947;. Interferon-&#947; release assays are used for the diagnosis of bovine and human tuberculosis and detect primarily effector and effector memory T cell responses. Central memory T cell responses by CD4+ T cells to vaccination, on the other hand, may be used to predict vaccine efficacy, as demonstrated with simian immunodeficiency virus infection of non-human primates, tuberculosis in mice, and malaria in humans. Several studies with mice and humans as well as unpublished data on cattle, have demonstrated that interferon-&#947; ELISPOT assays measure central memory T cell responses. With this assay, peripheral blood mononuclear cells are cultured in decreasing concentration of antigen for 10 to 14 days (long-term culture), allowing effector responses to peak and wane; facilitating central memory T cells to differentiate and expand within the culture.

Long-term cultured interferon-&#947; enzyme-linked immunospot assay is used as a measure of central memory responses and correlates with protective anti-mycobacterial vaccine responses. With this assay, peripheral blood mononuclear cells are stimulated with mycobacterial antigens and interleukin-2 for 14 days, enabling differentiation and expansion of central memory T cells.

Effector and memory T cells are generated through developmental programing of na&#239;ve cells following antigen recognition. If the infection is ...

Using a Bacterial Pathogen to Probe for Cellular and Organismic-level Host Responses

There are a variety of strategies bacterial pathogens employ to survive and proliferate once inside the eukaryotic cell. The so-called 'cytosolic' pathogens (Listeria monocytogenes, Shigella flexneri, Burkholderia pseudomallei, Francisella tularensis, and Rickettsia spp.) gain access to the infected cell cytosol by physically and enzymatically degrading the primary vacuolar membrane. Once in the cytosol, these pathogens both proliferate as well as generate sufficient mechanical forces to penetrate the plasma membrane of the host cell in order to infect new cells. Here, we show how this terminal step of the cellular infection cycle of L. monocytogenes (Lm) can be quantified by both colony-forming unit assays and flow cytometry and give examples of how both pathogen- and host-encoded factors impact this process. We also show a close correspondence of Lm infection dynamics of cultured cells infected in vitro and those of hepatic cells derived from mice infected in vivo. These function-based assays are relatively simple and can be readily scaled up for discovery-based high-throughput screens for modulators of eukaryotic cell function.

We describe both in vitro and in vivo infection assays that can be used to analyze the activities of host-encoding factors.

There are a variety of strategies bacterial pathogens employ to survive and proliferate once inside the eukaryotic cell. The so-called 'cytosolic' ...

A High-throughput Shigella-specific Bactericidal Assay

Serum bactericidal assays (SBAs) measure the functional activity of antibodies and have been used for many decades. SBAs directly measure antibody killing activity by assessing the ability of antibodies in serum to bind to bacteria and activate complement. This complement activation results in the lysis and killing of the target bacteria. These assays are valuable because they go beyond quantifying antibody production to elucidate the biological functions that these antibodies have, allowing researchers to study the role that antibodies may play in preventing infection. SBAs have been used to study immune responses for many human pathogens, but there is no widely accepted methodology for Shigella at present. Historically, SBAs have been very labor-intensive, requiring many time-consuming steps to accurately quantify surviving bacteria. This protocol describes a simple, robust, and high-throughput assay that measures functional antibodies specific for Shigella in serum in vitro. The method described here offers many advantages over traditional SBAs, including the use of frozen bacterial stocks, 96 well assay plates, a micro-culture system, and automated colony-counting. All of these modifications make this assay less labor-intensive and more high-throughput. This protocol is simpler and faster to perform than traditional SBAs while still using simple technologies and readily available reagents. The protocol has been successfully applied in multiple independent laboratories and the assay is robust and reproducible. The assay can be used to assess immune responses in pre-clinical as well as clinical studies. Quantifying shigellacidal antibody titers both before and after antigen exposure (either by immunization or infection) allows for a broader understanding of how functional antibody responses are generated and their contribution to protective immunity. The development of this standardized, well-characterized assay may greatly facilitate Shigella vaccine design.

A High-throughput Shigella-specific Bactericidal Assay

Here we present a protocol to measure Shigellacidal activity of antibodies in serum. Serum is mixed with bacteria and exogenous complement, incubated, and the reaction mixture is plated on agar plates. Viable bacteria form colonies which are counted, using an automated colony enumerator, and used to determine the bactericidal titer.

Serum bactericidal assays (SBAs) measure the functional activity of antibodies and have been used for many decades. SBAs directly measure antibody killing ...