Research in the Shao Lab is supported by Research Innovative Award from the College of Medicine and the Junior Faculty Pilot Award from the Department of Internal Medicine, University of Cincinnati and grant DK K01_095067 from NIDDK/NIH.

Experimental mice were bred and maintained in our mice colony. All animal work was conducted according to the guidelines of the Institutional Animal Care and Use Committee (IACUC) of the University of Cincinnati.
1. Preparation of CFSE labeled apoptotic thymocytes
<ol>
	<li>Euthanize two na&#239;ve C57/B6 mice by CO2 inhalation for 10 min and dissect to open the chest cavity, remove (pull out) the thymus with curved fine-tip forceps into tissue culture petri dish containing 10 mL ...

<ol>
	<li>Shao, W. H., Cohen, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disturbances+of+apoptotic+cell+clearance+in+systemic+lupus+erythematosus.">Disturbances of apoptotic cell clearance in systemic lupus erythematosus.</a> Arthritis Research and Therapy. 13 (1), 202 (2011).</li><li>Cohen, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Apoptotic+cell+death+and+lupus.">Apoptotic cell death and lupus.</a> Springer Seminars in Immunopathology. 28 (2), 145-152 (2006).</li><li>Wong, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Apoptosis+in+cancer:+from+pathogenesis+to+treatment.">Apoptosis in cancer: from pathogenesis to treatment.</a> Journal of Experimental and Clinical Cancer Research. 30, 87 (2011).</li><li>Baig, 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=Potential+of+apoptotic+pathway-targeted+cancer+therapeutic+research:+Where+do+we+stand.">Potential of apoptotic pathway-targeted cancer therapeutic research: Where do we stand.</a> Cell Death and Disease. 7, 2058 (2016).</li><li>Poon, I. K., Lucas, C. D., Rossi, A. G., Ravichandran, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Apoptotic+cell+clearance:+basic+biology+and+therapeutic+potential.">Apoptotic cell clearance: basic biology and therapeutic potential.</a> Nature Reviews Immunology. 14 (3), 166-180 (2014).</li><li>Qian, Y., Wang, H., Clarke, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impaired+clearance+of+apoptotic+cells+induces+the+activation+of+autoreactive+anti-Sm+marginal+zone+and+B-1+B+cells.">Impaired clearance of apoptotic cells induces the activation of autoreactive anti-Sm marginal zone and B-1 B cells.</a> Journal of Immunology. 172 (1), 625-635 (2004).</li><li>Hawkins, L. A., Devitt, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current+understanding+of+the+mechanisms+for+clearance+of+apoptotic+cells-a+fine+balance.">Current understanding of the mechanisms for clearance of apoptotic cells-a fine balance.</a> Journal of Cell Death. 6, 57-68 (2013).</li><li>Lemke, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biology+of+the+TAM+receptors.">Biology of the TAM receptors.</a> Cold Spring Harbor Perspective in Biology. 5 (11), 009076 (2013).</li><li>Stitt, T. N., 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=The+anticoagulation+factor+protein+S+and+its+relative,+Gas6,+are+ligands+for+the+Tyro+3/Axl+family+of+receptor+tyrosine+kinases.">The anticoagulation factor protein S and its relative, Gas6, are ligands for the Tyro 3/Axl family of receptor tyrosine kinases.</a> Cell. 80 (4), 661-670 (1995).</li><li>Linger, R. M., Keating, A. K., Earp, H. S., Graham, D. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TAM+receptor+tyrosine+kinases:+biologic+functions,+signaling,+and+potential+therapeutic+targeting+in+human+cancer.">TAM receptor tyrosine kinases: biologic functions, signaling, and potential therapeutic targeting in human cancer.</a> Advances in Cancer Research. 100, 35-83 (2008).</li><li>van der Meer, J. H., van der Poll, T., van 'T Veer, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TAM+receptors,+Gas6,+and+protein+S:+roles+in+inflammation+and+hemostasis.">TAM receptors, Gas6, and protein S: roles in inflammation and hemostasis.</a> Blood. 123 (16), 2460-2469 (2014).</li><li>Lemke, G., Burstyn-Cohen, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TAM+receptors+and+the+clearance+of+apoptotic+cells.">TAM receptors and the clearance of apoptotic cells.</a> Annal of the New York Academy of Sciences. 1209, 23-29 (2010).</li><li>Shao, W. H., Zhen, Y., Eisenberg, R. A., Cohen, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Mer+receptor+tyrosine+kinase+is+expressed+on+discrete+macrophage+subpopulations+and+mainly+uses+Gas6+as+its+ligand+for+uptake+of+apoptotic+cells.">The Mer receptor tyrosine kinase is expressed on discrete macrophage subpopulations and mainly uses Gas6 as its ligand for uptake of apoptotic cells.</a> Clinical Immunology. 133 (1), 138-144 (2009).</li><li>Scott, R. 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=Phagocytosis+and+clearance+of+apoptotic+cells+is+mediated+by+MER.">Phagocytosis and clearance of apoptotic cells is mediated by MER.</a> Nature. 411 (6834), 207-211 (2001).</li><li>Klarquist, J., Janssen, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+bm12+Inducible+Model+of+Systemic+Lupus+Erythematosus+(SLE)+in+C57BL/6+Mice.">The bm12 Inducible Model of Systemic Lupus Erythematosus (SLE) in C57BL/6 Mice.</a> Journal of Visualized Experiment. (105), e53319 (2015).</li><li>Malawista, A., Wang, X., Trentalange, M., Allore, H. G., Montgomery, R. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coordinated+expression+of+tyro3,+axl,+and+mer+receptors+in+macrophage+ontogeny.">Coordinated expression of tyro3, axl, and mer receptors in macrophage ontogeny.</a> Macrophage (Houst). 3, (2016).</li><li>Elmore, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Apoptosis:+a+review+of+programmed+cell+death.">Apoptosis: a review of programmed cell death.</a> Toxicologic Pathology. 35 (4), 495-516 (2007).</li><li>Ravichandran, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Find-me+and+eat-me+signals+in+apoptotic+cell+clearance:+progress+and+conundrums.">Find-me and eat-me signals in apoptotic cell clearance: progress and conundrums.</a> Journal of Experimental Medicine. 207 (9), 1807-1817 (2010).</li><li>Rock, K. L., Kono, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+inflammatory+response+to+cell+death.">The inflammatory response to cell death.</a> Annual Review in Pathology. 3, 99-126 (2008).</li><li>Roberts, K. M., Rosen, A., Casciola-Rosen, 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=Methods+for+inducing+apoptosis.">Methods for inducing apoptosis.</a> Methods in Molecular Medicine. 102, 115-128 (2004).</li><li>Progatzky, F., Dallman, M. J., Lo Celso, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+seeing+to+believing:+labelling+strategies+for+in+vivo+cell-tracking+experiments.">From seeing to believing: labelling strategies for in vivo cell-tracking experiments.</a> Interface Focus. 3 (3), 20130001 (2013).</li><li>Stijlemans, B., 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=Development+of+a+pHrodo-based+assay+for+the+assessment+of+in+vitro+and+in+vivo+erythrophagocytosis+during+experimental+trypanosomosis.">Development of a pHrodo-based assay for the assessment of in vitro and in vivo erythrophagocytosis during experimental trypanosomosis.</a> PLoS Neglected Tropical Diseases. 9 (3), 0003561 (2015).</li><li>Hochreiter-Hufford, A., Ravichandran, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clearing+the+dead:+apoptotic+cell+sensing,+recognition,+engulfment,+and+digestion.">Clearing the dead: apoptotic cell sensing, recognition, engulfment, and digestion.</a> Cold Spring Harbor Perspective in Biology. 5 (1), 008748 (2013).</li><li>Chen, S., So, E. C., Strome, S. E., Zhang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+Detachment+Methods+on+M2+Macrophage+Phenotype+and+Function.">Impact of Detachment Methods on M2 Macrophage Phenotype and Function.</a> Journal of Immunology Methods. 426, 56-61 (2015).</li><li>Fleit, S. A., Fleit, H. B., Zolla-Pazner, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Culture+and+recovery+of+macrophages+and+cell+lines+from+tissue+culture-treated+and+-untreated+plastic+dishes.">Culture and recovery of macrophages and cell lines from tissue culture-treated and -untreated plastic dishes.</a> Journal of Immunology Methods. 68 (1-2), 119-129 (1984).</li><li>Fine, N., Barzilay, O., Glogauer, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+Human+and+Mouse+Neutrophil+Phagocytosis+by+Flow+Cytometry.">Analysis of Human and Mouse Neutrophil Phagocytosis by Flow Cytometry.</a> Methods Molecular Biology. 1519, 17-24 (2017).</li><li>Summers, 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=Neutrophil+kinetics+in+health+and+disease.">Neutrophil kinetics in health and disease.</a> Trends in Immunology. 31 (8), 318-324 (2010).</li><li>Dale, D. C., Boxer, L., Liles, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+phagocytes:+neutrophils+and+monocytes.">The phagocytes: neutrophils and monocytes.</a> Blood. 112 (4), 935-945 (2008).</li></ol>

The authors have nothing to disclose.

Apoptosis is a highly conserved cell death process that involves many signal cascades and induces protein expression, secretion, and transportation. Apoptosis is often associated with cellular morphology changes17. Apoptotic cells actively release cytokines and chemokines that attract phagocytes to migrate to the site and initiate the process of engulfment, an extremely complex pathway under tight control18. On the other hand, necrotic cell death releases danger signals tha...

Our body generates 1-10 billion apoptotic cells on a daily basis. Such a large number of apoptotic cells must be cleared in a way that the immune responses remain quiescent. To ensure the clearance of apoptotic cells in a timely manner, numerous types of tissue resident cells and circulating cells develop mechanisms to engulf apoptotic cells1. Dysfunctional regulation of apoptosis has been implicated in the onset and progression of various inflammatory disease and autoimmunity2. Apoptosis also plays a critical role in the pathogenesis of cancer development and its subsequent resistance to conventional treatments3,4. Removal of apoptotic cells generally promotes an anti-inflammatory response, which may be linked to immunological tolerance5. Disturbance of apoptotic cell clearance drives self-immunization and contributes to the development of systemic autoimmune diseases in both humans and mice6.
When cells undergo apoptosis, they expose the phosphatidylserine (PtdSer) from the inner leaflet to the outer leaflet of the membrane. PtdSer will then be recognized by phagocytes through surface receptors. Over a dozen receptors have been identified to recognize and/or facilitate the engulfment of apoptotic cells. In general, there are at least three types of surface receptors involved in the apoptotic cell clearance: tethering receptors, recognize apoptotic cells; tickling receptors, initiate engulfment; chaperoning receptors, facilitate the whole process7. TAM receptor tyrosine kinases (TAM RTKs) consist of Tyro-3, Axl, and Mer and are primarily expressed by myeloid cells of the immune system8. The primary function of TAM RTKs is to serve as tethering receptors, facilitating the phagocytic removal of apoptotic cells and debris. Our group has studied TAM mediated apoptotic cell clearance in the setting of autoimmunity for many years. The vitamin K-dependent protein growth arrest specific protein 6 (Gas6) and protein S (ProS) binds to and activates TAM receptors9,10. Gas6 is produced in the heart, kidneys, and lungs. ProS is mainly produced in the liver11. TAM recognizes of apoptotic cells in such a way that the N-terminal of Gas6/ProS binds to the PtdSer on an apoptotic cell and the C-terminal of Gas6/ProS binds to TAM receptors that anchored on the surface of phagocytes. Together with the other receptors, engulfment of apoptotic cells occurs12. Though Mer can bind to both the ligands ProS and Gas6, we found that Gas6 appears to be the sole ligand for Mer-mediated macrophage phagocytosis of apoptotic cells, which can be blocked by anti-Mer antibody13. Macrophages are professional phagocytes. Rapid clearance of apoptotic cells by macrophages is important for the inhibition of inflammation and autoimmune responses against intracellular antigens. Mer receptor tyrosine kinase is critical for the macrophage engulfment and efficient clearance of apoptotic cells14. In mouse spleen, Mer mainly expresses on the marginal zone and tangible body macrophages13.
The protocol presented here describes a basic method to induce cell apoptosis and demonstrate ways to measure the process and the efficiency of efferocytosis. These protocols can be readily adapted to study efferocytosis by other cell types in engulfment of apoptotic cells of different origins.

<table border="0" cellpadding="0" cellspacing="0" style="width:832px;" width="832">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">Ack lysing buffer</td>
			<td style="width:131px;">GIBCO</td>
			<td style="width:135px;">A10492</td>
			<td style="width:275px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">Annexin V/7-AAD</td>
			<td style="width:131px;">BD Pharmingen</td>
			<td style="width:135px;">559763</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">Anti-Mer antibody</td>
			<td style="width:131px;">R&#38;D Systems</td>
			<td style="width:135px;">BAF591</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">CD11b-PE (clone M1/70)</td>
			<td style="width:131px;">BD Pharmingen</td>
			<td style="width:135px;">553311</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">CFSE</td>
			<td style="width:131px;">Invitrogen</td>
			<td style="width:135px;">C1157</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">DMSO</td>
			<td style="width:131px;">Sigma-Aldrich</td>
			<td style="width:135px;">D-2650</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">EDTA (0.5 mM)</td>
			<td style="width:131px;">GIBCO</td>
			<td style="width:135px;">15575-020</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">FACS tubes</td>
			<td style="width:131px;">BD Biosciences</td>
			<td style="width:135px;">352017</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">Frosted slides</td>
			<td style="width:131px;">Fisher Scientific</td>
			<td style="width:135px;">12-552-343</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">Horse Serum (Heat-inactivated)</td>
			<td style="width:131px;">Invitrogen</td>
			<td style="width:135px;">26050088</td>
			<td style="width:275px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">Lidocaine</td>
			<td style="width:131px;">Sigma-Aldrich</td>
			<td style="width:135px;">L-5647</td>
			<td style="width:275px;">Prepare 1% buffer in 1x PBS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">PBS, 1x</td>
			<td style="width:131px;">Corning</td>
			<td style="width:135px;">21040CV</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">RPMI-1640</td>
			<td style="width:131px;">Corning</td>
			<td style="width:135px;">10040CV</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:292px;">RXDX-106</td>
			<td style="width:131px;">Selleck Chemicals</td>
			<td style="width:135px;">CEP-40783</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:292px;">Staurosprine (100mg)</td>
			<td style="width:131px;">Fisher Scientific</td>
			<td style="width:135px;">BP2541-100</td>
			<td style="width:275px;">Add 214.3 ml of DMSO into 100mg to make 1mM stocking solution</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:292px;">Thioglycolate Medium Brewer Modified</td>
			<td style="width:131px;">BD Biosciences</td>
			<td style="width:135px;">243010</td>
			<td style="width:275px;">Prepare 3% thioglycolate buffer in 1&#180;PBS, autoclaved, and store in the dark for 3 months.</td>
		</tr>
	</tbody>
</table>

experimental analysis of apoptotic thymocyte engulfment by macrophages

Cell apoptosis is a natural process and plays a critical role in embryonic development, homeostatic regulation, immune tolerance induction, and resolution of inflammation. Accumulation of apoptotic debris in the body may trigger chronic inflammatory responses that lead to systemic autoimmune diseases over time. Impaired apoptotic cell clearance has been implicated in a variety of autoimmune diseases. Apoptotic clearance is a complex process rarely detected under physiological conditions. It involves abundant surface receptors and signaling molecules. Studying the process of apoptotic cell clearance provides insightful molecular mechanisms and subsequent biological responses, which may lead to the development of new therapeutics. Here, we describe protocols for the induction of apoptotic thymocytes, the preparation of peritoneal macrophages, and the analysis of apoptotic cell clearance by flow cytometry and microscopy. All cells will undergo apoptosis at a certain stage, and many residential and circulating cells can uptake apoptotic debris. Therefore, the protocol described here can be used in many applications to characterize apoptotic cell binding and ingestion by many other cell types.

Analysis of peritoneal macrophage-mediated engulfment of apoptotic thymocytes. Peritoneal macrophages and apoptotic cells were prepared and co-cultured as described in the protocol. Macrophages were detached and stained with PE conjugated anti-CD11b antibody for 20 min on ice. Macrophages were then washed and processed in a flow cytometer. As seen, there is no CFSE positive macrophage in the bottom right quadrant when no apoptotic cells were added into the culture (Figure 1<...

Watch this Scientific Journal Video about Experimental Analysis of Apoptotic Thymocyte Engulfment by Macrophages at JoVE.com

Experimental Analysis of Apoptotic Thymocyte Engulfment by Macrophages

Here, we present a protocol to prepare apoptotic thymocytes and peritoneal macrophages and analyze the efficiency of efferocytosis and the specific inhibitor-mediated blocking of apoptotic thymocytes engulfment. This protocol has a broad application in cell-mediated clearance of other particles including artificial beads and bacteria.

Cell apoptosis is a natural process and plays a critical role in embryonic development, homeostatic regulation, immune tolerance induction, and resolution ...

Our body generates one to 10 billion of apoptotic cells every day. The efficient clearance of these cells helps in removing cell debris and maintaining inventories. This method may be used in many applications to characterize apoptotic cell binding and ingestion by many other phagocytic cell types.Demonstrating this procedure will be Yuxuan Zhen, a senior technician in my lab. To harvest thymocytes, after opening the chest cavity of a naive C57 black 6 mouse, use curved fine tip forceps to pull out the thymus. Place the organ into a tissue culture dish containing 10 milliliters of RPMI 1640 Medium.Grind the whole thymus against the frosted ends of two microscope slides and filter the resulting tissue suspension through a 70 micrometer cell strainer into a 50 milliliter tube. Collect the thymocytes by centrifugation and resuspend the pellet in 40 milliliters. After counting, centrifuge the cells again and resuspend up to two times 10 to the eight cells in 20 milliliters of fresh PBS per 50 milliliter tube.Label the cells with five micromolar CFSE in 20 milliliters of PBS per tube. Invert the tubes two to three times to mix before incubating the thymocytes for no more than two minutes at room temperature protected from light. At the end of the incubation, stop the reaction with 10 milliliters of heat inactivated horse serum and collect the cells by centrifugation.Resuspend the labeled cells in 40 milliliters of fresh PBS for counting and centrifugation followed by an additional wash with 40 milliliters of medium. After the medium wash, resuspend the thymocytes at a seven times 10 to the six cells per milliliter of tissue culture medium concentration and seed the cells in a 100 millimeter tissue culture dish. Then add staurosporine to the cell culture at a one micromolar final concentration and place the plate in a tissue culture incubator for four hours.For peritoneal macrophage isolation, inject two C57 black 6 mice intraperitoneally with one milliliter of 3%aged thioglycollate at day zero before opening the abdominal skin without disturbing the peritoneum on day five. To flush the peritoneal cavity, use a 10 milliliter syringe equipped with an 18 gauge needle to quickly push 10 milliliters of wash buffer into the cavity before slowly aspirating the wash buffer for collection into a 50 milliliter tube. Wash the peritoneal lavage two times with PBS.Resuspend the peritoneal macrophages at a two times 10 to the six cells per milliliter of tissue culture medium concentration. Next seed 500 microliters of macrophages into each well of a 24 well plate and place the plate in a tissue culture incubator for two hours. At the end of the incubation, aspirate the supernatant to remove the floating cells and add 500 microliters of tissue culture medium to each well.Immediately add zero to 12 times 10 to the six thymocytes in 500 microliters of medium to each well of the culture and place the plate in the tissue culture incubator for four hours. At the end of the incubation, wash each well two times with fresh PBS to remove any free floating apoptotic cells followed by a single wash with staining buffer. Next label the plate-bound macrophages with 200 microliters of staining buffer supplemented with an appropriate anti-CD11b antibody per well and place the plate at four degrees Celsius for 20 minutes.In this representative experiment, up to 30%of the thioglycollate stimulated peritoneal macrophages demonstrated a positive signal in the CFSE channel indicating that these phagocytes had ingested CFSE-labeled apoptotic cells. Microscopic observation of macrophage engulfment of apoptotic cells is essential for investigating the capacity of macrophages to ingest apoptotic cells as CFSE positive macrophages spread out in the bottom right quadrant due to different intensities indicating that the number of apoptotic cells within individual macrophages is different. A higher ratio of apoptotic cells to macrophages not only increases the number of macrophages ingesting apoptotic cells but also enhances the ability of the macrophages to ingest more apoptotic cells.In another set of experiments, about 15%of the macrophages became CFSE positive when CFSE labeled apoptotic thymocytes were added to the macrophage culture for four hours indicating that these macrophages were the phagocytic macrophages. Mer antibody blocks macrophage efferocytosis in a dose-dependent manner and the overall blockage may account for about 30%of the efferocytosis efficiency in the current setting. In addition, a newly approved TAM receptor inhibitor attenuates macrophage efferocytosis in a dose-dependent manner up to an about 100 nanomolar concentration.Always remember to check the percentage of apoptotic cells as this number directly affects the efficiency of efferocytosis. The phagocytic macrophages can be further analyzed by Western blot to investigate the signaling molecules regulated by engulfment process and by microscopy to study the dynamics of engulfment.

experimental-analysis-of-apoptotic-thymocyte-engulfment-by-macrophages

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Immunology and Infection

6.8K Views.  University of Cincinnati. Our body generates one to 10 billion of apoptotic cells every day. The efficient clearance of these cells helps in removing cell debris and maintaining inventories. This method may be used in many applications to characterize apoptotic cell binding and ingestion by many other phagocytic cell types.Demonstrating this procedure will be Yuxuan Zhen, a senior technician in my lab. To harvest thymocytes, after opening the chest cavity of a naive C57 black 6 mouse, use curved fine tip forcep...