Name: using enhanced green fluorescence protein-expressing escherichia coli to assess mouse peritoneal macrophage phagocytosis
Uploaded: 2019-01-04T13:00:00
Description: Watch this Scientific Journal Video about Using Enhanced Green Fluorescence Protein-expressing Escherichia Coli to Assess Mouse Peritoneal Macrophage Phagocytosis at JoVE.com

The National Natural Science Foundation of China (no. 31800046) and the Natural Science Foundation of Liaoning Province (no. 20170540262) supported this work. This work was accomplished in the laboratories of the Scientific Research Center at the Second Hospital of Dalian Medical University. The authors would like to thank Xiao-Lin Sang for her assistance with the flow cytometry, and Bo Qu and Dong-Chuan Yang for their assistance in producing the video.

&#8203;All procedures were performed under the National Institutes of Health Guidelines for the Care and Use of Laboratory Animals, and the protocols were approved by the Animal Care and Use Committee of Dalian Medical University. Sixteen-month-old (with a body weight of 30-35 g) and eight-week-old (20-25 g) SPF (specific-pathogen-free) male C57BL/6 mice were obtained from the SPF animal center of Dalian Medical University. All mice were kept in animal housing with access to food and water ad libitum. The temper...

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The steps in this protocol are quite simple and straightforward. One of the critical steps is to induce EGFP expression on E. coli. Usually, when a gene from eukaryotes, like EGFP, is planned to express in prokaryotes like E. coli, there is a risk that the protein will form inactive aggregates (inclusion bodies), which changes the protein's native structure and activity. By using the pET-SUMO vector and constructing the pET-SUMO-EGFP plasmid, the EGFP-SUMO fusion protein expressed successfully, and the ...

Macrophage phagocytosis assays are often used to study the innate immune function. The innate immune response may indicate susceptibility to infection. Macrophage cell lines are widely used in immunology studies. However, the extended passage may cause gene loss and compromised immune functions in these cell lines. Thus, the primary peritoneal macrophages are the ideal object in which to study the cell function1.
Although the innate immune response was thought to be intact in the aged body, the phagocytic ability may decrease compared to that in the younger body2,3. Here, we will demonstrate a method to assess the phagocytosis of peritoneal macrophages from young (eight-week-old) and aged (16-month-old) mouse using EGFP-expressing E. coli, which is convenient, quick, and economically feasible. 
The use of an EGFP-expressing E. coli strain is one of the advantages of this assay because these bacteria are stable and display a strong fluorescence signal, even after macrophages are fixed by 4% (w/v) paraformaldehyde. Additionally, by using the EGFP-expressing E. coli, researchers do not need further staining after phagocytosis, which saves time. Furthermore, macrophages are immunoresponsive for E. coli surface antigen, making E. coli more suitable for the phagocytosis assay than using the EGFP-expressing fungi or fluorescein-labeled beads. 
With EGFP-expressing E. coli, a phagocytosis assay can be easily accomplished in 2 h and measured by both flow cytometry and fluorescence microscopy, depending on the researcher's purpose. Since this method directly measures the phagocytic ability, the results are more reproducible than other indirect methods. 
This method has also been validated in a RAW264.7 cell line and human peripheral blood mononuclear cells4. The text below provides the detailed step-by-step instructions for performing this assay and highlights the critical steps that the researchers may modify to meet the needs of their experiments.

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			<td height="25" style="height:25px;width:417px;">BD FACSCanto II Flow cytometer</td>
			<td style="width:176px;">BD Biosciences</td>
			<td style="width:123px;">-</td>
			<td style="width:171px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:417px;">Biotin anti-mouse CD16/32 Antibody</td>
			<td style="width:176px;">Biolegend</td>
			<td style="width:123px;">Cat101303</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:417px;">Champion pET SUMO Protein Expression system</td>
			<td style="width:176px;">Invitrogen</td>
			<td style="width:123px;">K300-01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:417px;">Custom Gene Synthesis Service</td>
			<td style="width:176px;">Takara Biotech.</td>
			<td style="width:123px;">-</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:417px;">DAPI(4&#39;,6-Diamidino-2-Phenylindole, Dihydrochloride)</td>
			<td style="width:176px;">ThermoFisher</td>
			<td style="width:123px;">D1306</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:417px;">F4/80-PE anti-mouse antibody for FACS</td>
			<td style="width:176px;">Biolegend</td>
			<td style="width:123px;">Cat123110</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:417px;">Leica DMI3000 B&#160; Inverted Microscope</td>
			<td style="width:176px;">Leica Microsystems</td>
			<td style="width:123px;">-</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:417px;">PE Rat IgG2a, &#954;-isotype control</td>
			<td style="width:176px;">Biolegend</td>
			<td style="width:123px;">Cat400507</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:417px;">Phalloidin 633 fluorescence dye conjugated working solution</td>
			<td style="width:176px;">AAT Bioquest</td>
			<td style="width:123px;">Cat23125</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:417px;">Thioglycollate medium</td>
			<td style="width:176px;">Sigma-Aldrich</td>
			<td style="width:123px;">T9032</td>
			<td></td>
		</tr>
	</tbody>
</table>

using enhanced green fluorescence protein-expressing escherichia coli to assess mouse peritoneal macrophage phagocytosis

This manuscript describes a simple and reproducible method to perform a phagocytosis assay. The first part of this method involves building a pET-SUMO-EGFP vector (SUMO = small ubiquitin-like modifier) and expressing enhanced green fluorescence protein (EGFP) in Escherichia coli (BL21DE). EGFP-expressing E. coli is coincubated with macrophages for 1 h at 37 &#176;C; the negative control group is incubated on ice for the same amount of time. Then, the macrophages are ready for assessment. The advantages of this technique include its simple and straightforward steps, and phagocytosis can be measured by both flow cytometer and fluorescence microscope. The EGFP-expressing E. coli are stable and display a strong fluorescence signal even after the macrophages are fixed with paraformaldehyde. This method is not only suitable for the assessment of macrophage cell lines or primary macrophages in vitro but also suitable for the evaluation of granulocyte and monocyte phagocytosis in peripheral blood mononuclear cells. The results show that the phagocytic capability of peritoneal macrophages from young (eight-week-old) mice is higher than that of macrophages from aged (16-month-old) mice. In summary, this method measures macrophage phagocytosis and is suitable for studying the innate immune system function.

The pET-SUMO vector utilizes a small ubiquitin-like modifier to allow the expression of native proteins in the E. coli. SUMO fusion can significantly enhance the EGFP solubility, allowing it to be detected easily. If the EGFP expression is successfully induced by lactose, green colonies can be observed in the dark (Figure 1A). Green dots, which represent the EGFP-expressing E. coli, can be observed under a fluorescence microscope using a 40x...

Watch this Scientific Journal Video about Using Enhanced Green Fluorescence Protein-expressing Escherichia Coli to Assess Mouse Peritoneal Macrophage Phagocytosis at JoVE.com

Using Enhanced Green Fluorescence Protein-expressing Escherichia Coli to Assess Mouse Peritoneal Macrophage Phagocytosis

Here, we present a protocol to assess mouse peritoneal macrophage phagocytosis using enhanced green fluorescence protein-expressing Escherichia coli.

Using Enhanced Green Fluorescence Protein-expressing Escherichia Coli to Assess Mouse Peritoneal Macrophage Phagocytosis

This manuscript describes a simple and reproducible method to perform a phagocytosis assay. The first part of this method involves building a ...

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