We are grateful to Lonza Group Ltd. for sponsoring this publication by covering the publication costs. We thank the Deutsche Infarktforschungshilfe, Wilhelm-Vaillant-Stiftung, Ernest-Solvay-Stiftung, and the Th&#252;ringer Ministerium f&#252;r Bildung, Wissenschaft und Kultur for financial support to SL.

1. Predifferentiation of THP-1 Macrophages
<ol>
	<li>Cultivate THP-1 cells in RPMI-1640 medium supplemented with 10% (v/v) fetal calf serum (FCS) and 1% (v/v) penicillin/streptomycin/L-glutamin (PSG) in a CO2 (5%) incubator at 37 &#176;C.</li>
	<li>Before transfection, split cells and transfer them to fresh RPMI medium as before. Cultivate cells for 24 hr.</li>
	<li>Seed 1.0-1.5 x 107 cells into a 75 cm&#178; tissue culture flask or 2.5 x 107 cells into a 150-cm&#178; tissue culture flask in RPMI-1640 medium and add 10% (v/v) FCS, 1% (v/v) PSG, 1% (v/v) sodium pyruvate, 1% (v/v) nonessential amino acids, 10&#160;ng/ml PMA, and 50 &#181;M &#946;-mercaptoethanol for 48 hr.</li>
</ol>
2. Preparation of Nucleofection
<ol>
	<li>Place Accutase I and all media into water bath at 37 &#176;C.</li>
	<li>Aspirate culture medium from flask and replace with 6 ml (75 cm&#178; flask) or 12 ml (150 cm&#178; flask) of Accutase I and incubate for 30 min at 37 &#176;C for full detachment of cells. Observe cell morphology after Accutase I treatment to ensure that cells have a round appearance. If some cells still appear to be attached, carefully rinse the flask with a micropipette or gently tap it to complete detachment. Do not use cell scrapers, as this will have a negative effect on cell vitality. Transfer cell suspension to a 15 ml tube.</li>
	<li>During Accutase I treatment, prepare the following media:
	<ol>
		<li>Prepare transfection medium: supplement cell culture medium with 1% (v/v) PSG, 1% (v/v) of nonessential amino acids, 1% (v/v) sodium pyruvate, and 5% (v/v) human serum (for siRNA) or 20% (v/v) human serum (for plasmid DNA); prepare a final volume of either 3 ml/sample for one 6-well plate or 4 ml/sample for two 12-well plates.</li>
		<li>Prepare cultivation medium: supplement culture medium with 1% (v/v) PSG, 1% (v/v) of nonessential amino acids, 1% (v/v) sodium pyruvate, and 5% (v/v) human serum (for siRNA) or 20% (v/v) human serum (for plasmid), 2.5 ng/ml PMA, and 50 &#181;M &#946;-mercaptoethanol; prepare a final volume of either 3 ml/sample for one 6-well plate or 4 ml/sample for two 12-well plates.</li>
	</ol>
	</li>
	<li>Centrifuge cell suspension for 5 min at 300 x&#160;g at room temperature.</li>
	<li>Aspirate Accutase I and resuspend cells in 1 ml of RPMI medium pre-warmed to 37 &#176;C; count cells to determine cell number. 
	NOTE: When fast automatic cell counting procedures are used, steps 2.4 and 2.5 may be omitted and cells can be counted immediately after detachment provided that prolonged exposure to Accutase I is avoided.</li>
	<li>For each transfection sample prepare aliquots in centrifuge tubes containing 2.0-2.5 x 106 cells.</li>
</ol>
3. Nucleofection of THP-1 Macrophages
<ol>
	<li>Centrifuge all aliquots for 10 min at 250 x&#160;g at room temperature.</li>
	<li>Dilute plasmid DNA or siRNA in nuclease-free water or an appropriate buffer. Keep the required volume of plasmid DNA or siRNA as small as possible.</li>
	<li>Prepare one Nucleofector cuvette with either 1 &#181;g of siRNA or 0.5 &#181;g of plasmid DNA for each transfection.</li>
	<li>Perform one transfection at a time. Aspirate supernatant from cell aliquot.</li>
	<li>Resuspend pelleted cells in Nucleofector solution to yield a total volume of 100 &#181;l of DNA/siRNA and Nucleofector solution. Keep the time of exposure to pure Nucleofector solution to a minimum and ensure that exposure time does not exceed 15 min.</li>
	<li>Mix resuspended cells and DNA/siRNA in Nucleofector cuvette by gentle tapping.</li>
	<li>Transfect cells by performing program Y-001 in Nucleofector 2b device.</li>
	<li>Transfer transfected cells into a reaction vial using disposable plastic Pasteur pipettes.</li>
	<li>Immediately add 500 &#181;l of prepared transfection medium.</li>
	<li>Repeat steps 3.4 to 3.9 for each transfection sample.</li>
</ol>
4. Post-Nucleofection Care
<ol>
	<li>Prepare either 6-well or 12-well plates for transfected cells. Pipette 2.5 ml of transfection medium into each well of a 6-well plate (1 well/transfection) or 1.75 ml of transfection medium into each well of a 12-well plate (2 wells/transfection).</li>
	<li>Mix cell suspensions thoroughly with a micropipette.</li>
	<li>Transfer the transfected cells into the prepared wells (either one well in a 6 well plate or two in a 12 well plate).</li>
	<li>Incubate plates for 4 hr in a humidified incubator (5% CO2, 37 &#176;C).</li>
	<li>Check reattachment of cells microscopically. 
	NOTE: A majority of cells should be adherent again. Occasionally, extending the incubation period by 1 hr increases the number of adherent cells in case of insufficient reattachment.</li>
	<li>Carefully aspirate transfection medium with a micropipette and replace with equal amount of cultivation medium. Aspirate only one well at a time.</li>
	<li>Incubate cells for required time period for maximal effect of plasmid or siRNA (24-72 hr). If incubation periods exceed 48 hr, replace medium after 48 hr.</li>
	<li>For additional treatment with effectors (e.g., cytokines, agonists, antagonists and inhibitors) use serum free medium without PMA and &#946;-mercaptoethanol. Time the end of the incubation period of the effector with the time of maximal effect of the plasmid or siRNA and plan the change of medium and addition of the effector accordingly. Do not maintain cells under serum free conditions for longer than 24 hr.</li>
</ol>

<ol><li>Ricardo, S. D., van Goor, H., Eddy, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Macrophage+diversity+in+renal+injury+and+repair%5BTitle%5D)+AND+%22J+Clin+Invest%22%5BJournal%5D)">Macrophage diversity in renal injury and repair.</a> J Clin Invest. 118 (11), 3522-3530 (2008).</li>
<li>Mosser, D. M., Edwards, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Exploring+the+full+spectrum+of+macrophage+activation%5BTitle%5D)+AND+%22Nat+Rev+Immunol%22%5BJournal%5D)">Exploring the full spectrum of macrophage activation.</a> Nat Rev Immunol. 8 (12), 958-969 (2008).</li>
<li>Morille, M., Passirani, C., Vonarbourg, A., Clavreul, A., Benoit, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Progress+in+developing+cationic+vectors+for+non-viral+systemic+gene+therapy+against+cancer%5BTitle%5D)+AND+%22Biomaterials%22%5BJournal%5D)">Progress in developing cationic vectors for non-viral systemic gene therapy against cancer.</a> Biomaterials. (24-25), 3477-3496 (2008).</li>
<li>Schnoor, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Efficient+non-viral+transfection+of+THP-1+cells%5BTitle%5D)+AND+%22J+Immunol+Methods%22%5BJournal%5D)">Efficient non-viral transfection of THP-1 cells.</a> J Immunol Methods. 344 (2), 109-115 (2009).</li>
<li>Maeß, M. B., Buers, I., Robenek, H., Lorkowski, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Improved+protocol+for+efficient+nonviral+transfection+of+premature+THP-1+macrophages%5BTitle%5D)+AND+%22Cold+Spring+Harb+Protoc%22%5BJournal%5D)">Improved protocol for efficient nonviral transfection of premature THP-1 macrophages.</a> Cold Spring Harb Protoc. 2011 (5), (2011).</li>
<li>Ma, W., Liu, Y., Ellison, N., Shen, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Induction+of+C-X-C+chemokine+receptor+type+7+%28CXCR7%29+switches+stromal+cell-derived+factor-1+%28SDF-1%29+signaling+and+phagocytic+activity+in+macrophages+linked+to+atherosclerosis%5BTitle%5D)+AND+%22J+Biol+Chem%22%5BJournal%5D)">Induction of C-X-C chemokine receptor type 7 (CXCR7) switches stromal cell-derived factor-1 (SDF-1) signaling and phagocytic activity in macrophages linked to atherosclerosis.</a> J Biol Chem. 288 (22), 15481-15494 (2013).</li>
<li>Xie, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Cell+surface+localization+of+ABCG1+does+not+require+LXR+activation%5BTitle%5D)+AND+%22Arterioscler+Thromb+Vasc+Biol%22%5BJournal%5D)">Cell surface localization of ABCG1 does not require LXR activation.</a> Arterioscler Thromb Vasc Biol. 26 (11), 143-144 (2006).</li>
<li>Buers, I., Robenek, H., Lorkowski, S., Nitschke, Y., Severs, N. J., Hofnagel, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((TIP47%2C+a+lipid+cargo+protein+involved+in+macrophage+triglyceride+metabolism%5BTitle%5D)+AND+%22Arterioscler+Thromb+Vasc+Biol%22%5BJournal%5D)">TIP47, a lipid cargo protein involved in macrophage triglyceride metabolism.</a> Arterioscler Thromb Vasc Biol. 29 (5), 767-773 (2009).</li>
<li>Robenek, H., Buers, I., Hofnagel, O., Lorkowski, S., Severs, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((GFP-tagged+proteins+visualized+by+freeze-fracture+immuno-electron+microscopy%3A+A+new+tool+in+cellular+and+molecular+medicine%5BTitle%5D)+AND+%22J+Cell+Mol+Med%22%5BJournal%5D)">GFP-tagged proteins visualized by freeze-fracture immuno-electron microscopy: A new tool in cellular and molecular medicine.</a> J Cell Mol Med. 13 (7), 1381-1390 (2009).</li>
<li>Guh, J. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Development+of+novel+adenosine+monophosphate-activated+protein+kinase+activators%5BTitle%5D)+AND+%22J+Med+Chem%22%5BJournal%5D)">Development of novel adenosine monophosphate-activated protein kinase activators.</a> J Med Chem. 53 (6), 2552-2561 (2010).</li>
<li>Park, E. K., Jung, H. S., Yang, H. I., Yoo, M. C., Kim, C., Kim, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Optimized+THP-1+differentiation+is+required+for+the+detection+of+responses+to+weak+stimuli%5BTitle%5D)+AND+%22Inflamm+Res%22%5BJournal%5D)">Optimized THP-1 differentiation is required for the detection of responses to weak stimuli.</a> Inflamm Res. 56 (1), 45-50 (2007).</li>
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<li>Angosto, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Evolution+of+inflammasome+functions+in+vertebrates%3A+Inflammasome+and+caspase-1+trigger+fish+macrophage+cell+death+but+are+dispensable+for+the+processing+of+IL-1b%5BTitle%5D)+AND+%22Innate+Immun%22%5BJournal%5D)">Evolution of inflammasome functions in vertebrates: Inflammasome and caspase-1 trigger fish macrophage cell death but are dispensable for the processing of IL-1b.</a> Innate Immun. 18 (6), 815-824 (2012).</li>
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Publication costs for this video-article are sponsored by&#160;Lonza Group Ltd.&#160;

The protocol outlined here presents a reliable and efficient way to transfect THP-1 macrophages which are usually rather difficult to transfect. Transfection can be achieved with transfection efficiencies of above 90% for siRNA without significant reduction of cell vitality. Efficiencies for plasmids may be less due to their size but transfection efficiencies of around 70% can be usually achieved. The efficiency of siRNA-mediated knockdown can reach 80 to 90% depending on the applied siRNA. A major advantage of this protocol is that it does not interfere with cell differentiation. After transfection the cells still respond normally to the differentiation agent PMA (Figure 1A to 1B and Figure 4)12. In addition cellular polarization by cytokine stimuli such as IL10 or LPS/IFN&#947; is unaffected12, although this also depends strongly on the medium selected for cultivation after transfection as shown in Figure 4.
There are several options within the procedure which can be modified in order to adapt the protocol to specific requirements. As shown in Figure 4 the cells react differently to the same IL10 stimulus depending on the culture medium selected after transfection. This indicates that the medium composition has strong influence on cellular behavior. As the effect imposed by the medium might differ for various experimental stimuli, it is possible that the optimal medium might change and therefore there is a need to verify the suitability of the medium for different experiments independently. However the RPMI-1640 medium, which is the default medium used for cultivation of THP-1 cells, has proven to be ill-suited for cultivation after transfection as a significant loss in cell vitality was observed. Furthermore the protocol can also be applied to THP-1 monocytes without prior PMA-induced differentiation, this obviously removes the need for cell detachment during the procedure but all remaining steps do not have to be adjusted. The THP-1 monocytes can be differentiated afterwards if required.
The most critical elements of the protocol are firstly the detachment and secondly the time required for transfection. The detachment must be performed as gently as possible, in order to maintain high cell viability. Therefore we recommend the comparatively mild enzymatic detachment by Accutase I over quite aggressive methods such as trypsinization. Further detachment methods such as treatment with Lidocain or scraping were found to be rather detrimental and should not be used. In the case that 30 min of Accutase I treatment should not be sufficient to detach all cells properly this is usually an indication of incorrectly stored or expired Accutase I solution or of too many freeze-thaw cycles. We have obtained good results by storing small aliquots of Accutase I at -20 &#176;C to reduce the number of freeze-thaw cycles. However when there is insufficient detachment either replace Accutase I with fresh Accutase or increase incubation time up to 1 hr. In addition gentle tapping or rinsing of the flask or plate can assist detachment. Regarding the required time for transfection the exposure time of the cells to pure Nucleofector solution has got high impact on cell survival and thus should be as short as possible. The best way to achieve this is to perform each transfection at a time (steps 2.10 to 2.15) and not multiple transfections in parallel.
If knockdown efficiency is low, this usually is not caused by low transfection efficiency, but this can be easily verified using flow cytometry or fluorescence microscopy and fluorescently labeled siRNA or a GFP encoding plasmid. Mostly the cause is an inefficient siRNA or plasmid DNA. Under these circumstances it should be considered to increase the amount of siRNA (up to 2-3 &#181;g) or plasmid DNA (up to 1-2 &#181;g) or to use a different siRNA or expression vector if available. Alternatively, satisfactory results might also be achieved by using a pool of several different siRNAs directed against the same target. Furthermore, time course experiments might be required to accurately determine the period of maximal effect, which is usually reached after 24 to 72 hr after transfection.
Apart from transfection by electroporation there are further well established techniques for transfection of mammalian cells. Frequently applied systems are chemical transfection agents which can form complexes with the cargo nucleic acid and then facilitate the transport into the cells. The most commonly used reagents are either based on different lipid species or can be chosen from a number of cationic polymers3. For both approaches a diverse selection is commercially available. These transfection reagents offer the advantage that they are usually easy to use, do not require much time, and work with adherent cells as well, thus removing the necessity for detachment. Unfortunately, macrophages are rather difficult to transfect by these methods as they do not proliferate significantly in vitro and possess defense mechanisms directed against foreign cytosolic DNA13-15. Thus, chemical transfection approaches frequently result in a severe reduction of cell viability. However as shown in Figure 2 there are chemical transfection agents which can successfully transfer siRNA into macrophages, but as flow cytometric (Figure 2A) and fluorescent microscopic (Figure 2B) analyses indicate they fail to achieve the same homogenous distribution of siRNA within the cells as obtained by Nucleofection. In fact, the flow cytometric data indicate that two different populations of transfected cells occur, firstly a population with similar fluorescence as the cells after Nucleofection is detected and secondly there is a population with more intense fluorescence. Definite confirmation is still required but we suppose that the first population is in the fluorescence microscopy identical with those cells which show a homogenous distribution of fluorescent siRNA within the cytosol while the second population likely corresponds to the cells with very bright agglomerates. The flow cytometric data shown in Figure 2A suggest that nucleofection results in less siRNA per cell than the alternative lipofection approach. However the data in Figure 3 shows that even the comparatively small amount of siRNA incorporated by Nucleofection is already sufficient for 80 to 90% knockdown of the target gene. Therefore the additional amount of siRNA incorporated by the second population after chemical transfection is very likely surplus and is thus more likely to cause undesired side effects than to further increase knockdown efficiency. Apart from that formation of intracellular agglomerates is already undesirable in itself since those siRNA molecules are likely not functional or at least less efficient than free siRNA molecules and might cause off target effects. Furthermore the true nature of these agglomerates is not yet clear. It is possible that these bright spots represent endosomes indicating that the siRNA was internalized by the cells but subsequently release from the endosomes failed and the siRNA remains trapped and therefore ineffective. Alternatively the spots could be agglomerates which are formed intracellularly. Functional evaluations of the chemical transfection are pending, therefore no definitive statements on knockdown efficiency can be made yet, still the existence of two distinct populations is already unfavorable as this means that all results describe the mean of both populations, this does therefore not correspond to either of the populations. For that reason Nucleofection is the superior approach.
Nevertheless there are also limitations to the transfection procedure outlined here. Since the cells have to be in suspension for Nucleofection adherent cells need to be detached, which presents an additional stress factor to the cells. Furthermore the entire protocol is rather time consuming. Since transfections cannot be performed simultaneously, but have to be performed quickly in order to avoid cell damage, the number of samples is limited to about 8 - 10 per experiment. Thus, this protocol is not suited for high throughput screening projects. For high throughput applications different Nucleofector systems are available. Firstly, there is the 4D-Nucleofector system that offers a 16 well strip format. For even larger throughput, there are the 96 well Shuttle system and the 384 well HT Nucleofector system. However as these newer systems work with conductive polymer electrodes instead of aluminum and therefore electrical conditions, i.e. programs and composition of Nucleofector solution, have changed accordingly, it needs to be determined if our protocol can be transferred to those systems.
However, despite these limitations the protocol presented here does yield a reliable and effective transfection of THP-1 cells which is superior to all other non-viral approaches. This protocol enables the investigation of the effects of altered gene expression in THP-1 cells which in all other aspects differentiate and polarize normally and thus show as little side effects of transfection as possible.

Among the cellular components of the human immune system, macrophages are of great importance for the innate immune response. Their tasks are diverse; they are involved in phagocytosis of pathogens and necrotic material, they play an important role in tissue homeostasis and produce and secrete a large number of cytokines to regulate and orchestrate the immune response1. Therefore macrophages are integrally involved in many physiological processes and pathophysiological conditions. Due to the diversity of their tasks, macrophages are a very heterogeneous and multifaceted cell type. This is achieved by different polarizations; depending on external stimuli macrophages can develop into different phenotypes2. Macrophages&#8217; variability and impact on the immune response make them a very interesting research subject. In order to elucidate their complex metabolic and regulatory functions, appropriate macrophage in vitro models are required which correctly reflect macrophage heterogeneity and variability.
Transfection of cells with plasmid DNA vectors or small interfering RNAs (siRNAs) in order to alter cellular gene expression has become a widely used and powerful tool in cell biology for investigating both gene regulation and gene function. Currently there is a large selection of different tools available for transfection of eukaryotic cells. These tools include the application of viral vectors, mechanical methods (such as gene guns), chemical approaches (which rely on polymers or lipids that can form complexes with nucleic acids), and electroporation of cells3. All of these approaches have their advantages and disadvantages and choosing the best suited from this wide array for a specific cell type and application can be a difficult and time consuming process.
Macrophages are notoriously difficult to transfect as almost all well-established transfection approaches drastically reduce macrophages&#8217; viability or interfere with their behavior, i.e. differentiation and in particular polarization. Therefore, we present here an efficient, non-viral protocol to transfect human THP-1 macrophages using the electroporation-based Nucleofector technology, which represents an optimized electroporation approach requiring reduced amounts of DNA. Nucleofection is well-suited for sensitive cells such as monocytes and macrophages. This protocol is an adaptation of previously published versions4,5.
In brief, phorbol 12-myristate 13-acetate (PMA) is used to differentiate human THP-1 monocytes for 48 hr into premature macrophages prior to transfection with siRNA or plasmid DNA. For transfection the predifferentiated macrophages are detached enzymatically by Accutase I treatment. The transfection is performed using a Nucleofector 2b device for electroporation of the cells. After transfection, differentiation is continued for another 24 to 48 hr as required. Finally, mature transfected macrophages are incubated with different kinds of compounds for functional studies.
This approach allows for the transfection of cell lines such as human THP-1 monocytes and macrophages and has been successfully applied in the past6-10. In contrast to most chemical transfection approaches, our modified Nucleofection procedure using premature macrophages yields high transfection efficiencies in combination with unimpaired cell viability, without the need to use viral vectors or add further carrier compounds with unknown side effects. In addition, the macrophages retain their full potential for differentiation as well as polarization thus allowing unimpeded functional investigations following transfection11.
Furthermore, the cell culture medium applied after Nucleofection strongly influences functional studies following transfection; in particular, the macrophages&#8217; capacity for polarization can be affected depending on the applied culture medium. Here four different types of cell culture media (IMDM, X-VIVO 20, LGM3 and Mouse T Cell Nucleofector medium) were tested under deactivating conditions using interleukin (IL) 10. Using THP-1 macrophages, we observed that cell responsiveness to IL10 is strongest when the Mouse T Cell Nucleofector medium is used in comparison to the other culture media mentioned above. These results demonstrate that appropriate optimization of all cell culture conditions is essential for successful transfection und subsequent functional studies as these may significantly improve experimental results.
As macrophages are involved in various human diseases, much research is focused on elucidating macrophage behavior as well as regulative mechanisms influencing macrophages or in turn controlled by macrophages. Therefore, this protocol is of relevance in many different research areas.

<table><tbody><tr><td>Accutase I</td><td>Sigma-Aldrich</td><td>A6964</td><td></td></tr><tr><td>Amino acids, nonessential</td><td>PAA</td><td>M11-003</td><td></td></tr><tr><td>Centrifuge tubes (15 ml)</td><td>TPP</td><td>TPP91015</td><td></td></tr><tr><td>Fetal calf serum (FCS gold)</td><td>PAA</td><td>A15-151</td><td></td></tr><tr><td>Human Monocyte Nucleofector Kit</td><td>Lonza</td><td>VPA-1007</td><td>Contains Nucleofector Solution, cuvettes, and Pasteur pipettes</td></tr><tr><td>Human serum off the clot</td><td>Lonza</td><td>C11-020</td><td></td></tr><tr><td>Isove&#039;s Modified Dulbecco&#039;s Medium (IMDM) with 25 mM HEPES and 25 mM L-glutamine</td><td>Lonza</td><td>12-722F</td><td></td></tr><tr><td>Lymphocyte Growth Medium 3 (LGM3)</td><td>Lonza</td><td>CC-3211</td><td></td></tr><tr><td>Mouse T Cell Nucleofector Medium</td><td>Lonza</td><td>VZB-1001</td><td></td></tr><tr><td>Nucleofector 2b</td><td>Lonza</td><td>AAD-1001</td><td></td></tr><tr><td>Penicillin / streptomycin / L-glutamine (100x)</td><td>Sigma-Aldrich</td><td>G1146</td><td></td></tr><tr><td>Phorbol 12-myristate 13-acetate (PMA)</td><td>Fisher Scientific</td><td>BP685</td><td></td></tr><tr><td>Roswell Park Memorial Institute 1640 Medium (RPMI 1640)</td><td>PAA</td><td>E15-840</td><td></td></tr><tr><td>siRNA / plasmid</td><td></td><td></td><td></td></tr><tr><td>Sodium pyruvate (100 mM)</td><td>Sigma-Aldrich</td><td>S8636</td><td></td></tr><tr><td>THP-1 human leukemia monocytes</td><td>CLS</td><td>300356</td><td></td></tr><tr><td>Tissue culture flasks (75 cm&amp;sup2;; 150 cm&amp;sup2;)</td><td>TPP</td><td>TPP90076/TPP90151</td><td></td></tr><tr><td>Tissue culture plates (6-well; 12-well)</td><td>TPP</td><td>TPP92406/TPP92012</td><td></td></tr><tr><td>Tubes (1.5 ml)</td><td>StarLab</td><td>S 1615-5500</td><td></td></tr><tr><td>Water (nuclease-free) or appropriate siRNA/plasmid buffer</td><td></td><td></td><td></td></tr><tr><td>X-Vivo 20 with gentamycin</td><td>Lonza</td><td>BE04-448Q</td><td></td></tr><tr><td>&amp;beta;-Mercaptoethanol</td><td>Sigma-Aldrich</td><td>M3148</td><td></td></tr></tbody></table>

highly efficient transfection of human thp-1 macrophages by nucleofection

Macrophages, as key players of the innate immune response, are at the focus of research dealing with tissue homeostasis or various pathologies. Transfection with siRNA and plasmid DNA is an efficient tool for studying their function, but transfection of macrophages is not a trivial matter. Although many different approaches for transfection of eukaryotic cells are available, only few allow reliable and efficient transfection of macrophages, but reduced cell vitality and severely altered cell behavior like diminished capability for differentiation or polarization are frequently observed. Therefore a transfection protocol is required that is capable of transferring siRNA and plasmid DNA into macrophages without causing serious side-effects thus allowing the investigation of the effect of the siRNA or plasmid in the context of normal cell behavior. The protocol presented here provides a method for reliably and efficiently transfecting human THP-1 macrophages and monocytes with high cell vitality, high transfection efficiency, and minimal effects on cell behavior. This approach is based on Nucleofection and the protocol has been optimized to maintain maximum capability for cell activation after transfection. The protocol is adequate for adherent cells after detachment as well as cells in suspension, and can be used for small to medium sample numbers. Thus, the method presented is useful for investigating gene regulatory effects during macrophage differentiation and polarization. Apart from presenting results characterizing macrophages transfected according to this protocol in comparison to an alternative chemical method, the impact of cell culture medium selection after transfection on cell behavior is also discussed. The presented data indicate the importance of validating the selection for different experimental settings.

Using this protocol for transfection of THP-1 macrophages with siRNA we usually achieve transfection rates of above 90% without significant reduction of cell vitality. Figure 1 shows representative data characterizing the state of the cells 24 hr after transfection with fluorescently labeled siRNA versus an untransfected control, which were not treated with Nucleofection reagents and pulse or siRNA but received all changes of culture media as transfected samples. In Figure 1A the cellular morphology is shown according to flow cytometric measurement. Microscopic images are shown in Figure 1B. Figures 1C and 1D represent the low rates for apoptosis (control: 1.5%; Nucleofection: 5.4%) and necrosis (control: 2.0%; Nucleofection: 3.2%) indicating unaffected cell vitality. Necrosis and apoptosis are slightly higher for the transfected sample as transfected THP-1 macrophages are more difficult to detach than untransfected cells, thus the probability of cell damage during detachment increases. Finally transfection efficiency is presented in Figure 1E. As the entire transfected population is shifted against the control, this indicates that all cells are transfected which is confirmed by fluorescence microscopic images (Figure 2B). Both flow cytometric data as well as fluorescence microscopic images indicate that all cells are consistently transfected with homogenous distribution of siRNA among cells as well as within cells. This is in contrast to many chemical transfection reagents, for comparison Figures 2A and 2B show the respective flow cytometric data and fluorescence microscopic images for a chemical transfection agent using a lipid based approach. These figures show that two distinct populations of transfected cells can be detected. The first population is similar to the transfected cells following Nucleofection. They are characterized by low overall fluorescence and homogenous distribution of siRNA within the cells. The second population is marked by a more intense fluorescence which originates from very bright intracellular agglomerates of siRNA. The cellular morphology remains unaffected for both transfection approaches as shown by differential interference contrast in Figure 2C. Transfections using plasmid DNA yield effectively similar results, for examples please refer to Robenek et al. (2009)9 or Xie et al. (2006)7.
The choice of the cell culture medium after transfection is of great relevance; therefore different cell culture media were tested in comparison. The selected media are all suitable for cultivation of THP-1 cells and were chosen according to recommendations of Lonza as applicable media for post-Nucleofection cultivation. Figure 3 represents the siRNA mediated knockdown efficiency using a siRNA directed against IL10RB (interleukin 10 receptor &#946; chain) mRNA. For all tested media the expression of IL10RB was significantly reduced to about 10 to 20% of the control level (Figure 3). However the transfected cells differ depending on the culture medium in their potential for polarization. THP-1 macrophages transfected with either unspecific control siRNA or IL10RB-specific siRNA were cultivated in different media after transfection and treated with IL10. Subsequently the expression levels of the IL10-induced gene SOCS3 (suppressor of cytokine signaling 3) on mRNA level were measured by RT-qPCR. Differences between culture media occur in regard to the extent of the induction of SOCS3 mRNA expression (Figure 4), the inductions for each of the tested media Mouse T Cell Nucleofector Medium, LGM3, X-VIVO 20 and IMDM were 19.5 [17.7-21.5], 11.5 [8.5-15.7], 8.0 [4.6-14.2] and 7.2 [5.6-9.5] fold, respectively. Therefore application of the Mouse T Cell Nucleofector medium is vital. In addition, differences in the effect of the knockdown of IL10RB on SOCS3 expression after IL10 treatment were observable, expression levels of SOCS3 mRNA were reduced to 9.5 [8.8-10.3] fold in Mouse T Cell Nucleofector medium, 2.1 [1.1-4.1] fold in LGM3, 4.8 [3.2-7.2] fold in X-VIVO 20 and 3.3 [2.7-3.9] fold in IMDM. These values correspond to reductions of SOCS3 expression in the different media to 49%, 18%, 60%, and 45%, respectively. Reduction of IL-10-induced SOCS3 expression after transfection of IL10RB siRNA confirms the successful downregulation of IL10RB by the transfection.
<img alt="Figure 1" fo:content-width="3in" src="/files/ftp_upload/51960/51960fig1highres.jpg" width="300" /> 
Figure 1.&#160;Characterization of transfected THP-1 macrophages. The characteristic status of the cells is unaffected as revealed by light microscopic and flow cytometric analyses of untransfected control cells versus THP-1 macrophages transfected according to the presented protocol. THP-1 macrophages were differentiated with 10 ng/ml PMA for 48 hr and transfected with fluorescently labeled (Alexa 488) unspecific control siRNA. 24 hr after transfection either images of live cells were taken (B), or the cells were detached by Accutase I treatment and analyzed by flow cytometry (A). Apoptosis and necrosis staining was performed using Annexin V-phycoerythrin (PE) (C) and 7-aminoactinomycin (7-AAD) (D). Transfection efficiency (E) was determined by flow cytometry using the fluorescence label attached to the siRNA. The fluorescence signal of the transfected cells (black) is shown against the control signal (grey).<a href="https://www.jove.com/files/ftp_upload/51960/51960fig1highres.jpg" target="_blank"> Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" fo:content-width="4in" src="/files/ftp_upload/51960/51960fig2highres.jpg" width="400" /> 
Figure 2.&#160;Comparison of intracellular distribution of siRNA after Nucleofection versus lipofection. THP-1 cells were differentiated for 48 hr according to this protocol and then transfected either by Nucleofection or by lipofection. The presented lipofection results were obtained using the Xtremegene siRNA kit according to the manufacturer&#8217;s recommendations with a charge ratio of reagent to siRNA of 4:1. 24 hr after transfection cells were either detached with Accutase I for flow cytometric analysis or evaluated microscopically with live cells. (A) Transfection efficiency and distribution of siRNA per cell within the population was determined by flow cytometry using the fluorescence label attached to the siRNA, controls transfected without siRNA are shown in grey, samples transfected with siRNA are shown in black. (B) Fluorescence microscopy images showing intracellular distribution of fluorescently labeled siRNA (Alexa Fluor 488); the scale bar represents 40 &#181;m. (C) Differential interference contrast image corresponding to the fluorescence image; the scale bar represents 40 &#181;m.<a href="https://www.jove.com/files/ftp_upload/51960/51960fig2highres.jpg" target="_blank"> Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" fo:content-width="5in" src="/files/ftp_upload/51960/51960fig3highres.jpg" width="500" /> 
Figure 3.&#160;siRNA-mediated knockdown of IL10RB in transfected THP-1 macrophages. THP-1 macrophages were transfected according to the outlined protocol. After transfection the cells were cultivated in four different culture media, namely Mouse T Cell Nucleofector medium (A), IMDM (B), LGM3 (C), and X-VIVO 20 (D), supplemented as described in the Protocol section. Cells were either transfected with unspecific control siRNA (Ctrl) or IL10RB-specific siRNA (IL10RB). As additional controls the following samples were included: Pulse control, i.e. cells which underwent transfection in the absence of siRNA (Pulse), and a medium control, i.e. cells that received only the changes of culture media but remained otherwise untreated. 24 hr after transfection the cells were incubated in serum-free medium with or without 50 ng/ml IL10 for further 24 hr. IL10RB expression was measured by RT-qPCR; diagrams show the mean of three independent experiments, error bars represent the standard error of the mean; * p &#60;0.05; ** p &#60;0.01; *** p &#60;0.001 vs. Ctrl.<a href="https://www.jove.com/files/ftp_upload/51960/51960fig3highres.jpg" target="_blank"> Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" fo:content-width="5in" src="/files/ftp_upload/51960/51960fig4highres.jpg" width="500" /> 
Figure 4.&#160;IL10-dependent regulation of SOCS3 after knockdown of IL10RB in transfected THP-1 macrophages. THP-1 macrophages were transfected according to the described protocol. After transfection the cells were cultivated in four different culture media Mouse T Cell Nucleofector medium (A), IMDM (B), LGM3 (C) and X-VIVO 20 (D) supplemented as described in the Protocol section. Cells were either transfected with unspecific control siRNA (Ctrl) or IL10RB-specific siRNA (IL10RB). As additional controls the following samples were included: Pulse control, i.e. cells which underwent transfection in the absence of siNRA (Pulse), and a medium control, i.e. cells that received only the changes of culture media but remained otherwise untreated. 24 hr after transfection the cells were incubated in serum free medium with or without 50 ng/ml IL10 for further 24 hr. SOCS3 expression was measured by RT-qPCR; diagrams show the mean of three independent experiments, error bars represent the standard error of the mean; *, # p &#60;0.05; **, ## p &#60;0.01; ***, ### p &#60;0.001 vs. Ctrl and vs. Ctrl + IL-10, respectively.<a href="https://www.jove.com/files/ftp_upload/51960/51960fig4highres.jpg" target="_blank"> Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Highly Efficient Transfection of Human THP-1 Macrophages by Nucleofection at JoVE.com

Highly Efficient Transfection of Human THP-1 Macrophages by Nucleofection

This protocol presents an efficient and reliable method to transfect human THP-1 macrophages with siRNA or plasmid DNA by electroporation with high transfection efficiency while maintaining high cell vitality and full macrophage capacity for differentiation and polarization.

Macrophages, as key players of the innate immune response, are at the focus of research dealing with tissue homeostasis or various pathologies. ...

highly-efficient-transfection-human-thp-1-macrophages

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Immunology and Infection

46.8K Views.  Friedrich Schiller University Jena. This protocol presents an efficient and reliable method to transfect human THP-1 macrophages with siRNA or plasmid DNA by electroporation with high transfection efficiency while maintaining high cell vitality and full macrophage capacity for differentiation and polarization.

Video: Highly Efficient Transfection of Human THP-1 Macrophages by Nucleofection

Transfecting Human Neural Stem Cells with the Amaxa Nucleofector

Transfection of primary mammalian neural cells, such as human neural stem/precursor cells (hNSPCs), with commonly used cationic lipid transfection reagents has often resulted in poor cell viability and low transfection efficiency.  Other mechanical methods of introducing a gene of interest, such as a &#8220;gene gun&#8221; or microinjection, are also limited by poor cell viability and low numbers of transfected cells.  The strategy of using viral constructs to introduce an exogenous gene into primary cells has been constrained by both the amount of time and labor required to create viral vectors and potential safety concerns.  We describe here a step-by-step protocol for transfecting hNSPCs using Amaxa's Nucleofector device and technology with electrical current parameters and buffer solutions specifically optimized for transfecting neural stem cells.  Using this protocol, we have achieved initial transfection efficiencies of ~35% and ~70% after stable transfection.  The protocol entails combining a high number of hNSPCs with the DNA to be transfected in the appropriate buffer followed by electroporation with the Nucleofector device.

Introducing a gene of interest into a cell is a powerful method for elucidating its function in vivo. This protocol describes an efficient method of transfecting a culture of human neural stem/precursor cells (hNSPCs) using the Nucleofector electroporation apparatus made by Amaxa.

Transfection of primary mammalian neural cells, such as human neural stem/precursor cells (hNSPCs), with commonly used cationic lipid transfection ...

Biology

A TIRF Microscopy Technique for Real-time, Simultaneous Imaging of the TCR and its Associated Signaling Proteins

Signaling is initiated through the T Cell Receptor (TCR) when it is engaged by antigenic peptide fragments bound by Major Histocompatibility Complex (pMHC) proteins expressed on the surface of antigen presenting cells (APCs). The TCR complex is composed of the ligand binding TCR&alpha;&beta; heterodimer that associates non-covalently with CD3 dimers (the &#949;&delta; and &#949;&gamma; heterodimers and the &zeta;&zeta; homodimer)1. Upon engagement of the receptor, the CD3 &zeta; chains are phosphorylated by the Src family kinase, Lck. This leads to the recruitment of the Syk family kinase, Zap70, which is then phosphorylated and activated by Lck. After that, Zap70 phosphorylates the adapter proteins LAT and SLP76, initiating the formation of the proximal signaling complex containing a large number of different signaling molecules2. 
The formation of this complex eventually results in calcium and Ras-dependent transcription factor activation and the consequent initiation of a complex series of gene expression programs that give rise to T cell differentiation2. TCR signals (and the resulting state of differentiation) are modulated by many other factors, including antigen potency and crosstalk with co-stimulatory/co-inhibitory, chemokine, and cytokine receptors 3-4. Studying the spatial and temporal organization of the proximal signaling complex under various stimulation conditions is, therefore, key to understanding the TCR signaling pathway as well as its regulation by other signaling pathways.
One very useful model system to study signaling initiated by the TCR at the plasma membrane in T cells is glass-supported lipid bilayers, as described previously5-6. They can be utilized to present antigenic pMHC complexes, adhesion, and co-stimulatory molecules to T cells-serving as artificial APCs. By imaging the T cells interacting with the lipid bilayer using total internal reflection fluorescence microscopy (TIRFM), we can restrict the excitation to within 100 nm of the space between the glass and the cell surface 7-8. This allows us to image primarily the signaling events occurring at the plasma membrane. As we are interested in imaging the recruitment of signaling proteins to the TCR complex, we describe a two-camera TIRF imaging system wherein the TCR, labeled with fluorescent Fab (fragment antigen binding) fragments of the H57 antibody (purified from hybridoma H57-597, ATCC, ATCC Number:HB-218) which is specific for TCR&beta;, and signaling proteins, tagged with GFP, may be imaged simultaneously and in real time. This strategy is necessary due to the highly dynamic nature of both the T cells and of the signaling events that are occurring at the TCR. This imaging modality has allowed researchers to image single ligands 9-11 as well as recruitment of signaling molecules to activated receptors and is an excellent system to study biochemistry in-situ12-16.

The compartmentalization of proteins either within the plasma membrane or into intracellular locations is one regulatory mechanism that can greatly influence signaling outcomes; hence, to understand signaling it is important to study the spatial and temporal behavior of the proteins involved. We describe here a TIRF microscopy based system to study signal transduction in T cells, but is broadly applicable.

Signaling is initiated through the T Cell Receptor (TCR) when it is engaged by antigenic peptide fragments bound by Major Histocompatibility Complex ...

piggyBac Transposon System Modification of Primary Human T Cells

The piggyBac transposon system is naturally active, originally derived from the cabbage looper moth1,2. This non-viral system is plasmid based, most commonly utilizing two plasmids with one expressing the piggyBac transposase enzyme and a transposon plasmid harboring the gene(s) of interest between inverted repeat elements which are required for gene transfer activity. PiggyBac mediates gene transfer through a "cut and paste" mechanism whereby the transposase integrates the transposon segment into the genome of the target cell(s) of interest. PiggyBac has demonstrated efficient gene delivery activity in a wide variety of insect1,2, mammalian3-5, and human cells6 including primary human T cells7,8. Recently, a hyperactive piggyBac transposase was generated improving gene transfer efficiency9,10.
Human T lymphocytes are of clinical interest for adoptive immunotherapy of cancer11. Of note, the first clinical trial involving transposon modification of human T cells using the Sleeping beauty transposon system has been approved12. We have previously evaluated the utility of piggyBac as a non-viral methodology for genetic modification of human T cells. We found piggyBac to be efficient in genetic modification of human T cells with a reporter gene and a non-immunogenic inducible suicide gene7. Analysis of genomic integration sites revealed a lack of preference for integration into or near known proto-oncogenes13. We used piggyBac to gene-modify cytotoxic T lymphocytes to carry a chimeric antigen receptor directed against the tumor antigen HER2, and found that gene-modified T cells mediated targeted killing of HER2-positive tumor cells in vitro and in vivo in an orthotopic mouse model14. We have also used piggyBac to generate human T cells resistant to rapamycin, which should be useful in cancer therapies where rapamycin is utilized15.
Herein, we describe a method for using piggyBac to genetically modify primary human T cells. This includes isolation of peripheral blood mononuclear cells (PBMCs) from human blood followed by culture, gene modification, and activation of T cells. For the purpose of this report, T cells were modified with a reporter gene (eGFP) for analysis and quantification of gene expression by flow cytometry.
PiggyBac can be used to modify human T cells with a variety of genes of interest. Although we have used piggyBac to direct T cells to tumor antigens14, we have also used piggyBac to add an inducible safety switch in order to eliminate gene modified cells if needed7. The large cargo capacity of piggyBac has also enabled gene transfer of a large rapamycin resistant mTOR molecule (15 kb)15. Therefore, we present a non-viral methodology for stable gene-modification of primary human T cells for a wide variety of purposes.

piggyBac Transposon System Modification of Primary Human T Cells

We describe a method to genetically modify primary human T cells with a transgene using the non-viral piggyBac transposon system. T cells modified to using the piggyBac transposon system exhibit stable transgene expression.

The piggyBac transposon system is naturally active, originally derived from the cabbage looper moth1,2. This non-viral system is plasmid based, most ...

Using RNA-interference to Investigate the Innate Immune Response in Mouse Macrophages

Macrophages are key phagocytic innate immune cells. When macrophages encounter a pathogen, they produce antimicrobial proteins and compounds to kill the pathogen, produce various cytokines and chemokines to recruit and stimulate other immune cells, and present antigens to stimulate the adaptive immune response. Thus, being able to efficiently manipulate macrophages with techniques such as RNA-interference (RNAi) is critical to our ability to investigate this important innate immune cell. However, macrophages can be technically challenging to transfect and can exhibit inefficient RNAi-induced gene knockdown. In this protocol, we describe methods to efficiently transfect two mouse macrophage cell lines (RAW264.7 and J774A.1) with siRNA using the Amaxa Nucleofector 96-well Shuttle System and describe procedures to maximize the effect of siRNA on gene knockdown. Moreover, the described methods are adapted to work in 96-well format, allowing for medium and high-throughput studies. To demonstrate the utility of this approach, we describe experiments that utilize RNAi to inhibit genes that regulate lipopolysaccharide (LPS)-induced cytokine production.

In this protocol, we describe methods to efficiently transfect murine macrophage cell lines with siRNAs using the Amaxa Nucleofector 96-well Shuttle System, stimulate the macrophages with lipopolysaccharide, and monitor the effects on inflammatory cytokine production.

Macrophages are key phagocytic innate immune cells.  When macrophages encounter a pathogen, they produce antimicrobial proteins and compounds to kill the ...

Quantification of Efferocytosis by Single-cell Fluorescence Microscopy

Studying the regulation of efferocytosis requires methods that are able to accurately quantify the uptake of apoptotic cells and to probe the signaling and cellular processes that control efferocytosis. This quantification can be difficult to perform as apoptotic cells are often efferocytosed piecemeal, thus necessitating methods which can accurately delineate between the efferocytosed portion of an apoptotic target versus residual unengulfed cellular fragments. The approach outlined herein utilizes dual-labeling approaches to accurately quantify the dynamics of efferocytosis and efferocytic capacity of efferocytes such as macrophages. The cytosol of the apoptotic cell is labeled with a cell-tracking dye to enable monitoring of all apoptotic cell-derived materials, while surface biotinylation of the apoptotic cell allows for differentiation between internalized and non-internalized apoptotic cell fractions. The efferocytic capacity of efferocytes is determined by taking fluorescent images of live or fixed cells and quantifying the amount of bound versus internalized targets, as differentiated by streptavidin staining. This approach offers several advantages over methods such as flow cytometry, namely the accurate delineation of non-efferocytosed versus efferocytosed apoptotic cell fractions, the ability to measure efferocytic dynamics by live-cell microscopy, and the capacity to perform studies of cellular signaling in cells expressing fluorescently-labeled transgenes. Combined, the methods outlined in this protocol serve as the basis for a flexible experimental approach that can be used to accurately quantify efferocytic activity and interrogate cellular signaling pathways active during efferocytosis.

Efferocytosis, the phagocytic removal of apoptotic cells, is required to maintain homeostasis and is facilitated by receptors and signaling pathways that allow for the recognition, engulfment, and internalization of apoptotic cells. Herein, we present a fluorescence microscopy protocol for the quantification of efferocytosis and the activity of efferocytic signaling pathways.

Studying the regulation of efferocytosis requires methods that are able to accurately quantify the uptake of apoptotic cells and to probe the signaling ...

Highly Efficient Transfection of Primary Macrophages with In Vitro Transcribed mRNA

Macrophages are phagocytic cells specialized in detecting molecules of non-self origin. To this end, they are equipped with a large array of pattern recognition receptors (PRRs). Unfortunately, this also makes macrophages particularly challenging to transfect as the transfection reagent and the transfected nucleic acids are often recognized by the PRRs as non-self. Therefore, transfection often results in macrophage activation and degradation of the transfected nucleic acids or even in suicide of the macrophages. Here, we describe a protocol that allows highly efficient transfection of murine primary macrophages such as peritoneal macrophages (PM) and bone marrow-derived macrophages (BMDM) with mRNA in vitro transcribed from DNA templates such as plasmids. With this simple protocol, transfection rates of about 50-65% for PM and about 85% for BMDM are achieved without cytotoxicity or immunogenicity observed. We describe in detail the generation of mRNA for transfection from DNA constructs such as plasmids and the transfection procedure.

Macrophages, especially primary macrophages, are challenging to transfect as they specialize in detecting molecules of non-self origin. We describe a protocol that allows highly efficient transfection of primary macrophages with mRNA generated from DNA templates such as plasmids.

Macrophages are phagocytic cells specialized in detecting molecules of non-self origin. To this end, they are equipped with a large array of pattern ...

Transfecting RAW264.7 Cells with a Luciferase Reporter Gene

Transfection of desired genetic materials into cells is an inevitable procedure in biomedical research studies. While numerous methods have been described, certain types of cells are resistant to many of these methods and yield low transfection efficiency1, potentially hindering research in those cell types. In this protocol, we present an optimized transfection procedure to introduce luciferase reporter genes as a plasmid DNA into the RAW264.7 macrophage cell line. Two different types of transfection reagents (lipid-based and polyamine-based) are described, and important notes are given throughout the protocol to ensure that the RAW264.7 cells are minimally altered by the transfection procedure and any experimental data obtained are the direct results of the experimental treatment. While transfection efficiency may not be higher compared to other transfection methods, the described procedure is robust enough for detecting luciferase signal in RAW264.7 without changing the physiological response of the cells to stimuli.

Transfection into the macrophage cell line, RAW264.7, is difficult due to the cell&#8217;s natural response against foreign materials. We described here a gentle yet robust procedure for transfecting luciferase reporter genes into RAW264.7 cells.

Transfection of desired genetic materials into cells is an inevitable procedure in biomedical research studies. While numerous methods have been ...

Electroporation-Based CRISPR-Cas9-Mediated Gene Knockout in THP-1 Cells and Single-Cell Clone Isolation

The human acute monocytic leukemia (AML) THP-1 cell line is widely used as a model to study the functions of human monocyte-derived macrophages, including their interplay with significant human pathogens such as the human immunodeficiency virus (HIV). Compared to other immortalized cell lines of myeloid origin, THP-1 cells retain many intact inflammatory signaling pathways and display phenotypic characteristics that more closely resemble those of primary monocytes, including the ability to differentiate into macrophages when treated with phorbol-12-myristate 13-acetate (PMA). The use of CRISPR-Cas9 technology to engineer THP-1 cells through targeted gene knockout (KO) provides a powerful approach to better characterize immune-related mechanisms, including virus-host interactions. This article describes a protocol for efficient CRISPR-Cas9-based engineering using electroporation to deliver pre-assembled Cas9:sgRNA ribonucleoproteins into the cell nucleus. Using multiple sgRNAs targeting the same locus at slightly different positions results in the deletion of large DNA fragments, thereby increasing editing efficiency, as assessed by the T7 endonuclease I assay. CRISPR-Cas9-mediated editing at the genetic level was validated by Sanger sequencing followed by Inference of CRISPR Edits (ICE) analysis. Protein depletion was confirmed by immunoblotting coupled with a functional assay. Using this protocol, up to 100% indels in the targeted locus and a decrease of over 95% in protein expression were achieved. The high editing efficiency makes it convenient to isolate single-cell clones by limiting dilution.

The THP-1 cell line is widely used as a model to investigate the functions of human monocytes/macrophages across various biology-related research areas. This article describes a protocol for efficient CRISPR-Cas9-based engineering and single-cell clone isolation, enabling the production of robust and reproducible phenotypic data.

The human acute monocytic leukemia (AML) THP-1 cell line is widely used as a model to study the functions of human monocyte-derived macrophages, including ...

Expression of Fluorescent Fusion Proteins in Murine Bone Marrow-derived Dendritic Cells and Macrophages

Dendritic cells and macrophages are crucial cells that form the first line of defense against pathogens. They also play important roles in the initiation of an adaptive immune response. Experimental work with these cells is rather challenging. Their abundance in organs and tissues is relatively low. As a result, they cannot be isolated in large numbers. They are also difficult to transfect with cDNA constructs. In the murine model, these problems can be partially overcome by in vitro differentiation from bone marrow progenitors in the presence of M-CSF for macrophages or GM-CSF for dendritic cells. In this way, it is possible to obtain large amounts of these cells from very few animals. Moreover, bone marrow progenitors can be transduced with retroviral vectors carrying cDNA constructs during early stages of cultivation prior to their differentiation into bone marrow derived dendritic cells and macrophages. Thus, retroviral transduction followed by differentiation in vitro can be used to express various cDNA constructs in these cells. The ability to express ectopic proteins substantially extends the range of experiments that can be performed on these cells, including live cell imaging of fluorescent proteins, tandem purifications for interactome analyses, structure-function analyses, monitoring of cellular functions with biosensors and many others. In this article, we describe a detailed protocol for retroviral transduction of murine bone marrow derived dendritic cells and macrophages with vectors coding for fluorescently-tagged proteins. On the example of two adaptor proteins, OPAL1 and PSTPIP2, we demonstrate its practical application in flow cytometry and microscopy. We also discuss the advantages and limitations of this approach.

In this article, we provide a detailed protocol for the expression of fluorescent fusion proteins in murine bone marrow derived dendritic cells and macrophages. The method is based on the transduction of bone marrow progenitors with retroviral constructs followed by differentiation into macrophages and dendritic cells in vitro.

Dendritic cells and macrophages are crucial cells that form the first line of defense against pathogens. They also play important roles in the initiation ...

Transfecting Primary Macrophages with Modified mRNA

Source: Herb, M. et al., <a href="https://app.jove.com/v/60143">Highly Efficient Transfection of Primary Macrophages with In Vitro Transcribed mRNA.</a> J. Vis. Exp. (2019)
This video demonstrates the process of transfecting primary macrophages with modified mRNA encoding green fluorescent protein. These modified mRNAs, designed to reduce immunogenicity and improve its stability, ensure the successful transfection and subsequent expression of green fluorescent proteins, which is confirmed through fluorescence microscopy.

Highly Efficient Transfection of Human THP-1 Macrophages by Nucleofection

Summary

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Highly Efficient Transfection of Primary Macrophages with In Vitro Transcribed mRNA

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