This work was supported by grants awarded to C.J.H. (Health research Council of New Zealand and Marsden Fund, Royal Society of New Zealand) and Z.W. (Faculty Research Development Fund from the University of Auckland). The authors thank Alhad Mahagaonkar for expert management of the zebrafish facility, the Biomedical Imaging Research Unit, School of Medical Sciences, University of Auckland for assistance with confocal imaging and Graham Lieschke for gifting the Tg(mpeg1:EGFP) reporter line.

1. Preparation of Drug-loaded Marina Blue-labeled Liposomes
NOTE: Liposomes carrying the blue fluorescent dye, Marina Blue and drug are prepared using a thin film hydration method with post insertion of poloxamer 188. All procedures are performed at room temperature unless otherwise specified. Control liposomes only carry Marina blue and PBS. The example here describes loading liposomes with a mitochondria-targeting antioxidant drug25 that is used in the representative results as a proof-of-concept.
<ol>
	<li>To prepare liposomes, dissolve 16.4 mg (22.2 &#181;mol) of the phospholipids 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (see Table of Materials), 4.3 mg (11.1 &#181;mol) cholesterol (see Table of Materials) and 2.8 mg (3.7 &#181;mol) 1,2-diseteroyl-sn-glycero-3-phosphocholine (see Table of Materials, in 3 mL of chloroform:methanol (3:1 v/v) in a 25 mL round-bottom flask.</li>
	<li>To the above mixture, add 31 nmol of Marina Blue 1,2-dihexadecanoyl-sn-glycero-phosphoethanolamine (see Table of Materials) and 300 nmol of a mROS inhibiting drug (see Table of Materials) and sonicate briefly to fully dissolve. For control liposomes, only add Marina Blue 1,2-dihexadecanoyl-sn-glycero-phosphoethanolamine. 
	NOTE: To avoid photobleaching of the light-sensitive Marina Blue fluorescent dye, protect all procedures from light, where possible. This is also important if the drug to be loaded is light-sensitive.</li>
	<li>Remove the solvent slowly on a rotary evaporator (see Table of Materials) over a temperature controlled water bath set to 45 &#176;C by rotating at 75 rpm under vacuum pressure (200 mbar for 15 min then 0 mbar for 20 min). This forms a dry thin lipid film within the glass walls of the flask that is further dried for 45 min under N2 to facilitate complete removal of the organic solvent.</li>
	<li>Following formation of the thin film, set the vacuum pressure to 40 mbar for 15 min, then purge with nitrogen gas for 30 min to ensure removal of residue solvent.</li>
	<li>Hydrate the thin film using 1 mL of phosphate-buffered saline (PBS, pH 7.4) and seal with parafilm before agitating the flask using a rotary evaporator over a 60 &#176;C water bath for 20 min in order to form vesicles.</li>
	<li>Subject the hydrated suspension to 7 cycles of freeze and thaw by freezing in liquid N2 for 3 min followed by immersion in a 45 &#176;C water bath for 7 min.</li>
	<li>Extrude liposomes through a membrane using a mini-extruder (see Table of Materials) and 1.0 &#181;m track-etched polycarbonate membranes (see Table of Materials) for 2-6 cycles in order to obtain large unilamellar vesicles. 
	NOTE: In order to achieve more favorable targeting towards macrophages, manipulate extrusion cycles until the diameter of liposomes is approximately 1 &#181;m26,27,28.</li>
	<li>Condense the fresh liposomes into a pellet by ultracentrifugation at 186,000 x g and incubate with 1 mL of 1% poloxamer 188 (see Table of Materials) solution (10 mg/mL in PBS) at 45 &#176;C and 750 rpm for 30 min using a thermomixer with a 2 mL microcentrifuge tube attachment (see Table of Materials).</li>
	<li>Ultracentrifuge the mixture at 186,000 x g for 1 h at 4 &#176;C and remove the supernatant in order to remove any unbound polymer or drug. Store the liposomes pellets at 4 &#176;C, protected from light.</li>
</ol>
2. Characterization of Liposome Size and Zeta Potential
<ol>
	<li>Dilute liposome formulation with ultrapure water (1:100) and measure the particle size, polydispersity index (PDI) and zeta potential of the liposomes using a dynamic light scattering analyzer (see Table of Materials), in triplicate at 25 &#176;C. 
	NOTE: The PDI is a measure of the size distribution of the nanoparticle population. PDI values &#60; 0.05 indicates a more uniform distribution while values closer to 1 indicate a larger size distribution. The zeta potential is the overall surface charge.</li>
</ol>
3. Calculation of Entrapment Efficiency and Drug Loading in Liposomes
NOTE: To determine the entrapment efficiency of drug in liposomes, the drug content contained in the supernatant and liposome pellet are measured.
<ol>
	<li>Resuspend the liposome pellet in 1 mL of PBS.</li>
	<li>Remove the supernatant, dilute 10 x with ultrapure water and analyze by high-performance liquid chromatography (HPLC).</li>
	<li>To determine the drug concentration within the liposomes, add 100 &#181;L of liposome suspension to 900 &#181;L of 10% triton-X100 solution (to destroy the lipid membrane, releasing the entrapped drug and preventing lipid build up within the HPLC column) and vortex for 3 min before analysis.</li>
	<li>Inject 20 &#956;L of sample into an HPLC system consisting of a quaternary pump, thermostat auto-sampler and a 3 &#956;m 250 x 4.6 mm column. Set the mobile phase (10 mM PBS pH 2.5, acetonitrile and methanol (30:40:30, v/v/v)) flow rate to 0.9 mL/min and obtain spectral profiles using a diode array detector set at 230 mM.</li>
	<li>Calculate the entrapment efficiency (EE) and drug loading (DL) using the following equations: 
	EE (%) = [Me / Mt] x 100 
	DL (%) = [Me / Mlip] x 100 
	Where Me is the mass of drug encapsulated, Mt is the total mass of drug used during formulation and Mlip is the total mass of the lipids (including cholesterol) and encapsulated drug.</li>
</ol>
4. Preparation and Injection of Liposomes
<ol>
	<li>Prepare borosilicate microinjection needles by inserting a thin wall borosilicate glass capillary (1 mm O.D. x 0.78 mm I.D. x 10 cm length) into a micropipette puller device (see Table of Materials) with the following generic puller settings (heat 680, pull 75, velocity 40, time 55 and pressure 530) to produce a tapered microinjection needle.</li>
	<li>Place the needles into a Petri dish onto the modeling clay and arrange in a way that the pulled end is not touching the bottom of the dish. Keep the Petri dish lid closed to avoid dust contamination until ready for use.</li>
	<li>Dilute freshly-prepared liposome formulations 1:1 in sterile PBS (pH 7.4) and briefly vortex (2-3 s) to mix. 
	NOTE: Protect liposomes from light until larvae are ready for microinjection.</li>
	<li>Set up adult zebrafish breeding pairs the night before and collect embryos as previously described by Rosen et al.29.</li>
	<li>Transfer the embryos into a Petri dish (100 mm x 20 mm style with approximately 60 embryos per dish) containing E3 medium (5 mM NaCl, 0.17 mM KCl, 0.33 mM CaCl2, 0.33 mM MgSO4) supplemented with 0.1% methylene blue to inhibit fungal growth. Remove all dead or unfertilized embryos and incubate overnight at 28.5 &#176;C.</li>
	<li>To facilitate live imaging, add 0.003% N-Phenylthiourea (PTU) to the E3 media when the embryos reach 24 h of development to prevent pigment formation (melanization).</li>
	<li>Manually dechorionate the embryos at approximately 30 h post fertilization (hpf) using fine tip forceps. 
	NOTE: Do not use enzymatic treatment to dechorionate embryos as this can cause epithelial damage and local inflammation thereby influencing immunological studies</li>
	<li>Let the embryos develop at 28.5 &#176;C until 2 days post fertilization (dpf).</li>
	<li>Prepare an injection plate by pouring enough 3% methyl cellulose (in E3 media) into the lid of a small 35 mm culture dish to form a thin film covering the entire surface. 
	NOTE: When preparing 3% methyl cellulose in E3 media, it takes several days for the methyl cellulose to dissolve with gentle agitation on an orbital shaker.</li>
	<li>Anaesthetize the larvae by incubating in E3 media supplemented with 200 &#181;g/mL of Tricaine.</li>
	<li>Collect a pool of approximately 20-25 larvae using a plastic transfer pipette and allow the embryos to concentrate at the tip of the pipette by gravity. Taking care to transfer the larvae with minimal liquid, place them in the middle of the 35 mm culture dish lid.</li>
	<li>Using a microcapillary loader, arrange the larvae in the following ways: anterior towards the top of the injection plate with the dorsal surface facing toward the microinjection needle, to inject into the hindbrain ventricle (Figure 2A-D); or, anterior towards the left of the injection plate (when injecting from the right) with the ventral surface facing towards the microinjection needle to inject into the sinus venosus (Figure 2I). 
	NOTE: When injected this way, hindbrain ventricle-resident (Figure 2E) and caudal hematopoietic tissue(CHT)-resident (Figure 2J) macrophages can be targeted, respectively. The CHT region of larval zebrafish is a hematopoietic site analogous to the mammalian fetal liver. Pay extra attention not to damage the embryos while arranging as this may cause local inflammation thereby influencing immunological studies.</li>
	<li>Take freshly prepared liposomes (from step 4.3) and back fill an injection needle with approximately 5 &#956;L of the liposome injection mix using an microcapillary loader (see Table of Materials). 
	NOTE: When assessing the localization of liposomes to the phagolysosomal compartments of macrophages (Figure 2H), supplement this injection mix with 200 &#956;g/mL of a red fluorescent marker of phagosomes (see Table of Materials) and 100 nM of a far red fluorescent marker of lysosomes (see Table of Materials) to mark phagosomes30,31 and lysosomes32, respectively.</li>
	<li>Mount the needle into a micromanipulator (see Table of Materials) connected to a magnetic stand and a pressure injector (see Table of Materials). Position under a stereomicroscope and set the injector to a pulse duration of approximately 50 ms and an injection pressure of approximately 40 psi.</li>
	<li>Cut the tip of the microinjection needle with clean fine tip forceps to generate an opening of approximately 5 &#956;m in diameter.</li>
	<li>Calibrate the volume to be injected by injecting a bolus into a drop of mineral oil positioned over the grid lines of a hemocytometer. Adjust the pulse duration and/or the injection pressure until the diameter of the bolus covers 2.5 of the smallest grid lines (this corresponds to a volume of approximately 1 nL).</li>
	<li>Carefully inject 1 nL of the liposome injection mix into the hindbrain ventricle of each larvae. 
	NOTE: When injecting into the hindbrain ventricle, take care not to penetrate too far ventrally (beyond the hindbrain) as this can disrupt the underlying vasculature leading to hemorrhages. When injecting into the sinus venosus, care should be taken to ensure the tip of the needle is just within the pericardium and not penetrating the yolk.</li>
	<li>Following injection, immediately transfer the injected larvae back into E3 media by adding E3 media to the injection plate and gently agitating the larvae out of the methyl cellulose using a plastic transfer pipette.</li>
	<li>Incubate the larvae at 28.5 &#176;C (protected from light) until analysis by live confocal imaging.</li>
</ol>
5. Confocal Imaging and Image Analysis to Confirm Macrophage Targeting of Liposomes
<ol>
	<li>Heat a water bath to 50 &#176;C.</li>
	<li>Anaesthetize liposome-injected larvae by transferring to a new Perti dish containing E3 media supplemented with 0.003% PTU and 200 &#181;g/mL Tricaine.</li>
	<li>Prepare live imaging mounting medium by dissolving 1% low melting point agarose in E3 media, supplemented with 0.003% PTU, in a microwave. Place in the water bath and once the solution has cooled to 50 &#176;C, add 200 &#181;g/mL of Tricaine.</li>
	<li>Keep the mounting medium in the 50 &#176;C water bath to prevent premature polymerization of the agarose.</li>
	<li>To image the dorsal surface of the hindbrain on a confocal microscope equipped with a water immersion lens (Figure 2E), embed the larvae as follows: Fill a 35 mm culture dish with the mounting medium (to a depth of approximately 5 mm) and let it polymerize. Excavate a small trench in the agarose that is of sufficient size to accommodate the yolk sac.</li>
	<li>Fill a plastic transfer pipette with molten mounting medium, expel a small quantity, and use it to collect the anaesthetized larvae. Immediately transfer the larvae into the culture dish and orientate the yolk sacs, ventral side down, into the excavated holes, using a microcapillary loader. Periodically maintain them in this position until the agarose polymerizes. Overlay with E3 media supplemented with 200 &#181;g/mL Tricaine. 
	NOTE: When transferring and positioning larvae, take care not to cause epithelial damage and local inflammation which can influence immunological studies. For positioning of larvae to live image the CHT region (Figure 2J), mount as described above, but position the larvae within the excavated hole laterally.</li>
	<li>When imaging on an inverted confocal microscope, embed the larvae, without the agarose bed, directly on the bottom of a glass bottom dish. Arrange them dorsal surface down (or laterally) and following polymerization, cover the entire dish surface with an even layer of mounting medium. Once polymerized, add a thin layer of E3 media supplemented with 200 &#181;g/mL of Tricaine.</li>
	<li>To live image the hindbrain ventricle on a confocal microscope, use the following settings: 512 x 512 pixels; 40 x 3 &#956;m Z-stacks (extending from dorsal-most surface of the hindbrain); 20x objective; 2.5x zoom. 
	NOTE: When comparing signal intensities between samples (for example when imaging the uptake of Marina Blue-labeled liposomes injected within reporter lines marking either macrophages [Tg(mpeg1:EGFP)33] or neutrophils [Tg(lyz:EGFP)34]), it is essential that laser settings are kept the same (e.g., pinhole diameter, laser voltage, offset and gain) to help ensure any differences are not an artifact of altered image acquisition settings.</li>
	<li>Use 3D image analysis software to quantify macrophage or neutrophil uptake of Marina Blue-labeled liposomes. To quantify the number of cells containing liposomes (Figure 2F) within a Z-stack, scroll through the individual Z sections and count the number of individual cells containing Marina Blue-labeled liposomes. To quantify the fluorescence intensity of liposomes within cells (Figure 2G), draw a region of interest around each cell (in the X, Y and Z dimensions) to quantify the total or mean fluorescence intensity of intracellular Marina Blue.</li>
</ol>

<ol>
	<li>Chow, A., Brown, B. D., Merad, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studying+the+mononuclear+phagocyte+system+in+the+molecular+age.">Studying the mononuclear phagocyte system in the molecular age.</a> Nature Reviews Immunology. 11 (11), 788-798 (2011).</li><li>Li, Q., Barres, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microglia+and+macrophages+in+brain+homeostasis+and+disease.">Microglia and macrophages in brain homeostasis and disease.</a> Nature Reviews Immunology. 18 (4), 225-242 (2018).</li><li>Krenkel, O., Tacke, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liver+macrophages+in+tissue+homeostasis+and+disease.">Liver macrophages in tissue homeostasis and disease.</a> Nature Reviews Immunology. 17 (5), 306-321 (2017).</li><li>Alderton, G. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumour+immunology:+turning+macrophages+on,+off+and+on+again.">Tumour immunology: turning macrophages on, off and on again.</a> Nature Reviews Immunology. 14 (3), 136-137 (2014).</li><li>Moore, K. J., Sheedy, F. J., Fisher, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Macrophages+in+atherosclerosis:+a+dynamic+balance.">Macrophages in atherosclerosis: a dynamic balance.</a> Nature Reviews Immunology. 13 (10), 709-721 (2013).</li><li>Lawrence, T., Natoli, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcriptional+regulation+of+macrophage+polarization:+enabling+diversity+with+identity.">Transcriptional regulation of macrophage polarization: enabling diversity with identity.</a> Nature Reviews Immunology. 11 (11), 750-761 (2011).</li><li>Chawla, A., Nguyen, K. D., Goh, Y. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Macrophage-mediated+inflammation+in+metabolic+disease.">Macrophage-mediated inflammation in metabolic disease.</a> Nature Reviews Immunology. 11 (11), 738-749 (2011).</li><li>Renshaw, S. A., Trede, N. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+model+450+million+years+in+the+making:+zebrafish+and+vertebrate+immunity.">A model 450 million years in the making: zebrafish and vertebrate immunity.</a> Disease models and mechanisms. 5 (1), 38-47 (2012).</li><li>Hall, C. J., 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=Immunoresponsive+gene+1+augments+bactericidal+activity+of+macrophage-lineage+cells+by+regulating+beta-oxidation-dependent+mitochondrial+ROS+production.">Immunoresponsive gene 1 augments bactericidal activity of macrophage-lineage cells by regulating beta-oxidation-dependent mitochondrial ROS production.</a> Cell Metabolism. 18 (2), 265-278 (2013).</li><li>Hall, C. J., 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=Blocking+fatty+acid-fueled+mROS+production+within+macrophages+alleviates+acute+gouty+inflammation.">Blocking fatty acid-fueled mROS production within macrophages alleviates acute gouty inflammation.</a> Journal of Clinical Investigation. 125 (5), 1752-1771 (2018).</li><li>Cambier, C. J., 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=Mycobacteria+manipulate+macrophage+recruitment+through+coordinated+use+of+membrane+lipids.">Mycobacteria manipulate macrophage recruitment through coordinated use of membrane lipids.</a> Nature. 505 (7482), 218-222 (2014).</li><li>Davis, J. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-time+visualization+of+mycobacterium-macrophage+interactions+leading+to+initiation+of+granuloma+formation+in+zebrafish+embryos.">Real-time visualization of mycobacterium-macrophage interactions leading to initiation of granuloma formation in zebrafish embryos.</a> Immunity. 17 (6), 693-702 (2002).</li><li>Madigan, C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Macrophage+Response+to+Mycobacterium+leprae+Phenolic+Glycolipid+Initiates+Nerve+Damage+in+Leprosy.">A Macrophage Response to Mycobacterium leprae Phenolic Glycolipid Initiates Nerve Damage in Leprosy.</a> Cell. 170 (5), 973-985 (2017).</li><li>Tobin, D. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+lta4h+locus+modulates+susceptibility+to+mycobacterial+infection+in+zebrafish+and+humans.">The lta4h locus modulates susceptibility to mycobacterial infection in zebrafish and humans.</a> Cell. 140 (5), 717-730 (2010).</li><li>Volkman, H. E., 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=Tuberculous+granuloma+induction+via+interaction+of+a+bacterial+secreted+protein+with+host+epithelium.">Tuberculous granuloma induction via interaction of a bacterial secreted protein with host epithelium.</a> Science. 327 (5964), 466-469 (2010).</li><li>Bowman, T. V., Zon, L. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Swimming+into+the+future+of+drug+discovery:+in+vivo+chemical+screens+in+zebrafish.">Swimming into the future of drug discovery: in vivo chemical screens in zebrafish.</a> ACS Chemical Biology. 5 (2), 159-161 (2010).</li><li>Kaufman, C. K., White, R. M., Zon, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+genetic+screening+in+the+zebrafish+embryo.">Chemical genetic screening in the zebrafish embryo.</a> Nature Protocols. 4 (10), 1422-1432 (2009).</li><li>Zon, L. I., Peterson, R. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+drug+discovery+in+the+zebrafish.">In vivo drug discovery in the zebrafish.</a> Nature Reviews Drug Discovery. 4 (1), 35-44 (2005).</li><li>Malam, Y., Loizidou, M., Seifalian, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liposomes+and+nanoparticles:+nanosized+vehicles+for+drug+delivery+in+cancer.">Liposomes and nanoparticles: nanosized vehicles for drug delivery in cancer.</a> Trends in Pharmacological Sciences. 30 (11), 592-599 (2009).</li><li>Torchilin, V. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+advances+with+liposomes+as+pharmaceutical+carriers.">Recent advances with liposomes as pharmaceutical carriers.</a> Nature Reviews Drug Discovery. 4 (2), 145-160 (2005).</li><li>Immordino, M. L., Dosio, F., Cattel, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stealth+liposomes:+review+of+the+basic+science,+rationale,+and+clinical+applications,+existing+and+potential.">Stealth liposomes: review of the basic science, rationale, and clinical applications, existing and potential.</a> International Journal of Nanomedicine. 1 (3), 297-315 (2006).</li><li>Astin, J. W., 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=Innate+immune+cells+and+bacterial+infection+in+zebrafish.">Innate immune cells and bacterial infection in zebrafish.</a> Methods in Cell Biology. 138, 31-60 (2017).</li><li>Zhang, W., 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=Post-insertion+of+poloxamer+188+strengthened+liposomal+membrane+and+reduced+drug+irritancy+and+in+vivo+precipitation,+superior+to+PEGylation.">Post-insertion of poloxamer 188 strengthened liposomal membrane and reduced drug irritancy and in vivo precipitation, superior to PEGylation.</a> Journal of Controlled Release. 203, 161-169 (2015).</li><li>Wu, Z., 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=Liposome-Mediated+Drug+Delivery+in+Larval+Zebrafish+to+Manipulate+Macrophage+Function.">Liposome-Mediated Drug Delivery in Larval Zebrafish to Manipulate Macrophage Function.</a> Zebrafish. 16 (2), 171-181 (2019).</li><li>Cader, M. Z., 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=C13orf31+(FAMIN)+is+a+central+regulator+of+immunometabolic+function.">C13orf31 (FAMIN) is a central regulator of immunometabolic function.</a> Nature Immunology. 17 (9), 1046-1056 (2016).</li><li>Chono, S., Tanino, T., Seki, T., Morimoto, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+particle+size+on+drug+delivery+to+rat+alveolar+macrophages+following+pulmonary+administration+of+ciprofloxacin+incorporated+into+liposomes.">Influence of particle size on drug delivery to rat alveolar macrophages following pulmonary administration of ciprofloxacin incorporated into liposomes.</a> Journal of Drug Targeting. 14 (8), 557-566 (2006).</li><li>Chono, S., Tanino, T., Seki, T., Morimoto, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Uptake+characteristics+of+liposomes+by+rat+alveolar+macrophages:+influence+of+particle+size+and+surface+mannose+modification.">Uptake characteristics of liposomes by rat alveolar macrophages: influence of particle size and surface mannose modification.</a> Journal of Pharmact and Pharmacology. 59 (1), 75-80 (2007).</li><li>Chono, S., Tauchi, Y., Morimoto, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+particle+size+on+the+distributions+of+liposomes+to+atherosclerotic+lesions+in+mice.">Influence of particle size on the distributions of liposomes to atherosclerotic lesions in mice.</a> Drug Development and Industrial Pharmacy. 32 (1), 125-135 (2006).</li><li>Rosen, J. N., Sweeney, M. F., Mably, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microinjection+of+zebrafish+embryos+to+analyze+gene+function.">Microinjection of zebrafish embryos to analyze gene function.</a> Journal of Visualized Experiments. (25), (2009).</li><li>Hall, C., Flores, M. V., Crosier, K., Crosier, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Live+cell+imaging+of+zebrafish+leukocytes.">Live cell imaging of zebrafish leukocytes.</a> Methods in Molecular Biology. 546, 255-271 (2009).</li><li>Kapellos, T. 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=A+novel+real+time+imaging+platform+to+quantify+macrophage+phagocytosis.">A novel real time imaging platform to quantify macrophage phagocytosis.</a> Biochemical Pharmacology. 116, 107-119 (2016).</li><li>Shen, K., Sidik, H., Talbot, W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Rag-Ragulator+Complex+Regulates+Lysosome+Function+and+Phagocytic+Flux+in+Microglia.">The Rag-Ragulator Complex Regulates Lysosome Function and Phagocytic Flux in Microglia.</a> Cell Reports. 14 (3), 547-559 (2016).</li><li>Ellett, F., Pase, L., Hayman, J. W., Andrianopoulos, A., Lieschke, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=mpeg1+promoter+transgenes+direct+macrophage-lineage+expression+in+zebrafish.">mpeg1 promoter transgenes direct macrophage-lineage expression in zebrafish.</a> Blood. 117 (4), 49-56 (2011).</li><li>Hall, C., Flores, M. V., Storm, T., Crosier, K., Crosier, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+zebrafish+lysozyme+C+promoter+drives+myeloid-specific+expression+in+transgenic+fish.">The zebrafish lysozyme C promoter drives myeloid-specific expression in transgenic fish.</a> BMC Developmental Biology. 7, 42 (2007).</li><li>Ahsan, F., Rivas, I. P., Khan, M. A., Torres Suarez, A. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeting+to+macrophages:+role+of+physicochemical+properties+of+particulate+carriers--liposomes+and+microspheres--on+the+phagocytosis+by+macrophages.">Targeting to macrophages: role of physicochemical properties of particulate carriers--liposomes and microspheres--on the phagocytosis by macrophages.</a> Journal of Controlled Release. 79 (1-3), 29-40 (2002).</li><li>Martin, W. J., Walton, M., Harper, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resident+macrophages+initiating+and+driving+inflammation+in+a+monosodium+urate+monohydrate+crystal-induced+murine+peritoneal+model+of+acute+gout.">Resident macrophages initiating and driving inflammation in a monosodium urate monohydrate crystal-induced murine peritoneal model of acute gout.</a> Arthritis and Rheumatology. 60 (1), 281-289 (2009).</li><li>Faires, J. S., McCarty, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acute+arthritis+in+man+and+dog+after+intrasynovial+injection+of+sodium+urate+crystals.">Acute arthritis in man and dog after intrasynovial injection of sodium urate crystals.</a> Lancet. 280, 682-685 (1962).</li><li>Martin, W. J., Harper, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Innate+inflammation+and+resolution+in+acute+gout.">Innate inflammation and resolution in acute gout.</a> Immunology and Cell Biology. 88 (1), 15-19 (2010).</li><li>Fenaroli, F., 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=Nanoparticles+as+drug+delivery+system+against+tuberculosis+in+zebrafish+embryos:+direct+visualization+and+treatment.">Nanoparticles as drug delivery system against tuberculosis in zebrafish embryos: direct visualization and treatment.</a> ACS Nano. 8 (7), 7014-7026 (2014).</li><li>Robertson, J. D., Ward, J. R., Avila-Olias, M., Battaglia, G., Renshaw, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeting+Neutrophilic+Inflammation+Using+Polymersome-Mediated+Cellular+Delivery.">Targeting Neutrophilic Inflammation Using Polymersome-Mediated Cellular Delivery.</a> Journal of Immunology. 198 (9), 3596-3604 (2017).</li><li>Le Guellec, D., Morvan-Dubois, G., Sire, J. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skin+development+in+bony+fish+with+particular+emphasis+on+collagen+deposition+in+the+dermis+of+the+zebrafish+(Danio+rerio).">Skin development in bony fish with particular emphasis on collagen deposition in the dermis of the zebrafish (Danio rerio).</a> International Journal of Developmental Biology. 48 (2-3), 217-231 (2004).</li><li>Kelly, C., Jefferies, C., Cryan, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeted+liposomal+drug+delivery+to+monocytes+and+macrophages.">Targeted liposomal drug delivery to monocytes and macrophages.</a> Journal of Drug Delivery. 2011, 727241 (2011).</li><li>Fidler, I. J., 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=Design+of+liposomes+to+improve+delivery+of+macrophage-augmenting+agents+to+alveolar+macrophages.">Design of liposomes to improve delivery of macrophage-augmenting agents to alveolar macrophages.</a> Cancer Research. 40 (12), 4460-4466 (1980).</li><li>Ng, A. 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=Formation+of+the+digestive+system+in+zebrafish:+III.+Intestinal+epithelium+morphogenesis.">Formation of the digestive system in zebrafish: III. Intestinal epithelium morphogenesis.</a> Developmenal Biology. 286 (1), 114-135 (2005).</li></ol>

The authors declare that no competing financial interests exist.

Here, we have provided a detailed protocol to formulate drug-loaded liposomes to specifically target macrophages in larval zebrafish. This method can be used to dissect the role of macrophages in certain disease models by ensuring direct targeted delivery of drugs specifically to macrophages. Moreover, it can be used when general toxicity of drugs limits their use when delivered by more conventional routes, like immersion. The protocol described here provides an alternative to other nanoparticulate systems that have been...

The mononuclear phagocyte system provides a first line of defense against invading pathogens. This system consists of monocytes, monocyte-derived dendritic cells and macrophages, which actively phagocytoze foreign pathogens, thereby limiting pathogen spread. In addition to these phagocytic and microbicidal effector functions, dendritic cells and macrophages are also capable of cytokine production and antigen-presentation to activate the adaptive immune system1. Of these cells, macrophages have received particular attention due to their diverse functional heterogeneity and involvement in multiple inflammatory diseases, from autoimmunity and infectious diseases to cancer2,3,4,5,6,7. The plasticity of macrophages and their ability to functionally adapt to the needs to their tissue environment necessitates experimental approaches to directly observe and interrogate these cells in vivo.
Larval zebrafish are an ideal model organism by which to study the function and plasticity of macrophages in vivo8. The optical transparency of larval zebrafish provides a window to directly observe the behavior of macrophages, especially when coupled with macrophage-marking transgenic reporter lines. Exploiting the live imaging potential and experimental tractability of larval zebrafish has led to many significant insights into macrophage function that have direct relevance to human disease9,10,11,12,13,14,15. Many of these studies have also taken advantage of the high conservation of drug activity in zebrafish (an attribute that underpins their use as a whole animal drug discovery platform16,17,18), by utilizing chemical interventions to pharmacologically manipulate macrophage function. To date, these pharmacological treatments have been mostly delivered either through immersion, which requires the drug to be water soluble, or by direct microinjection of free drug (Figure 1A). Limitations of these passive delivery strategies include off-target effects and general toxicity that may preclude assessing any impact on macrophage function. Additionally, when investigating drug effects on macrophages it is unknown whether the drugs are acting on the macrophages themselves or through more indirect mechanisms. When performing similar chemical intervention studies to investigate macrophage function, we recognized there was an unmet need to develop an inexpensive and straightforward delivery method to target drugs specifically to macrophages.
Liposomes are microscopic, biocompatible, lipid bilayered vesicles that can encapsulate proteins, nucleotides and drug cargo19. The unilamellar or multilamellar lipid bilayer structure of liposomes forms an aqueous inner lumen where water-soluble drugs can be incorporated while hydrophobic drugs can be integrated into the lipid membranes. In addition, the physicochemical properties of liposomes, including size, charge and surface modifications can be manipulated to tailor their targeting to specific cells20,21. These features of liposomes have made them an attractive vehicle to deliver drugs and enhance the precision of current treatment regimens20. As liposomes are naturally phagocytozed by macrophages (a feature exploited by their routine use in delivering clodronate specifically to macrophages for ablation experiments22), they present as an attractive option for macrophage-specific drug delivery (Figure 1B).
This protocol describes the formulation of drugs into blue fluorescent liposomes coated with the hydrophilic polymer poloxamer 188, that forms a protective layer on the liposome surface and has been shown to enhance drug retention and have superior biocompatibility23. Poloxamer was chosen for surface coating of liposomes as our previous research had shown that, when compared to polyethylene glycol modified liposomes, poloxamer modified liposomes showed better biocompatibility following subcutaneous injection of rat paws and similar pharmacokinetics in rabbits following intravenous infusion23. Protocols are also described for their microinjection into larval zebrafish and live imaging to assess their macrophage-targeting ability and localization to intracellular compartments necessary for liposome degradation and cytoplasmic drug delivery. As a proof-of-concept we have previously used this technique to target two drugs to macrophages to suppress their activation in a larval zebrafish model of acute gouty inflammation24. This drug delivery technique expands the chemical &#34;toolkit&#34; available to zebrafish researchers wanting to ensure macrophage-targeting of their drugs of interest.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)</td>
			<td>Avanti Polar Lipids, Inc.</td>
			<td>850355P</td>
			<td></td>
		</tr>
		<tr>
			<td>1,2-diseteroyl-sn-glycero-3-phosphocholine (DSPE)</td>
			<td>Avanti Polar Lipids, Inc.</td>
			<td>850367P</td>
			<td></td>
		</tr>
		<tr>
			<td>1.0 &#181;m Whatman Nuclepore Track-Etched polycarbonate membranes</td>
			<td>GE Healthcare Life Sciences</td>
			<td>110610</td>
			<td></td>
		</tr>
		<tr>
			<td>25 mL round-bottom flask</td>
			<td>Sigma-Aldrich</td>
			<td>Z278262</td>
			<td></td>
		</tr>
		<tr>
			<td>35 mm culture dish</td>
			<td>Thermo Scientific</td>
			<td>150460</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetonitrile</td>
			<td>Sigma-Aldrich</td>
			<td>34998</td>
			<td></td>
		</tr>
		<tr>
			<td>Agilent 1260 Infinity Diode Array Detector</td>
			<td>Agilent Technologies</td>
			<td>G4212B</td>
			<td></td>
		</tr>
		<tr>
			<td>Agilent 1260 Infinity Quaternary Pump</td>
			<td>Agilent Technologies</td>
			<td>G1311B</td>
			<td></td>
		</tr>
		<tr>
			<td>Agilent 1290 Infinity Series Thermostat</td>
			<td>Agilent Technologies</td>
			<td>G1330B</td>
			<td></td>
		</tr>
		<tr>
			<td>Avanti mini-extruder Avanti Polar Lipids Inc.</td>
			<td>Avanti Polar Lipids Inc.</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>borosilicate microinjection needles</td>
			<td>Warner Instruments</td>
			<td>203-776-0664</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>Sigma-Aldrich</td>
			<td>C4901-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>cholesterol</td>
			<td>Sigma-Aldrich</td>
			<td>C8667</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont No.5 fine tip forceps</td>
			<td>Fine Science Tools</td>
			<td>11251-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf Microloader pipette tip</td>
			<td>Eppendorf</td>
			<td>5242956003</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf SmartBlock 1.5 mL, thermoblock for 24 reaction vessels</td>
			<td>Eppendorf</td>
			<td>4053-6038</td>
			<td></td>
		</tr>
		<tr>
			<td>eyelash manipulator</td>
			<td>Ted Pella Inc.</td>
			<td>113</td>
			<td></td>
		</tr>
		<tr>
			<td>hemocytometer</td>
			<td>Hawksley</td>
			<td>BS.748</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>BDH Chemicals</td>
			<td>441474J</td>
			<td></td>
		</tr>
		<tr>
			<td>HPLC system</td>
			<td>Agilent Technologies</td>
			<td>1260 series HPLC system</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma-Aldrich</td>
			<td>P9541-1KG</td>
			<td></td>
		</tr>
		<tr>
			<td>low melting point agarose</td>
			<td>Invitrogen</td>
			<td>16520-100</td>
			<td></td>
		</tr>
		<tr>
			<td>LysoTracker Deep Red</td>
			<td>Invitrogen</td>
			<td>L12492</td>
			<td>1 mM stock solution in DMSO, keep at -20 &#176;C and protect from light.</td>
		</tr>
		<tr>
			<td>LysoTracker Deep Red</td>
			<td>Thermo Scientific</td>
			<td>L12492</td>
			<td></td>
		</tr>
		<tr>
			<td>magnetic stand</td>
			<td>Narishige</td>
			<td>GJ-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Marina Blue 1,2-dihexadecanoyl-sn-glycero-phosphoethanolamine (Marina Blue DHPE)</td>
			<td>Invitrogen</td>
			<td>M12652</td>
			<td>Keep at -20 &#176;C and protect from light.</td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Sigma-Aldrich</td>
			<td>34860</td>
			<td></td>
		</tr>
		<tr>
			<td>methyl cellulose</td>
			<td>Sigma-Aldrich</td>
			<td>M0387-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>methylene blue</td>
			<td>Alfa Aesar</td>
			<td>42771</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4</td>
			<td>Sigma-Aldrich</td>
			<td>230391-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>micromanipulator</td>
			<td>Narishige</td>
			<td>M-152</td>
			<td></td>
		</tr>
		<tr>
			<td>mineral oil</td>
			<td>Sigma-Aldrich</td>
			<td>M-3516</td>
			<td></td>
		</tr>
		<tr>
			<td>Mitochondria-targeting antioxidant MitoTEMPO</td>
			<td>Sigma-Aldrich</td>
			<td>SML0737</td>
			<td></td>
		</tr>
		<tr>
			<td>MitoSOX Red Mitochondrial Superoxide Indicator</td>
			<td>Thermo Scientific</td>
			<td>M36008</td>
			<td></td>
		</tr>
		<tr>
			<td>MitoTEMPO</td>
			<td>Sigma-Aldrich</td>
			<td>SML0737</td>
			<td>Keep at -20 &#176;C and protect from light.</td>
		</tr>
		<tr>
			<td>N-Phenylthiourea (PTU)</td>
			<td>Sigma-Aldrich</td>
			<td>P7629-10G</td>
			<td>Take care when handling, toxic.</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>BDH Chemicals</td>
			<td>27810.295</td>
			<td></td>
		</tr>
		<tr>
			<td>PBS (pH 7.4)</td>
			<td>Gibco</td>
			<td>10010-023</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri dish (100 mm x 20 mm)</td>
			<td>Corning Inc.</td>
			<td>430167</td>
			<td></td>
		</tr>
		<tr>
			<td>Phenomenex C18 Gemini-NZ 3 mm 250 mm x 4.6 mm column</td>
			<td>Phenomenex</td>
			<td>00G-4439-E0</td>
			<td></td>
		</tr>
		<tr>
			<td>pHrodo Red Escherichia coli BioParticles Conjugate</td>
			<td>Thermo Scientific</td>
			<td>P35361</td>
			<td></td>
		</tr>
		<tr>
			<td>pHrodo Red Escherichia coli BioParticles Conjugate</td>
			<td>Invitrogen</td>
			<td>P35361</td>
			<td>Keep at -20 &#176;C and protect from light. Make 1 mg/mL stock solution by dissolving 2 mg lyophilized product in 2 mL of PBS supplemented with 20 mM HEPES, pH 7.4.</td>
		</tr>
		<tr>
			<td>plastic transfer pipette</td>
			<td>Medi&#39;Ray</td>
			<td>RL200C</td>
			<td></td>
		</tr>
		<tr>
			<td>poloxamer 188</td>
			<td>BASF Corporation</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>pressure injector</td>
			<td>Applied Scientific Instruments</td>
			<td>MPPI-2</td>
			<td></td>
		</tr>
		<tr>
			<td>rotary evaporator</td>
			<td>B&#252;chi, Flawil, Switzerland</td>
			<td>B&#252;chi R-215 Rotavapor</td>
			<td></td>
		</tr>
		<tr>
			<td>Scanning confocal microscope</td>
			<td>Olympus</td>
			<td>Olympus FV1000 FluoView</td>
			<td></td>
		</tr>
		<tr>
			<td>Sorvall WX+ Ultracentrifuge</td>
			<td>Thermo Scientific</td>
			<td>75000090</td>
			<td></td>
		</tr>
		<tr>
			<td>stereomicroscope</td>
			<td>Leica</td>
			<td>MZ12</td>
			<td></td>
		</tr>
		<tr>
			<td>Tricaine</td>
			<td>Sigma-Aldrich</td>
			<td>A5040-25G</td>
			<td>Make 4 mg/mL stock solution (in deionzed H2O) and keep at -20 &#176;C.</td>
		</tr>
		<tr>
			<td>triton-X100</td>
			<td>Sigma-Aldrich</td>
			<td>X100-100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrasonic bath</td>
			<td>Thermo Scientific</td>
			<td>FB-11205</td>
			<td></td>
		</tr>
		<tr>
			<td>Volocity Image Analysis Software</td>
			<td>PerkinElmer</td>
			<td>version 6.3</td>
			<td></td>
		</tr>
		<tr>
			<td>water bath</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Zetasizer Nano</td>
			<td>Malvern Instruments Ltd</td>
			<td>Zetasizer Nano ZS ZEN 3600</td>
			<td></td>
		</tr>
	</tbody>
</table>

targeting drugs to larval zebrafish macrophages by injecting drug-loaded liposomes

Zebrafish (Danio rerio) larvae have developed into a popular model to investigate host-pathogen interactions and the contribution of innate immune cells to inflammatory disease due to their functionally conserved innate immune system. They are also widely used to examine how innate immune cells help guide developmental processes. By taking advantage of the optical transparency and genetic tractability of larval zebrafish, these studies often focus on live imaging approaches to functionally characterize fluorescently marked macrophages and neutrophils within intact animals. Due to their diverse functional heterogeneity and ever-expanding roles in disease pathogenesis, macrophages have received significant attention. In addition to genetic manipulations, chemical interventions are now routinely used to manipulate and examine macrophage behavior in larval zebrafish. Delivery of these drugs is typically limited to passive targeting of free drug through direct immersion or microinjection. These approaches rely on the assumption that any changes to macrophage behavior are the result of a direct effect of the drug on the macrophages themselves, and not a downstream consequence of a direct effect on another cell type. Here, we present our protocols for targeting drugs specifically to larval zebrafish macrophages by microinjecting drug-loaded fluorescent liposomes. We reveal that poloxamer 188-modified drug-loaded blue fluorescent liposomes are readily taken up by macrophages, and not by neutrophils. We also provide evidence that drugs delivered in this way can impact macrophage activity in a manner consistent with the mechanism of action of the drug. This technique will be of value to researchers wanting to ensure targeting of drugs to macrophages and when drugs are too toxic to be delivered by traditional methods like immersion.

The thin film hydration approach described here for the preparation of fluorescent liposomes enclosing drugs is a simple and cost-effective method. With the protocol used in this study, the liposomes are expected to be unilamellar23,24. The size, zeta potential, drug loading and entrapment efficiency of the liposomes produced are summarized in Table 1. The particle size of the liposomes (before and after drug loading) are similar (Table 1...

Watch this Scientific Journal Video about Targeting Drugs to Larval Zebrafish Macrophages by Injecting Drug-Loaded Liposomes at JoVE.com

Targeting Drugs to Larval Zebrafish Macrophages by Injecting Drug-Loaded Liposomes

Here, we describe the synthesis of drug-loaded liposomes and their microinjection into larval zebrafish for the purpose of targeting drug delivery to macrophage-lineage cells.

Zebrafish (Danio rerio) larvae have developed into a popular model to investigate host-pathogen interactions and the contribution of innate immune cells ...

targeting-drugs-to-larval-zebrafish-macrophages-injecting-drug-loaded

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JoVE Journal

Immunology and Infection

7.6K Views.  University of Auckland. Here, we describe the synthesis of drug-loaded liposomes and their microinjection into larval zebrafish for the purpose of targeting drug delivery to macrophage-lineage cells.

Video: Targeting Drugs to Larval Zebrafish Macrophages by Injecting Drug-Loaded Liposomes

Humanized Mouse Model to Study Bacterial Infections Targeting the Microvasculature

Neisseria meningitidis causes a severe, frequently fatal sepsis when it enters the human blood stream. Infection leads to extensive damage of the blood vessels resulting in vascular leak, the development of purpuric rashes and eventual tissue necrosis. Studying the pathogenesis of this infection was previously limited by the human specificity of the bacteria, which makes in vivo models difficult. In this protocol, we describe a humanized model for this infection in which human skin, containing dermal microvessels, is grafted onto immunocompromised mice. These vessels anastomose with the mouse circulation while maintaining their human characteristics. Once introduced into this model, N. meningitidis adhere exclusively to the human vessels, resulting in extensive vascular damage, inflammation and in some cases the development of purpuric rash. This protocol describes the grafting, infection and evaluation steps of this model in the context of N. meningitidis infection. The technique may be applied to numerous human specific pathogens that infect the blood stream.

Neisseria meningitidis is a human specific pathogen that infects blood vessels. In this protocol human microvessels are introduced into a mouse by grafting human skin onto immunocompromised mice. Bacteria adhere extensively to the human vessels, leading to vascular damage and development of the purpuric rash typically observed in human cases.

Neisseria meningitidis causes a severe, frequently fatal sepsis when it enters the human blood stream. Infection leads to extensive damage of the blood ...

Use of Shigella flexneri to Study Autophagy-Cytoskeleton Interactions

Shigella flexneri is an intracellular pathogen that can escape from phagosomes to reach the cytosol, and polymerize the host actin cytoskeleton to promote its motility and dissemination. New work has shown that proteins involved in actin-based motility are also linked to autophagy, an intracellular degradation process crucial for cell autonomous immunity. Strikingly, host cells may prevent actin-based motility of S. flexneri by compartmentalizing bacteria inside &#8216;septin cages&#8217; and targeting them to autophagy. These observations indicate that a more complete understanding of septins, a family of filamentous GTP-binding proteins, will provide new insights into the process of autophagy. This report describes protocols to monitor autophagy-cytoskeleton interactions caused by S. flexneri in vitro using tissue culture cells and in vivo using zebrafish larvae. These protocols enable investigation of intracellular mechanisms that control bacterial dissemination at the molecular, cellular, and whole organism level.

Use of Shigella flexneri to Study Autophagy-Cytoskeleton Interactions

To counteract pathogen dissemination, host cells reorganize their cytoskeleton to compartmentalize bacteria and induce autophagy. Using Shigella infection of tissue culture cells, host and pathogen determinants underlying this process are identified and characterized. Using zebrafish models of Shigella infection, the role of discovered molecules and mechanisms are investigated in vivo.

Shigella flexneri is an intracellular pathogen that can escape from phagosomes to reach the cytosol, and polymerize the host actin cytoskeleton to promote ...

Assessing Anti-fungal Activity of Isolated Alveolar Macrophages by Confocal Microscopy

The lung is an interface where host cells are routinely exposed to microbes and microbial products. Alveolar macrophages are the first-line phagocytic cells that encounter inhaled fungi and other microbes. Macrophages and other immune cells recognize Aspergillus motifs by pathogen recognition receptors and initiate downstream inflammatory responses. The phagocyte NADPH oxidase generates reactive oxygen intermediates (ROIs) and is critical for host defense. Although NADPH oxidase is critical for neutrophil-mediated host defense1-3, the importance of NADPH oxidase in macrophages is not well defined. The goal of this study was to delineate the specific role of NADPH oxidase in macrophages in mediating host defense against A. fumigatus. We found that NADPH oxidase in alveolar macrophages controls the growth of phagocytosed A. fumigatus spores4. Here, we describe a method for assessing the ability of mouse alveolar macrophages (AMs) to control the growth of phagocytosed Aspergillus spores (conidia). Alveolar macrophages are stained in vivo and ten days later isolated from mice by bronchoalveolar lavage (BAL). Macrophages are plated onto glass coverslips, then seeded with green fluorescent protein (GFP)-expressing A. fumigatus spores. At specified times, cells are fixed and the number of intact macrophages with phagocytosed spores is assessed by confocal microscopy.

A method to evaluate the ability of isolated mouse alveolar macrophages to control the growth of phagocytosed Aspergillus spores by confocal microscopy.

The lung is an interface where host cells are routinely exposed to microbes and microbial products. Alveolar macrophages are the first-line phagocytic ...

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.

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. ...

Modeling Mucosal Candidiasis in Larval Zebrafish by Swimbladder Injection

Early defense against mucosal pathogens consists of both an epithelial barrier and innate immune cells. The immunocompetency of both, and their intercommunication, are paramount for the protection against infections. The interactions of epithelial and innate immune cells with a pathogen are best investigated in vivo, where complex behavior unfolds over time and space. However, existing models do not allow for easy spatio-temporal imaging of the battle with pathogens at the mucosal level.
The model developed here creates a mucosal infection by direct injection of the fungal pathogen, Candida albicans, into the swimbladder of juvenile zebrafish. The resulting infection enables high-resolution imaging of epithelial and innate immune cell behavior throughout the development of mucosal disease. The versatility of this method allows for interrogation of the host to probe the detailed sequence of immune events leading to phagocyte recruitment and to examine the roles of particular cell types and molecular pathways in protection. In addition, the behavior of the pathogen as a function of immune attack can be imaged simultaneously by using fluorescent protein-expressing C. albicans. Increased spatial resolution of the host-pathogen interaction is also possible using the described rapid swimbladder dissection technique.
The mucosal infection model described here is straightforward and highly reproducible, making it a valuable tool for the study of mucosal candidiasis. This system may also be broadly translatable to other mucosal pathogens such as mycobacterial, bacterial or viral microbes that normally infect through epithelial surfaces.

In vivo spatio-temporal interactions of pathogen and immune defenses at the mucosal level are not easily imaged in existing vertebrate hosts. The method presented here describes a versatile platform to study mucosal candidiasis in live vertebrates using the swimbladder of the juvenile zebrafish as an infection site.

Early defense against mucosal pathogens consists of both an epithelial barrier and innate immune cells. The immunocompetency of both, and their ...

Proteomic Profiling of Macrophages by 2D Electrophoresis

The goal of the two-dimensional (2D) electrophoresis protocol described here is to show how to analyse the phenotype of human cultured macrophages. The key role of macrophages has been shown in various pathological disorders such as inflammatory, immunological, and infectious diseases. In this protocol, we use primary cultures of human monocyte-derived macrophages that can be differentiated into the M1 (pro-inflammatory) or the M2 (anti-inflammatory) phenotype. This in vitro model is reliable for studying the biological activities of M1 and M2 macrophages and also for a proteomic approach. Proteomic techniques are useful for comparing the phenotype and behaviour of M1 and M2 macrophages during host pathogenicity. 2D gel electrophoresis is a powerful proteomic technique for mapping large numbers of proteins or polypeptides simultaneously. We describe the protocol of 2D electrophoresis using fluorescent dyes, named 2D Differential Gel Electrophoresis (DIGE). The M1 and M2 macrophages proteins are labelled with cyanine dyes before separation by isoelectric focusing, according to their isoelectric point in the first dimension, and their molecular mass, in the second dimension. Separated protein or polypeptidic spots are then used to detect differences in protein or polypeptide expression levels. The proteomic approaches described here allows the investigation of the macrophage protein changes associated with various disorders like host pathogenicity or microbial toxins.

Macrophages are the key cells involved in host pathogenicity. Macrophages display phenotypic and functional diversity that can be analysed and detected by proteomic analysis. This article describes how to perform 2D electrophoresis of primary cultures of human macrophages differentiated into M1 or M2 phenotype.

The goal of the two-dimensional (2D) electrophoresis protocol described here is to show how to analyse the phenotype of human cultured macrophages. The ...

Non-invasive Imaging of the Innate Immune Response in a Zebrafish Larval Model of Streptococcus iniae Infection

The aquatic pathogen, Streptococcus iniae, is responsible for over 100 million dollars in annual losses for the aquaculture industry and is capable of causing systemic disease in both fish and humans. A better understanding of S. iniae disease pathogenesis requires an appropriate model system. The genetic tractability and the optical transparency of the early developmental stages of zebrafish allow for the generation and non-invasive imaging of transgenic lines with fluorescently tagged immune cells. The adaptive immune system is not fully functional until several weeks post fertilization, but zebrafish larvae have a conserved vertebrate innate immune system with both neutrophils and macrophages. Thus, the generation of a larval infection model allows the study of the specific contribution of innate immunity in controlling S. iniae infection.
The site of microinjection will determine whether an infection is systemic or initially localized. Here, we present our protocols for otic vesicle injection of zebrafish aged 2-3 days post fertilization as well as our techniques for fluorescent confocal imaging of infection. A localized infection site allows observation of initial microbe invasion, recruitment of host cells and dissemination of infection. Our findings using the zebrafish larval model of S. iniae infection indicate that zebrafish can be used to examine the differing contributions of host neutrophils and macrophages in localized bacterial infections. In addition, we describe how photolabeling of immune cells can be used to track individual host cell fate during the course of infection.

Non-invasive Imaging of the Innate Immune Response in a Zebrafish Larval Model of Streptococcus iniae Infection

Here, we present a protocol for the generation and imaging of a localized bacterial infection in the zebrafish otic vesicle.

The aquatic pathogen, Streptococcus iniae, is responsible for over 100 million dollars in annual losses for the aquaculture industry and is capable of ...

Quantification of Cytosolic vs. Vacuolar Salmonella in Primary Macrophages by Differential Permeabilization

Intracellular bacterial pathogens can replicate in the cytosol or in specialized pathogen-containing vacuoles (PCVs). To reach the cytosol, bacteria like Shigella flexneri and Francisella novicida need to induce the rupture of the phagosome. In contrast, Salmonella typhimurium replicates in a vacuolar compartment, known as Salmonella-containing vacuole (SCV). However certain mutants of Salmonella fail to maintain SCV integrity and are thus released into the cytosol. The percentage of cytosolic vs. vacuolar bacteria on the level of single bacteria can be measured by differential permeabilization, also known as phagosome-protection assay. The approach makes use of the property of detergent digitonin to selectively bind cholesterol. Since the plasma membrane contains more cholesterol than other cellular membranes, digitonin can be used to selectively permeabilize the plasma membrane while leaving intracellular membranes intact. In brief, following infection with the pathogen expressing a fluorescent marker protein (e.g. mCherry among others), the plasma membrane of host cells is permeabilized with a short incubation in digitonin containing buffer. Cells are then washed and incubated with a primary antibody (coupled to a fluorophore of choice) directed against the bacterium of choice (e.g. anti-Salmonella-FITC) and washed again. If unmarked bacteria are used, an additional step can be done, in which all membranes are permeabilized and all bacteria stained with a corresponding antibody. Following the staining, the percentage of vacuolar and cytosolic bacteria can be quantified by FACS or microscopy by counting single or double-positive events. Here we provide experimental details for use of this technique with the bacterium Salmonella typhimurium. The advantage of this assay is that, in contrast to other assay, it provides a quantification on the level of single bacteria, and if analyzed by microscopy provides the exact number of cytosolic and vacuolar bacteria in a given cell.

Quantification of Cytosolic vs. Vacuolar Salmonella in Primary Macrophages by Differential Permeabilization

We describe the quantification of cytosolic and vacuolar Salmonella typhimurium in bone-marrow derived macrophages using differential digitonin permeabilization.

Intracellular bacterial pathogens can replicate in the cytosol or in specialized pathogen-containing vacuoles (PCVs). To reach the cytosol, bacteria like ...

Phenotypic Characterization of Macrophages from Rat Kidney by Flow Cytometry

There is increasing evidence suggesting the important role of inflammation and, subsequently, macrophages in the development and progression of renal disease. Macrophages are heterogeneous cells that have been implicated in kidney injury. Macrophages may be classified into two different phenotypes: classically activated macrophages (M1 macrophages), that release pro-inflammatory cytokines and promote fibrosis; and alternatively activated macrophages (M2 macrophages) that are associated with immunoregulatory and tissue-remodeling functions. These macrophage phenotypes need to be discriminated and analyzed to determine their contribution to renal injury. However, there are scarce studies reporting consistent phenotypic and functional information about macrophage subtypes in inflammatory renal disease models, especially in rats. This fact may be related to the limited macrophage markers used in rats, contrary to mice. Therefore, novel strategies are necessary to quantify and characterize the renal content of these infiltrating cells in a reliable way. This manuscript details a protocol for kidney digestion and further phenotypic and quantitative analysis of macrophages from rat kidneys by flow cytometry. Briefly, kidneys were incubated with collagenase and total macrophages were identified according to the dual presence of CD45 (leukocytes common antigen) and CD68 (PAN macrophage marker) in live cells.This was followed by surface staining of CD86 (M1 marker) and CD163 (M2 marker). Rat peritoneal macrophages were used as positive control for macrophage marker detection by flow cytometry. Our protocol resulted in low cellular mortality and allowed characterization of different intracellular and surface protein markers, thus limiting the loss of cellular integrity observed in other protocols. Moreover, this procedure allows the use of macrophages for further techniques, including cell sorting and mRNA or protein expression studies, among others.

This manuscript describes a detailed protocol for phenotypic and quantitative analysis of resident macrophages from rat kidneys by flow cytometry. The resulting stained cells can be also used for other applications, including cell sorting, gene expression analysis or functional studies, thus increasing the information obtained in the experimental model.

There is increasing evidence suggesting the important role of inflammation and, subsequently, macrophages in the development and progression of renal ...

Using Zebrafish Models of Human Influenza A Virus Infections to Screen Antiviral Drugs and Characterize Host Immune Cell Responses

Each year, seasonal influenza outbreaks profoundly affect societies worldwide. In spite of global efforts, influenza remains an intractable healthcare burden. The principle strategy to curtail infections is yearly vaccination. In individuals who have contracted influenza, antiviral drugs can mitigate symptoms. There is a clear and unmet need to develop alternative strategies to combat influenza. Several animal models have been created to model host-influenza interactions. Here, protocols for generating zebrafish models for systemic and localized human influenza A virus (IAV) infection are described. Using a systemic IAV infection model, small molecules with potential antiviral activity can be screened. As a proof-of-principle, a protocol that demonstrates the efficacy of the antiviral drug Zanamivir in IAV-infected zebrafish is described. It shows how disease phenotypes can be quantified to score the relative efficacy of potential antivirals in IAV-infected zebrafish. In recent years, there has been increased appreciation for the critical role neutrophils play in the human host response to influenza infection. The zebrafish has proven to be an indispensable model for the study of neutrophil biology, with direct impacts on human medicine. A protocol to generate a localized IAV infection in the Tg(mpx:mCherry) zebrafish line to study neutrophil biology in the context of a localized viral infection is described. Neutrophil recruitment to localized infection sites provides an additional quantifiable phenotype for assessing experimental manipulations that may have therapeutic applications. Both zebrafish protocols described faithfully recapitulate aspects of human IAV infection. The zebrafish model possesses numerous inherent advantages, including high fecundity, optical clarity, amenability to drug screening, and availability of transgenic lines, including those in which immune cells such as neutrophils are labeled with fluorescent proteins. The protocols detailed here exploit these advantages and have the potential to reveal critical insights into host-IAV interactions that may ultimately translate into the clinic.

Systemic and localized zebrafish infection models for human influenza A virus are demonstrated. Using a systemic infection model, zebrafish can be used to screen antiviral drugs. Using a localized infection model, zebrafish can be used to characterize host immune cell responses.

Each year, seasonal influenza outbreaks profoundly affect societies worldwide. In spite of global efforts, influenza remains an intractable healthcare ...