The protocol has to be carried out in strict accordance with national and international legislations and local regulations. Blood from healthy donors that gave their consent to donate blood for research purposes has been obtained from Blood Transfusion Centers with which the Institutions have signed agreement. Special protections must be taken when using human blood. Experiments with HIV-1 must be performed in a biosafety level 3 or 2 (BSL-3 or 2) laboratory according to local legislation.
1. Preparation of Human Monocyte-derived Macrophages (hMDMs) by Density Gradient Centrifugation and Selection by Adhesion
2. Production and Quantification of HIV-1 Viral Stocks
NOTE: NLR4.3 HIV-1 Gag-iGFP (Green Fluorescent Protein) carrying an R5-tropic envelope, gift from M. Schindler 10 is used to infect macrophages and to see infected cells in real time.
3. Infection of hMDMs with HIV-1
4. Opsonization of Sheep Red Blood Cells
5. Live Cell Video Microscopy Phagocytosis Assay
6. Analysis of the Time-lapse Movies
FcR-mediated phagocytosis by HIV-1-infected and non-infected hMDMs is described here using IgG-opsonized SRBCs as model targets (Figure 1). The critical steps of this protocol are the preparation of hMDMs and the infection with HIV-1. Indeed, the yield and quality of differentiated macrophages varies among donors, as well as the infection rate with efficiencies in the range of 10-40%. In addition, the preparation of IgG-opsonized-SRBCs is also important to avoid damaging the erythrocytes, because this could induce their recognition and uptake as debris instead of by FcR-mediated phagocytosis. Optimal opsonization will ensure efficient phagocytosis.
Phagosome movement in living HIV-infected macrophages is analyzed in real-time with the BF channel on a spinning disk confocal microscope in the BSL-3 laboratory. The settings of the BF channel are critical to see the nucleus (Figure 2, blue circle) and for discriminating the external (Figure 2, red arrowheads) from the internalized SRBCs (Figure 2, red circles). The BF microscopy is considered as the simplest optical microscopy illumination technique sufficient to see the phagosomes, which are less refringent than the external SRBCs.
The first step after acquisition of image sequences is manual tracking on the ImageJ software (Figure 3). This point can be particularly long and tedious, because it is preferable to track each phagosome, one by one for all image sequences and it is considered that experiments need to be repeated with at least 3 donors per condition to reach a large enough sample size for statistical analysis (at least 30 phagosomes with 3 different donors).
The second step is the analysis in spreadsheet software to calculate the phagosome velocity during the first 5 min after internalization for each internalized SRBCs (Figure 4). For this, we plot for each phagosome the distance travelled during the first 5 min against the time. A representative example is shown in non-infected hMDMs on Figure 5A. Next we obtain the velocity of the phagosome, which is the slope of the linear regression curve. A velocity of 0.5384 µm/min was found for this phagosome.
Of note, it is possible to analyze the phagosome velocity during the first few minutes after internalization, as described here or in Dumas et al. 8, or later by analyzing the velocity over longer timescales. In our study, we observed that the phagosome velocity during the first 5 min after internalization in HIV-infected hMDMs is lower compared to non-infected hMDMs (Figure 5B).
Figure 1. Preparation of control and HIV-infected hMDMs for phagocytosis imaging. Monocytes are purified by adhesion (1) and differentiated into macrophages for 11 days with M-CSF (2). Next, hMDMs are infected with NLR4.3 HIV-1Gag-iGFP i) at an MOI between 0.02 and 0.03 for 8 days with washing on day 2 (3). (4) IgG-opsonized SRBCs are added onto hMDMs for phagocytosis during 1 hr. The phagosomes containing SRBCs are detectable on BF images (red circle, ii). Images are from the Servier images database. Bar = 10 µm. Please click here to view a larger version of this figure.
Figure 2. Real-time acquisition during phagocytosis by representative control and HIV-infected hMDMs. hMDMs are prepared and infected as described in Figure 1. The NLR4.3 HIV-1Gag-iGFP infected cells are detected with the 491 nm laser. Z-stacks of spinning disk confocal images are acquired and analyzed using both the microscope acquisition software and ImageJ (left panels). Galleries of BF images represent a non-infected (top panels corresponding to Movie 1) and a NLR4.3 HIV-1Gag-iGFP infected (bottom panels corresponding to Movie 2) cell during a 45 min acquisition (46 images with time indicated as hh:mm). The cell membrane (dotted black line), the nucleus (blue circle), the external SRBCs (some of them indicated with red arrowheads) and the internal SRBCs (some of them indicated with red circles) are detectable on BF images. Bar = 10 µm. Please click here to view a larger version of this figure.
Figure 3. Instruction steps for image analysis with Manual Tracking plugin on ImageJ. After opening the "Manual Tracking" plugin (1) and loading the time-lapse video in BF channel (2), enter the parameters of the acquisition (3). Click on "Add track" (4) and start the measurement of the tracking by clicking on one phagosome (5) to obtain a new window with X and Y positions of the chosen phagosome (6, red box). To follow the phagosome on the time sequence for convenience, vary the brightness and contrast (5'). Please click here to view a larger version of this figure.
Figure 4. Instruction steps for data analysis of phagosome migration velocity in spreadsheet software. (A) Assemble the X and Y position of the nucleus and each phagosome (red box) in a spreadsheet table. In another column (purple box), calculate the distance between the phagosome and the nucleus with Pythagoras' theorem where c represents the length between the nucleus and the SRBC and a and b the lengths of the other two sides of a right-angled triangle (B). (C) Finally, calculate the distance travelled by the phagosomes at each time (green box) by subtracting the distance between the SRBC and the nucleus at a given time from the initial distance at time 0. Please click here to view a larger version of this figure.
Figure 5. Quantification of phagosome migration velocity in control and HIV-infected hMDMs. (A) For each SRBC and just after SRBC internalization, the travelled distance towards the nucleus is measured and plotted against the time. Its velocity during the first 5 min is calculated using linear regression in spreadsheet software. A representative experiment is shown (the internal SRBC of Figure 3-4). (B) All velocities during the first 5 min are measured for 66 phagosomes in non-infected (5 donors) and 60 phagosomes in HIV-infected cells (4 donors). Data represent the mean ± SEM (Unpaired Student t test with Welch's correction; **, P <0,01). Please click here to view a larger version of this figure.
Movie 1: Phagosome movement in a representative non-infected macrophage. (Right click to download). The movement of opsonized red blood cells was detected in BF channel during 45 min of phagocytosis with one image per minute (46 images with time indicated as hh:mm). Bar = 10 µm.
Movie 2: Phagosome movement in a representative HIV-infected macrophage. (Right click to download). HIV-1 (NLR4.3 HIV-1 Gag iGFP)-infected macrophages were identified after illumination with the 491 laser. The movement of opsonized red blood cells was detected in BF channel during 45 min of phagocytosis with one image per minute (46 images with time indicated as hh:mm). Bar = 10 µm.
Falcon 100mm TC-Treated Cell Culture Dish | Corning | 353003 | For viral production |
Glass Bottom Dishes 35 mm uncoated 1.5 | MatTek corporation | P35G-1.5-14-C Case | For acquisition |
Falcon Tissue Culture Plates 6-well | Thermo Fischer Scientific | Corning. Inc. 353934 | For human monocyte-derived macrophages |
Ficoll-Plaque PLUS | Dominique Dutscher | 17-1440-03 | a neutral, highly branched, high-mass, hydrophilic polysaccharide in solution for density centrifugation |
DPBS, no calcium, no magnesium | Thermo Fischer Scientific | 14190-094 | Room temperature |
Dulbecco's Modified Eagle Medium (DMEM) 1X, liquid (High Glucose) | GIBCO, Molecular probes | 31966-021 | Conserved at 4°C ; for HEK cells culture |
RPMI 1640 medium GLUTAMAX Supplement | Life technologies | 61870-010 | Conserved at 4°C; for hMDMs culture |
Fœtal Calf Serum (FCS) | Eurobio | CVFSVF0001 | Conserved at -20°C ; decomplemented |
Penicillin-Streptomycin (10,000 U/mL) | Thermo Fischer Scientific | 15140-122 | Conserved at -20°C ; for hMDMs culture |
RPMI 1640 medium, no phenol red (10×500 ml) | Life technologies | 11835-105 | Warm in 37°C water bath before use ; for phagocytosis assay |
FuGENE6 Transfection Reagent | Promega | E2692 | Conserved at 4°C ; for viral production |
Sheep red blood cells (SRBCs) | Eurobio | DSGMTN00-0Q | Conserved in Alsever buffer at 4°C before use |
Anti-sheep red blood cells IgG | MP Biomedicals | 55806 | Conserved at 4°C |
Bovine Serum Albumin heat shock fraction, pH 7, ≥98% | Sigma | A7906 | Conserved at -20°C |
Inverted microscope DMI600 | Leica | ||
Confocal Spinning Disk Unit CSU-X1M1 | Yokogawa | ||
491 nm 50mW laser | COBOLT CALYPSO | ||
HCX PL APO CS Objectif | Leica | Objective lens ; Magnification 100x ; Numerical aperture 1.40 ; Immersion oil | |
CoolSnap HQ2 (FireWire) Camera | Photometrics | Pixel size 6.45 x 6.45 µm ; Definition 1392 x 1040 ; Encoding the image in 14 Bit | |
Metamorph 7.7.5 software | Molecular Devices | For the control of the microscope | |
GraphPad Prism software | For the statistics analysis |
Macrophages are phagocytic cells that play a major role at the crossroads between innate and specific immunity. They can be infected by the human immunodeficiency virus (HIV)-1 and because of their resistance to its cytopathic effects they can be considered to be persistent viral reservoirs. In addition, HIV-infected macrophages exhibit defective functions that contribute to the development of opportunistic diseases.
The exact mechanism by which HIV-1 impairs the phagocytic response of macrophages was unknown. We had previously shown that the uptake of various particulate material by macrophages was inhibited when they were infected with HIV-1. This inhibition was only partial and phagosomes did form within HIV-infected macrophages. Therefore, we focused on analyzing the fate of these phagosomes. Phagosome maturation is accompanied by migration of these compartments towards the cell center, where they fuse with lysosomes, generating phagolysosomes, responsible for degradation of the ingested material. We used IgG-opsonized Sheep Red Blood Cells as a target for phagocytosis. To measure the speed of centripetal movement of phagosomes in individual HIV-infected macrophages, we used a combination of bright field and fluorescence confocal microscopy. We established a method to calculate the distance of phagosomes towards the nucleus, and then to calculate the velocity of the phagosomes. HIV-infected cells were identified thanks to a GFP-expressing virus, but the method is applicable to non-infected cells or any type of infection or treatment.
Macrophages are phagocytic cells that play a major role at the crossroads between innate and specific immunity. They can be infected by the human immunodeficiency virus (HIV)-1 and because of their resistance to its cytopathic effects they can be considered to be persistent viral reservoirs. In addition, HIV-infected macrophages exhibit defective functions that contribute to the development of opportunistic diseases.
The exact mechanism by which HIV-1 impairs the phagocytic response of macrophages was unknown. We had previously shown that the uptake of various particulate material by macrophages was inhibited when they were infected with HIV-1. This inhibition was only partial and phagosomes did form within HIV-infected macrophages. Therefore, we focused on analyzing the fate of these phagosomes. Phagosome maturation is accompanied by migration of these compartments towards the cell center, where they fuse with lysosomes, generating phagolysosomes, responsible for degradation of the ingested material. We used IgG-opsonized Sheep Red Blood Cells as a target for phagocytosis. To measure the speed of centripetal movement of phagosomes in individual HIV-infected macrophages, we used a combination of bright field and fluorescence confocal microscopy. We established a method to calculate the distance of phagosomes towards the nucleus, and then to calculate the velocity of the phagosomes. HIV-infected cells were identified thanks to a GFP-expressing virus, but the method is applicable to non-infected cells or any type of infection or treatment.
Macrophages are phagocytic cells that play a major role at the crossroads between innate and specific immunity. They can be infected by the human immunodeficiency virus (HIV)-1 and because of their resistance to its cytopathic effects they can be considered to be persistent viral reservoirs. In addition, HIV-infected macrophages exhibit defective functions that contribute to the development of opportunistic diseases.
The exact mechanism by which HIV-1 impairs the phagocytic response of macrophages was unknown. We had previously shown that the uptake of various particulate material by macrophages was inhibited when they were infected with HIV-1. This inhibition was only partial and phagosomes did form within HIV-infected macrophages. Therefore, we focused on analyzing the fate of these phagosomes. Phagosome maturation is accompanied by migration of these compartments towards the cell center, where they fuse with lysosomes, generating phagolysosomes, responsible for degradation of the ingested material. We used IgG-opsonized Sheep Red Blood Cells as a target for phagocytosis. To measure the speed of centripetal movement of phagosomes in individual HIV-infected macrophages, we used a combination of bright field and fluorescence confocal microscopy. We established a method to calculate the distance of phagosomes towards the nucleus, and then to calculate the velocity of the phagosomes. HIV-infected cells were identified thanks to a GFP-expressing virus, but the method is applicable to non-infected cells or any type of infection or treatment.