Abstract
Use antibodies or sera to localize proteins to the surface of fixed, permeabilized Plasmodium falciparum-infected red blood cells.
Reagents
- 1% gelatin (w/v) in RPMI
- RPMI Media
- Store at 4C, warm up to 37C right before use.
- PBS
- Phosphate buffered saline, keep on ice.
- Fixative Solution
- 4% formaldehyde + 0.0075% glutaraldehyde in PBS
- Make fresh for every use. Thaw a fresh frozen aliquot of 25% glutaraldehyde every time you make this.
- Permeabilization Solution
- PBS + 0.1% Triton X-100
- Blocking Buffer
- 3% Bovine Serum Albumin (BSA) (w/v) in PBS
- 1.5 g in 50 mL, make a fresh, sterile filter, and keep it on ice during use.
- Alternative blocking solutions: 5% animal serum in PBS, or 5% nonfat dried milk powder in PBS.
- Antibodies and Nuclear Dye
- 1% (v/v) Polyethyleneimine (PEI) in water
- PEI is very viscous
- Sigma Cat. No. 408727-100mL
- Glass Coverslip
- No. 1.5 (0.17 mm, 0.16 – 0.19 mm) thickness is best for the DeltaVision Deconvolution microscope
- Microscope Slide
- Nail Polish
- To seal coverslips on a microscope slide
- Mounting Medium
- Right before using, place 2-3 crystals of p-phenylenediamine (~1 mm diameter) in a microcentrifuge tube and add 100 uL water. Vortex and let sit in the dark for 5 minutes. Centrifuge briefly and use the supernatant as an antifade solution. Make fresh every time.
Equipment
- Heat block set to 37 C
- Refrigerated microcentrifuge, or a microcentrifuge placed in a cold room (4C)
- Bunsen burner
Notes
- In this protocol, examples assume 12 mL (1 plate) of culture that is gelatin purified, which will be suspended in a 1 mL volume after purification.
- All centrifuge steps are at 2000 rpm in the microcentrifuge for 2 minutes.
- NEVER vortex to resuspend cells. If need be, gently flick the tube or pipet slowly up and down with a 1 mL pipet tip.
- Keep all solutions with fluorescent dye in the dark whenever possible!
Procedure
- Gelatin purify 12 mL of parasite culture to enrich for trophy and schizont stage parasites
- Thaw an aliquot of frozen 1% gelatin at 37C. Use two tubes for 12 mL of culture.
- Spin culture at 1400 rpm (394 g) for 5 minutes with a brake of 1 (low) and discard supernatant.
- Add a volume of RPMI that is equal to the volume of the pellet. (12 mL culture at 4% hematocrit should be 480 uL pellet)
- Add four times the org. pellet volume of 1% gelatin and aliquot 1 mL volumes to 1.5 mL Eppendorf tubes.
- For example, if the pellet is 480 uL, add 480 uL RPMI and mix. Aliquot 240 uL of this mixture into each of the four tubes. Add 960 uL of 1% gelatin to each of the tubes.
- Incubate at 37C for 10 minutes (Use different times for different applications, e.g. 20 minutes to get pure trophy). Uninfected blood and ring-stage infected red blood cells (iRBCs) will sediment in the pellet and mature-stage iRBCs remain in the suspension.
- Transfer the upper layer to another tube.
- Wash the pellet and upper suspension three times with PBS.
- Washing can take place in multiple tubes, but in the end, the 12 mL of culture after gelatin purification should yield roughly 40 uL of pellets. Resuspend this in a final volume of 1 mL to roughly recreate 4% hematocrit.
- Smear the iRBCs from the pellet and upper suspension to determine the percentage of parasites.
- Wash cells: Gently centrifuge cells and exchange media with room-temp PBS.
- Fix cells: Centrifuge cells and exchange media with a fixative solution. Incubate for 30 min @ RT
- Wash cells: To remove the fixative, centrifuge and wash cells in PBS twice.
- Permeabilise cells: To gently permeabilize cells, incubate in 0.1% triton/PBS for 10 min. Check for permeabilization – supernatant should be pink from released hemoglobin.
- Wash cells: Centrifuge and wash cells in PBS twice to remove detergent.
- Blocking step: Resuspend cells in a blocking buffer for a few hours at RT or overnight at 4C on a rotator or rocker.
- You can keep the cells at 4C for up to a week.
- Primary Antibody Step: Resuspend cells in antibody diluted 1:50 to 1:100 in blocking buffer for 1 hour at RT on a rotating or rocking platform.
- If you started with 12 mL culture, you don’t need to use all of it for one microscope slide. Use 125 uL suspension (5 uL pellet) per slide.
- Wash cells: Wash cells two times in PBS.
- Secondary Antibody Step: Resuspend cells in secondary antibody diluted 1:200 and DAPI (10mg/mL) diluted 1:500 in blocking buffer for 30 min at RT on a rotating or rocking platform. If you have a tertiary antibody, don’t add the DAPI until the tertiary antibody incubation step.
- Wash cells: Wash cells two times in PBS.
- (Optional) Tertiary Antibody Step: Resuspend cells in tertiary antibody diluted 1:200 and DAPI (10mg/mL) diluted 1:500 in blocking buffer for 30 min at RT on a rotating or rocking platform.
- Wash cells: Wash cells two times in PBS.
- Resuspend cells in PBS, wrap them in foil, and leave them to sit while you prepare the slides.
- Coat Coverslip with 1% PEI in water: Flame a coverslip over a Bunsen burner. With a glass capillary or pipet tip, drop a spot of PEI solution and spread it over the coverslip with the side of the capillary. Leave to dry.
- Add cells: Put a small drop (5-10 uL) of cells on the center of the coverslip and let sit for a few minutes.
- Add mounting media: Add 1.5 uL to the middle of the coverslip and mix by pipetting
- Add Slide: Flame a slide, let it cool, then place it over the coverslip. Keep slides in the dark as much as possible to prevent photobleaching of dyes.
- Seal the slide by painting the edges of the coverslip with nail polish or Valap (1:1:1 vaseline:lanolin: paraffin wax)