The overall goal of this CD14 magnetic beads separation technique is to isolate monocytes from the blood for their further differentiation into dendritic cells or macrophages in vitro. This method can help answer key questions in the field of immunology about the recognition, processing, and presentation of pathogens or antigens by dendritic cells. The main advantage of this isolation procedure is that the 98 to 99%pure monocyte population can be obtained.
Demonstrating the procedure will be Karolin Thurnes, a technician from our work group. Begin by splitting the blood pack volume among sterile 50 milliliter centrifuge tubes according to the amount of blood received. Adjust the final volume in each tube to 50 milliliters with sterile Dulbecco's PBS as necessary and centrifuge the samples.
Using a sterile one milliliter serological pipette connected to a laboratory vacuum pump, remove the plasma and platelet layers leaving the boundary layers undisturbed. Then, use a new 25 milliliter pipette to combine the mononuclear cell boundary layers from two of the tubes in the new sterile 50 milliliter conical tube. Next, add 15 milliliters of density gradient medium to each of 450 milliliter conical tubes and pipetting slowly and carefully, overlay 25 milliliters of pooled blood cells onto the density gradient in each tube.
Separate the cells by centrifugation. Then aspirate the plasma and platelet upper layers and transfer the PBMC interphases into new individual 50 milliliter conical tubes. Wash the PBMCs two times with up to 50 milliliters of sterile DPBS, pulling the cells after the first centrifugation and resuspending the pellet in 50 milliliters of fresh DPBS after the second.
After counting, collect the cells by centrifugation for monocyte magnetic particle isolation. To purify the monocytes by magnetic particle isolation, adjust the PBMC concentration to eight times 10 to the 7th cells per milliliter of isolation buffer. Next, vortex the anti-human CD14 magnetic particles thoroughly and mix 50 microliters of particles for every one times 10 to the 7th PBMCs into the cells, and transfer the cell bead solution to a sterile 15 milliliter tube.
After 30 minutes at room temperature, adjust the total volume to 12 milliliters of isolation buffer, and transfer two milliliters of the cell particle suspension into each of six sterile round bottom tubes. Immediately place the tubes onto the cell separation magnet for 10 minutes at room temperature. Then remove the supernatant containing the peripheral blood lymphocytes from each tube.
Remove the tubes from the magnet and add two milliliters of fresh isolation buffer to each cell sample. Gently pipette up and down to resuspend the cells and particles, and return the tubes to the magnet for another five minutes. At the end of the incubation, remove the supernatant again, and resuspend the cells in two milliliters of fresh isolation buffer as just demonstrated.
Then pull the CD14 positive monocyte containing cell fractions into a new 50 milliliter tube and bring the final volume of the tube up to 50 milliliters in sterile DPBS. To differentiate the purified monocytes into dendritic cells, collect the cells by centrifugaiton and resuspend the pellet in 50 milliliters of DPBS. After counting, spin down the cells again and resuspend the pellet at a one times 10 to the 6th cells per milliliter concentration and prewarmed culture medium.
Transfer three milliliters of cells into each well of a six well plate and add recombinant human Interleukin four and GMCSF to each well for a 48 hour incubation at 37 degrees Celsius and 5%carbon dioxide. On the second day of culture, restimulate the cells with fresh cytokines and return the plate to the incubator. On day five, pull the supernatants and gently pipette fresh medium into the wells several times to harvest the immature dendritic cells.
After density gradient separation, a typical PBMC fraction is comprised of about 4%B-lymphocytes, 28%monocytes and 68%other cells. 44%of which are t-lymphocytes. After magnetic particle separation, flow cytometric analysis of the negative fraction reveals a similar percentage of b-lymphocytes, a higher percentage of the other cell populations and a greatly reduced percentage of monocytes.
Characterization of the positive fraction demonstrates the high purificaiton efficiency with over 99%of the cells expressing CD14. After five days of Interleukin four and GMCSF simulation, the CD14 positive cells differentiate into immature CD83 negative DC-SIGN positive monocyte derived dendritic cells which are comparable to dermal dendritic cells in the morphology, behavior, and receptor expression. Once mastered, this technique can be completed in four to five hours if it is performed properly.
After watching this video, you should have a good understading of how to isolate monocytes from whole blood and differentiate them into dendritic cells. This technique is very important for researchers in the field of immunology to explore not only dendritic cell, but also monocyte and macrophage function in the primary in vitro human cell system. Following this procedure, other methods like microscopic analysis, flow cytometry, infection or antigen presentation essays can be performed to answer questions about dendritic cell biology, function and interactions with antigens.
Don't forget that working with blood can be hazardous and that precautions such as wearing gloves, a lab coat or having a hepatitis vaccination should always be taken before beginning this procedure.
