Intravital Imaging of Neutrophil Priming Using IL-1β Promoter-driven DsRed Reporter Mice

The overall goal of this procedure is to present a technology for monitoring the process of neutrophil priming in living animals. This method can help answer the key questions in the immunology field, such as visualization of the behavior and the function of priming the neutrophils in animal models of rarest diseases and disorders. The main advantage of this technique is that it combines three established methodologies, including fluorescent reporters in viral labeling and intravital imaging.

Breed heterozygous pIL1-DsRed mice with wild-type C57Black six mice. At three to four weeks, phenotype their pups. For each pup, prepare a 1.5 milliliter tube with 20 microliters of heparin.

To collect blood, hold a pup by its neck scruff and pierce the submandibular vein in the cheek pouch using a 5 millimeter lancet. Only a small puncture is needed. Collect three to five drops of blood per tube.

After making the collection, be sure to stop the bleeding and observe the animals for 30 minutes before returning them to the animal facility. To each sample tube, add 500 microliters of red blood cell lysing buffer. Then, vortex the tubes, and incubate them for five to 10 minutes on ice.

After the incubation, slowly add 400 to 500 microliters of fetal bovine serum under the cell suspensions in each tube. A clear interface should form between the layers. Next, centrifuge the samples at 1, 500 Gs for five minutes to collect cell pellets.

Discard the supernatent and resuspend the cells in 200 microliters of complete RPMI-1640 medium. Then, transfer each suspension to a flow cytometry tube and add 20 microliters of freshly made LPS Working Solution to each tube. Incubate the samples for four hours before performing flow cytometry.

To begin, anesthetize the mouse with an intraparetoneal injection of an anesthetic cocktail and confirm adequate sedation with a toe pinch test. Next, apply hair removal cream to the dorsal surface of both ears, wipe it off within a minute, and wash the skin with water. Measure the thickness of the ear where the applications were made using a micrometer.

Later, return the mouse in its own cage after it has recovered from the anesthesia, and allow the mouse to rest for at least three days before further testing. After three days, reanesthetize the mouse and measure the ear thickness again to make sure it is not irritated. Then, apply 12.5 microliters of 1.25%oxazolone onto each side of the right ear, and apply 12.5 microliters of the acetone olive oil vehicle solution onto each side of the left ear.

As always, observe the mouse recover from the anesthesia. 24 hours later, measure the thickness of the ear again under anesthesia to ensure the oxazolone induced skin inflammation has occurred. To begin, transfer 100 microliters of anti-lyse XG monocolonal antibody into a U100 insulin syringe with a 28 gauge needle.

Next, anesthetize a treated mouse as previously described. With the mouse abdomen down, apply gentle downward pressure to the skin dorsal and ventral to an eye to partially protrude the eyeball. Then, carefully place the needle, bevel down, approximately 30 degrees to the medial canthus and carefully insert the needle into the retro orbital sinus.

The penetration pressure will be relieved when the needle enters the sinus. Then, eject the content and remove the needle quickly. A small amount of bleeding suggests successful injection.

Now, immediately apply 1.25%oxazolone and vehicle solution onto the right and left mouse ears as before. Eight hours later, administer a second dose of the same antibody into each mouse. Also, to visualize the blood vessels, retro orbitally administer 100 microliters of fitc dextran.

For this procedure, first anesthetize the mouse as before. Then, apply veterinary ointment to the eyes to prevent dryness during imaging. Next, place a glass coverslip at the center of an imaging stage, and secure the edges of the coverslip with tape.

Also, add a drop of PVS to the coverslip. Now, position the mouse's ear over the coverslip, dorsal side down. Next, moisten the ventral surface of the mouse ear with a drop of PVS.

Then, mount the tip of the ear with a glass slide on top and secure the slide with tape. Now, turn on a multi laser fluorescence confocal microscope and the related equipment. Turn off the room lights to minimize ambient light exposure.

Then, record three dimensional images using the confocal microscope. For time lapse imaging experiments, record three dimensional images every two to four minutes for up to eight hours. All the while, watch for twitching whiskers, which indicates that the mouse is beginning to recover from the anesthesia.

In such situations, administer five to 10 microliters of a half dose of anesthetic cocktail via a butterfly needle. pIL-1-DsRed mice were screened for phenotypic DsRed fluorescence produced in peripheral blood leukocytes via flow cytometry. Circulating myeloid cells from wild-type mice minimally express DsRed, while the same cells from pIL1-DsRed mice express distinguishable DsRed signals.

IL-1 beta promoter activation is a marker of neutrophil priming, and can be best visualized in living pIL-1DsRed mice. Next, a skin sensitizer, oxazolone, was topically applied to the right ear. Later, the neutrophils were labeled before and after a second application of the oxazolone sensitizer via retro orbital injection.

Likewise, fitc dextran was injected to locate blood vessels. Many double labeled cells were found in the extravascular space, which represent primed neutrophils. A small number of cells were only labeled by the lyse XG antibody, which were probably resting neutrophils.

Moreover, a small population of DsRed positive cells were observed, which may comprise inflammatory monocytes and activated macrophage. Cell migratory paths were tracked to compare the two neutrophil populations. Both neutrophil populations showed a random migration once the extracellular space had been entered.

Interestingly, the putatively primed neutrophils exhibited a significantly higher velocity compared with their putatively resting counterparts. After its development, this technique paved the way for researchers in the field of immunology. Two explore the behavior and the function of many immune cells in various inflammatory states involving different t-cells.

After watching this video, you should have a good understanding of how to monitor the dynamic process of neutrophil priming in living animals.