This article describes a method for injecting Plasmodium sporozoites into the ears of anesthetized mice to study immune responses. The technique involves precise injection to ensure successful delivery of the non-infectious sporozoites into the dermis.
Begin with an anesthetized mouse under a stereomicroscope, with the underside of one of the mouse's ears fixed on the stage via adhesive tape.
The eyes are coated with an ointment to prevent them from drying.
Bring a syringe loaded with the sporozoite stage of Plasmodium, a malarial parasite. The live sporozoites are radiation-attenuated to render them non-infectious.
Using the stereomicroscope, inject into the top side of the ear, penetrating the outermost epidermis layer and releasing the sporozoites into the dermis.
Keep the needle in place briefly to prevent backflow of the injected suspension before removing it.
A visible swelling at the injection site, termed a papule, confirms a successful injection.
Perform multiple injections into the same ear.
Release the injected ear and repeat the injections into the other ear.
Post-injection, allow the mouse to recover.
The injected sporozoites trigger an immune response, priming the immune system against the parasite.
Before injecting the sporozoites, confirm the proper level of sedation of the experimental animal by toe pinch, and apply eye ointment to prevent corneal drying. Then, working quickly, use clear tape to gently fix the ventral side of the ear pinna under a stereomicroscope, and load a 10-microliter syringe equipped with a 35-gauge needle with 0.6 microliters of resuspended parasites.
Next, carefully insert the needle, bevel side up, beneath the epidermis on the dorsal side of the ear, and inject 0.15 microliters of sporozoites into the site. A characteristic papule will be observed at the injection site. After injecting the dermis three more times as just demonstrated, carefully remove the tape and monitor the mouse until it is fully recovered.
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