Assessing the Cellular Immune Response of the Fruit Fly, Drosophila melanogaster, Using an In Vivo Phagocytosis Assay

This in vivo phagocytosis assay allows researchers to carry out genetic screens and genome-wide association studies to identify novel genes that regulate phagocytosis in adult blood cells. This experiment is quantitative, easy to perform, and can be applied to the screening of live animals for host factors that influence pathogen recognition, uptake, and clearance. After pulling thin-wall glass capillaries with a needle puller, use a micrometer to hold the needle under a microscope, and use number five, fine-point, stainless-steel tweezers to break the tip to a 100-micrometer tip diameter.

To measure the volume of liquid that will be injected into each fly, load a capillary needle with sterile 5%food coloring in PBS, and expel the liquid onto a drop of mineral oil on a 0.01-millimeter stage micrometer. Dispense 10 microliters of 1.6 milligrams per milliliter particles onto a small square of Parafilm, and pull the liquid into the needle. Mount the needle into the injector nozzle, and line the anesthetized flies along their designated area on the fly pad, ventral side up, with the heads oriented toward the front of the pad.