There’s a kind of cell in your blood whose name sounds like something out of a horror movie: The word macrophage, translated from Greek, means “large eater.” These white blood cells crawl through your tissues looking for anything that doesn’t belong and then literally eating it. During that digestion process, the macrophages signal the presence of foreign invaders to other parts of the immune system. This pair of images captured by Sue Ludmann, M.S., an imaging specialist at the Allen Institute for Immunology, shows a single human macrophage that has just swallowed a handful of microscopic beads labeled fluorescent yellow. The black and white image in the slider on the left and the red fluorescent dye on the right show the macrophage’s internal scaffolding system, labeling a protein known as f-actin, letting Ludmann know that the immune cells have succeeded in fully engulfing the yellow beads. She’s currently establishing this imaging test using healthy human macrophages; ultimately, the team will study macrophages from patients with rheumatoid arthritis to study whether these large eaters are failing to do their job in this autoimmune disease.