A cross-disciplinary team at the University of Pennsylvania has found that T cells, a key part of the immune system, track down parasites with a movement strategy that’s similar to strategies used by predators like penguins to hunt their prey. The study, published in Nature, was conducted in mice infected with the Toxoplasma gondii parasite. The researchers used a powerful microscope that can display living tissues in three dimensions in real time to track the movements of T cells. Contrary to their expectations, the T cells did not move directly toward the parasite. But the movements were not random, either. Instead, their paths tended to have many short "steps" and occasional long "runs," with long and short pauses in between.