When a person is injured, cells called neutrophils are some of the first members of the immune system to respond. Once they arrive on the scene of an injury, the cells attack foreign pathogens trying to invade the tissue by engulfing the microorganisms and releasing inflammatory compounds that break the invaders down. But sometimes, neutrophils overstay their welcome, making it difficult for tissue to heal—something that occurs in chronic inflammatory disorders such as rheumatoid arthritis. To find treatments for these conditions, a research team led by Stephen A. Renshaw of the University of Sheffield, in England, screened a library of molecules using zebrafish larvae genetically engineered to have fluorescent neutrophils. The scientists nicked off the tips of the animals’ tail fins, added test molecules to the water in which the fish swam, and 12 hours later examined the number of fluorescing cells in the animals’ tails (Sci. Transl. Med. 2014, DOI: 10.1126/scitranslmed.3007672). One promising molecule that caused neutrophils to migrate away from the injury site is tanshinone IIA, a compound derived from the Chinese medicinal herb Salvia miltiorrhiza. “If we can work out exactly how tanshinone IIA is acting on the neutrophils, then we might be able to target this mechanism and develop new anti-inflammatory therapies,” Renshaw says.