To locate the source of an infection, immune cells called neutrophils take directions from local blood cells.

Neutrophils are the first responders to an infection, where they produce pathogen-killing compounds. To determine how they home in on infections and other injuries, a team led by Andrés Hidalgo at Spain's National Centre for Cardiovascular Research in Madrid imaged blood vessels in live mice that were showing an inflammatory response.

The authors discovered that neutrophils drifting in the bloodstream stuck to blood vessel walls and then sent out arm-like extensions. When these encountered blood cells called platelets — which are activated by injury to help to stop bleeding — the neutrophils began to migrate along the vessel wall and churn out toxic chemicals. Blocking communication between neutrophils and platelets lessened tissue damage from excessive inflammation in mouse models of sepsis, lung injury or stroke.

Science 346, 1234–1238 (2014)