An exit strategy for the clean-up crew

Macrophages race in to gobble up bacterial invaders, but what happens to the destroyers once the feast is over? Geoffrey Bellingan, Geoffrey Laurent (University College, London, UK), and colleagues find that the macrophages can slip back into the immune system because regulated adhesion molecules direct the macrophages to cells overlying lymphatic vessels.

The first attackers arriving at the scene of an infection in the abdominal cavity are neutrophils with a later peak in monocytes and macrophages. As the infection wanes, the neutrophils apoptose and are engulfed by macrophages. “The foot soldiers all shrivel up and die,” says Bellingan, “but no one really addressed how these other guys [the macrophages] would be cleared.”

The London team found that the macrophages departed through the lymphatics, with the activated inflammatory macrophages (rather than the resident macrophages) being cleared preferentially. The activated macrophages adhered...