Working up an appetite to promote repair

Neutrophils, monocytes, and macrophages are among the first immune responders to an infectious agent. Although a strong inflammatory response is essential to clear bacteria, the subsequent tissue repair responses that restore homeostasis after infection remain less clear. Neutrophils, which have remarkable phagocytic abilities and antipathogen defenses (1), are recruited en masse from the blood and bone marrow to sites of infection, where they function to capture and kill bacteria. Monocytes are also recruited to infection sites, and it has been presumed that these cells mature into macrophages and aid neutrophils in bacterial clearance. However, the exact functional role of recruited monocytes during bacterial infection was unknown. Monocytes are incredibly plastic and can functionally adapt during inflammation and injury to promote tissue repair (2–4). Although monocytes can phagocytose bacteria, is this their bona fide in vivo function, or can recruited monocytes acquire reparative roles?