Metchnikoff's policemen: macrophages in development, homeostasis and regeneration.

Over the past decade, modern genetic tools have permitted scientists to study the function of myeloid lineage cells, including macrophages, as never before. Macrophages were first detected more than a century ago as cells that ingested bacteria and other microbes, but it is now known that their functional roles are far more numerous. In this review, we focus on the prevailing functions of macrophages beyond their role in innate immunity. We highlight examples of macrophages acting as regulators of development, tissue homoeostasis, remodeling (the reorganization or renovation of existing tissues) and repair. We also detail how modern genetic tools have facilitated new insights into these mysterious cells.