Just as we take out the rubbish to keep a house tidy, the body must clean out waste and dead tissue to stay healthy. Macrophages (pictured in green) are the white blood cells in charge of this process, engulfing dead cells (shown in pink) to dispose of them. They perform day-to-day maintenance, as seen in the right panel, as well as clear out areas of inflammation, when the immune system responds to infection or damage (left panel), thanks to the combined action of two proteins on the cell surface. Known as Mer and Axl, they both detect cells which need to be removed, but each responds to a different type of problem: Mer recognises dead cells in otherwise healthy environments, while Axl is active in inflamed tissue. Failure to remove dead cells in either case may lead to autoimmune diseases, making these receptor proteins important targets for future research.
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