Macrophages are a type of white blood cell that engulfs and digests anything that does not look like a healthy cell including cancer cells, microbes, cellular debris, foreign substances, etc. Macrophages work by looking for proteins that are specific to healthy body cells, if that protein is not expressed the macrophage will ingest the microbe through a process called phagocytosis, which acts to defend the host against infection and injury.

Macrophages are also important in activating other white blood cells. When a macrophage finds an unhealthy or non-self cell, it initiates phagocytosis. During this process the macrophage will present parts of the ingested cell on its surface to alert other immune cells like T-cells.

Macrophages also play an important anti-inflammatory role and can decrease immune reactions through the release of chemicals called cytokines.