immune disorders
Innate Immunity
Monocytes and Macrophages
Macrophages develop from a type of white blood cell called monocytes. Monocytes become macrophages when they move from the bloodstream to the tissues. Monocytes move to the tissues when infection occurs. There, over a period of about 8 hours, monocytes enlarge greatly and produce granules within themselves, becoming macrophages. The granules are filled with enzymes and other substances that help kill and digest bacteria and other foreign cells. Macrophages stay in the tissues. They ingest bacteria, foreign cells, and damaged and dead cells. (The process of a cell ingesting a microorganism, another cell, or cell fragments is called phagocytosis, and cells that ingest are called phagocytes.) Macrophages secrete substances that attract other white blood cells to the site of the infection. They also help T cells recognize invaders and thus also participate in acquired immunity. 