Macrophages (Greek: big eaters, from makros "large" + phagein "eat"; abbr. MF), are a type of white blood cell that engulfs and digests cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the types of proteins specific to the surface of healthy body cells on its surface in a process called phagocytosis. Macrophages were first discovered by Élie Metchnikoff, a Russian bacteriologist, in 1884. They are found in essentially all tissues, where they patrol for potential pathogens by amoeboid movement. They play a critical role in non-specific defense (innate immunity), and also help initiate specific defense mechanisms (adaptive immunity) by recruiting other immune cells such as lymphocytes. In humans, dysfunctional macrophages cause severe diseases such as chronic granulomatous disease that result in frequent infections.