Wikipedia:Today's featured article/August 6, 2009

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Scanning electron micrograph of a neutrophil phagocytosing anthrax bacilli

Phagocytes are the white blood cells that protect the body by ingesting (phagocytosing) harmful foreign particles, bacteria and dead or dying cells. They are essential for fighting infections, and for subsequent immunity. Phagocytes are important throughout the animal kingdom, and are highly developed in vertebrates. One liter of human blood contains about six billion phagocytes. Phagocytes were first discovered in 1882 by Ilya Ilyich Mechnikov while he was studying starfish larvae. Phagocytes of humans and other animals are called professional or non-professional, depending on how effective they are at phagocytosis. The professional phagocytes include cells called neutrophils, monocytes, macrophages, dendritic cells, and mast cells. The main difference between professional and non-professional phagocytes is that the professional phagocytes have molecules called receptors on their surfaces that can detect harmful objects, such as bacteria, that are not normally found in the body. Phagocytes are therefore crucial in fighting infections, as well as in maintaining healthy tissues by removing dead and dying cells that have reached the end of their life-span. During an infection, chemical signals attract phagocytes to places where the pathogen has invaded the body. (more...)

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