In phagocytosis (literally, "cell eating"), large particles are enveloped by the cell membrane of a (usually larger) cell and internalized to form a food vacuole.

In animals, phagocytosis is performed by specialized phagocytotic cells or phagocytes, which serve to remove foreign bodies and thus fight infection. In vertebrates these include larger macrophages and smaller granulocytes, types of blood cells. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytosed. Virulent bacteria may need to be coated in antibodies before it is possible to consume them.

In many protists, phagocytosis is used as a means of feeding, providing part or all of their nourishment. This is called phagotrophic nutrition, as distinguished from osmotrophic nutrition which takes place by absorption. In some, such as amoebae, phagocytosis takes place by surrounding the target object with pseudopods, as in animal phagocytes. In other protozoa, for instance ciliates, there is a specialized groove or chamber in the cell where phagocytosis takes place. The resulting food vacuole may be merged with lysosomes containing digestive enzymes, and the resulting material is absorbed into the cytosol.

See also

• Endocytosis - an overview of related cellular processes.
• Neutrophil granulocyte - the most common type of granulocyte.
• Ilya Ilyich Mechnikov - a microbiologist who was awarded the Nobel Prize in Physiology or Medicine for discovery of the role of phagocytosis in higher animals.

Received wisdom dictates that macrophages and neutrophils represent 'professional phagocytes' but this merely reflects the greater amount of research performed on these cell types. A great body of evidence continues to mount showing that resident, neighbouring cells in a tissue will phagocytize their apoptotic (suicidal) neighbours, thus, maintaining tissue homeostasis. This clearance can, depending on the location, facilitate greater clearance than that achieved by resident macrophages!

The most important facet of phagocytosis is its control of inflammation. Depending on the phagocytosed particle phagocytosis can induce inflammation or, as is the case with apoptotic cells, induce resolution of inflammation. Phagocytosis is also involved in immune tolerance which prevents inflammation against normal components of the body.