Phagocytosis Process in Immunology

Phagocytosis   (from Ancient Greek φαγεῖν (phagein) , meaning 'to eat', and κύτος, (kytos) , meaning 'cell') is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis.
In a multicellular organism's immune system, phagocytosis is a major mechanism used to remove pathogens and cell debris. The ingested material is then digested in the phagosome. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytized. Some protozoa use phagocytosis as means to obtain nutrients.

Phagocytosis is one of the main mechanisms of the innate immune defense. It is one of the first processes responding to infection, and is also one of the initiating branches of an adaptive immune response. Although most cells are capable of phagocytosis, some cell types perform it as part of their main function. These are called 'professional phagocytes.' Phagocytosis is old in evolutionary terms, being present even in invertebrates.^[3]

Neutrophils, macrophages, monocytes, dendritic cells, osteoclasts and eosinophils can be classified as professional phagocytes.^[2] The first three have the greatest role in immune response to most infections.^[3]