Phagocytosis

Phagocytosis (from Ancient Greek φαγεῖν (phagein) 'to eat' and κύτος (kytos) '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.

In a multicellular organism's immune system, phagocytosis is a major mechanism used to remove pathogens and cell debris.

Where phagocytosis is used as a means of feeding and provides the organism part or all of its nourishment, it is called phagotrophy and is distinguished from osmotrophy, which is nutrition taking place by absorption.

[citation needed] The history of phagocytosis represents the scientific establishment of immunology as the process is the first immune response mechanism discovered and understood as such.

[1][2] The earliest definitive account of cell eating was given by Swiss scientist Albert von Kölliker in 1849.

[3] In his report in Zeitschrift für Wissenschaftliche Zoologie, Kölliker described the feeding process of an amoeba-like alga, Actinophyrys sol (a heliozoan) mentioning details of how the protist engulfed and swallowed (the process now called endocytosis) a small organism, that he named infusoria (a generic name for microbes at the time).

[5][6] Haeckel discovered that blood cells of sea slug, Tethys, could ingest Indian ink (or indigo[7]) particles.

[11] The role of neutrophils is patrolling the bloodstream and rapid migration to the tissues in large numbers only in case of infection.

Their role is not killing or clearance of microbes, but rather breaking them down for antigen presentation to the cells of the adaptive immune system.

[13] Fcγ receptor mediated phagocytosis includes formation of protrusions of the cell called a 'phagocytic cup' and activates an oxidative burst in neutrophils.

[17][18][19] Some bacteria, for example Treponema pallidum, Escheria coli and Staphylococcus aureus, are able to avoid phagocytosis by several mechanisms.

Following apoptosis, the dying cells need to be taken up into the surrounding tissues by macrophages in a process called efferocytosis.

As in phagocytic immune cells, the resulting phagosome may be merged with lysosomes (food vacuoles) containing digestive enzymes, forming a phagolysosome.

The food particles will then be digested, and the released nutrients are diffused or transported into the cytosol for use in other metabolic processes.