Phagocyte

Phagocytes are cells that are found in the blood, bone marrow and other tissues of vertebrates. [ cite web|url=http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookIMMUN.html |title=LYMPHATIC SYSTEM AND IMMUNITY |accessdate=2008-10-04 |last=Farabee |first=M.J. |date=2001 ] These cells ingest and destroy foreign, particulate matter such as microorganisms and debris by a process called phagocytosis. They are important in the immunity and resistance to infection.Fact|date=October 2008 The word is derived from "cell eater" in Greek.Fact|date=October 2008

Types

There are three main categories of phagocytes: [eMedicineDictionary|Phagocyte]
* macrophages (and monocytes)
* microphages, such as polymorphonuclear leukocytes (primarily neutrophils)
* dendritic cells

Functions

Phagocytes eat pathogens and are extremely useful as an initial immune system response to infection. They contain many lysosomes that enable them to digest foreign material. They engulf pathogens, debris, dead or dying cells and extracellular matrix. After engulfment into a phagosome, a lysosome which is filled with digestive enzymes (proteases) and oxygen radicals fuses with it to form the phagolysosome in which the phagocytosed material is digested. If the skin is broken, the first type of phagocyte that migrate to sites of injury are neutrophils. They fight bacteria by releasing cytotoxic granules and by phagocytosis. Phagocytosis is an active process in wound healing.

In pathogen phagocytosis, specialised antigen-presenting cells (B cells, dendritic cells and macrophages) present on their surfaces small peptides that resulted from the digestion, bound to MHC class II molecules. Helper T cells (CD4⁺) later recognize these antigens complemented with a second signal, and supplement the cell-mediated immune response.

Phagocytes can also induce apoptosis of normal and tumor cells, produce cationic proteins, complement components and clotting factors, arachidonic acid metabolites, prostaglandins, leukotrienes, thromboxanes, cytokines, proteases and hydrolases, reactive oxygen and nitrogen intermediates.

Resistance by pathogen

Many pathogens can delay or prevent the creation of the phagolysosome such as "Mycobacterium tuberculosis", "Salmonella typhi" and "Legionella". Others, such as the parasites of the genus "Leishmania", able to resist or circumvent being digested in the phagolysosome.

One function of T-helper cells is to activate phagocytes to digest intracellular pathogens.

Etymology

The word "phagocyte" means "cell that eats", and originates from the Greek words "phagein", meaning 'eat', and "kytos", meaning 'hollow'. Because hollows of the cork are cells, it means "cell".

References

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