phagocytose

Information about phagocytose

Enlarge picture
Steps of a macrophage ingesting a pathogen:
a. Ingestion through phagocytosis, a phagosome is formed
b. The fusion of lysosomes with the phagosome creates a phagolysosome; the pathogen is broken down by enzymes
c. Waste material is expelled or assimilated (the latter not pictured)

Parts:
1. Pathogens
2. Phagosome
3. Lysosomes
4. Waste material
5. Cytoplasm
6. Cell membrane


Phagocytosis is the cellular process of engulfing solid particles by the cell membrane to form an internal phagosome, or "food vacuole." The phagosome is usually delivered to the lysosome, an organelle involved in the breakdown of cellular components, which fuses with the phagosome. The contents are subsequently degraded and either released extracellularly via exocytosis, or released intracellularly to undergo further processing.

Phagocytosis is involved in the acquisition of nutrients for some cells, and in the immune system is a major mechanism used to remove pathogens and cell debris. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytosed.

Phagocytosis is a specific form of endocytosis involving the vesicular internalization of solid particles, such as bacteria, and is therefore distinct from other forms of endocytosis such as pinocytosis, the vesicular internalization of liquids.

Etymology

Phagocytosis is named from Greek roots: phagein - to eat, kytos - cell, and -osis - a suffix indicating a process; thus it can be translated literally as "the cellular process of eating." It should be noted that the process is only homologous to eating at the level of single-celled organisms; in multicellular animals the process has been adapted to eliminate debris and pathogens, as opposed to taking in fuel for cellular processes.

Phagocytic cells

PhagocyteDiagram
Neutrophil
Eosinophil
Basophil
Monocyte
Macrophage
Dendritic cell


Many protists are able to phagocytose particles, however in animals, phagocytosis is performed by specialized cells called phagocytes, which are able to remove foreign bodies and thus fight infection. In humans and many other animals, phagocytes include macrophages, monocytes, dendritic cells, and granulocytes[1]. The term professional phagocytes can be used to describe both macrophages and neutrophils, as these cells are considered to have phagocytosis as their primary function[2].

A great body of evidence continues to mount showing that resident, neighbouring cells in a tissue will phagocytize their apoptotic neighbours, thus maintaining tissue homeostasis. This clearance can, depending on the location, facilitate greater clearance than that achieved by resident macrophages.

Functions

Innate immunity

In humans, 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.

Adaptive immunity

For the activation of the adaptive immune response, phagocytosis is a necessary activation step. A T helper cell must be presented foreign particles bound to the major histocomptability complex class II (MHC II) receptor to become activated.

Nutrition

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, called the cytostome or mouth. The resulting phagosome may be merged with lysosomes containing digestive enzymes, forming a phagolysosome. The food particles will then be digested, and the released nutrients diffused or transported into the cytosol to use in other metabolic processes.

Resistance to phagocytosis

A substance or process which impedes or prevents the action of phagocyctes is termed antiphagocytic. Additionally, some bacteria may need to be opsonized before they are recognised as particles to be phagocytosed.

Certain intracellular pathogens, such the bacterial agents of leprosy and tuberculosis, are resistant to lysosomal degradation once internalised via phagocytosis.

Media

:*3-D Reconstruction of phagocytosis


    Phagocytosis by neutrophils
    A rapidly moving neutrophil can be seen taking up
    several conidia over an imaging time of 2 h with
    one frame every 30 s.



    A single dendritic cell can be seen here
    efficiently taking up at least four conidia in its vicinity.



    An active J774 macrophage is seen taking up at
    least three conidia. The J774 cells
    were treated with 5 ng/ml interferon-γ one night
    before filming with conidia. The observation
    was made over a period of 2.5 h every 30 s.



  • Problems seeing the videos? See .

See also

References

1. ^ Prescott, L. (1993). Microbiology, Wm. C. Brown Publishers, ISBN 0-697-01372-3
2. ^ Immunology at MCG 1/phagocyt

External links

 •  • [ e]
Membrane transport
Passive transportDiffusion - Facilitated diffusion - Osmosis
Active transportPrimary active transport - Secondary active transport
-cytosisExocytosis - Endocytosis (Phagocytosis, Pinocytosis)
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In cell biology, a phagosome is a vacuole formed around a particle absorbed by phagocytosis. The vacuole is formed by the fusion of the cell membrane around the particle. A phagosome is a cellular compartment in which pathogenic microorganisms can be killed and digested.
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Lysosomes are organelles that contain digestive enzymes (acid hydrolases). They digest excess or worn out organelles, food particles, and engulfed viruses or bacteria. The membrane surrounding a lysosome prevents the digestive enzymes inside from destroying the cell.
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In cell biology, an organelle is a specialized subunit within a cell, having a specific function, and separately enclosed within its own lipid membrane.

The name organelle
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Exocytosis (ek-soh-sy-TOH-sis) is the process by which a cell directs secretory vesicles to the cell membrane. These membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become
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immune system is a collection of mechanisms within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy
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A pathogen or infectious agent is a biological agent that causes disease or illness to its host.[1] The term is most often used for agents that disrupt the normal physiology of a multicellular animal or plant.
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Endocytosis (IPA: /ˌɛndoʊsaɪˈtoʊsɨs/) is a process whereby cells absorb material (molecules such as proteins) from the outside by engulfing it with their cell membrane.
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vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. If there is only one lipid bilayer, they are called unilamellar vesicles; otherwise they are called multilamellar.
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Bacteria

Phyla

Actinobacteria
Aquificae
Chlamydiae
Bacteroidetes/Chlorobi
Chloroflexi
Chrysiogenetes
Cyanobacteria
Deferribacteres
Deinococcus-Thermus
Dictyoglomi
Fibrobacteres/Acidobacteria
Firmicutes
Fusobacteria
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In cellular biology, pinocytosis ("cell-drinking", "bulk-phase pinocytosis", "non-specific, non-adsorptive pinocytosis") is a form of endocytosis, a process in which small particles are taken in by a cell by splitting into smaller particles.
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Greek}}} 
Writing system: Greek alphabet 
Official status
Official language of:  Greece
 Cyprus
 European Union
recognised as minority language in parts of:
 European Union
 Italy
 Turkey
Regulated by:
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Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of white blood cells and form an integral part of the immune system. Their name arrives from staining characteristics on hematoxylin and eosin (H&E) histological preparations.
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Eosinophil granulocytes, commonly referred to as eosinophils (or less commonly as acidophils), are white blood cells of the immune system that are responsible for combating infection by parasites in vertebrates.
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Basophils are the least common of the granulocytes, representing about 0.01% to 0.3% of circulating leukocytes (white blood cells). They contain large cytoplasmic granules which obscure the cell nucleus under the microscope.
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A monocyte is a leukocyte, part of the human body's immune system that protects against blood-borne pathogens and moves quickly (aprox. 8-12 hours) to sites of infection in the tissues. Monocytes are usually identified in stained smears by their large bilobate nucleus.
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Macrophages (Greek: "big eaters", from makros "large" + phagein "eat") are cells within the tissues that originate from specific white blood cells called monocytes.
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Dendritic cells (DCs) are immune cells and form part of the mammalian immune system. Their main function is to process antigen material and present it on the surface to other cells of the immune system, thus functioning as antigen-presenting cells.
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Eukarya
Whittaker & Margulis, 1978

Kingdom: Protista*
Haeckel, 1866

Typical phyla
  • Chromalveolata
  • Chromista

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A phagocyte is a cell that ingests and destroys foreign matter such as microorganisms or debris by a process known as phagocytosis.

Types of Phagocytes

There are three main categories of phagocytes: [1]
  • macrophages (and monocytes)

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Macrophages (Greek: "big eaters", from makros "large" + phagein "eat") are cells within the tissues that originate from specific white blood cells called monocytes.
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A monocyte is a leukocyte, part of the human body's immune system that protects against blood-borne pathogens and moves quickly (aprox. 8-12 hours) to sites of infection in the tissues. Monocytes are usually identified in stained smears by their large bilobate nucleus.
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Dendritic cells (DCs) are immune cells and form part of the mammalian immune system. Their main function is to process antigen material and present it on the surface to other cells of the immune system, thus functioning as antigen-presenting cells.
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Granulocytes are a category of white blood cells characterised by the presence of granules in their cytoplasm.[1] They are also called polymorphonuclear leukocytes (PMN or PML
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Apoptosis (pronounced ă-pŏp-tŏ’sĭs, apo tō' sis) is a form of programmed cell death in multicellular organisms. It is one of the main types of programmed cell death (PCD), and involves an orchestrated series of biochemical events leading to a
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See also:  and
The adaptive immune system is composed of highly specialized, systemic cells and processes that eliminate pathogenic challenges.
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T helper cells (also known as effector T cells or Th cells) are a sub-group of lymphocytes (a type of white blood cell or leukocyte) that plays an important role in establishing and maximizing the capabilities of the immune system.
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MHC Class II molecules are found only on a few specialized cell types, including macrophages, dendritic cells and B cells, all of which are professional antigen-presenting cells (APCs).
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Eukarya
Whittaker & Margulis, 1978

Kingdom: Protista*
Haeckel, 1866

Typical phyla
  • Chromalveolata
  • Chromista

..... Click the link for more information.

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