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. A phagolysosome is a membrane-enclosed Organelle which is formed from the fusing of a Lysosome and a Phagosome. Waste material is expelled or assimilated (the latter not pictured) Parts:
1. Assimilation is the process of taking digested food which is circulating the body and then using it to help rebuild cells Pathogens
2. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious Phagosome
3. In cell biology a phagosome is a Vacuole formed around a particle absorbed by Phagocytosis. Lysosomes
4. Lysosomes are Organelles that contain Digestive enzymes (acid Hydrolases. Waste material
5. Cytoplasm
6. The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane. Cell membrane

Phagocytosis is the cellular process of engulfing solid particles by the cell membrane to form an internal phagosome, or "food vacuole. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer In cell biology a phagosome is a Vacuole formed around a particle absorbed by Phagocytosis. " The phagosome is usually delivered to the lysosome, an organelle involved in the breakdown of cellular components, which fuses with the phagosome. Lysosomes are Organelles that contain Digestive enzymes (acid Hydrolases. In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed The contents are subsequently degraded and either released extracellularly via exocytosis, or released intracellularly to undergo further processing. Exocytosis (ek-soh-sy-TOH-sis Greek: Έξω - external and κύτος - cell is the durable process by which a cell directs secretory vesicles out of the Cell

Phagocytosis is involved in the acquisition of nutrients for some cells, and in the immune system it is a major mechanism used to remove pathogens and cell debris. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious 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 various liquids. Endocytosis is a process where cells absorb material ( Molecules such as proteins from the outside by engulfing it with their Cell membrane. A vesicle is a small bubble of liquid within a cell A more formal definition in Cell biology, would be that a vesicle is a relatively small intracellular membrane-enclosed The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have In Cellular biology, pinocytosis ("cell-drinking" "bulk-phase pinocytosis" "non-specific non-adsorptive pinocytosis" "fluid endocytosis"

Etymology

Phagocytosis is named from Greek roots: phago - to eat, kytos - cell, and -osis - a suffix indicating a process; thus it can be translated literally as "the cellular process of eating. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly " 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, except in the case of the Trichoplax. Trichoplax adhaerens is a simple balloon-like marine Animal with a body cavity filled with pressurized fluid

Process^[1]

Phagocytosis is activated by attachment to Pathogen-associated molecular patterns (PAMPS), which leads to NF-κB activation. Pathogen-associated molecular patterns, or PAMP s are small molecular motifs consistently found on Pathogens They are recognized by Toll-like receptors and NF-κB ( nuclear factor-kappa B) is a protein complex that is a Transcription factor. Opsonins such as C3b and |antibodies can act as attachment sites and aid phagocytosis of pathogens. An opsonin is any molecule that acts as a binding Enhancer for the process of Phagocytosis, for example by coating the negatively-charged molecules on the membrane C3b is a one of the elements formed by the cleavage of Complement component 3. Antibodies (also known as immunoglobulins, abbreviated Ig) are Gamma globulin Proteins that are found in Blood or other Bodily

Engulfment of material is facilitated by the actin-myosin contractile system. The phagosome of ingested material is then fused with the lysosome, leading to degradation

Degradation can be oxygen-dependent or oxygen-independent. Oxygen-dependent degradation depends on NADPH and the production of reactive oxygen species. Reactive oxygen species (ROS are ions or very small molecules that include Oxygen Ions free radicals, and Peroxides both inorganic and Hydrogen peroxide and myeloperoxidase activate a halogenating system which leads to the destruction of bacteria. Oxygen-independent degradation depends on the release of granules, containing proteolytic enzymes such as defensins, lysozyme and cationic proteins. Other antimicrobial peptides are present in these granules, including lactoferrin which sequesters iron to provide unfavourable growth conditions for bacteria.

Phagocytic cells

Phagocyte	Diagram
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. Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of White blood cells in humans and form an essential part of the Eosinophil granulocytes, usually called eosinophils (or less commonly acidophils) are White blood cells that are one of the Immune System components Monocyte is a type of Leukocyte, part of the Human body 's Immune system. Macrophages ( Greek: "big eaters" from makros "large" + phagein "eat" ( Mø) are cells within the tissues that Dendritic cells (DCs are Immune cells and form part of the Mammalian Immune system. Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this Phagocytes are cells that are found in the blood bone marrow and other tissues of Vertebrates. In humans and many other animals, phagocytes include macrophages, monocytes, dendritic cells, and granulocytes^[2]. Macrophages ( Greek: "big eaters" from makros "large" + phagein "eat" ( Mø) are cells within the tissues that Monocyte is a type of Leukocyte, part of the Human body 's Immune system. Dendritic cells (DCs are Immune cells and form part of the Mammalian Immune system. Granulocytes are a category of White blood cells characterised by 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^[3].

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. Its most important function is the transport of cells into the blood. 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. Immune system|Passive immunity|Innate immune system The adaptive immune system is composed of highly specialized systemic cells and processes that eliminate or prevent Pathogenic A T helper cell must be presented foreign particles bound to the major histocomptability complex class II (MHC II) receptor to become activated. 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 MHC ( Major histocompatibility complex) Class II molecules are found only on a few specialized cell types including Macrophages Dendritic cells and

Nutrition

In many protists, phagocytosis is used as a means of feeding, providing part or all of their nourishment. Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this This is called phagotrophic nutrition, as distinguished from osmotrophic nutrition, which takes place by absorption. In some, such as amoeba, phagocytosis takes place by surrounding the target object with pseudopods, as in animal phagocytes. Amoeba (sometimes amœba or ameba, plural amoebae) is a Genus of Protozoa that moves Pseudopods or pseudopodia (from the Greek word ψευδοπόδια, ψευδός "fake false" 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 ciliates are one of the most important groups of Protists common almost everywhere there is water — lakes ponds oceans rivers and soils with many ectosymbiotic A cytostome or cell mouth is a part of a cell specialized for Phagocytosis, usually in the form of a Microtubule -supported funnel or groove The resulting phagosome may be merged with lysosomes containing digestive enzymes, forming a phagolysosome. In cell biology a phagosome is a Vacuole formed around a particle absorbed by Phagocytosis. Lysosomes are Organelles that contain Digestive enzymes (acid Hydrolases. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins The food particles will then be digested, and the released nutrients are diffused or transported into the cytosol for use in other metabolic processes. The cytosol or intracellular fluid (or cytoplasmic matrix) is the liquid found inside cells.

Resistance to phagocytosis

A substance or process which impedes or prevents the action of phagocytes is termed antiphagocytic (for example, Yersinia pestis, the bacterium causing the plague). Yersinia pestis (formerly Pasteurella pestis) is a Gram-negative rod-shaped Bacterium belonging to the family The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Bubonic plague is the best-known manifestation of the bacterial disease plague, caused by the bacterium Yersinia pestis (formerly known as Additionally, some bacteria may need to be opsonized before they are recognised as particles to be phagocytosed. An opsonin is any molecule that acts as a binding Enhancer for the process of Phagocytosis, for example by coating the negatively-charged molecules on the membrane

Certain intracellular pathogens, such the bacterial agents of leprosy and tuberculosis, are resistant to lysosomal degradation once internalised via phagocytosis. Leprosy (from the Greek lepi (λέπι meaning scales on a fish or Hansen's disease, is a chronic disease caused by the bacterium Tuberculosis (abbreviated as TB for tubercle bacillus or T u' b' erculosis Bacillus --> is a common Lysosomes are Organelles that contain Digestive enzymes (acid Hydrolases.

Media

• 3-D Reconstruction of phagocytosis

Phagocytosis .

See also

• Antigen presenting cell
• Antigen presentation
• Pinocytosis

References

External links

• MeSH Phagocytosis