Phagocytosis is the process of capture of particles inside a cell, whether bacteria, parasites, apoptotic cells, in short, all kinds of foreign particles. involves several molecular processes. It occurs when these elements bind to receptors on the phagocyte surface, changing their three-dimensional structure and inducing the inclusion of the particle inside the cell. In the case of neutrophils humans, phagocytosis of bacteria occurs on average nine minutes. Each cell possesses phagocytic cell compartment called the phagosome (which is stored the particle to remove) which is the fusion cell fate with a lysosome or granule to form a phagolysosome , in the case of human neutrophils, the merger happens in a minute. The organelle has generated a battery of enzymatic methods to produce almost all cases the death of phagocytosed element in minutes. The dendritic cells and macrophages are not as effective as neutrophils and may prolong the process until several hours . Macrophages are slow and often expel half-digested material to the surrounding environment, this issue draws (recruit) more phagocytes. phagocytosed elements are very diverse: Some scientific techniques involve the induction of phagocytosis of even filings iron (in this way and using a magnet can be separated from other active phagocytes and other cells).

Each phagocyte has several types of receptors on their surface that recognize and engulf the particles that trigger the process of phagocytosis. Among them are the opsonins , Scavenger receptors and Toll-like receptors (TLRs). Opsonins trigger phagocytosis of bacteria coated with IgG or with protein supplement (which are activated by a signaling cascade that contribute to the depletion of foreign elements in the blood ). The Scavenger receptors recognize a wide variety of bacterial surface molecules. Toll-like receptors induce the inflammatory response in addition to phagocytosis, its name derives from the Toll-like receptors of Drosophila melanogaster , with whom bear some homology .

Modes of action

The role of phagocytes to destroy microbes or damaged cells, the process can be intra or extracellularly.

Mechanism of oxygen-dependent intracellular

When a phagocyte acts on a foreign body, like bacteria, their oxygen consumption increases. The increase in oxygen consumption is called oxidative burst , producing reactive oxygen species with antimicrobial effects. The oxygen compounds are toxic to both the pathogen to the cell itself, so it is retained in intracellular compartments . This method of destroying invading microbes through the use of carrier molecules of reactive oxygen species called oxygen-dependent intracellular killing. This mechanism is classified into two types.

  • The first type is dependent production of oxygen radical superoxide , which is a bactericidal substance rich in oxygen. The superoxide is converted in the presence of hydrogen peroxide into singlet oxygen through a reaction catalyzed by the enzyme called superoxide dismutase . Superoxide radicals also react with hydroxyl radicals , which contribute to the destruction of the invading microbe.
  • The second type involves the use of the enzyme myeloperoxidase , present in granules of neutrophils. When the granules fuse with the phagosome , myeloperoxidase is released to the phagolysosome, and this enzyme uses hydrogen peroxide and chlorine to generate hypochlorite ( the bleach is sodium hypochlorite diluted household). The bleach is extremely toxic to bacteria. The myeloperoxidase contains a pigment heme , which causes secretions rich in neutrophils, like pus and sputum infected are green.

intracellular oxygen-independent mechanism

Pus-stained micrograph of a Gram stain showing gonococci within a phagocyte and the size difference.Phagocytes also can kill microbes by four independent methods of oxygen, but more inefficient. The first uses electrically charged proteins that damage the membrane of bacteria. The second method uses lysozyme , these enzymes destroy the cell wall of bacteria. The third uses lactoferrin present in the granules of neutrophils, which remove iron from the medium, metal that is essential for bacteria. The fourth type uses proteases and hydrolytic enzymes that digest proteins act destroyed bacteria.

Mechanism extracellular

The interferon gamma (formerly called macrophage activating factor) is a promoter of the production of nitric oxide by macrophages. The source of the substance may be CD4 + , CD8 + T cells , NK cells , B lymphocytes , TNK lymphocytes , monocytes, macrophages and dendritic cells. nitric oxide is released by the macrophage and, due to its toxicity , kills the microbes located near the macrophage. Activated macrophages produce and secrete tumor necrosis factor . This cytokine (a type of signaling molecule ) kills tumor cells and infected with viruses , and helps activate the other immune system cells.

In some diseases, such as the rare chronic granulomatous disease , efficiency of phagocytes is affected and recurrent bacterial infections become a problem. In this disease, there is an anomaly that affects different elements dependent killing oxygen. Other rare congenital defects, such as Chediak-Higashi syndrome are also associated with a defective destruction of phagocytosed microbes.

Mechanism virus

The virus can only reproduce inside cells, and access to them using many of the receptors involved in immunity. Once inside, using the biological machinery of the cell for its own purposes, forcing it to create hundreds of identical copies of themselves. Although phagocytes and other components of the innate immune system can control the virus at some point, once they have penetrated into a cell, the adaptive immune response, specifically lymphocytes, are more important in the defense. In areas of viral infection, lymphocytes are often much more numerous than other immune cells, so in the meningitis virus. phagocytes to eliminate virus-infected cells.


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