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Encyclopedia > Complement system
A complement protein attacking an invader.

The complement system is a biochemical cascade of the immune system that helps clear pathogens from an organism, and promote healing. It is derived from many small plasma proteins that work together to form the primary end result of cytolysis by disrupting the target cell's plasma membrane.[1] Image File history File links Download high resolution version (855x658, 193 KB) Summary A complement protein attacking an invader. ... Image File history File links Download high resolution version (855x658, 193 KB) Summary A complement protein attacking an invader. ... Perforin is a cytolytic protein found in the granules of CD8 T-cells and NK cells. ... A Biochemical Cascade is a series of chemical reactions in which the products of one reaction are consumed in the next reaction. ... A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ... A pathogen (literally birth of pain from the Greek παθογένεια) is a biological agent that can cause disease to its host. ... Cytolysis is the lysis, or death, of cells due to the rupture of the cell membrane. ...


The actions of the complement system affect both innate immunity and acquired immunity. Innate immunity is immunity that the body possesses naturally, as opposed to adaptive immunity. ... The immune system is the collection of organs and tissues involved in the adaptive defense of a body against foreign biological material. ...


Activation of this system leads to cytolysis, chemotaxis, opsonization, immune clearance, and inflammation, as well as the marking of pathogens for phagocytosis. The complement system consists of more than 35 soluble and cell-bound proteins, 12 of which are directly involved in the complement pathways. The proteins account for 5% of the serum globulin fraction. Most of these proteins circulate as zymogens, which are inactive until proteolytic cleavage. The complement proteins are synthesized mainly by hepatocytes; however, significant amounts are also produced by monocytes, macrophages, and epithelial cells in the gastrointestinal and genitourinary tracts. The central nervous system is also able to produce complement components. Cytolysis is the lysis, or death, of cells due to the rupture of the cell membrane. ... Chemotaxis is a kind of taxis, in which bodily cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. ... An opsonin is any molecule that acts as a binding enhancer for the process of phagocytosis. ... An abscess on the skin, showing the redness and swelling characteristic of inflammation. ... A pathogen or infectious agent is a biological agent that causes disease or illness to its host. ... Phagocytosis is a form of endocytosis wherein large particles are enveloped by the cell membrane of a (usually larger) cell and internalized to form a phagosome, or food vacuole. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Globulin is one of the two types of serum proteins, the other being albumin. ... A zymogen or a proenzyme, is an inactive enzyme precursor. ... Proteolysis is the directed degradation (digestion) of proteins by cellular enzymes called proteases or by intramolecular digestion. ... Look up cleavage in Wiktionary, the free dictionary. ... Hepatocytes make up 60-80% of the cytoplasmic mass of the liver. ... Monocyte A monocyte is a leukocyte, part of the human bodys immune system that protect against blood-borne pathogens and move quickly to sites of infection in the tissues. ... A macrophage of a mouse stretching its arms to engulf two particles, possibly pathogens Macrophages (Greek: big eaters, makros = long, phagein = eat) are white blood cells, more specifically phagocytes, acting in the nonspecific defense as well as the specific defense system of vertebrate animals. ... In zootomy, epithelium is a tissue composed of a layer of cells. ... For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and... This page is a candidate to be moved to Wiktionary. ...


Three biochemical pathways activate the complement system: the classical complement pathway, the alternative complement pathway, and the mannose-binding lectin pathway. Antibodies, in particular the IgG1 class, can also "fix" complement. In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell, catalyzed by enzymes, resulting in either the formation of a metabolic product to be used or stored by the cell, or the initiation of another metabolic pathway (then called a flux generating step). ... This article may be too technical for most readers to understand. ... The alternative pathway of the complement system is a humoral component of the immune systems natural defence against infections which can operate without antibody participation. ... The Mannan-binding lectin pathway is homologous to the classical complement pathway. ...

Contents

Overview

The C1 protein, showing subunits C1r, C1s, and the C1q tails.

The three pathways all generate homologous variants of the protease C3-convertase. The classical complement pathway typically requires antibodies for activation (specific immune response), while the alternate pathway can be activated by C3 hydrolysis or antigens without the presence of antibodies (non-specific immune response). Mannose-binding lectin pathway belongs to the non-specific immune response as well. C3-convertase cleaves and activates component C3, creating C3a and C3b and causing a cascade of further cleavage and activation events. C3b binds to the surface of pathogens leading to greater internalization by phagocytic cells by opsonization. C5a is an important chemotactic protein, helping recruit inflammatory cells. Both C3a and C5a have anaphylatoxin activity (mast cell degranulation, increased vascular permeability, smooth muscle contraction). C5b initiates the membrane attack pathway, which results in the membrane attack complex (MAC), consisting of C5b, C6, C7, C8, and polymeric C9.[2] MAC is the cytolytic endproduct of the complement cascade; it forms a transmembrane channel, which causes osmotic lysis of the target cell. Kupffer cells and other macrophage cell types help clear complement-coated pathogens. As part of the innate immune system, elements of the complement cascade can be found in species earlier than vertebrates; most recently in the protostome horseshoe crab species, putting the origins of the system back further than was previously thought. Image File history File links Size of this preview: 540 × 540 pixelsFull resolution (540 × 540 pixel, file size: 22 KB, MIME type: image/png) Other versions Originally from en. ... Image File history File links Size of this preview: 540 × 540 pixelsFull resolution (540 × 540 pixel, file size: 22 KB, MIME type: image/png) Other versions Originally from en. ... Proteases (proteinases, peptidases, or proteolytic enzymes) are enzymes that break peptide bonds between amino acids of proteins. ... C3-convertase is the name of the enzyme composed of the C4b-C2b complex, which forms during the Classical pathyway of the complement system. ... In immunology, soluble C3-convertase, also known as iC3Bb, catalyzes the proteolytic cleavage of C3 into C3a and C3b as part of the alternative complement system. ... A phagocyte is a cell that ingests and destroys foreign matter such as microorganisms or debris via a process known as phagocytosis, in which these cells ingest and kill offending cells by a process analogous to cellular digestion, usually using lysosomes which carry potent enzymes that digests cell components such... An opsonin is any molecule that acts as a binding enhancer for the process of phagocytosis. ... C5a is a protein fragment released from complement component C5. ... Chemokines are a family of pro-inflammatory activation-inducible cytokines, or small protein signals secreted by cells. ... Anaphylatoxin, or anaphylotoxin, is a fragment (C3a, C4a or C5a) of the complement system that triggers degranulation of (release of substances from) mast cells or basophils, which is an important part of the immune system in all kinds of inflammation and especially as part of defense against parasites. ... Mast cells A mast cell (or mastocyte) is a resident cell of areolar connective tissue (loose connective tissue) that contains many granules rich in histamine and heparin. ... The degranulation process in a Mast cell. ... Cultured Smooth muscle of the aorta. ... The membrane attack complex (MAC) is formed on the surface of intruding pathogenic bacterial cells as a result of the activation of the complement system, and it is one of the ultimate weapons of the immune system. ... The membrane attack complex (MAC) is formed on the surface of intruding pathogenic bacterial cells as a result of the activation of the complement system, and it is one of the ultimate weapons of the immune system. ... Complement component 6 is a protein involved in the complement system. ... Complement component 7 is a protein involved in the complement system. ... Complement component 8 is a protein involved in the complement system. ... Complement component 9 is a protein involved in the complement system. ... Osmosis is the net movement of a solvent across a semipermeable membrane from a region of high solvent potential to an area of low solvent potential. ... Kupffer cells are reticulendothelial cells located in the liver. ...


Classical pathway

The classical and alternative complement pathways.
The classical and alternative complement pathways.

The classical pathway is triggered by activation of the C1-complex (which consists of one molecule C1q and two molecules C1r and C1s), either by C1q's binding to antibodies from classes M and G, complexed with antigens, or by its binding C1q to the surface of the pathogen. This binding leads to conformational changes in C1q molecule, which leads to the activation of two C1r (serine protease) molecules. Then they cleave C1s (another serine protease). The C1-complex now binds to and splits C2 and C4, producing C2a and C4b. The inhibition of C1r and C1s is controlled by C1-inhibitor. C4b and C2a bind to form C3-convertase (C4b2a complex: NB the 2a is actually the larger fragment of the two, contrary to conventional nomenclature designating 'b' fragments as the larger). Production of C3-convertase signals the end of the Classical Pathway, but cleavage of C3 by this enzyme brings us to the start of the Alternative Pathway. This article may be too technical for most readers to understand. ... Image File history File links Size of this preview: 494 × 599 pixelsFull resolution (688 × 834 pixel, file size: 125 KB, MIME type: image/png) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Complement system Classical complement pathway Alternative... Image File history File links Size of this preview: 494 × 599 pixelsFull resolution (688 × 834 pixel, file size: 125 KB, MIME type: image/png) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Complement system Classical complement pathway Alternative... This article may be too technical for most readers to understand. ... Each antibody binds to a specific antigen; an interaction similar to a lock and key. ... An antigen is a substance that stimulates an immune response, especially the production of antibodies. ... The C1q complex is potentially multivalent for attachment to the complement fixation sites of immunoglobulin. ... Complement component 1S is a protein involved in the complement system. ... Complement component 2 is a protein involved in the complement system. ... Complement component 4 is a protein involved in the complement system. ... C1-inhibitor (C1inh) is a serine protease inhibitor (serpin) protein, the main function of which is inhibition of the complement system. ...


Alternative pathway

The alternative pathway is triggered by C3 hydrolysis directly on the surface of a pathogen. It does not rely on a pathogen-binding protein like the other pathways.[1] In the alternative pathway, the protein C3 is produced in the liver, and is then cleaved into C3a and C3b by enzymes in the blood. If there is no pathogen in the blood, the C3a and C3b protein fragments will be deactivated. However, if there is a nearby pathogen, some of the C3b is bound to the plasma membrane of the pathogen. Then, it will bind to factor B. This complex will then be cleaved by factor D into Ba and the alternative pathway C3-convertase, Bb. The alternative pathway of the complement system is a humoral component of the immune systems natural defence against infections which can operate without antibody participation. ... ... BF is a protein involved in the complement system. ... DF is a protein involved in the complement system. ...


The C3bBb complex, which is "hooked" onto the surface of the pathogen, will then act like a "chain saw", catalyzing the hydrolysis of C3 in the blood into C3a and C3b, which positively effects the number of C3bBb hooked onto a pathogen.


After hydrolysis of C3, C3b complexes to become C3bBbC3b, which cleaves C5 into C5a and C5b. C5a and C3a are known to trigger mast cell degranulation. C5b with C6, C7, C8, and C9 (C5b6789) complex to form the membrane attack complex, also known as MAC, which is inserted into the cell membrane, "punches a hole", and initiates cells lysis. Mast cells A mast cell (or mastocyte) is a resident cell of areolar connective tissue (loose connective tissue) that contains many granules rich in histamine and heparin. ... MAC is also called the killer molecule. ...


Lectin pathway (MBL - MASP)

Main article: Mannan-binding lectin pathway

The lectin pathway is homologous to the classical pathway, but with the opsonin, mannan-binding lectin (MBL) and ficolins, instead of C1q. This pathway is activated by binding mannan-binding lectin to mannose residues on the pathogen surface, which activates the MBL-associated serine proteases, MASP-1, MASP-2, MASP-3, which can then split C4 into C4a and C4b and C2 into C2a and C2b. C4b and C2a then bind together to form C3-convertase, as in the classical pathway. Ficolins are homologous to MBL and function via MASP in a similar way. In invertebrates without an adaptive immune system, ficolins are expanded and their binding specificities diversified to compensate for the lack of pathogen-specific recognition molecules. Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ...


Regulation of the Complement System

The complement system has the potential to be extremely damaging to host tissues meaning its activation must be tightly regulated. The complement system is regulated by complement control proteins, which are present at a higher concentration in the blood plasma than the complement proteins themselves. Some complement control proteins are present on the membranes of self-cells preventing them being targeted by complement. One example is CD59, which inhibits C9 polymerisation during the formation of the membrane attack complex. The complement system has the potential to cause damage to host tissue. ... CD59 is an inhibitor of the complement membrane attack complex. ... MAC is also called the killer molecule. ...


Role in disease

It is thought that the complement system might play a role in many diseases with an immune component, such as Barraquer-Simons Syndrome, asthma, lupus erythematosus, glomerulonephritis, various forms of arthritis, autoimmune heart disease, multiple sclerosis, inflammatory bowel disease, and ischemia-reperfusion injuries. The complement system is also becoming increasingly implicated in diseases of the central nervous system such as Alzheimer's disease, and other neurodegenerative conditions. Glomerulonephritis is a primary or secondary autoimmune renal disease featuring inflammation of the glomeruli. ... Arthritis (from Greek arthro-, joint + -itis, inflammation; plural: arthritides) is a group of conditions where there is damage caused to the joints of the body. ...


Deficiencies of the terminal pathway predispose to both autoimmune disease and infections (particularly meningitis). Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. ... An infection is the detrimental colonization of a host organism by a foreign species. ... Meningitis is the inflammation of the protective membranes covering the central nervous system, known collectively as the meninges. ...


Modulation by infections

Recent research has suggested that the complement system is manipulated during HIV/AIDS to further damage the body.[3][4] The human immunodeficiency virus (HIV) is a frequently mutating retrovirus that attacks the human immune system and which has been shown to cause acquired immune deficiency syndrome (AIDS). ... AIDS (Acquired Immunodeficiency Syndrome or Acquired Immune Deficiency Syndrome, sometimes written Aids) is a human disease characterized by progressive destruction of the bodys immune system. ...


Additional images

References

  1. ^ a b Janeway CA Jr., Travers P, Walport M, Shlomchik MJ (2001). Immunobiology., 5th ed., Garland Publishing. (via NCBI Bookshelf) ISBN 0-8153-3642-X. 
  2. ^ Goldman AS, Prabhakar BS (1996). The Complement System. in: Baron's Medical Microbiology (Baron S et al, eds.), 4th ed., Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1. 
  3. ^ Bolger MS, Ross DS, Jiang H, Frank MM, Ghio AJ, Schwartz DA, Wright JR, Complement Levels and Activity in the Normal and LPS-Injured Lung, American Journal of Physiology: Lung Cellular and Molecular Physiology. 2006 Oct 27; PMID 17071722
  4. ^ Datta PK, Rappaport J, HIV and Complement: Hijacking an immune defence, Biomedicine and Pharmacotherapy, 2006 Nov; 60(9):561-568 PMID 16978830

A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... This article may be too technical for most readers to understand. ... Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ... The alternative pathway of the complement system is a humoral component of the immune systems natural defence against infections which can operate without antibody participation. ... C3-convertase is the name of the enzyme composed of the C4b-C2b complex, which forms during the Classical pathyway of the complement system. ... The membrane attack complex (MAC) is formed on the surface of intruding pathogenic bacterial cells as a result of the activation of the complement system, and it is one of the ultimate weapons of the immune system. ... Complement component 6 is a protein involved in the complement system. ... Complement component 7 is a protein involved in the complement system. ... Complement component 8 is a protein involved in the complement system. ... Complement component 9 is a protein involved in the complement system. ... Mannose binding lectin (MBL), also named mannose- or mannan-binding protein MBP, is an important factor in the innate immunity. ... Properdin is a globulin protein found in the blood serum of humans. ... The C1q complex is potentially multivalent for attachment to the complement fixation sites of immunoglobulin. ... Complement component 1R is a protein involved in the complement system. ... Complement component 1S is a protein involved in the complement system. ... Complement component 4 is a protein involved in the complement system. ... Complement component 2 is a protein involved in the complement system. ... In immunology, soluble C3-convertase, also known as iC3Bb, catalyzes the proteolytic cleavage of C3 into C3a and C3b as part of the alternative complement system. ... Complement component 5 is a protein involved in the complement system. ... C5a is a protein fragment released from complement component C5. ... MASP1 is a protein involved in the complement system. ... MASP2 is a protein involved in the complement system. ... BF is a protein involved in the complement system. ... DF is a protein involved in the complement system. ... C1-inhibitor (C1inh) is a serine protease inhibitor (serpin) protein, the main function of which is inhibition of the complement system. ... Decay accelerating factor is a protein involved in the complement system. ... Complement Factor I (fI) is a protein of the Complement system, first isolated in 1966 in guinea pig serum[1] that regulates complement activation by cleaving cell-bound or fluid phase C3b and C4b. ... C4BP (Complement C4B-binding protein) can refer to: C4BPA (protein) C4BPB (protein) Category: ... Factor H is a member of the regulators of complement activation family and is a complement control protein. ... A Complement receptor is a receptor of the complement system, a part of the mediated innate immune system. ... Complement receptor 1 Also known as CR1, CD35, C3b/C4b receptor and immune adherence receptor. ... Complement component receptor 2 is a protein involved in the complement system. ... Macrophage-1 antigen (or integrin alphaMbeta2) is a complement receptor (CR3) consisting of CD11b and CD18. ... Integrin alphaXbeta2 (p150,95, CR4) is a complement receptor composed of CD11c and CD18. ... Integrin alpha M is a protein involved in the complement system. ... CDC11c is a type I transmembrane protein found at high levels on most human dendritic cells, but also on monocytes, macrophages, neutrophils, and some B cells that induces cellular activation and helps trigger neutrophil respiratory burst; expressed in hairy cell leukemias, acute nonlymphocytic leukemias, and some B-cell chronic lymphocytic... CD18 is the beta subunit of LFA-1. ... C3a receptor is a protein involved in the complement system. ... C5AR1 is a receptor for C5a. ... A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ... Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. ... The immune system is the collection of organs and tissues involved in the adaptive defense of a body against foreign biological material. ... The innate immune system comprises the cells and mechanisms that defend the host from infection by other organisms, in a non-specific manner. ... Humoral immunity is the aspect of immunity that is mediated by secreted antibodies, produced in the cells of the B lymphocyte lineage (B cell). ... Cell-mediated immunity is an immune response that does not involve antibodies but rather involves the activation of macrophages and NK-cells, the production of antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. ... This article does not cite its references or sources. ... An abscess on the skin, showing the redness and swelling characteristic of inflammation. ... This article may be too technical for most readers to understand. ... The alternative pathway of the complement system is a humoral component of the immune systems natural defence against infections which can operate without antibody participation. ... Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ... Anaphylatoxin, or anaphylotoxin, is a fragment (C3a, C4a or C5a) of the complement system that triggers degranulation of (release of substances from) mast cells or basophils, which is an important part of the immune system in all kinds of inflammation and especially as part of defense against parasites. ... Cytokines are a group of proteins and peptides that are used in organisms as signaling compounds. ... White blood cells or leukocytes are cells which form a component of the blood. ... Each antibody binds to a specific antigen; an interaction similar to a lock and key. ... An antigen is a substance that stimulates an immune response, especially the production of antibodies. ... An antigen-presenting cell (APC) is a cell that displays foreign antigen complexed with MHC on its surface. ... MHC I (1hsa) vs MHC II (1dlh) (more details. ... Immunity is medical term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. ... Autoimmunity is the failure of an organism to recognize its own constituent parts (down to the sub-molecular levels) as self, which results in an immune response against its own cells and tissues. ... Immune or immunological tolerance is the process by which the immune system does not attack an antigen. ... Central tolerance is a condition caused by tumor cells caused by tumor antigens inhibiting the immune system which has no reaction. ... In medicine, immune deficiency (or immunodeficiency) is a state where the immune system is incapable of defending the organism from infectious disease. ... A phagocyte is a cell that ingests and destroys foreign matter such as microorganisms or debris via a process known as phagocytosis, in which these cells ingest and kill offending cells by a process analogous to cellular digestion, usually using lysosomes which carry potent enzymes that digests cell components such... 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. ... The reticuloendothelial system (RES), part of the immune system, consists of the phagocytic cells located in reticular connective tissue, primarily monocytes and macrophages. ... The allotype affects the constant region (labeled CL and CH1-3 in the diagram. ... In immunology, the immunoglobulin isotype refers to the type of chain. ... The idiotype affects the variable region (labeled VL and VH in the diagram. ...


  Results from FactBites:
 
1.4.3 Products of the complement system (1634 words)
Complement is a complex system containing more than 30 various glycoproteins present in serum in the form of components, factors, or other regulators and/or on the surface of different cells in the form of receptors.
The main functions of the complement cascade and its role in the acute inflammatory reaction are summarized in Table 1.8.
This new lectin pathway of complement activation is important not only for the killing of microorganisms through the interaction of carbohydrates on their surfaces and MBP or other collectins (humoral lectins found in humans and other mammals) but also for the opsonizing activity.
Complement system - Wikipedia, the free encyclopedia (1038 words)
The complement proteins are synthesized mainly by hepatocytes; however, significant amounts are also produced by monocytes, macrophages, and epithelial cells in the gastrointestinal and genitourinary tracts.
Three biochemical pathways activate the complement system: the classical complement pathway, the alternate complement pathway, and the mannose-binding lectin pathway.
The classical pathway is triggered by activation of the C1-complex (which consists of one molecule C1q and two molecules C1r and C1s), either by C1q's binding to antibodies from classes M and G, complexed with antigens, or by its binding C1q to the surface of the pathogen.
  More results at FactBites »

 
 

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