complement
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Related to complement: compliment, Complement system
complement
[kom´plĕ-ment]a term originally used to refer to the heat-labile factor in serum that causes immune cytolysis (lysis of antibody-coated cells). It is now used to refer to the entire functionally related system comprising at least 20 distinct serum proteins, their cellular receptors, and related regulatory proteins; this system is the effector not only of immune cytolysis but also of other biologic functions including anaphylaxis, phagocytosis, opsonization, and hemolysis.
Complement activation occurs by two different sequences, the classical pathway and the alternative pathway. All of the “components of complement,” designated C1 through C9 (C1 being composed of three distinct proteins, C1q, C1r, and C1s), participate in the classical pathway; the alternative pathway lacks components C1, C2, and C4 but adds factor b, factor d, and properdin. Regulatory proteins include factor h, factor i, clusterin, C3 nephritic factor, decay accelerating factor, homologous restriction factor, C1 inhibitor, C4 binding protein, membrane cofactor protein, protectin, and vitronectin.
The classical pathway is primarily activated by the binding of C1 to antigen-antibody complexes containing the immunoglobulins IgM or IgG. The alternative pathway can be activated by IgA immune complexes and also by nonimmunologic materials including bacterial endotoxins, microbial polysaccharides, and cell walls. Activation of the classical pathway triggers an enzymatic cascade involving C1, C4, C2, and C3; activation of the alternative pathway triggers a cascade involving C3 and factors B and D and properdin. Both pathways result in cleavage of C5 and formation of the membrane attack complex, which in its final state creates a pore in the cell wall and causes cell lysis. Complement activation also results in the formation of many biologically active complement fragments that act as anaphylatoxins, opsonins, or chemotactic factors. Fragments resulting from proteolytic cleavage of complement proteins are designated with lower-case-letter suffixes, e.g., C3a.
Complement activation occurs by two different sequences, the classical pathway and the alternative pathway. All of the “components of complement,” designated C1 through C9 (C1 being composed of three distinct proteins, C1q, C1r, and C1s), participate in the classical pathway; the alternative pathway lacks components C1, C2, and C4 but adds factor b, factor d, and properdin. Regulatory proteins include factor h, factor i, clusterin, C3 nephritic factor, decay accelerating factor, homologous restriction factor, C1 inhibitor, C4 binding protein, membrane cofactor protein, protectin, and vitronectin.
The classical pathway is primarily activated by the binding of C1 to antigen-antibody complexes containing the immunoglobulins IgM or IgG. The alternative pathway can be activated by IgA immune complexes and also by nonimmunologic materials including bacterial endotoxins, microbial polysaccharides, and cell walls. Activation of the classical pathway triggers an enzymatic cascade involving C1, C4, C2, and C3; activation of the alternative pathway triggers a cascade involving C3 and factors B and D and properdin. Both pathways result in cleavage of C5 and formation of the membrane attack complex, which in its final state creates a pore in the cell wall and causes cell lysis. Complement activation also results in the formation of many biologically active complement fragments that act as anaphylatoxins, opsonins, or chemotactic factors. Fragments resulting from proteolytic cleavage of complement proteins are designated with lower-case-letter suffixes, e.g., C3a.
Complement activation. Activation of the classical and alternative pathways leads to a common terminal pathway from C5 to C9. These complement components form the final membrane attack complex (MAC). Other intermediate complexes and fragments are also biologically active: opsonins facilitate phagocytosis, anaphylatoxins act on mast cells and mediate a release of histamine which acts on blood vessels, and chemotactic fragments and intermediate complexes attract leukocytes to the site of inflammation. Redrawn from Damjanov, 2000.
complement fixation the combining of complement with the antigen-antibody complex, rendering the complement inactive, or fixed. Its presence or absence as free, active complement can be shown by adding sensitized blood cells to the mixture. If free complement is present, hemolysis occurs; if not, no hemolysis is observed. This reaction is the basis of many serologic tests for infection, including the wassermann test for syphilis, and reactions for gonococcus infection, glanders, typhoid fever, tuberculosis, and amebiasis. Called also Bordet-Gengou phenomenon. See also immunity.
complement fixation tests tests that use antigen-antibody reaction and result in hemolysis to determine the presence of various organisms in the blood; see also complement fixation.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
com·ple·ment
(kom'plĕ-ment), Avoid the misspelling compliment.Ehrlich's term for the thermolabile substance, normally present in serum, that is destructive to certain bacteria and other cells sensitized by a specific complement-fixing antibody. Complement is a group of at least 20 distinct serum proteins, the activity of which is affected by a series of interactions resulting in enzymatic cleavages; it can follow one or the other of at least two pathways. In the case of immune hemolysis (classical pathway), the complex comprises nine components (designated C1 through C9) that react in a definite sequence and the activation of which is usually effected by the antigen-antibody complex; only the first seven components are involved in chemotaxis, and only the first four are involved in immune adherence or phagocytosis or are fixed by conglutinins. An alternative pathway (see properdin system) may be activated by factors other than antigen-antibody complexes, such as repeating polysaccharides or bacterial cell wall components, and involves components other than C1, C4, and C2 in the activation of C3. The terminal complement components form a membrane attack complex that leads to cytolysis of the target cell.
See also: component of complement.
See also: component of complement.
[L. complementum, that which completes, fr. com-pleo, to fill up]
Farlex Partner Medical Dictionary © Farlex 2012
complement
(kŏm′plə-mənt)n.
Immunology A complex system of proteins found in normal blood plasma that combines with antibodies to destroy pathogenic bacteria and other foreign cells. Also called alexin.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
complement
Immunologyadjective Pertaining to the complement system.
noun
(1) Any protein of the complement system.
(2) Complement system—first used for a heat-labile factor in serum that caused immune cytolysis of antibody coated cells, the complement system now refers to the entire functionally-related system, comprising ± 25 distinct serum proteins that mediate the nonspecific inflammatory response to various antigens through a complex sequence of enzymatic cleavages. Complement is thus the effector not only of immune cytolysis but also of other biologic functions; it is activated by 2 routes, the classic and alternative pathways.
Medspeak
noun A set of something.
Complement reference ranges
Ÿ Total Complement—40–100 Units.
Ÿ C1:
– C1q—70 µg/mL;
– C1r—34 µg/mL;
– C1s—31 µg/mL.
Ÿ C2—25 µg/mL.
Ÿ C3—1600 µg/mL.
Ÿ C4—600 µg/mL.
Ÿ C5—85 µg/mL.
Ÿ C6—75 µg/mL.
Ÿ C7—55 µg/mL.
Ÿ C8—55 µg/mL.
Ÿ C9—60 µg/mL.
Ÿ Factor B—200 µg/mL.
Ÿ Factor D—1 µg/mL.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.
complement
Immunology adjective Pertaining to the complement system noun1. Any protein of the complement system.
2. Complement system The term was first used for a heat labile factor in serum that caused immune cytolysis of antibody coated cells; it now refers to the entire functionally related system comprising ± 25 distinct serum proteins, which mediate the nonspecific inflammatory response to various antigens through a complex sequence of enzymatic cleavages; complement is thus the effector not only of immune cytolysis but also of other biologic functions; it is activated by 2 routes, the classic and alternative pathways. See Alternative pathway, Classic pathway, Complement activation Medtalk noun A set of something. See Chromosome complement.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.
com·ple·ment
(kom'plĕ-mĕnt)The thermolabile substance, normally present in serum, which is destructive to certain bacteria and other cells sensitized by a specific complement-fixing antibody. Complement is a group of at least 20 distinct serum proteins, the activity of which is affected by a series of interactions resulting in enzymatic cleavages and which can follow one or the other of at least two pathways. In the case of immune hemolysis (classical pathway), the complex comprises nine components (designated C1-C9) that react in a definite sequence and the activation of which is usually effected by the antigen-antibody complex; only the first seven components are involved in chemotaxis, and only the first four are involved in immune adherence or phagocytosis or are fixed by conglutinins. An alternative pathway (see properdin system)may be activated by factors other than antigen-antibody complexes and involves components other than C1, C4, and C2 in the activation of C3.
See also: component of complement
See also: component of complement
[L. complementum, that which completes, fr. com-pleo, to fill up]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
complement
A collection of about 20 serum proteins involved in the immune system process by which the action of antibodies against the invading agent (the ANTIGEN) is completed. Complement combines with antigen-antibody complexes to bring about the breakdown of the antigen-bearing cell or molecule. Some of the serum proteins form enzyme-activated cascades to produce molecules involved in INFLAMMATION, PHAGOCYTOSIS and cell rupture.Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
complement
the protein components of blood serum that can bind to antigen/antibody groups already formed on the surface of cells, thus enhancing destruction of the foreign body by PHAGOCYTES.Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
Complement
One of several proteins in the blood that acts with other proteins to assist in killing bacteria.
Mentioned in: Meningococcemia
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
com·ple·ment
(kom'plĕ-mĕnt)Thermolabile substance, normally present in serum, which is destructive to bacteria and other cells sensitized by a specific complement-fixing antibody.
[L. complementum, that which completes, fr. com-pleo, to fill up]
Medical Dictionary for the Dental Professions © Farlex 2012