complement fixation

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Related to complement fixation: Complement system


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. 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.


1. the act or operation of holding, suturing, or fastening in a fixed position.
2. the condition of being held in a fixed position.
3. in psychiatry, a term with two related but distinct meanings: (a) arrest of development at a particular stage (if this is temporary it is a normal reaction to difficulties, but if continued it is a cause of emotional problems); and (b) a close and suffocating attachment to some person, especially a childhood figure such as a parent.
4. in microscopy, the treatment of material so that its structure can be examined in greater detail with minimal alteration of the normal state, and also to provide information concerning the chemical properties (as of cell constituents) by interpretation of fixation reactions.
5. in chemistry, the process whereby a substance is removed from the gaseous or solution phase and localized, as in carbon dioxide or nitrogen fixation.
6. in ophthalmology, direction of the gaze so that the visual image of the object falls on the fovea centralis.
7. in film processing, the chemical removal of all unexposed and undeveloped silver compounds of the film emulsion, as on x-ray films.
complement fixation see complement fixation.
intermaxillary fixation (IMF) a technique used to stabilize a fractured jaw; the teeth are wired or banded together. Extreme caution must be exercised to insure that oral secretions and vomitus are not aspirated as the patient is unable to expectorate any fluids. Antiemetics are often administered to prevent vomiting. Wire cutters should be kept with the patient at all times.
Teeth wired in intermaxillary fixation. From Ignatavicius et al., 1995.

com·ple·ment fix·a·tion

1. antigen-antibody interactions cause a conformational shift in immunoglobulin structure promoting binding of C1 and subsequent activation of the complement cascade, that is, complement fixation.
See also: Bordet-Gengou phenomenon, Wassermann test.
2. an immunoassay using reference antibodies with complement fixation and lysis of red blood cells as an indicator of detectable antigen. The degree of hemolysis affects the optic density of the sample, which can be measured and compared with a standard reference concentration curve.
See also: Bordet-Gengou phenomenon, Wassermann test.

complement fixation

The binding of active serum complement to an antigen-antibody pair. It is the basis for various diagnostic tests to detect the presence of a specific antigen or antibody.

com·ple·ment fix·a·tion

(kom'plĕ-mĕnt fik-sā'shŭn)
A process in serum whereby an antigen-antibody combination is rendered unavailable to complete a reaction in a second antigen-antibody combination for which complement is necessary; the second system usually serves as an indicator (red blood cells plus specific hemolysin); if complement is fixed with the first antigen-antibody union, hemolysis does not occur, but, if complement is not so removed, it causes hemolysis in the second system.

complement fixation

The taking up of COMPLEMENT by antigen-antibody complexes. This process forms the basis of a number of tests to confirm infection with particular organisms.


Jules, Belgian bacteriologist and Nobel laureate, 1870-1961.
Bordet amboceptor
Bordetella - a genus of strictly aerobic bacteria that are pathogens of the mammalian respiratory tract.
Bordet-Gengou bacillus - a species that causes whooping cough. Synonym(s): Bordetella pertussis
Bordet-Gengou phenomenon - the phenomenon of complement fixation.
Bordet-Gengou potato blood agar - glycerin-potato agar with 25% of blood, used for the isolation of Bordetella pertussis.
Bordet-Gengou reaction - Synonym(s): complement fixation


Octave, French bacteriologist, 1875-1957.
Bordet-Gengou bacillus - see under Bordet
Bordet-Gengou phenomenon - see under Bordet
Bordet-Gengou potato blood agar - see under Bordet
Bordet-Gengou reaction - Synonym(s): complement fixation
Gengou phenomenon - noncellular antigens.

com·ple·ment fix·a·tion

(kom'plĕ-mĕnt fik-sā'shŭn)
A process in serum whereby an antigen-antibody combination is rendered unavailable to complete a reaction in a second antigen-antibody combination for which complement is necessary.
References in periodicals archive ?
These findings confirmed that RT-PCR is more reliable in detecting BEFV than complement fixation test.
(5) Main test advantages are low cost and better specificity, as compared to the complement fixation test, despite of false-positives observed with M.
Outcome 1 Alive at 5 months 2 Alive at 7 months 3 Alive at 10 years 4 Died before surgery 5 Recovered, died 8 years later of unrelated causes Abbreviations: Afib, atrial fibrillation; BID, twice daily; CAD, coronary artery disease; CF, complement fixation; CHF, congestive heart failure; CRI, chronic renal insufficiency; HLP, hyperlipidemia; HTN, hypertension; LAD, left anterior descending artery; LIMA, left internal mammary artery; QD, every day; RCA, right coronary artery; TIA, transient ischemic attack.
Evidence supporting complement fixation as the basis of ENL reactions is essentially indirect, derived from patients' sera and biopsied tissues.
He is still receiving therapy and serial complement fixation titers have decreased.
Antibody titer of the sample, for both Pasteurella multocida and FMD virus, was determined by Complement Fixation Test (CFT).
Evaluation of the complement fixation and indirect immunofluorescence tests in the early diagnosis of primary Q fever.
Other diagnostic techniques which can be used for the diagnosis of theileriosis are Complement Fixation Test (CFT), Reverse Line Blotting (RLB) system, Hybridization techniques, Serological test, IFAT (Immunoflourescent Antibody Technique), Latex Agglutination Test, Enzyme Linked Immunosorbent Assay (ELISA) and Loop Mediated Isothermal Amplification (LAMP).
Complement fixation for Coccidioides was attempted but was non-diagnostic due to anti-complement activity.
Search for the infectious agent Brucellosis Non-reagent Enzyme immunoassay Leptospirosis Non-reagent Enzyme immunoassay Toxoplasmosis Non-reagent Enzyme immunoassay HTLV-1, HTLV-2 Non-reagent Enzyme immunoassay Viral hepatitis Non-reagent Enzyme immunoassay types A, B, C Mononucleosis-two Non-reagent Monotest Hoff-Bauer samples Leishmaniasis Non-reagent Complement fixation reaction Paracoccidioidomycosis Non-reagent Complement fixation reaction Chagas disease Non-reagent Immunofluorescence Cytomegalovirus Non-reagent Chemiluminescence HIV 1 e 2-two samples Non-reagent Microparticle enzyme x with a 3-month-interval reaction PPD Non-reactive Table 3.
capsulatum, Blastomycosis dermatitidis, and Paracoccidioides brasiliensis by using complement fixation and immunodiffusion.

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