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complement deficiencyA state in which any of the complement proteins is subnormal
Complement deficiencies–associated disorders
C1r SLE, renal disease, repeated infections
C2 SLE, vasculitis, membranoproliferative glomerulonephritis, dermatomyositis
C3 Repeated infections
C5 SLE, gonococcal disease
C6 Relapsing meningococcal meningitis, gonococcal infection
C7 Raynaud's disease, chronic renal disease, gonococcal infection
C8 SLE, gonococcal infection
a complex series of enzymatic proteins occurring in normal serum that are triggered in a cascade manner by, and combine with, the antibody-antigen complexes, producing lysis when the antigen is an intact cell. Complement comprises 25 to 30 discrete proteins, labeled numerically as C1 to C9, and by letters, i.e. B, D, P, etc., and with C1 being divided into subcomponents C1q, C1r and C1s. Components C3 and C5 are involved in the generation of anaphylatoxin and in the promotion of leukocyte chemotaxis, the result of these two activities being the inflammatory response. C1 and C4 are involved in the neutralization of viruses. The components also combine in various sequences to participate in other biological activities, including antibody-mediated immune lysis, phagocytosis, opsonization and anaphylaxis. The complement system is known to be activated by the immunoglobulins IgM and IgG.
alternate complement pathway, alternative complement pathway
the sequence in which complement components C3 and C5 to C9 are activated without participation by C1, C2 and C4 or the presence of an antibody-antigen complex.
the sequence of reactions, each being the catalyst for the next, that leads to the terminal complement pathway and cell lysis. There are two pathways for activation of C3, the 'classical' (below) and the 'alternate' (above).
classical complement pathway
the one in which all of the complement components C1 to C9 participate and is triggered by antibody-antigen complexes.
various complement components may be deficient without serious effects on the host. C3 deficiency is most severe and occurs in humans, Brittany spaniels and Finnish-Landrace lambs. Increased susceptibility to infections results.
complement fixation tests
utilize antibody-antigen reaction and result in hemolysis to determine the presence of various organisms in the blood. Involves two stages. In the first, also referred to as the test system, antigen is mixed usually with serial dilutions of a test serum in the presence of complement. If the serum contains antibody, i.e. is positive, an antibody-antigen complex is formed which also binds (fixes) complement. In the second stage, also called the indicator system, sheep red blood cells coated with specific, usually rabbit anti-sheep red blood cell antibody are added. The red blood cells are said to be sensitized. If antibody was not present in stage 1, then the free complement lyses the sensitized sheep red blood cells. The basis of many serological tests including those for glanders, tuberculosis and contagious bovine pleuropneumonia. Called also Bordet-Gengou phenomenon. See also immunity.
complement regulatory proteins
a set of at least seven proteins that are present in plasma (C1 INH, C4b-binding protein, factor H and factor I) or present in cell membranes (decay-accelerating factor [DAF], membrane cofactor protein [MCP] and homologous restriction factor [HHF]) that modulate the complement proteins and protect 'innocent' bystander cells and tissues from complement damage.
terminal complement pathway
the final stages of complement activation in which C5, C6, C7, C8 and C9 are activated; common to both the alternate and classical pathways.