Complement system

complementcomplement cascadecomplement activationcomplement proteinscomplement proteincomplement pathwayimmunecomplement 5Acomplement activating enzymescomplement factor
The complement system is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane.wikipedia
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Immune system

immuneimmune responseimmune function
The complement system is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane.
These mechanisms include phagocytosis, antimicrobial peptides called defensins, and the complement system.

Classical complement pathway

classicalclassical pathwayclassical pathway of complement
Three biochemical pathways activate the complement system: the classical complement pathway, the alternative complement pathway, and the lectin pathway.
The classical complement pathway is one of three pathways which activate the complement system, which is part of the immune system.

Lectin pathway

lectinMannan-binding lectin pathwaylectin complement pathway
Three biochemical pathways activate the complement system: the classical complement pathway, the alternative complement pathway, and the lectin pathway.
The lectin pathway is a type of cascade reaction in the complement system, similar in structure to the classical complement pathway, in that, after activation, it proceeds through the action of C4 and C2 to produce activated complement proteins further down the cascade.

Liver

hepaticliver protein synthesislivers
The complement system consists of a number of small proteins that are synthesized by the liver, and circulate in the blood as inactive precursors.
Examples of highly liver-specific proteins include apolipoprotein A II, coagulation factors F2 and F9, complement factor related proteins, and the fibrinogen beta chain protein.

Phagocyte

phagocytesphagocytic cellsphagocytic
The end result of this complement activation or complement fixation cascade is stimulation of phagocytes to clear foreign and damaged material, inflammation to attract additional phagocytes, and activation of the cell-killing membrane attack complex.
Opsonin receptors increase the phagocytosis of bacteria that have been coated with immunoglobulin G (IgG) antibodies or with complement.

Inflammation

inflammatoryinflammatory responseinflamed
The end result of this complement activation or complement fixation cascade is stimulation of phagocytes to clear foreign and damaged material, inflammation to attract additional phagocytes, and activation of the cell-killing membrane attack complex.
These include the complement system activated by bacteria and the coagulation and fibrinolysis systems activated by necrosis, e.g. a burn or a trauma.

Antibody

antibodiesimmunoglobulinimmunoglobulins
The complement system is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane.
Thus, the Fc region ensures that each antibody generates an appropriate immune response for a given antigen, by binding to a specific class of Fc receptors, and other immune molecules, such as complement proteins.

Protease

proteasespeptidaseproteinase
When stimulated by one of several triggers, proteases in the system cleave specific proteins to release cytokines and initiate an amplifying cascade of further cleavages. The three pathways of activation all generate homologous variants of the protease C3-convertase.
These enzymes are involved in a multitude of physiological reactions from simple digestion of food proteins to highly regulated cascades (e.g., the blood-clotting cascade, the complement system, apoptosis pathways, and the invertebrate prophenoloxidase-activating cascade).

C3-convertase

C3 convertaseC3 convertasesclassical-complement-pathway C3/C5 convertase
The three pathways of activation all generate homologous variants of the protease C3-convertase.
C3 convertase (C4bC2b, formerly C4bC2a) belongs to family of serine proteases and is necessary in innate immunity as a part of the complement system which eventuate in opsonisation of particles, release of inflammatory peptides, C5 convertase formation and cell lysis.

Complement component 3

C3complement C3C3a
The classical complement pathway typically requires antigen-antibody complexes for activation (specific immune response), whereas the alternative pathway can be activated by spontaneous complement component 3 (C3) hydrolysis, foreign material, pathogens, or damaged cells.
It plays a central role in the complement system and contributes to innate immunity.

Adaptive immune system

adaptive immunityadaptive immune responseadaptive
The complement system can, however, be recruited and brought into action by antibodies generated by the adaptive immune system.
These antibodies bind to antigens, making them easier targets for phagocytes, and trigger the complement cascade.

Phagocytosis

phagocyticphagocytosedphagocytose
The complement system is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane.
Among these are receptors that recognise the Fc part of bound IgG antibodies, deposited complement or receptors, that recognise other opsonins of cell or plasma origin.

Anaphylatoxin

anaphylatoxinsanaphylotoxinanaphylotoxic
Both C3a and C5a have anaphylatoxin activity, directly triggering degranulation of mast cells as well as increasing vascular permeability and smooth muscle contraction.
Anaphylatoxins, or complement peptides, are fragments (C3a, C4a and C5a) that are produced as part of the activation of the complement system.

Jules Bordet

BordetJules Jean Baptiste Vincent BordetBordet, Jules Jean Baptiste Vincent
Jules Bordet, a young Belgian scientist in Paris at the Pasteur Institute, concluded that this principle has two components, one that maintained a "sensitizing" effect after being heated and one (alexin) whose toxic effect was lost after being heated.
In 1895 Bordet made his discovery that the bacteriolytic effect of acquired specific antibody is significantly enhanced in vivo by the presence of innate serum components which he termed alexine (but which are now known as complement).

Immune complex

immune complexesantigen-antibody complexantigen-antibody complexes
The classical complement pathway typically requires antigen-antibody complexes for activation (specific immune response), whereas the alternative pathway can be activated by spontaneous complement component 3 (C3) hydrolysis, foreign material, pathogens, or damaged cells.
After an antigen-antibody reaction, the immune complexes can be subject to any of a number of responses, including complement deposition, opsonization, phagocytosis, or processing by proteases.

Complement component 1q

C1qC1Q complexC1
This also occurs when C1q binds directly to the surface of the pathogen.
The complement component 1q (or simply C1q) is a protein complex involved in the complement system, which is part of the innate immune system.

Hans Ernst August Buchner

Hans BuchnerBuchner, Hans Ernst Angass
In 1891, Hans Ernst August Buchner, noting the same property of blood in his experiments, named the killing property "alexin", which means "to ward off" in Greek.
He called the substance "alexin", which was later named "complement" by Paul Ehrlich (1854–1915).

Complement component 4

C4C4bC4a
The C1r 2 s 2 component now splits C4 and then C2, producing C4a, C4b, C2a, and C2b (historically, the larger fragment of C2 was called C2a but is now referred to as C2b).
Complement component 4 (C4), in humans, is a protein involved in the intricate complement system, originating from the human leukocyte antigen (HLA) system.

Alternative complement pathway

alternative pathwayalternativealternate complement pathway
Three biochemical pathways activate the complement system: the classical complement pathway, the alternative complement pathway, and the lectin pathway.
The alternative pathway of the complement system is an innate component of the immune system's natural defense against infections.

Mast cell

mast cellsanaphylactic degranulationMast cell disease
Both C3a and C5a have anaphylatoxin activity, directly triggering degranulation of mast cells as well as increasing vascular permeability and smooth muscle contraction.
Complement proteins can activate membrane receptors on mast cells to exert various functions as well.

C8 complex

C88A8B
C5b initiates the membrane attack pathway, which results in the membrane attack complex (MAC), consisting of C5b, C6, C7, C8, and polymeric C9.
Complement component 8 is a protein involved in the complement system.

Complement component 7

C7C7 deficiencycomplement c7
C5b initiates the membrane attack pathway, which results in the membrane attack complex (MAC), consisting of C5b, C6, C7, C8, and polymeric C9.
Complement component 7 is a protein involved in the complement system of the innate immune system.

Properdin

Factor PProperdin deficiency
The C3bBb complex is stabilized by binding oligomers of factor P (properdin).
Properdin is the only known positive regulator of complement activation that stabilizes the alternative pathway convertases.

Complement factor I

Factor ICFIFactor I deficiency
C3b that is generated from C3 by a C3 convertase enzyme complex in the fluid phase is rapidly inactivated by factor H and factor I, as is the C3b-like C3 that is the product of spontaneous cleavage of the internal thioester.
Complement factor I (factor I) is a protein of the complement system, first isolated in 1966 in guinea pig serum, that regulates complement activation by cleaving cell-bound or fluid phase C3b and C4b.

Complement component 9

C9C9 deficiencycomplement c9
C5b initiates the membrane attack pathway, which results in the membrane attack complex (MAC), consisting of C5b, C6, C7, C8, and polymeric C9.
Complement component 9 (C9) is a MACPF protein involved in the complement system, which is part of the innate immune system.