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→Complement Fixation Pathways
Complement is so called because it complements the function of antibody. It is a [[Triggered Enzyme Cascade - WikiBlood|triggered enzyme cascade]] and there are more than 20 different proteins in the complement cascades, with most being enzymes or pro-enzymes. It can be activated by both the innate and adaptive immune systems and is one of the main innate protective mechanisms of invertebrates. Due to its destructive potential the complement system is heavily regulated but when activated it works largely by forming pore complexes as well as triggering acute inflammation and by promoting [[Phagocytosis|phagocytosis]] by [[Macrophages|macrophages]] and [[Neutrophils|neutrophils]].
Complement is so called because it complements the function of antibody. It is a [[Triggered Enzyme Cascade - WikiBlood|triggered enzyme cascade]] and there are more than 20 different proteins in the complement cascades, with most being enzymes or pro-enzymes. It can be activated by both the innate and adaptive immune systems and is one of the main innate protective mechanisms of invertebrates. Due to its destructive potential the complement system is heavily regulated but when activated it works largely by forming pore complexes as well as triggering acute inflammation and by promoting [[Phagocytosis|phagocytosis]] by [[Macrophages|macrophages]] and [[Neutrophils|neutrophils]].
==Complement Fixation Pathways==
==Complement Fixation Pathways==
[[Image:LH Complement pathway.png|thumb|right|250px|'''Classical and alternative pathways''']]
[[Image:LH Complement pathway.png|thumb|left|250px|'''Classical and alternative pathways''']]
===Classical Pathway===
===Classical Pathway===
[[Image:Complement Classical Pathway.png|thumb|left|250px|'''Classical pathway in detail''']]
[[Image:Complement Classical Pathway.png|thumb|right|250px|'''Classical pathway in detail''']]
<p>This pathway of the complement system is triggered by the binding of antibody to antigen. The only subclasses that can activate complement this way are the
<p>This pathway of the complement system is triggered by the binding of antibody to antigen. The only subclasses that can activate complement this way are the
[[IgM]] and certain [[IgG]]. The first step of complement activation is the binding of C1 to two Fc regions of the antibodies (IgM is such a strong activator of complement as it contains '''five''' Fc regions, while IgG contains '''one'''). C1 is actually a complex of C1q, C1r and C1s. C1q looks like a bunch of 6 tulips with each "flower" consisting of a globular protein head and a collagen "stem". C1q is required to trigger the cascade because two of it is the globular heads binds the two Fc regions. C1r and C1s then become activated when the C1q heads are antibody-bound. When they are activated they form the enzyme '''C1 esterase''' (serine protease).
[[IgM]] and certain [[IgG]]. The first step of complement activation is the binding of C1 to two Fc regions of the antibodies (IgM is such a strong activator of complement as it contains '''five''' Fc regions, while IgG contains '''one'''). C1 is actually a complex of C1q, C1r and C1s. C1q looks like a bunch of 6 tulips with each "flower" consisting of a globular protein head and a collagen "stem". C1q is required to trigger the cascade because two of it is the globular heads binds the two Fc regions. C1r and C1s then become activated when the C1q heads are antibody-bound. When they are activated they form the enzyme '''C1 esterase''' (serine protease).
At the same time as C3b¯Bb¯3b is being formed, Factors I and H are acting to breakdown C3b to iC3b which, as mentioned above, forms an opsonin for [[Phagocytosis|phagocytosis]].
At the same time as C3b¯Bb¯3b is being formed, Factors I and H are acting to breakdown C3b to iC3b which, as mentioned above, forms an opsonin for [[Phagocytosis|phagocytosis]].
[[Image:Complement Mannose Binding Lectin Pathway.png|thumb|left|250px|'''Mannose Binding Lectin pathway in detail''']]
[[Image:Complement Mannose Binding Lectin Pathway.png|thumb|right|250px|'''Mannose Binding Lectin pathway in detail''']]
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