Complement Activation

Lectin Pathway

Mannose-binding lectin (MBL) binds to foreign surface
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MBL-associated proteases (MASP1 + 2) bind MBL
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Generate activated C1-like complex
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Activated C1-like complex cleave C4
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(2 arrows forming C2a) Forms C4a and C4b
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C1-like complex and C4b cleaves C2
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C4b-C2b form complex (C3 convertase) [this is where classical, alternative and lectin pathway meet]
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*Convertase activate C3
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(2 arrows forming C3a) C3b
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C3b and C4b2b forms C5 convertase
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(2 arrows forming C5a) C5b
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C5b bind C6 and C7
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Gather C8, forms small pores
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Forms pores with C9 [formation of the Membrane Attack Complex (MAC)]

*One C3 convertase can actually cleave many C3, this is thus the amplification step