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Complement Cascade

The Complement system

  • Important mechanism to control infection
  • Promotes phagocytosis
  • Involved in bactericidal mechanisms
  • Promotes lymphocyte function
  • Mediates inflammation through mast cell degranulation and chemotaxis

 

Classical pathway
 Alternate pathway

 

  • IgG or 2 IgM fix to cell membrane
  • C1q binds to long chains and then to C1r and C1s
  • Whole activates C4 and C2. C2,4 cleaves C3 into components
  • C3a is chemotactic and anaphylactic. C3b is an opsonin and also acts with C2,4 to cleave C5
  • C5a is chemotactic and anaphylactic. C5b binds with C6, C, C8 and C9 to form membrane attack complex

 
  • C3 activated directly by endotoxins, viruses, bacteria, fungi
  • Does not need immunoglobulin activation

 

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