Complement System


  • plays an essential role in host defence against infectious agents and in the inflammatory process.
  • consists of about twenty plasma proteins that function either as enzymes or as binding proteins.
    The compliment system is made up of three pathways.
  • It can be activated by either the classic or the alternative pathways and will ultimately end up on the common pathway.
Classic Pathway
  • activated by the binding of antibody molecules (specifically IgM and IgG1, 2 and 3) to a foreign particle. This pathway is antibody-dependent.
  • The classic pathway involves the activation of compliments C1, C2 and C3.
    C3a is an anaphylatoxin but C3b goes on to initiate the final common pathway.