• A system of more than 30 serum and cell surface proteins that is involved in numerous function in inflammation and immunity
• Primary humoral defense system against bacterial and viral infections
• heat labile (can be destroyed by heating serum)
• most of the complement proteins are produced by the liver hepatocytes
• C3 is the most abundant serum complement protein
• Genes are scattered
• some of the
• components can increase in concentration two to three fold

Complement Functions

1.     Cytolysis of foreign organisms

2.     Opsonization and phagocytosis of foreign organisms

3.     Activation of inflammation and directed migration of leukocytes

4.     solubilization and clearance of immune complexes

5.     Enhancement of humoral response

The Complement Cascades

• activation involves the sequential activation of complement proteins, by either protein-protein interactions or by proteolytic cleavage.
• Amplification occurs at each step
• Zymogens- many complement proteins are activated by either conformational changes or proteolytic cleavage by other complement proteins
• Activation of these zymogens results in specific serine protease activities that are capable of cleaving other complement proteins, producing the cascade.

Activation

• initiated by the presence of Ag-Ab complexes (Classical Pathway), foreign cell surfaces (Alternative Pathway), or by Mannose on pathogenic organisms (Lectin (Phosphatidylcholine)Pathway)

Classical Pathway Activation

• activated primarily by IgG and IgM immune complexes
• IgM>IgG₃>IgG₁>IgG₂
• IgG₄, IgA, IgD, IgE do not activate

Tags: cell surface proteins, Complement, complement proteins, Cytolysis, humoral response, IgM immune complexes, inflammation, leukocytes, serine protease activities, serum, solubilization, zymogens

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