Functions of the Complement System

• Opsonization: The complement proteins coat the surface of pathogens, making it easier for phagocytic cells to engulf and destroy them.
• Cell lysis: The complement system can create a membrane attack complex (MAC) that forms pores in the membranes of target cells, leading to their destruction.
• Chemotaxis: Complement proteins attract immune cells to the site of infection, aiding in the inflammatory response.
• Clearance of immune complexes: The complement system helps in the removal of immune complexes from the circulation.

Activation Pathways

1. Classical Pathway: This pathway is activated by the binding of antibodies to the surface of pathogens, which then triggers a series of complement protein activations.
2. Lectin Pathway: This pathway is activated when mannose-binding lectin (MBL) binds to specific carbohydrates on the surface of pathogens, leading to complement activation.
3. Alternative Pathway: This pathway is continuously active at a low level and can be triggered by the presence of certain molecules on the surface of pathogens.

Regulation of the Complement System

Study Guide

1. The structure and function of complement proteins.
2. The three activation pathways and their differences.
3. The role of the complement system in immune defense.
4. The regulation of the complement system to prevent self-damage.
5. Disorders associated with complement system dysregulation.