Complement system

Definition

The complement system is a group of proteins that enhance the ability of antibodies and phagocytic cells to clear pathogens from an organism. It forms part of the innate immune response and also helps bridge innate and adaptive immunity.

5 Must Know Facts For Your Next Test

1. The complement system consists of over 30 proteins found in blood plasma.
2. It can be activated through three pathways: classical, lectin, and alternative.
3. Complement activation leads to opsonization, inflammation, and formation of the membrane attack complex (MAC) which lyses pathogens.
4. Regulatory proteins are crucial for preventing damage to host tissues by controlling complement activity.
5. Deficiencies in the complement system can lead to increased susceptibility to infections and autoimmune diseases.

Review Questions

• What are the three pathways that activate the complement system?
• How does opsonization contribute to pathogen clearance?
• What role do regulatory proteins play in the complement system?

Related terms

Opsonization: The process by which pathogens are marked for ingestion and destruction by phagocytes.

Membrane Attack Complex (MAC): A structure formed on the surface of pathogenic bacterial cells as a result of the activation of the host's complement system.

Phagocytosis: The process by which cells ingest and destroy foreign particles or microorganisms.