Complement

Definition

The complement system is a group of proteins in the blood that aids antibodies and phagocytic cells in clearing pathogens from an organism. It plays a crucial role in both innate and adaptive immunity.

5 Must Know Facts For Your Next Test

1. Complement activation can occur through three pathways: classical, lectin, and alternative.
2. The complement system enhances the ability of antibodies and phagocytes to clear microbes and damaged cells.
3. C3 convertase is a critical enzyme complex in the complement cascade, converting C3 into C3a and C3b.
4. Complement deficiencies can lead to increased susceptibility to infections and autoimmune diseases.
5. Regulatory proteins control the activity of the complement system to prevent damage to host tissues.

Review Questions

• What are the three pathways through which the complement system can be activated?
• How does the complement system assist in pathogen clearance?
• What roles do C3a and C3b play in the complement cascade?

Related terms

Opsonization:

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

Membrane Attack Complex (MAC): A structure formed on pathogen surfaces that leads to cell lysis.

Anaphylatoxins: Small peptides (e.g., C3a, C5a) that promote inflammation by acting on blood vessels.