Complement system

Definition

The complement system is a group of proteins in the blood that enhance the ability of antibodies and phagocytic cells to clear pathogens. It plays a crucial role in the innate immune response by promoting inflammation and attacking the pathogen's cell membrane.

5 Must Know Facts For Your Next Test

1. The complement system consists of about 30 small proteins that are primarily produced by the liver.
2. Activation of the complement system can occur through three pathways: classical, lectin, and alternative.
3. The end result of complement activation is the formation of the Membrane Attack Complex (MAC), which creates pores in the pathogen's cell membrane leading to its lysis.
4. Complement proteins can also act as opsonins, marking pathogens for destruction by phagocytes.
5. Regulatory proteins in plasma and on cell surfaces prevent uncontrolled complement activation and protect host cells.

Review Questions

• What are the three pathways through which the complement system can be activated?
• How does the Membrane Attack Complex (MAC) contribute to pathogen destruction?
• What role do regulatory proteins play in the functioning of the complement system?

Related terms

Phagocytosis:

The process by which a cell engulfs particles such as bacteria or other microorganisms.

Opsonization:

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

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