Complement system

Definition

The complement system is a group of proteins found in the blood that play a crucial role in the immune response by enhancing the ability of antibodies and phagocytic cells to clear pathogens from an organism. It consists of over 30 different proteins that can be activated in a cascade, leading to inflammation, opsonization of pathogens, and the formation of the membrane attack complex that can directly lyse foreign cells.

5 Must Know Facts For Your Next Test

1. The complement system can be activated through three pathways: the classical pathway, the lectin pathway, and the alternative pathway, each initiated by different triggers.
2. Activation of the complement system leads to a series of enzymatic reactions, amplifying the immune response and contributing to inflammation.
3. One of the primary functions of the complement system is opsonization, which enhances phagocytosis by marking pathogens for destruction by immune cells.
4. Deficiencies or dysregulation in the complement system can lead to increased susceptibility to infections and autoimmune diseases.
5. The complement system works closely with both innate and adaptive immune responses, bridging these two branches of immunity.

Review Questions

• How does the complement system enhance the immune response against pathogens?
  • The complement system enhances the immune response through several mechanisms, including opsonization, inflammation, and direct cell lysis. By marking pathogens with proteins like C3b, it makes them more recognizable to phagocytic cells, promoting their clearance. Additionally, activation of the complement leads to inflammation, which recruits more immune cells to the site of infection, further bolstering the body's defense against invaders.
• Discuss the implications of complement deficiencies on human health and immunity.
  • Complement deficiencies can lead to serious health issues, as individuals may become more susceptible to recurrent infections due to impaired opsonization and clearance of pathogens. Such deficiencies are also linked with autoimmune diseases because dysfunctional regulation of complement proteins can result in inappropriate activation that targets the body’s own tissues. Thus, understanding these deficiencies is crucial for developing targeted therapies and management strategies for affected individuals.
• Evaluate how the interplay between the complement system and other immune mechanisms contributes to effective pathogen clearance.
  • The interplay between the complement system and other immune mechanisms is essential for effective pathogen clearance. The complement system not only enhances phagocytosis through opsonization but also works in concert with antibodies produced during adaptive immunity. This synergy allows for a robust response where antibodies mark pathogens while complements facilitate their destruction. Additionally, inflammation induced by complement activation attracts various immune cells to infected sites, providing a coordinated attack against pathogens. This multifaceted approach underscores the importance of both innate and adaptive immunity working together for optimal defense.

Related terms

C3b:

A key protein in the complement system that acts as an opsonin, binding to pathogens to enhance their recognition and uptake by phagocytes.

Membrane Attack Complex (MAC): A structure formed by the complement proteins that creates pores in the membranes of target cells, leading to cell lysis and death.

Inflammation: A biological response to harmful stimuli such as pathogens or damaged cells, characterized by redness, heat, swelling, and pain, often mediated by complement proteins.