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What is the complement system?
Major pathway acting to protect against infection and inflammation
What triggers a cascade?
Interaction with complement components with each other in an enzyme
What are zymogens?
- Protease (complement component)
- require activation by enzyme cleavage
Function of the complement system?
- Production of opsininProduction of anaphylatoxinsDirect Killing of pathogens
- Others: Maintenance to homeostasis, enhancing Ag-specific immune response
Function of opsinin?
enhance phagocytosis of particles by macrophage and neutrophils
How do opsinin work?
- Coat bacteria which are then recognised by specific receptors on phagocytes (macrophages, neutrophils)
- Trigger phagocytosis of bacteria
Products of the complement cascade?
What do opsinin stimulate?
phagocytosis of bacteria (MOST IMPORTANT COMPLEMENT FUNCTION)
What are anaphylatoxins?
Peptide/fragments from cleavage of complement protein
What do anaphlatoxins do?
Induce local and systemic inflammatory response
Anaphylatoxins bind to many cell types. Give an example and what occurs?
- Bind to neurophils
- Stimulate directional migration
- migrate from area of lesser conc to area of higher conc
- chemotatic for neutrophils --> more phagocytes recruited to site of complement activation
What are the 3 pathways of active complement?
- Classical pathway
- Mannose-binding Lectin (MB-Lectin) pathway
- Alternative pathway
How is the classical pathway initiated?
binding of C1q to pathogen surface
How is mannose-binding lectin pathway initiated?
binding of mannose-binding lectin to carbohydrates on bacteria/virues
How is the alternative pathway initiated?
Binding of spontaneously active C3 in plasma to pathogen surface