Complement system Flashcards
What is the overall goal of the complement system?
composed of proteins that work together to destroy invaders and to signal other immune system players that the ATTACK IS ON.
in science terms: opsonize microbes, recruit phagocytes, and kill the microbes directly if they’re feeling crazy
What are the three pathways that make up the complement system?
- alternative pathway
- classical pathway
- lectin pathway
What is the most common complement protein, and what does it divide into?
C3 divides into C3a and C3b: This is typically the first step in the process and triggers inflammation and opsonize microbes
What is the second step in the complement system
C5 converts complex that produce C5a and C5b which perpetuate inflammation
Describe the complement activation
It is a cascade reaction where an inactive zymogen is activated into a protease which cleaves the next protein complement in the cascade, amplifying the cascade
What are the other proteolytic cascades that the complement works in cooperation with?
- blood coagulation pathways
2. kininkallikrein system (vasc permeability)
What does C3a do?
stimulates inflammation by attaching neutrophils
What does C3b do? And what happens if it is not activated within 60 seconds of its formation?
C3b attaches to the microbial surface to promote phagocytosis if it does not bind to a microbe, then it is neutrolized by the binding of water
What does C3 converts do?
It binds to the C3b fragment and forms a C5 converts which goes on to produce C5a and C5b
What does C5a do?
It changes in the permeability of the blood vessels; which Remember that is how the little neutrophils (chiuahah wtf spelling?) get out of the vessels
What does C5b do?
Is attached to a material membrane which initiates the formation of C6, C7, C8, and C9 which makes the membrane attack complex which cause bacterial leak and lysis DIE DIE DIE
Describe the steps of the alternative complement pathway IN DETAIL
- C3b that is in the microbial membrane binds to Protein B.
- Protein D comes in and snips Protein B in the Bb and Ba. Bb stays attached to form C3Bb
- The C3Bb binds another C3 protein and properdin comes in and stabilizes the protein protein interactions
- After this happens there are a bunch on C3b’s present on the surface
THENNN - C3Bb can bind to another C3b which causes the activation of the C5 convertase, which activates the MAC (C6/C7/C8)
- C9 is able to drill a hole in the bacterium membrane
Describe the steps of the classical complement pathway in detail
- IgM or IgG binds to the pathogen
- C1q is able to come in and bind to the Fc region on the IgM (several can bind)
- serine proteases C1r and C1s are activated
- C1r activates C1s and they can go and activate C2-C$
- C4bC2a is the C3 convertase
- C4bC2aC3b is the C% convertase
The system goes the same way and forms the Mac at the end
Describe the steps of the lectin pathway in detail
- in the blood, the MBL (made in the liver) binds to MASP 2
- MASP2 cleaves C4 to C4a and C4b and C2 to C2a and C2b
- C4b binds to pathogen and C2a binds to that and forms the C3 convertase
- C3 is broken down into C3a and C3b
- C4bC2aC3b acts as the C5 convertase, which activates MAC
What is the function of the DAF protein in the complement pathway?
Blocks the C2:C4b interaction, that does not allow for the C3 convertase to form
