Complement sytem Flashcards
What are the distinct phases of the complement system which result in the elimination of microbes?
- pattern recognition trigger
- protease cascade amplification/C3 convertase
- end processes
What are the 3 complement pathways?
- classical pathway
- MB-lectin pathway
- alternative pathway
What is the trigger for the classical pathway?
antigen-antibody complexes
What are the components of the classical pathway?
What are the components of the classical pathway?
What is the trigger for the MB-lectin pathway?
Mannose-binding lectin binds mannose on pathogen surfaces
What are the components of the MB-lectin pathway?
MBL, MASP-1, MASP-2
C4
C2
What are the components of the alternative pathway?
Pathogen surfaces
Describe the classical pathway of the complement system
- C1q binds to IgG antibody on antigen surface = ‘complement fixing’
- Activates C1r which cleaves C1s
- Activated C1s binds to C4 & enzymatically liberates C4a & C4b - C4b binds to antigen surface
- This also causes cleavage of C2 into C2a & C2b
- C2a binds to C4b
- Forms C3 convertase on antigen surface
- This splits C3 into C3a & C3b
- C3b joins C4bC2a complex to form C5 convertase
What are some consequences of complement activation?
- Inflammation
- Removal of particulate antigens & immune complexes (enhances phagocytosis)
- Cytolysis - formation of Membrane Attack Complex (MAC)
What effects can C3a & C5a have on cells/in the body, in terms of causing inflammation?
Smooth muscle contraction
Mast cell degranulation
Vasodilation > local oedema, local influx of antibody & complement, cell extravasation
Neutrophil activation
How does activation of the complement system cause removal of particulate antigens & immune complexes?
- Phagocytosis by non-specific adherence (macrophage)
- Opsonisation (phagocytic cells express receptors for IgG & C3b)
- Removal of immune complexes (in spleen/liver)
What is the function of the Membrane Attack Complex (MAC)?
Allows influx of water into cells > leads to osmotic lysis
