Complement Flashcards
What is a complement, what does it do and what does t involve?
A very complex system of about 50 different proteins found either in serum or as receptors on white cells
Mediates wide range of functions
Involves enzyme cascade
What are the 3 pathways that reusult in complement activation?
What can all 3 pathways result in?
- CLASSICAL PATHWAY
- LECTIN PATHWAY
- ALTERNATIVE PATHWAY
All 3 pathways result in an enzymatic activity capbable of cleaving C3.
When C3 is cleaved what does it produce?
what can each product cause?
C3 —- >C3b + C3a
C3b
Opaonisation
Immune complex solubilisation
C3a
ANAPHYLAXIS
CHEMOTAXIS
LYSIS
What can Deficiency in C3 cause?
Deficiency in C3 - Recurrent bacterial infections
What is the first component of the Classical Pathway?
What is it?
C1q -the first component of the Classical Pathway
- Hexavalent
- “Bunch of tulips” arrangement of 18 polypeptides
6 collagenous base and arm(stalk) regions
connected to 6 globular heads
What do globular heads of polypeptides do?
Globular heads - bind Fc of IgG or IgM
What immunoglobulins can activate the classic pathway?
Activated by IgG and IgM
What is the first componenet of the Lectin pathway?
What does it bind to?
MBL - Mannose binding lectin
similar structure to C1q
Binds sugars molecules found in repeating arrays on microbial surfaces
What is Alternative pathway activated by?
What does it produce?
What is it the first major line of defence against?
Directly activated by many types of micro-organism
Also produces a C3 convertase
Can function immediately i.e. before Antibody response
Hence first major line of defence against systemic
infection
What is Opsonisation?
What do phagocytes have receptors for?
Opsonisation is coating of micro-organisms by antibody or complement components.
Phagocytes have receptors for C3b
How does C3a perform anaphylaxis?
- C3a binds to receptors on mast cells
- histamine release
- vascular permeability
- recruitment of other components of
inflammatory response to infection site
How is C5a involved in Chemotaxis?
C5a binds to C5a receptors on phagocytes
A) Phagocyte migrates up concentration gradient of C5a to infection site
B) Phagocyte becomes stickier
Phagocytes stop moving and move through endothelium towards infection in underlying tissues
PHAGOCYTOSIS
What is the classic pathway controlled by?
(3)
- C1 inhibitor (can be deficient in C1 which will effect dental treatment)
- Decay accelerating factor (DAF)
- Complement receptor 1 (CR1)
What is the Alternative Pathway controlled by?
- Factor I
- Factor H
- CR1
