Complement 3 Flashcards
What happens to C3 in the alternative pathway?
It is cleaved spontaneously into C3a and C3b
What happens to C3b in the alternative pathway if there is no microbe?
It gets hydrolysed and remove to the liver
What happens to C3b in the alternative pathway if there is a microbe?
C3b binds to the microbial surface
What does C3b do once bound to the microbe in the alternative pathway?
It associates with factor B
What happens to factor B after it associates with C3b in the alternative pathway?
It is cleaved into Bb (which stays attached to C3b) by factor D
What can the C3b, Bb complex do in the alternative pathway?
Cleave many C3s
How is the alternative pathway an amplifying pathway?
Cleavage of C3 ends up leading t even more cleavage of C3
In the alternative pathway, what is C5 convertase made up of?
C3b, Bb and another C3b
What does C5 convertase do in the alternative pathway?
Cleave C5 into C5a and C5b
What stabilises the 3b, Bb complex?
Factor P
Other than on the surface of cells where can C3 convertase assemble?
The blood
What is the soluble c3 convertase made up of?
C3b and factor B
Lifespan of soluble c3 convertase?
v short
Why is complement not activated on self cells?
There are complement control proteins that stop it from being activated
Which type of bacteria is not sensitive to the membrane attack complex?
Gram +ves
What is similar about c4 and c4?
They both have an internal thioester bond
What happens once C5b is formed?
It joins with C6 and C7
Where is the C5b, C6 and C7 complex found?
On the membrane
What happens once the C5b, C6, C7 complex is formed?
C8 can join
What does C8 joining C5b, C6, C7 trigger?
The formation of a multimeric C9 MAC
What is the most potent anaphylatoxin?
C5a
How does the formation of the membrane attack complex/pore/C9 thing kill cells?
It allows extracellular fluids to enter
What can all complement control proteins (except DAF) do?
Recruit factor I enzyme which can cleave the complex
Examples of complement control proteins?
DAF, Factor I, Factor H, MCP, CR1, C4BP
What can decay accelerating factor (DAF) do?
Break down the C3b, Bb complex
What can factor I do?
Cleave C3b and C4b–> break down the c3 convertase enzyme
What is factor H?
A cofactor for Factor I
What are the cofactors of Factor I?
Factor H, CD46 (membrane cofactor protein), and CD35 (complement receptor 1)
What is a positive regulator of complement?
Factor P (properdin)
What does properdin do?
Stabilizes the alternative pathway c3 convertase on the bacterial surface
What does factor H do?
It can remove factor Bb from C3b
Factor H then binds to C3b instead
What happens once factor H is bound to C3b?
Factor I is recruited, and C3 is cleaved into non functional components
What does complement receptor 1 do?
Removes Bb from C3b, binds to C3b, recruits Factor I which then cleaves C3b
What does membrane cofactor protein do?
Act as a cofactor for factor I binding to C3b and Bb
