Complement 1 Flashcards
What is complement?
The heat-labile anti-microbial component in blood
Does each antibody have its own complement protein?
No
Role of complement?
Enhances/complements the ability of antibodies and phagocytic cells
How many plasma proteins are involved in the complement system?
~20
Which system can the complement system work with?
The clotting system
What are the three pillars of the complement system?
Release of small bioactive fragments
Fragments of the complement proteins bind to activating agents
Destroy the invader organism by forming pores on the target cell
Which small, bioactive fragments does complement release?
Small protein fragments–> anaphylatoxins
Role of anaphylatoxins?
Cause inflammation when cleaved
Can recruit cells to go to the site of infection if they are cleaved near to a microbe
What is opsonization?
Fragments of complement proteins binding to the activating agents
What do fragments of complement proteins cause to be formed once bound to a microbial cell surface?
Membrane attack complex
What are the three complement pathways?
Alternative pathway, lectin pathway, classical pathway
Why is the alternative pathway not exactly a pathway?
It is more of an acceleration mechanism–> once complement is activated it makes sure it stays activated
Lectin pathway?
Complement binds to sugars on surfaces
Oldest pathway of the complement system?
Lectin pathway
Which complement pathway evolved last?
Classical pathway
What is the classical pathway?
C-reactive protein/antibody binds to specific antigen on the pathogen surface
What do all three complement pathways lead to?
Cleavage of C3
What is the central complement component?
C3
What is c3 cleaved into?
c3a and c3b
What is C3A?
An anaphylatoxin
What is C3B?
An opsonin that binds covalently onto the surface of the microb/dead cells and tags the for destruction by phagocytes
Which part of c3 is important for the recruitment of immune cells?
C3A
Which complement components are involved in the classical pathway?
C1, C2, C4
Which complement components are involved in the lectin pathway?
MBL, MASP, C2, C4
Which complement components are involved in the alternative pathway?
C3, B, D
What do the different components of the complement system all end up forming?
C3 convertase enzyme
What does C3 convertase enzyme do?
Converts C3 into C3A and C3B
Why do anaphylatoxin fragments have an a after them (e.g. C4a)?
They are acidic
Why do opsonin (surface binding) fragments have an a after them (e.g. C5b)?
They are basic
What is C4a, C3a, C5a involved in?
Phagocyte recruitment
What is the most active anaphylatoxin?
C5a
How can complement cause damage?
Virus e.g. covid sits in lungs and activates it continuously–> inflammation
Also occurs in stroke–> complement overactivated which does a lot of damage
