7 - Complement Flashcards
What are complements and what is their function?
proteases that can form complexes | usually inactivated in the circulation
How are complement proteins activated?
when they are cleaved
Which immune system (innate or adaptive) are complements mainly part of?
innate
What are the 3 functions of complement?
lysis | opsonization | inflammation
What is opsonization? What is the purpose?
deposit itself on surface membrane = target it for phagocytosis | purpose = for phagocytic cells to recognize the opsonin
What 2 antibodies are the only ones that recognize complements?
IgM and IgG
What does the classical pathway recognize?
Ag/Ab complexes
What does the lectin pathway recognize?
polysaccharides on microbial or antigen surfaces
What does the alternative pathway recognize?
C3b (includes those from spontaneously cleaved C3)
What is the initiator of the classical pathway and what does it do?
C1 = cleaves C4 and C2 making it into C3 convertase
What is the initiator of the lectin pathway and does it do?
MASP = cleaves C4 and C2 making it into C3 convertase
What is the initiator of the alternative tickover pathway?
fluid-phase C3 convertase
What is complement deposition?
when complement protein deposits itself on membrane surface
What are the 2 functions of C3b?
opsonization | gets rid of Ag/Ab complexes = prevents it from accumulating
What is the autoimmune disease that Ag/Ab complexes have a role in when they accumulate and clot in the capillaries and joints?
systematic lupus erythematosus (SLE)
What are the 2 anaphylatoxins that causes inflammation?
C3a and C5a
In the classical and lectin pathways, what is C3 convertase made from? (nomenclature name)
C4bC2a
In the classical and lectin pathways, what is C5 convertase made from? (nomenclature name)
C4bC2aC3b
How stable are complement proteins and what does this indicate?
not stable = doesn’t last long = will degrade if not active
How does lysis occur due to complement proteins?
forms MAC complex = forms pore/hole on membrane = lysis
What are the complement proteins that form the MAC complex?
C5b, C6-9 (6, 7, 8, 9)
What is C3 convertase made from/formed in the Tickover alternative pathway?
C3bBb (Bb is from Factor B which was cleaved by Factor D)
What is properdin?
factor that stabilizes C3 convertase in the alternative pathway
What is C5 convertase made from/formed in the Tickover alternative pathway?
C3bBbC3b
What is MBL in the lectin pathway?
mannose-binding lectin = part of MASP complex
What is the role of thrombin in alternative pathway?
can activate the pathway | can cleave both C3 and C5 | activates blood clotting = activates complement
What are the 3 complement receptors?
CR1, CR2, C3aR/C5aR
What cells express CR1 receptors?
RBCs, phagocytes, B-cells
What does CR1 bind to?
C3b
What happens when CR1 binds to RBCs?
bring immune complexes to the liver for clearance via phagocytosis
What happens when CR1 binds to phagocytes?
helps bind to complement coated bacteria = ingestion and destruction
What happens when CR1 binds to B-cells?
induces processing of antigen and present it to T-cells
Which cells express CR2?
only B-cells
What does CR2 recognize/bind to?
C3b
What happens when CR2 binds to B-cells?
helps with B-cell intracellular signaling
What cells express the C3aR and C5aR receptors?
granulocytes
What do C3aR and C5aR recognize respectively?
C3a and C5a
What happens when either C3aR or C5aR binds to C3a or C5a?
release of pro-inflammatory cytokines and granules
