Complement 3 Flashcards
Which component of C3b binds to the surface of the microbe?
The thioester domain
Why does factor H not bind to microbial cells?
It has an affinity for sialic acid residues and glycosaminoglycans which are present on host cells but not microbial cells
Which domains of factor H bind to complement?
1,2,3,4
Which domains of factor H bind to surfaces?
19,20
What kind of binding does factor H do on nonself surfaces?
Weak binding
What kind of binding does factor H do on self surfaces?
Strong
What does weak binding lead to?
complement activation
What does strong binding lead to?
Complement -ve regulation
How can pathogens evade complement?
They have produced proteins that stabilise factor H, so the C3 is degreade on their surface
What is on the surface of smallpox that mimics the function of factor H?
SPICE
Role of C4 binding protein (C4BP)?
Inhibit C3 convertase
Additional roles of complement?
phagocytosis and clearance
What can the complement receptor on phagocytes bind to?
Antigens/microbes that have been opsonised by C3b
What happens once the complement receptor on a phagocyte has bound to an antigen/microbe?
The antigen/microbe can be taken up
How does HIV enter macrophages?
Complement activation and deposition of C3b on the surface of the virus
How is complement involved in clearance?
Cells that carry complement receptors can take up large immune complexes
What happens if there is a build up of immune complexes in the kidneys?
Kidney necrosis
Which cells are important in clearing immune complexes bc they have complement receptor 1 on their surface?
RBCs
Where are complement receptors found?
Erythrocytes, leukocytes, B and T cells, follicular dendritic cells, neutrophils and macrophages
Which cells is complement receptor 1 linked to?
Erythrocytes, leukocytes
Which cells is complement receptor 2 linked to?
B cells, T cells, follicular dendritic cells
Which cells is complement receptors 3 and 4 linked to?
Macrophages, neutrophils
Which complement receptor is widely expressed in cells?
C3a receptor
Where are C5a receptors found?
Lymphoid cells
