Complement Flashcards
What is the complement system?
a system of about 50 different proteins which mediates a wide range of functions and involves enzyme cascades to help eliminate infections microorganisms
What do components of an enzyme cascade circulate as?
inactive precursors
What are the names of the 3 main pathways that activate complement?
- classical
- lectin
- alternative
What is the central component of complement?
C3
What deficiency causes recurrent bacterial infections?
C3 deficiency
What do all 3 pathways result in?
C3 -> C3b and C3a
What happens to C3b
it is deposited onto the surface of microorganisms and marks it out for destruction
What is the first component of the classical pathway?
C1q
What shape is C1q
Hexavalent
How is C1q arranged?
bunch of tulips - 18 polypeptides
What molecules activate the classical pathway?
IgG and IgM
How does C1q bind to IgM/IgG molecules?
C1q engages globular heads with Fc region of IgM/IgG
What is cleaved by the classical pathway?
C4 and C2
What enzyme is formed by the classical pathway?
C3 convertase
What is the lectin pathway activated by?
Lectins
Name a protein that participates in the lectin pathway?
Mannose binding lectin (MBL)
What cleavage occurs in the lectin pathway?
C4 -> C4a + C4b
What cleavage occurs in the lectin pathway?
C4 -> C4a + C4b
What enzyme is produced by the lectin pathway?
C5 convertase
What pathway is the 1st major line of defence against systemic infection?
Alternative pathway
What pathway can function immediately?
Alternative pathway
What forms funnel-shaped holes in cell membranes?
membrane attack complex
What is it called when microorganisms/ complement components are coated, making them more susceptible to phagocytosis?
opsonisation
Why will microorganisms coated in C3b be phagocytosed more efficiently?
phagocytes have receptors for C3b
What is chemotaxis?
the directed migration of a cell in response to a chemical stimulus
What are anaphylatoxins?
complement products that are potent proinflammatory mediators
What are the 2 anaphylatoxins?
C3a and C5b
What is released when C3a binds to receptors on mast cells?
histamine
What controls the classical pathway?
C1 inhibitor
DAF
CR1
What is the alternative pathway controlled by?
Factor 1
Factor H
CR1
What is an immune complex?
antigen and antibody clumps
