Complement Flashcards

1
Q

What is the complement system?

A

a system of about 50 different proteins which mediates a wide range of functions and involves enzyme cascades to help eliminate infections microorganisms

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2
Q

What do components of an enzyme cascade circulate as?

A

inactive precursors

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3
Q

What are the names of the 3 main pathways that activate complement?

A
  1. classical
  2. lectin
  3. alternative
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4
Q

What is the central component of complement?

A

C3

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5
Q

What deficiency causes recurrent bacterial infections?

A

C3 deficiency

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6
Q

What do all 3 pathways result in?

A

C3 -> C3b and C3a

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7
Q

What happens to C3b

A

it is deposited onto the surface of microorganisms and marks it out for destruction

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8
Q

What is the first component of the classical pathway?

A

C1q

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9
Q

What shape is C1q

A

Hexavalent

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10
Q

How is C1q arranged?

A

bunch of tulips - 18 polypeptides

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11
Q

What molecules activate the classical pathway?

A

IgG and IgM

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12
Q

How does C1q bind to IgM/IgG molecules?

A

C1q engages globular heads with Fc region of IgM/IgG

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13
Q

What is cleaved by the classical pathway?

A

C4 and C2

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14
Q

What enzyme is formed by the classical pathway?

A

C3 convertase

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15
Q

What is the lectin pathway activated by?

A

Lectins

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16
Q

Name a protein that participates in the lectin pathway?

A

Mannose binding lectin (MBL)

17
Q

What cleavage occurs in the lectin pathway?

A

C4 -> C4a + C4b

18
Q

What cleavage occurs in the lectin pathway?

A

C4 -> C4a + C4b

19
Q

What enzyme is produced by the lectin pathway?

A

C5 convertase

20
Q

What pathway is the 1st major line of defence against systemic infection?

A

Alternative pathway

21
Q

What pathway can function immediately?

A

Alternative pathway

22
Q

What forms funnel-shaped holes in cell membranes?

A

membrane attack complex

23
Q

What is it called when microorganisms/ complement components are coated, making them more susceptible to phagocytosis?

A

opsonisation

24
Q

Why will microorganisms coated in C3b be phagocytosed more efficiently?

A

phagocytes have receptors for C3b

25
What is chemotaxis?
the directed migration of a cell in response to a chemical stimulus
26
What are anaphylatoxins?
complement products that are potent proinflammatory mediators
27
What are the 2 anaphylatoxins?
C3a and C5b
28
What is released when C3a binds to receptors on mast cells?
histamine
29
What controls the classical pathway?
C1 inhibitor DAF CR1
30
What is the alternative pathway controlled by?
Factor 1 Factor H CR1
31
What is an immune complex?
antigen and antibody clumps