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Immunology > Complement Cascade > Flashcards

Complement Cascade Flashcards

1
Q

3 functions of complement cascade

A
  1. anaphylatoxin production, inflammatory mediators that activate vascular epithelium and recruit phagocytes
  2. opsonization
  3. formation of MAC
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2
Q

alternative pathway

A

innate, first to be activated

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3
Q

lectin pathway

A

innate, second to be activated

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4
Q

classical pathway

A

acquired (has an innate function as well), last to be activated

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5
Q

T/F all complement components produced by liver in inactive form

A

true

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6
Q

C3bBb

A

C3 convertase of the alternative pathway

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7
Q

C4bC2a

A

C3 convertase of lectin and classical pathway

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8
Q

Importance of C3b deposition

A
  1. it’s a component of the C5 convertase which is necessary for formation of the MAC
  2. opsonin
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9
Q

C3a

A

anaphylatoxin

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10
Q

C3b2Bb

A

C5 convertase-important for generation of the MAC

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11
Q

Formation of C3bBb

A

C3b binds pathogen, then factor B binds that, then factor D cleaves resulting in the C3 convertase C3bBb

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12
Q

C3b

A

opsonin

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13
Q

C5 convertase

A

Cleaves C5 into C5a and C5b

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14
Q

C5a

A

anaphylatoxin, IMPORTANT chemotactic factor for neutrophils (along with IL-8)

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15
Q

C5b

A

first component of the MAC

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16
Q

MAC formation

A

C5b joins with C6 and C7 which then joins with C8 which then recruits 10-16 of C9 resulting in the production of a pore in the bacterial cell membrane resulting in disintegrity and death

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17
Q

MBP/MBL

A

mannose binding protein of the lectin pathway, binds mannose residues of the bacteria

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18
Q

MASP-1/2

A

MBP recruits these, they bind and then result in the cleavage of C4 and C2 which results in the formation of the C4aC2b convertase of the lectin pathway (C3 convertase does the same thing as in the alternative path)

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19
Q

Classical pathway involves ____

A

antibodies

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20
Q

Classical pathway initiation

A

when complement component C1 binds to antibody that is bound to its cognate antigen

21
Q

C1 molecule

A

has 6 C1q stalks with C1r and C1s. When C1 binds to an antigen-engaged antibody C1r cleaves C1s which then cleaves C4 and C2 to create the C4aC2b convertase of the classical pathway (C3 convertase does the same thing as in the other two pathways)

22
Q

C4a

A

anaphylatoxin

23
Q

C2b

A

anaphylatoxin

24
Q

Most efficient isotopes for initiation classical complement cascade?

A

IgM and IgG3

25
Q

Deposition of C3b leads to

A
  1. uptake and destruction of pathogen by phagocytes that have receptors for C3b
  2. creation of the MAC
26
Q

C4b2a3b

A

C5 convertase

27
Q

T/F Alternative pathway amplifies the other two pathways

A

true

28
Q

Innate classical pathway

A

C reactive protein produced by the liver during septic bacterial infections binds to phosphocholine residues on bacteria and mimics the IgM antibody and thus recruits the C1 molecule and initiates the classical complement cascade

29
Q

Complement is important for encapsulated bacteria because____

A

phagocytes can’t recognize PRRs on them bc they’re covered by the capsule but complement factors can be deposited on their surface which leads to phagocytic activity

30
Q

T/F there are no Fc receptors for IgM

A

true

31
Q

CR1

A

found on phagocytes

recognizes C3b and results in phagocytosis

32
Q

CR1 on RBCs

A

clearance of immune complex-IMPORTANT-if not cleaned up they cause vasculitis and kidney disfunction

33
Q

CR3 and CR4

A

found on phagocytes

recognize iC3b, breakdown of C3b and stimulate phagocytosis

34
Q

CR2

A

B cell co-receptor
it increases the signaling that results from B cell receptor binding to cognate antigen, decreasing the amount of costimulation signal needed from helper T cells

35
Q

C3a and C5a

A

role in activating mast cells

anaphylatoxins

36
Q

2 forms of regulation of complement

A
  1. passive

2. active

37
Q

passive regulation

A

hydrolization of thioester bonds

38
Q

C1 inhibitor

A

binds C1r:C1s and causes them to disassociate from C1q so they cannot cleave C4 and C2

39
Q

Deficiency of C1 inhibitor (HANE)

A

results in the overproduction of anaphylatoxins (which remember can stimulate mast cells) and cause angioedema episodes

40
Q

C4 binding protein

A

binds to the C4b component of the classical pathway C3 convertase, causing a displacement of the C2b fragment and making the C4 fragment susceptible to cleavage by factor I, permanently disabling that copy of the C3 convertase enzyme

41
Q

factor H

A

H binds to C3b, making it susceptible to cleavage by factor I. Once C3b is cleaved to form iC3b, it can no longer serve as a template for factor B binding, so that copy of C3b can never become part of a functional C3 convertase of the alternative pathway

42
Q

factor I

A

protease that cleaves C4b once C2 has been dissociated from it by C4-binding protein and it cleaves C3b that has been bound by factor H

43
Q

Factor I deficiency

A

this leads to depletion of C3, preventing activation of the complement cascades when they are really needed
also results in deficiency of iC3b

44
Q

decay accelerating factor (CD55)

A

a membrane-bound protein that gets its name from its ability to dissociate C3 convertase enzymes

45
Q

MCP

A

MCP binds to either C3b or C4b, they become susceptible to cleavage by factor I
membrane bound

46
Q

CR1

A

membrane-bound protein that binds to C3b and C4b, making them susceptible to factor I cleavage.

47
Q

CD59/protectin

A

prevents membrane attack complex formation on host cells by binding to the C5b,6,7,8 complex and preventing C9 from binding to the complex

48
Q

paroxymal noctural hemoglobulinuria

A

the inability to produce a phospoinositol glycolipid tail that anchors decay accelerating factor and CD59 (or protectin) into the membrane of host cells
results inperiodic episodes of intravascular erythrocyte lysis

Immunology (11 decks)

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