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Immunology > 4 - Innate 2: Complement > Flashcards

4 - Innate 2: Complement Flashcards

1
Q

What is complement

A

Group of proteins arranged in a biochemical cascade that aid in elimination of pathogens through mediating inflammation, opsonization, and direct lytic attack

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2
Q

Complement is a major component of ____ and ______ immune responses

A

Primitive and advanced

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3
Q

Is complement used by innate or adaptive immune responses?

A

Both

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4
Q

Complement consists of

A

16 different serum proteins and glycoproteins comprising 10% of total serum protein

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5
Q

What % of total serum protein is complement

A

Aroun 10%

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6
Q

Where is complement produced

A

Mostly in the liver

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7
Q

3 initiating complement activation pathways:

A
  1. Classical
  2. Alternative
  3. Lectin
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8
Q

List 3 complement activation pathways & what immune system they correlate to

A
  1. Classical - adaptive immune system
  2. Alternative - innate immune system
  3. Lectin - innate immune system
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9
Q

The classical pathway is initiated by

A

IgG or IgM (needs antigen presenting cell)

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10
Q

The alternative pathway is initiated by

A

Microbial surface vicinity (** and can also amplify classical cascade**)

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11
Q

Lectin pathway is initiated by

A

Mannose-binding lectin

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12
Q

Which pathway is the most ancient

A

Lectin

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13
Q

Do all 3 pathways result in the same outcome

A

Yes

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14
Q

How does complement kill invaders?

A

Pathogen presents foreign surface —> proteins recognize foreign stuff—> initiates common terminal pathway —> complement forms a big pore in pathogen which kills it

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15
Q

Opsonization

A

The coating of a particle with host protein

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16
Q

The classical activation pathway is activated by

A

Antigen-antibody complex (specifically IgG1, IgG3, and IgM)

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17
Q

In the classical pathway, immobilized antibody is recognized by

A

The C1 complex through C1q units

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18
Q

Classical pathway - once the immobilized antibody is recognized by the C1 complex through C1q units, what happens?

A

C1q binds to the complex, then undergoes a conformational change to activate C1r which starts cleaving subunit C1s. C1r is the first enzyme in the cascade

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19
Q

The classical activation pathway initiation is dependent on

A

Ca2+

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20
Q

Classical pathway - once C1 protease is active, what does it do next?

A

Cleaves C4 and C2

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21
Q

Classical pathway - once C4 and C2 are cleaved by active C1, what happens

A

Cleaved components C4b and C2a form classical C3 convertase C4b2a which is associated with the activating surface

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22
Q

Classical pathway - once classical C3 convertase C4b2a is formed, what happens next?

A

C4b2a cleaves C3 into C3a and C3b

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23
Q

Classical pathway - once C3a and C3b have been cleaved, what happens

A

Both C4b and C3b covalently bind to the activating surface via thiolester linkage

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24
Q

Classical pathway - a proportion of C3b will complex with

A

C4b2a to form the C5 converting complex C4b2a3b

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25
Q

Classical pathway - which molecules are “sticky”?

A

C4b2a and C4b2a3b - both stay physically attached to pathogen

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26
Q

Lectin pathway initiation

A

Antibody independent initiation (not specific). Mannose-binding lectin (MBL) behaves similarly to C1q. Binds to sugary residues common on pathogen surfaces.

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27
Q

MBL binds to

A

Mannose, fucose, and N-acetyl glucosamine (NAG) that are commonly present in cell walls of microbes.

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28
Q

Lectin pathway - MBL binding induces

A

Conformational change that induces autocatalysis of MBL-associated serine proteases (MASPs) that subsequently cleave C4 and C2.

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29
Q

Lectin pathway - Once the MASPs cleave C4 and C2, what happens

A

Classical pathway!

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30
Q

What is different between Classical and Lectin activated pathways?

A

Initiation event

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31
Q

Alternative activation pathway - relies on

A

A low-level serum hydrolysis of C3

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32
Q

Alternative Activation pathway - C3 in serum is

A

Continually hydrolyzed to C3(H20)

33
Q

Alternative pathway - C3(H20) comes into contact with Factor B and then

A

Turns in to C3(H20)B which then recruits factor D

34
Q

Alternative Pathway - once C3(H20)B is formed, what happens?

A

It recruits Factor D, and Ba is cleaved off. This creates C3(H20)Bb, which is also called Fluid-phase C3 convertase

35
Q

Alternative Activation Pathway - hydrolysed C3 in the presence of an “activator surface” binds

A

serum factors that form the C3 convertase C3bBB

36
Q

Alternative pathway - once C3bBb has been formed, what does it do?

A

C3bBb hydrolyses C3 into C3a and C3b, which establishes an amplification loop in the absence of regulators

37
Q

Alternative pathway - Once C3b has been cleaved, what does it do?

A

C3b complexes with C3bBb to form the C5 converting complex C3bBb3b (which is an alternative C5 convertase).

38
Q

Alternative Activation pathway - how does the body prevent activation on body cells?

A

Host cells possess surface carbohydrates and regulators that inactivate C3b, so they have non-activating surfaces

39
Q

Is the alternative pathway inherent to the classical pathway?

A

Yes, as it provides an amplification loop for C3 deposition

40
Q

Alternative pathway - which molecules are sticky

A

C3b - will stick to any surface nearby

41
Q

What is the terminal membrane attack pathway?

A

Classical, Lectin, and Alternative C’ pathways end with the formation of a C5 convertase complex (C4b2a3b & C3bBb3b)

42
Q

Terminal Membrane Attack Pathway - After formation of C5 convertase complex (C4b2a3b & C3bBb3b), what happens?

A

Cleavage of C5 to C5b initiates pathway involving C6, C7, C8, and multiple copies of C9 to form a rigid pore (Membrane Attack Complex (MAC) within the lipid bilayer of the target

43
Q

Terminal Membrane Attack Pathway - once the rigid pore/Membrane Attack Complex has been formed, what happens?

A

The MAC in the lipid bilayer of the target allows influx of solutes and electrolytes leading to osmotic swelling and sometimes lysis.
- a hole is punched in the surface of the pathogen which kills the pathogen

44
Q

Terminal Membrane Attack Pathway - in which order do C6, C7, C8, and C9 bind?

A

Numerical - have to go C6-C9 and each protein goes farther into the membrane than the protein before it (ie C9 goes deepest)

45
Q

Outcomes of complement activation:

A
  1. Opsonization of particles with proteins (C3b)
  2. Chemotaxis and activation
  3. Increased vascular permeability
  4. Target osmodysregulation and lysis
  5. Enhances adaptive immunity
  6. Immune complex clearance
46
Q

Outcomes of complement - Opsonization

A

C3b deposition enhances binding and uptake of microbes via CR1 and CR3 in professional phagocytes - enhanced clearance

47
Q

Outcomes of complement - Chemotaxis & activation

A

PMNs and Macrophages migrate along C3a and C5a gradients to site of complement activation

48
Q

outcomes of complement activation - increased vascular permeability

A

C3a and C5a triggers degranulation of Mast cells
Mast cells release vasoactive amines that increase vascular permeability and local blood flow

49
Q

Outcomes of complement - enhances adaptive immunity

A

Adjuvant effect in priming humoral immune response

50
Q

Outcomes of complement - immune complex clearance

A

Disaggregates immune complexes and aids erythrocyte-mediated transport and clearance

51
Q

Outcome: Direct target Lysis
Complement product: MAC
Action:

A

Osmodysregulation and lysis of target cells

52
Q

Outcome: Tissue Inflammation
Complement products: C3a & C5a
Action

A

Activation of mast cell degranulation leading to release of vasoactive amines (histamine and serotonin)

53
Q

Outcome:Endothelial Activation
Complement product: C3a & C5a

A

Increased expression of adhesion molecules

54
Q

Outcome: Chemotaxis
Complement product: C3a & C5a
Action:

A

Promotes migration of neutrophils, eosinophils, and macrophages towards the site of complement activation

55
Q

Outcome: Leukocyte Activation
Complement product: C5a (C3a & C4a)
Action:

A

Upregulation of adhesion moleculwes, phagocytes receptors, and antimicrobial effectors by neutrophils and monocytes

56
Q

Outcome: Opsonization
Complement product: C3b & iC3b
Action:

A

Enhancement of particle phagocytosis by macrophages and neutrophils

57
Q

Outcome: Promotion of humoral responses
Complement product: C3dg
Action:

A

Enhanced B cell activation. Retention of antigen complexes in B cell follicles

58
Q

Outcome: Immune complex clearance
Complement product: C3b (and iC3b)
Action:

A

Blocks growth and facilitates dissociation of immune complexes. Immobilization and clearance of immune complexes through interaction with CR1 on erythrocytes

59
Q

How are the complement pathways regulated?

A

The classical, lectin, alternative, and terminal attack pathways can all be stopped or downregulated at key points by soluble or membrane-associated complement control proteins

60
Q

Regulation of complement activation prevents

A

The complement innate defense system from acting on inappropriate targets, and also from acting in perpetuity

61
Q

Regulation of complement activation - alternative activation pathway works by:

A

Host membranes are rich in sialic acid residues (not present on pathogen surfaces) that promote binding of C3b to factor H.

Factor H, along with Factor I, inactivates and degrades inappropriately bound C3

62
Q

On host surfaces, spontaneously bound C3b is

A

Destroyed as fast as it is deposited

63
Q

SLIDE 19 !!! PICK 3 AND MEMORIZE THEM !!!!! HE SAID IN LECTURE!

A

Good luck & don’t f it up

64
Q

Can you be deficient in complement

A

Yes - genetic

65
Q

Deficiencies in components of the classical pathway have what effect

A

Little or no increased risk of infection. This suggests alternative and lectin pathways are sufficient for controlling infection

66
Q

Deficiencies in classical pathway components are associated with increased risk of

A

SLE (systematic Lupus Like) autoimmune disease thought to be due to impaired clearance of immune complexes by monocyte macrophage system

67
Q

A factor H deficiency results in

A

Unregulated activation of alternative pathway

68
Q

In pigs, factor H deficiency leads to

A

Type 2 membrane proliferation glomerulonephritis due to deposition of C3 components in glomerulus of kidney

69
Q

What are acute phase proteins

A

Proteins that increase or decrease in plasma concentrations in response to inflammation

70
Q

APP are mostly synthesized in

A

Liver in response to cytokines (particularly IL-6)

71
Q

APP actions

A

Maintains homeostasis of tissue
Reduces tissue damage associated with inflammatory process
Aids in propagating inflammatory rxn
Regulation of immune response
Protection against infection
Aids in tissue repair

72
Q

Positive APP (increase when animal’s infected)

A

C-reactive protein (CRP)
Serum Amyloid A (SAA)
Haptoglobin
Alpha-1-acid glycoprotein (AGP)
Ceruloplasmin
Fibrinogen

73
Q

Negative APP (goes down when animal infected)

A

Albumin
Transferrin

74
Q

What is the major APP in primates, dogs, and pigs

A

C-reactive protein (CRP)

75
Q

CRP binds to

A

Phosphocholine, polysaccharides, and glycolipids commonly found on surface of bacteria, parasites, and damaged cells

76
Q

CRP also binds to

A

For subsets on neutrophils and macrophages - increased clearance by phagocytosis

77
Q

What pathway does CRP induce

A

Classical pathway - binds C1q then induces cytokines and has both pro and anti-inflammatory actions

78
Q

CRP inhibits

A

Chemotaxis and modulation of neutrophil function

Immunology (18 decks)

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