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1.3 POM Immunology > Immune Evasion > Flashcards

Immune Evasion Flashcards

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1
Q

What 5 types of diversity does bacteria display?

A
  1. Genetic
  2. Habitat
  3. Morphological
  4. Functional
  5. Metabolic
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2
Q

What are 3 common features that bacteria often share?

A
  1. LPS in gram -ve (lipopolysaccharides)
  2. LTA in gram +ve (lipoteichoic acid)
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3
Q

What is the innate immune system?

A

First line of defence against all pathogens —> rapid + broad-spectrum

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4
Q

What are the 3 mechanisms of the innate immune system?

A
  1. Complement system
  2. Antibodies
  3. Phagocytes
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5
Q

What is the complement system?

A

Cascade of proteins that opsonise or lyse bacteria

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6
Q

What are the 4 key steps of all complement cascades

A
  1. Initiation
  2. C3 convertase formation
  3. C5 convertase formation
  4. MAC formation
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7
Q

How does C3b lead to the killing of bacteria?

A

Phagocytosis

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8
Q

What is the function of MAC in the complement cascade?

A

Lysis

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9
Q

What are the 3 pathways of initiating the complement system?

A
  1. Classical
  2. Lectin
  3. Alternative
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10
Q

What are the 47steps of the classical complement pathway?

A
  1. Specific antibody bind to pathogen surface (IgM/IgG)
  2. C1 binds to antibody so…
  3. C4 cleaved to C4b
    C2 cleaved to C2a
  4. C4b + C2a = C4b2a = C3 convertase
  5. C3 binds —> C3 cleaved to C3a + C3b
  6. C3 convertase + C3b = C4b2a3b = C5 convertase
  7. C5 binds —> C5 cleaved to C5a + C5b
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11
Q

What does C3 convertase consist of in the classical complement system?

A

C4b + C2a

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12
Q

What are the 7 steps of the lectin complement pathway?

A
  1. Lectin binds to pathogen surface
  2. C1 binds to lectin so…
  3. C4 cleaved to C4b
    C2 cleaved to C2a
  4. C4b + C2a = C4b2a = C3 convertase
  5. C3 binds —> C3 cleaved to C3a + C3b
  6. C3 convertase + C3b = C4b2a3b = C5 convertase
  7. C5 binds —> C5 cleaved to C5a + C5b
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13
Q

What does C3 convertase consist of in the lectin complement system?

A

C4b + C2a

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14
Q

What are the 4 steps of the alternative complement pathway?

A
  1. C3 spontaneously activated —> C3 cleaved to C3a + C3b
  2. C3b bind to pathogen surface
  3. Bb binds —> C3b + Bb = C3bBb = C3 convertase
  4. C3 convertase + C3b = C3bBbC3b = C5 convertase
  5. C5 binds —> C5 cleaved to C5a + C5b
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15
Q

What does C3 convertase consist of in the alternative complement system?

A

C3b + Bb

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16
Q

What does C5 convertase consist of in the complement system?

A

C3 convertase + 3b
(C4b2a3b or C3bBbC3b)

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17
Q

What is difference about activation of the alternative complement system? (2)

A
  1. Activated spontaneously
  2. May be continuously activated at a low level
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18
Q

What is MAC?

A

Membrane Attack Complex
- Causes lysis of pathogen

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19
Q

How does MAC eliminate harmful microbes?

A

Creates pores in pathogen membrane —> influx of liquid into cell —> lysis of cell

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20
Q

What are the 4 steps of MAC production?

A

1.C5 binds to C5 convertase —> C5a + C5b
2. C5b binds to pathogen surface
3. C6,7 and 8 bind —> C5b-8
4. Many C9s bind in a circle —> pore in membrane

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21
Q

What is opsonisation?

A

Process marking pathogens for destruction by phagocytic cells

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22
Q

What is phagocytosis?

A

Engulfing and digestion of pathogens

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23
Q

What are the 4 phagocytes?

A
  1. Neutrophils
  2. Monocytes
  3. Macrophages
  4. Dendritic cells
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24
Q

What is a phagosome?

A

Vesicle in cell containing ingested pathogen (endocytosis)

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25
What is a phagolysosome?
Vesicle formed when a phagosome and lysosome fuse ---> where pathogen is killed by enzymes in phagocytosis
26
Which 2 molecules act as opsonins for phagocytosis?
1. C3b 2. Antibodies (IgG)
27
How does C3b act as an opsonin?
Binds to pathogen surface ---> phagocyte CR binds
28
How does IgG act as an opsonin?
Binds to pathogen antigen ---> phagocyte FcR binds
29
What does opsonisation allow for? (2)
1. Increased phagocytosis efficiency 2. Removal of invading microorganisms
30
Which phagocyte receptors does C3b bind to?
CR (complement receptor)
31
Which phagocyte receptors does FcR bind to?
FcR
32
How are bacteria recognised by the immune system?
1. Complement system 2. Antibodies
33
What are the 2 important properties of the innate immune system?
1. Fast (hours) 2. Broad-spectrum ---> all pathogens
34
What does an impaired innate immune system lead to?
Infection
35
What are the 3 common causes of an impaired immune system?
1. Complement protein deficiency 2. Antibody deficiency 3. Neutropenia ---> inhibits phagocytosis
36
What is immune evasion?
Strategies pathogens have evolved to survive against the immune system ---> successfully infect host
37
What are the 6 strategies pathogens use to evade the immune system?
1. Avoid recognition 2. Inhibit phagocytosis 3. Kill immune system cells 4. Disrupt the immune response 5. Mimic host molecules 6. Survive inside cells
38
How do bacteria evade the complement system? (2)
1. Avoid recognition 2. Inhibit phagocytosis
39
How do bacteria evade the antibodies? (2)
1. Avoid recognition 2. Inhibit phagocytosis
40
How do bacteria evade phagocytosis?
Kill phagocytes
41
Is staphylococcus aureus gram positive or negative?
Gram +ve
42
Why is S. aureus an opportunistic bacteria?
Live harmlessly on skin ---> invade when skin barrier broken ---> cause infection
43
Is S. aureus always pathogenic?
No ---> usually live harmlessly on skin
44
When does S. aureus cause an infection?
Upon entry into the body
45
Where is S. aureus usually found? (2)
1. Skin 2. Mucosal membranes
46
What are the 4 symptoms of S. aureus?
1. Osteomyelitis 2. Endocarditis 3. Bacteraemia/sepsis 4. Skin and soft tissue infection
47
What proportion of MRSA infections are hospital-acquired?
86%
48
How does S. aureus evade the complement system? (4)
1. Degrade C3 2. Inhibits C1 3. Prevents C3 and C5 convertase production
49
How does S. aureus degrade C3?
Produces Aur protease
50
How does S. aureus inhibit C1?
Produces Sbi ---> binds to IgG ---> C1 can't recognise IgG ---> No classical pathway
51
How does S. aureus prevent C3 and C5 convertase production?
Produces SCIN protein ---> bind to C3bBb ---> No alternative pathway
52
What does Aur do to disrupt the complement pathway?
Degrade C3b
53
What does Sbi do to disrupt the complement pathway?
Binds to IgG antibodies ---> C1 can't bind (classical)
54
What does SCIN do?
Binds to C3bBb ---> C3b can't bind (alternative)
55
How does S. aureus inhibit C5?
SSL7 protein binds
56
What does SSL7 do to disrupt the complement pathway?
Binds to C5 ---> C5 convertase can't bind
57
How does S. aureus evade phagocytosis? (4)
1. Hide antigens via capsule 2. Block antibody Fc 3. Digest/modify antibodies 4. Block FcRs
58
How does S. aureus hide its antigens?
Express capsule round surface
59
How does S. aureus prevent normal opsonisation?
Produce protein A ---> bind to antibody Fc region ---> FcR can't bind
60
How does S. aureus degrade antibodies?
Produce SAK ---> converts plasminogen to plasmin ---> cleaves antibody
61
How does S. aureus inhibit FcRs?
Produces FLIPr ---> binds to FcRs on phagocyte ---> can't bind to Fc regions of opsonising antibodies
62
How does S. aureus kill phagocytes?
Releases toxins
63
Which 4 toxins does S. aureus release?
1. α-toxin 2. PVL 3. LukAB 4. PSMs
64
Which 3 phagocytes does α-toxin kill?
1. Neutrophils 2. Monocytes 3. Macrophages
65
Which 3 phagocytes does PVL kill?
1. Neutrophils 2. Monocytes 3. Macrophages
66
Which phagocyte does LukAB kill?
Neutrophils
67
Which 4 phagocytes do PSMs kill?
All: 1. Neutrophils 2. Monocytes 3. Macrophages 4. Dendritic cells
68
Which 4 S. aureus toxins kill neutrophils?
All: 1. α-toxin 2. PVL 3. LukAB 4. PSMs
69
Which 3 S. aureus toxins kill monocytes?
1. α-toxin 2. PVL 4. PSMs
70
Which 3 S. aureus toxins kill macrophages?
1. α-toxin 2. PVL 4. PSMs
71
Which S. aureus toxin kills dendritic cells?
PSMs

1.3 POM Immunology (13 decks)

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