Microbial Immune Evasion Mechanisms

Question 1

What is balanced pathogenicity?

Answer 1

Properties of microbe vs properties of host

Question 2

What are the properties of microbe?

Answer 2

Adhesins
Toxins
Capsule

Question 3

What are the properties of the host?

Answer 3

Natural barriers
Defensive cells
Antibacterial peptides
Innate and adaptive immune responses

Question 4

What are the two virulence factors?

Answer 4

Adhesins and toxins

Question 5

What do adhesins promote?

Answer 5

Colonisation and adhesion

Question 6

What do toxins promote?

Answer 6

Tissue damage

Question 7

What are the facets of pathogen evasion of complement?

Answer 7

Failure to trigger
Negative binding
Disrupt regulation
Block/expel MAC

Question 8

What do leucocidins do?

Answer 8

Kill pathogens

Question 9

How does staphylococci stop opsonisation?

Answer 9

Produces protein A

Binds to the Fc portion of IgG

Question 10

How do intracellular pathogens evade phagocytosis?

Answer 10

Promote own uptake
Inhibit phagosome-lysosome fusion
Escape phagosome-lysosome into the cytoplasm
Resist oxidative killing by producing catalases/peroxidase

Question 11

How can intracellular pathogens promote their own uptake?

Answer 11

CR3 or mannose lectin receptor

Question 12

How do pathogens conceal antigens?

Answer 12

Hide inside cells
Block MHC antigen presentation
Surface uptake of host molecules

Question 13

How can pathogens cause immunosuppression?

Answer 13

Downregulation of MHC and receptors

Increase in apoptosis and leading to a cytokine switch of IgA proteases

Question 14

What happens if streptococcus pneumoniae enters the lungs?

Answer 14

Bypasses surfactants

Cause inflammation in the lungs and damage endothelial cells

Question 15

What are the mechanisms for evasion of the adaptive immune response?

Answer 15

Concealment of antigen
Immunosuppression
Antigenic variation
Persistence/latency/reactivation

Question 16

How do viruses evade the immune system?

Answer 16

Latency
Decrease in antigenic presentation
Decrease in MHC expression
Mutation of epitopes

Question 17

Which viruses evade by latency?

Answer 17

VZV

Herpes simplex

Question 18

Which viruses decrease antigenic presentation?

Answer 18

Herpes simplex

Question 19

Which virus decreases MHC expression?

Answer 19

Cytomegalovirus

Question 20

What epitope mutations happen?

Answer 20

B cell - neutralisation by antibody escape

T cells - CD8+ escape mutants of HIV

Question 21

What are the antigenic variation phenotype changes that take place?

Answer 21

Colony morphology
Virulence
Serotype 
loose flagella
Change surface sugars

Question 22

What does antigenic diversity produce?

Answer 22

Genetically stable and alternative forms of antigens in a population of microbes

Question 23

What does antigenic variation produce?

Answer 23

Successive expression of alternative forms of an antigen in a specific clone or its progeny

Question 24

What is phase variation?

Answer 24

On/off an antigen at low frequency

Question 25

When does antigenic variation occur?

Answer 25

During course of infection in an individual host

Question 26

Why does influenza have a high potential for variation?

Answer 26

Many types of surface proteins and a segmented genome