Microbial Immune Evasion Mechanisms

Question 1

What aspects of immunity have pathogens evolved to overcome?

Answer 1

• Natural defences: mucosal layers, skin
• Innate immunity: complement system and macrophages
• Adaptive immunity: antigen specificity and memory antibodies T cells - CD4 helper cells and CD8 cytotoxic cells

Question 2

What are 6 roles of the complement? How can certain features of pathogens overcome this system?

Answer 2

• Induces inflammatory response
• Promotes chemotaxis
• Increases phagocytosis by opsonisation
• Increases vascular permeability
• Mast cell degranulation
• Lysis of cell membranes

Microbes can:
- Fail to trigger: LPS, capsules
- Negative binding: coating w non-fixing IgA - won’t trigger the complement system bc that needs IgG and IgM. capsule blocks C3b binding, capsule prevents C3b receptor access
- Disrupt regulation: factor H sequestration
- Block/expel MAC: C5a proteases, blebbing

Question 3

Name some examples of intracellular pathogens, what makes them ‘intracellular’?

Answer 3

they can survive inside living cells which ensure they’re hidden from serum killing, complement and antibodies

e.g. mycobacterium tuberculosis, listeria, salmonella

Question 4

Production of which receptors by microbes lead to antibody inhibition?

Answer 4

Fc receptors

Question 5

Name the 7 mechanisms that allow pathogens to live in macrophages

Question 6

What are the 4 mechanisms by which microbes can bypass adaptive immunity?

Answer 6

1. Concealment of antigen [i.e. hiding in the cells, other sites, blocking MHC antigen presentation
2. Immunosuppression, so decreasing MHC, receptors, apoptosis and switching to IgA proteases
3. Antigenic variation

4) Persistence/latency/reactivation

Question 7

What are the 4 mechanisms by which viruses evade the immune system?

Answer 7

1. Latency
2. Decrease antigenic presentation
3. Decrease MHC expression
4. The mutations of epitopes

Question 8

Define: Antigenic Diversity, Antigenic Variation, Phase variation

Question 9

Outline the general principle of antigenic variation inNeisseria gonorrhoeae

Question 10

Describe the role of bacterial capsular polysaccharides in pathogenesis

Question 11

Explain the concept of viral antigenic diversity and show how this influences infectivity and disease spread, using influenza as an example

Question 12

With strep pneumoniae as an example, explain its pathogenic mechanisms which allow it to bypass the immune systems in place

Question 13

Using vacilla zoster and herpes simplex as an example, explain how latency allows microbes to evade immune systems