Microbial Immune Evasion Mechanisms

Question 1

EVASION OF INNATE IMMUNITY:
How do Viruses affect the Complement system?

How do Intracellular Viruses carry out immunoevasion?

Answer 1

• • Failure to trigger Complement
  • Poor binding to Complement, Capsule blocks C3b binding
  • Block/Expel MAC
• • Hidden from Serum killing, Complement, and Antibodies
  • Prevents Opsonisation
  • Promotes its own uptake and Prepares the cell for invasion
  • Poor Phagosome-Lysosome fusion
  • Escapes Phagolysosome to enter the cytoplasm
  • Controls Antigen presentation on MHC to prevent CD8 and Macrophage activation

Question 2

EVASION OF ADAPTIVE IMMUNITY:
What’s one main way in which Viruses can evade here? How does it do this?

What are the other ways it can evade here?

Answer 2

• • Concealment of its Antigen by:
  o Hiding in cells and Privileged sites
  o Block MHC antigen presentation
  o Surface uptake of host molecules
• • Immunosuppression through Apoptosis, ↓MHC, ↓Receptors
  • Antigenic variation
  • Persistence, Latency and Reactivation

Question 3

ANTIGEN VARIATION:
What is Antigenic Diversity/Polymorphism?

What is Antigenic Variation?
→ What is Phase Variation?
→ When do these both occur?
→ How does this occur in N. Gonorrhoeae?

What occurs in Antigenic DRIFT? What can this lead to?

What occurs in Antigenic SHIFT? What can this lead to?

Answer 3

• Genetically stable and different forms of antigens in a population of microbes
• Successive expression of different forms of an antigen in a specific clone or its offspring
  → On/Off expression of an antigen at low frequency
  → During course of infection in host or in community spread
  → N. Gonorrhoeae switches off its expression of Pilli after entry
• Mutation + Selection = EPIDEMICS
• Gene reassortment = PANDEMICS