🌞 Pathogen Evasion Strategies

Question 1

Why do pathogens evolve mechanisms to evade the immune system?

Answer 1

Enable cont replication w host

Question 2

How can pathogens avoid recognition by PRRs?

Answer 2

• Antigenic variation (e.g. N. gonorrhoeae) → changes surface Ags
• Capsule (e.g. S. pneumoniae) → masks PAMPs
• Proteases (e.g. IgA protease) → degrade PRRs/opsonins
• PRR signaling inhibition (e.g. viral TLR blockers)
• Host mimicry (e.g. H. pylori LPS mimics Lewis Ags)
• Biofilms (e.g. P. aeruginosa) → block PRR access

Question 3

How can viruses interfere with cytokine signalling?

Answer 3

• Viral cytokine homologs (e.g. viral IL-10) → mimic/block host cytokines
• Cytokine receptor inhibition → block/degrade host receptors
• Block JAK/STAT (e.g. Vaccinia virus) → inhibit downstream signaling
• Suppress cytokine gene expression → block transcription factors (e.g. NF-κB, IRFs)

Question 4

What are examples of pathogens that inhibit phagosome-lysosome fusion?

Answer 4

• Mycobacterium tuberculosis: Inhibits phagosome-lysosome fusion
• Legionella pneumophila: Modifies phagosome to prevent fusion
• Salmonella spp.: Alters phagosome to avoid lysosome fusion

Question 5

How can pathogens evade or inhibit complement activation?

Answer 5

• Capsule: Masks surface, prevents complement binding (e.g., S. pneumoniae)
• Regulatory proteins: Inactivate complement (e.g., N. gonorrhoeae)
• Surface modifications: Avoid recognition (e.g., B. burgdorferi)
• Proteases: Degrade complement proteins (e.g., S. aureus)
• Mimicry: Prevents opsonization (e.g., Group B Streptococcus)