Microbial Immune evasion mechanisms

Question 1

What are some pathogenic mechanisms?

Answer 1

Adhesins
Toxins
Capsule

Question 2

What are some defensive mechanisms?

Answer 2

natural barriers
Defensive cells
Antibacterial peptides e.g. defensins(AMPs)
Innate and adaptive immune response

Question 3

How do bacteria evade the complement system in the innate system? (multiple ways)

Answer 3

• Capsules preferentially binds to wrong antibody and block C3b binding so improper activation of classical complement pathway
• removes factor H
• blebbing - releases complement
• C5a proteases from bacteria break down C5a complement needed in inflammation

Question 4

How can bacteria avoid complement, antibodies and serum kiling?

Answer 4

Hiding as intracellular pathogens inside macrophages (prevent phagocytosis)

Question 5

How does staphlococci evade immune response?

Answer 5

They have leucocidins whcih is a potent enzyme that kills macrophages and neutrophils

Also have protein A that binds to FC portion of antibody presenting it from binding to phagcytes cells for phagocytosis

Question 6

What is factor H and why is its removal a way to evade immune response?

Answer 6

Factor H is needed for somplement regulation, removing it means no complement

Question 7

Give an example of an intracellular pathogen?

Answer 7

Mycobacterium tuberculosis
Salmonella
Listeria

Question 8

How do pathogens avoid phagocytosis?

Answer 8

Kill macrophages (e.g. leucocidins)
Prevent opsonisation (protein A)
Block contact (capsules)
Intracellular pathogens

Question 9

What are the different ways intracellular pathogens are able to live inside macrophages and evade immune response?!!!

Answer 9

• Promote own uptake safely by causing actin rearrnagement
• Prepare cell for invasion
• Inhibit phagosome-lysosome fusion (bacteria can’t be killed)
• Escape phagolysosome into cytoplasm
• Resist oxidative killing so after normal takeup, bacteria is not destroyed (normally bacteria taken up due to complement C3B on macrophage surface, and reactive oxidative species destroy pathogen)
• Present decoy antigen (insufficient response to kill bacteria is induced)
• Bacteria produces protein mimicing FC receptor so antibodies stick on wrong