Immune Evasion Flashcards
(23 cards)
Why are surface modifications important to immune evasion?
Many immune responses (complement, phagocytosis) begin by recognising microbial surface structures
What are two bacteria that rely on capsules?
- Neisseria meningitidis: capsule resists complement-mediated killing
- S. pneumoniae: capsule is key to avoid opsonisation
What is an example of a bacteria that uses modified LPS?
Salmonella modifies lipid A of LPS
What are two ways Salmonella modifies lipid A?
ArnT- adds aminoarabinose which reduces LPS charge; less TLR4 recognition
EptA/EptB - Adds phosphoethanolamine;§ evades detection
What immune modulator does HIV secrete?
Nef protein; downregulates MHC I; hides from CD8+ T cells
What immune modulator does Herpes Simplex secrete?
ICP47; blocks MHC I antigen presentation
What immune modulator does Salmonella enterica secrete?
Injects SopB and SipA via T3SS; alters cytoskeleton and immune signalling
How does Herpes Simplex manipulate cell death pathways?
Latency-Associated Transcript (LAT) prevents neuron apoptosis
What are 3 mechanisms through which pathogens can avoid immune surveillance?
- Latency
- Controlling PAMP expression
- Intracellular lifestyle
What are some viruses that undergo latency?
- HSV
- EBV
- HIV
What is latency?
Where pathogens remain dormant with minimal protein expression
What are some mechanisms of latency?
- Gene silencing (no peptides for MHC I)
- Integration into host genome (HIV)
- Inhibition of apoptosis
What is an example of PAMP expression control?
Salmonella Typhimurium stops flagellin gene transcription, and
Listeria monocytogenes shuts down flagella presentation at 37 degrees in host.
Avoids detection by TLR5
What are the benefits of intracellular lifestyle?
- Hide from antibodies/complement
- Access intracellular nutrients
- Spread cell-to-cell
What are some examples of intracellular pathogens?
- Listeria
- Chlamydia
- Salmonella
- M. tb
What does Listeria monocytogenes use to attach to and invade cells?
InIA
How does Listeria escape the phagosome?
Via Listeriolysin O and phospholipases
How does Listeria spread to neighbouring cells?
Through hijacking host actin
What are three examples of pathogens that use antigenic variation?
- HIV
- Neisseria
- T. brucei
How does HIV do antigenic variation?
Envelope glycoprotein antigens gp120 and gp41 mutate rapidly
How does Neisseria undergo antigenic variation?
Switches pili and outer membrane proteins via recombination and phase variation
What are two other pathogens (other than Neisseria) that undergo phase variation?
- Streptococcus pneumoniae: variation of capsule and surface proteins
- Salmonella: variation of H1 & H2 flagellar antigens
