POM MOCK 8 - Immune evasion, cell injury, plasma Flashcards
How do neutrophils get from blood to pathogen in tissue?
Pathogen triggers release of C3a and C5a. Endothelial cells express ICAM allowing for neutrophil adhesion. Neutrophil transmigration occurs. Gradient of C3a and C5a detected by neutrophils via their C3aR and C5aR receptors. Neutrophils move towards gradient of complement and bacteria proteins.
Why is staphylococcus aureus regarded as an opportunistic pathogen?
Lives in our microbiota and is harmless however can become harmful in certain situations (immunocompromised or unhealthy individuals).
What can staphylococcus aureus cause?
Skin infections and can also lead to life threatening sepsis.
What can streptococcus pyogenes cause?
Pharyngitis, skin infection, scarlet fever and sepsis.
How does a capsule polysaccharide evade the immune system?
Hides antigenic structures. Antibodies or complement proteins can’t bind.
What surface protein does s.aureus express?
Protein A
What surface protein does S.pyogenes express?
M protein.
What do surface proteins expressed by bacteria do to evade immune system?
Binds antibodies by the fc region (constant region) rather than the fab region (variable region). This prevents normal opsonization and so neutrophils can’t detect.
What do proteases that are released do to evade immune system and what proteases does s.pyogenes release?
They cleave antibodies. Prevents normal opsonisation and so neutrophils can’t detect. S.pyogenes = Ides.
How does antigenic variation help evade immune system?
Prevents pathogen from being detected by immune cells.
What does C3a and C5a do?
Enhances inflammation. Chemoattraction by forming complement protein gradient.
3 ways in which bacteria evade complement system?
Cleave complement factors. Inhibit complement convertases. Recruit negative regulators of complement cascade to bacterial surface.
How does the bacterial protease ‘aur’ evade the immune system?
Cleaves C3. Prevents c3a and c3b deposition. Prevents c5a formation. This result in less inflammation, less recruitment of immune cells, less opsonisation and no MAC formation.
What do s.aureus and s.pyogenes produce that degrades complement protein C3?
Aur and SpeB.
Explain how s.aureus inhibits C3 or C5 convertases?
S. aureus produces SCIN protein which binds to C3bBb and inhibits formation of C3 convertase and C5 convertase.
What does inhibition of C3 or C5 convertases result in?
Prevents C3b deposition, C3a formation, C5a formation. This result in less inflammation, less recruitment of immune cells, less opsonisation and no MAC formation.
What does recruitment of complement negative regulators result in?
Inhibits formation of C3 convertase and C5 convertase. Prevents C3b deposition, C3a formation, C5a formation. This result in less inflammation, less recruitment of immune cells, less opsonisation and no MAC formation.
What do TLR detect?
Microbial structures.
What do CLEC receptors detect?
Microbial carbohydrates.
What do FPR detect?
Microbial peptides.
How can neutrophils indirectly detect microbes?
Detect opsonised microbes through their Fc receptors or complement receptors.
What is CXCL8?
Chemokine.
What does S.aureus CHIPs do
Releases CHIPs which binds to C5aR and prevents binding of C5a. This prevents neutrophils moving to the area of infection.
What does S.pyogenes do to inhibit chemotaxis?
Releases SpyCEP which cleaves CXCL8. CXCL8 can’t bind to CXR1/2 and so migration to site of infection doesn’t occur.
How does S.aureus prevent antibody mediated phagocytosis?
They release molecules that bind to Fc receptors on neutrophils and prevent detection of opsonised bacteria. FLIPR targets IgG Fc receptor and SSL5 target IgA Fc Receptor.
What toxins does s.aureus release to kill neutrophils?
PVL Toxin, LukAB, LukDE
