Bacterial Immune Evasion Flashcards
What is a pyogenic disease?
one that causes pus to be produced
What are pyogenic diseases mediated by>
Hydrolytic enzymes and cytotoxins
What are systemic diseases mediated by?
Toxins
What hydrolytic enzymes does S. auerus have and what do they cause?
Lipases, nucleases and hyalauronic acid - cause tissue destruction
How is chemotaxis inhibited by S. Aureus?
S. Aureus expresses CHIPS protein which binds to C5R and FPR (formlyated protein receptors) which means C5a and FP cannot bind, and therefore neutrophils cannot migrate up the gradient
what are the three methods of evading antibody opsonisation?
Hide antigens
Disrupt antibody functions
Prevent detection
How does staph Aureus hide its antigens?
S. Aureus has a capsule which helps to hide the antigenic structures that can be detected by the immune system
How does S. aureus prevent detected by antibodies?
Has SSL10 - a secreted protein which binds to the Fc region of IgG which prevents the Fc receptors on neutrophils from detecting IgG on the surface of the bacteria molecule
How does S. aureus disrupt antibody function?
SpA binds to the IgG Fc region instead of their Fab region, which prevents normal opsonisation thus disrupting the normal function of the antibodies
What are the four key steps in the complement cascade?
- Initiation
- Formation of C3 convertase
- formation of C5 convertase
- MAC formation
What are the 4 ways in which S. aureus evades complement opsonisation?
- Inhibit the complement convertases
- Inhibit C3 processing
- Inhibit MAC formation
- Degrade complement components
What protein binds to C3bBb and prevents the formation of C3 convertase and C5 convertase?
SCIN
How does S. aureus inhibit complement convertase?
SCIN protein binds C3bBb and inhibits the formation of C3 convertase and C5 convertase
Which S. aureus protein binds C3d in C3 to induce a conformational change?
Efb protein
when Efb protein binds C3d region of C3, what effect does this have?
induces a conformation change and prevents the binding of factor B to C3, so no C3bBb can be made
All three complement pathways result in what?
The formation of C3 convertase
What is a key step in the complement system?
The deposition of C3b on the surface of the microbe
What does the deposition of C3b on the microbe allow?
The detected of the microbe by certain receptors on neutrophils / phagocytes