Toxins and secretion systems 2 Flashcards
General idea of superantigens?
Activate the host immune system without processing by antigen presenting cells
How do superantigens work?
Superantigen “cross-links” MHC II with TCR, regardless of a fitting antigen
Result of superantigen working?
A massive cytokine release, nonspecific response, shock and death (inflammation symptoms)
Strength of normal antigen induced t cell response vs superantigen induced?
Normal = 0.0001-0.001%
Super = up to 20%
Example of superantigen?
Streptococcal toxic shock syndrome
How does Streptococcus pyogenes enter the body?
Via wounds
How does Streptococcus pyogenes cross epithelial barriers
Can cleave host cell junction proteins e.g. E-cadherin using Streptolysin S
What is sepsis?
organ dysfunction due to dysregulated host immune response to infection.
What are AB toxins usually amde up of?
1 A and 5 B subunits
What do the A and B subunits do?
A–> actual toxin
B–> delivers the A subunit into the cell
What does the B subunit of an AB toxin do specifically?
Determines tissue specificity of the toxin.
Toxin can exert its effect at a different body site to where the infecting bacteria are
What toxin does Clostridium botulinum produce?
AB type exotoxin, neutotoxin
How is the AB toxin produced by Clostridium botulinum a neurotoxin?
Blocks NT release
What are the different serotypes of the AB toxin produced by Clostridium botulinum?
8, A-H
What is the mode of action of the botulinum toxin?
It binds to the presynaptic membrane on stimulatory motor neurons and blocks Ach release
What does the action of the botulinum toxin lead to?
Muscle receives no stimulus and so does not contract–> death by suffocation
What is flaccid paralysis?
Muscle receives no stimulus and does not contract
What is the AB toxin produced by Clostridium tetani?
Tetanus toxin, tetanospasmin
WHat happens to the tetanus toxin and the clostridium tetani bacteria that produces it?
The bacteria stays in the wound, but the toxin spreads systematically via the motor neurons (reaches SC)
Where does the tetanus toxin bind?
Specific gangliosides at the terminals of inhibitory neurons
Mode of action of tetanus toxin?
it blocks the release of glycine which would otherwise prevent the release of Ach by motor neurons
Why is glycine released at neuromuscular junctions?
To prevent ACh binding
Result of tetanus toxin action?
Constant ACh release, so uncontrolled muscle contraction–> death by suffocation
Why do bacteria need secretion systems?
Nutrient acquisition, toxin delivery, cell-cell communication, defence mechanisms and virulence factor secretion
