Infetion 4 Flashcards
(27 cards)
How may our bodies deal with intracellular pathogens?
Cause the infected cells to undergo apoptosis
Main immune evasion categories?
Stealth, subversion, avoidance/resistance
SSAR
What is immune evasion - stealth?
avoid triggering response, avoid the pathogen being recognized by the immune system
What is immune evasion - subversion?
manipulate, divert, dampen responses
What is immune evasion - avoidance/resistance?
Targets are varied to avoid recognition. In some cases, there may be direct destruction of immune effectors.
Examples of immune evasion beginning during initial attachment?
EPEC forming a pedestal, keeping the bacteria away from the hosts cell surface
Biofilm–> protective extracellular matrix
What are defensins?
host secreted antimicrobial peptides
Designed to kill bacteria entering crypts to protect stem cells and avoid infection
How do defensins work?
Bind to bacterial membrane based on the -ve charge, and either punch holes in the membrane or are internalised and kill the cell from within
Two ways that defensins can kill a bacterial cell?
Form pores in the cell membrane and rupture the cell
Enter the cell and inhibit cellular functions, killing the cell
How doe EPEC deal with anti-microbial peptides?
Outer membrane protease (OmpT) production
Key mechanism of bacterial stealth?
Form an extensive polysaccharide capsule around the cell
How does a polysaccharide capsule provide the bacterial cell with stealth?
It hides many of the features on the bacterial cell surface that the innate immune system would recognise
Where may the genes for a capsule be?
Pathogenicity island
How does Klebsiella evade phagocytosis?
It’s capsule has sialic acid residues which mimic host cells
How does Klebsiella evade antimicrobial peptides?
The capsule binds them and prevents them from reaching the target site on the CSM
How does Klebsiella evade complement?
The antibodies bind to the capsule, not the CSM
How does Klebsiella evade the inflammatory response?
Shields antigens (like lipopolysaccharide) from immune receptors
What is phase variation?
A reversible, but heritable form of gene switching, often for surface antigens
How does phase variation help avoidance?
Some proteins, which are required for cell function but are also recognised by the immune system may be randomly switched off to evade the immune system
What is antigenic variation?
Permanent rearrangement of antigen genes, causing a change in structure
How does Neisseria meningitidis carry out antigenic variation?
Has many diff (silent) pili loci which can recombine with the variable region in the main pili genes, causing antigenic variation
Main difference between antigenic variation and phase variation?
Antigenic variation is more permanent
WHy does salmonella activate pro-infammatory response?
Inflammation loosens tight junctions and attracts neutrophils into the gut lumen
Why does salmonella want neutrophils in the gut lumen?
Neutrophils attack microbial cells (competitors of salmonella) in the gut lumen
