Microbial Immune Evasion Mechanisms Flashcards
What is balanced pathogenicity?
Properties of microbe vs properties of host
What are the properties of microbe?
Adhesins
Toxins
Capsule
What are the properties of the host?
Natural barriers
Defensive cells
Antibacterial peptides
Innate and adaptive immune responses
What are the two virulence factors?
Adhesins and toxins
What do adhesins promote?
Colonisation and adhesion
What do toxins promote?
Tissue damage
What are the facets of pathogen evasion of complement?
Failure to trigger
Negative binding
Disrupt regulation
Block/expel MAC
What do leucocidins do?
Kill pathogens
How does staphylococci stop opsonisation?
Produces protein A
Binds to the Fc portion of IgG
How do intracellular pathogens evade phagocytosis?
Promote own uptake
Inhibit phagosome-lysosome fusion
Escape phagosome-lysosome into the cytoplasm
Resist oxidative killing by producing catalases/peroxidase
How can intracellular pathogens promote their own uptake?
CR3 or mannose lectin receptor
How do pathogens conceal antigens?
Hide inside cells
Block MHC antigen presentation
Surface uptake of host molecules
How can pathogens cause immunosuppression?
Downregulation of MHC and receptors
Increase in apoptosis and leading to a cytokine switch of IgA proteases
What happens if streptococcus pneumoniae enters the lungs?
Bypasses surfactants
Cause inflammation in the lungs and damage endothelial cells
What are the mechanisms for evasion of the adaptive immune response?
Concealment of antigen
Immunosuppression
Antigenic variation
Persistence/latency/reactivation
How do viruses evade the immune system?
Latency
Decrease in antigenic presentation
Decrease in MHC expression
Mutation of epitopes
Which viruses evade by latency?
VZV
Herpes simplex
Which viruses decrease antigenic presentation?
Herpes simplex
Which virus decreases MHC expression?
Cytomegalovirus
What epitope mutations happen?
B cell - neutralisation by antibody escape
T cells - CD8+ escape mutants of HIV
What are the antigenic variation phenotype changes that take place?
Colony morphology Virulence Serotype loose flagella Change surface sugars
What does antigenic diversity produce?
Genetically stable and alternative forms of antigens in a population of microbes
What does antigenic variation produce?
Successive expression of alternative forms of an antigen in a specific clone or its progeny
What is phase variation?
On/off an antigen at low frequency
When does antigenic variation occur?
During course of infection in an individual host
Why does influenza have a high potential for variation?
Many types of surface proteins and a segmented genome
