immune evasion Flashcards
mode of action of neutrophils?
bacteria enter
opsonisation
complement triggered
gradient of c3a and c5a and bacterial proteins formed
c3a and c5a bind to receptors, ICAM is expressed on endothelial cells
causes neutrophils to adhere to blood vessel surface
migrates across blood vessel and gets primed by bacterial products
chemotaxis
activation
then either:
phagocytosis
degranulation- release of reactive oxygen species, can kill bacteria
then inflammation
staphylococcus aureus gram stain, characteristics?
gram positive, grape clusters, spherical bacteria. commensal and lives harmlessly in nose of 30% human population
can cause skin infections to more severe diseases
streptococcus pyogenes gram stain, characteristics?
gram positive, spherical, chains
commensal in the throat
can cause pharyngitis, skin infections, scarlet fever and sepsis
what is antibody opsonisation?
binding of antibodies to bacterial antigens allowing:
deposition of complement in the classical complement pathway
neutrophils and other phagocytes to detect invading microbes
how do bacteria subvert opsonisation?
HIDE ANTIGENS: bacteria can have a capsule on their surface - hides antigenic structures
DISRUPTS FUNCTION: Spa and M surface proteins can bing antibodies via their Fc region rather than the Fav region- prevents normal opsonisation
DEGRADE ANTIBODIES: proteases can cleave or modify antibodies
PREVENT DETECTION
MODIFY ANTIGENICITY
pathogenic bacteria which can express capsule?
s. aureus, s. pyogenes, E. coli
(pseudomonas aeruginosa, s. pneumonia, s. agalacticae)
What is complement opsonisation?
the complement system is composed of many proteins which interact to opsonise pathogens or directly kill them by MAC formation
hat are the key steps of the complement cascade?
- initiation
- formation of C3 convertase
- formation of C5 convertase
- MAC formation
how do bacteria disrupt the complement cascade?
- degrade complement components
- inhibit convertases
- recruit host-derived regulators (fH, C4BP)
- inhibit complement components
what does protein SpeB do?
degrade C3- prevents C3b deposition, C3a formation and C5a formation
what does SCIN s.aureus protein do?
binds C3bBb and inhibits formation of C3 converts and C5 convertase, preventing C3b deposition and C3a and C5a formation
what do immune receptors do?
detect microbes/microbial products, leading to activation/priming of neutrophils
What receptors do conserved microbial structures bind to?
TLR
what receptors do microbial carbohydrates bind to?
CLEC
receptors do formulated peptides bind to?
FPR
