Immune Evasion Flashcards
(21 cards)
what constitutes our immune response?
neutrophils
eosinophils
basophils
dendritic cells
macrophages
function of neutrophils?
perform effector functions –> kill microbes
most abundant leukocyte in blood
why must neutrophil responses be balanced?
to prevent infection, but also prevent damage to host
steps of how neutrophils work?
1) microbes enter body and become opsonised with antibodies and complement
2) results in production of gradient of C3a and C5a as well as bacterial proteins and peptides
3) C3a and C5a bind to their receptors on endothelial cells which causes endothelial cells to express ICAM at their surface
4) when neutrophils contact endothelial cells they detect this increase in ICAM, roll along surface and then transmigrate across endothelial layer
5) they become primed by gradient of c3a and c5a
6) migrate towards complement components and bacterial proteins via chemotaxis
7) become activated and perform effector functions -> can be phagocytosis or degranulation
8) neutrophils also recruit other immune cells
what is staph. aureus?
gram positive bacteria which is commensal and lives harmlessly in some humans
OPPORTUNISTIC so has the ability to cause minor-severe infections in some people
s.pygogenes?
gram-positive
can live harmlessly in the throat of humans
also opportunistic, can cause a range of disease e.g. skin infections
antibody opsonisation?
antibodies bind to bacterial antigens which allows:
deposition of complement
neutrophils and other phagocytes the ability to detect invading microbes
capsule polysaccharide?
one of the ways how bacteria evade antibody opsonisation
bacteria express capsule on their surface
this capsule hides antigenic structures that would be detected by antibodies
surface proteins
Spa (protein A) and M surface proteins bind antibodies via Fc region but not Fab region
this prevents normal opsonisation
neutrophils cannot detect S.aureus or S.pyogenes
proteases?
another method to evade antibody opsonisation
proteases cleave or modify antibodies
this prevents normal opsonisation and therefore neutrophils cannot detect s.pyogenes
what are the 3 mechanisms via which the bacteria can evade antibodies?
capsule expression
inhibit antibody opsonisation
degrade antibodies via proteases
antigenic variation?
switching up the antigens expressed at surface
complement opsonisation?
made up of a large number of proteins that react with one another to opsonise pathogens or directly kill them via MAC formation
steps of complement cascade?
1) initiation
2) formation of C3 convertase
3) formation of C5 convertase
4) MAC formation
degradation of C3?
a method of evading complement opsonisation
proteases degrade C3
prevents cascade
C3b not deposited
C3a not formed
C5a not formed
inhibition of C3/C5 convertases?
SCIN protein binds C3bBb and inhibits formation of C3 convertase and C5 convertase
This again, prevents:
C3b deposition
C3a formation
C5a formation
recruitment of negative regulators?
e.g. factor H
these inactivate C3b
three strategies of bacteria complement evasion?
degrade C3
inhibit complement convertases
recruit negative regulators
how do neutrophils sense and respond to their environment?
express hundreds of different immune receptors at their surface, secretory vesicles and granules
these receptors enable them to sense and respond to their environment
how do immune receptors detect bacteria?
directly detect microbes or microbial products e.g.
conserved microbial structures (via TLR receptors)
microbial carbohydrates (via CLEC receptors)
formylated peptides (via FPR receptors)
indirect detection of bacteria
microbes can become opsonised by antibodies or complement
neutrophils detect opsonised microbes through Fc receptors or complement receptors
