IMMUNE EVASION Flashcards
why must neutrophil responses be balanced
prevent infection+prevent damage (inflammation) to host
what is staphylococcus aureus?
.A gram positive bacterium
.minor skin infection
.severe/life threatening disease
how does S.aureus avoid detection?
S. aureus expresses capsule on its surface
This helps to hide antigenic structures that can be detected by innate and adaptive immune components, such as complement and antibodies
Spa surface protein binds antibodies via their Fc region not their Fab region
Spa prevents normal opsonisation, and therefore neutrophils cannot detect S. aureus
Other bacteria express surface proteins that bind antibodies including:
streptococcus dysgalactiae (Protein G binds IgG) Peptostreptococcus magnus (protein L binds IgG) Streptococcus agalactiae (beta protein binds IgA)
what is SSL10
A SECRETED protein which binds to the Fc region of IgG
SSL10 prevents the Fc receptors on neutrophils from detecting IgG on the surface of S. aureus
What do multiple proteins do in order to achieve immune evasion?
1) hide antigens
2) distrupt functions
3) prevent detection
how is antibody opsonisation prevented?
.
1) Hide antigens
2) Disrupt functions
3) Prevent detection
4) Degrade antibodies
5) Modify antigenicity
what is complement opsonisation
complement system is comprised with large number of proteins which react with one another to opsonise pathogens or directly kill them by membrane attack complex formation (MAC)
what are the key stages in the complement cacade?
Initiation
Formation of C3 convertase
Formation of C5 convertase
MAC formation
how does S.aureus evade bacterial opsonisation?
S. aureus SCIN protein binds C3bBb and inhibits formation of C3 convertase and C5 convertase
This prevents
C3b deposition
C3a formation
C5a formation
S. aureus Efb protein binds C3d in C3 which induces …..
conformation changes
what prevents binding of factor B to C3 and C3dg binding CR2
S. aureus Efb protein binding to C3d in C3 which induces conformation changes.
what other bacteria release proteins binding to C3
M.catarrhalis (UspAs)
what proteins inhibit complement convertases
SCIN,Efb
what proteins inhibit C3 processing
Efb, Ecb,Sbi
what proteins inhibit MAC formation
SSL7
Bacterial proteins prevent C3b/MAC deposition by:
1) Inhibit C3/C5 convertases
2) Bind complement factors and prevent their processing (INHIBITION)
3) cleave component factors (DEGRADATION)
4) acquire host-derived complement regulators
How do neutrophils sense and respond to their environment?
.Expression of many immune receptors at their surface/secretory vesicles(SV) and granules
. immune receptors sense+respond to environment
what can neutrophils detect?
.microbes
.microbial products
.self proteins
What are pathogen recognition receptors (PRRs)
Receptors that directly detect microbes or microbial products leading to neutrophil priming/activation
what detects conserved microbial structures?
TLR receptors
what do TLR receptors detect?
conserved microbial structures
What detects microbial carbohydrates?
CLEC receptors
what do CLEC receptors detect?
microbial carbohydrates
