microbial immune evasion mechanisms Flashcards
how may pathogens resist complement
LPS layer and capsule prevent complement from binding = failure to start cascade.
some bacteria coat themselves with IgA (which doesnt fix complement) = failure to start cascade
what is phagocytosis
primary mechanism by which pathogens are dealt with. generally done via opsonisation.
engulf bacteria
how may bacteria combat phagocytosis
producing leucocidins (kill leukocytes) express protein =binds to Fc of IgG .'. prevent opsonisation block contact of opsonins via teh capsule
how do intracellular pathogens (eg bacteria living in macrophages) evade the immune system
inside macrophage .’. immune system cant reach
promote own uptake
prevent phagolysosome fusion: .’. not killed
escape phagolysosome .’. get into cytoplasm
produce catalses/perioxidase .’.resists oxidative kiling
how may microbes evade the adaptive immune system
Production of Fc Receptors by Microbes Concealment of Antigen: Immunosuppression Antigenic variation Persistance/latency/reactivation
how does microbial Fc receptors allow for evasion of the adaptive immune system
certain pathogens have genes -> express Fc on their own surface .’. microbe can bind antibodies the wrong way around .’. antibody cannot opsonise properly
how does microbial concealment of antigen allow for evasion of the adaptive immune system
microbe conceals itself .’. not recognised by immune system .’. microbe can divide etc
does this by: hidiing inside cells/in privledged sites, `blocking antigen MHC presentation
how does immunosuppression by the microbe allow for evasion of the adaptive immune system
intracellular organsms inhibit MHC-antigen expression
lots of intracellular bacteria and viruses can decrease receptors on surface of cells or induce/prevent apoptosis
can alter TH1/2 balance of the immune system
how does antigenic variation of the microbe allow for evasion of the adaptive immune system
overcomes adaptive immunity by having different antigens that allow multiple strains to exist in a population and continue infection
what is streptococci Pneumonia
causes pneumonia and is a gram +ve bacterium
pathology of streptococcus pneumoniae
transmites via aerosol. enters nasopharynx and start to colonise. here.
it can cause middle ear infections. can be inhaled into lungs
how does S. Pneumoniae evade immune mechanisms of the nasopharynx
releases adhesins that bind to cell surface molecules and release sIgA proteases to break sIgA that is present in the mucous
how does S. Pneumoniae evade immune mechanisms of the lungs
lung has tight epithelial junctions, surfactant and some antimicrobial peptides
bacteria release sIgA proteases. also releases Pneuomolysin (toxin) causing lysis of epithelial surface of the lungs
immune defences in the lung
tight epithelial junctions, surfactants (acts like mucus) and some anti-microbial peptides.
how does S. Pneumoniae evade the adaptive immune response
hard for phagocytosis due to capsule surrounding it
Have teichoic acids on their surface = inflammation damaging the lung
coninuing damage to lung -> pneumonia and see dead neutrophils, pus, dead tissue accumulate. all this damage means bacteria can access the blood .’. bacteraemia
how does S. Pneumoniae evade the adaptive immune response
hard for phagocytosis due to capsule surrounding it
Have teichoic acids on their surface = inflammation damaging the lung
coninuing damage to lung -> pneumonia and see dead neutrophils, pus, dead tissue accumulate. all this damage means bacteria can access the blood .’. bacteraemia
what kind of immunity is needed to combat viruses
are intracellular pathogens so the cell-mediated immunity is required to combat them.
how do viruses evade the immune system
latency; decrease antigenic presentation whilst inside cells; decrease MHC expression; MMC mimics
what is the immune strategy - persistence
it will lay latent and then when it reactivates it can be shed and infect new naive individuals.
how do viruses decrease antigenic presentation whilst inside cells
eg herpes simplex prevents peptides being transferred by MHC by binding and inhibiting TAP
how do viruses decrease MHC expression
Cytomegalovirus (CMV) can do this, CD8+ cells don’t know that the cell is infected
how do viruses evade the immune system - MHC mimics
produces molecules that mimic the normal MHC
How do MHC 1 work
all nucleated cells express MHC1, is scanned by CD8+. If MHC1 = self-peptide nothing happens. If infected with virus then MHC will hold viral peptides, recognised by CD8+ .’. becomes CTL and kills infected cell
what is an NK cell
natural killer cell work by generically detecting MHC on cell surface (which tells that cell is healthy
