Parasite immune evasion Flashcards
Parasite diversity
Unicellular
Multicellular
Arthropod ecto- and endo-
Toxoplasma gondii
apicomplexan parasite that cycles between cats (definitive host) and other organisms (intermediate hosts)
How can humans become incidental hosts for toxoplasma gondii?
uncooked meat
oocysts shed by cats
Acute toxoplasma gondii
mediated by tachyzoites, which can cross placenta and infect foetus
Chronic toxoplasma gondii
established by cysts containing bradyzoites in tissues, esp. the brain
How can control of tachyzoites be mediated?
interferon-gamma or INF-gamma mechanisms
How does the immune system target cysts?
CD8+ cells
Microglia
Macrophages
Entamoeba histolytica
rhizopod amoeba causing amoebic dysentery and amoebic liver absscesses in humans
Transmission of entamoeba histolytica
food or water contaminated with cyst-containing human faeces
How is immunity against entamoeba histolytica mediated?
In the gut: slgA against lectin expressed on the surface of trophozoites
Trichinella spiralis
Multicellular endoparasite.
Nematode parasite of pigs, rats, and other mammals that can be contracted bu humans from consumption of undercooked pork and horsemeat
Trichinella spiralis locations
Adults reside in the gut, whilst first-stage larvae encyst in the muscle
Immunity to a multicellular ectoparasite
Basophils play essential role in host resistance to ticks
Immune evasion method: safehouse
Intracellular niche exploited by parasites
Variety of immune evasion strategies
Induction of inappropriate Th2 response
Prevention of phagosomal fusion
Attenuation of iNOS pathway
Immune evasion: be quiet and don’t attract attention
Encystation and dormancy (or v slow growth)us a common strategy
Immune evasion: camouflage
Juvenile stage of liver flukes adsorb IgM, preventing eosinophil adhesion
Blood fluckes can like for >20 years in definitive host; cover outer layer w host antigens
Immune evasion: keep changing disguise
Outer membranocalyx of adult schistosoma mansoni has a half life of five days & composition of membrane proteins and glycans changes over time
Immune evasion: neutralise any threats
Avoidance of complement cascaded by surface components
IgG digestion by cysteine proteases
Digestion of eotaxin (eosinophil chemokine) by a metalloprotease
Immune evasion: false info
Cystatins (cystein proteinase inhibitors) are secreted by several nematodes, preventing processing of APCs
