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Parasite/pathogen
Evasion mechanisms
| Question | Answer |
|---|---|
| What are evasion and manipulation? | - host defences are blocked - host phenotype changes |
| What is passive evasion? | - where no parasite-bourne moleules are secreted - there are a number of mechanisms that may be employed |
| What is hiding and mimicry? | - way to avoid detection ie. Schistosomiasis possess a tegument, shown to utilise surface molecules that share glycosylation patterns with their host hemocytes |
| What is antigenic variation? | - variant surface glycoproteins change identity and protect invariant surface antigens from immune recognition - individuals may be detected and killed but the population survives due to stochastic switching of antigen coat - ie. African trypanosomes |
| What is antigenic shift? | - two or more different strains of a virus mix to form a new subtype with a mix of the antigens on its surface |
| What is antigenic drift? | - where a virus gradually changes its surface proteins allowing it to invade a host system over time |
| What is quiescence and capsule formation? | - dormancy/inactivity (seen in bacteria and viruses) - in bacteria: protection mechanism against antibiotics and may from polysaccharide capsules to escape phagocytosis - in viruses quiescence reduces viral protein production |
| Toxoplasma: a case study | - most carry it -128 copies produced, cell lyses and infects another - cysts occasionally break and cause a wave of infection, causing a light flu but eventually becoming asymptomatic - only a problem for the immunocompromised and fetuses |
| What is active interference? | - the parasite produces molecules that directly interfere with host machinery ie. Interference with recognition Block the hosts regulatory network Distort essential cellular function – e.g. apoptosis Impede actions of effectors |
| What are decoy molecules? | ie. orthopox viruses - the type I interferon response involves a family or pro inflammatory cytokines that help control virus infections, they are secreted from infected cells |
| - secrete soluble proteins that bind to interferon I proteins with high affinities to reduce antiviral action and prevent infected cells signaling to healthy cells | |
| What is deactivation? | - schistosomes also mimic host production of immune cell inactivating hormones - this renders lethal hemocytes inactive and harmless |
| What are injecting effectors? | Some bacteria have type III secretory (T3SS) systems which inject effector molecules into cells |
| ie. Bordetella pertussis (whooping cough) - uses T3SS to inject effector molecules into cells stimulating anti-inflammatory interleukin-10 (IL-10), blocking neutrophil recruitment | |
| How do manipulate signalling networks work? | IL-10 is an important negative regulator of inflammation (so neutrophil response), T cell responses and dendritic cell maturation (so antigen presentation and adaptive immunity coordination) - prime target for parasites |
| Viruses for HIV, Hepatitis B and Hepatitis C all stimulate IL-10 production Viruses for Herpes and pox viruses also create their own versions |
Created by:
rose.coo
Popular Ecology sets