up and down regulation of parasites

Meißner Markus meissner.markus at t-online.de
Wed Apr 26 13:28:44 EST 2000


Helmut Gieseke schrieb:
> 
> Can anyone give information on up-regulation of Parasite (by the host) that
> ensures survival?  It is written that Toxoplasma down-regulates and forms
> tissue cysts when the Host produces an immune response.  If the parasite did
> not do this, it could kill the host quickly (down-regulation increases
> Toxoplasma's opportunity to infect another host).  Is there an example of
> the opposite = the parasite up-regulates (caused by the host's immune
> response or some other reaction by the host) and its survival/reinfection
> successes are increased.  Many thanks.
> H. Gieseke
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> ---


You´re right that Toxoplasma gondii builds tissue cysts, but this is not
a real down-regulation. The parasite rather differentiates into slow
growing Bradyzoites (the fast growing life stage is called Tachyzoite).
In this stage the parasites protein expression pattern is changed, that
means some genes are downregulated and other certain genes are
upregulated.
True is that this is a strategy to escape the hosts immune response but
without this differentiation the parasite would not kill an
immunocompetent host but would be completely removed from the host.
Only in immunodeficient hosts the parasite is capable of killing the
host. This is the case in HIV-patients where the tissue cysts in the
brain start to differentiate into the fast growing Tachyzoites. Sincfe
the immunesystem of this patients is not able to remove them anymore the
parasite will kill the host. 

Well, I hope I was able to answer Your questions......
Sincerly Yours,
Mark






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