Corey Burke (BIO) cburke at chuma.cas.usf.edu
Thu Mar 21 10:47:38 EST 1996

On 20 Mar 1996, JRicklefs wrote:

> How are vaccine's made?  I know some of them can be made by a weakened
> virus that is infected into a person then that person survives the
> weakened virus then is immune, but this doesn't work with all viruses why?
> When a person is exposed to a weakend virus (some viruses) the immune 
system responds by producing antibodies (Abs) to the invading antigens 
(Ags) which are bits and peices of the virus. After this exposure has 
been delt with the immune system forms memory cells that will quickly 
recoqnize the virus the next time the body is exposed to it. This works 
with some viruses and not others due in part to the fact that viruses use 
the host cells to replicate (DNA, or RNA). Viruses have an unstable genome (DNA or RNA) and are prone to 
mutate, some at a high rate. If you are exposed to a virus (such as the 
flu) this winter your immune system will respond and make memory cells 
for future exposures, but by next winter the same flu virus will have 
mutated and will no longer be recoginzed by your immune system. Still 
other viruses have ways of "tricking" the immune system into thinking 
that they are self cells (HIV actually invades cells of the imune system).

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