Superinfection question

[James Gibbs]

: In a previous article, mdcabl at cc.newcastle.edu.au () says:

: >Hi all,
: >Just wondering.  What happens when two different species of virus
: >attempt to infect the same cell? Is there still a block on superinfection? I
: >especially wonder if perhaps a cytoplasmic virus can replicate in the same cell
: >if it already has an retro virus infection like AIDS.  I have been told that
: >non-HIV viral infection in AIDS pateints is a problem.  Are the two viruses
: >competing for the same cells or just finding different parts of the host to
: >replicate in?  Finally has anyone researched how viruses which co-exist in the
: >same host compete against each other, if at all?  I couldn't find anything on
: >medline on this.  Any theories or speculations are welcome.
: >Cheers,
: >Allen Black
: >Dept. of Pathology
: >Univ. of Newcastle
: >

Since you didn't get any other replies that answered your question, I'll 
take a shot at it. There is a distinct block to superinfection that is 
produced by retroviruses. This block is specific for retroviruses that 
use the same receptor, so that if two retroviruses use the same cellular 
receptor, infection with one will effectively block superinfection with 
the second. However, if the two retroviruses use different receptors, 
there will be no block to superinfection and both can infect the same 
cell. The block to superinfection with retroviruses is due to 
downregulation of the receptor molecule on the surface of the cell. In 
the case of HIV, prior infection with HIV will down-regulate surface CD4 
receptor, but will not, to my knowledge, interfere with superinfection 
with other viruses. The caveat is that cells infected in vitro can 
undergo considerable cytopathic effects that will in general interfere 
with general metabolism of the cell (i.e. the cell is dead) and this 
would probably inhibit replication of all viruses. The cytopathic effects 
of HIV in vivo is nowhere near as extreme, so I doubt there would be much 
interference with superinfection of non-HIV viruses.

--
Jim Gibbs                                         gibbs at fas.harvard.edu
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