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Pathology of Viruses

Ian A. York york at mbcrr.dfci.harvard.edu
Sat Apr 8 09:58:05 EST 1995

In article <Bk28wW7.ksturts at delphi.com> Keith Sturts <ksturts at delphi.com> writes:
>Can anyone explain to a layman what the pathology mechanism is that
>creates 'symptoms' of virus invasion?

	It sort of depends on how much molecular detail you're after.  
Rarely is it known in great detail exactly why a cell is killed.  At the 
level of the host, there are many, many overlapping causes for the 
symptoms one sees.  Here are a few:

(1)  Cell death.  In general, cells infected with a virus ultimately 
die.  There are exceptions, but they are the minority.  The cause of the 
cell death can range from direct lysis by the virus during the egress 
process; inhibition of vital cell processes - eg a recent paper shows 
that polioviruses block glycosylation;  diversion of normal cell 
processes to the process of viral replication and translation; apoptosis; 
and so on.

(2)  Immune response to the virus.  Very often the first symptoms of a 
viral infection are not due to the virus, per se, but to the host 
response to the virus.  If, for example, you give a person a small dose 
of interferon - or many other cytokines - you get a syndrome that looks a 
lot like "the flu".  The symptoms of a cold are primarily those of the 
body's response to the virus.  This also includes misdirected immune 
responses, as for instance the non-neutralizing antibody response which 
causes many problems in feline infectious peritonitis.  

(3)  A combination of 1 and 2.  Specific cytotoxic lymphocytes often 
destroy virus-infected cells. 

(4)  A more general perturbation of homeostasis.  A broad category that 
could include things like the warts induced by papillomaviruses, the 
downregulation of the epidermal growth factor receptor caused by 
adenoviruses, the various soluble receptor analogues expressed by 
poxviruses, tumours, the cytokine homologues expressed by a number of 
herpesviruses, etc etc.  

The question is a good one, but it's almost impossible to answer in any 
detail for viruses in general.  There are too many possibilities.  E mail 
me if you have more specific questions.

Ian York   (york at mbcrr.harvard.edu)
Dana-Farber Cancer Institute, 44 Binney St., Boston MA 02115
Phone (617)-632-3921     Fax  (617)-632-2627

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