JC Virus and PMLeukoenkephalopathy

Ian A. York york at mbcrr.dfci.harvard.edu
Thu Nov 17 12:36:45 EST 1994

In article <3ag0cj$rca at mserv1.dl.ac.uk> n.panjwani at ic.ac.uk writes:
>I have come across mention that JC Virus and BK Virus, (which cause PML and
>Haemorrhagic Cystitis, respectively on reactivation/reinfection), are
>reactivated by pregnancy. I have no idea how pregnancy can cause
>immunosuppression, so perhaps the cause is hormonal. Can anyone shed light
>on how pregnancy reactivates latent human polyomaviruses (JCV and BKV)

 	The viruses can indeed reactivate during pregnancy (see: Journal of
Virology  65(8):4515-9, 1991; Journal of Medical Virology  41(1):11-7,
1993) although I think that it is neither a common nor a serious
complication of pregnancy. 
	It isn't clear to me (warning: I'm not an expert on the viruses or
on pregnancy) why the reactivation occurs.  There is some degree of
immunosuppression in pregnancy as a rule (see: Journal of Clinical
Endocrinology & Metabolism 74(3):645-53, 1992; Medical Hypotheses
35(2):159-64, 1991;  Research in Immunology 141(2):175-81, 1990) - however
this immunosuppression is slight, and is not to be considered in the same
category as other reasons for JC and BK virus reactivation (e.g. 
transplant immunosuppression, AIDS).  It seems to me from the little
reading I've done on this that the amount of immunosuppression may be
quite variable depending on regions of the body - i.e. a number of studies
have shown quite profound immunosuppressive factors in cell culture,
whereas overall immune parameters look pretty normal - and, of course,
there is a very specialized and profound suppression of the immune
response to the fetus, which can be considered an allograft.  I wonder
whether there might be a localized defect in immune regulation at the site
of viral latency for these viruses.  This is speculation, though. 
	Hormonal reactivation is also possible, but I don't know much 
about that - there are certainly hormone-responsive viruses (Moloney 
Mammary Tumour Virus of mice, e.g.) but I don't know that the polyoma 
viruses respond that way.

Ian York   (york at mbcrr.harvard.edu)
Dana-Farber Cancer Institute, 44 Binney St., Boston MA 02115
Phone (617)-632-4328     Fax  (617)-632-2627

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