In article <4hkfl1$9ic at is.bbsrc.ac.uk>, Mike Whelan <whelan at bbsrc.ac.uk> wrote:
>haviland at KIDS.WUSTL.EDU ("David L. Haviland, Ph.D.") wrote:
>>>I'm curious as to why Herpes infections (such as Zoster) are more severe
>>in adults than in children. Any thoughts? I'm curious as to what
>>differences there may be in adult vs. "pediatric" immune systems. I've
> just a thought, but is it to do with primary versus secondary
>infections? We know that many of the herpes viruses are
>immuno-regulators, for example, ICP47 found in HSV downregulates MHC-I
>via TAP. Consequently, any infection that overcomes these features
>must, by its very nature, be more severe.
[I've cross-posted this to bionet.virology, and set followups back to
bionet.immunology only]
First, I don't think it's a case of primary vs. secondary infections.
Adults infected with VZV for the first time tend to have more severe
responses than do children infected for the first time. The same is true
for some other herpesviruses - e.g. Epstein-Barr virus - but I don't
think it's universally true: I'm not aware of anything suggesting this is
true for herpes simplex, for example (though I may be wrong).
Second, while immunoregulation is almost certainly involved in the
pathogenesis (and incidentally, I'd tend to say that probably all
herpesviruses are immunomodulators, but the specific functions haven't yet
been identified for many) the role of this immunomodulation is not
necessarily predictable. Experience with some other viruses (adenoviruses
and some pox viruses) suggests that removing immune regulatory genes from
the virus can lead (perhaps counterintuitively) to a more severe disease.
I'd tentatively suggest, actually, that one reason for the more severe
disease is the contribution of a more competent immune system in adults
to the symptoms. (This presumes that at least some of the symptoms of
the disease are immune-mediated. I think this is probably true, but I
don't know that it's been looked at very closely.)
There is a reasonable amount of data on neonatal immune systems, and
their difference from adults, but that's not really relevant to this -
here we're talking about immune responses in children under - what? about
4 -5 years of age? I'm not familiar with any studies looking at
differences, but they're probably out there. Grossly, children have
competent immune systems, in that they can respond to infectious agents
in general, vaccines, etc. It might only take a minor change, though - a
slight change in the Th1/Th2 balance, perhaps - to cause fairly dramatic
changes in the host-parasite interaction.
Or, to summarize this post: I don't know.
Ian
--
Ian York (iayork at panix.com) <http://www.panix.com/~iayork/>
"-but as he was a York, I am rather inclined to suppose him a
very respectable Man." -Jane Austen, The History of England
