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This is my non-medical profession guess:
I believe that one of the theories explaining the 'viral trigger' for celiac
disease was the similarity of protein sequences between a particular virus
protein and  wheat gliadin protein.  If this was true, you would produce IgG
that would recognize both the gliadin and the virus.  In the absence of gliadin
I would speculate that if you were subsequently exposed to or infected with the
original virus again you might stimulate the production of antibodies that you
'learned' to make against gliadin and the blood test would pick this up.
 
As long as I'm here I've got one other observation to share:  Long before we
knew about celiac it was traditional medicine in our family that loose bowel
movements (especially during a stomach virus episode) could be corrected with
steamed rice or rice water (or bananas and browned apple slices).  Is it
coincidence that these are all gluten free?  Or is it a clue to a problem with
gluten sensitivity of varying degree in the general population?
 
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