Dear Pat,

     Tell your ped that SIgA has been found excreted unchanged in the stool of
breastfed babies, strongly implying that it is not digested by the gut.   Tell
her to read:  Goldman, A.S. et al, "Immunologic Protection of the Premature
Newborn by Human Milk"  Seminars in Perinatology, Vol. 18, No 6. p. 495.
Better yet, tell her to read all of Vol 18 since it is devoted to
breastfeeding (especially the preterm infant).
     Probably most of the protective effect of breastmilk is from coating of
mucosal surfaces against pathogens.  The article states "there is no proof
that ingested secretory IgA antibodies are absorbed into the circulation."

     Hope this helps,

     Cindy Neary