Human alpha-lactalbumin and bovine beta-lactoglobulin absorption in infants.

We investigated gut permeability to human alpha-lactalbumin (ALA) and bovine beta-lactoglobulin (BLG) in 20 infants from birth to 8 months or until weaning, before which they were on a strictly cow's-milk-free diet. We measured the proteins with a sensitive, solid-phase, double-sandwich immunofluorometric assay. Median (range) levels of serum ALA on days 3-4 after birth, and at 1 and 2 months of age were 31 (12-225), 6 (0-55), and 2 (0-16) micrograms/l serum per g ALA given per kg body weight, respectively. At 3, 5, and 8 months of age, only trace amounts of ALA were found. One week after weaning, serum BLG was found in 5/13 infants (38%) and at 2 weeks in 3/14 infants (21%), with median concentrations of 7 and 4 micrograms/l serum per g BLG given per kg body weight, respectively. No ALA could be detected in any of these samples. In absorption of ALA, the four infants who had allergic symptoms did not differ from those without symptoms. Thus, systemic absorption of ALA and BLG does occur in infants. Absorption of ALA is greatest after birth, when 3 x 10(-4) (median) of the given antigens are absorbed, but absorption decreases rapidly. The gut may often be transiently permeable to BLG when cow's-milk-based formula is started.