HMOs comprise a family of free oligosaccharides with high
structural diversity and represent the third largest group of bioactive
molecules in human milk. Colostrum contains 20e25 g/L of
HMOs, however, further milk production maturation is accompanied
by the decrease of HMOs content to 5e20 g/L [11]. The
composition of oligosaccharides differ between women and vary
over the stage of lactation, diet and other biological parameters
(reviewed in Kunz et al. [12]). Over 200 unique HMOs have been
discovered and more than 100 have been structurally solved and
characterized [13]. The vast majority of HMOs contain a lactose,
polylactosamine or lacto-N-biose core. Further modification by the
addition of differently linked fucose or sialic acids increases their
structural diversity and, in addition, provides resistance against
enzymatic digestion [14,15]. Among the multiple functions of
HMOs which have been described [9,11,16e19], immunomodulation
is one of the most remarkable. The molecules modulate immune
responses indirectly, by changing the infant gut microbiota
composition, and directly, by affecting immune cells on a systemic
level, after entering the blood circulation [20]. The absorption rate
of HMOs from the GI tract has been reported to be about 1% [21]
and their systemic level was suggested to be within the range of
10e100 mg/mL [22], which might be sufficient for the interaction
with cell receptors