>Background: Human milk provides a multitude of glycoproteins, including highly glycosylated α-1-acid glycoprotein (AGP), which elicits anti-inflammatory and immunomodulatory properties. The milk AGP glycoforms may provide the breastfed infant with a wide range of biological benefits. Here, we analyzed the reactivity of O-linked sugar-specific lectins with human milk AGP over the process of lactation and compared the results with those of the lactating mother's plasma.>Materials and Methods: Relative amounts of human skim milk AGP O-glycans were analyzed in early colostrum, colostrum, and transitional and mature milk samples of 127 healthy mothers by lectin–AGP enzyme-linked immunosorbent assay using sialyl T (sialyl-α2,3/α2,6 Galβ1,3GalNAc-), asialyl T (Galβ1,3GalNAc-), and Tn (GalNAc-) antigen-specific biotinylated Artocarpus integrifolia (Jacalin), Arachis hypogaea (PNA), and Vicia villosa (VVA) lectins, respectively.>Results: Milk AGP elicited high expression of Jacalin- and PNA-reactive glycotopes and low expression of VVA-reactive glycotopes, which were absent on plasma AGP of lactating mothers and healthy individuals. The expression of sialyl, asialyl T, and Tn glycotopes of human milk AGP was lactation stage related. The relative amount of Jacalin-reactive AGP glycotope was highest in the colostrum samples and then decreased starting from Day 8 of lactation. In contrast, an increase of the relative amount of PNA-reactive glycotope with milk maturation was observed. The relative amount of VVA-reactive glycotope remained almost constant over the development of lactation.>Conclusions: Milk AGP differs from mother's plasma AGP by the presence of O-linked sialylated and asialylated T as well as Tn antigens. The variation of the expression of sialylated and asialylated T and Tn antigens on AGP is associated with milk maturation.
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