Terminal glycotope expression on milk fibronectin differs from plasma fibronectin and changes over lactation

Fibronectin (FN) is a multifunctional glycoprotein appearing in various glycovariants with potential biological activities. Using lectins we analyzed the expression of terminal glycotopes on human milk fibronectin over lactation and compared it with that of the mother's plasma.

FN concentration and relative amounts of its fucosylated and sialylated glycovariants as well as O-glycans were analyzed in early colostrum, colostrum, transitional and mature milk samples of 132 healthy mothers by lectin-FN-ELISA using α2,3- and α2,6-sialic acid, α1,2-, α1,3-, and α1,6-fucose, and sialyl-T, asialyl-T and Tn antigen specific biotinylated Maackia amurensis, Sambucus nigra, Ulex europaeus, Tetragonolobus purpureus, Lens culinaris, Artocarpus integrifolia, Arachis hypogaea, and Vicia villosa lectins, respectively.

FN concentration was almost unchanged during human milk maturation and was about 150 times lower than in plasma of lactating mothers. Milk FN elicited significantly higher expression of sialylated glycotopes including sialyl-T antigen than plasma FN, and contained fucose-linked glycans, as well as T and Tn antigens absent in plasma FN. With milk maturation the expression of α2,6-sialylated, sialyl-T, α1,6- and α1,2-fucosylated epitopes decreased in transitional milk compared with colostrum, whereas that of asialyl-T antigen increased. The expression levels of α2,3-sialyl- and α1,3-fucosyl-glycotopes and Tn antigen on FN were low and did not change over lactation.

The expression of terminal sugars on milk FN is different from that of plasma FN of the lactating mother and is associated with milk maturation. The analysis of degree of milk sialylation and fucosylation should be considered during control of biochemical quality of milk collected in milk banks.