Alterations of N-glycan branching and expression of sialic acid on amniotic fluid alpha-1-acid glycoprotein derived from second and third trimesters of normal and prolonged pregnancies

BackgroundAlterations in the AGP glycoform pattern are not only disease related, but also can occur during physiological processes such as pregnancy. In this paper, possible changes in human amniotic fluid AGP glycan branching and in the type of sialic acid glycosidic attachment to glycans were analyzed with regard to different stages of human pregnancy.MethodsCrossed-affinity immunoelectrophoresis with concanavalin A was used to study AGP branching and lectin–ELISA with two agglutinins from Maackia amurensis and Sambucus nigra was applied to differentiate α2,3 and α2,6 type sialic acid attachments.ResultsDespite almost unchanged levels of total amniotic fluid AGP during pregnancy, alterations in N-glycan branching and in the expression of sialic acid linkage on AGP were found to be associated with different stages of normal pregnancy. Amniotic fluid AGP glycans derived from third trimester compared with those from the second trimester had a higher percentage of tri- and tetra-antennary sialylated N-glycans. In the second trimester, sialic acid α2,6 linkage occurred twice as frequently as α2,3 linkage, while during the third trimester α2,3 linkage increased and both types of linkage appeared in equal proportion.ConclusionsBranched and α2,3-sialylated AGP glycoforms in amniotic fluid could contribute to natural innate fetomaternal defense.