A study on the microheterogeneity of alpha-fetoproteins produced by yolk sac and germ cell tumors

It is generally believed that the lower the grade of differentiation of glycoprotein-producing cells, the more often modification by bisecting N-acetylglucosamine (GlcNAc) or fucose (Fuc) at the sugar chain of the glycoprotein or increase in branching of side chains occurs. We examined the characteristics of the alpha-fetoprotein (AFP) sugar chain stored in amniotic and exocoelomic fluid during 5-9 weeks of gestation and analyzed serum-derived AFP of patients with germ cell tumors.

Total AFP concentrations in embryonic fluid at 5-9 weeks of gestation (n = 11) and serum of patients with germ cell tumors (n = 7) were measured using a radioimmunoassay (RIA) method. The percentages of AFPs reactive with Lens culinaris agglutinin (LCA), concanavalin A (Con A), erythroagglutinating phytohemagglutinin-E4 (E-PHA) and Ricinus communis agglutinin-120 (RCA 120) were obtained by lectin-affinity electrophoresis coupled with antibody-affinity blotting.

It was revealed that at 5-9 weeks of gestation, AFP variants that had been modified by the Fuc residue, which bound to the GlcNAc residue at the reducing end of the sugar chain, and bisecting GlcNAc residues gradually decreased as pregnancy advanced; however, the presence of N-acetylneuraminic acid (Neu5Ac) at the nonreducing ends changed little.

It appears very likely that the changes in the relative amounts of AFP variants in the embryonic fluid during early pregnancy were due to differentiation of the yolk sac. The grade of differentiation of yolk sac tumors was very similar to that of the normal yolk sac at around 6 weeks of gestation.