Two‐dimensional lectin affinity electrophoresis of α‐fetoprotein: Characterization of erythroagglutinating phytohemagglutinin‐dependent microheterogeneity forms

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Abstract
By means of two-dimensional lectin affinity electrophoresis of human α-fetoprotein (AFP) from different sources, AFP bands separated with erythroagglutinating phytohemagglutinin (E-PHA) were further characterized with other lectins of known oligosaccharide specificities. The results with a cord serum AFP revealed that not only AFP-P2 (E-PHA-nonreactive) but also AFP-P4 and P5 (E-PHA-reactive) had affinities for Concanavalin A (Con A) and Allomyrina dichotoma lectin (allo A), indicating that the cord serum AFP has nonbisected biantennary complex-type oligosaccharides with the terminal galactose on Man α1 → 6 residue sialylated at the C-6, but not C-3, position. On the other hand, the results with a hepatoblastoma (HUH-6 C1–5 cell line) AFP showed that not only AFP-P5 but also AFP-P1 (E-PHA-nonreactive) and P3 (E-PHA-less reactive) had Con A-nonreactive AFP and that AFP-P1 had AFP-A1 (allo A-nonreactive) and AFP-A2 (allo A-less reactive), and AFP-P3 and P4 had AFP-A1s (allo A-nonreactive), as main components, in addition to the spots of cord serum AFP. Most of the E-PHA-dependent bands of AFP were further subdivided with Lens culinaris agglutinin (LCA-A) into LCA-A-reactive, weakly reactive and nonreactive spots. Similar results were obtained with AFP preparations from hepatocullular carcinomas and other malignancies, indicating that the bisected bi-(or tri-and tetra-) antennary sugar chains with the exposed terminal galactose of the Man α 1 → 6 arm as well as those with the C-3 sialylated galactose residues could be expressed in AFP upon malignant transformation. The two-dimensional lectin affinity electrophoresis thus proves useful for further characterization of lectin-dependent AFP bands.

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