Serum alpha-fetoprotein subfractions identified by Ricinus communis agglutinin I in hepatic malignancies, yolk sac tumor, benign hepatic diseases, and fetal stage.

Using Ricinus communis agglutinin I (RCA-I) affinity crossed-line immunoelectrophoresis, alpha-fetoprotein (AFP) subfractions were studied in sera from patients with primary hepatic cancer (PHC), hepatic metastasis of gastric cancer (HMGC), yolk sac tumor (YST), acute or chronic hepatitis or hepatic cirrhosis. Fetal AFP subfractions were also examined in amniotic fluids or in culture fluids of fetal tissues. RCA-I non-reactive subfraction was commonly found in PHC, HMGC, YST, benign hepatic diseases, and fetal stage. RCA-I weakly reactive (WR) or strongly reactive (SR) subfraction was noted only in malignant diseases. RCA-I has a specific affinity to terminal galactose in oligosaccharide, and the presence of sialic acid on galactose residue(s) inhibits the affinity with RCA-I. Therefore, common AFP subfraction non-reactive with RCA-I was assumed to be galactosialyl form, while RCA-I WR and SR subfractions found only in malignancies were monogalactosyl and digalactosyl, respectively. Clinically this approach to detect the RCA-I WR or SR subfraction facilitates a differential diagnosis of AFP-producing malignancies and benign conditions.