Immunoelectron microscopic observation of alpha-fetoprotein synthesis in human non-malignant liver tissues using immunoperoxidase methods.

Alpha-fetoprotein (AFP) synthesis in non-malignant liver tissue of 34 patients with chronic hepatitis or liver cirrhosis, some of whom also had hepatocellular carcinoma (HCC), was studied by light and ultrastructural immunohistochemistry using peroxidase-labeled anti-human AFP. Simultaneously, the serum level of AFP was measured in these patients by radioimmunoassay. AFP-positive cells were identified in non-malignant liver tissue of 7 patients with elevation of serum AFP. AFP was demonstrated in several hepatocytes which were clustered in hepatic lobules, and also in some bile ductular cells which were distributed in the periphery of portal tracts. In an immunoelectron microscopic study of AFP-positive hepatocytes, dense reaction products of anti-AFP were localized in the membranes and cisternae of rough endoplasmic reticulum (r-ER), perinuclear space (PNS) and Golgi apparatus. The prominent feature of AFP-positive hepatocytes was abundant r-ER encompassing many mitochondria. As to AFP-positive bile ductular cells, they had scanty cytoplasm and few intracytoplasmic organelles and were surrounded by basement membrane. AFP was focally localized in the r-ER of such bile ductular cells. These observations suggest that AFP can be produced by malignant and non-malignant liver cells and that in non-malignant liver tissues, AFP can be produced by two distinct cell types; bile ductular cells and hepatocytes themselves.