Immunohistochemical differentiation of yolk sac-type alpha-fetoprotein from hepatic-type alpha-fetoprotein

In order to differentiate yolk sac-type alpha-fetoprotein (AFP) from hepatic-type AFP, 5 yolk sac tumors (YSTs) and 6 hepatocellular carcinomas (HCCs) were examined immunohistochemically by the peroxidase-antiperoxidase (PAP) method for AFP, and paradoxical concanavalin A (P-Con A) staining, which has been reported to detect glycoprotein including AFP. In all 5 YSTs, AFP was negative for P-Con A staining. On the other hand, AFP was strongly positive for the same staining in all 6 HCCs. A similar staining pattern for AFP was observed in human yolk sac endodermal cells and embryonal hepatocytes. Thus, it was clarified that yolk sac-type AFP was unable to bind with Con A, in contrast with hepatic-type AFP, on tissue sections. It was concluded that the PAP method for AFP and P-Con A staining might facilitate the immunohistochemical differentiation of these two types of AFP, and that it would be useful for clarifying the histogenesis of various AFP-secreting tumors.