Immunohistochemistry of carcinoembryonic antigen in the small intestine.

Carcinoembryonic antigen (CEA) was demonstrated in formalin-fixed paraffin embedded sections of normal small intestine using an immunoperoxidase method. In all the sections studied the antigen was present over the surface of the villi, within goblet cells and lining the crypt lumens. At the electron microscopic level CEA was identified in mucin granules of goblet cells and in the glycocalyx but not intracytoplasmically. During the study cross-reactivity of antiCEA with Paneth cell granules, red blood cells and endothelium was observed. The shared antigenic determinants responsible for these immunological cross-reactions between CEA and other tissue glycoproteins were found to be carbohydrate in nature. Even when well controlled, misleading immunohistochemical results may be caused by immunological cross-reactions.