Thirty monoclonal antibodies (MoAbs) to human α-fetoprotein (AFP) were compared with one another by two methods: Immunoaffinity electrochromatography or additive ELISA. The first method permitted to analyse the epitopes of native AFP in solution [Abelev et al., Immunol Lett 1994;40:133–138] while the other approach also detects the epitopes of conformationally modified (partly denatured) AFP fixed on the plastic [Yazova et al., Immunol Lett 1990;25:325–330]. Competitive analysis of all MoAbs revealed 10 epitopes, 9 expressed on native AFP and 1 only on the partly denatured molecule. The cross-reactions between separate MoAbs allowed to include them into 6 distinct epitope clusters, or immunodominant groups with the characteristic patterns of reactivity. The obtained epitope map of AFP is necessary for the construction of AFP detection kits as well as for the identification of its antigenic and functional subfractions.

No abstract

The immunological heterogeneity of human α-fetoprotein (AFP) was demonstrated using immunoaffinity electrochromatography on monoclonal antibodies (MoAbs) to 3 non-cross-reacting epitopes of this protein. At least 4 subfractions expressing different epitopes were found in the native AFP. These subfractions demonstrated molecular weights similar to the major component of the original AFP. The difference between epitope F₅-positive and F₅-negative subfractions disappeared when epitope-negative subfraction was conformationally changed after fixation onto nitrocellulose membrane (NCM). Thus, the epitope under study exists in two forms on the native human AFP molecule: an open and a cryptic form. The cryptic form could be revealed after partial denaturation by fixation on NCM. The epitope variants of AFP could possess different functions in multifunctional AFP. The AFP epitope heterogeneity found in this work should be taken into account when constructing diagnostic AFP kits and when isolating purified AFP using anti-AFP MoAbs.

The AgB10 antigen of bile canaliculi of the mouse hepatocyte was identified using monoclonal antibodies. The Mr value of 116000 for AgB10 was measured by immunoblotting. The tissue localization of AgB10 was studied by light and electron microscopy using the immunoperoxidase technique. AgB10 was predominantly present on the microvillus membrane of bile canaliculi, the brush border of intestinal mucosa and apical surfaces of the epithelial cells in some other organs. A small amount of AgB10 was detected on the basolateral domain of the hepatocytes. AgB10 was specific for hepatocytes and was not found in the other cell types of the liver. In primary hepatocyte culture, AgB10 was localized on the surface of cells during the first 24 h, predominantly at the sites of cell-cell and cell-substratum contacts. After 48 h of culture AgB10 gradually disappeared from contacting cell surfaces and became concentrated only in the reconstituted bile canaliculi.

No abstract