The AFP-synthesizing cells were identified by ultrastructural localization of the antigen in regenerating liver of adult mice after CCl4 poisoning. An indirect immunoperoxidase method with rabbit anti-mouse AFP and peroxidase conjugates of anti-rabbit IgG or their Fab' was used. Good preservation of AFP and tissue structure, and sufficient permeability for the conjugates were obtained after 20' prefixation of small liver specimens in 8% formaldehyde -0.05% glutaraldehyde followed by 16 h fixation in 8% formaldehyde. The intracellular localization of AFP observed in the light microscope in most cases corresponded to its synthesis and secretion. It was found in two cell types, both concentrated mainly in the perinecrotic zones and constituting only a small part of the whole cell population. Most of the AFP-producing cells were normal differentiated hepatocytes without any structural signs of damage. A few smaller cells with active AFP synthesis were present in some animals. By their ultrastructure they resembled the oval cells found during chemical hepatocarcinogenesis in rats.

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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.

Localization of afp independent of the presence of serum was demonstrated only in a limited number of tumour cells in a fp-positive hepatocellular carcinomas. These cells usually formed three-dimensional groups with a definite tendency to localize near blood vessels and capillaries. Haematoxylin-eosin staining did not reveal any morphological di'erence between ah-positive and -negative tumour cells.Alpha-foetoprotein (afp) was found in the sera

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.