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Biomedical subjects

G I Abelev

Publications and source records attributed to G I Abelev.

At least 19 recordsLinked to original sources
PubMed2001

Epitope mapping of human alpha-fetoprotein.

The epitope structure of human alpha-fetoprotein (AFP) was studied using more than 50 monoclonal antibodies (MAB) to human AFP. These MAB obtained from various world laboratories of the TD-2 AFP Workshops of the International Society for Oncodevelopmental Biology and Medicine (ISOBM-1996-1998-2000) were analyzed by competitive immunoaffinity electrochromatography (IAE) on nitrocellulose membranes (NCM). Five types of interaction of the AFP-MAB complex with the MAB fixed on NCM were found: 1) complete neutralization; 2) partial neutralization; 3) unidirectional neutralization; 4) enhanced binding; 5) lack of interaction. By IAE, 51 MAB were found to recognize 23 different epitopes in the AFP molecule. Based on these findings, an epitope map of AFP was designed which consists of eight epitope clusters and eight individual epitopes. The epitope location is considered with respect to the conformational state of the AFP molecule. Possible causes of the five types of interaction found on neutralization are discussed.

Antibodies, Monoclonal↗
PubMed2001

[alpha-Fetoprotein (biology)].

The paper gives a historical overview of the origin and experimental analysis of alpha-fetoprotein (AFP) regulation and its reexpression in malignant tumors. It shows how a specific hepatoma-specific antigen that was later identified as the major protein component of embryonic serum was found and isolated during searches for murine hepatoma-specific antigens. Later on it was shown that AFP was synthesized by the yolk sac endoderm of the embryo and, later, by the fetal liver and its synthesis drastically diminishes in the adult animal liver. AFP synthesis restores in the moderately differentiated hepatomas and temporarily in the murine regenerating liver. The same regularity, but in other quantitative ratio, occurs in man. Analyzing the causes of AFP reexpression in the regenerating liver has indicated that suppression of AFP synthesis in the mature hepatocytes is reversible and controlled by the position of a hepatocyte in the liver plate: when the hepatocyte is included into the plate, it becomes fully differentiated with AFP suppression. Hepatocytic isolation from the plate leads to its "dedifferentiation" and AFP reexpression. AFP reexpression takes place in the perinecrotic cell layer in the liver poisoned by CCl4. Hepatocytic isolation from the liver and explantation into the cultured tissue results in strong reexpression of AFP while incorporation of the isolated hepatocytes in the three-dimensional extracellular matrix (ECM) leads to AFP suppression together with hepatocytic "maturation". Hepatocytic interaction with defective ECM does not suppress AFP synthesis. Our hypothesis suggests that disturbance of cell-ECM interactions during transformation and tumor progression is the main reason of AFT reappearance in liver tumors.

Animals↗
PubMed2000

Differentiation mechanisms and malignancy.

This review considers the relationship between differentiation mechanisms and the genesis and maintenance of tumor phenotype. To a certain extent, carcinomas preserve differentiation markers of normal tissue, and hemoblastoses precisely reflect the direction and differentiation level of their precursor cells. Both tumor types retain the ability to differentiate. Mechanisms of T and B cell differentiation are reviewed considering the activation of protooncogenes by translocation to the region of tissue-specific genes including the immunoglobulin (Ig) and T cell receptor (TCR) genes. Apart from the classical oncogenes (MYC, PRAD, BCL-2), heterologous differentiation of trans-factors can be activated in a similar manner. Their activation at inappropriate time and place induces oncogenic transformation in a number of hemoblastoses. Chimeric genes and fused proteins are analyzed, including their genesis by specific translocation resulting in transformation and their role in differentiation and maintenance of the tumor phenotype. Induction of terminal differentiation in leukemia can have significant therapeutic effect. These hemoblastoses include hairy cell leukemia, promyelocytic leukemia, and in part chronic myeloid leukemia. Specific attention is given to the role of intercellular interactions in the control of tumor growth and maintenance of a differentiated state of the cells. It is suggested that alterations in these interactions during tumor progression simultaneously stimulate malignant growth and decrease differentiation level, thus inducing re-expression of embryonic antigens in the tumors.

Carcinoma↗
PubMed1999

Cellular aspects of alpha-fetoprotein reexpression in tumors.

The cellular basis of AFP synthesis in normal development, liver regeneration, hepatocarcinogenesis and in tumors is discussed in the review. The attempt is made to interpret the production of AFP by germ cell and liver tumors as a consequence of their origin from the cell types producing AFP in normal conditions. Thus, AFP in germ cell tumors is explained by the development of the yolk sac visceral endoderm (YSVE) in teratocarcinomas, since YSVE is the first site of AFP synthesis in the embryo. The next site of AFP production is embryonal hepatoblast and just hepatoblastomas are the maximal producers of AFP among liver cancers. The reason for AFP resumption in hepatocellular carcinomas (HCC) is not yet clear. This problem is discussed in the light of possible role of oval cells in the HCC origin and the concept of the two states of the mature hepatocyte, associated and non-associated with AFP production. The crucial role of extracellular matrix in the control of AFP-producing state of hepatocyte is emphasized.

Animals↗
PubMed1999

[Immunology of cancer].

The paper present a brief review of progress in cancer immunology in the past 50 years and its use in the immunodiagnosis, immunoprevention, and immunotherapy of cancer. Tumor markers have been a basis of the serological diagnosis of some tumors and the immunophenotyping of leukemia. Hepatitis B virus vaccination should reduce the incidence of hepatic cell carcinoma. Investigations have provided impetus to the design of molecular genetic anticancer vaccines which are being tested in the clinical setting.

Antibodies, Neoplasm↗
PubMed1998

Inducible protein in rat hepatomas with expression alternative to alpha-fetoprotein.

The rat hepatoma cell line McA RH7777 was cloned into alpha-fetoprotein-producing (AFP+) and non-producing (AFP-) sublines. A monoclonal antibody (MAb A2/3) reacting with an antigen (Ag A2/3) present only in AFP- clones or AFP- cells in mixed clones was obtained. Ag A2/3 was absent from the liver of embryonic, fetal, newborn and adult rats, but it was present in gastric and intestinal mucosa of adult rats. Ag A2/3 was found to be a heavy metal-inducible protein: Cd2+ and Pb2+ strongly induced the expression of Ag A2/3 in vivo in the liver of adult rats, while xenobiotics and CCl4 were not active in this respect. In vitro Cd2+ and Pb2+ induced Ag A2/3 expression in several AFP+ clones, leading to a simultaneous marked decrease of AFP+ cells from such clones. The effect of Cd2+ in the induction of Ag A2/3 and suppression of AFP was reversible. SDS PAGE revealed one protein band with an m.w. close to 45,000, which was not sensitive to mercaptoethanol. Despite its inducible properties, Ag A2/3 was shown not to belong to metallothioneins, cytochrome P-450, glutathion-transferase or heat shock proteins families, well-known as being inducible cell stress proteins. Expression of Ag A2/3 could be one of the factors determining the high amplitude of AFP production by individual liver tumors. The nature of Ag A2/3 and its alternative expression with respect to AFP remain to be studied.

Animals↗
PubMed1998

Epitope mapping of human alpha-fetoprotein.

Thirty monoclonal antibodies (MoAbs) to human alpha-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.

Antibodies, Monoclonal↗
PubMed1998

Conformational variants of human alpha-fetoprotein.

The immunological heterogeneity of human alpha-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.

Antibodies, Monoclonal↗
PubMed1996

[Automation on membranes: countercurrent isotachophoresis and immunoelectrochromatography].

The review discusses two related methods--counterflow isotachophoresis and immunoaffinity electrochromatography on porous membranes developed by the authors. The methods exploit the peculiarity of electroendosmosis in porous membranes at the conditions of discontinues electrophoresis. There are described the principles and application of the above methods for automatic performance of electrophoretic analysis of low-protein biological fluids, of western blotting, epitope analysis of monoclonal antibodies and multiantigen assays. The possibility of DNA-binding protein detection is also considered.

Automation↗
PubMed1994

Electrochromatography: a method for automatic immunoaffinity chromatography on porous membranes.

Electrochromatography (ECHR) exploits a very high electro-osmotic counterflow developed in porous membranes at discontinuous electrophoresis. This counterflow exceeds considerably the anodic migration of any negatively charged protein and is used as a 'conveyer belt' for sequential transfer of immunoreagents to the specific adsorbents (antigens or antibodies) fixed on the nitrocellulose membrane. This approach was applied for simultaneous detection of two antigens (alpha-fetoprotein and carcino-embryonic antigen) in one sample, for determination of subfractions of alpha-fetoprotein, different in their epitope specificity, and for detection of L chains with certain idiotype on the background of heterogeneous L fraction. ECHR was used also for the partition of different antibodies to DNA adducts, demonstrating the possibility of applying this method to the study of DNA-binding proteins.

Antibodies, Monoclonal↗
PubMed1991

Counterflow affinity isotachophoresis on cellulose acetate membranes.

Counterflow isotachophoresis on cellulose acetate membranes of human alpha-fetoprotein (AFP) was performed with concanavalin A, lentil lectin, and castor bean lectin driven by electroendosmotic counterflow. This counterflow caused a uniform stream of lectin to migrate towards the cathode against AFP with carrier ampholytes in steady-state position. Retardation of microheterogeneity forms bound to lectins was observed, giving results comparable to standard crossed affinity immunoelectrophoresis. Smaller amounts of lectins and more diluted samples of AFP could be used in the described method.

Ricinus communis↗
PubMed1990

Immuno-isotachophoretic determination of monoclonal immunoglobulin light chains produced by neoplastic B-cells: use in diagnosis, monitoring and detection of residual disease.

We suggest that countercurrent isotachophoresis performed on cellulose acetate membranes (ITP-CAM) should be used for detecting trace amounts of Bence-Jones protein (BJP) in urine of patients with chronic lymphocytic leukemia (CLL), non-Hodgkin's lymphoma (NHL) and related diseases. ITP-CAM allows simultaneous concentration and electrophoretic separation of proteins present in highly diluted solutions, as well as easy immunological detection of separated substances. BJP was found in 24 out of 42 patients with CLL, 33 of 56 with NHL and 3 of 3 with Waldenström macroglobulinemia. Twenty-three patients were followed during the course of chemo- or radiotherapy. In 19 cases the BJP findings correlated well with clinical status. In no case of partial or complete clinical response did BJP completely disappear from the urine.

B-Lymphocytes↗
PubMed1989

Performance of multistep immunochemical reactions by counterflow isotachophoresis on nitrocellulose membranes--I. Immunoblotting.

Urine with trace amounts of different proteins from healthy people or B-lymphoma patients was concentrated and separated simultaneously by counterflow isotachophoresis on cellulose acetate membranes (CAM). The protein zones were blotted onto nitrocellulose membrane (NCM) by direct contact of CAM and NCM. NCM-blots were exposed to second isotachophoresis with the leading electrolyte 0.06 M Tris-HCl and the terminating one, 0.012 M Tris-beta-alanine. Under these conditions the moving boundary formed by Cl-/beta-alanine- migrated towards the anode with decreasing velocity. At a certain point the rate of migration of the moving boundary became completely compensated by the electroendosmotic counterflow. In this steady state position the boundary stopped on the NCM support, while the electroendosmotic rate in the area before the boundary was much higher than the rate of the opposite migration of any protein to the anode. Under these conditions electroendosmosis served as a "conveyer belt" which transferred consecutively the immunoreagents, antibodies, immunoconjugates, or antiperoxidase-peroxidase system through the protein blots "printed" on NCM. The immunoblots obtained in this way were developed by the substrate for the immunoenzyme complex used in the experiment. The technique could be used to characterize light chains present in the urine of normal donors and monoclonal light chains in the urine of patients with B-cell malignancies.

B-Lymphocytes↗
PubMed1989

Performance of multistep immunochemical reactions by counterflow isotachophoresis on nitrocellulose membranes--II. Epitope analysis of monoclonal antibodies.

The method for comparison of epitope specificity of different monoclonal antibodies to one antigen, using a panel of monoclonal antibodies to mouse and human alpha-fetoprotein is described. The method used exploits the special properties of electroendosmotic flow in nitrocellulose membranes under the conditions of anionic isotachophoresis. Electroendosmosis allows successive transfer of several immunoreagents to the dots of monoclonals previously bound to the nitrocellulose membrane. The inhibition of antigen binding to monoclonal dot, if the antigen is mixed with excess of another monoclonal antibody, demonstrates that both monoclonals are directed to the same epitope, and vice versa. The method requires neither purified monoclonals nor antigens, or radio labelling, and is performed semi-automatically. It was shown that each monoclonal antibody to mouse and human alpha-fetoprotein had its own epitope specificity.

Animals↗