When working with monoclonal antibodies (MCAB) to an individual antigen (AG) it is necessary to determine that epitope specificity, i.e., their targeting toward the same or different determinants. Competitive analysis of MCAB is usually used for this purpose, by solidphase radioimmunoassay [4], for which purified AG and radioactive labeling of each of the MCAB to be compared are required. In the investigation described below it is shown that epitope specificity of MCAB can be analyzed by counterflow isotachophoresis (ITP) on a nitrocellulose membrane (NCM) [I] on a model of MCAB to human (HAFP) and mouse (MAFP) a-fetoprotein (AFP). The method does not require purified AG or MCAB, or their radioactive labeling, it canbe performed automatically, and requires only the simplest electrophoretic equipment. Rat MCAB to MAFP and mouse MCAB to HAFP were used. Rat MCAB were obtained as described previously [6]. Culture media (CM) of three hybridomas (D6, G~, Ha), both initial and concentrated tenfold by precipitation with (NH~)2SO~ (0.33 of saturation), were used for analysis. MCAB to HAFP were obtained by fusing the splenocytes of a mouse immunized with a purified HAFP preparation and myeloma X63-AgS.653 cells. MCAB of three cell lines (D1o, De, Es) in mouse ascites fluid were used. Rabbit antiserum of MAFP (anti-MAFP) was obtained as described previously [2] and neonatal mouse serum (NMS) was used as the MAFP preparation. A commercial immunodiagnostic serum for primary carcinoma of the liver (N. F. Gamaleya Institute of Epidemiology and Microbiology, Academy of Medical Sciences of the USSR), including rabbit anti-HAFP and AG, containing 50 ~g HAFP in i ml and with a large excess of serum albumin, was used as the system for determining HAFP. Mouse MCAB to rat L~ IgG (rat anti-L K containing 3 mg of antibodies in i ml [5] and rat IgG (i0 mg/ml), generously provided by A. Yu. Rudenskii (AllUnion Research Institute of Genetics, Main Administration of the Microbiological Industry of the USSR), were used. Fab'-fragments of donkey antiserum to rabbit IgG, conjugated with horseradish peroxidase (P) (Fab'-P), were obtained by V. S. Poltorandina by the method in [8]. To abolish cross reactions between reagents used in the analysis, embryonic calf serum (ECS) was added to the anti-MAFP, and rat IgG and ECS were added to the Fab'-P in concentrations chosen beforehand.
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