Highly sensitive solid-phase enzyme immunoassay for terminal deoxynucleotidyl transferase

A highly sensitive and specific solid-phase enzyme immunoassay system for terminal deoxynucleotidyl transferase (TdT, EC 2.7.7.31) has been developed by the use of monospecific antibody against calf thymus TdT and β-d-galactosidase from Escherichia coli as label. The immunoassay system was composed of solid phase (polystyrene beads) with immobilized F(ab′)₂ antibody fragments and the antibody Fab′ fragments labeled with β-d-galactosidase. The minimum detectable concentration of calf TdT was 0.1 ng/ml (0.01 ng/assay), making it more sensitive than the radioimmunoassay or enzyme immunoassay methods that use alkaline phosphatase as label, as reported previously. The assay system cross-reacted with human TdT, and TdT in neoplastic cells or sera from leukemic patients was successfully detected by the present immunoassay method.