Kinetic stability of the L19 / ED-B complex. (A) Real-time interaction analysis of the antigen binding properties of antibody solutions detected using a BIAcore instrument. (i) ScFv(L19) binding to recombinant ED-B immobilized on a microsensor chip. Note that after the initial baseline, the antibody binding to the antigen is detected as an increase of resonance units (RUs). The following flat dissociation profile demonstrates the kinetic stability of the complex. (ii) scFv(D1.3) binding to the ED-B-coated sensor chip of (I). (iii) scFv(L19) binding to a microsensor chip coated with hen egg lysozyme. Specific antigen binding is detected only in sensorgram (I). (B) Measurement of the kinetic dissociation constant of¹²⁵I-labeled L19/ED-B complex immobilized on a microtiter plate, by competition of the complex with a molar excess of unlabeled recombinant ED-B and radioactive counting (see Materials and Methods).