Binding to recombinant CD30 by ELISA. Microtiter plates were coated with a recombinant CD30-Fc fusion protein (R&D Systems). After blocking the wells with 5% BSA solution, protein A-purified 5F11 was incubated at varying concentrations at 37°C. After 1 hour the wells were washed with PBS-tween and the bound antibodies were detected by incubating the cells with an alkaline phosphatase-labeled goat anti-human IgG F(ab)₂-specific probe at 37°C. The excess probe was washed from the wells and the plate was developed with pNPP. The optical density (O.D.) at 405 to 650 nm was determined using a microtiter plate reader. All measurements were done in triplicate and error bars represent standard deviations.