To establish the binding target of D29 Fab-IgG, competition ELISA against epitope-characterized monoclonal antibodies was carried out. Plates were prepared as for direct binding ELISA. After blocking, serially diluted m3H5, m4G2 or m2H2 was added to the plates and incubated for 1 hr at RT, followed by addition of D29 Fab-IgG at 2.5 mg/ml and incubation for 1 hr at RT. Bound antigen-antibody complexes were detected by HRP-conjugated anti-human IgG-Fc secondary antibody (Pierce), and developed as described above.