Screening of scFv-Fcs binding to cell surface CD9. (A) Western blot analysis of scFv-Fc expression. HRP-conjugated rabbit anti-human IgG (Fc-specific) antibody was used to detect scFv-Fc in culture supernatant. (B) Flow cytometric analysis of scFv-Fc binding. Culture supernatants containing scFv-Fcs were analyzed for the ability to bind HEK293 (open histogram) and HEK293-CD9 (shaded histogram) by flow cytometry. HA6 represents an scFv-Fc recognizing HAV used as a negative control, and MM2/57 represents an anti-CD9 mAb used as a positive control. The binding of scFv-Fc and MM2/57 was detected by FITC-conjugated rabbit anti-human IgG (Fc-specific) antibody and FITC-conjugated goat anti-mouse IgG antibody, respectively.