Reactivity of FMC25 and SZ1 against the hGPIX C-ext mutants. The WT GPIX and the 6 hGPIX C-ext mutants were expressed on the surface of CHOαβ cells, and the binding of anti-GPIX moAbs FMC25 and SZ1 was examined. An isotype-matched IgG was used as the negative control (gray solid histogram). Open histograms (black) depict the binding of FMC21 and SZ1 to CHOαβ cells expressing the mutants.