Fluorescence Luminex immunoassay of mouse and human anti-fVIII Ab calibrator. Various molar concentrations (0.01-1.0 nM) of immunoglobulin in PBS/0.1% albumin/0.05% Tween 20 were added to wells containing rfVIII-coupled beads and ovalbumin-coupled beads (nonspecific binding control). Binding of mouse Ab was detected with goat anti–mouse Ig–R-PE, whereas binding of human Ab was detected with mouse anti–human Ig–R-PE. Each point is a mean of 8 independent determinations plus or minus SD. The figure demonstrates the validation of a mouse anti-fVIII Ab as a suitable calibrator for the determination of antibodies to fVIII in human plasma.