Inhibition of rFVIII activity by LE IgG in the presence or absence of vWF. Plasma-derived FVIII (containing vWF) (○), rFVIII alone (▪), or rFVIII complexed with vWF at a 1:50 wt:wt ratio (□) were incubated with various concentrations of patient LE IgG. The residual FVIII activity was measured in a chromogenic assay and expressed as percent inhibition of control.