Immunostaining of BHK cells transfected with WT or Cys38Arg factor XI.

Cells grown on glass slides were reacted with 2 different anti–factor XI monoclonal antibodies, and immune complexes were detected by antimouse IgG coupled to alkaline phosphatase. The mAb-3 directed against an epitope on apple 2 detected Cys38Arg factor XI in the cells, whereas the mAb-5 directed against an epitope on apple 1 (the site of the mutation) failed to detect Cys38Arg factor XI. Original magnification × 200.