Sialidase pretreatment of sialoadhesin-transfected COS cells unmasks their ability to mediate red blood cell binding. (A) Untreated sialoadhesin-transfected COS cells. (B)Vibrio Cholerae sialidase-treated sialoadhesin-transfected COS-7 cells. (C) Vibrio Cholerae sialidase-treated mock-transfected COS cells.