Decreased adhesion to VWF and insensitivity to RAM.1 of GPIb/V/IX cells containing a GPIbβ(Ser166Gly) mutation.

K562 cells expressing the wild-type complex (GPIb/V/IX) or containing a Ser166Gly mutation of GPIbβ (GPIb(βSer166Gly)/V/IX) were perfused over a bovine (BVWF) or human VWF (HVWF) matrix at a shear rate of 150 s^-1 as described in Figure 1. The cells were preincubated with 10 μg/mL RAM.1 (■) or control rat IgG1 (▪) for 10 minutes before perfusion through the VWF-coated capillaries. The number of adherent cells was counted off-line at 10 minutes. Adhesion to HSA was less than 5 cells/field. Cells containing the GPIb(βSer166Gly) mutation had approximately half the adhesive capacity of control cells on bovine or human VWF and this residual adhesion was unaffected by RAM.1 treatment. Results are expressed as the mean ± SEM of 3 separate experiments. *P < .05.