Spontaneous, fibrinogen-dependent aggregation of AM-1 cells. Cells were resuspended in Tyrode’s buffer in the presence of 300 μg/mL of fibrinogen and with or without 20 μmol/L FK633 or 20 μg/mL PT25-2. Cells were then rotated for 20 minutes on a horizontal rotator. Aggregate formation was stopped by adding equal amount of 0.5% formaldehyde and incubating for 30 minutes. Shown are photographs representative of three independent experiments.