Soluble fibrinogen-dependent aggregation of CHO-α_IIbβ₃ (616-690del) cells. Cells (2.5 × 10⁶/mL) were incubated without or with fibrinogen (1 mg/mL) for 15 minutes at room temperature in a final volume of 250 μL and then plated onto BSA-precoated wells. When indicated, cells were preincubated for 5 to 15 minutes with either 10 mM EDTA or 10 μg/mL anti-β₃ antibody H1a. An irrelevant mAb was used as negative control (not shown). Aggregate formation was visualized by phase-contrast microscopy as described in “Materials and methods.” Original magnification, × 100.