Functional effect of vWF–A₁-domain transfected COS-7 cells on human platelets. (A) Representative plot of recorded aggregation subsequent to incubation of COS-7 cells with platelets at a ratio of 1:200. (B) Comparison of aggregation subsequent to incubation of human A₁-domains (aa 473-713: H_473-713/aa 475-709: H_475-709) transfected COS-7 cells with platelets at ratios of 1:200 and 1:600. (C) Dose-dependent effects of porcine (•) and human (○) A₁-domain expressing cells incubated with human washed platelets, prepared as described in Materials and Methods (180,000 platelets/μL). All experiments were performed in the presence of MgCl₂ (1.0 mmol/L), CaCl₂ (1.0 mmol/L), and fibrinogen (final concentration: 800μg/mL). Aggregation was determined as percentage of maximal light transmission 10 minutes after addition of COS-7 cells. ⁺P < .05 (Mann-Whitney Rank Sum test); **P < .001 and *P < .05 (Student's t-test) for the porcine versus human comparison (n = 5 or 6 separate transfections). Error bars indicate standard errors of the mean.