VWF is required for Stx-induced thrombocytopenia. CASA/Adamts13^−/− mice that were either deficient for VWF (Vwf^−/−, solid line with diamonds) or expressing VWF (Vwf^+/+ or Vwf^+/−, dashed line with squares) were injected via the lateral tail vein with Stx (250 pg/g body weight) and followed for 5 days. Blood from the retro-orbital plexus was obtained daily for automated platelet count analysis. For each group of mice, the platelet count data were averaged and expressed as the percentage change from baseline values obtained before injection of Stx. The number of mice injected was 16 for the Vwf^+/+ and Vwf^+/− group and 9 for the Vwf^−/− group. The error bars represent the standard error of the mean.