Expression of CD63 on GPVI-deficient platelets and control platelets induced by (A) collagen type I and (B) CRP-XL, measured by flow cytometry using FITC-labeled anti-CD63 antibody. Neither collagen nor CRP-XL induced CD63 expression on GPVI-deficient platelets. Fluorescence of unstimulated control platelets is defined as 1. Data shown are representative of two similar experiments.