Expression of GP Ib in the platelets of individuals with different GP Ib genotypes. (A) Flow cytometry histograms of platelets from three individuals with the genotypes indicated. GP Ib was detected with WM23 and a FITC-conjugated secondary antibody. The ordinate represents the relative cell number; the abscissa represents the log fluorescence intensity. (B) Average GP Ib levels from flow cytometry determinations on three individuals with each genotype. The experiments were performed six times and the mean fluorescence intensities from the individual experiments were averaged and are represented as mean ± SEM. The differences in the levels of GP Ib in the platelets of individuals with T/C and C/C genotypes as compared with T/T individuals were both statistically significant (P = .01 and P < .005, respectively, Student’s two-tailt-test, n = 6). The increased expression in the C/C individuals compared with those with the T/C genotype also showed a trend toward statistical significance (P = .075). (C) Immunoblot of whole platelet lysates from three individuals. The membrane was probed with WM23. The same blot was stripped and reprobed with antibody G 1.9 against GP IIb as a control for loading.