In vitro assessment of platelet function in SLFN14^K208N/+mice. (A) Resting platelet surface glycoprotein expression levels. GP1ba⁺ platelets were costained for the indicated surface receptors in whole blood. Median fluorescence intensity (MFI) from 4 to 6 mice per genotype. Data are mean ± standard error of the mean (SEM); significance was assessed using Welch’s t test for multiple comparisons. (B) P-selectin (i) and activated αIIbβ3 (JON/A) (ii) expression on SLFN14^K208N/+ mouse platelets in response to the indicated agonist stimulation. Data are MFI (mean ± SEM) for 9 mice per genotype per condition. Significance was assessed by Sidak’s 2-way analysis of variance. (C) Platelet reactivity in washed platelets in response to 0.01 U/mL (i), 0.03 u/mL (ii), or 0.06 U/mL (iii) thrombin. (D) Platelet reactivity in washed platelets in response to 1 µg/mL (i) or 3 µg/mL (ii) collagen. (E) Platelet reactivity in washed platelets in response 1 µg/mL (i), 3 µg/mL (ii), or 10 µg/mL (iii) collagen-related peptide. Representative traces of 3 to 6 mice per genotype per condition are shown. (F) Platelet spreading and adhesion in SLFN14^K208N/+ mice. SLFN14^K208N/+ platelets spread on collagen or fibrinogen under resting and thrombin-preactivated conditions (0.1 U/mL thrombin). Representative differential interference contrast and fluorescent phalloidin–stained images are shown from 3 mice per genotype/condition. Scale bar, 10 μm.