Interaction between SMOC1 and thrombin. (A) Thrombin activity in the presence of solvent (Sol) or recombinant human SMOC1 (rSMOC1) and in the absence and presence of antibodies directed against SMOC1 (abS1). The thrombin inhibitor dabigatran (Dab) was included as control; n = 3 to 7 independent experiments. ***P < .001, 1-way ANOVA and Bonferroni test. (B) Effect of a SMOC1 antibody (abS1; 0.625 ng/µL) on the thrombin-induced aggregation of washed human platelets. Immunoglobulin G (IgG) was included as control; n = 6 independent donors. *P < .05, **P < .01, 2-way ANOVA and Bonferroni test. (C) Thrombin-induced (0.1 U/mL) clot retraction in platelet-rich plasma (3 × 10⁸ platelets per mL), in the presence of calcium (20 mmol/L) and 10 µL of erythrocytes to enhance the contrast of the clot. The clots were allowed to retract for up to 1 hour; n = 6 independent donors. ***P < .001, Student t test. (D) Microscale thermophoresis assay for the interaction between fluorescently labeled thrombin and recombinant SMOC1 or heat-denatured (Denat.) recombinant SMOC1 (0.1-20 µmol/L). The dotted lines indicate the beginning and the end of the laser pulse; n = 3 independent experiments. AU, arbitrary units.