Limited fibrinolysis promotes clot retraction. (A) rtPA was administered onto partly retracted thrombi that were 20 minutes old. Changes to the thrombus size and fibrin amount were quantified over the next 60 minutes and data expressed as a percentage of values at t = 5 minutes. Results depict the mean ± SEM (n = 8), where *P < .05 and **P < .01 by 1-way ANOVA with Tukey correction. (B-C) Confocal maximum intensity projection of platelets (B; Dylight 649 anti-mouse GP1bα antibody; blue), fibrin (Alexa Fluor 546 anti-fibrin antibody; red), and plasminogen–fluorescein isothiocyanate (FITC) (green) (B,Ci) within the same thrombus before rtPA administration (t = 0 min), after a period of overt fibrinolysis (t = +30 min) and after subsequent retraction of the unlyzed remaining fibrin network (t= +60 min). (Cii) Schematic depicts the size of the fibrin network at t = 0, 30, and 60 minutes after rtPA delivery. The direction of blood flow (B, arrow) and scale bars (B, 10 μm; Ci, 20 μm) are shown.