RB- and thrombin/RB-induced photothrombosis manifest divergent patterns of platelet aggregation and fibrin(ogen) extension. (A) Using DyLight488-conjugated anti-GPIbβ antibody to label platelets, intravital microscopy showed the lack of platelet aggregation after systemic intravenous injection of 80 U/kg thrombin and laser photoactivation (supplemental Video 2; n = 3). In contrast, photoactivation after intravenous injection of RB (50 mg/kg) or thrombin/RB (T+RB) induced platelet aggregates of different compactness (see also supplemental Videos 3 and 4, respectively). Arrows indicate the site of photoactivation. (B) Imaging analysis showed a lower average intensity of anti-GPIbβ/platelet fluorescence signals in the T+RB clots (n = 33 in 8 mice) than in RB photothrombosis clots (n = 31 in 6 mice; P = .0002 by unpaired Student t test). (C) Intravital microscopy of FITC-conjugated fibrinogen showed the lack of fibrin(ogen) extension after photoactivation in thrombin-alone injection (supplemental Video 5) and restricted fibrin(ogen) deposits after RB photothrombosis (supplemental Video 6), in contrast to appreciable expansion of fibrin(ogen) deposits in T+RB photothrombosis (supplemental Video 7; n = 3 for each group). Scale bars, 50 μm.