Depletion of Tregs reduces intracerebral thrombosis and improves cerebral blood flow after stroke. (A) Accumulation of fibrin(ogen) in the infarcted (I) and contralateral (C) cortices and basal ganglia of naive DEREG mice and Treg-depleted DEREG mice (DEREG + DT) was analyzed by immunoblotting 23 hours after 60 minutes of tMCAO and quantified. Three representative immunoblots of each group are shown. The higher fibrin(ogen) signal detectable also in the healthy contralateral (= left) hemisphere of nondepleted DEREG mice is probably a consequence of increased thrombotic activity in this region because of massive ipsilateral infarct swelling. DT indicates diphtheria toxin; AU, arbitrary units. (B) The number of thrombotic vessels (thrombosis index) in the ischemic basal ganglia of DEREG mice and Treg-depleted DEREG mice was counted from H&E-stained brain sections on day 1 after 60 minutes of tMCAO. Although numerous occlusions of vessel lumina were found in naive DEREG mice (arrows), the microvascular patency was significantly increased in the absence of Tregs (arrowheads). (C) Reduced intracerebral thrombosis was related to improved CBF, fewer tissue infarctions as reflected by lower apparent diffusion coefficient (ADC) values, and a lower infarct probability in Treg-depleted DEREG mice as revealed by MRI at ultra-high-field strength (17.6 Tesla) on day 1 after 60 minutes of tMCAO. *P < .05, **P < .001, and ***P < .0001 between the indicated groups.