Activated, resident Tregs accumulate in venous blood clots. (A) Representative transversal ultrasound views of thrombi with ligature position marked and thrombus outlined for size determination; ultrasound data show the size progression of thrombi in C57BL/6 mice (n = 5 group/time point). (B) Treg frequencies in thrombi, adjacent venous walls, spleen, and blood during thrombus resolution. (C) Treg CD69- and KLF2-expression kinetics in KLF2^GFP mice. Representative day 14 flow cytometric profiles; mean ± SEM values are shown (**P ≤ .005;***P ≤ .0005; ns, not significant; spleen/blood, n = 10; thrombus/vein, n = 5 group/time point). All statistical differences were tested using an unpaired Student t test (2 tailed). Profiles are representative of 3 independent experiments.