Usefulness of serial in vivo imaging to directly assess the role of inflammation in thrombus resolution and organization.

Deep vein thrombosis (DVT) remains a significant health problem. Although animal models have provided significant insights into the DVT pathophysiology, time-course assessment in a same animal is technically limited. Recently, we reported a novel murine saphenous DVT model for in vivo visualization of spatiotemporal dynamics of inflammatory cells. This study further shed a light on the resolution and organization process of DVT using serial in vivo imaging technique. Similar with ferric chloride-induced thrombus model, our saphenous DVT model allowed serial in vivo imaging with fluorescence microscopy. However, unlike ferric chloride-induced thrombus model, we observed a significant decrease of DVT burden. Red blood cells area gradually decreased followed by fibrin and collagen deposition over time, although ferric chloride model induced platelet-rich arterial thrombus. Histological assessment revealed that neutrophils influx peaked 3 h after DVT induction, followed by macrophages' migration at 120 h' post-induction, indicating similar organization process with traditional stasis-induced DVT model. Ly6G/Ly6C positive cells at 3 h predicted the reduction of DVT burden (r > 0.8; P < 0.01), suggesting that inflammatory response at acute phase plays pivotal role in DVT resolution. MMP-9 expression was observed and colocalized with neutrophils at early timepoints in both traditional stasis-induced DVT model and our femoral imaging models. Taken together, our in vivo imaging model might allow better understanding of the resolution and organization processes in DVT.