Time-dependent appearance of intrathrombus neutrophils and macrophages in a stasis-induced deep vein thrombosis model and its application to thrombus age determination.

We immunohistochemically examined neutrophils and macrophages in venous thrombi, which developed in the ligation of the inferior vena cava (IVC). Myeloperoxidase (MPO)-positive neutrophils and F4/80-positive macrophages were detected in the whole course of thrombi after IVC ligation. Morphometrically, the number of neutrophils was greatest at 1 day after IVC ligation and, thereafter, gradually decreased with an increase of the post-ligation interval. In contrast, the number of macrophages peaked at 7 days after ligation. The number of intrathrombus neutrophils was significantly higher than that of intrathrombus macrophages at 1 and 3 days, and the average ratios of neutrophils to macrophages (N/M ratios) were 6.8 +/- 1.1 (4.8-9.0) and 2.5 +/- 0.4 (1.7-4.2) at 1 and 3 days, respectively. After more than 5 days, all samples had N/M ratios of <2.0 (0.2-1.4). These observations suggest that an N/M ratio of >2.0 indicates a thrombus age of 1-3 days. To differentiate between 1- and 3-day-old thrombi, an N/M ratio markedly exceeding 5.0 strongly indicates an age of 1 day. Furthermore, an N/M ratio of 1.0 or less probably indicates an age of more than 5 days. The present study demonstrated that the immunohistochemical detection of intrathrombus neutrophils and macrophages was suitable to determine the age of venous thrombi.