Abstract Body (Do not enter title and authors here): Background: A disorganized thrombus jeopardizes its stability, leading to an augmented risk of fatal acute complications following deep vein thrombosis (DVT). One of its plausible causes is impaired immune cell responses. While the importance of the cytokine interleukin-6 (IL-6) in immune responses is well established, its action towards DVT organization is poorly elucidated. Accordingly, we aimed to investigate the role of IL-6 in the acute immunoinflammatory orchestration of DVT organization in vivo.
Methods and Results: We performed total ligation of the infrarenal inferior vena cava (IVC) in 8–12-week-old male C57BL/6J mice a day after starting continuous, subcutaneous mini-osmotic pump infusion of recombinant IL-6 (rIL-6; 1.2 µg/day, n = 21) or vehicle (n = 21), after which DVT pathology was examined. Exogenous IL-6 administration significantly decreased DVT mass at day 2 (16.6±1.9 vs. 23.0±0.9 mg/cm; p<0.01) and day 4 (16.2±1.6 vs. 21.4±0.8 mg/cm; p<0.05) compared to vehicle-treated mice. Intriguingly, rIL-6-treated mice’s DVT exhibited distal tropism of a macroscopically white lesion with abundant neutrophils and platelet accumulation, indicating enhanced DVT organization (Figures A–B). Quantitative polymerase chain reaction (qPCR) analysis revealed the distal edge upregulation of leukocyte chemoattractants, leukocyte-platelet interaction markers, and extracellular matrix regulator genes, confirming that the IL-6-driven inflammatory response was linked to augmented DVT organization. Spatiotemporally, real-time intravital imaging on stasis- and irradiation-induced saphenous vein thrombosis among intraperitoneal rIL-6 (0.3 µg/mouse)-treated mice demonstrated marked acute leukocyte and platelet recruitment with subsequent aggregation to the distal edge of the thrombus (Figures C–D), which consequently yielded an enhanced thrombus resolution at the distal edge.
Conclusions: Our findings suggest that IL-6-driven inflammation results in distal tropism of leukocyte-platelet infiltration, which is important for modulating thrombus organization and subsequent DVT amelioration. This study presents a novel insight into the immunothrombosis process, with potential clinical implications for DVT.