Modulation of interleukin-6 and its effect on late vein wall injury in a stasis mouse model of deep vein thrombosis

OBJECTIVE: Deep vein thrombosis (DVT) and its sequela, post-thrombotic syndrome (PTS), remain a clinically significant problem. Interleukin-6 (IL-6) is a proinflammatory cytokine that is elevated in patients who develop PTS. We hypothesized that genetic deletion of IL-6 and the use of anti–IL-6 pharmacologic agents would be associated with decreased late vein wall injury. METHODS: Wild-type C57BL/6J (WT) and IL-6(−/−) mice underwent induction of stasis venous thrombosis by ligation of the infrarenal IVC. Vein wall inferior vena cava and thrombus were harvested at 21 days after ligation and analyzed by Western blot and immunohistochemistry of the vein wall using monocyte markers CCR2 and arginase 1, the endothelial marker CD31, and fibroblast markers DDR2 and FSP-1. Two anti–IL-6 pharmacologic agents (gp130 [glycoprotein 130] and tocilizumab) were tested and compared with low-molecular-weight heparin (LMWH) as the reference standard in WT mice. Plasma was collected at 4 and 48 hours to confirm the pharmacologic agents’ effects. RESULTS: Less fibrosis but no increase in luminal endothelialization was found in IL-6(−/−) mice compared with WT mice at 21 days. The IL-6(−/−) mice had fewer DDR2- and arginase 1-positive cells in the vein wall compared with the WT mice. However, no difference was found in the CCR2(+) cells. Despite documented in vivo activity, exogenous gp130 and tocilizumab were not associated with decreased vein wall fibrosis or increased endothelial luminal coverage at 21 days. LMWH therapy, both before and after treatment, was not associated with decreased vein wall fibrosis at 21 days. CONCLUSIONS: IL-6 genetic deletion was associated with less fibrotic vein wall injury at a late time point, consistent with the PTS timeframe. However, neither the standard of care LMWH nor two available anti–IL-6 agents showed antifibrotic biologic effects in this model.