Tumor Necrosis Factor-α Induces Leukocyte Recruitment by Different Mechanisms in Vivo and in Vitro

It is well established that E-selectin is the endothelial adhesion molecule that is primarily responsible for mediating leukocyte rolling on TNF-α-stimulated cultured endothelial cells. Despite this, few studies in in vivo inflammatory models have observed reduced leukocyte accumulation using mAbs against E-selectin. The objective of this study was to compare the function of E-selectin on endothelial cells in vitro with its role in TNF-α-induced leukocyte recruitment in vivo using EL246, a mAb that blocks the function of E-selectin on activated feline endothelial cells. In vitro experiments using feline endothelial cells showed that EL246 functionally inhibits E-selectin-dependent leukocyte recruitment induced by TNF-α, without affecting the function of other rolling mechanisms. Intravital microscopy of single 25- to 40-μm venules in the feline mesentery was then used to examine leukocyte rolling and adhesion in response to superfusion with TNF-α. TNF-α treatment significantly increased the number of both rolling and adherent leukocytes and significantly decreased leukocyte rolling velocity. Treatment with EL246 (1 mg/kg), either i.v. at the start of the TNF-α protocol or directly into the superior mesenteric artery after 3 h of TNF-α treatment, had no effect on leukocyte rolling, adhesion, or rolling velocity. However, treatment with the selectin-binding carbohydrate, fucoidan, reduced leukocyte rolling to below baseline levels. These results suggest that in contrast to its prominent role on cultured endothelial cells, E-selectin does not contribute to leukocyte recruitment in TNF-α-stimulated feline mesenteric venules in vivo.