LTB4 Activates the MAP Kinase Pathway in Endothelial Cells to Cause Long-Lasting Neutrophil Tethering, MCP-1 and NO Releases.

Leukotriene B4 (LTB4), a potent chemotactic and immune-modulating eicosanoid, signals via two receptors (BLT1 and BLT2), leading to rapid but transient migratory, adhesive and secretory responses in phagocytes. Previously, we reported that BLT1 is the predominating BLT in human umbilical vein endothelial cells (HUVEC). However, little is known about how ligation of these receptors affects adhesive and secretory endothelial responses over time. Here, we demonstrate that in HUVEC, LTB4 dose-dependently and stereospecifically causes a biphasic tethering of neutrophils, where the second phase is robust, similar to that induced by lipopolysaccharide, and persists for 3-8 h. LTB4 also causes up-regulation of E-selectin, ICAM-1 and VCAM-1 and release of MCP-1 and nitric oxide (but not of IL-8 or HMGB1). These responses appeared to be mediated via BLT1 and BLT2 as judged by BLT1 shRNA gene silencing and/or treatment with BLT1 and BLT2 specific antagonists prior to LTB4 activation of HUVEC. Moreover, LTB4 responses used primarily the MAP kinase/Erk pathway. Our findings suggest a new role for LTB4 not only in early but also in late vascular inflammatory responses.