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

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.