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

## TL;DR

LTB4 causes long-term neutrophil attachment and releases MCP-1 and NO in endothelial cells via the MAP kinase pathway.

## Contribution

LTB4's role in prolonged neutrophil tethering and vascular inflammation via BLT1 and BLT2 receptors is newly identified.

## Key findings

- LTB4 induces biphasic neutrophil tethering in HUVEC, with a long-lasting second phase.
- LTB4 up-regulates E-selectin, ICAM-1, VCAM-1, and releases MCP-1 and NO.
- LTB4 signaling via BLT1 and BLT2 uses the MAP kinase/Erk pathway.

## Abstract

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.

Leukotriene B4 (LTB4), a potent leukocyte chemoattractant, links early innate and late adaptive immune responses. Here, we show that LTB4 activates endothelial cells to rapid but short‐lived as well as to later robust and prolonged tethering of neutrophils, partly via LTB4 receptors BLT1 and BLT2. LTB4 up‐regulated E‐selectin, ICAM‐1 and VCAM‐1 and release of MCP‐1 and NO via the MAP kinase pathway, suggesting a novel role for LTB4 in vascular inflammation.