Abstract

The aim of this study was to evaluate the consequences of interleukin (IL)-4-induced 15-lipoxygenase (15-LO) expression on leukotriene B₄ (LTB₄) synthesis in human monocytes. Human monocytes incubated for 24, 48, and 72 h with IL-4 (10 ng/ml) were stimulated with Ca²⁺-ionophore A23187 (calcimycin; 5 μM) or opsonized zymosan. 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE], LTB₄, and arachidonic acid (AA) release were measured by high-performance liquid chromotography/radioimmunoassay, liquid chromotography/tandem mass spectrometry (LC/MS/MS), or gas chromatography/mass spectrometry. 15-LO activity was evaluated in AA-treated monocytes. 15-LO, 5-lipoxygenase (5-LO) and 5-LO activating protein (FLAP) expression were analyzed by reverse transcription-polymerase chain reaction. Neutrophil chemotactic activity was evaluated using a microtaxis chamber assay. A23187-induced synthesis of 15(S)-HETE was significantly increased after treatment with IL-4 (10 ng/ml) for 48 and 72 h (p < 0.001). Concomitant decrease of LTB₄ release was observed after 72 h of incubation with IL-4 (p < 0.001). LC/MS/MS analysis confirmed the production of 15(S)-HETE and the significant inhibition of LTB₄ synthesis in IL-4-treated monocyte after challenge with opsonized zymosan. IL-4 treatment induced 15-LO enzymatic activity as well as 15-LO mRNA, but did not affect either 5-LO or FLAP mRNA expression in monocytes. Supernatant from IL-4-treated monocytes showed significantly lower neutrophil chemotactic activity than controls. 15(S)-HETE significantly inhibited LTB₄ production induced by A23187-stimulated human monocytes without affecting AA release. IL-4-induced expression of 15-LO in monocytes caused a significant reduction of LTB₄ production. Whereas this effect did not reflect changes in 5-LO and FLAP mRNA expression, synthetic 15(S)-HETE was able to significantly inhibit the synthesis of LTB₄, without affecting AA release.