Generation of leukotriene B₄ by human lung fragments and purified human lung mast cells

Leukotriene B₄ (LTB₄) is a potent stimulus for neutrophil chemotaxis, aggregation, and activation. Although this mediator has been postulated as a possible stimulus for the neutrophil accumulation seen after mast cell triggering in vivo, the ability of human mast cells to produce this leukotriene has never been described. The purpose of this study was to investigate the ability of purified human lung mast cells and mast cells in lung fragments to generate leukotriene B₄ after immunologic (anti-IgE) and nonimmunologic (calcium ionophore, A23187) activation. Release of LTB₄ was quantitated by 2 specific radioimmunoassays with biochemical characterization by high performance liquid chromatography. In a first series of experiments using radioimmunoassay 1, purified human lung mast cells (n = 10) released LTB₄ in response to both an immunologic and nonimmunologic stimulus in a time- and dose-dependent manner. In response to an optimum concentration of anti-IgE (3 μg/ml), mast cells of 4.5 to 98% purity, generated 6.2 ± 1.7 ng immunoreactive LTB₄ (iLTB₄)/10⁶ mast cells. HPLC characterization revealed that 30 ± 0.3% of the iLTB₄ coeluted with standard synthetic LTB₄ in these studies. In a second series of experiments using radioimmunoasssay 2, mast cell activation resulted in the release of 0.5 to 1 ng iLTB₄/10⁶ mast cells with > 75% coeluting with synthetic LTB₄. Thus, we estimate that human lung mast cells can generate approximately 1 to 2 ng of LTB₄ per million mast cells. In further studies, we demonstrated that human lung mast cells, unlike human neutrophils, neither metabolize LTB₄ nor retain significant quantities of LTB₄ intracellularly after cell activation. Lung fragments (n = 5) spontaneously released 5.3 ± 1.4 ng iLTB₄/g tissue, a quantity that was not statistically different from the 8.7 ± 3.4 ng iLTB₄/g tissue released after stimulation with anti-IgE (1 μg/ml). HPLC characterization showed that 51.5 ± 6% of this material coeluted with standard synthetic LTB₄ (radioimmunoassay 1). We conclude that human lung mast cells synthesize and release physiologically significant quantities of leukotriene B₄ after immunologic and nonimmunologic activation. However, other lung cells such as alveolar macrophages produce, quantitatively, more of this leukotriene. Whether mast cell release of this mediator is responsible for the neutrophil influx seen after mast cell triggering in vivo remains to be determined.