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.
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine