Potentiation of leukotriene production following sequestration of neutrophils in isolated lungs: indirect evidence for intercellular leukotriene A4 transfer

Granulocyte (polymorphonuclear leukocyte, PMN) sequestration in the microvascular bed with release of different mediators has been implicated in the pathogenesis of inflammatory and allergic disorders in many organs including the lung. In the present study, we investigated the profile and quantity of leukotriene (LT) generation in isolated blood-free perfused rabbit lungs, in isolated PMNs in vitro and in rabbit lungs, following administration of PMNs, mimicking pulmonary leukostasis. Following stimulation with increasing concentrations of the calcium ionophore A 23137 (0.1 to 2 mumol/L), LTs were detected in the buffer fluid by their chromatographic mobility in different high-performance liquid chromatography (HPLC) systems, by on- line peak spectrum analysis, and by post-HPLC radioimmunoassay (RIA). In isolated lungs, a dose-dependent generation of cysteinyl LTs greater than LTB4, in the complete absence of omega-oxidation products of LTB4 as well as nonenzymatic hydrolysis products of LTA4, was evoked. PMNs in vitro showed a typical profile of LT liberation (LTB4, 20-OH-, and COOH-LTB4, nonenzymatic LTA4 metabolites). In the model of pulmonary leukostasis, the presence of omega-oxidation products of LTB4 indicated metabolic integrity of the trapped PMNs. Nonenzymatic hydrolysis products of LTA4 were, however, not detected in the combined system, whereas the cysteinyl LTs increased markedly. This profile suggests intercellular transfer of PMN-derived LTA4 to lung cells in the microenvironment. In addition, at 2 mumol/L A23187, the sum of all LTA4- derived products surpassed the arithmetic sum of the isolated preparations more than threefold. This potentiation of an LT generation under conditions of pulmonary leukostasis may be of biologic significance for amplification of inflammatory events.