Leukotriene generation and metabolism in isolated human lung macrophages

We studied the generation and metabolism of leukotrienes (LTs) in human lung macrophages obtained from lung tissue of patients with central bronchial carcinoma. By counterflow centrifugation macrophages were enriched with a purity of more than 95-100%. A time and dose dependent generation of LTB4 and LTC4 was determined by specific radioimmunoassays after stimulation with the Ca-ionophore and anti-IgE. The amount of LTB4 exceeded the amount of LTC4. The concentrations of leukotrienes in the macrophage fraction amounted to 4.3 +/- 2.2 ng LTB4 and 0.6 +/- 0.05 ng LTC4/1 x 10(7) cells after 5 min of incubation with the Ca-ionophore. The LTB4 levels decreased to 3.0 +/- 0.6 ng after 60 min indicating the metabolism of the generated LTB4 by human lung macrophages. This was confirmed by incubation of the cells with exogenously added [3H]LTB4. LTB4 was converted into unpolar products as was identified by thin-layer chromatography and high-performance liquid chromatography; a comparison with the fibroblast cell line L929 which is known to convert LTB4 into the dihydro-LTB4 metabolite (5,12-dihydroxyeicosatrienoic acid) indicates that human lung macrophages use the same pathway of metabolization. Biological inactivation as determined by chemotaxis and cross-reaction with the LTB4 antiserum correlates with the degree of LTB4 metabolism. Moreover, the macrophages convert LTC4 into LTD4 and LTE4 by the enzymatic activity of the gamma-glutamyltranspeptidase and dipeptidase. Our data emphasize that the human alveolar macrophage not only produces arachidonic acid metabolites but modulates the local inflammatory potential by its metabolizing capacity for leukotrienes.