Synthesis of leukotriene C and other arachidonic acid metabolites by mouse pulmonary macrophages

Abstract

Mouse resident pulmonary macrophages were subdivided into alveolar (PAM) and interstitial (PTM) populations on the basis of accessibility to pulmonary lavage, and zymosan-induced arachidonic acid (20:4) metabolism was examined in both populations labeled with [3H]20:4. Maximal phagocytic doses of unopsonized zymosan induced the specific release of 11% of phospholipid 20:4 by PTM and 4.6% by PAM. Direct fatty acid analysis of [3H]20:4-labeled PTM cultured in the presence or absence of zymosan indicated that the specific activity of the [3H]20:4 in cell phospholipid provided an accurate measure of 20:4 released by the cells, and could therefore be used to quantitate the synthesis of 20:4 metabolites by PTM in vitro. The single major 20:4 metabolite of PTM was the slow-reacting substance leukotriene C, which was synthesized in quantities of 3-4 pmol/μg cell protein (280-370 pmol/106 cells), and comprised 20-25% of the released 20:4. PTM also synthesized prostaglandin E2, prostacyclin, thromboxane A2, and hydroxyeicosatetraenoic acids. In contrast, PAM produced leukotrienes D and E in addition to leukotriene C, prostaglandin E2, thromboxane A2, and hydroxyeicosatetraenoic acids. Prostacyclin formation by PAM was not observed. These studies define a set of experimental conditions for the study of 20:4 metabolism by pulmonary macrophages, and demonstrate that these cells are rich sources of LTC as well as other 20:4 oxygenated products.