Sources of Arachidonic Acid in Human Lung Macrophages

The aim of this study was to define the lipid pools in which arachidonic acid (AA) is stored and from which it is released upon activation of human lung macrophages (HLM). HLM incorporate exogenous AA into neutral lipids (triglycerides) and into the major phospholipid classes. HLM also possess an AA pool not previously reported in other human cells. Initial characterization of this arachidonate-containing lipid suggests it is bis-(monoacylglyceryl)-phosphate (BMP). HLM labeled with 3H-AA for 24 h released 7.6 and 15.5% of their total radioactivity in the supernatant after 30 min of stimulation with TPA (10--6M) and the Ca2+ ionophore A23187 (10--6M), respectively. AA was released from all phospholipid pools, mostly from phosphatidylethanolamine and phosphatidylcholine. In contrast, the amount of radioactivity in the triglyceride pool rapidly increased in activated HLM. These data demonstrate the existence of a novel AA-containing phospholipid in HLM, tentatively identified as BMP, and that, although these cells contain large stores of AA in triglycerides, the only sources of AA available for eicosanoid synthesis in stimulated HLM are phospholipids.