Glycerophospholipids containing arachidonic acid (20:4) serve as the precursors for an arrayof biologically active lipid mediators, most of which are produced by macrophages. We have appliedmass spectrometry-based lipid profiling technology to evaluate the glycerophospholipid structure andcomposition of two macrophage populations, resident peritoneal macrophages and RAW264.7 cells, withregard to their potential for 20:4-based lipid mediator biosynthesis. Fatty acid analysis indicated thatRAW264.7 cells were deficient in 20:4 (10 ± 1 mol %) compared to peritoneal macrophages (26 ± 1mol %). Mass spectrometry of total glycerophospholipids demonstrated a marked difference in thedistribution of lipid species, including reduced levels of 20:4-containing lipids, in RAW264.7 cells comparedto peritoneal macrophages. Enrichment of RAW264.7 cells with 20:4 increased the fatty acid to 20 ± 1mol %. However, the distribution of the incorporated 20:4 remained different from that of peritonealmacrophages. RAW264.7 cells pretreated with granulocyte-macrophage colony stimulating factor followedby lipopolysaccharide and interferon-
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mobilized similar quantities of 20:4 and produced similar amountsof prostaglandins as peritoneal macrophages treated with LPS alone. LPS treatment resulted in detectablechanges in specific 20:4-containing glycerophospholipids in peritoneal cells, but not in RAW264.7 cells.20:4-enriched RAW264.7 cells lost 88% of the incorporated fatty acid during the LPS incubation withoutadditional prostaglandin synthesis. These results illustrate that large differences in glycerophospholipidcomposition may exist, even in closely related cell populations, and demonstrate the importance ofinterpreting the potential for lipid-mediator biosynthesis in the context of overall glycerophospholipidcomposition.