Prostaglandin Endoperoxide Synthase (Cyclooxygenase): Ultrastructural Localization to Nonmembrane-Bound Cytoplasmic Lipid Bodies in Human Eosinophils and 3T3 Fibroblasts
Lipid bodies are nonmembrane-bound cytoplasmic inclusions which are prominent in cells engaged in inflammatory responses. Using postembedding immunogold localization with a primary anti-PGH (prostaglandin endoperoxide) synthase monoclonal antibody, PGH synthase was localized by electron microscopy to lipid bodies of two prostaglandin-forming cells: human eosinophils and murine 3T3 fibroblasts. Freshly isolated eosinophils from a hypereosinophilic syndrome donor and peripheral blood eosinophils maintained in coculture with 3T3 fibroblasts and granulocyte-macrophage colony-stimulating factor were studied. In both cell types, lipid bodies were the predominant structures labeled with anti-PGH synthase. Labeling was absent in controls. In both human eosinophils and murine fibroblasts, lipid bodies represent sites of localization of PGH synthase – the rate-limiting initial enzyme in the formation of prostaglandins – and may serve as specific sites of formation of cyclooxygenase-pathway-derived eicosanoids.