Lipopolysaccharide-Induced Leukocyte Lipid Body Formation In Vivo: Innate Immunity Elicited Intracellular Loci Involved in Eicosanoid Metabolism

Abstract

Lipid bodies are rapidly inducible, specialized cytoplasmic domains for eicosanoid-forming enzyme localization, which we hypothesize to have specific roles in enhanced inflammatory mediator production during pathological conditions, including sepsis. However, little is known about the origins, composition, or functions of lipid bodies in vivo. We show that lipid body numbers were increased in leukocytes from septic patients in comparison with healthy subjects. Analogously, the intrathoracic administration of LPS into mice induced a dose- and time-dependent increase in lipid body numbers. Pretreatment with anti-CD14 or anti-CD11b/CD18 mAb drastically inhibited LPS-induced lipid body formation. Moreover, LPS failed to form lipid bodies in C3H/HeJ (TLR4 mutated) mice, demonstrating a requisite role for LPS receptors in lipid body formation. LPS-induced lipid body formation was also inhibited by the platelet-activating factor-receptor antagonists, suggesting a role for endogenous platelet-activating factor. The eicosanoid-forming enzymes, 5-lipoxygenase and cyclooxygenase-2, were immunolocalized within experimentally induced (LPS in mice) or naturally occurring (septic patients) lipid bodies. The proinflammatory cytokine involved in the pathogenesis of sepsis, TNF-α, was also shown to colocalize within lipid bodies. Prior stimulation of leukocytes to form lipid bodies enhanced the capacity of leukocytes to produce leukotriene B4 and PGE2. In conclusion, our studies indicate that lipid bodies formed after LPS stimulation and sepsis are sites for eicosanoid-forming enzymes and cytokine localization and may develop and function as structurally distinct, intracellular sites for paracrine eicosanoid synthesis during inflammatory conditions.