Introduction The current shortage of accurate and readily available, validated biomarkers of disease severity in sepsis is an important limitation when attempting to stratify patients into homogeneous groups, in order to study pathogenesis or develop therapeutic interventions. The aim of the present study was to determine the cytokine profile in plasma of patients with severe sepsis by using a multiplex system for simultaneous detection of 17 cytokines.

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.

Lipid bodies (also known as lipid droplets) are emerging as inflammatory organelles with roles in the innate immune response to infections and inflammatory processes. In this study, we identified MCP-1 as a key endogenous mediator of lipid body biogenesis in infection-driven inflammatory disorders and we described the cellular mechanisms and signaling pathways involved in the ability of MCP-1 to regulate the biogenesis and leukotriene B4 (LTB4) synthetic function of lipid bodies. In vivo assays in MCP-1−/− mice revealed that endogenous MCP-1 produced during polymicrobial infection or LPS-driven inflammatory responses has a critical role on the activation of lipid body-assembling machinery, as well as on empowering enzymatically these newly formed lipid bodies with LTB4 synthetic function within macrophages. MCP-1 triggered directly the rapid biogenesis of distinctive LTB4-synthesizing lipid bodies via CCR2-driven ERK- and PI3K-dependent intracellular signaling in in vitro-stimulated macrophages. Disturbance of microtubule organization by microtubule-active drugs demonstrated that MCP-1-induced lipid body biogenesis also signals through a pathway dependent on microtubular dynamics. Besides biogenic process, microtubules control LTB4-synthesizing function of MCP-1-elicited lipid bodies, in part by regulating the compartmentalization of key proteins, as adipose differentiation-related protein and 5-lipoxygenase. Therefore, infection-elicited MCP-1, besides its known CCR2-driven chemotactic function, appears as a key activator of lipid body biogenic and functional machineries, signaling through a microtubule-dependent manner.

Dengue fever is an emerging viral disease transmitted by arthropods to humans in tropical countries. Dengue hemorrhagic fever (DHF) is escalating in frequency and mortality rates. Here we studied the involvement of macrophage migration inhibitory factor (MIF) in dengue virus (DENV) infection and its pathogenesis. Patients with DHF had elevated plasma concentrations of MIF. Both leukocytes from these patients and macrophages from healthy donors infected in vitro with DENV showed a substantial amount of MIF within lipid droplets. The secretion of MIF by macrophages and hepatocytes required a productive infection and occurred without an increase in gene transcription or cell death, thus indicating active secretion from preformed stocks. In vivo infection of wild-type and mif-deficient (Mif(-/-)) mice demonstrated a role of MIF in dengue pathogenesis. Clinical disease was less severe in Mif(-/-) mice, and they exhibited a significant delay in lethality, lower viremia, and lower viral load in the spleen than wild-type mice. This reduction in all parameters of severity on DENV infection in Mif(-/-) mice correlated with reduced proinflammatory cytokine concentrations. These results demonstrated the contribution of MIF to the pathogenesis of dengue and pointed to a possible beneficial role of neutralizing MIF as an adjunctive therapeutic approach to treat the severe forms of the disease.

Macrophage migration inhibitory factor (MIF) is a cytokine playing a critical role in the pathophysiology of experimental sepsis. The purpose of this study was to determine the levels of MIF and to compare those to interleukin-6 (IL-6) levels in predicting mortality among critically ill patients with sepsis. The levels of MIF and IL-6 were measured in 25 patients with septic shock, 17 patients with sepsis, and 11 healthy volunteers. The median plasma concentrations of MIF and IL-6 were significantly higher in patients with septic shock and in patients with sepsis than in healthy controls. MIF levels were significantly different between survivors and nonsurvivors, as were IL-6 levels. Discriminatory power in predicting mortality, as assessed by the areas under receiver operating characteristic curves (AUROC), was 0.793 for MIF and 0.680 for IL-6. Finally, high plasma levels of MIF (> 1100 pg/mL) had a sensitivity of 100% and a specificity of 64% to identify the patients who eventually would evolve to a fatal outcome. Thus, our data suggest that an elevated MIF level in recently diagnosed septic patients appears to be an early indicator of poor outcome and a potential entry criterion for future studies with therapeutic intervention aiming at MIF neutralization.