Role of inducible nitric oxide synthase-derived nitric oxide in lipopolysaccharide plus interferon-gamma-induced pulmonary inflammation

Anti-inflammatory Effect of Polyunsaturated Fatty Acid N-Acylethanolamines Mediated by Macrophage Activity In Vitro and In Vivo

In recent years, there has been increasing interest in studying the anti-inflammatory activity of polyunsaturated fatty acid ethanolamides (N-acylethanolamines, NAE), which are highly active lipid mediators. The results of this study demonstrate that a dietary supplement (DS) of fatty acid-derived NAEs reduces LPS-induced inflammation. The processes of cell proliferation, as well as the dynamics of Iba-1-, CD68-, and CD163-positive macrophage activity within the thymus and spleen were studied. The production of pro-inflammatory cytokines (TNF, IL1β, IL6, and INFγ), ROS, NO, and nitrites was evaluated in the blood serum, thymus, and LPS-stimulated RAW264.7 mouse macrophages. In vitro and in vivo experiments have shown that DS (1) prevents LPS-induced changes in the morphological structure of the thymus and spleen; (2) levels out changes in cell proliferation; (3) inhibits the activity of Iba-1 and CD68-positive cells; (4) reduces the production of pro-inflammatory cytokines (TNF, IL1β, IL6, and INFγ), ROS, and CD68; and (5) enhances the activity of CD-163-positive cells. In general, the results of this study demonstrate the complex effect of DS on inflammatory processes in the central and peripheral immune systems.

Mesenchymal Stromal Cell Exosomes Mediate M2-like Macrophage Polarization through CD73/Ecto-5'-Nucleotidase Activity

Mesenchymal stem/stromal cell (MSC) exosomes have been shown to alleviate immune dysfunction and inflammation in preclinical animal models. This therapeutic effect is attributed, in part, to their ability to promote the polarization of anti-inflammatory M2-like macrophages. One polarization mechanism has been shown to involve the activation of the MyD88-mediated toll-like receptor (TLR) signaling pathway by the presence of extra domain A-fibronectin (EDA-FN) within the MSC exosomes. Here, we uncovered an additional mechanism where MSC exosomes mediate M2-like macrophage polarization through exosomal CD73 activity. Specifically, we observed that polarization of M2-like macrophages by MSC exosomes was abolished in the presence of inhibitors of CD73 activity, adenosine receptors A_2A and A_2B, and AKT/ERK phosphorylation. These findings suggest that MSC exosomes promote M2-like macrophage polarization by catalyzing the production of adenosine, which then binds to adenosine receptors A_2A and A_2B to activate AKT/ERK-dependent signaling pathways. Thus, CD73 represents an additional critical attribute of MSC exosomes in mediating M2-like macrophage polarization. These findings have implications for predicting the immunomodulatory potency of MSC exosome preparations.

Effect of gamma-irradiated honey bee venom on gene expression of inflammatory and anti-inflammatory cytokines in mice

In this study, the effect of gamma-irradiated honey bee venom (doses of 0, 2, 4, 6, and 8 kGy, volume of 0.1 ml and concentration of 0.2 mg/ml) was evaluated on the reduction of allergen compounds and the gene expression of inflammatory and anti-inflammatory cytokines in mice. Hence, edema activity induced by the bee venom irradiated at 4, 6, and 8 kGy was reduced, compared with the control group and that irradiated at 2 kGy. In contrast, the paw edema induced by the bee venom irradiated at 8 kGy increased, compared with 4 and 6 kGy. At all the time periods, there was a significant decrease in the gene expression of interferon gamma (IFN-γ), interleukin 6 (IL-6), and interleukin 10 (IL-10) in the bee venoms irradiated at 4, 6, and 8 kGy, compared with the control group and that irradiated at 2 kGy. In contrast, there was an increase in the gene expression of IFN-γ and IL-6 in the bee venom irradiated at 8 kGy, compared with those irradiated at 4 and 6 kGy. Therefore, gamma irradiation at 4 and 6 kGy reduced the gene expression of cytokines at each time period by decreasing the allergen compounds of honey bee venom.

An immunosuppressive peptide from the horsefly inhibits inflammation by repressing macrophage maturation and phagocytosis

Ectoparasites repress host immune responses while they obtain nutrition from their hosts. Understanding the immunosuppressive mechanisms between ectoparasites and their hosts will provide new strategies to develop potential immunosuppressive drugs against immune disorder diseases. Previously, we have discovered that a small peptide, immunoregulin HA, from the horsefly (Hybomitra atriperoides) may play an immunosuppressive role in rat splenocytes. However, the targeting cells and detailed mechanisms of immunoregulin HA in immunosuppressive reactions are not well defined. Here, we show that immunoregulin HA reduces the secretion of proinflammatory cytokines upon lipopolysaccharide (LPS) stimulation. Interestingly, we discover that the major cytokines repressed by immunoregulin HA are secreted by macrophages, rather than by T cells. Furthermore, immunoregulin HA inhibits macrophage maturation and phagocytosis. Mechanically, the activations of c-JUN N-terminal kinase and extracellular signal-regulated kinase upon LPS stimulation are decreased by immunoregulin HA. Consistently, immunoregulin HA treatment exhibits an anti-inflammatory activity in a mouse model of adjuvant-induced paw inflammation. Taken together, our data reveal that immunoregulin HA conducts the anti-inflammatory activity by blocking macrophage functions.

Much More than M1 and M2 Macrophages, There are also CD169(+) and TCR(+) Macrophages

Monocytes are considered to be precursor cells of the mononuclear phagocytic system, and macrophages are one of the leading members of this cellular system. Macrophages play highly diverse roles in maintaining an organism's integrity by either directly participating in pathogen elimination or repairing tissue under sterile inflammatory conditions. There are different subpopulations of macrophages and each one has its own characteristics and functions. In this review, we summarize present knowledge on the polarization of macrophages that allows the generation of subpopulations called classically activated macrophages or M1 and alternative activated macrophages or M2. Furthermore, there are macrophages that their origin and characterization still remain unclear but have been involved as main players in some human pathologies. Thus, we also review three other categories of macrophages: tumor-associated macrophages, CD169(+) macrophages, and the recently named TCR(+) macrophages. Based on the literature, we provide information on the molecular characterization of these macrophage subpopulations and their specific involvement in several human pathologies such as cancer, infectious diseases, obesity, and asthma. The refined characterization of the macrophage subpopulations can be useful in designing new strategies, supplementing those already established for the treatment of diseases using macrophages as a therapeutic target.

Endothelial nitric oxide synthase deficient mice are protected from lipopolysaccharide induced acute lung injury

Lipopolysaccharide (LPS) derived from the outer membrane of gram-negative bacteria induces acute lung injury (ALI) in mice. This injury is associated with lung edema, inflammation, diffuse alveolar damage, and severe respiratory insufficiency. We have previously reported that LPS-mediated nitric oxide synthase (NOS) uncoupling, through increases in asymmetric dimethylarginine (ADMA), plays an important role in the development of ALI through the generation of reactive oxygen and nitrogen species. Therefore, the focus of this study was to determine whether mice deficient in endothelial NOS (eNOS^-/-) are protected against ALI. In both wild-type and eNOS^-/- mice, ALI was induced by the intratracheal instillation of LPS (2 mg/kg). After 24 hours, we found that eNOS^-/-mice were protected against the LPS mediated increase in inflammatory cell infiltration, inflammatory cytokine production, and lung injury. In addition, LPS exposed eNOS^-/- mice had increased oxygen saturation and improved lung mechanics. The protection in eNOS^-/- mice was associated with an attenuated production of NO, NOS derived superoxide, and peroxynitrite. Furthermore, we found that eNOS^-/- mice had less RhoA activation that correlated with a reduction in RhoA nitration at Tyr³⁴. Finally, we found that the reduction in NOS uncoupling in eNOS^-/- mice was due to a preservation of dimethylarginine dimethylaminohydrolase (DDAH) activity that prevented the LPS-mediated increase in ADMA. Together our data suggest that eNOS derived reactive species play an important role in the development of LPS-mediated lung injury.

Central memory CD8+ T lymphocytes mediate lung allograft acceptance

Memory T lymphocytes are commonly viewed as a major barrier for long-term survival of organ allografts and are thought to accelerate rejection responses due to their rapid infiltration into allografts, low threshold for activation, and ability to produce inflammatory mediators. Because memory T cells are usually associated with rejection, preclinical protocols have been developed to target this population in transplant recipients. Here, using a murine model, we found that costimulatory blockade-mediated lung allograft acceptance depended on the rapid infiltration of the graft by central memory CD8+ T cells (CD44(hi)CD62L(hi)CCR7+). Chemokine receptor signaling and alloantigen recognition were required for trafficking of these memory T cells to lung allografts. Intravital 2-photon imaging revealed that CCR7 expression on CD8+ T cells was critical for formation of stable synapses with antigen-presenting cells, resulting in IFN-γ production, which induced NO and downregulated alloimmune responses. Thus, we describe a critical role for CD8+ central memory T cells in lung allograft acceptance and highlight the need for tailored approaches for tolerance induction in the lung.

Real-time whole-body visualization of Chikungunya Virus infection and host interferon response in zebrafish

Chikungunya Virus (CHIKV), a re-emerging arbovirus that may cause severe disease, constitutes an important public health problem. Herein we describe a novel CHIKV infection model in zebrafish, where viral spread was live-imaged in the whole body up to cellular resolution. Infected cells emerged in various organs in one principal wave with a median appearance time of ∼14 hours post infection. Timing of infected cell death was organ dependent, leading to a shift of CHIKV localization towards the brain. As in mammals, CHIKV infection triggered a strong type-I interferon (IFN) response, critical for survival. IFN was mainly expressed by neutrophils and hepatocytes. Cell type specific ablation experiments further demonstrated that neutrophils play a crucial, unexpected role in CHIKV containment. Altogether, our results show that the zebrafish represents a novel valuable model to dynamically visualize replication, pathogenesis and host responses to a human virus.

Chikungunya, a re-emerging disease caused by a mosquito-transmitted virus, is an important public health problem. We developed a zebrafish model for chikungunya virus infection. For the first time, rise and death of virus-infected cells could be live imaged in the entire body of a vertebrate. We observed a widespread wave of apparition of newly infected cells during the first day after inoculation of the virus. We then found that infected cells died at a strongly organ-dependent rate, accounting for the progressive shift of virus localization. Notably, the virus persisted in the brain despite apparent recovery of infected zebrafish. We found this recovery to be critically dependent on the host type I interferon response. Surprisingly, we identified neutrophils as a major cell population expressing interferon and controlling chikungunya virus.

Intestinal alkaline phosphatase administration in newborns decreases systemic inflammatory cytokine expression in a neonatal necrotizing enterocolitis rat model

BACKGROUND

Supplementation of intestinal alkaline phosphatase (IAP), an endogenous protein expressed in the intestines, decreases the severity of necrotizing enterocolitis (NEC)-associated intestinal injury and permeability. We hypothesized that IAP administration is protective in a dose-dependent manner of the inflammatory response in a neonatal rat model.

MATERIALS AND METHODS

Pre- and full-term newborn Sprague-Dawley rat pups were sacrificed on day of life 3. Control pups were vaginally delivered and dam fed. Preterm pups were delivered via cesarean section and exposed to intermittent hypoxia and formula feeds containing lipopolysaccharide (NEC) with and without IAP. Three different standardized doses were administered to a group of pups treated with 40, 4, and 0.4U/kg of bovine IAP (NEC+IAP40, IAP4, or IAP0.4U). Reverse transcription-real-time polymerase chain reaction (RT-PCR) for inducible nitric oxide synthase (iNOS) and tumor necrosis factor (TNF)-α on liver and lung tissues and serum cytokine analysis for interleukin (IL)-1β, IL-6, IL-10, and TNF-α were performed. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests, expressed as mean±standard error of the mean and P≤0.05 considered significant.

RESULTS

Levels of cytokines IL-1β, IL-6, and TNF-α increased significantly in NEC versus control, returning to control levels with increasing doses of supplemental enteral IAP. Hepatic and pulmonary TNF-α and iNOS messenger ribonucleic acid expressions increased in NEC, and the remaining elevated despite IAP supplementation.

CONCLUSIONS

Proinflammatory cytokine expression is increased systemically with intestinal NEC injury. Administration of IAP significantly reduces systemic proinflammatory cytokine expression in a dose-dependent manner. Early supplemental enteral IAP may reduce NEC-related injury and be useful for reducing effects caused by a proinflammatory cascade.

Nitric oxide for the adjunctive treatment of severe malaria: hypothesis and rationale

We hypothesize that supplemental inhaled nitric oxide (iNO) will improve outcomes in children with severe malaria receiving standard antimalarial therapy. The rationale for the hypothesized efficacy of iNO rests on: (1) biological plausibility, based on known actions of NO in modulating endothelial activation; (2) pre-clinical efficacy data from animal models of experimental cerebral malaria; and (3) a human trial of the NO precursor l-arginine, which improved endothelial function in adults with severe malaria. iNO is an attractive new candidate for the adjunctive treatment of severe malaria, given its proven therapeutic efficacy in animal studies, track record of safety in clinical practice and numerous clinical trials, inexpensive manufacturing costs, and ease of administration in settings with limited healthcare infrastructure. We plan to test this hypothesis in a randomized controlled trial (ClinicalTrials.gov Identifier: NCT01255215).

Immunomodulation by a combination of nitric oxide and glucocorticoids in a human endotoxin model

BACKGROUND

inflammatory reactions arise in reaction to a variety of pathogenic insults. The combination of inhaled nitric oxide (iNO) and glucocorticoids (GC) may attenuate endotoxin-induced inflammatory responses. It has been shown that the combination of iNO (30 p.p.m.) and steroids blunted the inflammatory response in a porcine endotoxin model, but not in humans. Therefore, we investigated whether a clinically 'maximal' dose of iNO in combination with GC could modulate the systemic inflammatory response in a human endotoxin model.

METHODS

a double-blind, cross-over, placebo-controlled randomized study including 15 healthy Caucasian volunteers (five females, 10 males). Performed at the Intensive Care Unit in a university hospital. iNO 80 p.p.m. or placebo (nitrogen) was started 2h before administration of endotoxin (2 ng/kg). Thirty minutes later, GC (2mg/kg, hydrocortisone) was administered intravenously. Blood samples and clinical signs were collected before and up to 24 h after the endotoxin injection.

RESULTS

body temperature and heart rate increased significantly subsequent to endotoxin challenge. The plasma levels of IFN-γ, IL-1β, IL-2, 4 5, 6, 8, 10, 12, 13 and TNFα were markedly elevated. However, HMGB-1 and sRAGE were unaffected. No difference between placebo/GC and iNO/GC treatment was observed in the clinical or cytokine response, neither was there any difference between the first and the second exposure to endotoxin.

CONCLUSIONS

pre-treatment with iNO 80 p.p.m. along with GC (2mg/kg) administrated after the endotoxin challenge could not modulate the systemic inflammatory response in this model of human experimental inflammation.

NOS2 regulation of NF-kappaB by S-nitrosylation of p65

Signal transduction in the NF-kappaB transcription factor pathway is inhibited by inducible nitric oxide synthase (NOS2) activity, although the molecular mechanism(s) are incompletely understood. We have previously shown that nitric oxide (NO), derived from NOS2 consequent upon cytokine stimulation, attenuates NF-kappaB p50-p65 heterodimer DNA binding and have identified the p50 monomer as a locus for inhibitory S-nitrosylation. We now show that the binding partner of p50, NF-kappaB p65, is also targeted by NO following cytokine stimulation of respiratory epithelial cells and macrophages and identify a conserved cysteine within the Rel homology domain that is the site for S-nitrosylation. S-Nitrosylation of p65 inhibits NF-kappaB-dependent gene transcription, and nuclear levels of S-nitrosylated p65 correlate with decreased DNA binding of the p50-p65 heterodimer. NOS2 regulates cytokine-induced S-nitrosylation of p65, resulting in decreased NF-kappaB binding to the NOS2 promoter, thereby inhibiting further NOS2 expression. Collectively, these findings delineate a mechanism by which NOS2 modulates NF-kappaB activity and regulates gene expression in inflammation.

Effect of honey bee venom on microglial cells nitric oxide and tumor necrosis factor-alpha production stimulated by LPS

Abnormal activation of microglial cells has been implicated in various neurodegenerative diseases. Results showed that venom (KBV) produced and purified in Korea regulated lipopolysaccharides (LPS)-induced nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) in the murine microglia, BV-2 cell line. The production of proinflammatory cytokines, NO, and TNF-alpha was examined by LPS in BV-2 cell. The effect of KBV on the expression of inducible nitric oxide synthase (iNOS) and TNF-alpha was investigated by Western blot and RT-PCR in LPS-stimulated BV-2 cells. KBV suppressed the NO, iNOS, and TNF-alpha production, and decreased the levels of iNOS and TNF-alpha mRNA. These results suggest that KBV has anti-inflammatory properties that inhibit iNOS and TNF-alpha expression. KBV could be useful in inhibiting the production of inflammatory cytokine and NO production in neurodegenerative diseases. Further studies on the pharmacological aspects of the individual components of KBV are recommended.

Conditional expression of interferon-γ to enhance host responses to pulmonary bacterial infection

Strategies to augment host defense against pulmonary infection run the risk of inducing excess pulmonary inflammation and tissue injury. To address this problem, we investigated conditional expression in lung tissue of the murine interferon-gamma (IFN-gamma) transgene. A recombinant adenoviral vector (AdTetIFN) was constructed by placing a murine IFN-gamma cDNA downstream of a tetracycline (Tet)-responsive promoter, inserted into a replication-defective adenoviral vector. Co-infection of target cells with AdTetIFN and a second vector encoding a reverse tetracycline controlled transactivator allowed doxycycline (Dox)-regulated IFN-gamma production. We then administered 10(8) plaque-forming units (PFU) of AdTetIFN to mice by intratracheal injection. When the mice were provided with Dox in drinking water (0.5mg/ml in 5% sucrose), there was significant release of IFN-gamma in lavage fluid by ELISA in comparison to mice on water/sucrose alone (399+/-74 pg/ml vs undetectable, p<0.01). IFN-gamma in lavage fluid was associated with upregulation of Class II Major histocompatibility complex markers on alveolar macrophages by flow cytometry, suggesting macrophage activation. We then injected AdTetIFN into mice three days prior to challenge with 10(4) CFU Klebsiella pneumoniae. Test mice were maintained on water+Dox and control mice on water+sucrose. Bacterial burden was assayed in lung tissue at serial intervals. At 24h after challenge, mice on doxycycline had significantly lower infection burden in comparison to mice on water/sucrose (0.77+/-0.05 colony forming units/lung for 10(8) PFU AdTetIFN plus Dox compared to 1.4+/-0.11 colony-forming units/lung for AdTetIFN without Dox, p<0.05). Survival of the vector treated mice given doxycycline in drinking water was also enhanced. Microscopic examination of lavaged cells showed a significant increase in pulmonary neutrophils in the AdTetIFN+Dox mice in comparison to AdTetIFN+sucrose mice (16+/-1.0 x 10(5) vs 10+0.8 cells/lung, p<0.05). We conclude that local release of IFN-gamma can be selectively activated to enhance neutrophil recruitment and host resistance to bacterial pneumonia.

Rho-kinase (ROCK-1 and ROCK-2) upregulation in oleic acid-induced lung injury and its restoration by Y-27632

The possible contribution of Rho/Rho-kinase signalling in oleic acid (100 mg kg-1, i.v., for 4 h)-induced lung injury was investigated in rats. Furthermore, the possible protective effect of the administration of a Rho-kinase inhibitor, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632, 0.5-5 mg kg-1, i.v., 15 min before the administration of oleic acid), was also examined. Western blot analysis as well as histopathological examination revealed that Rho-kinase (ROCK-1 and ROCK-2) was upregulated in lungs obtained from oleic acid-administrated rats. In addition, the markers of oxidative and nitrosative stress, i.e., malondialdehyde, myeloperoxidase, 3-nitro-L-tyrosine and nitrite/nitrate, in serum and lung tissue were also increased in the injury group. Treatment of rats with 5 mg kg-1 Y-27632 reversed the oleic acid-induced lung damage, which was demonstrated by histopathological assessment and confirmed in Western blot experiments: ROCK-blots were more intense in the oleic acid group than in control and Y-27632 treatment reversed ROCK upregulation. In addition, malondialdehyde, myeloperoxidase, 3-nitro-L-tyrosine and nitrite/nitrate were also normalized after the administration of Y-27632 (0.5 mg kg-1 and 5 mg kg-1). These findings suggest that ROCK-1 and ROCK-2 are involved in oleic acid-induced lung damage in rats, and that inhibition of this enzyme by Y-27632 may have a protective effect against such damage. Consequently, Rho kinase inhibitors may be potential therapeutic agents in the treatment of acute respiratory distress syndrome (ARDS).

Determination of Nitric Oxide–Donor Effects on Tissue Gene Expression In Vivo Using Low‐Density Gene Arrays

Gene array technology has been used to examine gene expression changes following drug treatments, including administration of nitric oxide (NO) donors. High-density arrays represent a powerful and popular method to analyze a large number of genes simultaneously. On the other hand, low-density arrays, available commercially at a lower cost, allow for the use of gene-specific primers, which reduces the risk of cross-hybridization among genes with similar sequence. For certain experiments in which the hypothesis is focused on a selected set of genes, use of low-density arrays might be more productive and cost-effective. Here, we describe our experience using low-density arrays to examine the effect of exposure to the NO-donor isobutyl nitrite on the expression of 23 cancer- and angiogenesis-related genes in mouse tissues. Detailed descriptions of data capture procedures, statistical tests, and confirmation studies using real-time quantitative (RTQ) reverse transcription polymerase chain reaction (RT-PCR) are presented. Three simple statistical methods, namely Student's t test, significant analysis of microarrays (SAM), and permutation adjusted t statistics (PATS), were applied on our gene array data, and their utilities were compared. All three methods yielded concordant results for the most significant genes, namely vascular endothelial growth factor (VEGF), VEGF receptor 3, Smad5, and Smad7. RT-PCR confirmed VEGF upregulation as observed via gene arrays. PATS appeared to be more robust than SAM in handling our small gene array data set. This statistical method, therefore, appears more suited for analyzing low-density gene array data. We conclude that low-density gene array is a useful screening method that can be performed with lower cost and less cumbersome data treatment.

Blockade of CXCR3 receptor:ligand interactions reduces leukocyte recruitment to the lung and the severity of experimental idiopathic pneumonia syndrome

Idiopathic pneumonia syndrome (IPS) is a frequently fatal complication after allogeneic stem cell transplantation (allo-SCT) that responds poorly to standard immunosuppressive therapy. The pathophysiology of IPS involves the secretion of inflammatory cytokines including IFN-gamma and TNF-alpha along with the recruitment of donor T cells to the lung. CXCR3 is a chemokine receptor that is expressed on activated Th1/Tc1 T cell subsets and the expression of its ligands CXCL9 (monokine induced by IFN-gamma (Mig)) and CXCL10 (IFN-gamma-inducible protein 10 (IP-10)) can be induced in a variety of cell types by IFN-gamma alone or in combination with TNF-alpha. We used a lethally irradiated murine SCT model (B6 --> bm1) to evaluate the role of CXCR3 receptor:ligand interactions in the development of IPS. We found that Mig and IP-10 protein levels were significantly elevated in the bronchoalveolar lavage fluid of allo-SCT recipients compared with syngeneic controls and correlated with the infiltration of IFN-gamma-secreting CXCR3(+) donor T cells into the lung. The in vivo neutralization of either Mig or IP-10 significantly reduced the severity of IPS compared with control-treated animals, and an additive effect was observed when both ligands were blocked simultaneously. Complementary experiments using CXCR3(-/-) mice as SCT donors also resulted in a significant decrease in IPS. These data demonstrate that interactions involving CXCR3 and its primary ligands Mig and IP-10 significantly contribute to donor T cell recruitment to the lung after allo-SCT. Therefore, approaches focusing on the abrogation of these interactions may prove successful in preventing or treating lung injury that occurs in this setting.

Direct regulation of lipolysis by interleukin-15 in primary pig adipocytes

We recently provided evidence that interleukin-15 (IL-15) is expressed lowly in the pig adipocyte and that interferon-gamma (IFN-gamma) markedly increases this expression through a pathway regulated in part by protein kinase C. In the present study, we tested the hypothesis that IL-15 acts directly on the adipocyte to regulate lipid accretion by enhancing lipolysis or suppressing lipogenesis. Using recombinant porcine IL-15, we determined that this cytokine stimulates lipolysis in a dose-dependent manner (P < 0.001). Furthermore, comparative studies with other cytokines showed that IL-15 is more potent in its acute stimulation of lipolysis than either TNF-alpha, IL-6, or LPS (P < 0.001). When specific inhibitors of protein kinase A or Janus kinase are present, the lipolytic effect of IL-15 is attenuated (P < 0.01). These data indicate that, in addition to its regulation of muscle protein accretion and T-cell growth and development, IL-15 also targets the adipocyte directly to alter stimulate lipolysis. Thus, when induced by IFN-gamma or other inflammatory mediators, IL-15 may be a significant homeorhetic factor that mobilizes and directs energy away from the adipocyte to other cells during the acute phase of the inflammatory response.