Evros Vassiliou

Prostaglandin E2 induces IL-23 production in bone marrow-derived dendritic cells.

Interleukin‐23, a recently described cytokine produced by activated antigen‐presenting cells, including dendritic cells, is a p19/p40 heterodimer. The p40 subunit is shared with IL‐12, the major Th1‐driving cytokine, while p19 is distantly related to IL‐12 p35. IL‐23 has pro‐ inflammatory actions, inducing IL‐17 secretion from activated CD4+ T cells, and stimulating the proliferation of memory CD4+ T cells. Here, we examined the effects of PGE2, a well‐known immunomodulator, on the production of IL‐23 by bone marrow‐ derived dendritic cells (BM‐ DCs). Our results indicate that PGE2 increases the production of functional IL‐23 from immature BM‐DCs in a time‐ and dose‐dependent manner. PGE2 induces both the expression of p19 and p40, without affecting p35 expression. The effect of PGE2 is mediated through the specific receptors EP2/4 and is mimicked by cAMP‐inducing agents, such as forskolin and dbcAMP. Although PGE2 also induces IL‐1β and IL‐6 expression in non‐stimulated DCs, the stimulatory effect of PGE2 on IL‐23 production is not mediated through IL‐1β or IL‐6. GM‐CSF, the pro‐ inflammatory cytokine required for the generation of BM‐DCs, amplifies the IL‐23 inducing activity of PGE2 in a synergistic manner. Recent studies described both pro‐ and anti‐ inflammatory effects of PGE2, and our results suggest an additional mechanism for its pro‐ inflammatory role, particularly significant for autoimmune diseases, such as rheumatoid arthritis.

Oleic acid and peanut oil high in oleic acid reverse the inhibitory effect of insulin production of the inflammatory cytokine TNF-α both in vitro and in vivo systems

BackgroundChronic inflammation is a key player in pathogenesis. The inflammatory cytokine, tumor necrosis factor-alpha is a well known inflammatory protein, and has been a therapeutic target for the treatment of diseases such as Rheumatoid Arthritis and Crohns Disease. Obesity is a well known risk factor for developing non-insulin dependent diabetes melitus. Adipose tissue has been shown to produce tumor necrosis factor-alpha, which has the ability to reduce insulin secretion and induce insulin resistance. Based on these observations, we sought to investigate the impact of unsaturated fatty acids such as oleic acid in the presence of TNF-α in terms of insulin production, the molecular mechanisms involved and the in vivo effect of a diet high in oleic acid on a mouse model of type II diabetes, KKAy.MethodsThe rat pancreatic beta cell line INS-1 was used as a cell biological model since it exhibits glucose dependent insulin secretion. Insulin production assessment was carried out using enzyme linked immunosorbent assay and cAMP quantification with competitive ELISA. Viability of TNF-α and oleic acid treated cells was evaluated using flow cytometry. PPAR-γ translocation was assessed using a PPRE based ELISA system. In vivo studies were carried out on adult male KKAy mice and glucose levels were measured with a glucometer.ResultsOleic acid and peanut oil high in oleic acid were able to enhance insulin production in INS-1. TNF-α inhibited insulin production but pre-treatment with oleic acid reversed this inhibitory effect. The viability status of INS-1 cells treated with TNF-α and oleic acid was not affected. Translocation of the peroxisome proliferator- activated receptor transcription factor to the nucleus was elevated in oleic acid treated cells. Finally, type II diabetic mice that were administered a high oleic acid diet derived from peanut oil, had decreased glucose levels compared to animals administered a high fat diet with no oleic acid.ConclusionOleic acid was found to be effective in reversing the inhibitory effect in insulin production of the inflammatory cytokine TNF-α. This finding is consistent with the reported therapeutic characteristics of other monounsaturated and polyunsaturated fatty acids. Furthermore, a diet high in oleic acid, which can be easily achieved through consumption of peanuts and olive oil, can have a beneficial effect in type II diabetes and ultimately reverse the negative effects of inflammatory cytokines observed in obesity and non insulin dependent diabetes mellitus.

Prostaglandin E2 inhibits TNF production in murine bone marrow-derived dendritic cells

Exposure to pathogens induces dendritic cells to release inflammatory cytokines and chemokines. The inflammatory response is controlled by endogenous agents such as anti-inflammatory cytokines, glucocorticoids, anti-inflammatory neuropeptides, and lipid mediators. This study is the first report on the inhibition by prostaglandin E2 (PGE2) of TNF release from bone marrow-derived dendritic cells stimulated with lipopolysaccharide (LPS), a TLR4 ligand, or peptidoglycan, a TLR2 ligand. The inhibition of TNF occurs at both mRNA and protein level. The inhibitory effect of PGE2 is mediated by the EP2 and EP4 receptors, and involves both PKA signaling and mediation by DC-derived IL-10. Intraperitoneal administration of PGE2 together with LPS results in a reduction in serum TNF and intracellular TNF in peritoneal exudate cells, compared to LPS alone. In addition, administration of PGE2 in vivo reduces the numbers of CD11c+ DCc that accumulate in the peritoneal cavity in response to LPS. The various implications of the PGE2-induced reduction in TNF are discussed.

Prostaglandin E2 inhibits production of the inflammatory chemokines CCL3 and CCL4 in dendritic cells

Dendritic cells bridge innate and adaptive immunity and participate in both responses. Upon capture of pathogens, dendritic cells release inflammatory cytokines and chemokines, attracting other immune cells to the infection site. Anti‐inflammatory cytokines, glucocorticoids, anti‐inflammatory neuropeptides, and lipid mediators such as prostaglandin E2 (PGE2) limit and control the inflammatory response. In this study we report that exogenous PGE2 inhibits CCL3 (MIP‐1α) and CCL4 (MIP‐1β) expression and release from dendritic cells stimulated with either lipopolysaccharide (LPS), a TLR4 ligand, or peptidoglycan, a TLR2 ligand. The inhibition is dose‐dependent and occurs at both the mRNA and protein levels. The inhibitory effect is mediated through EP2 and EP4 receptors and requires the presence of PGE2 at the time of LPS stimulation. Intraperitoneal administration of PGE2 together with LPS results in a reduction in the levels of CCL3 and CCL4 released in the peritoneal fluid, a reduction in the number of dendritic cells accumulating in the peritoneal cavity, and a reduction in CCL3 amount per cell in the peritoneal cell population. These results suggest that one of the mechanisms by which endogenous PGE2 acts as an anti‐inflammatory agent, is the inhibition of inflammatory chemokine release from activated dendritic cells, preventing the excess accumulation of activated immune cells.

Prostaglandin E2 promotes the survival of bone marrow-derived dendritic cells.

Since dendritic cells (DC) participate in both innate and adaptive immunity, their survival and expansion is tightly controlled. Little is known about the mechanisms of DC apoptosis. PGE2, an arachidonic acid metabolite, plays an essential role in DC migration. We propose a novel function for PGE2 as a DC survival factor. Our studies demonstrate that PGE2 protects DC in vitro against apoptosis induced by withdrawal of growth factors or ceramide. DC matured in conditions that inhibit endogenous PGE2 release are highly susceptible to apoptosis and exogenous PGE2 re-establishes the more resistant phenotype. The antiapoptotic effect is mediated through EP-2/EP-4 receptors and involves the PI3K → Akt pathway. PGE2 leads to increased phosphorylation of Akt, protection against mitochondrial membrane compromise, and decreased caspase 3 activity. Macroarray data indicate that PGE2 leads to the down-regulation of a number of proapoptotic molecules, i.e., BAD, several caspases, and granzyme B. In vivo, higher numbers of immature and Ag-loaded CFSE-labeled DC are present in the draining lymph nodes of mice inoculated with PGE2 receptor agonists, compared with animals treated with ibuprofen or controls injected with PBS. This suggests that PGE2 acts as an endogenous antiapoptotic factor for DC and raises the possibility of using PGE2 agonists to increase the survival of Ag-loaded DC following in vivo administration.

Docosahexaenoic acid prevents dendritic cell maturation and in vitro and in vivo expression of the IL-12 cytokine family

BackgroundAcute and chronic inflammation play essential roles in inflammatory/autoimmune conditions. Protective anti-inflammatory effects of the n-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were reported in animal models of colitis, sepsis, and stroke. Since dendritic cells (DC) represent the essential cellular link between innate and adaptive immunity and have a prominent role in tolerance for self-antigens, we sought to investigate the impact of DHA on DC maturation and proinflammatory cytokine production.MethodsMurine bone marrow-derived DC were treated with DHA and stimulated with various toll-like receptor (TLR) ligands. Flow cytometry was used to determine the levels of surface maturation markers and endocytic activity. Cytokine expression and secretion were measured by real-time RT-PCR and ELISA assays. PPARγ and NFκB activity in nuclear extracts were determined by binding to specific oligonucleotide sequences using ELISA-based assays. In vivo effects of DHA were assessed in splenic DC from LPS-inoculated mice maintained on a DHA-enriched diet.ResultsDHA maintained the immature phenotype in bone marrow-derived DC by preventing the upregulation of MHCII and costimulatory molecules (CD40, CD80 and CD86) and maintaining high levels of endocytic activity. DHA inhibited the production of pro-inflammatory cytokines, including the IL-12 cytokine family (IL-12p70, IL-23, and IL-27), from DC stimulated with TLR2, 3, 4, and 9 ligands. DHA inhibition of IL-12 expression was mediated through activation of PPARγ and inhibition of NFκBp65 nuclear translocation. DHA exerted a similar inhibitory effect on IL-12 and IL-23 expression in vivo in LPS-inoculated mice maintained on a DHA-enriched diet.ConclusionsExposure of bone marrow-derived DC to DHA resulted in the maintenance of an immature phenotype and drastic reduction in proinflammatory cytokine release. DHA inhibited the expression and secretion of the IL-12 cytokine family members (IL-12p70, IL-23 and IL-27), which play essential roles in the differentiation of the proinflammatory Th1/Th17 effector cells. The effect of DHA on IL-12 expression was mediated through activation of PPARγ and inhibition of NFκB. Inhibition of IL-12 and IL-23 expression was also evident in splenic DC from mice fed a DHA-enriched diet, suggesting that dietary DHA acts as an anti-inflammatory agent in vivo.

Bone marrow-derived dendritic cells generated in the presence of resolvin E1 induce apoptosis of activated CD4+ T cells.

In contrast to the role of dendritic cells (DC) in immunity and tolerance, little is known about their possible role in the resolution of inflammatory processes. In addition to the reduction in the number of infiltrating immune cells, the elimination of effector T cells already present at the inflammatory site represents an essential step toward resolution. Recently, lipid mediators such as the omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid and their metabolites, including resolvin E1 (RvE1), have been shown to accumulate in inflammatory foci during the resolution phase. RvE1 has been reported to reduce immune cell infiltration and proinflammatory cytokine production. In this study we report that DC exposed to RvE1, especially during differentiation, acquire the capacity to induce apoptosis of activated T cells through the induction and activity of indoleamine 2,3-dioxygenase. To our knowledge, this study is the first to report on an omega-3 fatty acid derivative inducing indoleamine 2,3-dioxygenase expression in DC. RvE1-exposed DC maintain an immature chemokine receptor expression pattern even following TLR stimulation, with high CCR5 and no CCR7 expression. This effect implies that DC exposed to RvE1 and pathogens remain at the inflammatory site, instead of migrating to lymph nodes, and induce apoptosis in effector T cells infiltrating the inflammatory site. To our knowledge, the DC described in this study represent a new functional DC subtype, whose essential function resides in the resolution of inflammation.

Modulating the inflammatory properties of activated microglia with Docosahexaenoic acid and Aspirin

BackgroundMicroglia are considered the “resident macrophages” of the brain. When in their resting state, microglia perform routine maintenance and immune surveillance. Once activated, either by injury or an immune stimulus, microglia secrete a variety of pro-inflammatory molecules, such as Nitric Oxide, superoxide, and inflammatory cytokines. Up-regulation of pro-inflammatory molecules is transient, and does not cause neurodegeneration. However, if up-regulation lasts for an extended period of time, neurodegeneration ensues.Many neurodegenerative diseases are characterized by chronic inflammation due to microglial activation. Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) have been proposed as possible preventative treatments for neurodegenerative diseases, due to their anti-inflammatory properties. Docosahexaenoic Acid (DHA) is an omega-3 polyunsaturated fatty acid (PUFA) that has potent anti-inflammatory properties. This research work sought to elucidate whether microglial activation can be modulated by combining Aspirin, a classical NSAID, with Docosahexaenoic Acid, a natural anti-inflammatory agent. The combined ability of Aspirin and DHA to modulate microglial activation was determined in the context of pro-inflammatory cytokines, Nitric Oxide levels, as well as total Glutathione levels.ResultsDocosahexaenoic Acid increased total Glutathione levels in microglia cells and enhanced their anti-oxidative capacity. It reduced production of the pro-inflammatory cytokines TNF-α and IL-6 induced through TLR-3 and TLR-4 activation. Furthermore, it reduced production of Nitric Oxide. Aspirin showed similar anti-inflammatory effects with respect to TNF-α during TLR-3 and TLR-7 stimulation. Aspirin did not show any redection in terms of Nitric Oxide production. Combination of Aspirin and Docosahexaenoic Acid showed augmentation in total Glutathione production during TLR-7 stimulation as well as a reduction in IL-6, TNF-α and Nitric Oxide.ConclusionsCollectively, these findings highlight the combination of Docosahexaenoic Acid and Aspirin as a possible measure against inflammation of the nervous system, thus leading to protection against neurodegenerative diseases with an inflammatory etiology.

TH2 lymphocytes secrete functional VIP upon antigen stimulation.

In addition to the peptidergic innervation, immune cells may also represent a source for VIP in the lymphoid organs. Previous studies reported increased VIP mRNA and protein expression in mitogen-stimulated B and T lymphocytes. To determine whether specific T cell subsets are responsible for VIP production, we derived TH1 and TH2 effector cell lines from T-cell receptor transgenic mice. TH1 and TH2 cells were stimulated with the specific (pigeon cytochrome C peptide) or nonspecific (ovalbumin) antigen presented by MHC class II compatible antigen-presenting cells. Upon stimulation with the specific antigen, TH2, but not TH1 cells express VIP mRNA and intracelllular VIP protein, as determined by Northern blots and FACS analysis. Supernatants harvested from antigen-stimulated TH2 cells contain secreted VIP, as determined by Elisa, and induce cAMP in HEK293 cells transfected with the specific VIP/PACAP receptor VPAC1. These results confirm that TH2, but not TH1 cells, express and secrete functional VIP following specific antigen stimulation. The release of VIP within the lymphoid microenvironment following antigenic stimulation provides a physiological basis for the immunoregulatory effects of VIP on neighboring immune cells, such as downregulation of macrophage activation, effects on lymphocyte migration, on antigen-induced T cell apoptosis, and on T cell differentiation.

Dietary docosahexaenoic acid alleviates autistic-like behaviors resulting from maternal immune activation in mice.

The prevalence of autism spectrum disorders over the last several decades has risen at an alarming rate. Factors such as broadened clinical definitions and increased parental age only partially account for this precipitous increase, suggesting that recent changes in environmental factors may also be responsible. One such factor could be the dramatic decrease in consumption of anti-inflammatory dietary omega-3 (n-3) polyunsaturated fatty acids (PUFAs) relative to the amount of pro-inflammatory omega-6 (n-6) PUFAs and saturated fats in the Western diet. Docosahexaenoic acid (DHA) is the principle n-3 PUFA found in neural tissue and is important for optimal brain development, especially during late gestation when DHA rapidly and preferentially accumulates in the brain. In this study, we tested whether supplementation of a low n-3 PUFA diet with DHA throughout development could improve measures related to autism in a mouse model of maternal immune activation. We found that dietary DHA protected offspring from the deleterious effects of gestational exposure to the viral mimetic polyriboinosinic-polyribocytidilic acid on behavioral measures of autism and subsequent adulthood immune system reactivity. These data suggest that elevated dietary levels of DHA, especially during pregnancy and nursing, may help protect normal neurodevelopment from the potentially adverse consequences of environmental insults like maternal infection.