Prostaglandin E2 and IL-23 plus IL-1β differentially regulate the Th1/Th17 immune response of human CD161(+) CD4(+) memory T cells

The role of PGE2 and EP receptors on lung's immune and structural cells; possibilities for future asthma therapy

Asthma is the most common airway chronic disease with treatments aimed mainly to control the symptoms. Adrenergic receptor agonists, corticosteroids and anti-leukotrienes have been used for decades, and the development of more targeted asthma treatments, known as biological therapies, were only recently established. However, due to the complexity of asthma and the limited efficacy as well as the side effects of available treatments, there is an urgent need for a new generation of asthma therapies. The anti-inflammatory and bronchodilatory effects of prostaglandin E2 in asthma are promising, yet complicated by undesirable side effects, such as cough and airway irritation. In this review, we summarize the most important literature on the role of all four E prostanoid (EP) receptors on the lung's immune and structural cells to further dissect the relevance of EP2/EP4 receptors as potential targets for future asthma therapy.

Facilitation of colonic T cell immune responses is associated with an exacerbation of dextran sodium sulfate-induced colitis in mice lacking microsomal prostaglandin E synthase-1

Background

Microsomal prostaglandin E synthase-1 (mPGES-1) is a key enzyme that acts downstream of cyclooxygenase and plays a major role in inflammation by converting prostaglandin (PG) H₂ to PGE₂. The present study investigated the effect of genetic deletion of mPGES-1 on the development of immunologic responses to experimental colitis induced by dextran sodium sulfate (DSS), a well-established model of inflammatory bowel disease (IBD).

Methods

Colitis was induced in mice lacking mPGES-1 (mPGES-1^−/− mice) and wild-type (WT) mice by administering DSS for 7 days. Colitis was assessed by body weight loss, diarrhea, fecal bleeding, and histological features. The colonic expression of mPGES-1 was determined by real-time PCR, western blotting, and immunohistochemistry. The impact of mPGES-1 deficiency on T cell immunity was determined by flow cytometry and T cell depletion in vivo.

Results

After administration of DSS, mPGES-1^−/− mice exhibited more severe weight loss, diarrhea, and fecal bleeding than WT mice. Histological analysis further showed significant exacerbation of colonic inflammation in mPGES-1^−/− mice. In WT mice, the colonic expression of mPGES-1 was highly induced on both mRNA and protein levels and colonic PGE₂ increased significantly after DSS administration. Additionally, mPGES-1 protein was localized in the colonic mucosal epithelium and infiltrated inflammatory cells in underlying connective tissues and the lamina propria. The abnormalities consistent with colitis in mPGES-1^−/− mice were associated with higher expression of colonic T-helper (Th)17 and Th1 cytokines, including interleukin 17A and interferon-γ. Furthermore, lack of mPGES-1 increased the numbers of Th17 and Th1 cells in the lamina propria mononuclear cells within the colon, even though the number of suppressive regulatory T cells also increased. CD4⁺ T cell depletion effectively reduced symptoms of colitis as well as colonic expression of Th17 and Th1 cytokines in mPGES-1^−/− mice, suggesting the requirement of CD4⁺ T cells in the exacerbation of DSS-induced colitis under mPGES-1 deficiency.

Conclusions

These results demonstrate that mPGES-1 is the main enzyme responsible for colonic PGE₂ production and deficiency of mPGES-1 facilitates the development of colitis by affecting the development of colonic T cell–mediated immunity. mPGES-1 might therefore impact both the intestinal inflammation and T cell–mediated immunity associated with IBD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41232-021-00188-1.

Comparative evaluation of the protective effects of oral administration of auraptene and umbelliprenin against CFA-induced chronic inflammation with polyarthritis in rats

This study aimed to evaluate the anti-inflammatory effect of Auraptene (AUR) and Umbelliprenin (UMB) in a rat model of rheumatoid arthritis (RA) induced by using complete Freund's adjuvant (CFA). Paw swelling of adjuvant arthritis rats measured at various times after CFA injection. Over 15 days of RA induction, mediator/cytokine-mediated processes involved in managing the regulation and resolving RA's inflammation were also quantified with ELISA. Histopathological changes were also assessed under a microscope 15 days after the CFA injection. AUR at all doses and UMB administration only at a 16 mM /kg administration dose significantly reduced CFA-induced paw edema level compared to the control group. UMB (64 and 32 mM) and AUR (64, 32, and 16 mM) could reduce the PGE2 (p < .0001-.01) and NO (p < .0001-.05) levels in the treatment groups compared to the negative control group. However, these compounds showed no significant effect on the TNF-α, IFN-γ, TGF-β, IL-4, and IL-10 levels than the control group (p > .05). Unlike indomethacin and prednisolone, treatment of rats with AUR (16, 32, and 64 mM/kg) and UMB (16 and 32 mM/kg) reduced the level of IL-2 (p < .0001). In all treatment groups, the serum level of IL-17 was significantly reduced compared to the CFA group (p < .001-0.05). We suggested AUR and UMB could diminish inflammation by reducing the serum level of IL-17 and could be considered a proper alternative in the treatment of IL-17 related inflammatory diseases such as rheumatoid arthritis. Given that AUR and UMB apply their anti-inflammatory effects by changing distinct cytokine release/inhibition patterns, their potential application in diverse inflammatory diseases seems different.

Effect of Malus asiatica Nakai Leaf Flavonoids on the Prevention of Esophageal Cancer in C57BL/6J Mice by Regulating the IL-17 Signaling Pathway

Background

The aim of this study was to observe the preventive effect of flavonoids extracted from Malus asiatica Nakai leaves (FMANL) on esophageal cancer in mice, especially the ability of FMANL to regulate the interleukin 17 (IL-17) signaling pathway during this process.

Materials and Methods

The C57BL/6J mice were treated with 4-nitroquinoline N-oxide (4NQO) to induce esophageal cancer, and the visceral tissue index and the serum and esophageal tissue indexes of mice were used to verify the effect of FMANL.

Results

The experimental results showed that FMANL can effectively control the changes in visceral tissue caused by esophageal cancer. FMANL could increase the cytokine levels of interleukin 10 (IL-10), monocyte chemotactic protein 1 (MCP-1) and decrease the cytokine levels of tumor necrosis factor alpha (TNF-α), interferon-γ (IFN-γ), interleukin 6 (IL-6), and interleukin 12p70 (IL-12p70) in serum of mice with esophageal cancer. FMANL could also reduce CD3⁺, CD4⁺, and CD8⁺ and enhance CD19⁺ mouse peripheral blood lymphocytes. The results of qPCR and Western blot analysis showed that FMANL could down-regulate the mRNA and protein expression levels of IL-17, interleukin 23 (IL-23), interleukin 1 beta (IL-1β), chemokine (C-X-C) ligand 1 (CXCL1), chemokine (C-X-C) ligand 2 (CXCL2), S100 calcium-binding protein A8 (S100A8), S100 calcium-binding protein A9 (S100A9), matrix metalloprotein 9 (MMP-9), and matrix metalloprotein 13 (MMP-1) in mice with esophageal cancer. High-performance liquid chromatography (HPLC) detection showed that FMANL contained 10 chemicals, including rutin, hyperoside, isoquercitrin, dihydroquercetin, quercitrin, hesperidin, myricetin, baicalin, neohesperidin dihydrochalcone, and quercetin.

Conclusion

It could be concluded that FMANL can effectively prevent experimentally induced esophageal cancer in mice, and its effects might be obtained from 10 compounds present in FMANL.

IL-23 in inflammatory bowel diseases and colon cancer

Studies in recent years have identified a pivotal role of the cytokine IL-23 in the pathogenesis of inflammatory bowel diseases (IBD: Crohn´s disease, ulcerative colitis) and colitis-associated colon cancer. Genetic studies revealed that subgroups of IBD patients have single nucleotide polymorphisms in the IL-23R gene suggesting that IL-23R signaling affects disease susceptibility. Furthermore, increased production of IL-23 by macrophages, dendritic cells or granulocytes has been observed in various mouse models of colitis, colitis-associated cancer and IBD patients. Moreover, in several murine models of colitis, suppression of IL-12/IL-23 p40, IL-23 p19 or IL-23R function led to marked suppression of gut inflammation. This finding was associated with reduced activation of IL-23 target cells such as T helper 17 cells, innate lymphoid cells type 3, granulocytes and natural killer cells as well as with impaired production of proinflammatory cytokines. Based on these findings, targeting of IL-23 emerges as important concept for suppression of gut inflammation and inflammation-associated cancer growth. Consistently, neutralizing antibodies against IL-12/IL-23 p40 and IL-23 p19 have been successfully used in clinical trials for therapy of Crohn´s disease and pilot studies in ulcerative colitis are ongoing. These findings underline the crucial regulatory role of IL-23 in chronic intestinal inflammation and colitis-associated cancer and indicate that therapeutic strategies aiming at IL-23 blockade may be of key relevance for future therapy of IBD patients.

Genetic determinants of co-accessible chromatin regions in activated T cells across humans

Over 90% of genetic variants associated with complex human traits map to non-coding regions, but little is understood about how they modulate gene regulation in health and disease. One possible mechanism is that genetic variants affect the activity of one or more cis-regulatory elements leading to gene expression variation in specific cell types. To identify such cases, we analyzed ATAC-seq and RNA-seq profiles from stimulated primary CD4⁺ T cells in up to 105 healthy donors. We found that regions of accessible chromatin (ATAC-peaks) are co-accessible at kilobase and megabase resolution, consistent with the three-dimensional chromatin organization measured by in situ Hi-C in T cells. Fifteen percent of genetic variants located within ATAC-peaks affected the accessibility of the corresponding peak (local-ATAC-QTLs). Local-ATAC-QTLs have the largest effects on co-accessible peaks, are associated with gene expression and are enriched for autoimmune disease variants. Our results provide insights into how natural genetic variants modulate cis-regulatory elements, in isolation or in concert, to influence gene expression.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Eicosanoid receptors: Targets for the treatment of disrupted intestinal epithelial homeostasis

The importance of cyclooxygenase and lipoxygenase pathways and the consequent eicosanoid synthesis in the physiology and pathophysiology of the intestinal epithelium is currently being established. Each eicosanoid (prostanoid, leukotriene, hydroxyeicosatetraenoic acid) preferentially recognizes one or more receptors coupled to one or more signal-transduction processes. This overview focuses on the role of eicosanoid receptors in the maintenance of intestinal epithelium physiology through the control of proliferation/differentiation/apoptosis processes. Furthermore, it is reported that the role of these receptors on the regulation of the barrier function of the intestinal epithelium have arisen through the regulation of absorption/secretion processes, tight-junction state and the control of the intestinal immune response. Also, this review considers the implication of AA cascade in the disruption of epithelial homeostasis during inflammatory bowel diseases and colorectal cancer as well as the therapeutic values and potential of the eicosanoid receptors as novel targets for the treatments of the pathologies above mentioned.

Differential effects of HIV transmission from monocyte-derived dendritic cells vs. monocytes to IL-17+CD4+ T cells

HIV infection leads to CD4 helper T cell (Th) loss, but not all Th cells are equally depleted. The contribution of other immune cells in the Th depletion also remains unclear. This study investigates HIV transmission from monocyte-derived dendritic cells (MDDCs) vs. monocytes to Th17 and Th1 cells using an allogeneic coculture model. The addition of HIV to MDDCs increased the expression of the negative regulatory molecule PD-L1 and decreased the expression of the activation markers HLA-DR and CD86, whereas the virus up-regulated HLA-DR and CD86, but not PD-L1, on monocytes. Coculturing of CD4⁺ T cells with MDDCs pretreated with HIV led to the decline of Th17, but not Th1, responses. In contrast, pretreatment of monocytes with HIV increased Th17 without affecting Th1 responses. The enhanced Th17 responses in the cocultures with HIV-treated monocytes were also accompanied by high numbers of virus-infected CD4⁺ T cells. The Th17 expansion arose from memory CD4⁺ T cells with minimal contribution from naïve CD4⁺ T cells. The Th17-enhancing activity was mediated by the HIV envelope and did not require productive virus infection. Comparison of MDDCs and monocytes further showed that, although HIV-treated MDDCs reduced Th proliferation and increased the activation of the apoptosis mediator caspase-3, HIV-treated monocytes enhanced Th proliferation without increasing the active caspase-3 levels. This study indicates the potential role of distinct myeloid cell populations in shaping Th17 responses during HIV infection.

Lipopolysaccharide-Mediated Induction of Concurrent IL-1β and IL-23 Expression in THP-1 Cells Exhibits Differential Requirements for Caspase-1 and Cathepsin B Activity

The inflammasome is a multimeric protein complex required for interleukin (IL)-1β production. Upon lipopolysaccharide (LPS) triggering of toll-like receptor (TLR)-4 and subsequent ATP signaling, the NOD-like receptor containing-pyrin domain 3 (NLRP3) inflammasome is activated to cleave pro-caspase-1 into caspase-1, allowing the secretion of IL-1β. IL-1β is known to function with IL-23 in the regulation of IL-17-producing CD4(+) T cells, Th17 cells, in adaptive immunity. Recently, studies have shown that IL-1β and IL-23 together activate IL-17-producing innate lymphoid cells, demonstrating that the pair may exhibit additional effects on cell differentiation. Using an in vitro model of bacterial infection, LPS treatment of human monocytic cells, we investigated the molecular mechanisms involved in the co-expression of IL-1β and IL-23. We found that IL-1β is partially required for optimal LPS-induced IL-23 production. We also found that IL-23 production was partially dependent on ATP signaling via the P2X7 receptor, whereas IL-1β production required this signaling. Furthermore, we identified a novel role for cathepsin B activity in IL-23 production. Taken together, this study identifies differential requirements for the co-expression of IL-1β and IL-23. Due to their similar roles in Th17 differentiation, characterization of the regulatory mechanisms for LPS-induced IL-1β and IL-23 may reveal novel information into the pathology of the inflammatory response particularly during bacterial infection.

Fatty acids, lipid mediators, and T-cell function

Research toward the mechanisms underlying obesity-linked complications has intensified during the last years. As a consequence, it has become clear that metabolism and immunity are intimately linked. Free fatty acids and other lipids acquired in excess by current feeding patterns have been proposed to mediate this link due to their immune modulatory capacity. The functional differences between saturated and unsaturated fatty acids, in combination with their dietary intake are believed to modulate the outcome of immune responses. Moreover, unsaturated fatty acids can be oxidized in a tightly regulated and specific manner to generate either potent pro-inflammatory or pro-resolving lipid mediators. These oxidative derivatives of fatty acids have received detailed attention during the last years, as they have proven to have strong immune modulatory capacity, even in pM ranges. Both fatty acids and oxidized fatty acids have been studied especially in relation to macrophage and T-cells functions. In this review, we propose to focus on the effect of fatty acids and their oxidative derivatives on T-cells, as it is an active area of research during the past 5 years. The effect of fatty acids and their derivatives on activation and proliferation of T-cells, as well as the delicate balance between stimulation and lipotoxicity will be discussed. Moreover, the receptors involved in the interaction between free fatty acids and their derivatives with T-cells will be summarized. Finally, the mechanisms involved in modulation of T-cells by fatty acids will be addressed, including cellular signaling and metabolism of T-cells. The in vitro results will be placed in context of in vivo studies both in humans and mice. In this review, we summarize the latest findings on the immune modulatory function of lipids on T-cells and will point out novel directions for future research.

Antagonizing arachidonic acid-derived eicosanoids reduces inflammatory Th17 and Th1 cell-mediated inflammation and colitis severity

During colitis, activation of two inflammatory T cell subsets, Th17 and Th1 cells, promotes ongoing intestinal inflammatory responses. n-6 polyunsaturated fatty acid- (PUFA-) derived eicosanoids, such as prostaglandin E2 (PGE2), promote Th17 cell-mediated inflammation, while n-3 PUFA antagonize both Th17 and Th1 cells and suppress PGE2 levels. We utilized two genetic mouse models, which differentially antagonize PGE2 levels, to examine the effect on Th17 cells and disease outcomes in trinitrobenzene sulfonic acid- (TNBS-) induced colitis. Fat-1 mice contain the ω3 desaturase gene from C. elegans and synthesize n-3 PUFA de novo, thereby reducing the biosynthesis of n-6 PUFA-derived eicosanoids. In contrast, Fads1 Null mice contain a disrupted Δ5 desaturase gene and produce lower levels of n-6 PUFA-derived eicosanoids. Compared to Wt littermates, Fat-1 and Fads1 Null mice exhibited a similar colitic phenotype characterized by reduced colonic mucosal inflammatory eicosanoid levels and mRNA expression of Th17 cell markers (IL-17A, RORγτ, and IL-23), decreased percentages of Th17 cells and, improved colon injury scores (P ≤ 0.05). Thus, during colitis, similar outcomes were obtained in two genetically distinct models, both of which antagonize PGE2 levels via different mechanisms. Our data highlight the critical impact of n-6 PUFA-derived eicosanoids in the promotion of Th17 cell-mediated colonic inflammation.

Interleukin-1β promotes the induction of retinal autoimmune disease

Interleukin-1β (IL-1β) is a potent proinflammatory cytokine that plays a critical role in initiating immunoinflammatory responses. In this study, we generated recombinant mouse IL-1β and anti-mouse IL-1β polyclonal antibodies to examine the effect of IL-1β on experimental autoimmune uveoretinitis (EAU), a mouse model for T cell-mediated eye autoimmune disease. Administration of mouse IL-1β by i.p. in the priming phase, but not in the effector phase, of immune response of EAU enhanced disease scores and its related immune responses including DTH, Ag-specific T cell proliferation and the production of IL-17 and IFN-γ. Furthermore, administration of anti-IL-1β antibody in the priming phase reduced EAU scores. These results suggest that IL-1β is an important mediator in the pathogenesis of autoimmune diseases such as uveitis.

Interleukin 17 contributes to the chronicity of inflammatory diseases such as rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease leading to joint destruction and bone resorption. The proinflammatory cytokine interleukin 17 (IL-17), primarily produced by Th17 cells, has been shown to be involved in all stages of the disease and to be an important contributor of RA chronicity. Three major processes drive the IL-17-mediated chronicity. Several epigenetic events, enhanced in RA patients, lead to the increased production of IL-17 by Th17 cells. IL-17 then induces the production of several inflammatory mediators in the diseased synovium, which are further synergistically enhanced via combinations of IL-17 with other cytokines. IL-17 also promotes the survival of both the synoviocytes and inflammatory cells and promotes the maturation of these immune cells. This leads to an increased number of synoviocytes and inflammatory cells in the synovial fluid and in the synovium leading to the hyperplasia and exacerbated inflammation observed in joints of RA patients. Furthermore, these IL-17-driven events initiate several feedback-loop mechanisms leading to increased expansion of Th17 cells and thereby increased production of IL-17. In this review, we aim to depict a complete picture of the IL-17-driven vicious circle leading to RA chronicity and to pinpoint the key aspects that require further exploration.

Polyunsaturated Fatty Acid-derived lipid mediators and T cell function

Fatty acids are involved in T cell biology both as nutrients important for energy production as well as signaling molecules. In particular, polyunsaturated fatty acids are known to exhibit a range of immunomodulatory properties that progress through T cell mediated events, although the molecular mechanisms of these actions have not yet been fully elucidated. Some of these immune activities are linked to polyunsaturated fatty acid-induced alteration of the composition of cellular membranes and the consequent changes in signaling pathways linked to membrane raft-associated proteins. However, significant aspects of the polyunsaturated fatty acid bioactivities are mediated through their transformation to specific lipid mediators, products of cyclooxygenase, lipoxygenase, or cytochrome P450 enzymatic reactions. Resulting bioactive metabolites including prostaglandins, leukotrienes, and endocannabinoids are produced by and/or act upon T leukocytes through cell surface receptors and have been shown to alter T cell activation and differentiation, proliferation, cytokine production, motility, and homing events. Detailed appreciation of the mode of action of these lipids presents opportunities for the design and development of therapeutic strategies aimed at regulating T cell function.

Increased IL-23 and IL-17 expression by peripheral blood cells of patients with primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a typical autoimmune disease for which the pathogenesis remains unclear. IL-23 and IL-17 are pro-inflammatory cytokines of the "IL-23/IL-17 axis," which may play a key role in the pathogenesis of autoimmune diseases. In this study, we investigated the expression of IL-23 and IL-17 in the peripheral blood of patients with PBC and its clinical significance. We used quantitative PCR to determine mRNA expressions of IL-23, IL-23 receptor, and IL-17 in peripheral blood mononuclear cells (PBMC) from PBC patients. ELISA's were used to determine patients' serum levels of IL-23 and IL-17. IL-23- and IL-17-producing cells in liver biopsis were also analyzed. Compared to a healthy control group, the mRNA expression levels of IL-23 p19, its corresponding receptor, IL-23R, and IL-17 in PBMC's from PBC patients were significantly increased, and these levels were correlated with PBC disease stages. PBC patients' serum levels of IL-23 and IL-17 were higher than those in a post-hepatic cirrhosis group and a healthy group, and were significantly higher in the early PBC disease stages than in the advanced PBC stages. There were significantly more IL23+ and IL-17+ mononuclear cells in portal areas of liver tissues in advanced stages of this disease than in the early stages. The serum levels of IL-23 and IL-17 in PBC patients were positively correlated with serum GGT levels. Thus, IL-23 and IL-17 may play an important role in the pathogenesis of PBC by promoting inflammation. Because the IL-23 and IL-17 levels in the peripheral blood of PBC patients were increased and were correlated with clinical stages, they may be indices that could be used to clinically monitor PBC.

The IL17A and IL17F loci have divergent histone modifications and are differentially regulated by prostaglandin E2 in Th17 cells

Prostaglandin E2 (PGE2), IL-23 and IL-1β are implicated in inflammatory bowel disease susceptibility, likely in part by modulating IL-17 producing CD4(+) T helper (Th17) cells. To better understand how these three mediators affect Th17 cell memory responses, we characterized the gene expression profiles of activated human peripheral CD4(+) effector memory T cells and sorted Th17 memory cells from healthy donors concurrent with IL17A mRNA induction mediated by PGE2 and/or IL-23 plus IL-1β. We discovered that PGE2 and IL-23 plus IL-1β differentially regulate Th17 cytokine expression and synergize to induce IL-17A, but not IL-17F. IL-23 plus IL-1β preferentially induce IL-17F expression. The addition of PGE2 to IL-23 plus IL-1β only enhances IL-17A expression as mediated by the PGE2 EP4 receptor, and promotes a switch from an IL-17F to an IL-17A predominant immune response. The human Th17 HuT-102 cell line was also found to constitutively express IL-17A, but not IL-17F. We went on to show that the IL17A and IL17F loci have divergent epigenetic architectures in unstimulated HuT-102 and primary Th17 cells and are poised for preferential expression of IL17A. We conclude that the chromatin for IL17A and IL17F are distinctly regulated, which may play an important role in mucosal health and disease.

PGE2 differentially regulates monocyte-derived dendritic cell cytokine responses depending on receptor usage (EP2/EP4)

Dendritic cells (DCs) are central players in coordinating immune responses, both innate and adaptive. While the role of lipid mediators in the immune response has been the subject of many investigations, the precise role of prostaglandins has often been plagued by contradictory studies. In this study, we examined the role of PGE(2) on human DC function. Although studies have suggested that PGE(2) specifically plays a role in DC motility and cytokine release profile, the precise receptor usage and signaling pathways involved remain unclear. In this report we found that irrespective of the human donor, monocyte-derived dendritic cells (MoDCs) express three of the four PGE(2) receptor subtypes (EP(2-4)), although only EP(2) and EP(4) were active with respect to cytokine production. Using selective EP receptor antagonists and agonists, we demonstrate that PGE(2) coordinates control of IL-23 release (a promoter of Th17, an autoimmune associated T cell subset) in a dose-dependent manner by differential use of EP(2) and EP(4) receptors in LPS-activated MoDCs. This is in contrast to IL-12, which is dose dependently inhibited by PGE(2) through both receptor subtypes. Low concentrations (∼1-10nM) of PGE(2) promoted IL-23 production via EP(4) receptors, while at higher (>50 nM), but still physiologically relevant concentrations, IL-23 is suppressed by an EP(2) dependent mechanism. These results can be explained by differential regulation of the common subunit, IL-12p40, and IL-23p19, by EP(2) and EP(4). By these means, PGE(2) can act as a regulatory switch of immune responses depending on its concentration in the microenvironment. In addition, we believe these results may also explain why seemingly conflicting biological functions assigned to PGE(2) have been reported in the literature, as the concentration of ligand (PGE(2)) fundamentally alters the nature of the response. This finding also highlights the potential of designing therapeutics which differentially target these receptors.

T helper type 17 cells expand in patients with myasthenia-associated thymoma

Myasthenia gravis (MG) is a prototypical CD4(+) T cell-dependent autoimmune disease mediated by anti-acetylcholine receptor autoantibodies (AChR-Abs). Certain subsets of helper T cells are suggested to be involved in the pathogenesis of MG, including Th1 and regulatory T cells (Treg). However, whether the recently identified Th17 cells play a role in the development of MG and its prognosis is still unknown. Here, we demonstrated that Th17 cells and their associated cytokines are increased, while the Treg cells are decreased in the peripheral blood mononuclear cells (PBMCs) from MG patients with thymomas (TM), but not from those with normal thymus (NT) or thymic hyperplasia (TH). Furthermore, the quantity of Th17 cells correlates with the quantitative myasthenia gravis (QMG) score in patients with TM. We also found a significant positive relationship between the frequency of Th17 cells (%) and the concentration of AChR antibodies in patients with MG. Therefore, the Th17/Treg imbalance in TM may suggest MG with certain pathological subtype, and the increase in Th17 cells may reveal the severity of the disease, which is valuable in the diagnosis and choice of therapeutic strategy for patients with MG.

Prostaglandin E2 affects T cell responses through modulation of CD46 expression

The ubiquitous protein CD46, a regulator of complement activity, promotes T cell activation and differentiation toward a regulatory Tr1-like phenotype. The CD46-mediated differentiation pathway is defective in several chronic inflammatory diseases, underlying the importance of CD46 in controlling T cell function and the need to understand its regulatory mechanisms. Using an RNA interference-based screening approach in primary T cells, we have identified that two members of the G protein-coupled receptor kinases were involved in regulating CD46 expression at the surface of activated cells. We have investigated the role of PGE(2), which binds to the E-prostanoid family of G protein-coupled receptors through four subtypes of receptors called EP 1-4, in the regulation of CD46 expression and function. Conflicting roles of PGE(2) in T cell functions have been reported, and the reasons for these apparent discrepancies are not well understood. We show that addition of PGE(2) strongly downregulates CD46 expression in activated T cells. Moreover, PGE(2) differentially affects T cell activation, cytokine production, and phenotype depending on the activation signals received by the T cells. This was correlated with a distinct pattern of the PGE(2) receptors expressed, with EP4 being preferentially induced by CD46 activation. Indeed, addition of an EP4 antagonist could reverse the effects observed on cytokine production after CD46 costimulation. These data demonstrate a novel role of the PGE(2)-EP4 axis in CD46 functions, which might at least partly explain the diverse roles of PGE(2) in T cell functions.

Characterization of an arachidonic acid-deficient (Fads1 knockout) mouse model

Arachidonic acid (20:4(Δ5,8,11,14), AA)-derived eicosanoids regulate inflammation and promote cancer development. Previous studies have targeted prostaglandin enzymes in an attempt to modulate AA metabolism. However, due to safety concerns surrounding the use of pharmaceutical agents designed to target Ptgs2 (cyclooxygenase 2) and its downstream targets, it is important to identify new targets upstream of Ptgs2. Therefore, we determined the utility of antagonizing tissue AA levels as a novel approach to suppressing AA-derived eicosanoids. Systemic disruption of the Fads1 (Δ5 desaturase) gene reciprocally altered the levels of dihomo-γ-linolenic acid (20:3(Δ8,11,14), DGLA) and AA in mouse tissues, resulting in a profound increase in 1-series-derived and a concurrent decrease in 2-series-derived prostaglandins. The lack of AA-derived eicosanoids, e.g., PGE₂ was associated with perturbed intestinal crypt proliferation, immune cell homeostasis, and a heightened sensitivity to acute inflammatory challenge. In addition, null mice failed to thrive, dying off by 12 weeks of age. Dietary supplementation with AA extended the longevity of null mice to levels comparable to wild-type mice. We propose that this new mouse model will expand our understanding of how AA and its metabolites mediate inflammation and promote malignant transformation, with the eventual goal of identifying new drug targets upstream of Ptgs2.