Differential effects of the tryptophan metabolite 3-hydroxyanthranilic acid on the proliferation of human CD8+ T cells induced by TCR triggering or homeostatic cytokines

Production of indoleamine 2,3-dioxygenase (IDO) by tumor cells, leading to tryptophan depletion and production of immunosuppressive metabolites, may facilitate immune tolerance of cancer. IDO gene is also expressed in dendritic cells (DC) upon maturation induced by lipopolysaccarides or IFN. We investigated IDO gene expression in melanoma cell lines and clinical specimens as compared to mature DC (mDC). Furthermore, we explored effects of L-kynurenine (L-kyn) and 3-hydroxyanthranilic acid (3-HAA) on survival and antigen-dependent and independent proliferation of CD8(+) cells. We observed that IDO gene expression in cultured tumor cells and freshly excised samples is orders of magnitude lower than in mDC, providing highly efficient antigen presentation to CD8(+) T cells. Non toxic concentrations of L-kyn or 3-HAA did not significantly inhibit antigen-specific CTL responses. However, 3-HAA, but not L-kyn markedly inhibited antigen-independent proliferation of CD8(+) T cells induced by common receptor gamma-chain cytokines IL-2, -7 and -15. Our data suggest that CD8(+) T cell activation induced by antigenic stimulation, a function exquisitely fulfilled by mDC, is unaffected by tryptophan metabolites. Instead, in the absence of effective T cell receptor triggering, 3-HAA profoundly affects homeostatic proliferation of CD8(+) T cells.     

Oxidant stress during inflammation: anti-inflammatory effects of antioxidants

Local oxidative changes have been investigated during granulomatous inflammation in the rat. Lipid peroxidation occurred independently of the prostaglandin biosynthetic pathways in the kaolin granuloma pouch model. Elevated levels of malonaldehyde, the monitor of lipid peroxidation, were found in the plasma and livers of rats with a remote localized inflammation. The hepatic antioxidant capacity of these rats was markedly reduced, while aminopyrine metabolism was impaired, as reflected by the increased half-life of this drug. The aminopyrine half-life was longer in rats with a stronger inflammatory response. Local administration of free radical scavengers and antioxidants inhibited granuloma formation depending on the type of scavenger used. Thus scavengers of superoxide and hydroxyl radicals were ineffective as anti-inflammatory agents, whereas a scavenger of hydrogen peroxide and two lipid antioxidants markedly inhibited granuloma formation. The results indicate that several states of reduced oxygen and lipid peroxides are involved in the inflammatory response, and that the oxidative events are not limited to the inflamed site.     

The role of neutrophils during intestinal inflammation

Polymorphonuclear leukocytes or neutrophils play a critical role in the maintenance of intestinal homeostasis. They have elegant defense mechanisms to eliminate microbes that have translocated across a single layer of mucosal epithelial cells that form a critical barrier between the gut lumen and the underlying tissue. During the inflammatory response, neutrophils also contribute to the recruitment of other immune cells and facilitate mucosal healing by releasing mediators necessary for the resolution of inflammation. Although the above responses are clearly beneficial, excessive recruitment and accumulation of activated neutrophils in the intestine under pathological conditions such as inflammatory bowel disease is associated with mucosal injury and debilitating disease symptoms. Thus, depending on the circumstances, neutrophils can be viewed as either good or bad. In this article, we summarize the beneficial and deleterious roles of neutrophils in the intestine during health and disease and provide an overview of what is known about neutrophil function in the gut.     

The NLRP3 inflammasome: role in airway inflammation

Asthma is characterized by airway inflammation, airway hyperresponsiveness and airway remodelling. Uncontrolled airway inflammation or repeated asthma exacerbations can lead to airway remodelling, which cannot be reversed by current pharmacological treatment, and consequently lead to decline in lung function. Thus, it is critical to understand airway inflammation in asthma and infectious exacerbation. The inflammasome has emerged as playing a key role in innate immunity and inflammation. Upon ligand sensing, inflammasome components assemble and self‐oligomerize, leading to caspase‐1 activation and maturation of pro‐IL‐1β and pro‐IL‐18 into bioactive cytokines. These bioactive cytokines then play a pivotal role in the initiation and amplification of inflammatory processes. In addition to facilitating the proteolytic activation of IL‐1β and IL‐18, inflammasomes also participate in cell death through caspase‐1‐mediated pyroptosis. In this review, we describe the structure and function of the inflammasome and provide an overview of our current understanding of role of the inflammasome in airway inflammation. We focus on nucleotide‐binding domain and leucine‐rich repeat protein 3 (NLRP3) inflammasome as it is the best‐characterized subtype shown expressed in airway and considered to play a key role in chronic airway diseases such as asthma.     

The role of hyaluronic acid in inflammation and wound healing

We have previously hypothesized that hyaluronic acid (HA) and fibrin specifically interact and help orchestrate the early stages of the inflammatory response and wound healing (J. Theoretic. Biol. 119, 219, 1986). In the present work we have extended studies to confirm this prediction. Several approaches were used to show that human fibrinogen specifically binds to hyaluronic acid. In addition, this latter glycosaminoglycan greatly stimulated the in vitro formation of fibrin clots induced by thrombin. The presence of hyaluronic acid also altered the structure of the final fibrin gel. Removal of circulating hyaluronic acid in blood is therefore probably vital in order to maintain normal haemostasis. Evidence is presented to suggest that an endocytic receptor recycling process is responsible for the ability of liver endothelial cells to perform this function and remove HA from the blood. Although hyaluronic acid levels are initially low in a blood clot, the proposed wound-healing model explains why and how HA levels increase and the functional and structural significance of this polysaccharide during wound healing.     

The anti-inflammatory effects of omalizumab confirm the central role of IgE in allergic inflammation

Anti-IgE therapy with omalizumab reduces serum levels of free IgE and downregulates expression of IgE receptors (Fc epsilonRI) on mast cells and basophils. In the airways of patients with mild allergic asthma, omalizumab reduces Fc epsilonRI+ and IgE+ cells and causes a profound reduction in tissue eosinophilia, together with reductions in submucosal T-cell and B-cell numbers. In patients with seasonal allergic rhinitis, omalizumab inhibits the allergen-induced seasonal increases in circulating and tissue eosinophils. Omalizumab decreases Fc epsilonRI expression on circulating dendritic cells, which might lead to a reduction in allergen presentation, T(H)2 cell activation, and proliferation. As a systemic anti-IgE agent, omalizumab has demonstrated clinical efficacy in patients with moderate and severe allergic asthma and in those with seasonal and perennial allergic rhinitis, as well as in patients with concomitant allergic asthma and allergic rhinitis. The anti-inflammatory effects of omalizumab at different sites of allergic inflammation and the clinical benefits of anti-IgE therapy in patients with allergic asthma and allergic rhinitis emphasize the fundamental importance of IgE in allergic inflammation.     

The outsiders: emerging roles of ectonucleotidases in inflammation

Research on the biological roles of ectonucleoidases has revealed that CD73, an ecto-5 nucleotidase, plays a special role in the extracellular conversion of adenosine monophosphate to adenosine-specifically, as a checkpoint that determines whether the extracellular environment is proinflammatory (characterized by adenosine 5′-triphosphate-mediated responses) or anti-inflammatory (adenosine-mediated responses). Inactivating or inhibiting CD73 attenuates the extracellular formation of adenosine, exacerbating the severity of various inflammatory diseases. In this issue of Science Translational Medicine, Fl?gel and colleagues showed that CD73 can be pharmacologically exploited to convert an inactive adenosine precursor to an active, anti-inflammatory adenosine analog. In addition to attenuating inflammation associated with collagen-induced arthritis in a mouse model, this prodrug approach was site-selective, because the metabolic conversion relies on CD73, which is up-regulated in the inflammatory locus (the joint).     

The role of hyaluronic acid in SEB-induced acute lung inflammation

We investigated the role of the extracellular matrix component, hyaluronic acid (HA) in SEB-induced ALI/ARDS. Intranasal exposure of mice to SEB led to a significant increase in the level of soluble hyaluronic acid in the lungs. Similarly, in an endothelial cell/spleen cell co-culture, SEB exposure led to significant increases in soluble levels of hyaluronic acid, cellular proliferation, and cytokine production compared with SEB-exposed spleen cells or endothelial cells alone. Exposure of SEB-activated spleen cells to hyaluronic acid led to increased cellular proliferation and increased cytokine production. SEB-induced cytokine production and proliferation in vitro were significantly reduced by the hyaluronic acid blocking peptide, Pep-1. Finally, treatment of SEB-exposed mice with Pep-1 significantly reduced SEB-induced ALI/ARDS, through reduction of cytokine production and numbers of lung inflammatory cells, compared to mice treated with a control peptide. Together, these results suggest the possibility of targeting HA for the treatment of SEB-induced ALI/ARDS.     

Proteasomal inhibition in intracerebral hemorrhage: neuroprotective and anti-inflammatory effects of bortezomib

Inflammation is an important pathophysiologic mechanism of injury induced by intracerebral hemorrhage (ICH). The ubiquitin-proteasome system (UPS) regulates the inflammatory responses via the up-regulation of several pro-inflammatory molecules. In this study, we determined that a potent proteasome inhibitor, bortezomib, exerted therapeutic effects in experimental model of ICH. Either bortezomib (0.05, 0.2, 0.5, 1mg/kg) or vehicle was intravenously administered 2h after ICH induction. The high doses of bortezomib caused high mortality rates. Bortezomib at 0.2 mg/kg reduced the early hematoma growth and alleviated hematoma volume and brain edema at 3 days after ICH, compared with the ICH-vehicle group. The numbers of myeloperoxidase(+) neutrophils, Ox42(+) microglia, and TUNEL(+) cells in the perihematomal regions were decreased by bortezomib. Bortezomib induced significant decrements of mRNA expression of TNF-alpha and IL-6. The production of iNOS and COX2 was also reduced significantly by bortezomib. We concluded that the early treatment with bortezomib induced a reduction in the early hematoma growth and mitigated the development of brain edema, coupled with a marked inhibitory effect on inflammation in ICH.     

Prevention of T cell-driven complement activation and inflammation by tryptophan catabolism during pregnancy

Indoleamine 2,3 dioxygenase (IDO) activity during pregnancy protects developing fetuses from maternal immune responses in CBA mice. We show here that fetal allografts were rejected only in mating combinations where paternally inherited tissue antigens elicited potent maternal T cell responses after exposure to IDO inhibitor. IDO inhibitor treatment triggered extensive inflammation at the maternal-fetal interface in susceptible mating combinations, which was characterized by complement deposition and hemorrhagic necrosis. Identical inflammatory responses occurred in B cell-deficient (RAG-I-/-) mothers that carried a monoclonal cohort of CD8+ T cells specific for a single paternally inherited fetal major histocompatibility complex antigen. Thus, fetal allograft rejection was accompanied by a unique form of inflammation that was characterized by T cell-dependent, antibody-independent activation of complement. In contrast, no inflammation, complement deposition or T cell infiltration was elicited when mice carrying syngeneic fetuses were exposed to IDO inhibitor. These data show that IDO activity protects the fetus by suppressing T cell-driven local inflammatory responses to fetal alloantigens.     

The role of complement in inflammation during experimental pneumococcal meningitis

The mechanism whereby an effective bactericidal inflammatory reaction develops in the subarachnoid space is not clearly defined. While normal cerebrospinal fluid is deficient in complement, immunoglobulin and leukocytes, these serum components appear in cerebrospinal fluid (CSF) during the course of bacterial meningitis. Using a rabbit model of pneumococcal meningitis we examined the role of the alternate complement pathway in three early events important to the defense of the subarachnoid space: leukocyte chemotaxis, phagocyte mediated bacterial killing, and clearance of bacterial components from the cerebrospinal fluid space. Rabbits treated with cobra venom factor to deplete complement were inoculated intracisternally with encapsulated (type II or XIX) pneumococci. Following complement depletion, there was a dramatic (at least 100-fold) decrease in the LD50 for these strains. Nevertheless, complement depletion did not affect the magnitude of CSF leucocytosis or the rate of clearance of bacterial particles from CSF. A short delay in the appearance of leukocytes in CSF was found in the absence of complement. The major effect of complement depletion, however, was to diminish the efficiency of leukocyte mediated killing of encapsulated bacteria in the CSF. Although the short delay in the onset of leukocytosis in the complement depleted animals is consistent with a chemotactic role of complement in the normal animal, the quantitatively normal leukocytosis in the complement depleted rabbits clearly indicates that important chemotaxins other than complement function in CSF. Inhibition of leukocytosis by indomethacin and diclofenac suggests that metabolite(s) of the arachidonic acid pathway may perform such a chemotactic role. A major role of complement in the defense of the subarachnoid space appears to be as an opsonin needed for the effective bactericidal activity of leukocytes. It is the lack of this function that best explains the greatly decreased LD50 value of encapsulated pneumococci in the complement depleted animal.     

Effect of 3-hydroxyanthranilic acid in the immunosuppressive molecules indoleamine dioxygenase and HLA-G in macrophages

Indoleamine 2,3-dioxygenase (IDO) and human leukocyte antigen-G (HLA-G) are two molecules involved in immune tolerance. 3-Hydroxyanthranilic acid is an IDO downstream metabolite that can produce an important immune suppression. In dendritic cells, it induces HLA-G cell surface expression and secretion to the medium. The relationship between IDO and HLA-G seems to be dependent on the cell type. In this study we analyzed the effect of the tryptophan metabolite 3-hydroxyanthranilic acid in these two proteins in monocytes and macrophages. This compound decreased IDO activity while increased HLA-G surface expression in macrophages, but not in monocytes. Also, 3-hydroxyanthranilic acid decreased HLA-G1 shedding, but not HLA-G5 secretion by macrophages. These results stress the importance of 3-hydroxyanthranilic acid as a modulator of the immune response.     

Potentiation of diclofenac-induced anti-inflammatory response by aminoguanidine in carrageenan-induced acute inflammation in rats: The role of nitric oxide

Objective: To investigate whether aminoguanidine (AG) treatment enhances the anti-inflammatory effect of diclofenac in an acute inflammation model in rats.Material and methods: In 48 rats carrageenan-induced paw edema was used as an acute inflammation model. Inflammatory activity was assessed at 1.5, 3 and 6 h after sub-planter injection of carrageenan (0.1 ml of a 1% solution in 0.85% saline). The anti-inflammatory effect of diclofenac (25 mg/kg, i.p.) was studied in comparison to that of the selective inducible nitric oxide synthase (iNOS) inhibitor, AG, and of nitric oxide donor, sodium nitroprusside (SNP).Results: AG, failed to inhibit inflammation during the first 3 h following carrageenan administration, but caused a slight, although statistically insignificant inhibition at 6 h. Diclofenac significantly reduced the carrageenan-induced edema in rat paw at all the time points studied. Administration of diclofenac after AG pretreatment caused significant (P < 0.001) reduction in edema that was double that of diclofenac alone 6 h after carrageenan injection. Administration of SNP as a single dose after AG pretreatment prevented any potentiation of anti-inflammatory response that was observed in the case of AG combined with diclofenac treatment.Conclusion: These results show that AG markedly potentiates the anti-inflammatory activity of diclofenac at 6 h and this potentiation effect is nitric oxide-dependent.Received 28 October 2002; returned for revision 1 April 2003; accepted by I. Ahnfelt-Rønne 5 May 2003     

The roles of thrombin and protease-activated receptors in inflammation

Inflammation and coagulation constitute two host defence systems with complementary physiological roles in limiting tissue damage, restoring homeostasis and eliminating invading pathogens, functions reliant on effective regulation of both processes at a variety of levels. Dysfunctional activation or regulation of either pathway may lead to pathology and contribute to human diseases as diverse as myocardial infarction and septic shock. The serine protease thrombin, a key protein in the coagulation pathway, can activate cellular signalling directly via proteolytic cleavage of the N-terminal domain of a family of G protein-coupled receptors or indirectly through the generation of molecules such as activated protein C. These events transmit signals to many cell types and can elicit the production of various pro-inflammatory mediators such as cytokines, chemokines and growth factors, thereby influencing cell activation, differentiation, survival and migration. This review discusses recent progress in understanding how thrombin and protease-activated receptors influence biological processes, highlighting the detrimental and protective cellular effects of thrombin and its signalling pathways.