Leukotriene B4 induces interleukin 5 generation from human T lymphocytes

G Protein-Coupled Receptors in Asthma Therapy: Pharmacology and Drug Action

Asthma is a heterogeneous inflammatory disease of the airways that is associated with airway hyperresponsiveness and airflow limitation. Although asthma was once simply categorized as atopic or nonatopic, emerging analyses over the last few decades have revealed a variety of asthma endotypes that are attributed to numerous pathophysiological mechanisms. The classification of asthma by endotype is primarily routed in different profiles of airway inflammation that contribute to bronchoconstriction. Many asthma therapeutics target G protein-coupled receptors (GPCRs), which either enhance bronchodilation or prevent bronchoconstriction. Short-acting and long-acting β 2-agonists are widely used bronchodilators that signal through the activation of the β 2-adrenergic receptor. Short-acting and long-acting antagonists of muscarinic acetylcholine receptors are used to reduce bronchoconstriction by blocking the action of acetylcholine. Leukotriene antagonists that block the signaling of cysteinyl leukotriene receptor 1 are used as an add-on therapy to reduce bronchoconstriction and inflammation induced by cysteinyl leukotrienes. A number of GPCR-targeting asthma drug candidates are also in different stages of development. Among them, antagonists of prostaglandin D2 receptor 2 have advanced into phase III clinical trials. Others, including antagonists of the adenosine A2B receptor and the histamine H4 receptor, are in early stages of clinical investigation. In the past decade, significant research advancements in pharmacology, cell biology, structural biology, and molecular physiology have greatly deepened our understanding of the therapeutic roles of GPCRs in asthma and drug action on these GPCRs. This review summarizes our current understanding of GPCR signaling and pharmacology in the context of asthma treatment. SIGNIFICANCE STATEMENT: Although current treatment methods for asthma are effective for a majority of asthma patients, there are still a large number of patients with poorly controlled asthma who may experience asthma exacerbations. This review summarizes current asthma treatment methods and our understanding of signaling and pharmacology of G protein-coupled receptors (GPCRs) in asthma therapy, and discusses controversies regarding the use of GPCR drugs and new opportunities in developing GPCR-targeting therapeutics for the treatment of asthma.

Eicosanoid Control Over Antigen Presenting Cells in Asthma

Asthma is a common lung disease affecting 300 million people worldwide. Allergic asthma is recognized as a prototypical Th2 disorder, orchestrated by an aberrant adaptive CD4+ T helper (Th2/Th17) cell immune response against airborne allergens, that leads to eosinophilic inflammation, reversible bronchoconstriction, and mucus overproduction. Other forms of asthma are controlled by an eosinophil-rich innate ILC2 response driven by epithelial damage, whereas in some patients with more neutrophilia, the disease is driven by Th17 cells. Dendritic cells (DCs) and macrophages are crucial regulators of type 2 immunity in asthma. Numerous lipid mediators including the eicosanoids prostaglandins and leukotrienes influence key functions of these cells, leading to either pro- or anti-inflammatory effects on disease outcome. In this review, we will discuss how eicosanoids affect the functions of DCs and macrophages in the asthmatic lung and how this leads to aberrant T cell differentiation that causes disease.

Importance of the leukotriene B4-BLT1 and LTB4-BLT2 pathways in asthma

For several decades, the leukotriene pathways have been implicated as playing a central role in the pathophysiology of asthma. The presence and elevation of numerous metabolites in the blood, sputum, and bronchoalveolar lavage fluid from asthmatics or experimental animals adds support to this notion. However, targeting of the leukotriene pathways has had, in general, limited success. The single exception in asthma therapy has been targeting of the cysteinyl leukotriene receptor 1, which clinically has proven effective but only in certain clinical situations. Interference with 5-lipoxygenase has had limited success, in part due to adverse drug effects. The importance of the LTB4-BLT1 pathway in asthma pathogenesis has extensive experimental support and findings, albeit limited, from clinical samples. The LTB4-BLT1 pathway was shown to be important as a neutrophil chemoattractant. Despite observations made more than two decades ago, the LTB4-BLT1 pathway has only recently been shown to exhibit important activities on subsets of T lymphocytes, both as a chemoattractant and on lymphocyte activation, as well as on dendritic cells, the major antigen presenting cell in the lung. The role of BLT2 in asthma remains unclear. Targeting of components of the LTB4-BLT1 pathway offers innovative therapeutic opportunities especially in patients with asthma that remain uncontrolled despite intensive corticosteroid treatment.

Black currant seed oil supplementation of mothers enhances IFN-γ and suppresses IL-4 production in breast milk

BACKGROUND

The first year of infancy is crucial for the development of atopic immune response. Inadequate early Th1 and Treg responses and increased production of Th2 cytokines are associated with atopy. Breast milk contains several immunomodulatory cytokines and other factors that might influence the maturation of the infant's immune system. We assessed the cytokines in breast milk of mother of newborn infants and their associations with black currant seed oil (BCSO) supplementation during pregnancy, mother's atopic status and the development of infant's atopic dermatitis.

METHODS

Mothers and infants from an intervention study by black currant seed oil (n = 31) or olive oil as placebo (n = 30) were included in the study. Breast milk samples were collected during the first 3 months of breastfeeding. Breast milk levels of IL-4, IL-5, IL-10, IL-12, IFN-γ and TNF were measured by Luminex technology.

RESULTS

BCSO intervention group had decreased level of IL-4 (p = 0.044) and elevated level of IFN-γ (p = 0.014) in breast milk as compared to olive oil group. No significant differences were observed in IL-5, IL-10, IL-12 and TNF levels between the BCSO and olive oil groups. Mothers who had atopic dermatitis had significantly decreased levels of IL-10 (p = 0.044) in breast milk. Breast milk of the mothers of the children who developed atopic dermatitis had lower levels of IFN-γ (p = 0.039) as compared to the breast milk of the mothers of the children without dermatitis.

CONCLUSION

Dietary intervention with BCSO had immunomodulatory effects on breast milk cytokine production towards Th2 to Th1 immunodeviation.

Leukotriene B4, an endogenous stimulator of the innate immune response against pathogens

Leukotriene B4 (LTB4) is an endogenous lipid mediator of inflammation derived from arachidonic acid by the sequential action of cytosolic phospholipase A2 and 5-lipoxygenase. This mediator was initially recognized for its involvement in the recruitment of neutrophils. However, in the last decade, LTB4 has been clearly demonstrated to play a significant role in the control of microbial infections through its ability to activate host innate defenses. In this review, we will focus on the modulator effects of LTB4 on the innate defenses and discuss its therapeutic potential against viral pathogens.

Proinflammatory and immunoregulatory roles of eicosanoids in T cells

Eicosanoids are inflammatory mediators primarily generated by hydrolysis of membrane phospholipids by phospholipase A2 to ω-3 and ω-6 C20 fatty acids that next are converted to leukotrienes (LTs), prostaglandins (PGs), prostacyclins (PCs), and thromboxanes (TXAs). The rate-limiting and tightly regulated lipoxygenases control synthesis of LTs while the equally well-controlled cyclooxygenases 1 and 2 generate prostanoids, including PGs, PCs, and TXAs. While many of the classical signs of inflammation such as redness, swelling, pain, and heat are caused by eicosanoid species with vasoactive, pyretic, and pain-inducing effects locally, some eicosanoids also regulate T cell functions. Here, we will review eicosanoid production in T cell subsets and the inflammatory and immunoregulatory functions of LTs, PGs, PCs, and TXAs in T cells.

Leukotriene D4 and interleukin-13 cooperate to increase the release of eotaxin-3 by airway epithelial cells

INTRODUCTION

Airway epithelial cells play a central role in the physiopathology of asthma. They release eotaxins when treated with T(H)2 cytokines such as interleukin (IL)-4 or IL-13, and these chemokines attract eosinophils and potentiate the biosynthesis of cysteinyl leukotrienes (cysLTs), which in turn induce bronchoconstriction and mucus secretion. These effects of cysLTs mainly mediated by CysLT(1) and CysLT(2) receptors on epithelial cell functions remain largely undefined. Because the release of inflammatory cytokines, eotaxins, and cysLTs occur relatively at the same time and location in the lung tissue, we hypothesized that they regulate inflammation cooperatively rather than redundantly. We therefore investigated whether cysLTs and the T(H)2 cytokines would act in concert to augment the release of eotaxins by airway epithelial cells.

METHODS

A549 cells or human primary bronchial epithelial cells were incubated with or without IL-4, IL-13, and/or LTD(4). The release of eotaxin-3 and the expression of cysLT receptors were assessed by ELISA, RT-PCR, and flow cytometry, respectively.

RESULTS

IL-4 and IL-13 induced the release of eotaxin-3 by airway epithelial cells. LTD(4) weakly induced the release of eotaxin-3 but clearly potentiated the IL-13-induced eotaxin-3 release. LTD(4) had no effect on IL-4-stimulated cells. Epithelial cells expressed CysLT(1) but not CysLT(2). CysLT(1) expression was increased by IL-13 but not by IL-4 and/or LTD(4). Importantly, the upregulation of CysLT(1) by IL-13 preceded eotaxin-3 release.

CONCLUSIONS

These results demonstrate a stepwise cooperation between IL-13 and LTD(4). IL-13 upregulates CysLT(1) expression and consequently the response to cysLTs This results in an increased release of eotaxin-3 by epithelial cells which at its turn increases the recruitment of leukocytes and their biosynthesis of cysLTs. This positive amplification loop involving epithelial cells and leukocytes could be implicated in the recruitment of eosinophils observed in asthmatics.

Role of leukotrienes on protozoan and helminth infections

Leukotrienes (LTs), formed by the 5-lipoxygenase-(5-LO-) catalyzed oxidation of arachidonic acid, are lipid mediators that have potent proinflammatory activities. Pharmacologic or genetic inhibition of 5-LO biosynthesis in animals is associated with increased mortality and impaired clearance of bacteria, fungi, and parasites. LTs play a role in the control of helminth and protozoan infections by modulating the immune system and/or through direct cytotoxicity to parasites; however, LTs may also be associated with pathogenesis, such as in cerebral malaria and schistosomal granuloma. Interestingly, some proteins from the saliva of insect vectors that transmit protozoans and secreted protein from helminth could bind LTs and may consequently modulate the course of infection or pathogenesis. In addition, the decreased production of LTs in immunocompromised individuals might modulate the pathophysiology of helminth and protozoan infections. Herein, in this paper, we showed the immunomodulatory and pathogenic roles of LTs during the helminth and protozoan infections.

Leukotrienes and airway inflammation

BACKGROUND

Asthma is a common chronic inflammatory disease of the airways characterized by airway obstruction and hyperresponsiveness. Leukotrienes (LTs) are lipid mediators that contribute to many aspects of asthma pathogenesis. As the LT pathway is relatively steroid-resistant, its blockade by alternative strategies is a desirable component of asthma management. Cysteinyl LT (cysLT) receptor 1 antagonists (LTRAs) have been utilized worldwide for more than 10years, and while their efficacy in asthma is well accepted, their limitations are also evident.

SCOPE OF REVIEW

In this review, we summarize the biological effects of LTs in asthma, review recent advances in LT receptors, and consider possible new therapeutic targets in the LT pathway that offer the potential to achieve better control of asthma in the future.

MAJOR CONCLUSIONS

CysLTs play pathogenetic roles in many aspects of asthma, and blockade of cysLT receptor 1 by currently available LTRAs is certainly beneficial in disease management. On the other hand, the limitations of LTRAs are also apparent. Recent studies have revealed new receptors for cysLTs other than classical cysLT receptors 1 and 2, as well as the potential importance of LTB(4) in asthma.

GENERAL SIGNIFICANCE

Recent findings provide clues to new approaches for targeting the LT pathway that may overcome the current limitations of LTRAs and achieve superior control of asthma. This article is part of a Special Issue entitled: Biochemistry of Asthma.

5-lipoxygenase and cyclooxygenase-2 in porcine parasitic bronchopneumonia: immunohistochemical and biochemical investigations

Eicosanoids are products of arachidonic acid metabolism and have numerous biological roles. The present study aimed to investigate the role of 5-lipoxygenase (5-LOX)- and cyclooxygenase-2 (COX-2)- dependent enzymatic pathways in the pathogenesis of porcine parasitic bronchopneumonia caused by Metastrongylus spp. Pulmonary tissue samples from healthy control and parasitized pigs were processed for histopathological, immunohistochemical and biochemical investigations. In control animals, immunohistochemistry demonstrated that 5-LOX and COX-2 expression was almost exclusively limited to the bronchiolar epithelial cells. Parasitized pigs had greater 5-LOX- and COX-2- specific immunoreactivity, involving a wide range of cell types within foci of granulomatous and eosinophilic bronchopneumonia. Biochemical investigations demonstrated the presence of 5-LOX (and the related product Leukotriene B(4)) and COX-2 (and the related product prostaglandin E(2); PGE(2)) in all tissues under study. COX-2 activity and PGE(2) concentration were significantly higher in diseased lungs compared with normal healthy controls. These findings demonstrate that 5-LOX and COX-2 are differentially expressed in normal versus lungworm-infected lungs and therefore suggest that both biochemical pathways are likely to be involved in the pathogenesis of porcine parasitic bronchopneumonia.

Leukotriene A4 hydrolase expression in PEL cells is regulated at the transcriptional level and leads to increased leukotriene B4 production

Primary effusion lymphoma (PEL) is a herpesvirus-8-associated lymphoproliferative disease characterized by migration of tumor cells to serous body cavities. PEL cells originate from postgerminal center B cells and share a remarkable alteration in B cell transcription factor expression and/or activation with classical Hodgkin's disease cells. Comparative analysis of gene expression by cDNA microarray of BCBL-1 cells (PEL), L-428 (classical Hodgkin's disease), and BJAB cells revealed a subset of genes that were differentially expressed in BCBL-1 cells. Among these, four genes involved in cell migration and chemotaxis were strongly up-regulated in PEL cells: leukotriene A4 (LTA4) hydrolase (LTA4H), IL-16, thrombospondin-1 (TSP-1), and selectin-P ligand (PSGL-1). Up-regulation of LTA4H was investigated at the transcriptional level. Full-length LTA4H promoter exhibited 50% higher activity in BCBL-1 cells than in BJAB or L-428 cells. Deletion analysis of the LTA4H promoter revealed a positive cis-regulatory element active only in BCBL-1 cells in the promoter proximal region located between -76 and -40 bp. Formation of a specific DNA-protein complex in this region was confirmed by EMSA. Coculture of ionophore-stimulated primary neutrophils with BCBL-1 cells leads to an increased production of LTB4 compared with coculture with BJAB and L-428 cells as measured by enzyme immunoassay, demonstrating the functional significance of LTA4H up-regulation.

Role of the LTB4/BLT1 pathway in allergen-induced airway hyperresponsiveness and inflammation

LTB4, a proinflammatory lipid mediator generated from arachidonic acid through the action of 5-lipoxygenase, has been known for over two decades and is implicated in a wide variety of inflammatory disorders. BLT1, a G-protein-coupled receptor, has recently been identified as a high affinity receptor specific for LTB4. Recent studies in allergen-induced airway hyperresponsiveness and inflammation using mice lacking BLT1 have shown crucial new roles for leukotriene B4 and BLT1 in Th2 cytokine IL-13 production from lung T cells and recruitment of antigen-specific effector CD8+ T cells, suggesting novel mechanisms for their actions. The leukotriene B4-BLT1 pathway is an important target for the treatment of bronchial asthma.

Downregulation of leukotriene biosynthesis by thymoquinone attenuates airway inflammation in a mouse model of allergic asthma

Chronic airway inflammation is a key feature of bronchial asthma. Leukotrienes are potent inflammatory mediators that play a role in the pathophysiology of asthma, and their levels are elevated in the airways in response to allergen challenge. We examined the anti-inflammatory effect of thymoquinone (TQ), the active principle in the volatile oil of Nigella sativa seeds, on leukotriene (LT) biosynthesis in a mouse model of allergic asthma. Mice sensitized and challenged with ovalbumin (OVA) antigen had an increased amounts of leukotriene B4 and C4, Th2 cytokines, and eosinophils in bronchoalveolar lavage (BAL) fluid. In addition, there was also a marked increase in lung tissue eosinophilia and goblet cell numbers. Administration of TQ before OVA challenge inhibited 5-lipoxygenase, the main enzyme in leukotriene biosynthesis, expression by lung cells and significantly reduced the levels of LTB4 and LTC4. This was accompanied by a marked decrease in Th2 cytokines and BAL fluid and lung tissue eosinophilia, all of which are characteristics of airway inflammation. These results demonstrate the anti-inflammatory effect of TQ in experimental asthma.

Treatment of asthma with antileukotrienes: first line or last resort therapy?

Twenty five years after the structure elucidation of slow reacting substance of anaphylaxis, antileukotrienes are established as a new therapeutic modality in asthma. The chapter reviews the biochemistry and pharmacology of leukotrienes and antileukotrienes with particular focus on the different usage of antileukotrienes for treatment of asthma and rhinitis in Europe and the US. Further research needs and new areas for leukotriene involvement in respiratory diseases are also discussed.

Leukotrienes play a role in the control of parasite burden in murine strongyloidiasis

It is clear that leukotrienes mediate inflammatory response; new aspects of leukotriene function have recently been described. In this study, we demonstrate that leukotrienes are key chemical mediators in the control of parasite burdens in mice infected with Strongyloides venezuelensis. High leukotriene levels were detected in the lungs and small intestines of Swiss mice. In infected Swiss mice treated with MK886, a leukotriene synthesis inhibitor, numbers of adult worms, and eggs/g/feces were greater than in infected-only animals. The MK886 treatment inhibited leukotriene B(4) production in the lungs and small intestines, albeit on different postinfection days. Similarly, parasite burdens and eggs/g/feces were greater in 5-lipoxygenase(-/-) mice than in wild-type animals. These observation were confirmed by histopathological study of the duodena. We subsequently observed significant lower numbers of eosinophils and mononuclear cells in the blood, peritoneal cavity fluid, and bronchoalveolar lavage fluid of Swiss mice treated with MK886. In the lung parenchyma of infected animals, MK886 significantly inhibited synthesis of IL-5 at the beginning of infection, whereas levels of IL-12 increased progressively throughout the postinfection period. However, levels of leukotriene C(4), PGE(2), TNF-alpha, IL-3, IL-4, IFN-gamma, and IL-10 were comparable between the treated and untreated groups. Nevertheless, IgE and IgG1 (but not IgG2a) synthesis was also significantly inhibited by MK886 administration. Therefore, in S. venezuelensis-infected mice, adult worm and egg burdens are leukotriene dependent. These findings indicate potential immunostimulatory strategies involving leukotriene administration, and may serve as an alert to physicians treating Strongyloides stercoralis-infected patients presenting asthma-like symptoms because use of 5-lipoxygenase inhibitors may worsen the infection.

Leukotriene B4 receptor-1 is essential for allergen-mediated recruitment of CD8+ T cells and airway hyperresponsiveness

Recent studies in both human and rodents have indicated that in addition to CD4+ T cells, CD8+ T cells play an important role in allergic inflammation. We previously demonstrated that allergen-sensitized and -challenged CD8-deficient (CD8-/-) mice develop significantly lower airway hyperresponsiveness (AHR), eosinophilic inflammation, and IL-13 levels in bronchoalveolar lavage fluid compared with wild-type mice, and that all these responses were restored by adoptive transfer of in vivo-primed CD8+ T cells or in vitro-generated effector CD8+ T cells (T(EFF)). Recently, leukotriene B4 and its high affinity receptor, BLT1, have been shown to mediate in vitro-generated T(EFF) recruitment into inflamed tissues. In this study we investigated whether BLT1 is essential for the development of CD8+ T cell-mediated allergic AHR and inflammation. Adoptive transfer of in vivo-primed BLT1+/+, but not BLT1-/-, CD8+ T cells into sensitized and challenged CD8-/- mice restored AHR, eosinophilic inflammation, and IL-13 levels. Moreover, when adoptively transferred into sensitized CD8-/- mice, in vitro-generated BLT1+/+, but not BLT1-/-, T(EFF) accumulated in the lung and mediated these altered airway responses to allergen challenge. These data are the first to show both a functional and an essential role for BLT1 in allergen-mediated CD8+ T(EFF) recruitment into the lung and development of AHR and airway inflammation.

Requirement for leukotriene B4 receptor 1 in allergen-induced airway hyperresponsiveness

RATIONALE

Leukotriene B4 (LTB4) is a rapidly synthesized, early leukocyte chemoattractant that signals via its cell surface receptor, leukotriene B4 receptor 1 (BLT1), to attract and activate leukocytes during inflammation. A role for the LTB4-BLT1 pathway in allergen-induced airway hyperresponsiveness and inflammation is not well defined.

OBJECTIVES

To define the role of the LTB4 receptor (BLT1) in the development of airway inflammation and altered airway function.

METHODS

BLT1-deficient (BLT1 -/-) mice and wild-type mice were sensitized to ovalbumin by intraperitoneal injection and then challenged with ovalbumin via the airways. Airway responsiveness to inhaled methacholine, bronchoalveolar lavage fluid cell composition and cytokine levels, and lung inflammation and goblet cell hyperplasia were assessed.

RESULTS

Compared with wild-type mice, BLT1 -/- mice developed significantly lower airway responsiveness to inhaled methacholine, lower goblet cell hyperplasia in the airways, and decreased interleukin (IL)-13 production both in vivo, in the bronchoalveolar lavage fluid, and in vitro, after antigen stimulation of lung cells in culture. Intracellular cytokine staining of lung cells revealed that bronchoalveolar lavage IL-13 levels and numbers of IL-13(+)/CD4+ and IL-13(+)/CD8+ T cells were also reduced in BLT1 -/- mice. Reconstitution of sensitized and challenged BLT1 -/- mice with allergen-sensitized BLT1 +/+ T cells fully restored the development of airway hyperresponsiveness. In contrast, transfer of naive T cells failed to do so.

CONCLUSION

These data suggest that BLT1 expression on primed T cells is required for the full development of airway hyperresponsiveness, which appears to be associated with IL-13 production in these cells.

Leukotriene B4 Protects Latently Infected Mice against Murine Cytomegalovirus Reactivation following Allogeneic Transplantation

Human CMV is often associated with transplant rejection and opportunistic infections such as pneumonia in immunosuppressed patients. Current anti-CMV therapies, although effective, show relatively high toxicity, which seriously limits their long-term use. In this study, we provide evidence that leukotriene B(4) (LTB(4)) plays an important role in the fight against murine CMV (MCMV) infection in vivo. Intravenous administration of 50 and 500 ng/kg/day of LTB(4) to mice infected with a lethal dose of MCMV significantly increases their survival (50 and 70%, respectively), compared with the placebo-treated group (10% of survival). In mice infected with a sublethal dose of MCMV and treated daily with 50 ng/kg/day of LTB(4), the salivary gland viral loads were found to be reduced by 66% compared with the control group. Furthermore, using an allogeneic bone marrow transplantation mouse model, the frequency of MCMV reactivation from latently infected mice was much lower (38%) in LTB(4) (500 ng/kg)-treated mice than in the placebo-treated group (78%). Finally, in experiments using 5-lipoxygenase-deficient mice, MCMV viral loads in salivary glands were found to be higher in animals unable to produce leukotrienes than in the control groups, supporting a role of endogenous 5-lipoxygenase products, possibly LTB(4), in host defense against CMV infection.

Blockade of endogenous leukotrienes exacerbates pulmonary histoplasmosis

Leukotrienes are classical mediators of inflammatory response. New aspects of leukotriene function have recently been described. We examine here the previously unreported role that leukotrienes play in the regulation of cytokines in a murine model of histoplasmosis. We demonstrate that administration of MK 886, a leukotriene synthesis inhibitor, caused Histoplasma capsulatum-infected mice to die by the day 15 of infection, whereas the correlating death rate in untreated infected mice was 0%. Treating infected animals with MK 886 inhibited leukotriene synthesis but increased leukocyte recruitment to the lungs. Subsequent to this phenomenon, levels of tumor necrosis factor alpha, interleukin-1 (IL-1), IL-6, and KC chemoattractant cytokines and fungi in the lung parenchyma increased, as did inflammatory response. In contrast, IL-2, IL-5, IL-12, and gamma interferon cytokine levels actually decreased. Thus, murine response to pulmonary histoplasmosis may be leukotriene modulated. This finding may enable us to alter the course of the immune response and inflammation caused by histoplasmosis. The data from the present study suggest an important new strategy for immunologic or drug intervention in human patients.

Leukotriene B4 receptor BLT1 mediates early effector T cell recruitment

Leukotriene B4 (LTB4) was originally described as a potent lipid myeloid cell chemoattractant, rapidly generated from innate immune cells, that activates leukocytes through the G protein-coupled receptor BLT1. We report here that BLT1 is expressed on effector CD4+ T cells generated in vitro as well as in vivo when effector T cells migrate out of the lymphoid compartment and are recruited into peripheral tissues. BLT1 mediated LTB4-induced T helper type 1 (T(H)1) and T(H)2 cell chemotaxis and firm adhesion to endothelial cells under flow, as well as early CD4+ and CD8+ T cell recruitment into the airway in an asthma model. Our findings show that the LTB4-BLT1 pathway is involved in linking early immune system activation and early effector T cell recruitment.

BLT1 and BLT2: the leukotriene B(4) receptors

Two receptors for leukotriene B(4) (LTB(4)) have been molecularly identified: BLT1 and BLT2. Both receptors are G protein-coupled seven transmembrane domain receptors, whose genes are located in very close proximity to each other in the human and mouse genomes. The two receptors differ in their affinity and specificity for LTB(4): BLT1 is a high-affinity receptor specific for LTB(4), whereas BLT2 is a low-affinity receptor that also binds other eicosanoids. The two receptors also differ in their pattern of expression with BLT1 being expressed primarily in leukocytes, whereas BLT2 is expressed more ubiquitously. By mediating the activities of LTB(4), these receptors participate both in host immune responses and in the pathogenesis of inflammatory diseases. Reduced disease severity in animal inflammatory models seen with LTB(4) receptor antagonists and in mice with targeted deletion of BLT1 have revealed important roles for LTB(4) and its receptors in regulating pathologic inflammation.

In vitro effects of eicosanoids derived from different 20-carbon fatty acids on T helper type 1 and T helper type 2 cytokine production in human whole-blood cultures

BACKGROUND

Different series prostaglandins (PGs) and leukotrienes (LTs) are synthesized from different 20 carbon fatty acid precursors. The effects of the different series of PGs and LTs on production of T helper type 1 (Th1) and Th2 cytokines by human cells are not well established.

OBJECTIVE

To characterize the influence of PGs and LTs produced from different fatty acid precursors on the Th1 and Th2 cytokine profile in mitogen-stimulated human whole-blood cultures.

METHODS

Blood from healthy adult males was diluted and cultured with concanavalin A in the presence or absence of a range of concentrations of various PGs or LTs. Cytokine concentrations in culture supernatants were analysed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

PGE1, PGE2 and PGE3 significantly and dose-dependently decreased the concentrations of the Th1 cytokines IL-2 and IFN-gamma by up to 50% and 70%, respectively. The three PGs exhibited similar potency towards IFN-gamma production. At the highest concentration used (10-6 m) PGE1, but not PGE2 or PGE3, increased the concentration of the Th2 cytokine IL-4 by about 70%. IL-10 production was not affected by PGs. The ratio of the concentrations of IFN-gamma to IL-4 was significantly decreased at PGE concentrations of 10-7 and 10-6 M with all three PGEs having similar effects. LTB4, LTC4 and LTC5 did not significantly affect production of the cytokines studied.

CONCLUSION

PGE produced from different fatty acids significantly decrease Th1 cytokine production resulting in a shift in the Th1, Th2 balance in favour of a Th2 response. PGE produced from different fatty acid precursors are equipotent in their effects on human T lymphocytes. Thus, although changes in the pattern of dietary fatty intakes may contribute to the increased prevalence of atopic disease, this would probably not be mediated through substitution of one PGE with another from a different series. It may, however, be mediated through a change in the total amount of PGE produced at the site of antigen presentation.

Bacterial challenge stimulates formation of arachidonic acid metabolites by human keratinocytes and neutrophils in vitro

Although the interactions of bacteria with keratinocytes induce the synthesis of various mediators, the capability of epithelial cells to form arachidonic acid mediators has not been studied, and therefore the first part of this study was initiated. The complex mixture of epithelium-derived mediators suggests that chemoattraction is not their only effect on neutrophils and that they may also affect neutrophil mediator synthesis. The effect of epithelium-derived mediators on neutrophil eicosanoide synthesis was evaluated in the second part of this study. We incubated human keratinocytes with human-pathogenic bacteria for 2 h and harvested the supernatants after 4, 6, 10, and 18 h of culture. Subsequently, the supernatants were coincubated for 5 min with human neutrophils with or without arachidonic acid. The formation of the arachidonic acid metabolites prostaglandin E(2) (PGE(2)), leukotriene B(4) (LTB(4)), 12-hydroxyeicosatetraenoic acid (12-HETE), and 15-HETE in keratinocytes and neutrophils was measured by reverse-phase high-pressure liquid chromatography. We demonstrated for the first time that keratinocytes produced significant amounts of LTB(4) and 12-HETE 4 to 6 h after bacterial challenge. Upon stimulation with epithelial supernatants, neutrophils produced significant amounts of PGE(2), LTB(4), 12-HETE, and 15-HETE throughout the observation period of 18 h, with a maximum synthesis by supernatants harvested 4 to 10 h after bacterial infection. The results of the study suggest that arachidonic acid mediator formation by epithelial cells following bacterial challenge may act as an early inflammatory signal for the initiation of the immune response. The epithelial supernatants were capable of inducing the formation of arachidonic acid mediators by neutrophils, which may have further regulatory effects on the immune response.

Production of prostaglandins and leukotrienes by pathogenic fungi

These studies demonstrate that pathogenic fungi (dermatophytic, subcutaneous, and systemic) have the ability to produce eicosanoids both from simple metabolites and from arachidonic acid. Host-derived eicosanoids have been previously demonstrated to enhance fungal colonization and atopic disease development. Thus, fungus-derived eicosanoids represent a potential class of novel virulence factors.

Anti-inflammatory drugs: new multitarget compounds to face an old problem. The dual inhibition concept

In this short review we have tried to focus on some new relevant aspects of the pharmacological control of inflammation. The clinical availability of new drugs able to produce a selective inhibition of type 2 cyclooxygenase (COX-2), the enzyme thought to be mainly responsible for generating arachidonic-acid-derived inflammatory mediators, has been the origin of much hope. However, expectations of having an effective and completely safe non-steroidal anti-inflammatory drug (NSAID) have been only partially fulfilled. Emerging information has challenged some aspects of the original hypothesis indicating COX-2 as devoid of 'housekeeping' physiological functions. Moreover, the recently available clinical studies have indicated only a relatively small improvement in the tolerability of the newer 'selective' COX-2 inhibitors over the classical COX-1/COX-2 mixed type NSAIDs. The new appreciation of the role of other arachidonic acid derivatives, the leukotrienes (LTS), in producing and maintaining inflammation has generated considerable interest in drugs able to block LTS receptors or to produce a selective inhibition of 5-lipoxygenase (5-LO), the initial key enzyme of the leukotriene pathway. These drugs are now included among the effective therapies of asthma but appear, in the few clinical studies performed, to be an insufficient single therapeutic approach in other inflammatory diseases. Drugs able to block equally well both COX and 5-LO metabolic pathways (dual inhibitors) have been developed and experimentally evaluated in the last few years, but none are available on the market yet. The pharmacological rationale at the basis of their development is strong, and animal studies are indicative of a wide range of anti-inflammatory activity. What appears most impressive from the available studies on dual inhibitors is their almost complete lack of gastric toxicity, the most troublesome side effect of NSAIDs. The mechanism of the gastric-sparing properties of these drugs is not yet completely understood; however, it appears that leukotrienes significantly contribute to gastric epithelial injury particularly when these compounds represent the major arachidonic acid derivatives present in the gastric mucosa after inhibiton of prostanoid production.

Leukotriene inhibitors and non-steroidal therapies in the treatment of asthma

Asthma is the most common chronic disease of childhood whose morbidity and mortality continues to rise [1]. Drugs used in the treatment of asthma must be targeted at reversing three principle pathophysiologic features: bronchoconstriction, mucus plugging/hypersecretion and inflammation. In the past two decades, the contribution of airway inflammation to the development and progression of asthma symptoms and airway pathology has become a critical focus. Chronic airway inflammation can lead to the progressive decline and irreversible loss of lung function and airway remodelling [2]. In recent years, therapies aimed at diminishing airway inflammation have been at the forefront of asthma management. Steroids have been extensively studied and used as primary anti-inflammatory agents in the management of the asthmatic patient with persistent symptoms of varying severity. Within the last decade, however, several additional non-steroidal classes of drugs have begun to emerge as anti-inflammatory agents for the treatment of asthma. This article will focus on these non-steroidal drugs which have been developed and investigated within the last 5 years. Particular emphasis will be placed on leukotriene receptor antagonists, but anti-IgE and anti-IL-4 therapies, as well as phosphodiesterase inhibitors will also be discussed. Of these new therapies, only two leukotriene receptor antagonists, montelukast (Singulairtrade mark, Merck) and zafirlukast (Accolatetrade mark, AstraZeneca) and the 5-lipoxygenase inhibitor, zileuton (Zyflotrade mark, Abbott Laboratories), have been recommended, approved and are currently available for use in the treatment of paediatric patients with asthma in the United States.

Evaluation of the measurement of leukotriene B4 concentrations in exhaled condensate as a noninvasive method for assessing mediators of inflammation in the lungs of calves

OBJECTIVE

To determine whether measurement of an inflammatory mediator in exhaled condensate could provide a noninvasive method for evaluating lungs of calves.

ANIMALS

84 calves < or = 2 months old.

PROCEDURE

Concentration of leukotriene B4 (LTB4) was evaluated in the exhaled condensate of healthy calves and calves with experimentally induced respiratory tract infections. For collection of samples of exhaled condensate, the total amount of exhaled air was directed into a cooled double-jacketed tube. Each tube was sealed and stored at -80 C. The LTB4 concentration was measured, using an ELISA.

RESULTS

In exhaled condensates of clinically healthy calves, normally distributed and highly reproducible LTB4 concentrations (mean +/- SD, 116.1 +/- 55.4 pg/ml) were measured. After experimentally induced infection with Pasteurella multocida serovar D, LTB4 in exhaled condensate increased significantly (mean, 179% increase), compared with basal concentrations before infection; this increase in LTB4 was significantly correlated with deterioration in lung function. In 2 of 4 calves experimentally infected with bovine respiratory syncytial virus, the LTB4 concentration in exhaled condensate increased (300 to 400% increase), compared with baseline values, which was associated with development of bronchial hyperresponsiveness after infection.

CONCLUSIONS AND CLINICAL RELEVANCE

Collection of exhaled condensate is tolerated well by calves and is an acceptable method for obtaining fluid from exhaled air originating from the lungs. This method provides alternatives for diagnosing and evaluating treatment of naturally acquired and experimentally induced diseases of the lungs and airways in calves.

The role of eosinophils and neutrophils in inflammation

The eosinophil is well recognized as a central effector cell in the inflamed asthmatic airway. Eosinophils release toxic basic proteins and lipid mediators such as cysteinyl-leukotrienes that cause bronchial epithelial damage and airflow obstruction. Eosinophil-selective cytokines and chemokines including interleukin (IL)-5, eotaxin and RANTES may represent targets for novel asthma therapies. In contrast, the role of the neutrophil in asthma remains relatively obscure. Recent evidence from the ENFUMOSA project and elsewhere suggests that neutrophils not only contribute to acute asthma exacerbations, but also are present in high numbers in the airways of patients with chronic severe asthma. Production by neutrophils of lipid mediators, reactive oxygen intermediates (ROI) and proteases such as elastase, may contribute to airflow obstruction, epithelial damage and remodelling. Leukotriene B4 and cytokines such as IL-8, granulocyte-macrophage colony stimulating factor (GM-CSF), and tumour necrosis factor (TNF)alpha chemoattract neutrophils and reduce neutrophil apoptosis, and selective agents directed against these may prevent neutrophil influx and accumulation. Airway neutrophilia remains apparent in severe asthma patients even after treatment with high doses of corticosteroids. In vitro, corticosteroids paradoxically enhance neutrophil survival by reducing apoptosis, so corticosteroid therapy may exacerbate neutrophil activity in vivo. Both corticosteroids and cytokines may suppress neutrophil apoptosis by upregulating endogenous synthesis of leukotriene (LT)B4. Specific blockade of LTB4 synthesis or LTB4 receptors may induce neutrophil apoptosis and combat the unwanted effects of high-dose steroids on neutrophil survival. Phagocytosis of apoptotic neutrophils stimulates important signals that down-regulate pro-inflammatory cytokine production by macrophages, allowing resolution and repair processes to prevail.

Production of the potent neutrophil chemokine, growth-related protein alpha (GROalpha), is not elevated in cystic fibrosis children

Progressive neutrophil-mediated lung damage causes much of the morbidity and mortality in cystic fibrosis (CF). Neutrophil chemoattractants implicated in CF include interleukin (IL-)8, tumour necrosis factor (TNFalpha) and leukotriene (LT)B4, but growth-related protein alpha (GROalpha), a highly potent neutrophil chemokine, has not been investigated. Atopic status has been considered to contribute to the marked heterogeneity of pulmonary disease in CF. We hypothesized that GROalpha may be produced in biologically-significant amounts in the CF lung, and that enhanced production of GROalpha, IL-8 or LTB4 may contribute to the poorer lung function seen in atopic CF patients compared to non-atopic CF patients. GROalpha, IL-8 and LTB4 levels in the sputum of atopic and non-atopic CF patients were assessed by immunoassays, and GROalpha and IL-8 levels were also assessed in the plasma of CF patients and normal controls. As expected, there were high levels of IL-8 and LTB4 in most CF sputum samples, and IL-8 levels were higher in CF plasma than in control plasma (P=0.02). In contrast, GROalpha was undetectable (< 5 pg ml(-1)) in the sputum of 21 out of 25 CF patients, with low levels (range 144-825 pg ml(-1)) in the remainder, and median levels of GROalpha in CF plasma (33 pg ml(-1), n=24) were not significantly different from controls (34 pg ml(-1), n=25). Lung function [forced expiratory volume in 1 sec (FEV1) and forced vital capacity (FVC)] was significantly poorer in atopic CF compared to non-atopic CF patients (P<0.02), but sputum levels of GROalpha, IL-8 and LTB4 were not different between the subgroups. Our results suggest that unlike LTB4 and IL-8, GROalpha does not contribute to neutrophilic inflammation in the CF lung, and other factors must determine the impaired lung function observed in atopic CF patients. These results may have important implications in the development of chemokine receptor antagonists as novel anti-inflammatory agents in CF.

Intracellular expression and serum levels of eosinophil peroxidase (EPO) and eosinophil cationic protein in asthmatic children

BACKGROUND

Eosinophils are involved in the chronic inflammatory response in asthma and their basic proteins are thought to play a major pathophysiological role in this process. While serum levels of basic proteins have been used to monitor the ongoing allergic disease, little is known about the intracellular expression of these proteins in clinical situations.

OBJECTIVE

The aim of the study was to determine the intracellular expression of eosinophil cationic protein (ECP) and eosinophil peroxidase (EPO) in asthmatic children and control subjects and relate it to serum levels of both proteins, lung function tests and immunoglobulin (Ig)E levels.

METHODS

Serum ECP and EPO concentrations were determined by immunoassays in 13 asthmatic children (mean age: 9 +/- 1 years, mean FEV1: 92 +/- 10% predicted, geometric mean PC20 histamine 0.5 mg/mL) and 10 age-matched, healthy control subjects. A flow cytometric single cell assay was employed to detect intracellular ECP and EPO in peripheral blood eosinophils.

RESULTS

While serum concentrations of both ECP (asthma: median 15.0 microg/L [range 3.6-57.7] vs control: 5.9 microg/L [2.7-9.1]; P = 0.02) and EPO (22.9 microg/L [5.2-82.5] vs 7. 2 microg/L [2.5-12.7]; P = 0.008) were significantly elevated in asthmatics, the intracellular expression of ECP and EPO (measured as mean fluorescence intensity) was decreased (EG1: 55.3 [17.7-120.8] vs 100.3 [46.5-264.4]; P = 0.01; EG2: 80.2 [24.1-135.3] vs 133.7 [32. 1-244.9]; P = 0.04 and EPO: 49.7 [23.1-155.8] vs 94.9 [28.8-115.2]; P = 0.03). In asthmatics there was a significant correlation of FEV1 with intracellular ECP and of bronchial hyperresponsiveness with serum EPO and ECP. Furthermore, total IgE levels were positively correlated with serum EPO only.

CONCLUSION

We conclude that in asthmatics the intracellular content of ECP and EPO in peripheral eosinophils is reduced possibly due to degranulation. Epitope masking in activated eosinophils or a shift to early bone marrow-derived progenitors with less granule proteins are further possible explanations.

In vitro and in vivo pharmacological characterization of SB 201993, an eicosanoid-like LTB4 receptor antagonist with anti-inflammatory activity

Leukotriene B4 (LTB4) and 12-(R)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-[R]-HETE) have been postulated to contribute to the pathophysiology of inflammatory diseases. SB 201993, (E)-3-[[[[6-(2-carboxyethenyl)-5-[[8-(4-methoxyphenyl)octyl] oxy]-2-pyridinyl] methyl] thio] methyl] benzoic acid, identified from a chemical series designed as ring-fused analogs of LTB4, was evaluated as an antagonist of LTB4- and 12-(R)-HETE-induced responses in vitro and for anti-inflammatory activity in vivo. SB 201993 competitively antagonized [3-H]-LTB4 binding to intact human neutrophils (Ki = 7.6 nM) and to membranes of RBL 2H3 cells expressing the LTB4 receptor (RBL 2H3-LTB4R; IC50 = 154 nM). This compound demonstrated competitive antagonism of LTB4- and 12-(R)-HETE-induced Ca2+ mobilization responses in human neutrophils (IC50s of 131 nM and 105 nM, respectively) and inhibited LTB4-induced Ca2+ mobilization in human cultured keratinocytes (IC50 = 61 nM), RBL 2H3-LTB4R cells (IC50 = 255 nM) and mouse neutrophils (IC50 = 410 nM). SB 201993 showed weak LTD4-receptor binding affinity (Ki = 1.9 microM) and inhibited 5-lipoxygenase (IC50 of 3.6 microM), both in vitro and ex vivo. In vivo, SB 201993 inhibited LTB4-induced neutrophil infiltration in mouse skin and produced dose-related, long lasting topical anti-inflammatory activity against the fluid and cellular phases of arachidonic acid-induced mouse ear inflammation (ED50 of 580 microg/ear and 390 microg/ear, respectively). Similarly, anti-inflammatory activity was also observed in the murine phorbol ester-induced cutaneous inflammation model (ED50 of 770 and 730 microg/ear, respectively, against the fluid and cellular phases). These results indicate that SB 201993 blocks the actions of LTB4 and 12-(R)-HETE and inhibits a variety of inflammatory responses; and thus may be a useful compound to evaluate the role of these mediators in disease models.

Asthma and leukotrienes: antileukotrienes as novel anti-asthmatic drugs

Antileukotriene drugs inhibit the formation or action of leukotrienes, which are potent lipid mediators generated from arachidonic acid in lung tissue and inflammatory cells. The leukotrienes were discovered in basic studies of arachidonic acid metabolism in leucocytes 20 years ago and were found to display a number of biological activities which may contribute to airway obstruction. Clinical studies with antileukotriene drugs have indeed demonstrated that leukotrienes are significant mediators of airway obstruction evoked by many common trigger factors in asthma. Moreover, treatment trials have established that this new class of drugs has beneficial anti-asthmatic properties, and several antileukotrienes have recently been introduced as new therapy of asthma. This communication presents an overview of the biosynthesis of leukotrienes, their biological effects and clinical effects of antileukotrienes in the treatment of asthama.

Allergen-stimulated leukotriene B4 and interleukin-8 levels in patients with asthma and allergic rhinitis-modulation by a lipid pathway inhibitor

BACKGROUND

Leukotriene B4 (LTB4), a potent chemokinetic mediator for neutrophils, is enhanced by interleukin-8 (IL-8) and may play a key role in the inflammatory response of asthma.

OBJECTIVE

The aim of the present study was to investigate whether zileuton, a 5-lipoxygenase antagonist known to inhibit LTB4 production and recruitment of eosinophils/neutrophils in bronchoalveolar fluid, could affect the production of LTB4 and IL-8 by allergen-stimulated peripheral blood mononuclear cells in vitro from patients with asthma and/or allergic rhinitis.

METHODS

Peripheral blood mononuclear cells were isolated using Ficoll-Hypaque density gradient from 14 subjects (2 with asthma, 11 with asthma and allergic rhinitis, and 1 with allergic rhinitis) and were stimulated by selected allergens (grass, tree, mite, and mold) in the absence or presence of 1 and 10 microM of zileuton. Supernatants were collected and assayed for LTB4 and IL-8 levels using RIA and ELISA, respectively.

RESULTS

Levels of LTB4 were significantly elevated in peripheral blood mononuclear cells stimulated with mold, grass, and tree compared with the unstimulated control group (P<.05). Levels of IL-8 were significantly elevated in all allergen-stimulated peripheral blood mononuclear cells, except mold, compared with the unstimulated control group (P<.05). Zileuton significantly reduced production of LTB4 by mold and tree-stimulated peripheral blood mononuclear cells. By contrast, no effect of zileuton on IL-8 production was observed in allergen-stimulated peripheral blood mononuclear cells.

CONCLUSIONS

The zileuton-induced attenuation of LTB4 production by allergen-stimulated peripheral blood mononuclear cells from patients with asthma and/or allergic rhinitis occurs independently from the allergen-stimulated IL-8 production.

The role and contribution of leukotrienes in asthma

LEARNING OBJECTIVES

Reading this article will reinforce the reader's knowledge of the biochemistry and pharmacology of leukotrienes (LTs), including the enzymes and cells involved in their synthesis, the receptors that mediate their biologic effects, and the evidence that cysteinyl leukotrienes (CysLT) may play an important role in asthma. The 5-lipoxygenase inhibitors, 5-lipoxygenase-activating protein antagonists, and CysLT receptor antagonists are three classes of LTs modulators now in clinical use. The effects of these agents in clinical models of asthma induced by allergens, exercise, and aspirin and in multicenter asthma trials are reviewed.

DATA SOURCES

Key papers published in peer-reviewed journals.

STUDY SELECTION

Key papers published in peer-reviewed journals.

CONCLUSIONS

The pharmacology of these new medications and experience in clinical trials suggest that they may play a therapeutic role in the treatment of asthma.

Involvement of leukotriene B4 in murine dermatitis models

Leukotriene B4 (LTB4) is a product of the 5-lipoxygenase pathway of arachidonic acid (AA) metabolism. LTB4 is a potent chemotactic factor for neutrophils and has been postulated to play an important role in a variety of pathological conditions including rheumatoid arthritis, psoriasis, and inflammatory bowel disease. To investigate the role of LTB4 in dermatitis, we used S-(4-dimethylaminobenzyl)-N-[(2S)-3-mercapto-2-methylpropionyl]-L- cysteine (SA6541), a potent leukotriene A4 (LTA4) hydrolase inhibitor. SA6541 inhibited LTB4 production with an IC50 value of 270 nM in vitro. 5-Hydroperoxyeicosatetraenoic acid (5-HPETE) or AA injection induced LTB4 production and neutrophil influx in mouse ear. SA6541 inhibited 5-HPETE- and AA-induced LTB4 production and neutrophil influx in mouse ear when administered orally at a dose of 50 mg/kg. SA6541 also inhibited 5-HPETE-induced prostaglandin E2 (PGE2) production, probably by an indirect effect through the inhibition of LTB4 production. These results suggest that LTB4 may be important in the pathogenesis of dermatitides such as psoriasis.

Mechanisms of gastrointestinal reactions to food

Much of the genetic information that modulates mucosal immune responses was encoded several million years ago and has subsequently been subjected to modifications selected by the impact of microorganisms and food antigens. Confronted with these challenges, the intestinal immune system has developed two arms: (1) immune exclusion performed mainly by secretory IgA antibodies to inhibit colonization of pathogenic microorganisms and penetration of harmful antigens; and (2) down-regulatory mechanisms to avoid local and peripheral overreaction (hypersensitivity) towards innocuous substances. The latter phenomenon is called oral tolerance and apparently explains why most individuals show no adverse immune reactions food. When the mucosal barrier function is insufficient, tolerance to dietary antigens is abrogated in genetically susceptible individuals. This is most likely to occur during the vulnerable period after birth before the immunoregulatory network has been established. Breast-feeding appears to be immunologically important during this period, not only to substitute for the infant's lacking secretory antibodies but also because of its immune-modulating effects.

Immune functions and immunopathology of the mucosa of the upper respiratory pathways

The specific defence of airway mucosae depends primarily on secretory immunity. The B cells involved are initially stimulated in organized mucosa-associated lymphoid tissue, apparently including the tonsils and adenoid. From these inductive sites, memory cells migrate to secretory effector sites where they differentiate terminally to immunoglobulin (Ig)-producing plasma cells. Locally produced Ig consists mainly of J chain-containing dimers and larger polymers of IgA (pIgA) that are selectively transported through glandular cells by an epithelial receptor called secretory component or the pIg receptor. IgG can participate in immune exclusion because it reaches the secretions by passive diffusion. However, its proinflammatory properties render IgG antibodies of local immunopathological importance when elimination of penetrating antigens is unsuccessful. T helper (Th) cells activated in this process may by a Th2 cytokine profile promote persistent inflammation with extravasation and priming of eosinophils. This development appears to be part of the late-phase allergic reaction, perhaps initially driven by interleukin-4 (IL-4) released from mast cells that are subjected to IgE-mediated activation, and subsequently also by Th2 cell activation. Eosinophils are potentially tissue-damaging, particularly after priming with IL-5. Various cytokines up-regulate adhesion molecules on endothelial and epithelial cells, thereby enhancing migration of eosinophils into the mucosa, and perhaps in addition causing aberrant immune regulation within the epithelium. Soluble antigens bombarding the epithelial surfaces normally seem to induce several immunosuppressive mechanisms, but mucosal homeostasis appears less patent in the airways than oral tolerance to dietary antigens operating in the gut.

Ex vivo evidence for PGE2 and LTB4 involvement in cutaneous leishmaniasis: relation with infection status and cytokine production

Ex vivo culture of spleen cells from BALB/c mice infected with 2 x 10(6) Leishmania major (L. major) promastigotes were cultured with ConcanavalinA (ConA) or leishmanial antigen (L. Ag) and tested for prostaglandin E2 (PGE2) and for leukotriene B4 (LTB4), in order to study their involvement in the evolution of cutaneous leishmaniasis and the connexion with lymphokine-mediated responses. The data were compared with those obtained in BALB/c mice protected against L. major by sublethal irradiation (550 rad; cured mice). In the unprotected BALB/c mice the levels of PGE2 that were responsible for the depression of interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF alpha) Th1-associated cytokines and for the relative increase in the interleukin-4 (IL-4) became higher and higher as the lesion progressed. On the contrary, the cured mice produced levels of PGE2 similar to normal uninfected controls, high levels of TNF alpha and IFN-gamma and low levels of IL-4. Elevated levels of LTB4 were detected in the early stage of infection in the unprotected mice compared to cured ones, a sign of more intense inflammation and a stimulus for the recruitment of inflammatory cells. The observation that exogenous LTB4 was able to enhance in vitro both Th1 cytokines in cured mice and Th2 cytokines in unprotected ones suggests that LTB4 could act in the recruitment of the T cells already committed to Th1 or Th2 phenotype.