Roles of cysteinyl leukotrienes and their receptors in immune cell-related functions.

The cysteinyl leukotrienes (cys-LTs), leukotriene C4, (LTC4), LTD4, and LTE4, are lipid mediators of inflammation. LTC4 is the only intracellularly synthesized cys-LT through the 5-lipoxygenase and LTC4 synthase pathway and after transport is metabolized to LTD4 and LTE4 by specific extracellular peptidases. Each cys-LT has a preferred functional receptor in vivo; LTD4 to the type 1 cys-LT receptor (CysLT1R), LTC4 to CysLT2R, and LTE4 to CysLT3R (OXGR1 or GPR99). Recent studies in mouse models revealed that there are multiple regulatory mechanisms for these receptor functions and each receptor plays a distinct role as observed in different mouse models of inflammation and immune responses. This review focuses on the integrated host responses to the cys-LT/CysLTR pathway composed of sequential ligands with preferred receptors as seen from mouse models. It also discusses potential therapeutic targets for LTC4 synthase, CysLT2R, and CysLT3R.

5-Lipoxygenase and cysteinyl leukotriene receptor 1 regulate epidermal growth factor-induced cell migration through Tiam1 upregulation and Rac1 activation.

Cell migration is an essential step for tumor metastasis. The small GTPase Rac1 plays an important role in cell migration. Previously, we reported that epidermal growth factor (EGF) induced two waves of Rac1 activation; namely, at 5 min and 12 h after stimulation. A second wave of EGF-induced Rac1 activation was required for EGF-induced cell migration, however, the spatiotemporal regulation of the second wave of EGF-induced Rac1 activation remains largely unclear. In this study, we found that 5-lipoxygenase (5-LOX) is activated in the process of EGF-induced cell migration, and that leukotriene C4 (LTC4 ) produced by 5-LOX mediated the second wave of Rac1 activation, as well as cell migration. Furthermore, these effects caused by LTC4 were found to be blocked in the presence of the antagonist of cysteinyl leukotriene receptor 1 (CysLT1). This blockage indicates that LTC4 -mediated CysLT1 signaling regulates the second EGF-induced wave of Rac1 activation. We also found that 5-LOX inhibitors, CysLT1 antagonists and the knockdown of CysLT1 inhibited EGF-induced T cell lymphoma invasion and metastasis-inducing protein 1 (Tiam1) expression. Tiam1 expression is required for the second wave of EGF-induced Rac1 activation in A431 cells. Therefore, our results indicate that the 5-LOX/LTC4 /CysLT1 signaling pathway regulates EGF-induced cell migration by increasing Tiam1 expression, leading to a second wave of Rac1 activation. Thus, CysLT1 may serve as a new molecular target for antimetastatic therapy. In addition, the CysLT1 antagonist, montelukast, which is used clinically for allergy treatment, might have great potential as a novel type of antimetastatic agent.

Cutting edge: Leukotriene C4 activates mouse platelets in plasma exclusively through the type 2 cysteinyl leukotriene receptor.

Leukotriene C4 (LTC4) and its extracellular metabolites, LTD4 and LTE4, mediate airway inflammation. They signal through three specific receptors (type 1 cys-LT receptor [CysLT1R], CysLT2R, and GPR99) with overlapping ligand preferences. In this article, we demonstrate that LTC4, but not LTD4 or LTE4, activates mouse platelets exclusively through CysLT2R. Platelets expressed CysLT1R and CysLT2R proteins. LTC4 induced surface expression of CD62P by wild-type mouse platelets in platelet-rich plasma (PRP) and caused their secretion of thromboxane A2 and CXCL4. LTC4 was fully active on PRP from mice lacking either CysLT1R or GPR99, but completely inactive on PRP from CysLT2R-null (Cysltr2(-/-)) mice. LTC4/CysLT2R signaling required an autocrine ADP-mediated response through P2Y12 receptors. LTC4 potentiated airway inflammation in a platelet- and CysLT2R-dependent manner. Thus, CysLT2R on platelets recognizes LTC4 with unexpected selectivity. Nascent LTC4 may activate platelets at a synapse with granulocytes before it is converted to LTD4, promoting mediator generation and the formation of leukocyte-platelet complexes that facilitate inflammation.

Cysteinyl leukotriene signaling through perinuclear CysLT(1) receptors on vascular smooth muscle cells transduces nuclear calcium signaling and alterations of gene expression.

Leukotrienes are pro-inflammatory mediators that are locally produced in coronary atherosclerotic plaques. The response induced by cysteinyl leukotrienes (CysLT) in human coronary arteries may be altered under pathological conditions, such as atherosclerosis. The aim of the present study was to elucidate cysteinyl leukotriene signaling in vascular smooth muscle cells (SMCs) and the effects of inflammation on this process. Immunohistochemical analysis of human carotid endarterectomy samples revealed that the CysLT(1) leukotriene receptor was expressed in areas that also stained positive for α-smooth muscle actin. In human coronary artery smooth muscle cells, lipopolysaccharide significantly upregulated the CysLT(1) receptor and significantly enhanced the changes in intracellular calcium induced by leukotriene C(4) (LTC(4)). In these cells, the CysLT(1) receptor exhibited a perinuclear expression, and LTC(4) stimulation predominantly enhanced nuclear calcium increase, which was significantly inhibited by the CysLT(1) receptor antagonist MK-571. Microarray analysis revealed, among a number of significantly upregulated genes after 24 h stimulation of human coronary artery smooth muscle cells with LTC(4), a 5-fold increase in mRNA levels for plasminogen activator inhibitor (PAI)-2. The LTC(4)-induced increase in PAI-2 expression was confirmed by real-time quantitative PCR and ELISA and was inhibited by the CysLT(1) receptor antagonist MK-571 and by calcium chelators. In summary, pro-inflammatory stimulation of vascular SMCs upregulated a perinuclear CysLT(1) receptor expression coupled to nuclear calcium signaling and changes in gene expression, such as upregulation of PAI-2. Taken together, these findings suggest a role of nuclear CysLT(1) receptor signaling in vascular SMCs inducing gene expression patterns associated with atherosclerosis.

Conjunctival goblet cell secretion stimulated by leukotrienes is reduced by resolvins D1 and E1 to promote resolution of inflammation.

The conjunctiva is a mucous membrane that covers the sclera and lines the inside of the eyelids. Throughout the conjunctiva are goblet cells that secrete mucins to protect the eye. Chronic inflammatory diseases such as allergic conjunctivitis and early dry eye lead to increased goblet cell mucin secretion into tears and ocular surface disease. The purpose of this study was to determine the actions of the inflammatory mediators, the leukotrienes and the proresolution resolvins, on secretion from cultured rat and human conjunctival goblet cells. We found that both cysteinyl leukotriene (CysLT) receptors, CysLT(1) and CysLT(2,) were present in rat conjunctiva and in rat and human cultured conjunctival goblet cells. All leukotrienes LTB(4), LTC(4), LTD(4), and LTE(4), as well as PGD(2), stimulated goblet cell secretion in rat goblet cells. LTD(4) and LTE(4) increased the intracellular Ca(2+) concentration ([Ca(2+)](i)), and LTD(4) activated ERK1/2. The CysLT(1) receptor antagonist MK571 significantly decreased LTD(4)-stimulated rat goblet cell secretion and the increase in [Ca(2+)](i). Resolvins D1 (RvD1) and E1 (RvE1) completely reduced LTD(4)-stimulated goblet cell secretion in cultured rat goblet cells. LTD(4)-induced secretion from human goblet cells was blocked by RvD1. RvD1 and RvE1 prevented LTD(4)- and LTE(4)-stimulated increases in [Ca(2+)](i), as well as LTD(4) activation of ERK1/2. We conclude that cysteinyl leukotrienes stimulate conjunctival goblet cell mucous secretion with LTD(4) using the CysLT(1) receptor. Stimulated secretion is terminated by preventing the increase in [Ca(2+)](i) and activation of ERK1/2 by RvD1 and RvE1.

Leukotrienes modulate secretion of progesterone and prostaglandins during the estrous cycle and early pregnancy in cattle: an in vivo study.

Recently, we showed that leukotrienes (LTs) regulate ovarian cell function in vitro. The aim of this study was to examine the role of LTs in corpus luteum (CL) function during both the estrous cycle and early pregnancy in vivo. mRNA expression of LT receptors (BLT for LTB(4) and CYSLT for LTC(4)), and 5-lipoxygenase (5-LO) in CL tissue and their localization in the ovary were studied during the estrous cycle and early pregnancy. Moreover, concentrations of LTs (LTB(4) and C(4)) in the CL tissue and blood were measured. 5-LO and BLT mRNA expression increased on days 16-18 of the cycle, whereas CYSLT mRNA expression increased on days 16-18 of the pregnancy. The level of LTB(4) was evaluated during pregnancy compared with the level of LTC(4), which increased during CL regression. LT antagonists influenced the duration of the estrous cycle: the LTC(4) antagonist (azelastine) prolonged the luteal phase, whereas the LTB(4) antagonist (dapsone) caused earlier luteolysis in vivo. Dapsone decreased progesterone (P(4)) secretion and azelastine increased P(4) secretion during the estrous cycle. In summary, LT action in the bovine reproductive tract is dependent on LT type: LTB(4) is luteotropic during the estrous cycle and supports early pregnancy, whereas LTC(4) is luteolytic, regarded as undesirable in early pregnancy. LTs are produced/secreted in the CL tissue, influence prostaglandin function, and serve as important factors during the estrous cycle and early pregnancy in cattle.

Participation of leukotriene C(4) in the regulation of suicidal erythrocyte death.

Eryptosis, the suicidal death of erythrocytes, is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the erythrocyte surface. Eryptosis is triggered by increase in cytosolic Ca(2+) concentration upon energy depletion. The present study explored the involvement of leukotrienes. Western blotting was employed to detect the cysteinyl-leukotriene receptor cysLT1, competitive immune assay to determine leukotriene release from erythrocytes, Fluo3 fluorescence to estimate cytosolic Ca(2+) concentration, forward scatter to analyse cell volume and annexin V-binding to disclose phosphatidylserine exposure. As a result, erythrocytes expressed the leukotriene receptor CysLT1. Glucose depletion (24 hours) significantly increased the formation of the cysteinyl-leukotrienes C(4)/D(4)/E(4). Leukotriene C(4) (10 nM) increased Ca(2+) entry, decreased forward scatter, activated caspases 3 and 8, and stimulated annexin V-binding. Glucose depletion similarly increased annexin V-binding, an effect significantly blunted in the presence of the leukotriene receptor antagonist cinalukast (1 microM) or the 5-lipoxygenase inhibitor BW B70C (1 microM). In conclusion, upon energy depletion erythrocytes form leukotrienes, which in turn activate cation channels, leading to Ca(2+) entry, cell shrinkage and cell membrane scrambling. Cysteinyl-leukotrienes thus participate in the signaling of eryptosis during energy depletion.

Analysis of 927T > C CYSLTR1 and –444A > C LTC4S polymorphisms in children with asthma

Introduction: The cysteinyl leukotrienes (Cys-LTs) are potent inflammatory mediators in asthma. It has been suggested that the different response of patients to Cys-LTs inhibitors could be due to the presence of polymorphisms in the genes implicated in this pathway. Methods: In this study, polymorphisms 927T > CCYSLTR1 and –444A > C LTC4S were analysed in a Spanish population of 188 individuals (109 asthmatic children and 79 controls). Standardised history, skinprick tests and lung function measurements were performed in all patients. Genotypes were determined by sequencing after PCR amplification. Results: Differences were observed in 927T > CCYSLTR1, regarding the severity of asthma in males. A greater presence of allele C in the population with persistent asthma versus the control group (Fisher’sp-value = 0.001; Monte Carlo p-value = 0.003; OR:12.35; 95 %CI: 2.18-70.00) was observed. Differences were also detected in the combined study of both polymorphisms, among controls and asthmatic patients (Monte Carlo p-value = 0.0002). In the group of males with asthma, an increase of AC variant (–444A LTC4S and 927C CYSLTR1) and a reduction in the AT genetic combination were detected. Conclusions: The combined study of polymorphisms in genes of the leukotriene pathway could explain the differences observed in the studies reported on polymorphism –444A < C LTC4S individually analysed

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Identification of regions required for apical membrane localization of human multidrug resistance protein 2.

Multidrug resistance proteins MRP1 and MRP2 transport a wide range of endo- and xenobiotics. However, with the exception of certain parts of the brain, MRP1 traffics to basolateral membranes of polarized cells, whereas MRP2 is apical in location and thus it is particularly important for systemic elimination of such compounds. Different regions of MRP1 and MRP2 seem to target them to their respective membrane locations. In addition to two "core" membrane spanning domains (MSDs) characteristic of ATP-binding cassette transporters, MRP1 and MRP2 have a third NH2-terminal MSD (MSD0), which is not required for basolateral targeting of MRP1, or for transport of at least some substrates. Here, we demonstrate that all elements necessary for apical targeting of MRP2 reside in MSD0 and the adjacent cytoplasmic loop (CL) 3. Furthermore, we show that this region of MRP2 can target the core of MRP1 to an exclusively apical location. Within MRP2 CL3, we identified a lysine-rich element that is essential for apical targeting. When introduced into MRP1, this element alone is sufficient to result in partial apical localization. However, exclusive targeting to the apical membrane seems to require the integrity of the entire region encompassing MSD0 and CL3 of MRP2. Because CL3 of MRP1 is critical for binding, transport, or both of several compounds, we also examined the function of hybrids containing all, or portions of MRP2 MSD0 and CL3. Our results indicate that CL3 is important for interaction with both the glutathione and glucuronide conjugates tested, but that different regions may be involved.

Eoxins are proinflammatory arachidonic acid metabolites produced via the 15-lipoxygenase-1 pathway in human eosinophils and mast cells.

Human eosinophils contain abundant amounts of 15-lipoxygenase (LO)-1. The biological role of 15-LO-1 in humans, however, is unclear. Incubation of eosinophils with arachidonic acid led to formation of a product with a UV absorbance maximum at 282 nm and shorter retention time than leukotriene (LT)C4 in reverse-phase HPLC. Analysis with positive-ion electrospray tandem MS identified this eosinophil metabolite as 14,15-LTC4. This metabolite could be metabolized to 14,15-LTD4 and 14,15-LTE4 in eosinophils. Because eosinophils are such an abundant source of these metabolites and to avoid confusion with 5-LO-derived LTs, we suggest the names eoxin (EX)C4, -D4, and -E4 instead of 14,15-LTC4, -D4, and -E4, respectively. Cord blood-derived mast cells and surgically removed nasal polyps from allergic subjects also produced EXC4. Incubation of eosinophils with arachidonic acid favored the production of EXC4, whereas challenge with calcium ionophore led to exclusive formation of LTC4. Eosinophils produced EXC4 after challenge with the proinflammatory agents LTC4, prostaglandin D2, and IL-5, demonstrating that EXC4 can be synthesized from the endogenous pool of arachidonic acid. EXs induced increased permeability of endothelial cell monolayer in vitro, indicating that EXs can modulate and enhance vascular permeability, a hallmark of inflammation. In this model system, EXs were 100 times more potent than histamine and almost as potent as LTC4 and LTD4. Taken together, this article describes the formation of proinflammatory EXs, in particular in human eosinophils but also in human mast cells and nasal polyps.

Cysteinyl-leukotrienes and their receptors in asthma and other inflammatory diseases: critical update and emerging trends.

Cysteinyl-leukotrienes (cysteinyl-LTs), that is, LTC4, LTD4, and LTE4, trigger contractile and inflammatory responses through the specific interaction with G protein-coupled receptors (GPCRs) belonging to the purine receptor cluster of the rhodopsin family, and identified as CysLT receptors (CysLTRs). Cysteinyl-LTs have a clear role in pathophysiological conditions such as asthma and allergic rhinitis (AR), and have been implicated in other inflammatory conditions including cardiovascular diseases, cancer, atopic dermatitis, and urticaria. Molecular cloning of human CysLT1R and CysLT2R subtypes has confirmed most of the previous pharmacological characterization and identified distinct expression patterns only partially overlapping. Interestingly, recent data provide evidence for the immunomodulation of CysLTR expression, the existence of additional receptor subtypes, and of an intracellular pool of CysLTRs that may have roles different from those of plasma membrane receptors. Furthermore, genetic variants have been identified for the CysLTRs that may interact to confer risk for atopy. Finally, a crosstalk between the cysteinyl-LT and the purine systems is being delineated. This review will summarize and attempt to integrate recent data derived from studies on the molecular pharmacology and pharmacogenetics of CysLTRs, and will consider the therapeutic opportunities arising from the new roles suggested for cysteinyl-LTs and their receptors.

Five-lipoxygenase pathway of arachidonic acid metabolism in carcino-genesis and cancer chemoprevention.

Aberrant arachidonic acid metabolism has recently received intensive attention in the field of cancer research. Recent discoveries regarding the long-term cardiovascular side effects of cyclooxygenase 2 inhibitors have cast doubts on their use for cancer chemoprevention. Although such a problem does not undermine the importance of cyclooxygenase 2 as a cancer chemopreventive target, investigation into other AA-metabolizing pathways that are also important in inflammation and inflammation-associated carcinogenesis is necessary. Here, the important role of the 5-lipoxygenase pathway in carcinogenesis is reviewed. Inhibition of the 5-lipoxygenase pathways clearly has chemopreventive effects on various cancers, and hence further studies on its enzymes, metabolites and receptors for cancer chemoprevention and therapy are warranted.

Toll-like receptor agonists differentially regulate cysteinyl-leukotriene receptor 1 expression and function in human dendritic cells.

BACKGROUND: Dendritic cells (DCs) acquire, during their maturation, the expression of the chemokine receptor CCR7 and the ability to migrate to lymph nodes in response to CC chemokine ligand 19 (CCL19). This migration is impaired in mice lacking the leukotriene (LT) C4 transporter and restored by addition of exogenous LTC4. OBJECTIVE: To define the role of LT in human DC function, we studied the expression and function of the cysteinyl-leukotriene (CysLT) receptors during DC differentiation from monocytes and subsequent maturation. METHODS: Receptor expression was measured by flow cytometry and real-time PCR. Responsiveness to LTD4 stimulation was assessed by calcium flux and chemotaxis. RESULTS: Maturation of DC with LPS, a classic Toll-like receptor 4 agonist, reduced CysLT receptor 1 (CysLT1) expression by 50%, whereas CysLT receptor 2 expression was increased. In contrast, the Toll-like receptor 3 agonist poly inosinic and cytidylic acid (polyI:C) had no effect on receptor expression. Downregulation of CysLT1 expression by LPS could not be mimicked by TNF-alpha alone or in combination with IL-1beta or IL-6. It was, however, prevented by inhibitors of COX and could be reproduced by a combination of TNF-alpha and prostaglandin E2. Immature DCs and DCs matured with polyI:C, but not with LPS, responded to LTD4 with a robust cytosolic calcium flux, which was prevented by the CysLT1 antagonist montelukast. LTD4 induced DC chemotaxis and enhanced DC migration in response to CCL19 in DCs matured with polyI:C, but only weakly in DCs matured with LPS. CONCLUSION: Our data suggest that human DCs may differentially respond to leukotriene, depending on their maturational stimuli. CLINICAL IMPLICATIONS: Our study demonstrates that some microbial agents can reduce the migration of dendritic cells in response to leukotrienes, with potential for differential involvement of these cells in allergic inflammation.

[Leukotrienes: potential therapeutic targets in cardiovascular diseases]. / Les leucotriènes: des cibles thérapeutiques potentielles dans le traitement des maladies cardiovasculaires.

Leukotrienes are potent inflammatory mediators synthesized locally within the cardiovascular system through the 5-lipoxygenase pathway of arachidonic acid metabolism. The leukotrienes, consisting of dihydroxy leukotriene LTB4 and the cysteinyl leukotrienes LTC4, LTD4 and LTE4, act by targeting cell surface receptors expressed on inflammatory cells and on structural cells of vessel walls. LTB, induces leukocyte activation and chemotaxis via high- and low-affinity receptor subtypes (BLT1 and BLT2), respectively. Recently, BLT, receptors were found on human vascular smooth muscle cells, inducing their migration and proliferation. Cysteinyl leukotrienes are vasoconstrictors and induce endothelium-dependent vascular responses through the CysLT, and CysLT2 receptor subtypes. There is also pharmacological evidence for the existence of further CysLT receptor subtypes. Taken together, experimental and genetic studies suggest a major role of leukotrienes in atherosclerosis and in its ischemic complications such as acute coronary syndromes and stroke. Furthermore, the effects on vascular smooth muscle cells suggest a role in the vascular remodeling observed after coronary angioplasty, as well as in aortic aneurysm. Further experimental and clinical studies are needed to determine the potential of therapeutic strategies targeting the leukotriene pathway in cardiovascular disease.

Mast cell mediators in citric acid-induced airway constriction of guinea pigs.

We demonstrated previously that mast cells play an important role in citric acid (CA)-induced airway constriction. In this study, we further investigated the underlying mediator(s) for this type of airway constriction. At first, to examine effects caused by blocking agents, 67 young Hartley guinea pigs were divided into 7 groups: saline + CA; methysergide (serotonin receptor antagonist) + CA; MK-886 (leukotriene synthesis inhibitor) + CA; mepyramine (histamine H1 receptor antagonist) + CA; indomethacin (cyclooxygenase inhibitor) + CA; cromolyn sodium (mast cell stabilizer) + CA; and compound 48/80 (mast cell degranulating agent) + CA. Then, we tested whether leukotriene C4 (LTC4) or histamine enhances CA-induced airway constriction in compound 48/80-pretreated guinea pigs. We measured dynamic respiratory compliance (Crs) and forced expiratory volume in 0.1 s (FEV0.1) during either baseline or recovery period. In addition, we detected histamine level, an index of pulmonary mast cell degranulation, in bronchoalveolar lavage (BAL) samples. Citric acid aerosol inhalation caused decreases in Crs and FEV0.1, indicating airway constriction in the control group. This airway constriction was significantly attenuated by MK-886, mepyramine, cromolyn sodium, and compound 48/80, but not by either methysergide or indomethacin. Both LTC4 and histamine infusion significantly increased the magnitude of CA-induced airway constriction in compound 48/80-pretreated guinea pigs. Citric acid inhalation caused significant increase in histamine level in the BAL sample, which was significantly suppressed by compound 48/80. These results suggest that leukotrienes and histamine originating from mast cells play an important role in CA inhalation-induced noncholinergic airway constriction.

Expression of leukotriene C4 synthase mRNA by the choroid plexus in mouse brain suggests novel neurohormone functions of cysteinyl leukotrienes.

Leukotriene C(4) is a potent mediator of allergic and inflammatory reactions, and is formed from arachidonic acid and glutathione through the sequential action of 5-lipoxygenase and leukotriene C(4) synthase (LTCS). These enzymes are predominantly expressed in cells of myeloid lineage. In this report, we have investigated LTCS mRNA expression in mouse brain. Expression was demonstrated using RT-PCR and RNase protection assays. In situ hybridization experiments showed exclusive staining of the choroid plexus of all brain ventricles. This expression pattern may provide a mechanism for the generation of LTC(4) on the cerebral side of the blood-brain barrier and suggests a possible novel regulator function of LTC(4) in the formation of cerebrospinal fluid.

Up-regulation of cysteinyl leukotriene 1 receptor by IL-13 enables human lung fibroblasts to respond to leukotriene C4 and produce eotaxin.

Cysteinyl leukotrienes (CysLTs) play an important role in eosinophilic airway inflammation. In addition to their direct chemotactic effects on eosinophils, indirect effects have been reported. Eotaxin is a potent eosinophil-specific chemotactic factor produced mainly by fibroblasts. We investigated whether CysLTs augment eosinophilic inflammation via eotaxin production by fibroblasts. Leukotriene (LT)C(4) alone had no effect on eotaxin production by human fetal lung fibroblasts (HFL-1). However, LTC(4) stimulated eotaxin production by IL-13-treated fibroblasts, thereby indirectly inducing eosinophil sequestration. Unstimulated fibroblasts did not respond to LTC(4), but coincubation or preincubation of fibroblasts with IL-13 altered the response to LTC(4). To examine the mechanism(s) involved, the expression of CysLT1R in HFL-1 was investigated by quantitative real-time PCR and flow cytometry. Only low levels of CysLT1R mRNA and no CysLT1R protein were expressed in unstimulated HFL-1. In contrast, stimulation with IL-13 at a concentration of 10 ng/ml for 24 h significantly up-regulated both CysLT1R mRNA and protein expression in HFL-1. The synergistic effect of LTC(4) and IL-13 on eotaxin production was abolished by CysLT1R antagonists pranlukast and montelukast. These findings suggest that IL-13 up-regulates CysLT1R expression, which may contribute to the synergistic effect of LTC(4) and IL-13 on eotaxin production by lung fibroblasts. In the Th2 cytokine-rich milieu, such as that in bronchial asthma, CysLT1R expression on fibroblasts might be up-regulated, thereby allowing CysLTs to act effectively and increase eosinophilic inflammation.

[Studies on the experimental allergic rhinitis induced by Japanese cedar pollen--role of cysteinyl leukotrienes in nasal allergic symptoms].

Cysteinyl leukotrienes (CysLTs: LTC4, LTD4, and LTE4) are a family of potent inflammatory mediators that appear to contribute to the pathophysiologic features of allergic rhinitis. Because treatment with a CysLT1 receptor antagonist and a 5-lipoxygenase inhibitor modified allergen-induced nasal blockage in patients with allergic rhinitis, and CysLTs were detected in nasal cavity lavage fluid, it has been suggested that CysLTs act as significant inflammatory mediators in allergic rhinitis. The role of CysLTs was evaluated in our experimental allergic rhinitis model in sensitized guinea pigs which shows biphasic nasal blockage, sneezing and nasal hyperresponsiveness to LTD4 induced by repetitive inhalation challenge with Japanese cedar pollen. In this model, the CysLT1 receptor antagonist pranlukast suppressed the late-phase nasal blockage but not early blockage and sneezing. Nasal hyperresponsiveness (nasal blockage) to LTD4 was largely blocked by pranlukast, naphazoline, and N omega-nitro-L-arginine-methyl ester. The results demonstrate that nasal blockage induced by CysLTs is mainly due to dilatation of nasal blood vessels, which can be induced by the nitric oxide produced through CysLT1 receptor activation. On the other hand, when pollen inhalation challenge was performed in the presence of nasal hyperresponsiveness, antigen-induced biphasic nasal blockage and sneezing were considerably enhanced and CysLTs contributed to both symptoms, suggesting that nasal hyperresponsiveness induces aggravation of antigen-induced nasal symptoms. The results presented in this study further suggest that our model is a good representative of human allergic rhinitis and offer evidence that CysLTs are chemical mediators mainly responsible for allergic nasal symptoms.