Native and IgE-primed rat peritoneal mast cells exert pro-inflammatory activity and migrate in response to yeast zymosan upon Dectin-1 engagement

Mast cells (MCs) play an essential role in host defense, primarily because of their location, their ability to pathogen destruction via several mechanisms, and the pattern recognition receptors they express. Even though most data is available regarding MC activation by various bacteria- or virus-derived molecules, those cells' activity in response to constituents associated with fungi is not recognized enough. Our research aimed to address whether Saccharomyces cerevisiae-derived zymosan, i.e., β-(1,3)-glucan containing mannan particles, impacts MC activity aspects. Overall, the obtained results indicate that zymosan has the potential to elicit a pro-inflammatory response of rat peritoneal MCs. For the first time ever, we provided evidence that zymosan induces fully mature MC migration, even in the absence of extracellular matrix (ECM) proteins. Moreover, the zymosan-induced migratory response of MCs is almost entirely a result of directional migration, i.e., chemotaxis. We found that zymosan stimulates MCs to degranulate and generate lipid mediators (cysLTs), cytokines (IFN-α, IFN-β, IFN-γ, GM-CSF, TNF), and chemokine (CCL2). Zymosan also upregulated mRNA transcripts for several cytokines/chemokines with pro-inflammatory/immunoregulatory activity. Moreover, we documented that zymosan activates MCs to produce reactive oxygen species (ROS). Lastly, we established that the zymosan-induced MC response is mediated through activation of the Dectin-1 receptor. In general, our results strongly support the notion that MCs contribute to innate antifungal immunity and bring us closer to elucidate their role in host-pathogenic fungi interactions. Besides, provided findings on IgE-sensitized MCs appear to indicate that exposure to fungal zymosan could affect the severity of IgE-dependent disorders, including allergic ones.

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.

Cysteinyl leukotriene receptor 1 expression identifies a subset of neutrophils during the antiviral response that contributes to postviral atopic airway disease

BACKGROUND

Viral respiratory tract infections increase the risk of development and exacerbation of atopic disease. Previously, we demonstrated the requirement for a neutrophil (PMN) subset expressing CD49d to drive development of postviral atopic airway disease in mice.

OBJECTIVE

We sought to determine whether human CD49d⁺ PMNs are present in the nasal mucosa during acute viral respiratory tract infections and further characterize this PMN subset in human subjects and mice.

METHODS

Sixty subjects (5-50 years old) were enrolled within 4 days of acute onset of upper respiratory symptoms. Nasal lavage for flow cytometry and nasal swabs for viral PCR were performed at enrollment and during convalescence. The Sendai virus mouse model was used to investigate the phenotype and functional relevance of CD49d⁺ PMNs.

RESULTS

CD49d⁺ PMN frequency was significantly higher in nasal lavage fluid during acute respiratory symptoms in all subjects (2.9% vs 1.0%, n = 42, P < .001). In mice CD49d⁺ PMNs represented a "proatopic" neutrophil subset that expressed cysteinyl leukotriene receptor 1 (CysLTR1) and produced TNF, CCL2, and CCL5. Inhibition of CysLTR1 signaling in the first days of a viral respiratory tract infection was sufficient to reduce accumulation of CD49d⁺ PMNs in the lungs and development of postviral atopic airway disease. Similar to the mouse, human CD49d⁺ PMNs isolated from nasal lavage fluid during a viral respiratory tract infection expressed CysLTR1.

CONCLUSION

CD49d and CysLTR1-coexpressing PMNs are present during symptoms of an acute viral respiratory tract infection in human subjects. Further study is needed to examine selective targeting of proatopic neutrophils as a potential therapeutic strategy to prevent development of postviral atopic airway disease.

Phospholipase A2 in experimental allergic bronchitis: a lesson from mouse and rat models

Background

Phospholipases A₂ (PLA₂) hydrolyzes phospholipids, initiating the production of inflammatory lipid mediators. We have previously shown that in rats, sPLA₂ and cPLA₂ play opposing roles in the pathophysiology of ovalbumin (OVA)-induced experimental allergic bronchitis (OVA-EAB), an asthma model: Upon disease induction sPLA₂ expression and production of the broncho-constricting CysLTs are elevated, whereas cPLA₂ expression and the broncho-dilating PGE₂ production are suppressed. These were reversed upon disease amelioration by treatment with an sPLA₂ inhibitor. However, studies in mice reported the involvement of both sPLA₂ and cPLA₂ in EAB induction.

Objectives

To examine the relevance of mouse and rat models to understanding asthma pathophysiology.

Methods

OVA-EAB was induced in mice using the same methodology applied in rats. Disease and biochemical markers in mice were compared with those in rats.

Results

As in rats, EAB in mice was associated with increased mRNA of sPLA₂, specifically sPLA₂gX, in the lungs, and production of the broncho-constricting eicosanoids CysLTs, PGD₂ and TBX₂ in bronchoalveolar lavage (BAL). In contrast, EAB in mice was associated also with elevated cPLA₂ mRNA and PGE₂ production. Yet, treatment with an sPLA₂ inhibitor ameliorated the EAB concomitantly with reverting the expression of both cPLA₂ and sPLA₂, and eicosanoid production.

Conclusions

In both mice and rats sPLA₂ is pivotal in OVA-induced EAB. Yet, amelioration of asthma markers in mouse models, and human tissues, was observed also upon cPLA₂ inhibition. It is plausible that airway conditions, involving multiple cell types and organs, require the combined action of more than one, essential, PLA₂s.

Sceptridium ternatum extract exerts antiasthmatic effects by regulating Th1/Th2 balance and the expression levels of leukotriene receptors in a mouse asthma model

AIM OF THE STUDY

Sceptridium ternatum Lyon (ST), a common Chinese herb, has been used in treatment of allergic asthma and whooping cough. In the present study, we investigated the Th1/Th2 ratio of peripheral blood and mRNA levels of leukotriene receptors after the treatment of ST in allergic asthma mouse model.

MATERIALS AND METHODS

Mouse asthma model was developed by ovalbumin (OVA) sensitization followed by the inhalation of aerosol allergen. Montelukast (10mg/kg), as a positive control drug, and ST were administrated six days before the OVA sensitization for ten days. Airway responsiveness was evaluated by the Medlab 12.0 biological signal processing system. The ratio of Th1/Th2 cells was determined by flow cytometry. The expression level of Cyslt1 was measured by PCR. Pathological changes of lung tissues were examined by H&E staining.

RESULTS

ST significantly reduced the airway responsiveness, elevated the ratio of Th1/Th2, and decreased Cyslt1 mRNA level in a dose-dependent manner. High-dose ST distinctly prevented the pathological changes of lung tissues.

CONCLUSION

High-dose ST had the same efficacy as Montelukast in a mouse asthma model, and ST could be a potential anti-asthmatic agent.

[Rotenone-induced changes of cysteinyl leukotriene receptor 1 expression in BV2 microglial cells]

OBJECTIVE

To prepare and identify a polyclonal antibody (pAb) against (mouse) cysteinyl leukotriene receptor 1 (CysLT(1)) and to investigate the changes of CysLT(1) receptor expression in BV2 microglial cells after rotenone treatment.

METHODS

Rabbits were immunized with KLH-coupled CysLT(1) peptide to prepare the pAb. The titer of the pAb in rabbit plasma was detected by ELISA method, and the specificity of the pAb was tested by antigen blockade. After BV2 cells were treated with rotenone (0.01-1 μmol/L) for 24 h, the expression of CysLT(1) was determined by immunostaining, Western blotting and RT-PCR.

RESULT

The pAb showed a titer of 1/32728, and was not cross-reacted with antigens of CysLT(2) receptor and GPR17. Immunostaining, Western blotting and RT-PCR analysis showed the expression of CysLT(1) receptor in BV2 microglia. Rotenone at 1μmol/L significantly induced an increased expression of CysLT(1) receptor.

CONCLUSION

The prepared CysLT(1) receptor polyclonal antibody has a high titer and high specificity to meet testing requirements of Western blotting and immunostaining; CysLT(1) is associated with rotenone-induced injury of BV2 microglial cells.

[Preparation and identification of polyclonal antibody against cysteinyl leukotriene receptor 2]

OBJECTIVE

To prepare and identify a polyclonal antibody against cysteinyl leukotriene receptor (CysLT(2)receptor).

METHODS

Rabbits were immunized with KLH-coupled CysLT(2) receptor peptide to prepare the polyclonal antibody (pAb). The titer of the pAb in rabbit plasma was detected by indirect ELISA, and the specificity of the pAb was tested by antigen blockade. The tissue distribution of CysLT(2) receptor was detected by Western blot and immunohistochemistry with the prepared pAb.

RESULT

The pAb showed a titer higher than 1/1047296, and was specific to CysLT(2) receptor, without cross-reaction with the antigens of CysLT(1) receptor and GPR17. A higher expression of CysLT(2) receptor in kidney, brain and lung of rats and mice was detected by Western blot analysis using the prepared pAb. The molecular weight of CysLT(2) receptor protein was about 40 kD. Immunohistochemical examination showed that CysLT(2) receptor was expressed mainly in the neuron, and partly in astrocytes in rat brain.

CONCLUSION

The prepared CysLT(2) receptor pAb has high sensitivity and specificity, and can be used in Western blot and immunohistochemistry.

[Preparation and identification of a polyclonal antibody against novel cysteinyl leukotriene receptor GPR17]

OBJECTIVE

To prepare and identify a polyclonal antibody (pAb) against GPR17, a novel cysteinyl leukotriene receptor.

METHODS

Rabbits were immunized with KLH-coupled GPR17 peptide to prepare the pAb. The titer of the pAb in rabbit plasma was detected by indirect ELISA, and the specificity of the pAb was tested by antigen blockade. GPR17 tissue distribution was detected by Western blot with the pAb.

RESULTS

The pAb showed a titer as high as 1:16 364,and was not cross-reacted with the antigens of CysLT(1) and CysLT(2) receptors. A higher expression of GPR17 in the rat brain and heart was detected using the newly prepared pAb. The molecular weigh of GPR17 protein was about 43 kD.

CONCLUSION

The prepared GPR17 pAb has high sensitivity and specificity,and can be used in Western blot for detecting GPR17.

A functional G300S variant of the cysteinyl leukotriene 1 receptor is associated with atopy in a Tristan da Cunha isolate

Atopy is a well-defined immune phenotype that is reported to be a risk factor for asthma. Among the many loci that contribute to a genetic predisposition to asthma, the cysteinyl leukotriene receptor genes and their variants have been important subjects of study because they are functionally and pharmacologically implicated in the atopy phenotype affecting many asthma subjects. Moreover, the product of cysteinyl-leukotriene 1 receptor gene (CysLT1), located at Xq13.2, is targeted by LT receptor antagonists. In our earlier association study, the M201V variant of the cysteinyl-leukotriene 2 receptor gene (CysLT2), located at 13q14, was implicated in atopic asthma. Here we report the screening of the coding region of the CysLT1, gene in the highly asthmatic Tristan da Cunha population. In this population, we discovered a CysLT1 G300S variant that is carried with a significantly higher frequency in atopics and asthmatics from the Tristan da Cunha population. Furthermore, we report the asthma independent association of the CysLT1 G300S variant with atopy. Subsequently, we compared the changes conferred by each SNP on CysLT function. The CysLT1 300S receptor interacts with LTD4 with significantly greater potency. For the 300S variant, a statistically significant decrease in the effector concentration for half-maximum response (EC50) for intracellular Ca flux and total InsP generation is observed. Other aspects of the receptor function and activity, such as desensitization, pharmacologic profile in response to montelukast, and cellular localization, are unchanged. These in vitro analyses provide evidence that the 300S CysLT1 variant, found more commonly in atopics in the Tristan da Cunha population, encodes a functionally more sensitive variant.

Cysteinyl leukotriene receptor antagonist MK-571 alters bronchoalveolar lavage fluid proteome in a mouse asthma model

Cysteinyl leukotriene receptor type 1 (leukotriene CysLT(1) receptor) antagonist is one of the most effective anti-inflammatory agents for asthma. The spectrum of protein targets that can be regulated by leukotriene CysLT(1) receptor antagonist in asthma is not fully understood. The present study tried to identify novel protein targets of a selective leukotriene CysLT(1) receptor antagonist MK-571 in allergic airway inflammation by analyzing the proteome of mouse bronchoalveolar lavage fluid. BALB/c mice sensitized and challenged with ovalbumin showed increased pulmonary inflammatory cell infiltration, airway mucus production and serum ovalbumin-specific IgE level. MK-571 inhibited all these allergic airway inflammation endpoints. Lavage fluid proteins were resolved by two-dimensional gel electrophoresis and identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The level of fourteen bronchoalveolar lavage fluid protein spots was markedly altered by MK-571. A family of chitinases (Ym1, Ym2 and acidic mammalian chitinase), lungkine, surfactant protein-D and gamma-actin have been found for the first time to be down-regulated by leukotriene CysLT(1) receptor antagonist in mouse allergic airways. Some of the down-regulatory effects were confirmed with reverse transcription-polymerase chain reaction analyses. Taken together, we have identified novel protein targets that can be regulated by leukotriene CysLT(1) receptor antagonist in mouse allergic airway inflammation, and our findings reveal additional pharmacological actions of leukotriene CysLT(1) receptor antagonist in the treatment of asthma.

Concordant modulation of cysteinyl leukotriene receptor expression by IL-4 and IFN-gamma on peripheral immune cells

Arachidonic acid can be metabolized to form a group of compounds known as the cysteinyl leukotrienes (CysLT) that bind to one of two receptors to mediate their actions. On circulating cells, expression of the leukotriene receptors is low, but in inflamed tissue the receptor number is dramatically increased. We hypothesized that the cytokine milieu present during inflammation can increase receptor expression on infiltrating immune cells. Various cell populations were purified from peripheral blood and stimulated in vitro with cytokines characteristic of allergic inflammatory disorders, and CysLT receptor expression was measured using quantitative PCR analysis, Western blot, and flow cytometry. IL-4, but not IL-13, was able to significantly induce mRNA and protein levels for both CysLT receptor 1 and 2 from T cells and B cells. CysLT2 receptor expression was also significantly increased in monocytes and eosinophils after IL-4 stimulation. Surprisingly, CysLT2 receptor expression was increased in monocytes, T cells, and B cells when IFN-gamma was used as the stimulus. Factors involved in eosinophil growth and survival were tested for their ability to alter CysLT receptor expression. These results support the concept that cytokines increase expression of both receptors on lymphocytes and granulocytes, allowing these cells to be more responsive to secreted leukotrienes at sites of inflammation.

Cysteinyl Leukotriene Receptor Expression in Aspirin-Sensitive Nasal Polyposis Patients

BACKGROUND

The aim of this study was to detect cysteinyl leukotriene (Cys-LT) receptors in aspirin-sensitive nasal polyposis patients, and compare them with nasal polyposis and chronic rhinosinusitis patients without aspirin sensitivity.

METHODS

The formalin-fixed, paraffin-embedded tissue blocks of a total of 52 patients undergoing endoscopic sinus surgery were reviewed by an experienced head and neck pathologist. Of these 52 cases, there were 22 nasal polyposis cases with aspirin sensitivity, 15 nasal polyposis cases without aspirin sensitivity and 15 chronic rhinosinusitis cases without aspirin sensitivity. Immunohistochemical analyses for Cys-LT(1) receptors were performed with polyclonal rabbit antibody.

RESULTS

Eosinophil receptor intensity levels were 27.68, 21.67, and 14.40, respectively. This was statistically insignificant (p <0.089). Mast cell receptor intensity levels were 8.41, 5.27, and 4.27, respectively. In the aspirin-sensitive group, mast cell receptor intensity was significantly higher when compared to the nasal polyposis and chronic rhinosinusitis group (p < 0.0001 and p < 0.0001, respectively). The difference in Cys-LT(1) receptor immunoreactivity in both eosinophils and mast cells among the 3 groups was also found to be statistically significant (p < 0.001).

CONCLUSIONS

Our study revealed that nasal polyps of aspirin-sensitive patients were infiltrated with eosinophils and mast cells, Cys-LT(1) receptor proportions in these inflammatory cells were found to be higher and Cys-LT(1) receptor immunoreactivity in eosinophils and mast cells was increased.

Pharmacotherapy of diseases mediated by 5-lipoxygenase pathway eicosanoids

Inflammatory eicosanoids generated by the 5-lipoxygenase (5-LO) pathway of arachidonic acid metabolism are now known to have at least 6 receptors: OXE, which recognizes 5-HETE and 5-oxo-ETE; a putative receptor recognizing a potent 5-oxo-ETE metabolite, FOG(7); the LTB(4) receptors, BLT1 and BLT2; the cysteinyl leukotriene receptors, CysLT(1) and CysLT(2), which recognize leukotrienes LTC(4), LTD(4), LTE(4) and LTF(4). The 5-LO pathway is activated in many diseases and invokes inflammatory responses not affected by glucocorticoids, but therapy with selective BLT1 or CysLT(1) antagonists in asthma has met with variable success. Studies show that 5-LO pathway eicosanoids are not primary mediators in all cases of asthma, but may be especially important in severe persistent asthma, aspirin- and exercise-induced asthma, allergic rhinitis, COPD, idiopathic pulmonary fibrosis, atherosclerosis, atopic dermatitis, acne and ischemia-related organ injury. These disorders appear to involve multiple 5-LO pathway eicosanoids and receptor subtypes, suggesting that inhibition of the pathway at the level of 5-LO may be necessary for maximal efficacy.

Cysteinyl leukotriene receptor 1 promoter polymorphism is associated with aspirin-intolerant asthma in males

BACKGROUND

Cysteinyl leukotrienes (CysLTs) play important roles in the pathogenesis of eosinophilic airway inflammation characterized by bronchoconstriction, mucus secretion and airway hyper-responsiveness via cysteinyl leukotriene receptor 1 (CysLTR1)-mediated mechanism. CysLTR1-selective antagonists have anti-bronchoconstrictive and anti-inflammatory effects in asthma, particularly aspirin-intolerant asthma (AIA).

METHODS

To investigate the association of CysLTR1 with AIA development, we identified three single nucleotide polymorphisms (SNPs), -634C>T, -475A>C, -336A>G, in the 5' upstream region of CysLTR1 gene using a direct sequencing method in 105 AIA patients, 110 ASA-tolerant asthma (ATA) patients and 125 normal healthy controls (NC).

RESULTS

Significant differences were observed in allele frequencies of the three SNPs within male subjects; Male AIA patients had higher frequencies of the minor alleles of these three SNPs than male control groups (P=0.03 for AIA vs. NC; P=0.02 for AIA vs. ATA). Moreover, three-SNP haplotype, ht2 [T-C-G], was associated with increased disease risk (odds ratio (OR)=2.71, P=0.03 for AIA vs. NC; OR=2.89, P=0.02 for AIA vs. ATA) in males. CysLTR1 haplotypes were also associated with altered gene expression; luciferase activity was significantly enhanced with the ht2 [T-C-G] construct in comparison with the ht1 [C-A-A] construct in human Jurkat cells (P=0.04).

CONCLUSION

These results suggest that genetic variants of CysLTR1 are associated with AIA in a Korean population, and may modulate CysLTR1 expression.

The role of leukotrienes in the pathophysiology of inflammatory disorders: is there a case for revisiting leukotrienes as therapeutic targets?

Leukotrienes (LTs), a family of lipid mediators, play a key role in the pathogenesis of inflammation. They are synthesized in the leucocytes from arachidonic acid (AA) via the actions of 5-lipoxygenase (5-LO). LTs are classified into two classes: LTB(4) and cysteinyl LTs (CysLTs). LTB(4) is one of the most potent chemoattractant mediators of inflammation. It exerts its actions through a seven transmembrane-spaning G protein receptors, LTB4 R-1 and LTB4 R-2. CysLTs (LTC(4), LTD(4), and LTE(4)) are potent bronchoconstrictors that play an important role in asthma. They induce their actions through G protein coupled receptors, CysLT R-1 and CysLT R-2. LTs are involved in the pathogenesis of inflammatory disorders specially asthma, rheumatoid arthritis (RA) and inflammatory bowel disease (IBD). Therefore, LTs modifiers, LTs inhibitors or antagonists, represent important therapeutic advance in the management of inflammatory diseases. Zileuton, zafirlukast and montelukast are LTs modifiers that are approved to use for the treatment of inflammatory disorders.

927T>C polymorphism of the cysteinyl-leukotriene type-1 receptor (CYSLTR1) gene in children with asthma and atopic dermatitis

Asthma and atopic dermatitis share several common features and Cysteinyl-leukotrienes are mediators that participate in the pathogenesis of both diseases. Recently, a new polymorphism (927T>C) has been identified in cysteinyl-leukotriene type-1 receptor (CYSLTR1) gene. This gene is found on the X chromosome. The aim of this study was to analyze this SNP in a population of children with asthma and atopic dermatitis. In this study, 166 individuals, 79 adult controls (CTR) and 87 children with asthma (AA) were included. Forty-one patients with asthma presented atopic dermatitis (AA-AD). Adults were chosen as controls to confirm lack of development of asthma and allergy during childhood. Standardized history, physical examination, skin prick tests, and lung function measurements were performed in all patients. The 927T>C CYSLTR1 SNP was analyzed by direct sequencing after PCR amplification. In males (53 individuals), the C allele was significantly more common among AA-AD patients (47%) than in CTR (8%) (Fisher's p < 0.005; Monte Carlo p < 0.008; OR:9.78; 95%CI: 1.73-55.30). When comparing AA-AD vs. AA-NAD (patients with asthma but not atopic dermatitis), significant differences were observed, (47% vs. 15%, Fisher's p = 0.014; Monte Carlo p = 0.022; OR: 4.97; 95%CI: 1.29-19.13). No differences in allele distribution were observed between these disease sub-groups in females. The 927T>C is a silent SNP; however, it could affect transcription or translation or may be linked to an unidentified, functional polymorphism and thus may pre-dispose male children to asthma and atopic dermatitis in our population. Further studies are needed to confirm these findings.

Analysis of 927T> C CYSLTRI and -444A > C LTC4S polymorphisms in patients with asthma

BACKGROUND

The cysteinyl leukotrienes (cys-LTs) are proinflammatory mediators synthesized through the 5-lipoxygenase pathway of arachidonic acid metabolism. Cys-LTs exert their biological action by binding two types of G-protein-coupled seven transmembrane receptors, CYSLTR1 and CYSLTR2. The contribution of the cys-LT receptors to bronchial asthma has been established by the therapeutic efficacy of biosynthetic inhibitors and selective CYSLTR1 blockers.

OBJECTIVE

The present study was designed to analyse two different polymorphisms 927T>C CYSLTR1 and -444A>C LTC4S, and to determine whether there is an association between these polymorphisms and the asthma phenotype in a Spanish population.

METHODS

Both single nucleotide polymorphisms (SNPs) were analysed in 208 individuals (130 asthmatic subjects and 78 controls). A standardized history, physical examination, skin prick tests and lung function measurement were taken from all patients. Genotypes were determined by direct sequencing after polymerase chain reaction (PCR) amplification.

RESULTS

In the group of male patients, the C allele of 927T> C CYSLTRI was more common among patients with asthma than controls. No association was detected between the -444A> C LTC4S polymorphism and the asthma phenotype. The combination of 927T CYSLTR1 and -444A LTC4S was less common in male patients with asthma than in controls (Fisher's P-value =.039; Monte Carlo P-value (after 104 simulations)= .045 and the combination of 927C CYSLTR1 and -444A LTC4S was slightly more frequent in patients with asthma. No differences were observed in the female group.

CONCLUSIONS

The results suggest a certain trend of associations that could help to explain some controversial results in association studies of these genes from the leukotriene pathway, when considered individually. Further studies are needed to confirm such an association.

Pranlukast, a Leukotriene Receptor Antagonist, Inhibits Interleukin-5 Production via a Mechanism Distinct from Leukotriene Receptor Antagonism

BACKGROUND

Pranlukast, a cysteinyl leukotriene receptor 1 (CysLTR1) antagonist, inhibits not only airway smooth muscle contraction, but also allergic inflammation. The aim of this study was to determine the mechanism of pranlukast-induced interleukin-5 (IL-5) inhibition in allergic inflammation.

METHODS

Surgically resected human lung tissue was passively sensitized in vitro with mite-allergen-sensitized sera, followed by stimulation with mite allergen after pretreatment of the tissue with pranlukast, dexamethasone, or both. The IL-5 protein level in the culture medium was measured, and in situ hybridization of IL-5 and CysLTR1 mRNA was performed using lung tissues.

RESULTS

Pretreatment of lung tissues with pranlukast alone significantly decreased the amount of IL-5 protein in the culture medium by 40%. The combination of pranlukast and dexamethasone synergistically enhanced this effect. Quantitative in situ hybridization with image analysis revealed abundant expression of IL-5 mRNA in eosinophils, lymphocytes, and mast cells in sensitized and allergen-stimulated lung tissues. CysLTR1 mRNA was detected in macrophages, smooth muscle cells, eosinophils, and mast cells, but was less expressed in lymphocytes. Pranlukast-induced inhibition of IL-5 mRNA expression was noted in various cells, irrespective of their CysLTR1 mRNA expression status. In addition, cysteinyl leukotrienes per se failed to upregulate the IL-5 production.

CONCLUSION

Our results indicate that pranlukast inhibits IL-5 synthesis via a mechanism distinct from CysLTR1 antagonism.

Effects of a cysteinyl leukotriene receptor antagonist on eosinophil recruitment in experimental allergic rhinitis

The cysteinyl leukotrienes (cysLTs) are potent lipid mediators in allergic disease, acting through a receptor (cysLT1-R) which can be targeted in rhinitis and asthma. We investigated the effects of cysLT1-R antagonism in experimental allergic rhinitis, focusing on bone marrow eosinophil progenitor responses. BALB/c mice were sensitized, then given daily intranasal ovalbumin for 2 weeks, with montelukast sodium (5 mg/kg or 2.5 mg/kg) or placebo by gavage. Bone marrow eosinophil/basophil colonies were enumerated, and colony cells were morphologically assessed as indices of eosinophil differentiation and maturation. Montelukast treatment resulted in a significant decrease of eosinophils in the nasal mucosa, and in either bone marrow interleukin (IL)-5-, but not IL-3-, or granulocyte-macrophage colony-stimulating factor-responsive eosinophil/basophil colony-forming units, and IL-5-stimulated eosinophil maturation. These results indicate that cysLT1-R antagonism in vivo limits both IL-5-responsive eosinophilopoiesis, acting at several stages of eosinophil differentiation and maturation. The anti-allergic effects of cysLT1-R antagonists are consistent with the concept that cysLTs and IL-5 act together in the recruitment of eosinophils and eosinophil progenitors from the marrow during upper airway allergic inflammation.

Participation of chemical mediators in the development of experimental allergic conjunctivitis in rats

In the present study, we investigated the participation of chemical mediators in the development of experimental allergic conjunctivitis in rats. Cetirizine (a histamine H1 receptor antagonist), ramatroban (a thromboxane A2 (TXA2) receptor antagonist) and zafirlukast (a cysteinyl leukotrienes (cys-LTs) receptor antagonist) were orally administered from day 14 to day 42 during repeated topical antigen challenge. An increase in reactivity to antigen- and histamine-induced eye scratching behavior was observed by topical sensitization in sensitized rats. Although increased reactivity to antigen was not influenced by cetirizine, ramatoroban and zafirlukast, increased reactivity to histamine was significantly inhibited by ramatroban. The development of conjunctival edema was also observed for topical sensitization. Cetirizine caused no inhibition of the development of conjunctival edema, but ramatroban and zafirlukast inhibited the development of conjunctival edema. In addition, the number of eosinophils in the conjunctiva was increased by topical sensitization. Cetirizine had no significant effect on the increase in the number of eosinophils. However, ramatroban and zafirlukast were effective in inhibiting an increase in the number of eosinophils induced by topical sensitization. These results indicate that TXA2 is involved in increased histamine reactivity, and TXA2 and cys-LTs are associated with not only the conjunctival edema but also eosinophil infiltration during the development of experimental allergic conjunctivitis in rats.

Role for cysteinyl leukotrienes in allergen-induced change in circulating dendritic cell number in asthma

BACKGROUND

Dendritic cells are important antigen-presenting cells. After an allergen inhalation, their numbers rapidly decrease in circulation and increase in the airway mucosa.

OBJECTIVE

To investigate whether allergen-induced changes in the number of circulating dendritic cells are mediated by cysteinyl leukotrienes.

METHODS

In a randomized, double-blind, crossover study, we examined the effects of 2 weeks of treatment with pranlukast (a cysteinyl leukotriene 1 [CysLT1] receptor antagonist) 300 mg twice daily and placebo on allergen-induced changes in airway responses and circulating dendritic cells in 15 subjects with mild asthma. We examined by flow cytometry, before and at 3 hours and 24 hours after allergen inhalation, the proportion of myeloid (CD33+) and plasmacytoid (CD123+) dendritic cells (HLA-DR+, CD14-, CD16-) among all peripheral blood mononuclear cells. The fraction of dendritic cells expressing CysLT1 receptor was also determined.

RESULTS

Compared with placebo, pranlukast significantly attenuated both the maximum early (by 55%) and the late (by 39%) asthma responses, the allergen-induced methacholine airway hyperresponsiveness, and the increase in macrophage inflammatory protein 1alpha and 3alpha in induced sputum. A significantly greater proportion of CD33+ cells (55%) expressed CysLT1 receptor compared with CD123+ cells (11%). Consistent with this, pranlukast prevented the allergen-induced decrease in CD33+ dendritic cells at 3 hours postallergen (mean Delta from baseline, +4.4%) compared with placebo (mean Delta, -8.4; P <.05), but not CD123+ cells.

CONCLUSION

Pretreatment with pranlukast attenuated allergen-induced airway responses and the decrease in circulating myeloid dendritic cells, demonstrating a novel role of cysteinyl leukotrienes in dendritic cell trafficking.

Cysteinyl leukotriene 1 receptor controls the severity of chronic pulmonary inflammation and fibrosis

The cysteinyl leukotrienes (cys-LTs), leukotriene (LT) C(4), LTD(4), and LTE(4), are smooth muscle constrictors that signal via the CysLT(1) receptor. Here we report that the cys-LTs play an important role in chronic pulmonary inflammation with fibrosis induced by bleomycin in mice. Targeted disruption of LTC(4) synthase, the pivotal enzyme for cys-LT biosynthesis, protected significantly against alveolar septal thickening by macrophages and fibroblasts and collagen deposition. In contrast, targeted disruption of the CysLT(1) receptor significantly increased both the concentration of cys-LTs in the bronchoalveolar lavage fluid and the magnitude of septal thickening as defined by morphology, digital image analysis, and deposition of reticular fibers. These findings change our understanding of the pathobiology mediated by the cys-LTs by revealing their role in chronic inflammation with fibrosis, likely via the CysLT(2) receptor, and by uncovering a dual role for the CysLT(1) receptor, namely proinflammatory acute constriction of smooth muscle and antiinflammatory counteraction of chronic injury.

Interferon-gamma modulates cysteinyl leukotriene receptor-1 expression and function in human airway myocytes

Leukotrienes play a critical role in promoting bronchoconstriction in asthma. The purpose of this study was to examine whether interferon (IFN)-gamma, a cytokine upregulated in asthmatic airways, modulates leukotriene (LT)D4 receptor expression and contractile responses in cultured human airway smooth muscle (HASM) cells. Treatment of HASM cells with IFN-gamma (10 to 1,000 U/ml) stimulated a dose-dependent increase in cell-surface expression of cysteinyl leukotriene receptor 1 (CysLT1) as determined by flow cytometry. CysLT1 messenger RNA (mRNA) levels were also significantly enhanced by IFN-gamma, as demonstrated by reverse transcription-polymerase chain reaction. To determine the functional relevance of increased CysLT1 expression in HASM, cell stiffness responses to LTD4 were measured with magnetic twisting cytometry. IFN-gamma (1,000 U/ml for 24 h) markedly increased LTD4-induced changes in cell stiffness, from 4.6 +/- 1 [mean +/- SEM]% to 24.4 +/- 3.7% (n = 8, p < 0.05). Montelukast, a CysLT1 antagonist, completely inhibited LTD4-induced increases in cell stiffness. IFN-gamma had no effect on the cell stiffness responses to bradykinin, another contractile agonist. Collectively, these data suggest that IFN-gamma increases LTD4 responses in HASM cells by increasing cell-surface expression of CysLT1. Our data suggest that increased levels of IFN-gamma in asthmatic individuals may promote airway hyperresponsiveness and asthma exacerbations by directly modulating contractile responses of HASM.

Cysteinyl leukotriene receptor 1 is also a pyrimidinergic receptor and is expressed by human mast cells

The cysteinyl leukotrienes (cys-LTs) LTC(4), LTD(4), and LTE(4) are a class of peptide-conjugated lipids formed from arachidonic acid and released during activation of mast cells (MCs). We now report that human cord-blood-derived MCs (hMCs) express the CysLT1 receptor, which responds not only to inflammation-derived cys-LTs, but also to a pyrimidinergic ligand, UDP. hMCs express both CysLT1 protein and transcript, and respond to LTC(4), LTD(4), and UDP with concentration-dependent calcium fluxes, each of which is blocked by a competitive CysLT1 receptor antagonist, MK571. Stably transfected Chinese hamster ovary cells expressing the CysLT1 receptor also exhibit MK571-sensitive calcium flux to all three agonists. Both hMCs and CysLT1 transfectants stimulated with UDP are desensitized to LTC(4), but only partially to LTD(4). Priming of hMCs with IL-4 for 5 days enhances their sensitivity to each agonist, but preferentially lowers their threshold for activation by LTC(4) and UDP (approximately 3 log(10)-fold shifts in dose-response for each agonist) over LTD(4) (1.3 log(10)-fold shift), without altering CysLT1 receptor mRNA or surface protein expression, implying the likely induction of a second receptor with CysLT1-like dual ligand specificity. hMCs thus express the CysLT1 receptor, and possibly a closely related IL-4-inducible receptor, which mediate dual activation responses to cys-LTs and UDP, providing an apparent intersection linking the inflammatory and neurogenic elements of bronchial asthma.

Leukotriene B4 is the functional ligand binding to and activating the cloned chemoattractant receptor, CMKRL1

We recently described a novel chemoattractant receptor, provisionally named CMKRL1, which has turned out to be the first cloned leukotriene (LT) receptor. Present binding assays using tritiated LTB4 and isolated membranes from COS-7 cells, transiently transfected with cDNA encoding this receptor, yielded a linear Scatchard plot showing expression of only a single, high-affinity receptor population with a mean Kd of 2.1 nM and Bmax of 17.0 pmoles/mg protein. Sham-transfected cells exhibited no specific binding. LTB4 elicited concentration-dependent increases in intracellular calcium measured with Fura-2 in individual CHO cells stably expressing CMKRL1. No response was seen with sham-transfected control cells, or in calcium-free medium which suggests that calcium mainly originates from extracellular sources. The LTB4-induced cellular calcium increment was blocked in the presence of a monoclonal antibody, raised against a synthetic peptide corresponding to the extracellular tail of CMKRL1 and capable of visualizing the receptor by fluorescence immunocytochemistry. Taken together the analyses show that LTB4 is the endogenous ligand for CMKRL1 which is, thus, identical to the LTB4 receptor, designated BLTR according to the NC-IUPHAR nomenclature.