Leukotrienes in bile during the early and the late airway responses after allergen challenge of sensitized rats

CysLT1 Receptor Is Protective against Oxidative Stress in a Model of Irritant-Induced Asthma

The bronchoconstrictive and proinflammatory properties of cysteinyl leukotrienes (cysLTs) in allergic asthma mediate their effects predominantly through the cysLT1 receptor (cysLT1R). However, the role of cysLTs and cysLT1R in innate immune-triggered asthma is largely unexplored. We explored the synthesis of cysLTs and cysLT1R as determinants of airway responses in an oxidative stress-induced model of irritant asthma. Wild-type (WT) mice exposed to 100 ppm Cl2 for 5 min had airway neutrophilia, increased cysLT production, and pulmonary expression of cysLT-related biosynthetic genes. CysLT1R-deficient (CysLTr1(-/-)) mice that were exposed to Cl2 demonstrated airway hyperresponsiveness to inhaled methacholine significantly greater than in WT BALB/c mice. Compared to WT mice, airway neutrophilia and keratinocyte chemoattractant production levels were higher in CysLTr1(-/-) mice and airway hyperresponsiveness was ameliorated using a granulocyte depletion Ab. CysLTr1(-/-) mice also demonstrated prolonged bronchial epithelial cell apoptosis following Cl2 WT mice showed increased antioxidant and NF erythroid 2-related factor 2 (Nrf2) gene expression, Nrf2 nuclear translocation in bronchial epithelial cells, and increased reduced glutathione/oxidized glutathione following Cl2 exposure whereas CysLTr1(-/-) mice did not. Furthermore, CysLTr1(-/-) mice demonstrated increased pulmonary E-cadherin expression and soluble E-cadherin shedding compared with WT mice. Loss of a functional cysLT1R results in aberrant antioxidant response and increased susceptibility to oxidative injury, apparently via a cysLT1R-dependent impairment of Nrf2 function.

Expression of colonic vasoactive intestinal peptide receptor and calcitonin gene-related peptide receptor in irritable bowel syndrome

AIM: To investigate the expression of vasoactive intestinal peptide receptor (VIPR) and calcitonin gene-related peptide receptor (CGRPR) in the colon mucosa of patients with irritable bowel syndrome (IBS), and to study their possible roles.

METHODS: Endoscopic biopsies of the sigmoid colon were collected from 20 patients with diarrhea-predominant IBS (IBS-D), 8 with constipation-predominant IBS (IBS-C) and 8 healthy volunteers (controls). The mRNA expression of VIPR and CGRPR was evaluated by qRT-PCR. The immunohistochemical method was conducted to detect the expression of VIPR and CGRPR proteins. The results of immunohistochemistry were analyzed with Image Pro plus 6.0.

RESULTS: Elevation of the mRNA expression of VIPR was found in IBS-D patients compared with IBS-C patients and controls (2.89 ± 1.74 vs 0.85 ± 0.6, 0.62 ± 0.31, P < 0.05). No significant difference was observed between IBS-C patients and controls. The expression of CGRPR mRNA was elevated in IBS-D patients compared with controls (1.86 ± 1.36 vs 0.77 ± 0.5, P < 0.05), but no significant difference was observed between IBS-C and IBS-D/controls. Compared with healthy controls, significant up-regulation of VIPR and CGRPR was found in IBS-D and IBS-C patients (VIPR: 0.24 ± 0.03, 0.17 ± 0.02 vs 0.13 ± 0.01, P < 0.05; CGRPR: 0.23 ± 0.02, 0.18 ± 0.02 vs 0.13 ± 0.02, P < 0.05), and a significant difference was also observed between IBS-D and IBS-C patients (P < 0.05).

CONCLUSION: VIPR and CGRPR are involved in the pathophysiology of IBS in certain ways. The possible roles of VIPR and CGRPR in the colon suggest that further studies of the alterations of these neuropeptide receptors may be useful in understanding IBS pathophysiology.

Site of allergic airway narrowing and the influence of exogenous surfactant in the Brown Norway rat

Background

The parameters R_N (Newtonian resistance), G (tissue damping), and H (tissue elastance) of the constant phase model of respiratory mechanics provide information concerning the site of altered mechanical properties of the lung. The aims of this study were to compare the site of allergic airway narrowing implied from respiratory mechanics to a direct assessment by morphometry and to evaluate the effects of exogenous surfactant administration on the site and magnitude of airway narrowing.

Methods

We induced airway narrowing by ovalbumin sensitization and challenge and we tested the effects of a natural surfactant lacking surfactant proteins A and D (Infasurf®) on airway responses. Sensitized, mechanically ventilated Brown Norway rats underwent an aerosol challenge with 5% ovalbumin or vehicle. Other animals received nebulized surfactant prior to challenge. Three or 20 minutes after ovalbumin challenge, airway luminal areas were assessed on snap-frozen lungs by morphometry.

Results

At 3 minutes, R_N and G detected large airway narrowing whereas at 20 minutes G and H detected small airway narrowing. Surfactant inhibited R_N at the peak of the early allergic response and ovalbumin-induced increase in bronchoalveolar lavage fluid cysteinyl leukotrienes and amphiregulin but not IgE-induced mast cell activation in vitro.

Conclusion

Allergen challenge triggers the rapid onset of large airway narrowing, detected by R_N and G, and subsequent peripheral airway narrowing detected by G and H. Surfactant inhibits airway narrowing and reduces mast cell-derived mediators.

Small animals models for drug discovery

There has been an explosion of studies of animal models of asthma in the past 20 years. The elucidation of fundamental immunological mechanisms underlying the development of allergy and the complex cytokine and chemokines networks underlying the responses have been substantially unraveled. Translation of findings to human asthma have been slow and hindered by the varied phenotypes that human asthma represents. New areas for expansion of modeling include virally mediated airway inflammation, oxidant stress, and the interactions of stimuli triggering innate immune and adaptive immune responses.

Identification with MRI of the pleura as a major site of the acute inflammatory effects induced by ovalbumin and endotoxin challenge in the airways of the rat

Inflammatory effects in the rat lung have been investigated, non-invasively by MRI, at early time points (3 and 6 h) after ovalbumin (OA) or endotoxin (LPS) challenges. Six hours after challenge with OA, a strong, even inflammatory signal was present around the periphery of the lung in a region corresponding to the pleura. Histological analysis confirmed the presence of marked edema associated with the pleural cavity of OA-treated animals. Lower levels of pleural edema were observed in MRI and histological evaluation of LPS-treated animals and no abnormality was observed in actively sensitized and naïve, saline-treated groups. Diffuse edematous signals were detected in the lung 3 and 6 h after challenge with OA or LPS; the signal volumes were larger at both time points following OA instillation. Bronchoalveolar lavage (BAL) fluid analysis performed 6 h after challenge revealed increased levels of protein and greater cellular activation in OA- than in LPS-treated animals. Furthermore, increased levels of peribronchial edema were found by histology 6 h after OA. BAL fluid and histological assessments demonstrated that the inflammatory signals were due to edema and not mucus as no significant changes in BAL mucin concentrations or differences in goblet cells were identified between OA or LPS challenge and their respective vehicle groups. Our data show that MRI is able to detect, non-invasively, inflammatory signals in both the lung and the pleura in spontaneously breathing animals, highlighting its potential to study the consequences of pulmonary insults on both sites.

A small molecule, orally active, alpha4beta1/alpha4beta7 dual antagonist reduces leukocyte infiltration and airway hyper-responsiveness in an experimental model of allergic asthma in Brown Norway rats

alpha(4)beta(1) and alpha(4)beta(7) integrins are preferentially expressed on eosinophils and mononuclear leukocytes and play critical roles in their recruitment to inflammatory sites. We investigated the effects of TR14035, a small molecule, alpha(4)beta(1)/alpha(4)beta(7) dual antagonist, in a rat model of allergic asthma. Actively sensitized rats were challenged with aerosol antigen or saline on day 21, and the responses evaluated 24 and 48-h later. TR14035 (3 mg kg(-1), p.o.) was given 1-h before and 4-h after antigen or saline challenge. Airway hyper-responsiveness to intravenous 5-hydroxytryptamine was suppressed in TR14035-treated rats. Eosinophil, mononuclear cell and neutrophil counts, and eosinophil peroxidase and protein content in the bronchoalveolar lavage fluid (BALF) were decreased in TR14035-treated rats. Histological study showed a marked reduction of lung inflammatory lesions by TR14035. At 24-h postchallenge, antigen-induced lung interleukin (IL)-5 mRNA upregulation was suppressed in TR14035-treated rats. By contrast, IL-4 levels in BALF were not significantly affected by TR14035 treatment. IL-4 selectively upregulates vascular cell adhesion molecule-1 (VCAM-1), which is the main endothelial ligand of alpha(4) integrins. Intravital microscopy within the rat mesenteric microcirculation showed that 24-h exposure to 1 microg per rat of IL-4 induced a significant increase in leukocyte rolling flux, adhesion and emigration. These responses were decreased by 48, 100 and 99%, respectively in animals treated with TR14035. In conclusion, TR14035, by acting on alpha(4)beta(1) and alpha(4)beta(7) integrins, is an orally active inhibitor of airway leukocyte recruitment and hyper-responsiveness in animal models with potential interest for the treatment of asthma.

Rat models of asthma and chronic obstructive lung disease

The rat has been extensively used to model asthma and somewhat less extensively to model chronic obstructive pulmonary disease (COPD). The features of asthma that have been successfully modeled include allergen-induced airway constriction, eosinophilic inflammation and allergen-induced airway hyperresponsiveness. T-cell involvement has been directly demonstrated using adoptive transfer techniques. Both CD4+ and CD8+ T cells are activated in response to allergen challenge in the sensitized rat and express Thelper2 cytokines (IL-4, IL-5 and IL-13). Repeated allergen exposure causes airway remodeling. Dry gas hyperpnea challenge also evokes increases in lung resistance, allowing exercise-induced asthma to be modeled. COPD is modeled using elastase-induced parenchymal injury to mimic emphysema. Cigarette smoke-induced airspace enlargement occurs but requires months of cigarette exposure. Inflammation and fibrosis of peripheral airways is an important aspect of COPD that is less well modeled. Novel approaches to the treatment of COPD have been reported including treatments aimed at parenchymal regeneration.

Changes in histology and expression of cytokines and chemokines in the rat lung following exposure to ovalbumin

Brown Norway (BN) and Fischer 344 (F344) rats were exposed to aerosol of 1% ovalbumin (OVA) solution for 30 min at 1 week after the second sensitization with 1 mg of OVA at 2-week intervals. Changes in the histology and expression of cytokines and chemokines in the lung were examined for up to 96 h after the exposure. The lung weight significantly increased in BN rats but not in F344 rats. Histologically, in the lung of BN rats, multiple foci of hemorrhage in the alveolar space with infiltration of eosinophils and macrophages in the surrounding alveolar septa were first observed. Thereafter, granulomatous lesions developed in the preexisting hemorrhagic foci, finally resulting in formation of multiple eosinophilic granulomas. On the other hand, in F344 rats, infiltration of eosinophils and macrophages was observed around the vessels and bronchi. Thereafter it progressed gradually, resulting in mild thickening of alveolar septa. The levels of Th1- (interferon-gamma and interleukin 2 (IL-2)) and Th2-related cytokines (IL-4 and IL-5) and chemokines (eotaxin and monocyte chemoattractant protein-1) mRNAs measured by reverse transcription-polymerase chain reaction method were elevated in the lung of both strains, and the levels were higher in BN rats than in F344 rats. These results suggest that BN rats are more sensitive to OVA-sensitization/inhalation than F344 rats and that the difference in the severity of lung lesions between BN and F344 rats may reflect the difference in the expression levels of cytokines and chemokines between these two strains.

Mast-cell activation augments the late phase reaction in experimental immune-mediated blepharoconjunctivitis

BACKGROUND

How the early phase allergic reaction affects the late phase reaction remains unclear. We examined this issue with an experimental model of allergic conjunctivitis that permits the two reactions to be disconnected from each other.

METHODS

Experimental immune-mediated blepharoconjunctivitis (EC) was initiated in Brown Norway rats by transferring ovalbumin (OVA)-specific T cells and then challenging with OVA-containing eye drops. To induce early phase reaction, a mast-cell activator, C48/80, was challenged together with or without OVA. Rats were evaluated clinically and eyes were harvested for histologic examination and for evaluation of chemokine expression by reverse-transcriptase PCR.

RESULTS

The rats challenged with OVA alone developed the T-cell-mediated late phase reaction histologically, but not clinically, in the absence of early phase reaction. While rats challenged with C48/80 with or without OVA exhibited clinical signs of the early phase reaction, the clinical late phase reaction was observed only in the OVA+C48/80 group. Eosinophilic infiltration into the conjunctiva during the late phase reaction of the OVA+C48/80 group markedly exceeded that of rats challenged with either OVA or C48/80 alone. RANTES (regulated on activation, normal T-cell expressed and secreted), an eosinophil attractant, was expressed both in the OVA+C48/80 and OVA groups, while eotaxin was expressed at equivalent levels in all three groups.

CONCLUSION

The mast-cell-mediated early phase reaction potentiates the T-cell-mediated late phase reaction, and RANTES is involved in eosinophilic infiltration induced by antigen-specific T cells. Other molecules induced by allergen-specific T cells activated in an as yet unknown manner by the mast cells may be responsible for the infiltration of eosinophils.

The immunomodulatory actions of prostaglandin E2 on allergic airway responses in the rat

PGE(2) has been reported to inhibit allergen-induced airway responses in sensitized human subjects. The aim of this study was to investigate the mechanism of anti-inflammatory actions of PGE(2) in an animal model of allergic asthma. BN rats were sensitized to OVA using Bordetella pertussis as an adjuvant. One week later, an aerosol of OVA was administered. After a further week, animals were anesthetized with urethan, intubated, and subjected to measurements of pulmonary resistance (R(L)) for a period of 8 h after OVA challenge. PGE(2) (1 and 3 micro g in 100 micro l of saline) was administered by insufflation intratracheally 30 min before OVA challenge. The early response was inhibited by PGE(2) (3 micro g). The late response was inhibited by both PGE(2) (1 and 3 micro g). Bronchoalveolar lavage fluid from OVA-challenged rats showed eosinophilia and an increase in the number of cells expressing IL-4 and IL-5 mRNA. These responses were inhibited by PGE(2). Bronchoalveolar lavage fluid levels of cysteinyl-leukotrienes were elevated after OVA challenge and were reduced after PGE(2) to levels comparable with those of sham challenged animals. We conclude that PGE(2) is a potent anti-inflammatory agent that may act by reducing allergen-induced Th2 cell activation and cysteinyl-leukotriene synthesis in the rat.

The strength of the OVA-induced airway inflammation in rats is strain dependent

To examine the influence of genetics on the OVA-induced allergic inflammatory response in lungs we compared rats that are genetically Th2-predisposed (Brown Norway, inbred) or not genetically predisposed (Sprague Dawley, outbred). Rats were sensitized with ovalbumin (OVA) and challenged four weeks later with OVA aerosol. Eighteen hours after challenge, lung tissue was studied for evaluation of numbers of eosinophils, neutrophils, macrophages and mast cells, as well as for expression of P-selectin, E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells. From a separate portion of the pulmonary tissue, leucocytes were isolated to analyse numbers of IFNgamma and IL-4 producing cells (ELISPOT assay) and frequencies of T-cell subsets and B cells. We found increased numbers of eosinophils and neutrophils in the lung, an increased number of IL-4 producing cells in lung cell isolates and increased levels of serum (OVA- specific)-IgE in both rat strains. In addition, expression of E-selectin and ICAM-1 was up regulated in both rat strains whereas expression of VCAM-1 was only up regulated in the BN rat. Although the 'allergic' Th2 response to OVA was detectable in both rat strains, it was more pronounced in the BN rat than in the SD rat. However, the SD rat, which is not predisposed to respond in either a Th2 or Th1-like way, appeared capable of mounting an allergic response to OVA. This suggests that other factors than genetic contribute to allergic disease.

Immediate allergic response in small airways

The role of small airways in the immediate allergic response is largely unknown. We therefore used the model of precision-cut lung slices (PCLS) in combination with quantitative videomicroscopy to study the early allergic response to allergen in airways ranging from 50 to 900 microm. After PCLS from untreated Wistar rats had been passively sensitized for 16 h with serum from sensitized Brown Norway rats, exposure to 0.1% ovalbumin resulted in an immediate allergic response. Both extent (r = 0.74, p < 0.0001) and velocity (r = 0.49, p < 0.0001) of the allergen-induced bronchoconstriction increased with decreasing airway size. In addition, we observed that smaller airways not only contracted stronger and quicker, but that they also relaxed faster, suggesting that smaller airways are more reactive in principle. The allergen-induced bronchoconstriction in PCLS was prevented by the serotonin receptor antagonist ketanserin (IC(50) 6 nM), but not by antagonists directed against histamine, acetylcholine, PAF, or endothelin receptors, or by cyclooxygenase or lipoxygenase inhibitors. Like allergen, serotonin provoked responses that were stronger in smaller airways. These findings suggest that the immediate allergic response in rat PCLS depends largely on serotonin and that this response can occur in nearly all airway generations, but is most pronounced in the smallest airways, that is, the terminal bronchioles.

Inhaled budesonide inhibits OVA-induced airway narrowing, inflammation, and cys-LT synthesis in BN rats

The objective of the present investigation was to examine the effects of an inhaled glucocorticoid, budesonide, on antigen-induced production of cysteinyl leukotrienes (cys-LTs) and pulmonary inflammatory cell infiltration in the Brown Norway rat, an animal model of asthma. Two weeks after sensitization to ovalbumin, rats were treated with budesonide (2.5 mg/kg) 18 and 1 h before challenge with antigen. Budesonide abolished the late response to ovalbumin (P<0.02) and strongly inhibited the in vivo synthesis of N-acetyl-leukotriene E(4), an indicator of cys-LT synthesis, during this period (P<0.005). Both total bronchoalveolar lavage (BAL) cells (P<0.01) and BAL macrophages (P<0.005) were markedly reduced to approximately 25% of their control levels after treatment with budesonide. It can be concluded that inhibition of the antigen-induced late response in Brown Norway rats by budesonide is associated with reductions in both BAL macrophages and cys-LT synthesis. It is possible that the effect of budesonide on cys-LT synthesis is related to its effects on pulmonary macrophages.

Bradykinin-induced airway constriction in guinea-pigs: role of leukotriene D(4)

Tachykinins (TK) have been implicated in both bradykinin-(BK) and hyperpnea-induced broncho-constriction (HIB) in the guinea-pig. However, TKs appear to have an indirect effect in HIB by releasing leukotriene (LT)D(4). We postulated that BK may cause bronchoconstriction through a cascade involving TK and LTD(4). We examined the role of TK and LTD(4)in BK-induced bronchoconstriction in ventilated Hartley guinea-pigs. Respiratory resistance (R(rs)) was monitored for 2 h following insufflation of BK (150 nM). Animals were pretreated with propranolol, then with either neurokinin (NK)1 (CP-99,994)+NK2 (SR-48,968) receptor antagonists or pranlukast (90 microg or 900 microg), an LTD(4)antagonist. Control animals received no pretreatment. BK-induced bronchoconstriction was significantly lower in NK1/NK2 (128%+/-6% baseline R(rs)SEM) and pranlukast (90 microg; 205+/-22, 900 microg; 169+/-20) animals compared to controls (284+/-22), P<0.0001 ANOVA. Bile from control and saline challenged animals was analysed for LTD(4)by HPLC and radio-immunoassay. However, LTD(4)excretion rate showed no significant difference over a 2-h collection period following insufflation of either BK or saline, respectively; baseline =2.5 pmol/h+/-0.6 SEM vs. 2.3+/-0.2, 0-1 h=2.8+/-0.7 vs. 2.0+/-0.6, 1-2 h=2.3+/-0.6 vs. 1.7+/-0.7. We conclude that BK-induced bronchoconstriction is mediated in part through the release of both TK and LTD(4), but the latter is released in insufficient quantities to be detectable by biliary analysis.

Intratracheal administration of anaphylatoxin C5a potentiates antigen-induced pulmonary reactions through the prolonged production of cysteinyl-leukotrienes

The effects of intratracheal administration of anaphylatoxin C5a on airway inflammation have been studied using two sources of material, zymosan activated serum (ZAS) and purified rat C5a des Arg, in order to determine the influence of complement activation on allergic airway disorders.The intratracheal administration of ovalbumin (OA) to OA-sensitized rats generated two phases of airway response, an immediate airway response (IAR) occurring within 15 min and a late airway response (LAR) beginning 4-6 h after the allergen challenge. The simultaneous administration of ZAS and OA into the trachea generated a sustained elevation of airway resistance (Raw) following IAR, while that of OA or ZAS alone resulted in Raw returning nearly to the baseline just after the IAR. The elevation of Raw after the combined challenge of OA and ZAS was significantly inhibited by pretreatment with a CysLT(1) receptor antagonist, pranlukast 30 mg/kg, but after that OA or ZAS alone was not significantly inhibited by pranlukast. The intratracheal administration of purified C5a produced an airway response that was similar to, but higher than, that evoked by ZAS. Namely, the challenge with OA plus C5a resulted in a higher IAR than OA plus ZAS, and also caused an early animal death up to 6 h, which was prevented by a combined pretreatment with pranlukast and the H(1) receptor antagonist, diphenhydramine.A histological examination at 6 h after the OA challenge identified an infiltration of inflammatory cells into the bronchial submucosal tissue, with a predominance of neutrophils and fewer eosinophils. On the other hand, a histological examination after the OA and ZAS challenge showed more severe infiltration of granulocytes into the bronchial submucosal tissue than that with OA or ZAS alone. The challenge with OA plus C5a was associated with severe perivascular leakage in the lungs and the combined pretreatment with both the antagonists led to a marked reduction in perivascular leakage. The quantitation of N-acetyl-leukotriene E(4) (N-Ac-LTE(4)), a major metabolite of cysteinyl-leukotrienes (cysLTs), in the bile indicated a significantly greater and longer excretion of cysLTs, from 1 to 6 h after the combined challenge, than that after either OA or ZAS alone. This suggested a prolonged generation of cysLTs in the lung by the combined challenge.In conclusion, our findings suggest that anaphylatoxin C5a may mediate the airway inflammatory response induced by a specific antigen challenge partly through a prolonged production of cysLTs and the release of histamine.

Dichotomy between neurokinin receptor actions in modulating allergic airway responses in an animal model of helper T cell type 2 cytokine-associated inflammation

Neurokinins (NKs), which include substance P (SP) and neurokinin A (NKA), act through NK-1 and NK-2 receptors. There is considerable evidence of interaction between the neurogenic and the immune systems, and NKs are candidates for mediating such interactions. We hypothesized that selective inhibition of pulmonary NK-1 or NK-2 receptors may modulate immune responses so as to prevent the development of allergic airway responses in the atopic BN rat sensitized to ovalbumin (OA). To address this hypothesis, we have validated our animal model by showing that NK-1 and NK-2 receptors are expressed in the lungs, and that SP is released in the airways after allergen challenge. The selective NK-1 (CP-99,994) or NK-2 (SR-48968) antagonists before allergen challenge failed to reduce the allergic early airway responses. In contrast, both neurokinin antagonists decreased allergen-induced late airway responses in OA-challenged animals. However, only the NK-2 antagonist decreased the eosinophil numbers in the bronchoalveolar lavage (BAL). Likewise, the NK-2, but not NK-1, antagonist decreased both Th1 (INF-gamma) and Th2 (IL-4 and -5) cytokine expression in BAL cells by in situ hybridization. These results provide initial in vivo evidence linking neurokinins to the regulation of cytokine expression in cells without discrimination as to their phenotype. We conclude that there is a dichotomy between NK receptors in the modulation of the allergic airway inflammation, which has important implications for future therapeutic strategies for asthma using the NK antagonists.

Effect of TEI-9874, an inhibitor of immunoglobulin E production, on allergen-induced asthmatic model in rats

As TEI-9874, 2-(4-(6-cyclohexyloxy-2-naphtyloxy)phenylacetamide)ben zoic acid reduces allergen-specific immunoglobulin E (IgE) production by human peripheral blood mononuclear cells in vitro, we evaluated its potency on an allergen-induced asthmatic model in Brown-Norway rats. Inhaled ovalbumin induced the immediate-phase asthmatic response, the late-phase asthmatic response, the infiltration of leukocytes into bronchoalveolar lavage fluid, and an increase of serum anti-ovalbumin IgE. These parameters were suppressed by the treatment with TEI-9874 (3, 10, and 30 mg/kg p.o.). The ovalbumin-induced airway hyperresponsiveness was prevented by TEI-9874 (30 mg/kg p.o.). Furthermore, the suppression of the immediate-phase asthmatic response and the late-phase asthmatic response by TEI-9874 was almost completely extinguished by the exogenous administration of rat anti-ovalbumin antiserum. These results indicate that the efficacy of TEI-9874 on the asthmatic response is mainly mediated by the suppression of allergen-specific IgE production and TEI-9874 appears to be a good candidate as therapy for IgE-mediated allergic asthma.

Antigen-induced airway inflammation and hyper-responsiveness does not enhance airway responses to a subsequent antigen challenge in rats

Brown-Norway (BN) rats develop airway hyper-responsiveness and lung eosinophilia 18-24 h after ovalbumin (OA) challenge. We hypothesized therefore that allergen-induced airway inflammation would further enhance airway responses to a subsequent antigen challenge. Animals were sensitized to both OA and bovine serum albumin (BSA) and, 14 days later, challenged by aerosols with both antigens 24 h apart. Measurements of pulmonary resistance (RL) were made for 8 h after the second antigen challenge and bronchoalveolar lavage (BAL) was performed. Animals were divided into three groups and received two challenges as follows: saline-BSA (n=9), OA-saline (n=8) and OA-BSA (n=10). Sensitization was confirmed by measurements of specific OA-IgE and BSA-IgE. Early responses [determined as the highest value of RL within the first 30 min after the challenge] were absent in all study groups. The late responses [determined from the area under the RL versus time curve from 120 to 480 min after the challenge] were significantly greater in animals challenged with BSA (15.16+/-3.86) compared to saline (3.76+/-4.09; P<0.05). However previous exposure to OA did not further increase the late response in animals subsequently challenged with BSA (20.11+/-3.67) despite enhanced airway responsiveness to LTD4 at this time point. BAL eosinophils and lymphocytes were significantly increased following BSA challenge in previously OA-challenged animals, compared to numbers retrieved from animals previously exposed to saline (P<0.05). These data indicate that previous exposure to OA did not further increase the LR to a second antigen challenge despite substantial increases in airway inflammatory cells and airway hyper-responsiveness to LTD4.

CD8+ T Cells Modulate Late Allergic Airway Responses in Brown Norway Rats

To test the hypothesis that CD8+ T cells may suppress the allergen-induced late airway response (LAR) and airway eosinophilia, we examined the effect of administration of Ag-primed CD8+ T cells on allergic airway responses, bronchoalveolar lavage (BAL) leukocytes, and mRNA expression for cytokines (IL-4, IL-5, and IFN-γ) in OVA-sensitized Brown Norway rats. On day 12 postsensitization to OVA, test rats were administered 2 million CD8+ T cells i.p. isolated from either the cervical lymph nodes (LN group; n = 8) or the spleen (Spl group; n = 6) of sensitized donors. On day 14, test rats were challenged with aerosolized OVA. Control rats were administered PBS i.p. on day 12, and challenged with OVA (n = 10) or BSA (n = 6) on day 14. The lung resistance was measured for 8 h after challenge. BAL was performed at 8 h. Cytospin slides of BAL were analyzed for major basic protein by immunostaining and for cytokine mRNA by in situ hybridization. The LAR was significantly less in the LN group (1.8 ± 0.5 U; p &lt; 0.01) and BSA controls (1.4 ± 0.7; p &lt; 0.01), but not in the Spl group (6.7 ± 2.2), compared with that in OVA controls (8.1 ± 1.8). In BAL, the number of major basic protein-positive cells was lower in the LN and Spl groups compared with OVA controls (p &lt; 0.05 and p &lt; 0.01). IL-4- and IL-5-positive cells were decreased in the LN group compared with the OVA controls (p &lt; 0.01). INF-γ-positive cells were increased in the LN and Spl groups compared with the OVA controls (p &lt; 0.01). Serum OVA-specific IgE levels were unaffected by CD8+ T cell transfers. These results indicate that Ag-primed CD8+ T cells have a potent suppressive effect on LAR.

Involvement of cysteinyl leukotrienes in airway smooth muscle cell DNA synthesis after repeated allergen exposure in sensitized Brown Norway rats

Airway smooth muscle thickening is a characteristic feature of airway wall remodelling in chronic asthma. We have investigated the role of the leukotrienes in airway smooth muscle (ASM) and epithelial cell DNA synthesis and ASM thickening following repeated allergen exposure in Brown Norway rats sensitized to ovalbumin. There was a 3 fold increase in ASM cell DNA synthesis, as measured by percentage bromodeoxyuridine (BrdU) incorporation, in repeatedly ovalbumin-exposed (4.1%, 3.6-4.6; mean, 95% c.i.) compared to chronically saline-exposed rats (1.3%, 0.6-2.1; P<0.001). Treatment with a 5-lipoxygenase enzyme inhibitor (SB 210661, 10 mg kg(-1), p.o.) and a specific cysteinyl leukotriene (CysLT1) receptor antagonist, pranlukast (SB 205312, 30 mg kg(-1), p.o.), both attenuated ASM cell DNA synthesis. Treatment with a specific leukotriene B4 (BLT) receptor antagonist (SB 201146, 15 mg kg(-1), p.o.) had no effect. There was also a significant, 2 fold increase in the number of epithelial cells incorporating BrdU per unit length of basement membrane after repeated allergen exposure. This response was not inhibited by treatment with SB 210661, pranlukast or SB 201146. A significant increase in ASM thickness was identified following repeated allergen exposure and this response was attenuated significantly by SB 210661, pranlukast and SB 201146. Rats exposed to chronic allergen exhibited bronchial hyperresponsiveness to acetylcholine and had significant eosinophil recruitment into the lungs. Treatment with SB 210661, pranlukast or SB 201146 significantly attenuated eosinophil recruitment into the lungs, whilst having no significant effect on airway hyperresponsiveness. These data indicate that the cysteinyl leukotrienes are important mediators in allergen-induced ASM cell DNA synthesis in rats, while both LTB4 and cysteinyl leukotrienes contribute to ASM thickening and eosinophil recruitment following repeated allergen exposure.

Strain dependence of the airway response to dry-gas hyperpnea challenge in the rat

The aim of the study was to investigate strain dependence and mechanisms of airway responses to dry-gas hyperpnea challenge in the rat. We studied responses in a strain that is hyperresponsive to methacholine, Fischer 344 (F-344); in two normoresponsive strains, Lewis and ACI; and in an atopic but normoresponsive strain, Brown Norway (BN). We examined the effects of a neurokinin (NK) 1-receptor (CP-99994), an NK2-receptor (SR-48968), and a leukotriene D4 (LTD4)-receptor antagonist (pranlukast) on responses to hyperpnea challenge in BN rats. The animals were ventilated with a tidal volume of 8 ml/kg and a frequency of 150 breaths/min with either a dry or humidified mixture of 5% CO2-95% O2 for 5 min for hyperpnea challenge, whereas responses to challenge were measured during spontaneous breathing. Pulmonary resistance increased after dry-gas challenge in BN and ACI but not in F-344 and Lewis rats. CP-99994, SR-48968, and pranlukast significantly attenuated the increase in pulmonary resistance after dry-gas challenge. There were no significant differences in responsiveness to airway challenge with LTD4 among the BN, F-344 and ACI rats. We conclude that responses to dry-gas hyperpnea challenge are strain dependent in rats and are mediated by NKs and LTD4.

Repeated allergen inhalations induce DNA synthesis in airway smooth muscle and epithelial cells in vivo

Airway smooth muscle (ASM) mass appears to be increased in the bronchi of patients with chronic severe asthma. Although the precise mechanisms that induce these changes are unknown, increases in ASM mass are caused, in part, by ASM cell proliferation. After allergen challenge in rats, it has been possible to demonstrate an increase in ASM mass by morphometric techniques. To examine whether hyperplasia is involved in ASM cell growth in vivo, we investigated whether repeated allergen challenges in sensitized Brown Norway rats stimulated DNA synthesis in airway epithelial and ASM cells. Animals that were actively sensitized to ovalbumin (OA) received either three aerosolized OA or saline challenges at 5-day intervals. DNA synthesis was measured by indirect immunohistochemical techniques with an anti-bromodeoxyuridine (BrdU) antibody. OA inhalations increased ASM mass as determined by morphometry and also induced DNA synthesis in both airway epithelial and ASM cells in the airways of sensitized animals compared with saline-challenged control animals. ASM mass was increased in large- and medium-sized airways but not in small airways. However, the number of BrdU-positive ASM cells normalized to basement membrane length was also greater in the large- and medium-sized airways compared with that in the small airways. When the number of BrdU-positive epithelial cells was normalized to basement membrane length, there was no difference among airway sizes and the number of BrdU-positive epithelial cells. These data suggest that DNA synthesis is induced in both airway epithelial and ASM cells after inhalational antigen challenge.

Leflunomide, a novel immunomodulating agent, prevents the development of allergic sensitization in an animal model of allergic asthma

BACKGROUND

Leflunomide is a new anti-inflammatory and immunomodulating agent which is showing promise in several immune disorders, especially rheumatoid arthritis. Its activity profile suggests it may be of use in modulating allergic sensitization.

OBJECTIVE

To investigate the effectiveness of leflunomide in preventing the development of allergic sensitization.

METHODS

Fifty-three brown Norway rats were sensitized by intraperitoneal injection of ovalbumin and adjuvant (ricin) on day 0. To determine the ability of leflunomide to inhibit primary allergic sensitization six rats were treated with A77 1726, the active metabolite of leflunomide, from day 0 through day 5, six were treated from day 5 through day 10, and nine rats acted as controls. On day 14, ovalbumin-specific serum antibody levels and the magnitude of the early-phase airway response (EAR) after inhalation allergen challenge were assessed. To determine the ability of acute topical treatment with leflunomide to inhibit mast cell degranulation, three groups of five animals received either vehicle, 100 microg A77 1726, or 1000 g A77 1726 60 min prior to aerosol allergen challenge. To determine the effects of leflunomide treatment in vivo on mast cell function in vitro, mast cells were obtained by bronchoalveolar lavage from 17 rats (nine treated with leflunomide and eight controls). Allergen-specific and non-specific degranulation (48/80 induced) were studied.

RESULTS

In the leflunomide treated rats both ovalbumin-specific IgE and IgG levels were significantly reduced, and the increases in lung resistance and lung elastance were essentially abolished, compared to those of the control group. Non significant differences were found in any of the parameters between the two leflunomide treated groups. Topical pre-treatment with leflunomide did not prevent the allergen-induced EAR. Treatment with leflunomide in vivo prevented allergen-induced mast cell degranulation in vitro because the mast cells lacked IgE on their surface. Non allergen-specific degranulation was normal and allergen-induced degranulation could be restored by passive sensitization.

CONCLUSIONS

These data suggests that leflunomide can prevent primary allergic sensitization and prevent allergen-induced EAR by inhibiting production of allergen-specific IgE antibodies. Further studies in atopic conditions are warranted.

Roles of adhesion molecules ICAM-1 and alpha4 integrin in antigen-induced changes in microvascular permeability associated with lung inflammation in sensitized brown Norway rats

Increased microvascular permeability and mucosal edema are pathological features of airway inflammation in asthma. In this study, we investigated the characteristics of the edema response occurring in a model of antigen-induced lung inflammation in sensitized brown Norway rats and examined the effects of monoclonal antibodies (mAbs) to adhesion molecules on this response. Ovalbumin (OA) challenge-induced increases in lung permeability were determined by the leakage of 125I-labeled bovine serum albumin (BSA) into the extravascular tissues of the lungs 24 h after challenge in animals intravenously injected (prechallenge) with this tracer. Inflammatory cell infiltration into the alveolar space was determined by bronchoalveolar lavage (BAL). Mean extravascular plasma volume in the lung increased 233% as compared with control (P < 0.005) at 24 h and increased to 517% by 72 h. The 24-h edema response was completely inhibited by two oral doses (0.1 mg/kg) of dexamethasone 1 h before, and 7 h after, challenge. Intraperitoneal administration of the anti-rat ICAM-1 mAb 1A29, or anti-rat alpha4 integrin mAb TA-2 (2 mg/kg at 12 and 1 h before, and 7 h after, antigen challenge), significantly suppressed eosinophil infiltration into the alveolar space without inhibiting the enhanced microvascular leakage and lung edema. Determination of plasma antibody concentrations by ELISA of mouse IgG1 indicated that sufficient concentrations of the appropriate mAb were present to block alpha4- or ICAM-1-dependent adhesion. The results suggest that increases in microvascular permeability and plasma leakage occurred independently of eosinophil accumulation.

Hyperpnea-induced bronchoconstriction is dependent on tachykinin-induced cysteinyl leukotriene synthesis

The purpose of the study was to test the hypothesis that tachykinins mediate hyperpnea-induced induced bronchoconstriction indirectly by triggering cysteinyl leukotriene (LT) synthesis in the airways. Guinea pigs (350-600 g) were anesthetized with xylazine and pentobarbital sodium and received hyperpnea challenge (tidal volume 3.5-4.0 ml, frequency 150 breaths/min) with either humidified isocapnic gas (n = 6) or dry gas (n = 7). Dry gas challenge was performed on animals that received MK-571 (LTD4 antagonist; 2 mg/kg i.v.; n = 5), capsaicin (n = 4), neurokinin (NK) antagonists [NK1 (CP-99994) + NK2 (SR-48968) (1 mg/kg i.v.); n = 6], or the H1 antihistamine pyrilamine (2 mg/kg i.v.; n = 5). We measured the tracheal pressure and collected bile for 1 h before and 2 h after hyperpnea challenge. We examined the biliary excretion of cysteinyl LTs; the recovery of radioactivity in bile after instillation of 1 microCi [3H]LTC4 intratracheally averaged 24% within 4 h (n = 2). The major cysteinyl LT identified was LTD4 (32% recovery of radioactivity). Cysteinyl LTs were purified from bile of animals undergoing hyperpnea challenge by using reverse-phase high-pressure liquid chromatography and quantified by radioimmunoassay. There was a significant increase in the peak value of tracheal pressure after challenge, indicating bronchoconstriction in dry gas-challenged animals but not after humidified gas challenge. MK-571, capsaicin, and NK antagonists prevented the bronchoconstriction; pyrilamine did not. Cysteinyl LT levels in the bile after challenge were significantly increased from baseline in dry gas-challenged animals (P < 0.05) and were higher than in the animals challenged with humidified gas or dry gas-challenged animals treated with capsaicin or NK antagonists (P < 0.01). The results indicate that isocapnic dry gas hyperpnea-induced bronchoconstriction is LT mediated and the role of tachykinins in the response is indirect through release of LTs. Endogenous histamine does not contribute to the response.

Transfer of allergic airway responses with antigen-primed CD4+ but not CD8+ T cells in brown Norway rats

Activated CD4+ helper T cells have been demonstrated in asthmatic airways and postulated to play a central role in eliciting allergic inflammation; direct evidence of their involvement seems to be lacking. We hypothesized that CD4+ T cells have the potential to induce allergic responses to antigen challenge, and tested this hypothesis in a model of allergic bronchoconstriction, the Brown Norway rat, using the approach of adoptive transfer. Animals were actively sensitized to either ovalbumin (OVA) or BSA and were used as donors of T cells. W3/25(CD4)+ or OX8(CD8)+ T cells were isolated from the cervical lymph nodes of sensitized donors and transferred to naive BN rats. 2 d after adoptive transfer recipient rats were challenged by OVA inhalation, and changes in lung resistance (RL), bronchoalveolar lavage (BAL) cells, and serum levels of antigen-specific IgE were studied. After OVA challenge recipients of OVA-primed W3/25+ T cells exhibited sustained increases in RL throughout the entire 8-h observation period and had significant bronchoalveolar lavage eosinophilia, which was detected by immunocytochemistry using an antimajor basic protein mAb. Recipients of BSA-primed W3/25+ T cells or OVA-primed OX8+ T cells failed to respond to inhaled OVA. OVA-specific immunoglobulin E was undetectable by ELISA or skin testing in any of the recipient rats after adoptive transfer. In conclusion, antigen-induced airway bronchoconstriction and eosinophilia were successfully transferred by antigen-specific W3/25+ T cells in Brown Norway rats. These responses were dependent on antigen-primed W3/25+ T cells and appeared to be independent of IgE-mediated mast cell activation. This study provides clear evidence for T cell mediated immune mechanisms in allergic airway responses in this experimental model.

Allergen-induced airway responses in rats pretreated with Sephadex

Even though the eosinophil is potentially an important contributor to airway narrowing during the late allergic airway response, direct evidence of its participation is lacking. Therefore, we examined the effects of eosinophilia induced by Sephadex on the magnitude of the late airway response of sensitized rats following allergen challenge. Brown Norway rats were actively sensitized to ovalbumin (OA). At the same time and 14 days later, a test group was administered Sephadex G200 (0.5 mg intravenously). The animals were challenged with an aerosol of OA and pulmonary resistance (RL) was measured over 6 h. The early response to OA reached a peak more rapidly and the magnitude of the late response, measured as the area under the curve of RL against time, was significantly greater in the Sephadex-treated group (48.3; geometric mean) compared to the control animals (18.9; p < 0.02). The percentage of eosinophils was increased in the bronchoalveolar lavage of Sephadex-treated animals (4%) compared to the controls (0.9%; p < 0.02) following OA challenge. These results demonstrate that Sephadex induces eosinophilia in Brown Norway rats and is associated with an increase in the late allergic airway response. This is consistent with the hypothesis that the eosinophil is an important determinant of the late response.

Role of leukotriene D4 in allergen-induced increases in airway smooth muscle in the rat

The purpose of the study was to investigate whether allergen-induced hyperresponsiveness to methacholine and an increase in airway smooth muscle (ASM) in Brown Norway (BN) rats could be mediated by LTD4, an important mediator of allergic airway responses. Male BN rats, 8 to 12 wk of age, were sensitized with ovalbumin (OA). Rats were exposed 2 wk later to aerosols of saline (n = 6), OA (n = 8), or OA after pretreatment with the LTD4 antagonist MK-571 (2 mg/kg intraperitoneally, n = 9), on six occasions at 5-day intervals. Airway responsiveness to methacholine (the concentration required to double pulmonary resistance, EC200 RL) was measured immediately before the first aerosol exposure and 2 days after the last exposure. ASM was quantitated by morphometry, and areas were standardized for size using the epithelial basement membrane length (BM). Following OA challenges EC200 RL decreased from 6.5 to 3.1 mg/ml (p < 0.05) but did not change significantly after saline or OA exposures in MK-571-pretreated animals. ASM/BM2 in the large airways was significantly greater, 3.41 +/- 0.19 x 10(-3), after OA compared with 2.35 +/- 0.22 x 10(-3) for saline exposures (p < 0.01). The ASM/BM2 after OA exposures but with MK-571 pretreatment (2.75 +/- 0.25 x 10(-3)) was intermediate in value. The results indicate that both the increase in airway responsiveness and the increase in ASM following repeated antigen exposures appear to be mediated predominantly by LTD4.