Cellular markers of inflammation in the airways of allergic sheep with and without allergen-induced late responses

Variability of the Sheep Lung Microbiota

Sequencing technologies have recently facilitated the characterization of bacterial communities present in lungs during health and disease. However, there is currently a dearth of information concerning the variability of such data in health both between and within subjects. This study seeks to examine such variability using healthy adult sheep as our model system. Protected specimen brush samples were collected from three spatially disparate segmental bronchi of six adult sheep (age, 20 months) on three occasions (day 0, 1 month, and 3 months). To further explore the spatial variability of the microbiotas, more-extensive brushing samples (n = 16) and a throat swab were taken from a separate sheep. The V2 and V3 hypervariable regions of the bacterial 16S rRNA genes were amplified and sequenced via Illumina MiSeq. DNA sequences were analyzed using the mothur software package. Quantitative PCR was performed to quantify total bacterial DNA. Some sheep lungs contained dramatically different bacterial communities at different sampling sites, whereas in others, airway microbiotas appeared similar across the lung. In our spatial variability study, we observed clustering related to the depth within the lung from which samples were taken. Lung depth refers to increasing distance from the glottis, progressing in a caudal direction. We conclude that both host influence and local factors have impacts on the composition of the sheep lung microbiota.

IMPORTANCE

Until recently, it was assumed that the lungs were a sterile environment which was colonized by microbes only during disease. However, recent studies using sequencing technologies have found that there is a small population of bacteria which exists in the lung during health, referred to as the "lung microbiota." In this study, we characterize the variability of the lung microbiotas of healthy sheep. Sheep not only are economically important animals but also are often used as large animal models of human respiratory disease. We conclude that, while host influence does play a role in dictating the types of microbes which colonize the airways, it is clear that local factors also play an important role in this regard. Understanding the nature and influence of these factors will be key to understanding the variability in, and functional relevance of, the lung microbiota.

Vaccination induced changes in pro-inflammatory cytokine levels as an early putative biomarker for cognitive improvement in a transgenic mouse model for Alzheimer disease

Several pieces of experimental evidence suggest that administration of anti-β amyloid (Aβ) vaccines, passive anti-Aβ antibodies or anti-inflammatory drugs can reduce Aβ deposition as well as associated cognitive/behavioral deficits in an Alzheimer disease (AD) transgenic (Tg) mouse model and, as such, may have some efficacy in human AD patients as well. In the investigation reported here an Aβ 1-42 peptide vaccine was administered to 16-month old APP+PS1 transgenic (Tg) mice in which Aβ deposition, cognitive memory deficits as well as levels of several pro-inflammatory cytokines were measured in response to the vaccination regimen. After vaccination, the anti-Aβ 1-42 antibody-producing mice demonstrated a significant reduction in the sera levels of 4 pro-inflammatory cytokines (TNF-α, IL-6, IL-1 α, and IL-12). Importantly, reductions in the cytokine levels of TNF-α and IL-6 were correlated with cognitive/behavioral improvement in the Tg mice. However, no differences in cerebral Aβ deposition in these mice were noted among the different control and experimental groups, i.e., Aβ 1-42 peptide vaccinated, control peptide vaccinated, or non-vaccinated mice. However, decreased levels of pro-inflammatory cytokines as well as improved cognitive performance were noted in mice vaccinated with the control peptide as well as those immunized with the Aβ 1-42 peptide. These findings suggest that reduction in pro-inflammatory cytokine levels in these mice may be utilized as an early biomarker for vaccination/treatment induced amelioration of cognitive deficits and are independent of Aβ deposition and, interestingly, antigen specific Aβ 1-42 vaccination. Since cytokine changes are typically related to T cell activation, the results imply that T cell regulation may have an important role in vaccination or other immunotherapeutic strategies in an AD mouse model and potentially in AD patients. Overall, these cytokine changes may serve as a predictive marker for AD development and progression as well as having potential therapeutic implications.

Anti-allergic cromones inhibit histamine and eicosanoid release from activated human and murine mast cells by releasing Annexin A1

Background and Purpose

Although the ‘cromones’ (di-sodium cromoglycate and sodium nedocromil) are used to treat allergy and asthma, their ‘mast cell stabilising’ mechanism of pharmacological action has never been convincingly explained. Here, we investigate the hypothesis that these drugs act by stimulating the release of the anti-inflammatory protein Annexin-A1 (Anx-A1) from mast cells.

Experimental approach

We used biochemical and immuno-neutralisation techniques to investigate the mechanism by which cromones suppress histamine and eicosanoid release from cord-derived human mast cells (CDMCs) or murine bone marrow-derived mast cells (BMDMCs) from wild type and Anx-A1 null mice.

Key results

CDMCs activated by IgE-FcRε1 crosslinking, released histamine and prostaglandin (PG) D₂, which were inhibited (30–65%) by 5 min pre-treatment with cromoglycate (10 nM) or nedocromil (10 nM), as well as dexamethasone (2 nM) and human recombinant Anx-A1 (1–10 nM). In CDMCs cromones potentiated (2–5 fold) protein kinase C (PKC) phosphorylation and Anx-A1 phosphorylation and secretion (3–5 fold). Incubation of CDMCs with a neutralising anti-Anx-A1 monoclonal antibody reversed the cromone inhibitory effect.

Nedocromil (10 nM) also inhibited (40–60%) the release of mediators from murine bone marrow derived-mast cells from wild type mice activated by compound 48/80 and IgE-FcRε1 cross-linking, but were inactive in such cells when these were prepared from Anx-A1 null mice or when the neutralising anti-Anx-A1 antibody was present.

Conclusions and Implications

We conclude that stimulation of phosphorylation and secretion of Anx-A1 is an important component of inhibitory cromone actions on mast cells, which could explain their acute pharmacological actions in allergy. These findings also highlight a new pathway for reducing mediator release from these cells.

Animal models of airway inflammation and airway smooth muscle remodelling in asthma

Asthma is a complex disease that involves chronic inflammation and subsequent decline in airway function. The widespread use of animal models has greatly contributed to our understanding of the cellular and molecular pathways underlying human allergic asthma. Animal models of allergic asthma include smaller animal models which offer 'ease of use' and availability of reagents, and larger animal models that may be used to address aspects of allergic airways disease not possible in humans or smaller animal models. This review examines the application and suitability of various animal models for studying mechanisms of airway inflammation and tissue remodelling in allergic asthma, with a specific focus on airway smooth muscle.

Anti-asthmatic action of quercetin and rutin in conscious guinea-pigs challenged with aerosolized ovalbumin

The effects of quercetin and rutin on the asthmatic responses were studied in ovalbumin (OA)-sensitized conscious guinea pigs challenged with aerosolized-OA. We measured the specific airway resistance (sRaw) in the double-chambered plethysmograph during the immediate-phase response (IAR) and late-phase response (LAR) at 3 approximately 10 min and 24 hr after OA challenge, respectively. We counted leukocytes in bronchoalveolar lavage fluid (BALF) using Wright's stain, as well as in lung tissue fixed with 10% formalin and stained with H & E stain. Quercetin and rutin (7.5 mg/kg, p.o.) significantly and dose-dependently inhibited both sRaw on IAR (31.60 and 26.44%) and LAR (29.87 and 28.69%) but with less efficacy than dexamethasone (3 mg/kg) and salbutamol (0.3 mg/kg), which inhibited IAR by 36.71 and 69.45%, and LAR by 67.23 and 0%, respectively, Quercetin and rutin (15 mg/kg) also inhibited production of histamine, PLA2, and EPO, and recruitment of leukocytes, particularly neutrophils and eosinophils, during LAR. respectively. Dexamethasone (3 mg/kg) also significantly reduced the recruitment of neutrophils, eosinophils, and lymphocytes in BALF, and salbutamol (0.3 mg/kg) reduced neutrophils and eosinophils with lower activity than dexamethasone. These results indicate that quercetin and rutin may be useful in the treatment of IAR and LAR in asthma via inhibition of histamine release, PLA2, and EPO, and reduced recruitment of neutrophils and eosinophils into the lung.

Modeling of asthma, COPD and cystic fibrosis in sheep

Sheep naturally allergic to Ascaris suum antigen have been used to study the pathophysiology of asthma and more recently allergic rhinitis, chronic obstructive pulmonary disease (COPD) and cystic fibrosis. The utility of the model as it relates to the study of these diseases is discussed.

Animal models of asthma

Animal models of asthma are a tool that allows studies to be conducted in the setting of an intact immune and respiratory system. These models have highlighted the importance of T-helper type 2 driven allergic responses in the progression of asthma and have been useful in the identification of potential drug targets for interventions involving allergic pathways. However, a number of drugs that have been shown to have some efficacy in animal models of asthma have shown little clinical benefit in human asthmatics. This may be due to a number of factors including the species of animal chosen and the methods used to induce an asthmatic phenotype in animals that do not normally develop a disease that could be characterized as asthma. The range of animal models available is vast, with the most popular models being rodents (inbred mice and rats) and guinea-pigs, which have the benefit of being easy to handle and being relatively cost effective compared with other models that are available. The recent advances in transgenic technology and the development of species-specific probes, particularly in mice, have allowed detailed mechanistic studies to be conducted. Despite these advances in technology, there are a number of issues with current animal models of asthma that must be recognized including the disparity in immunology and anatomy between these species and humans, the requirement for adjuvant during senitization in most models, the acute nature of the allergic response that is induced and the use of adult animals as the primary disease model. Some larger animal models using sheep and dogs have been developed that may address some of these issues but they also have different biology from humans in many ways and are extremely costly, with very few probes available for characterizing allergic responses in the airway in these species. As research in this area continues to expand, the relative merits and limitations of each model must be defined and understood in order to evaluate the information that is obtained from these models and to extrapolate these findings to humans so that effective drug therapies can be developed. Despite these issues, animal models have been, and will continue to be, vital in understanding the mechanisms that are involved in the development and progression of asthma.

Chronic airway disease: deteriorating pulmonary function in sheep associated with repeated challenges of house dust mite

The aim of this work was to characterize lung function and cellular responses in a large animal model for chronic asthma. All sheep were sensitized to house dust mite (HDM) by subcutaneous injection of HDM before lung challenges. Groups of sheep were given weekly lung challenges with either HDM (n = 12) or saline (control, n = 5) for 3 months. Post challenge, there were significant increases in lung resistance in 7 out of 12 HDM-challenged sheep, compared to control sheep. In HDM-responding sheep, there was a progressive increase in the magnitude of HDM-induced resistance throughout the trial. All HDM-challenged sheep developed BAL eosinophilia and bronchial hyperresponsiveness. In conclusion, sheep chronically challenged intralung with HDM consistently develop airway hyperresponsiveness and eosinophilia, whereas allergen-specific bronchoconstriction is observed in just over half of these sheep.

Lung function and airway inflammation in rats following exposure to combustion products of carbon-graphite/epoxy composite material: comparison to a rodent model of acute lung injury

Pulmonary function and inflammation in the lungs of rodents exposed by inhalation to carbon/graphite/epoxy advanced composite material (ACM) combustion products were compared to that of a rodent model of acute lung injury (ALI) produced by pneumotoxic paraquat dichloride. This investigation was undertaken to determine if short-term exposure to ACM smoke induces ALI; and to determine if smoke-related responses were similar to the pathogenic mechanisms of a model of lung vascular injury. We examined the time-course for mechanical lung function, infiltration of inflammatory cells into the lung, and the expression of three inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha), macrophage inflammatory protein-2 (MIP-2) and interferon-gamma (IFN-gamma). Male Fischer-344 rats were either exposed to 26.8-29.8 g/m(3) nominal concentrations of smoke or were given i.p. injections of paraquat dichloride. Measurements were determined at 1, 2, 3, and 7 days post exposure. In the smoke-challenged rats, there were no changes in lung function indicative of ALI throughout the 7-day observation period, despite the acute lethality of the smoke atmosphere. However, the animals showed signs of pulmonary inflammation. The expression of TNF-alpha was significantly increased in the lavage fluid 1 day following exposure, which preceded the maximum leukocyte infiltration. MIP-2 levels were significantly increased in lavage fluid at days 2, 3, and 7. This followed the leukocyte infiltration. IFN-gamma was significantly increased in the lung tissue at day 7, which occurred during the resolution of the inflammatory response. The paraquat, which was also lethal to a small percentage of the animals, caused several physiologic changes characteristic of ALI, including significant decreases in lung compliance, lung volumes/capacities, distribution of ventilation, and gas exchange capacity. The expression of TNF-alpha and MIP-2 increased significantly in the lung tissue as well as in the lavage fluid. Increased MIP-2 levels also preceded the maximum neutrophil infiltration. The differences in the time-course and primary site of TNF-alpha, MIP-2, and IFN-gamma expression; and the differences in the temporal relationship between their expression and infiltration of inflammatory cells may have accounted for the differences in lung function between paraquat treated and ACM smoke exposed animals.

Inhibition of allergic late airway responses by inhaled heparin-derived oligosaccharides

Inhaled heparin has been shown to inhibit allergic bronchoconstriction in sheep that develop only acute responses to antigen (acute responders) but was ineffective in sheep that develop both acute and late airway responses (LAR) (dual responders). Because the antiallergic activity of heparin is molecular-weight dependent, we hypothesized that heparin-derived oligosaccharides (<2, 500) with potential anti-inflammatory activity may attenuate the LAR in the dual-responder sheep. Specific lung resistance was measured in 24 dual-responder sheep before and serially for 8 h after challenge with Ascaris suum antigen for demonstration of early airway response (EAR) and LAR, without and after treatment with inhaled medium-, low-, and ultralow-molecular-weight (ULMW) heparins and "non-anticoagulant" fractions (NAF) of heparin. Airway responsiveness was estimated before and 24 h postantigen as the cumulative provocating dose of carbachol that increased specific lung resistance by 400%. Only ULMW heparins caused a dose-dependent inhibition of antigen-induced EAR and LAR and postantigen airway hyperresponsiveness (AHR), whereas low- and medium-molecular-weight heparins were ineffective. The effects of ULMW heparin and ULMW NAF-heparin were comparable and inhibited the LAR and AHR even when administered "after" the antigen challenge. The ULMW NAF-heparin failed to inhibit the bronchoconstrictor response to histamine, carbachol, and leukotriene D(4), excluding a direct effect on airway smooth muscle. In six sheep, segmental antigen challenge caused a marked increase in bronchoalveolar lavage histamine, which was not prevented by inhaled ULMW NAF-heparin. The results of this study in the dual-responder sheep demonstrate that 1) the antiallergic activity of inhaled "fractionated" heparins is molecular-weight dependent, 2) only ULMW heparins inhibit the antigen-induced EAR and LAR and postantigen AHR, and 3) the antiallergic activity is mediated by nonanticoagulant fractions and resides in the ULMW chains of <2,500.

Comparative effects of a glucocorticosteroid, theophylline and the peptido-leukotriene-antagonist CGP 45715A on antigen-induced early and late phase airway response and inflammatory cell influx in sensitised guinea pigs

A novel model of allergic early and late-phase reaction in the airways of conscious guinea pigs was developed and the effect of established and novel antiasthmatic drugs on peak of immediate response, late phase response and associated inflammatory cell influx investigated. Guinea pigs were sensitised twice in adjuvant (50 mg/kg silica + 0.1 ml/kg Bordetella pertussis). Under cover of 10 mg/kg i.p. mepyramine guinea pigs exhibited still a pronounced immediate reaction. During a screening phase about 75% of guinea pigs demonstrated a late phase reaction of decrease of tidal volume between 4-10 h after ovalbumin inhalation. In a cross over study theophylline at 50 mg/kg p.o. (-1 h before ovalbumin) tended to attenuate not only the peak of the immediate reaction by about 69% (P>0.05, n = 12), but inhibited the airway late phase response significantly (P<0.05, 5-10 h, n = 12). Methylprednisolone (40 mg/kg p.o. 1 h before ovalbumin) did not inhibit the immediate response, but the late phase response. In contrast the cysteinyl-leukotriene antagonist CGP 45715A (Iralukast; 30 mg/kg p.o. 2 h before ovalbumin) neither interfered with the peak of the immediate, nor with the late phase response. When bronchoalveolar lavage by orotracheal route was performed 24 h after ovalbumin inhalation, total cell count, eosinophils, neutrophils, macrophages and lymphocytes were significantly increased in ovalbumin-controls compared to sham (n = 5; P<0.05). Methylprednisolone reduced significantly the antigen-induced increase of total cell count and eosinophil number. Neither theophylline nor the cysteinyl-leukotriene receptor antagonist attenuated the antigen-associated cell influx. The results do not provide evidence for a major role of cysteinyl-leukotrienes in the late phase response and inflammatory cell influx in this model.

Blockade of late-phase airway responses and airway hyperresponsiveness in allergic sheep with a small-molecule peptide inhibitor of VLA-4

The leukocyte integrin very late antigen-4 (VLA-4) (alpha 4 beta 1, CD49d/CD29) is an adhesion receptor predominantly expressed on lymphocytes, monocytes, and eosinophils, but not on neutrophils. Recent studies with monoclonal antibodies against VLA-4 suggest that antigen-induced late responses and airway hyperresponsiveness (AHR) may depend on the recruitment and/or activation of VLA-4-expressing leukocytes. To further test this hypothesis, we administered by aerosol either a potent small-molecule inhibitor of VLA-4, which prevents VLA-4-mediated binding to fibronectin (CS-1 ligand mimic), or an inactive control (30 mg twice daily for 3 d, and on the fourth day 0.5 h before and 4 h after antigen challenge) to six sheep with airway hypersensitivity to Ascaris suum antigen. Treatment with the small-molecule VLA-4 inhibitor resulted in a significant decrease in the early antigen-induced bronchial response (40%, p < 0.05), and almost complete blockade of the late-phase airway response (88%, p < 0.05). Moreover, at 24 h after antigen challenge, AHR to inhaled carbachol was not observed when the animals were dosed with the small-molecule VLA-4 inhibitor. In accord with protection against the functional abnormalities associated with antigen challenge, analysis of biopsy specimens taken 24 h after challenge indicated that the total numbers of VLA-4-positive cells (lymphocytes, eosinophils, and metachromatic-staining cells) in the group treated with the VLA-4 inhibitor did not increase, whereas these cells increased in the control group. The active agent, but not the inactive control, significantly blocked macrophage adherence to fibronectin (FN), indicating that the CS-1 ligand interfered with VLA-4-mediated adhesion in sheep cells. These results support our previous findings with a monoclonal antibody to VLA-4, and demonstrate that a small-molecule VLA-4 inhibitor, when given by aerosol, has a protective effect against antigen-induced late responses and AHR in allergic sheep.

Characterisation of a novel airway late phase model in the sensitized guinea pig which uses silica and Bordetella pertussis as adjuvant for sensitization

The objective of the present investigation was to validate a novel model of allergic late phase reaction in the airways of conscious guinea pigs by monitoring airway function with CO2-forced respiration. In addition airway inflammation as one possible cause for the development of airway late phase reaction was characterized by a novel technique which consists of bronchoalveolar lavage via the orotracheal route. Guinea pigs were sensitized twice at 2-week intervals with ovalbumin in silica and Bordetella pertussis. Two weeks after the booster sensitization all guinea pigs showed an acute decrease of tidal volume under CO2-forced respiration 5-15 min after antigen challenge. In contrast 42 out of 68 (= 62%) screened guinea pigs exhibited airway late phase response between 4-10 h after aerosol antigen challenge. During a subsequent cross-over study methylprednisolone (twice at 16 and 1 h before ovalbumin) did not significantly interfere with the acute response. In contrast the airway late phase response as well the associated eosinophil influx into the bronchoalveolar lavage were attenuated by the steroid. In conclusion, the sensitization procedure in combination with the novel method for monitoring airway function allowed measurement of a reproducible airway late phase response in about 60% of sensitized guinea pigs. The sensitivity of exclusively the late phase response and eosinophil influx to treatment with a glucocorticoid not only correlates this model with clinical pharmacotherapy but also strengthens the inflammatory nature of this model.

Quantitation of eosinophil and neutrophil infiltration into rat lung by specific assays for eosinophil peroxidase and myeloperoxidase. Application in a Brown Norway rat model of allergic pulmonary inflammation

Conditions for measuring selectively eosinophil peroxidase (EPO) and the neutrophil myeloperoxidase (MPO) in inflamed rat lung were determined. EPO could be specifically measured with o-phenylene diamine as chromogen at pH 8.0 in the presence of 3 mM bromide and MPO with tetramethylbenzidine as chromogen at pH 5.0 in the absence of bromide but with the EPO inhibitor, resorcinol. Aeroallergen challenge of sensitized Brown Norway rats with ovalbumin, but not with saline, resulted in a pronounced eosinophilic lung inflammation with some focal hemorrhages and an increase in lung wet weights. Quantitation of the eosinophil and neutrophil accumulation required lyophilization of lung samples, a hypotonic wash to remove contaminating hemoglobin, which interfered with the MPO assay, followed by extraction with the detergent cetyltrimethylammonium chloride. Based on lung EPO and MPO activities and standardization of enzyme activity with purified eosinophils and neutrophils, the total number of eosinophils and neutrophils in the lungs was calculated at 24 h (n = 19), 48 h (n = 9) and 72 h (n = 4) after challenge, as 56 +/- 6.4 x 10(6), 119 +/- 28 x 10(6) and 108 +/- 33 x 10(6) for eosinophils, respectively, and 94 +/- 6.8 x 10(6), 49 +/- 5.0 x 10(6) and 32 +/- 5.5 x 10(6) for neutrophils, respectively. We conclude that, with the assay conditions outlined here, EPO and MPO can be used to quantitate the tissue infiltration of eosinophils and neutrophils in the rat even in mixed inflammatory reactions.

Effect of nedocromil sodium on allergen-induced airway responses and changes in the quantity of airway smooth muscle in rats

BACKGROUND

Allergen exposures induce growth of airway smooth muscle in the Brown Norway rat.

OBJECTIVE

The purpose of the study was to examine the role of mediators associated with the early and late responses in the induction of airway smooth muscle growth.

METHODS

Nedocromil sodium was administered to block early and late responses in ovalbumin-sensitized and ovalbumin-challenged rats undergoing single or multiple challenges (5 times at 5-day intervals) with ovalbumin. Airway smooth muscle was quantitated by morphometry on lungs removed 2 days after the final challenge.

RESULTS

Nedocromil sodium administered before ovalbumin challenge blocked both the early and late responses. When administered 2 hours after ovalbumin challenge, it also blocked the late response. Rats undergoing challenge with aerosolized ovalbumin five times at 5-day intervals were also treated with nedocromil before (n = 10) or 2 hours after (n = 10) each ovalbumin inhalation, respectively. The quantity of airway smooth muscle standardized for size was greater after ovalbumin challenge (0.069 +/- 0.005) compared with saline controls (0.033 +/- 0.003, p < 0.005). Nedocromil significantly reduced the airway smooth muscle (0.036 +/- 0.003, p < 0.005) when administered before ovalbumin. However, the airway smooth muscle in rats that received nedocromil 2 hours after ovalbumin challenge (0.046 +/- 0.003), although lower than in ovalbumin-challenged rats (p < 0.01), was still significantly higher than in saline-treated rats (p < 0.05).

CONCLUSIONS

Allergen-induced early responses, late responses, and airway inflammation are antagonized by nedocromil. The mediators of both the early and late responses contribute to allergen-induced airway smooth muscle growth, a process that can be prevented by administration of nedocromil.

Plasma thrombospondin levels in sheep with allergic asthma

STUDY OBJECTIVE

In search of a better universal marker of tissue inflammation in allergic reactions, we studied platelet activation and its relation to allergic asthma in sheep.

SETTING

University research laboratory.

SUBJECTS

Twenty-three allergic sheep.

DESIGN AND INTERVENTIONS

We serially measured plasma thrombospondin (TSP), a glycoprotein secreted from activated platelets, using enzyme-linked immunosorbent assay with a monoclonal antibody. We validated the assay by establishing a standard curve that closely matches that of humans.

MEASUREMENTS AND RESULTS

Of the 23 allergic sheep tested, 10 demonstrated early airway response (ER group) and 13 had early and late dual airway responses (DR group) to inhaled Ascaris suum antigen. TSP was measured before, and at 0, 1, 2, 3, 4, 6, 8, and 24 h postantigen challenge. Both groups showed an increase in plasma TSP level after antigen challenge, but only the DR group showed a significant increase in TSP at I h (threefold) and 8 h (sixfold) postchallenge. The two sheep that received carbachol challenge showed a slight rise in TSP at 8 h postchallenge. There was a significant correlation between the TSP level at I h and the peak early airway response in the DR group.

CONCLUSIONS

These results suggest that the two groups of allergic sheep may have two distinct induction processes leading to airway obstruction. The dual peak rise in TSP level that coincided with the airway response also suggests that an early priming effect exists in the DR group, which might have led to the late response. We conclude that intravascular platelet activation often occurs in mast cell-mediated allergic disorders. Therefore, plasma TSP may be useful for monitoring the course of allergic disorders.

Alpha 4-integrins mediate antigen-induced late bronchial responses and prolonged airway hyperresponsiveness in sheep

Eosinophils and T lymphocytes are thought to be involved in allergic airway inflammation. Both cells express the alpha 4 beta 1-integrin, very late antigen-4 (VLA-4, CD49d/CD29); alpha 4-integrins can promote cellular adhesion and activation. Therefore, we examined the in vivo effects of a blocking anti-alpha 4 monoclonal antibody, HP 1/2, on antigen-induced early and late bronchial responses, airway hyperresponsiveness, inflammatory cell influx, and peripheral leukocyte counts in allergic sheep. Sheep blood lymphocytes, monocytes, and eosinophils expressed alpha 4 and bound HP 1/2. In control sheep, Ascaris antigen challenge produced early and late increases in specific lung resistance of 380 +/- 42% and 175 +/- 16% over baseline immediately and 7 h after challenge, respectively, as well as airway hyperresponsiveness continuing for 14 d after antigen challenge. Treatment with HP 1/2 (1 mg/kg, i.v.) 30 min before antigen challenge did not affect the early increase in specific lung resistance but inhibited the late-phase increase at 5-8 h by 75% (P < 0.05) and inhibited the post-antigen-induced airway hyperresponsiveness at 1, 2, 7, and 14 d (P < 0.05, for each time). Intravenous HP 1/2 given 2 h after antigen challenge likewise blocked late-phase airway changes and postchallenge airway hyperresponsiveness. Airway administration of HP 1/2 (16-mg dose) was also effective in blocking these antigen-induced changes. Response to HP 1/2 was specific since an isotypic monoclonal antibody, 1E6, was ineffective by intravenous and aerosol administration. Inhibition of leukocyte recruitment did not totally account for the activity of anti-alpha 4 antibody since HP 1/2 neither diminished the eosinopenia or lymphopenia that followed antigen challenge nor consistently altered the composition of leukocytes recovered by bronchoalveolar lavage. Because airway administration of HP 1/2 was also active, HP 1/2 may have inhibited cell activation. Reduction of platelet-activating factor-induced eosinophil peroxidase release from HP 1/2-treated eosinophils supports such a mechanism. These findings indicate a role for alpha 4-integrins in processes that lead to airway late phase responses and persisting airway hyperresponsiveness after antigen challenge.

Effect of dexamethasone on airway inflammation and responsiveness after antigen challenge of the rat

The purpose of this study was to examine the effects of dexamethasone on airway responsiveness and lung inflammation of rats at 8 h, 32 h, and 7 d after allergen challenge. Brown-Norway male rats, 7 to 8 wk old, were actively sensitized to ovalbumin (OA) and challenged 14 d later. The rats were divided into a control group (n = 31) and a test group (n = 34) that received dexamethasone (DEXA) (0.3 mg/kg intraperitoneally) 14 h and 2 h before saline or OA challenge. For challenge, rats were anesthetized with pentobarbital and intubated endotracheally. Aerosols of OA (5% wt/vol in saline) were administered for 5 min. Responsiveness to inhaled aerosols of methacholine and the total and differential leukocyte counts in the large airways (generations 0 to 5), small airways, and parenchyma isolated by tissue mincing and digestion were measured at 8 h, 32 h, and 7 d after OA challenge. The cellular influx into the airways and parenchyma was highest at 8 h and decreased progressively over 7 d. DEXA significantly inhibited the cellular influx after allergen challenge. At 8 h, cellular return from the large airways was 3.61 +/- 0.5 x 10(6) (controls) versus 1.0 +/- 0.2 x 10(6) (DEXA), and from the small airways and parenchyma was 31.7 +/- 2.8 x 10(6) (controls) versus 21.9 +/- 2.9 x 10(6) (DEXA) (p < 0.05). The differences were attributable mostly to decreases in neutrophils in DEXA-treated animals. In control animals, neutrophil yield fell between 8 and 32 h, whereas eosinophils and 32 h, whereas eosinophil and lymphocyte counts increased.(ABSTRACT TRUNCATED AT 250 WORDS)

A rapid biochemical method for measuring antigen-induced pulmonary eosinophil margination in allergic guinea pigs

The ability of purified guinea pig peritoneal eosinophils (EOS) to oxidise 3,3',5,5'-tetramethylbenzidine (TMB) was assessed in the presence/absence of Br- (3 mM), and compared with that of unpurified elicited peritoneal polymorphonuclear leukocytes (PMN). Br- selectively stimulated EOS peroxidase activity in a cell number-dependent manner, which was not significantly affected by the presence of diluted lung homogenate. By comparison with the peroxidase activity of added purified EOS, lung parenchyma homogenate from naive guinea pigs was estimated to contain 1.04 +/- 0.18 x 10(5) cells/mg wet tissue (n = 6), a value comparable to those calculated from published histological analyses. This was not significantly increased by ovalbumin (OA) allergen inhalation in unsensitised guinea pigs (1.4 x 10(5) EOS/mg), but was increased two-fold over the latter control to 3.0 +/- 0.18 x 10(5) cells/mg after 17 h in animals sensitised by a single injection of OA and subsequently exposed to an aerosol of bronchoactive allergen (n = 13, p < 0.05). Similar results were obtained in a parallel study using bronchoalveolar lavage (saline challenge, 20.2 +/- 2.2% EOS in lavage fluid; OA challenge, 47.1 +/- 3.6% EOS; n = 6, p < 0.05). In animals that had been doubly sensitised (two injections) to OA, the pulmonary eosinophilic response measured biochemically was more pronounced (4.9 +/- 0.2 x 10(5) cells/mg) and was significantly greater than both a non-specific protein inhalation in this sensitisation group, and OA inhalation in singly sensitised animals (n = 12, p < 0.05). Sera from the latter group was shown to contain five times less specific anti-OA IgG than the doubly sensitised animals, suggesting that EOS margination in guinea pigs is proportionate to the animals' immune status for a defined immunological challenge. These data demonstrate that in vivo EOS migration into the whole guinea pig lung can be rapidly determined by biochemical methods, and thus facilitate the in vivo assessment of novel therapeutic agents against the eosinophilic inflammation characteristic of human allergic asthma.

Effect of nedocromil sodium on specific mediator- and antigen-induced airway responses in allergic sheep

This study evaluated the airway effects of nedocromil sodium in the sheep model of allergic bronchoconstriction. Nedocromil sodium provided statistically significant protection against both reflex- and mediator-induced bronchoconstriction in allergic sheep as assessed by bronchial responses to inhaled bradykinin and platelet-activating factor, respectively. When administered before antigen challenge, nedocromil sodium blocked both the immediate and late asthmatic response and prevented the subsequent increase in airway hyperresponsiveness. The protective effect of nedocromil sodium against the antigen-induced late response was associated with a significant decrease in the number of airway eosinophils measured by bronchoalveolar lavage. Although nedocromil sodium has no direct bronchodilatory activity, it prevented antigen-induced contractions in sheep tracheal smooth muscle in vitro. These results suggest that nedocromil sodium is active in the sheep model of allergic bronchoconstriction and may be useful in the treatment of reversible obstructive airway disease in human beings.

Nedocromil sodium. An updated review of its pharmacological properties and therapeutic efficacy in asthma

Nedocromil sodium, the disodium salt of a pyranoquinoline dicarboxylic acid, has anti-inflammatory properties in vitro, in animal models of asthma, and in humans, as evidenced by inhibition of inflammatory cell activation and mediator release, early and late allergen-induced bronchoconstriction and airway hyperresponsiveness. Recent therapeutic trials confirm the safety and efficacy of inhaled nedocromil sodium as adjunctive therapy in adult patients whose asthma is not adequately controlled by beta-agonists alone. Nedocromil sodium has also been shown to improve symptoms when added to existing treatment with methylxanthines and corticosteroids. Some studies show nedocromil sodium to be successful replacement therapy for methylxanthines, in addition to enabling a modest reduction in inhaled corticosteroids in some patients. Thus, nedocromil sodium may be suitable in patients with asthma as an adjunct to existing therapy, as an alternative to regularly administered oral and inhaled beta-agonists and oral methyl-xanthines, and potentially, to low dose inhaled corticosteroids as maintenance therapy in patients with mild to moderate asthma being considered for corticosteroid therapy.

The role of 5-lipoxygenase products in preclinical models of asthma

BACKGROUND

The action of 5-lipoxygenase on arachidonic acid generates potent inflammatory mediators that may contribute to the pathophysiology of asthma.

METHODS

Using the potent and selective 5-lipoxygenase inhibitor BI-L-239, we have examined the role of 5-lipoxygenase products in three animal models of asthma.

RESULTS

In vitro BI-L-239 inhibited 5-lipoxygenase product generation from human lung mast cells, alveolar macrophages, and peripheral blood leukocytes with a concentration that would provide 50% inhibition values of 28 to 340 nmol/L. A 36-fold selectivity for immunoreactive leukotriene C4 versus immunoreactive prostaglandin D2 inhibition was demonstrated in mast cells. In anesthetized cynomolgus monkeys, inhaled BI-L-239 provided dose-dependent inhibition of the inhaled Ascaris-induced immunoreactive leukotriene C4 release (maximum, 73%; bronchoalveolar lavage [BAL], 20 minutes), late-phase bronchoconstriction (maximum, 41%; +6 to 8 hours), and neutrophil infiltration (maximum, 63%; BAL, +8 hours). In conscious sheep, inhaled BI-L-239 provided dose-dependent inhibition of the inhaled Ascaris-induced late-phase bronchoconstriction (maximum, 66%; +6 to 8 hours) and increase in airway responsiveness (maximum, 82%; carbachol, +24 hours). The acute bronchoconstriction was shortened, and neutrophil infiltration diminished (maximum, 61%; BAL, +8 hours) in this model. Finally in conscious actively sensitized guinea pigs pretreated with pyrilamine and indomethacin, inhaled BI-L-239 attenuated acute bronchoconstriction (maximum, 80%; +5 to 15 minutes), leukocyte infiltration (58%; BAL, +3 days) and increase in airway responsiveness (100%; methacholine, +3 days) induced by three alternate-day ovalbumin inhalations.

CONCLUSIONS

In conclusion, results in these three animal models indicate that 5-lipoxygenase products may be major contributors to the bronchoconstriction (especially late phase), leukocyte infiltration, and airway hyperresponsiveness that characterize asthma.

Inflammatory cell populations in the airways and parenchyma after antigen challenge in the rat

We examined the effects of sensitization and antigen challenge on the cellular populations retrieved from the large airways (LA) (generations zero to 5 approximately) and small airways and parenchyma (S/P) of the rat. Male Brown-Norway rats, 7 to 8 wk of age, were either actively sensitized to ovalbumin (n = 24) or sham-sensitized to saline (n = 9), and, 14 days later, they were anesthetized with urethane, intubated endotracheally, and challenged. Aerosols of ovalbumin (5% wt/vol in saline for 5 min) or saline were administered to 12 and six rats, respectively, and measurements of pulmonary resistance (RL) were made for 8 h. The early airway response (ER) was calculated as the highest value of RL in the first hour after challenge, and the late response (LR) was calculated as an increase in RL to greater than 200% of the baseline value in the 4- to 8-h period after challenge. Rats were killed by exsanguination, LA were separated from S/P, and cells were isolated after tissue mincing and digestion with collagenase. Total and differential cell counts and lymphocyte subsets were determined. Antigen challenge significantly increased the cellular yield (mostly neutrophils) from the LA and S/P. Animals with a LR had a lower total cellular yield from the LA and S/P than did animals without a LR. The animals with a LR also had a lower yield of eosinophils and lymphocytes from the S/P than did animals challenged with saline alone. Cellular yields were not lower in the animals with an isolated ER after antigen challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of a cysteinyl leukotriene antagonist (ONO-1078) on antigen-induced responses in allergic sheep

The cysteinyl leukotrienes (LTC4/D4/E4) are putative mediators of asthma. In this study we used sheep allergic to Ascaris suum antigen to examine the effects of a novel orally active cysteinyl LT antagonist, ONO-1078, on antigen-induced early and late responses, airway inflammation, post challenge (24 h) airway hyperresponsiveness (AHR) and mucociliary clearance. Airway responses to antigen were determined by measuring specific lung resistance (SRL) before and for 8 h after challenge, bronchoalveolar lavage (BAL) was used to estimate airway inflammation, and airway responsiveness was measured by determining the carbachol dose that increased SRL by 400% (PC400). We also used a radiographic technique to measure the antigen-induced change in tracheal mucus velocity (TMV), a marker of mucociliary clearance. In two trials separated by at least 21 days, sheep were treated once with ONO-1078 (30 mg/kg, p.o.) and once with placebo (0.5% methylcellulose), 2 h before and 4 h after antigen challenge. Treatment with ONO-1078 (n = 7) provided 40% protection (p < 0.10) against the peak early increase in SRL, resulted in a more rapid reversal of the early response, and provided 96% protection against the peak late (6-8 h) increase in SRL. ONO-1078 also inhibited the AHR 24 h after challenge. In the drug trial, PC400 was unchanged as compared to pre-challenge, whereas in the placebo trial, PC400 was decreased 1.4-fold (p < 0.05). Treatment however, did not affect BAL cell numbers or differential.(ABSTRACT TRUNCATED AT 250 WORDS)

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

The Brown Norway rat produces high levels of IgE in response to active immunization and develops both early and late airway constrictor responses after subsequent allergen challenge. We have used this model of allergic asthma to investigate the temporal relationship between the in vivo synthesis of peptidoleukotrienes (peptido-LTs) and the late response. Brown Norway rats that had been sensitized by injection of ovalbumin 2 to 3 wk prior to the commencement of the experiment were subjected to bile duct cannulation and tracheal intubation. The rats were challenged 2 h later by intratracheal instillation of ovalbumin. Lung resistance was measured before and at frequent intervals after antigen challenge. Biliary peptido-LTs (LTC4, LTD4, LTE4, and N-acetyl-LTE4) were measured by a combination of high pressure liquid chromatography and radioimmunoassay in bile samples collected for a period of 1 h before instillation of ovalbumin, and between zero and 1 h, 1 and 4 h, 4 and 6 h, and 6 and 8 h, subsequently. All of the 10 rats subjected to antigen challenge developed early responses. Of these, six also developed late responses, whereas two died about 1 h after challenge. The levels of peptido-LTs excreted in bile between 4 and 8 h after antigen challenge (corresponding in time to the late responses) were about four times higher in the ovalbumin-instilled rats that developed late responses (n = 6) than in the ovalbumin-sensitized control rats that had been subjected to instillation of saline (n = 6; p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicologic testing of inhaled pharmaceutical aerosols

This paper reviews technical issues related to the toxicologic testing of inhaled pharmaceuticals. Although there are commonalities between approaches to general and inhalation toxicity testing, there also are specific challenges in the toxicity testing of inhaled pharmaceuticals. A major issue is that of dose; inhaled dose is more difficult to determine than intravenous or oral doses. Also, it is harder to relate dose in laboratory animals to that in man for inhalation exposure than for other routes of administration. Additionally, in the case of inhaled pharmaceuticals, people generally inhale through the mouth, whereas most laboratory animals inhale primarily through the nose. This presents significant challenges in exposure methodology and technology that often need innovative approaches involving alteration to particle size of the agent or dosing procedure. Because the respiratory tract is the site of deposition, local respiratory toxicity and possible damage to lung cells need to be assessed. Systemic toxicity also needs to be evaluated and may be an issue in some cases. Special studies on pulmonary function, mucociliary clearance, or immune response may be needed, depending on the nature of the inhaled pharmaceutical. This review explores the main issues involved in toxicity testing of inhaled pharmaceuticals, the approaches that have been used, and the current and future challenges.

Effects of ketotifen on airway responses to allergen challenge in the actively sensitized brown Norway rat

The purpose of the study was to examine the effect of ketotifen on the airway responses and the recruitment of the inflammatory cells into the airways of sensitized rats after antigen challenge. Twenty-five Brown Norway rats, 7-9 weeks old, were actively sensitized to ovalbumin (OA) (1 mg s.c.) and Bordetella pertussis vaccine (10(9) bacilli i.p.). At 14 days after sensitization rats were anesthetized with urethane (1.1 g/kg i.p.) and intubated endotracheally. Aerosols of OA (5% W/V in saline for 5 min) were administered to control rats (Group A; n = 9), to a low-dose ketotifen group (Group B; 1 mg/kg PO; n = 8) and a high-dose ketotifen group (Group C; 10 mg/kg; PO for 10 days; n = 9). Pulmonary resistance (RL) was measured at baseline, and every 15 min for up to 8 h after OA. The magnitude of the early response was 241 +/- 51% in A (% baseline RL; mean +/- SE), and significantly less in B(119 +/- 7%) and C(131 +/- 16%) (p < 0.01). The late response was significantly lower in C than A but not B. The total cell number in bronchoalveolar lavage at 8 h after OA challenge was significantly higher in A than B and C (p < 0.01). The lymphocyte and eosinophil counts were reduced in B and C compared to A (p < 0.05). A positive correlation was found between the late response and total number of cells recovered in the BAL (r = 0.78) (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The 5-lipoxygenase inhibitor zileuton blocks antigen-induced late airway responses, inflammation and airway hyperresponsiveness in allergic sheep

Leukotrienes are thought to be involved in allergen-induced airway responses. To test this hypothesis we used a newly described 5-lipoxygenase inhibitor, zileuton, and examined its effect on antigen-induced early and late bronchial responses, airway inflammation and airway hyperresponsiveness in allergic sheep. Early and late responses were determined by measuring specific lung resistance (SRL) before and serially for 8 h after antigen challenge. Airway inflammation was assessed by bronchoalveolar lavage performed before, 8 h after and 24 h after antigen challenge. Airway responsiveness was measured before and 24 h after challenge by determining the dose of inhaled carbachol that caused a 400% increase in SRL (PD400%). The sheep (n = 8) were challenged with Ascaris suum antigen once after vehicle treatment (methylcellulose) and once after treatment with zileuton (10 mg/kg in methylcellulose, p.o.) given 2 h before antigen challenge. Trials were separated by at least 21 days. Zileuton had no effect on the early bronchoconstrictor response to antigen but the drug inhibited the late bronchial response by 55% (P less than 0.05). Unlike the control trial, there was no significant increase in bronchoalveolar lavage eosinophils at 8 h post challenge in the zileuton-treated sheep. Furthermore, zileuton treatment blocked (P less than 0.05) the airway hyperresponsiveness seen 24 h after challenge. Ex vivo formation of leukotriene B4 was inhibited over several hours after a single oral dose of zileuton, indicating that the compound was acting as a 5-lipoxygenase inhibitor in vivo. These results suggest that 5-lipoxygenase metabolites contribute to allergen-induced late responses, airway inflammation and airway hyperresponsiveness in this animal model of asthma.

Pharmacological modulation of a model of bronchial inflammation after aerosol-induced active anaphylactic shock in conscious guinea pigs

Twenty-four hours after an active anaphylactic shock induced by inhalation of antigen in conscious guinea pigs sensitized by a large dose of ovalbumin in complete Freund's adjuvant, a noteworthy bronchial inflammation, characterized by increased numbers of neutrophils, mononuclear cells and eosinophils in the bronchoalveolar lavage fluid, was observed. Some drugs administered after the anaphylactic shock were investigated using this model. Disodium cromoglycate primarily reduced the number of mononuclear cells and eosinophils. Dexamethasone and theophylline decreased the number of eosinophils. Salbutamol and mepyramine increased neutrophils. Indomethacin did not give rise to any significant effect. This test appears to be of use for the investigation of anti-inflammatory compounds in the prophylactic treatment of asthma.

A bradykinin-antagonist blocks antigen-induced airway hyperresponsiveness and inflammation in sheep

The effects of a new bradykinin-antagonist, NPC-567 (D-Arg [hydroxyproline3, D-phenylalanine7] bradykinin) were studied on antigen-induced airway hyperresponsiveness and inflammation in allergic sheep (n = 7). Specific lung resistance (sRL) was used to assess airway responses to inhaled Ascaris suum-antigen. Airway responsiveness was determined from slopes of cumulative dose-response-curves (DRC) to inhaled carbachol. DRCs were performed at baseline and 2 h after an inhalation challenge with antigen. Bronchoalveolar lavage, performed before antigen-challenge and after the post-challenge DRC was used to assess antigen-induced inflammatory changes. For these studies NPC-567 was given as an aerosol (20 breaths, 10 mg/ml) 30 min before antigen challenge and (400 breaths, 2 mg/ml) co-administered with the Ascaris suum antigen. The immediate increase in specific lung resistance (sRL) after antigen challenge was not different with (232 +/- 152% increase) or without drug pre-treatment (148 +/- 129% increase). In the control trial, antigen challenge led to an increase in slope of the post-challenge DRC by 123 +/- 118% compared to baseline (p less than 0.05). This hyperresponsiveness was almost completely prevented by NPC-567 (increase in slope 32 +/- 64%, p less than 0.05 vs. control). Similarly, the antigen-induced inflammatory response, characterized by a significant 3.3-fold increase over baseline in the percentage of neutrophils in the control-experiment, was blocked by the bradykinin-antagonist. These results suggest that bradykinin may be involved in the pathogenesis of antigen-induced airway inflammation and the consequent development of airway hyperresponsiveness in sheep.

YM461, a PAF antagonist, blocks antigen-induced late airway responses and airway hyperresponsiveness in allergic sheep

We examined the effect of an orally active antagonist, YM461, of platelet activating factor (PAF) on antigen-induced early and late airway responses and on the development of airway hyperresponsiveness 24 h after challenge in allergic sheep. Early and late airway responses were determined by measuring specific lung resistance (SRL) before and periodically after challenge. Airway responsiveness was determined from the slopes of dose-response curves of SRL vs. increasing doses of carbachol aerosol. The sheep were challenged with Ascaris suum antigen once after vehicle treatment (control) and once 1 h after oral administration of 3 or 10 mg/kg YM461 (each trial was greater than or equal to 14 days apart). Airway responsiveness to carbachol was determined 1-3 days prior to and 24 h after antigen challenge. In control 1 and control 2 trials antigen challenge caused significant peak early (288 and 292%, respectively) and peak late (103 and 124%, respectively) increases over baseline in SRL. SRL returned to baseline 24 h after challenge but the sheep developed airway hyperresponsiveness as indicated by the 2.6-fold increases in the slopes of the carbachol dose-response curves in the control trials. YM461, 3 and 10 mg/kg p.o., significantly inhibited the late responses (66 and 82%, respectively) and blocked the development of airway hyperresponsiveness at 24 h. The early responses were not significantly reduced in either trial. These results suggest that PAF contributes to the antigen-induced late airway responses and associated airway hyperresponsiveness in allergic sheep.

Pharmacology of allergen-induced early and late airway responses and antigen-induced airway hyperresponsiveness in allergic sheep

The pharmacology of antigen-induced early and late phase airway responses and the associated antigen-induced airway hyperresponsiveness was studied in allergic sheep. Data from studies with anti-allergic agents and specific receptor antagonists, especially leukotriene antagonists and antagonists of platelet activating factor (PAF), have led to the hypothesis that allergen-induced late responses in allergic sheep are linked to a heightened metabolism of arachidonic acid via the 5-lipoxygenase pathway. This increases leukotriene production during the acute allergic reaction, which results in a more prolonged acute bronchoconstriction and subsequently a more severe airway inflammation. These recruited inflammatory cells can then release mediators and other cell products which contribute to the late response and airway hyperresponsiveness.

Effect of nedocromil sodium on antigen-induced airway responses in allergic sheep

We studied the effects of nedocromil sodium and sodium cromoglycate on early and late bronchial responses, the airway inflammation associated with the late response to inhaled Ascaris suum antigen in allergic sheep in vivo, and the antigen-induced contractile responses of sheep tracheal smooth muscle in vitro. In addition, we examined the effect of nedocromil sodium on the development of antigen-induced airway hyper-responsiveness in this model. Pretreatment with either nedocromil sodium or sodium cromoglycate was effective in blocking antigen-induced early and late responses in allergic sheep. Both drugs also prevented the influx of eosinophils into the airways as assessed by bronchoalveolar lavage, observed during the late response in this model. No difference in drug potency was observed in vivo, but in vitro nedocromil sodium was 10-fold more potent than sodium cromoglycate against antigen-induced contractions of sheep tracheal smooth muscle. Nedocromil sodium was effective in blocking antigen-induced late responses and the subsequent development of airway hyper-responsiveness irrespective of whether the drug was given before antigen challenge or after the immediate response to antigen but before the late response. These findings indicate that nedocromil sodium is effective in the sheep model of asthma and therefore may be beneficial in the treatment of reversible obstructive airway disease in man.