Airway allergy to trimellitic anhydride in guinea pigs: different time courses of IgG1 titer and airway responses to allergen challenge

Health Effects of Trimellitic Anhydride Occupational Exposure: Insights from Animal Models and Immunosurveillance Programs

Acid anhydrides are used by chemical industries as plasticizers. Trimellitic acid (TMA) is an acid anhydride widely utilized in factories to produce paints, varnishes, and plastics. In addition to causing direct irritant effects, TMA can augment antibody responses in exposed factory workers leading to occupational asthma. Therefore, industries producing TMA have implemented occupational immunosurveillance programs (OISPs) to ensure early diagnosis and medical management, involving exposure reduction/ complete removal of sensitized workers from exposure areas. Multiple animal models (mice strains, rat stains, guinea pig, swine) with different exposure patterns (dermal, nasal, vapor inhalation exposures for different time frames) have been described to elucidate the pathophysiology of TMA exposure. In TMA factories, in spite of implementing advanced environmental controls and personal protective measures to limit exposure, workers become TMA-sensitized. Animal models revealed sIgG, sIgE, sIgA, and sIgM along with pulmonary lesions, cellular infiltrates, alveolar hemorrhage, and pneumonitis associated with TMA exposure. Molecular studies showed involvement of specific functional gene clusters related to cytokine and chemokine responses, lung remodeling, and arginase function. However, thus far, there is no evidence supporting fetotoxic or carcinogenic effects of TMA. OISP data showed IgG and IgE responses in exposed factory workers. Interestingly, timelines for detectable sIgG response, in conjunction with its magnitude, have been shown to be a predictor for future sIgE response. OISPs have been very successful so far at creating a healthy and safe working environment for TMA-exposed factory workers. Graphical Abstract Trimellitic Acid (TMA), used to produce paints, varnishes and plastics, can cause irritant-mediated and immune-mediated occupational health problems. NCBI pubmed search indicated that multiple animal models (different animal types, with chronic vs. acute exposure type, using TMA dust/suspension applied via dermal or other routes) have been used by investigators to elucidate the pathobiology of TMA-exposure. Several outcomes have been measured including humoral, lung/ airway, lymph nodes and dermal/ ear thickening responses. Studies on human subjects have been conducted mostly as parts of Occupational immunosurveillance programs (OISPs) implemented to identify TMA-sensitized workers (using ImmunoCAP and Skin prick testing), monitoring them longitudinally and their medical management including exposure reduction/ complete removal of sensitized workers from exposure areas. Clinical management also includes identification of irritant-induced and/ or immune-mediated outcomes of TMA occupational exposure. Collectively, these studies have led to important insights into the pathomechanism of TMA-exposure and have been very successful at creating a safe working environment for TMA-exposed factory workers.

Immunologic effector mechanisms in animal models of occupational asthma

Occupational asthma is a form of immunotoxicity resulting from an exaggerated immune response to substances encountered in the workplace. Symptoms include reversible airway obstruction, airway hyperresponsiveness, airway remodeling, mucus production and cellular infiltration into the lung, particularly eosinophilia. The asthmatic response is divided into the induction phase, occurring after initial exposure to allergen, followed by the effector phase where a subsequent exposure to the allergen results in the respiratory symptoms. Animal models have been used to investigate the asthmatic response and this review will focus on mechanistic studies of the effector phase. Variables that may impact the effector phase include strain and species of animal, dose of allergen, route of exposure, and developmental stage of the animal. Both trimellitic anhydride (TMA) and ovalbumin are known causes of occupational asthma. Ovalbumin is also a reference protein allergen in immunology, and TMA is used as a prototype of a low molecular weight respiratory allergen. Differences in effector mechanisms for TMA and ovalbumin have been noted in different animal models. Studies in the guinea pig provide the most direct comparisons of effector mechanisms of TMA and ovalbumin, with differences in the role of the complement system and arachidonate metabolites being noted. Besides the guinea pig, the Brown Norway rat, and various mouse strains provide useful asthma models for TMA and ovalbumin. However, studies of effector mechanisms are somewhat lacking in either of these species using TMA as the allergen. Continued studies are indicated to determine if unique effector mechanisms can be identified for the many different causes of occupational asthma.

How long do the systemic and ventilatory responses to toluene diisocyanate persist in dermally sensitized mice?

BACKGROUND

Years after removal from exposure, workers with occupational asthma still show respiratory symptoms and airway hyperresponsiveness on re-exposure to the offending agent.

OBJECTIVE

We investigated the persistence of the respiratory responsiveness to toluene diisocyanate (TDI) in a mouse model.

METHODS

BALB/C mice received dermal applications of TDI on days 1 and 8, and a single intranasal instillation of TDI on day 10, 15, 20, 25, 30, 40, 50, 60, or 90. After instillation, early (1 hour) changes in ventilatory function and methacholine responsiveness (22 hours) were assessed. Cell counts and macrophage inflammatory protein 2 were measured in bronchoalveolar lavage. Total serum IgE, IgG(1), and IgG(2a) were quantified. Lymphocyte subpopulations were assessed in auricular and cervical lymph nodes, and release of IL-4 and IFN-gamma by these lymph node cells was measured.

RESULTS

Toluene diisocyanate-treated mice showed immediate ventilatory changes, increased methacholine reactivity, and an influx of neutrophils and macrophage inflammatory protein 2 in bronchoalveolar lavage as long as 50 days after initial treatment. These mice also showed a relative increase in CD19(+) cells and a decrease in CD4(+) and CD8(+) cells in auricular lymph nodes. Increased release of IL-4 and IFN-gamma in auricular lymph node cells was observed only until 20 days after sensitization. Total serum IgE, IgG(1), and IgG(2a) remained significantly elevated in TDI-sensitized mice until 90 days after dermal sensitization.

CONCLUSION

Ventilatory and lung inflammatory responses decrease with increasing delay between sensitization and challenge, despite persistent humoral signs of sensitization.

Animal models to test respiratory allergy of low molecular weight chemicals: a guidance

At present, there are no widely applied or fully validated test methods to identify respiratory LMW allergens, i.e. compounds that are considered capable of inducing allergic asthma. Most tests have been investigated using strong respiratory allergens. Moreover, they are meant to detect the potential of a chemical to induce respiratory sensitisation at relatively high doses. Consequently, the sensitivity of the tests is not well-known, and they do not provide information on low doses such as generally found in occupational situations, and on threshold levels to be used in risk assessment. In addition, the various test methods use different application routes, i.e. intradermal, topical or inhalation exposure, and different parameters. Therefore standardised and validated dose-response test methods are urgently required in order to be able to identify respiratory allergens and to recommend safe exposure levels for consumers and workers. In the present paper, methods or testing strategies are described to detect respiratory sensitisation and/or allergy. Overall, assays that utilize only an induction phase may serve as indicators of respiratory sensitisation potential whereas assays that use both an induction and an elicitation or challenge phase may provide information on potency and presence of thresholds. The dermal route as sensitisation route has the advantage of the respiratory tract not being exposed to the allergen prior to challenge which facilitates the distinction between irritant and allergic effects.

Maturational changes in airway remodeling after chronic exposure to ovalbumin in sensitized guinea pigs: role of cell renewal of airway resident cells

We wanted to know whether airway remodeling caused by chronic exposures to antigen differed depending on the degree of maturation of animals. We sensitized guinea pigs at different stages of maturation: juvenile (approximately 200 g in body weight), adult (400 g), and old animals (800 g). Then, animals were repeatedly challenged with inhaled ovalbumin (0.3% or 3%) or vehicle twice a week for 6 wk. After the final challenge, the lungs were excised for the histologic evaluation of changes in the thickness of the inner wall area (Ti), the smooth muscle area (Tm), and the outer wall area (To) in noncartilaginous airway dimensions. To clarify whether or not the observed changes were due to renewal of airway cells, we stained the samples with labeled nucleotide 5'-bromo-2'-deoxyuridine (BrdU), which we injected repeatedly during the challenge periods. Chronic exposures to antigen induced airway wall thickening regardless of their stages of maturation. However, prominent areas of thickening differed between the three groups. Ti increased more remarkably in juvenile and adult animals than in old ones. By contrast, Tm significantly increased only in old animals. BrdU staining revealed more renewal of epithelial cells in juvenile and adult animals than in old ones (juvenile >or=adult > old), suggesting that increased renewal of epithelial cells contributed to the thickening of Ti in juvenile and adult animals. By contrast, only a slight increase in smooth muscle cell renewal was found even in old animals, indicating that an increase in Tm was due to factors such as hypertrophy. These results show that the development of antigen-induced airway remodeling is partly modified by the degree of maturation of animals in vivo.

Trimellitic anhydride (TMA) dust induces airway obstruction and eosinophilia in non-sensitized guinea pigs

Trimellitic anhydride (TMA) causes asthma after a latency period of sensitization. In non-sensitized humans and animals, limited studies indicate that TMA exposure may also cause symptoms of asthma without a latency period. Our previous studies (J. Pharmacol. Exp. Ther. 296 (2001) 284) in a guinea pig model of TMA-induced asthma demonstrated that sensitization and the complement system were required for eosinophilia. TMA conjugated to guinea pig serum albumin (TMA-GPSA) was used to elicit the response. Since occupational exposure to TMA occurs by inhalation of dust, the present studies determined if exposure to TMA dust in a non-sensitized guinea pig elicited airway obstruction and inflammation, and whether a significantly greater response occurred after a latency period of sensitization. Guinea pigs were intradermally injected with either corn oil (non-sensitized animals) or 30% TMA (sensitized animals). Three weeks later they were challenged by intratracheal insufflation with 1 mg TMA dust or lactose dust (control) using a dry powder delivery device. Pulmonary resistance, dynamic lung compliance, mean arterial blood pressure and heart rate were monitored for 10 min. In non-sensitized guinea pigs, significant increases in pulmonary resistance and decreases in dynamic lung compliance and blood pressure occurred after TMA challenge. In sensitized animals, the same dose of TMA caused significantly greater effects compared to non-sensitized animals. In a separate experiment, cellular infiltration into the lung was determined 24 h after challenge with TMA dust or lactose dust. In both non-sensitized and sensitized animals, eosinophils in the lung tissue were increased after TMA dust challenge compared to controls. Thus, these studies suggest that the response in non-sensitized animals differs depending on whether TMA dust or TMA-GPSA is used to elicit the response. TMA dust elicits significant airway obstruction and eosinophilia in a non-sensitized animal, with even greater airway obstruction occurring in a sensitized animal.

Immunotoxicology of organic acid anhydrides (OAAs)

Organic acid anhydrides (OAAs) have considerable economic importance due to their extensive use in the production of alkyd, epoxy, and polyester resins. Occupational exposure to OAAs has been associated with a variety of health effects, which may be classified into two major categories of direct toxicity/irritant and hypersensitivity. The hypersensitivity diseases associated with OAA exposure are thought to be related to the reactivity of these chemicals and in particular their ability to form protein conjugates that may be recognized as neo-antigens by the immune system. This review will present a brief discussion of the basic chemistry of these compounds and the environmental and biological monitoring methods used for exposure measurements. The clinical syndromes associated with exposure to these compounds will be discussed along with factors that may affect disease susceptibility. Finally, animal models that have been developed to examine the mechanisms of disease will be discussed.

Trimellitic anhydride-induced cellular infiltration into Guinea pig lung varies with age but not gender

BACKGROUND

In humans the incidence of asthma changes with age and gender. Immature guinea pigs have been used to model the allergic response to the occupational allergen trimellitic anhydride (TMA) where exposure to adults is paramount. We hypothesized that the TMA-induced allergic response in immature guinea pigs was similar to mature animals, regardless of gender.

METHODS

Sexually immature and mature female and male guinea pigs were sensitized intradermally with TMA. Three weeks after sensitization they were challenged intratracheally with TMA conjugated to guinea pig serum albumin (TMA-GPSA) or GPSA as a control. Twenty-four hours later cell infiltration into the lung was determined. TMA-specific IgG(1) and IgG(2) were measured in plasma and the complement activation product C3a was measured in the bronchoalveolar lavage fluid.

RESULTS

In control animals, numbers of eosinophils and neutrophils varied with age and gender. The TMA-GPSA- induced cellular infiltration was similar in all age/gender groups. However, neutrophils in the lung tissue increased only in immature animals. IgG antibodies differed between groups but did not account for differences in cell infiltration. C3a correlated with the extent of cell infiltration in all groups except mature females.

CONCLUSIONS

TMA-induced neutrophilia differs with age. TMA-induced changes in eosinophils and macrophages did not vary with age or gender. The relationship between complement activation and inflammation in mature females differs from that in the other groups, suggesting mediators of the response may change with age and gender. Effects of age and gender need to be considered in animal models of the allergic response.

The role of IgG1 and IgG2 in trimellitic anhydride-induced allergic response in the guinea pig lung

Trimellitic anhydride (TMA) is a small molecular weight chemical used in the paint and plastics industry that can cause asthma-like symptoms in humans. Guinea pigs sensitized intradermally with TMA will respond to antigen challenge with asthma-like symptoms, including an immediate bronchoconstriction and a delayed cellular infiltration into the lung, particularly eosinophil infiltration. Sensitized guinea pigs produce TMA-specific IgG1, which is thought to be important in asthmatic reactions in this animal model; however, they also produce TMA-specific IgG2 antibody. The purpose of the present study was to determine the role of IgG1 and IgG2 in the TMA-induced immediate bronchoconstriction and delayed cellular infiltration in the guinea pig. Guinea pigs were passively sensitized by intratracheal instillation of TMA-specific IgG2, an antibody preparation enriched with TMA-specific IgG1, or a combination of the two. The allergic response was induced by intratracheal instillation of TMA conjugated to guinea pig serum albumin (TMA-GPSA). A significantly greater bronchoconstrictor response was observed in animals sensitized with a combination of the IgG2 and IgG1 preparation compared to those sensitized with IgG2 or the IgG1 preparation alone. Cellular infiltration was quantified 24 h after antigen challenge by differential cell counts of bronchoalveolar lavage (BAL) cells as well as by using eosinophil peroxidase (EPO) and myeloperoxidase (MPO) activity as a measure of the numbers of eosinophils and neutrophils, respectively. In the BAL, passively sensitizing with IgG2 alone resulted in an increase in both TMA-induced MPO and EPO activity. In contrast, in the lung, passively sensitizing with a partially purified preparation of TMA-specific IgG1 alone resulted in a significant increase in TMA-induced EPO activity. Passively sensitizing with IgG2 in conjunction with the IgG1 preparation resulted in an enhanced cellular infiltration and lung injury over that seen with either antibody preparation alone. These data demonstrate an augmentation of IgG1-mediated responses by the addition of IgG2 and suggest a significant role for both subclasses of IgG antibodies in this guinea pig model of TMA-induced occupational asthma.

Relationship between IgG1 levels and airway responses in guinea pigs actively and passively sensitized to hexahydrophthalic anhydride

Organic acid anhydrides (OAAs) are industrial chemicals that may cause induction of specific IgE and airway symptoms in exposed workers. They are a good model for studies of relationships between chemical structure and the sensitizing potential of reactive low-molecular-weight compounds. Hexahydrophthalic anhydride (HHPA) is such a compound. This study aimed to evaluate the relationship between specific IgG1 levels and airway responses in a model to predict the sensitizing potential of OAAs. Guinea pigs were either actively or passively sensitized to HHPA. For active sensitization, guinea pigs were injected i.d. with 0.1 ml of olive oil (vehicle) or 0.05, 0.5, or 5% HHPA in olive oil. Passive sensitization was performed by i.p. injection of different volumes of antisera (0.75-6 ml, either unheated to keep IgE or heated to destroy IgE) taken from HHPA-sensitized guinea pigs. Specific antibody levels were evaluated with ELISA and passive cutaneous anaphylaxis. Animals were challenged 16-18 days after active sensitization, or 2 days after passive sensitization, by intratracheal instillation with HHPA conjugated to guinea pig serum albumin (HHPA-GPSA; 0.05% in saline), and the immediate effects on lung resistance (RL), and plasma extravasation, measured as Evans blue dye extravasation, for up to 6 min were recorded. Active sensitization caused production of specific IgG1. Provocation with HHPA-GPSA caused an increase of both RL and Evans blue dye extravasation, which was dependent upon the active sensitization dose. Challenge with HHPA-GPSA in passively sensitized guinea pigs also produced an increase in both RL and Evans blue dye extravasation which was related to the IgG1 level. In the guinea pig model of HHPA-induced airway allergy, the airway responses are closely related to the serum levels of specific IgG1. Thus, the IgG1 levels induced by the immunization may reflect the sensitizing potential of HHPA.

Bronchial hyperresponsiveness, epithelial damage, and airway eosinophilia after single and repeated allergen exposure in a rat model of anhydride-induced asthma

Bronchial hyperresponsiveness (BHR) and damage of the epithelium, as well as eosinophilia in the airway wall, induced by trimellitic anhydride (TMA) in sensitized brown Norway rats were studied. Rats were challenged once or seven times with aerosol of TMA conjugated to rat serum albumin (TMA-RSA) 3 weeks after intradermal TMA sensitization. Airway responsiveness (-log PC300 of acetylcholine i.v.) was measured 24 h after allergen challenge. Epithelial lesion and eosinophil infiltration in the airway walls were quantified under light microscopy, and TMA-specific IgE and IgG in serum were evaluated with ELISA. High levels of TMA-specific IgE and IgG were found in all rats in the sensitized groups compared to nonsensitized groups (P < 0.001). Repeated allergen challenges of 0.03% TMA-RSA for 7 consecutive days enhanced the level of TMA-specific IgG, compared to single challenge (P < or = 0.05). Single allergen challenge of 0.3% TMA-RSA had a nonsignificant tendency to produce BHR in sensitized rats compared to nonsensitized rats (P = 0.06). However, repeated allergen challenges (0.003% and 0.03% TMA-RSA for 7 consecutive days) produced significant BHR in sensitized rats (P < 0.05). Furthermore, repeated low-dose (0.003%) TMA-RSA challenge produced more BHR than a 10 times higher single dose (0.03%) (P < 0.05). Slight damage of the airway epithelium was seen in sensitized and repeat-challenged groups. However, bronchial eosinophilia was found in the sensitized and single-challenged groups, but not in nonsensitized nonchallenged, and sensitized repeat-challenged groups (P < 0.005). We conclude that the brown Norway rat can be sensitized with TMA, and that repeated low-dose allergen challenges produce slight epithelial damage and BHR which is independent of ongoing eosinophilia in the airway wall.

Antibody specificity to the chemical structures of organic acid anhydrides studied by in-vitro and in-vivo methods

The objective of the study was to evaluate the structure-activity relationship for the antigenic activity of different organic acid anhydrides (OAAs). The specificity of guinea pig (GP) IgG1 to different anhydrides was studied by ELISA-inhibition, PCA, and airway provocation tests of cross-reactivity with different OAA conjugates. In the airway provocation tests, lung resistance and plasma extravasation of Evan's Blue dye was measured. The ELISA-inhibition tests showed a wide range in antibody specificity. Modelling of ring configuration, methyl group substitution, double bond position, and cis/trans isomerism of anhydride forming carboxyl groups influenced the specificity. There was a general consistency in cross-reactivity of anti-cis-hexahydrophthalic anhydride IgG1 versus GP serum albumin conjugates of trans-hexahydrophthalic anhydride, phthalic anhydride, and succinic anhydride as shown by ELISA-inhibition, PCA, and airway provocation tests. It is concluded that various modifications of the chemical structures of a hapten are recognized by the hapten-specific antibodies, and that these differences may have clinical relevance. In particular, the ring structure and the positions of double bonds and of methyl groups are important. Further, the in-vitro ELISA-inhibition tests show a good agreement with the in-vivo PCA and bronchial provocation tests.

Anaphylactic bronchoconstriction in immunized guinea pigs provoked by inhalation and intravenous administration of hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride

We established a guinea-pig model of anaphylactic bronchoconstriction provoked in immunized animals by inhalation and intravenous administration of 4,4-methyltetrahydrophthalic anhydride (MTHPA) and hexahydrophthalic anhydride (HHPA). Guinea pigs were immunized intradermally with either MTHPA (n = 8) or HHPA (n = 8) suspended in olive oil. Control animals (n = 8) were injected with olive oil alone. After 4 weeks, the animals were challenged during mechanical ventilation by inhalation or intravenous administration of MTHPA or HHPA conjugated with guinea-pig serum albumin (GPSA). Airway flow, and airway and esophageal pressures were measured. Resistance (R) and static compliance (Cst) of the respiratory system (rs), lung (1), and chest wall were studied with the flow-interruption technique. After challenge with MTHPA-GPSA or HHPA-GPSA, R,rs and R,1 increased dramatically while Cst,rs and Cst,1 decreased, and severe arterial hypoxia developed. The reaction occurred at a well-defined dose of anhydride and lasted about 30 min. When the same dose was repeated after 30 min, the response was much attenuated. MTHPA and HHPA can induce asthma in guinea pigs. The dose-response curve at antigen challenge is steep. Once a threshold dose is reached, a severe reaction occurs. The reactivity is then exhausted. This model may be suitable for assessing occupational asthma caused by acid anhydrides and possibly by other low-molecular-weight chemicals.

Inflammatory responses in skin and airways after allergen challenge in brown Norway rats sensitized to trimellitic anhydride

Trimellitic anhydride (TMA) is a low-molecular-weight compound which causes occupational allergy. Brown Norway rats were sensitized to TMA injected intradermally (0.3% TMA suspended in oil). Three weeks later, we examined responses to either free TMA injected intradermally, or TMA conjugated to rat serum albumin (TMA-RSA) given by inhalation (0.5%, nebulized for 15 min). Twenty-one days after the sensitization, Evans blue dye was given i.v. (20 mg/kg), and extravasation of dye in skin was measured 30 min after oil or TMA injections (0.03-10% in oil). In a separate series of experiments, we evaluated the accumulation of eosinophils in the skin after single and repeated injections of TMA (0.03-0.3%). The injection sites were removed and fixed in formalin 18-24 h after the last injection. In a third series of experiments, we evaluated the effects of airway exposure to TMA-RSA (0.5% in 0.9% saline) on the accumulation of eosinophils in the bronchial wall counted with quantitative light microscopy. Intradermal injections of free TMA caused a dose-dependent increase of Evans blue dye extravasation which was significantly higher in sensitized animals than in controls. Skin histology revealed a significant and dose-dependent increase in eosinophils after repeated TMA injections in sensitized animals. Exposure to aerosolized TMA-RSA caused a significant increase of eosinophils in the bronchial wall of sensitized rats compared with nonsensitized rats. Sensitized animals showed significantly higher levels of specific IgG and IgE. We conclude that brown Norway rats can be used as a model of TMA-induced allergic inflammation, mimicking occupational asthma.

Induction of nitric oxide synthase in a model of allergic occupational asthma

We have studied the induction of nitric oxide during late allergic responses, using a guinea pig model of trimellitic anhydride (TMA)-induced airway allergy. TMA is a low molecular weight chemical which can cause occupational asthma. The activity of nitric oxide synthase (NOS) was investigated by the detection of 3H-labeled citrulline formation from 3H-labeled arginine. In sensitized animals, challenge with TMA conjugated to guinea pigs albumin (TMA-GPSA) increased the activity of Ca(2+)-independent NOS (inducible NOS; iNOS) in lung and bronchial tissues at 15-17 h after challenge compared to nonsensitized animals. The induction of iNOS activity was associated with an associated with an increased level of nitrite, an end metabolite of the l-arginine-NO pathway, in bronchoalveolar lavage fluid. In contrast to iNOS, the activity of Ca(2+)-dependent NOS (constitutive NOS; cNOS) was not affected by the allergen challenge. These results demonstrate that iNOS in bronchial tissue is induced late after allergen challenge in sensitized guinea pig.

Treatment with cyclosporin A during sensitization with trimellitic anhydride attenuates the airway responses to allergen challenge three weeks later

The present studies examined the effects of oral treatment with cyclosporin A, betamethasone or azelastine administered over the time of sensitization with trimellitic anhydride on allergen-induced airway responses, compared to those of control animals given corn oil alone. Drugs were given for 8 days. The animals were sensitized with trimellitic anhydride (0.1 ml of 0.3% w/v) in corn oil given intradermally on days 4 and 5 of drug treatment. Three to four weeks after sensitization with free trimellitic anhydride, the animals were anesthetized, tracheostomized and challenged with trimellitic anhydride conjugated to guinea pig serum albumin (trimellitic anhydride-guinea pig serum albumin; 0.5%; 50 microliters) instilled via the airway route. In the same animal, we measured both lung resistance (RL) to monitor airflow obstruction, and extravasation of Evans Blue dye (20 mg/kg) to quantify airway plasma exudation. In control animals, instillation of trimellitic anhydride-guinea pig serum albumin into the tracheal lumen caused a slowly progressing increase in RL over the observation period (6 min), in addition to extravasation of Evans Blue dye at all airway levels. In animals treated with 50 mg/kg of cyclosporin A, both the allergen-induced increase in RL and extravasation of Evans Blue dye in intrapulmonary airways were significantly attenuated. However, neither betamethasone nor azelastine significantly affected these responses. We conclude that cyclosporin A may influence the immune system in the guinea pig during the induction of allergy, thus leading to attenuation of allergen-induced airway obstruction at later time points.