Reproducibility of early and late asthmatic responses to allergen challenge in a large group of asthmatics

EAACI position paper on the clinical use of the bronchial allergen challenge: Unmet needs and research priorities

Allergic asthma (AA) is a common asthma phenotype, and its diagnosis requires both the demonstration of IgE-sensitization to aeroallergens and the causative role of this sensitization as a major driver of asthma symptoms. Therefore, a bronchial allergen challenge (BAC) would be occasionally required to identify AA patients among atopic asthmatics. Nevertheless, BAC is usually considered a research tool only, with existing protocols being tailored to mild asthmatics and research needs (eg long washout period for inhaled corticosteroids). Consequently, existing BAC protocols are not designed to be performed in moderate-to-severe asthmatics or in clinical practice. The correct diagnosis of AA might help select patients for immunomodulatory therapies. Allergen sublingual immunotherapy is now registered and recommended for controlled or partially controlled patients with house dust mite-driven AA and with FEV1 ≥ 70%. Allergen avoidance is costly and difficult to implement for the management of AA, so the proper selection of patients is also beneficial. In this position paper, the EAACI Task Force proposes a methodology for clinical BAC that would need to be validated in future studies. The clinical implementation of BAC could ultimately translate into a better phenotyping of asthmatics in real life, and into a more accurate selection of patients for long-term and costly management pathways.

Allergen Provocation Tests in Respiratory Research: Building on 50 Years of Experience

Allergen provocation test is an established model of allergic airway diseases, including asthma and allergic rhinitis, allowing the study of allergen-induced changes in respiratory physiology and inflammatory mechanisms in sensitised individuals as well as their associations. In the upper airways, allergen challenge is focused on the clinical and pathophysiological sequelae of the early allergic response and applied both as a diagnostic tool and in research settings. In contrast, the bronchial allergen challenge has almost exclusively served as a research tool in specialised research settings with a focus on the late asthmatic response and the underlying type 2 inflammation. The allergen-induced late asthmatic response is also characterised by prolonged airway narrowing, increased non-specific airway hyperresponsiveness and features of airway remodelling including the small airways, and hence, allows the study of several key mechanisms and features of asthma. In line with these characteristics, the allergen challenge has served as a valued tool to study the crosstalk of the upper and lower airways and in proof of mechanism studies of drug development. In recent years, several new insights into respiratory phenotypes and endotypes including the involvement of the upper and small airways, innovative biomarker sampling methods and detection techniques, refined lung function testing as well as targeted treatment options, further shaped the applicability of the allergen provocation test in precision medicine. These topics, along with descriptions of subject populations and safety, in line with the updated GINA2021, will be addressed in this paper.

Comparison of bronchial and nasal allergen provocation in children and adolescents with bronchial asthma and house dust mite sensitization

BACKGROUND

Bronchial allergen provocation (BAP) is an established tool for the diagnosis of allergy in patients with asthma, but its use is limited by the potential risk of severe asthmatic reactions. Nasal provocation testing (NPT) may be an alternative safe method and does not require sophisticated equipment.

OBJECTIVE

The aim of this prospective study was to evaluate the concordance of both methods in patients with asthma and house dust mite (HDM) sensitization.

METHODS

A total of 112 patients with HDM sensitization underwent BAP and had the following parameters analysed: decrease in FEV1, exhaled NO, and total and specific IgE. Within 12 weeks, NPT with HDM was performed in 74 patients with a median age of 9 years (range, 5-16 years). The results were evaluated using the Lebel score which quantifies major symptoms like rhinorrhea, nasal obstruction, sneezes and minor symptoms, such as pruritus, conjunctivitis and pharyngitis.

RESULTS

Fifty-seven of 74 patients had an early asthmatic reaction, of which 41 were identified using the Lebel score. The Lebel score had a sensitivity of 71.9% and a positive predictive value (PPV) of 89.1%. In addition, an eNO ≥ 10 ppb (AUC 0.78), a specific IgE Dermatophagoïdes pteronyssinus ≥ 25.6 kU/L (AUC 0.76) and a specific IgE Dermatophagoïdes farinae ≥ 6.6 kU/L (AUC 0.78) were good predictors of an early asthmatic reaction.

CONCLUSION

A sequential use of NPT prior to BAP is justified to establish the relevance of HDM allergy. In patients with a negative NPT, BAP is still recommended to rule out a HDM-induced asthmatic reaction.

Inhaled allergen bronchoprovocation tests

The allergen bronchoprovocation test is a long-standing exacerbation model of allergic asthma that can induce several clinical and pathophysiologic features of asthma in sensitized subjects. Standardized allergen challenge is primarily a research tool, and when properly conducted by qualified and experienced investigators, it is safe and highly reproducible. In combination with validated airway sampling and sensitive detection techniques, allergen challenge allows the study of several features of the physiology of mainly TH2 cell-driven asthma in relation to the kinetics of the underlying airway pathology occurring during the allergen-induced late response. Furthermore, given the small within-subject variability in allergen-induced airway responses, allergen challenge offers an adequate disease model for the evaluation of new (targeted) controller therapies for asthma in a limited number of subjects. In proof-of-efficacy studies thus far, allergen challenge showed a fair positive predicted value and an excellent negative predictive value for the actual clinical efficacy of new antiasthma therapies, underscoring its important role in early drug development. In this review we provide recommendations on challenge methods, response measurements, sample size, safety, and harmonization for future applications.

Increase in allergen-specific IgE and ex vivo Th2 responses after a single bronchial challenge with house dust mite in allergic asthmatics

BACKGROUND

  Airway responsiveness to allergen in patients with allergic asthma is studied by bronchial allergen challenge. Although the typical features of the early and late responses on lung function and bronchial inflammation after allergen challenge are well known, little has been reported as yet on any changes in systemic allergic and immunologic parameters after 4-6 weeks.

METHODS

  In a clinical study, 27 subjects with allergic asthma and house dust mite (HDM) allergy underwent a bronchial allergen challenge with HDM. Blood samples were collected before and 5 weeks after allergen challenge. Serum levels of total IgE and allergen-specific IgE were measured, and peripheral blood mononuclear cells were isolated and stimulated ex vivo with HDM to determine the allergen-specific T-cell cytokine response.

RESULTS

  Five weeks after bronchial allergen challenge with HDM, the amount of circulating IgE against HDM and the major allergenic components Der p1 and Der p2 was significantly increased (10.8% and 8.8%, respectively). IgE antibodies against other environmental allergens decreased (grass pollen) or remained unchanged (cat dander). Allergen-induced Th2-cytokine production was also significantly increased (P< 0.001, P=0.014, and P=0.006 for IL-4, IL-5, and IL-13, respectively). The increase in Der p1- and Der p2-specific IgE in serum correlated with increased numbers of Th2-cytokine-producing cells (Rs=0.56, P=0.002 and Rs=0.54, P=0.004 for IL-4 and IL-13, respectively).

CONCLUSIONS

  A single bronchial allergen challenge with HDM is accompanied by increased levels of allergen-specific IgE for HDM in serum and an enhanced Th2 response to HDM still detectable 5 weeks after challenge.

Magnitude of late asthmatic response to allergen in relation to baseline and allergen-induced sputum eosinophilia in mild asthmatic patients

BACKGROUND

Late asthmatic response (LAR) to allergen challenge is a validated method for studying the pathogenesis of and new treatments for asthma in the laboratory.

OBJECTIVE

To evaluate the relationship between the magnitude of allergen-induced LAR and clinical and biological determinants, including sputum and blood eosinophil percentages and eosinophil cationic protein concentrations.

METHODS

Thirty-eight untreated mild asthmatic patients (mean age, 21.2 years) were selected for the presence of allergen-induced early asthmatic response (EAR) and LAR. Each patient measured methacholine responsiveness (provocation dose that caused a decrease in forced expiratory volume in 1 second of 20% [PD20FEV1]) at baseline, differential blood cell counts and eosinophil cationic protein levels in blood and induced sputum, and serum neutrophil chemotactic activity at baseline and 24 hours after allergen challenge.

RESULTS

A correlation was found between LAR (as area under the curve [AUC]) and sputum eosinophil percentages at baseline (r = 0.51; P = .001) and 24 hours after allergen challenge (r = 0.44; P < .007). Furthermore, we found significant correlations between AUC LAR and AUC EAR, baseline methacholine PD20FEV1, baseline blood eosinophil percentages, and baseline serum neutrophil chemotactic activity. A stepwise multiple regression analysis showed that the stronger determinants of AUC LAR were baseline sputum eosinophilia and AUC EAR.

CONCLUSION

Baseline sputum eosinophilia and functional findings are determinants of the magnitude of allergen-induced LAR.

Inhaled formaldehyde exposure: effect on bronchial response to mite allergen in sensitized asthma patients

BACKGROUND

Formaldehyde, an indoor air pollutant, is known to be an irritant and an etiologic factor in occupational asthma. An epidemiologic study suggests that it may also increase the risk of childhood asthma for concentrations above 60 microg/m(3).

AIM

To evaluate the influence of pre-exposure to low-dose formaldehyde (100 microg/m(3) in 30 min according to the World Health Organization's recommended maximum value for indoor environments) on bronchial response to Dermatophagoides pteronyssinus.

METHOD

Nineteen asthmatic subjects were included. Each subject underwent a mite allergen bronchial challenge test immediately after a standardized exposure in a chamber to formaldehyde or air (random order). Induced sputum were collected 24 h before and after mite challenge.

RESULTS

After formaldehyde inhalation, patients developed an immediate bronchial response at a significantly lower dose of mite allergen than after air exposure (the geometric mean PD(20) for Der p 1 was 34.3 ng after formaldehyde and 45.4 ng after placebo, P = 0.05). The late-phase reaction, expressed as the maximum fall in forced expiratory volume in 1 s (FEV(1)) from baseline, was significantly higher after formaldehyde (15%vs 11%, P = 0.046).

CONCLUSION

Our study demonstrated that exposure to low levels of formaldehyde significantly enhanced bronchial responsiveness to mite allergen in mite-sensitized subjects with asthma.

Impact of a soluble phospholipase A2 inhibitor on inhaled allergen challenge in subjects with asthma

The possible roles of secretory phospholipases A2 (sPLA2) in asthma include the release of arachidonic acid from cellular membranes, generation of lysophospholipids, sPLA2-mediated activation of cPLA2 with increased leukotriene production, and surfactant degradation. LY333013 is a potent inhibitor of sPLA2. This study examined the impact of two doses of LY333013 vs. placebo on allergen-induced bronchoconstriction following inhaled allergen challenge in atopic asthmatics. Fifty subjects were randomly assigned to treatment, and 40 subjects completed the study. A double-blind, placebo-controlled, random order, crossover study design was used. LY333013 had no impact on the primary outcome variables of the areas under the FEV1 response curve early (0-3 hours) (AUC(early)) and late (3-8 hours) (AUC(Iate)) following inhaled allergen challenge. No significant drug-related adverse effects were observed. The response to inhaled allergen challenge was reproducible and confirms the utility of this technique as a model in which to screen compounds for further testing in asthmatic patients.

One week treatment with salmeterol does not prevent early and late asthmatic responses and sputum eosinophilia induced by allergen challenge in asthmatics

Salmeterol is an effective long-acting beta(2)-agonist bronchodilator, able to inhibit, as a single dose, asthmatic responses induced by several stimuli including allergen, and the subsequent increase in sputum eosinophilia. Aim of the present study was to investigate whether these effects of salmeterol persisted after 1 week of continuous treatment, or whether a loss of the bronchoprotective effects of salmeterol can occur over time. We investigated in a cross-over double blind placebo-controlled study, the protective effect of 1 week treatment with salmeterol on allergen-induced early and late responses and the associated airway inflammation in 15 atopic asthmatic subjects. Eosinophil percentage and Eosinophil Cationic Protein (ECP) concentration in peripheral blood and in hypertonic saline induced sputum were measured at baseline and 24 h after allergen inhalation. Salmeterol partially inhibited early asthmatic response, but it did not inhibit late asthmatic response in comparison with placebo. Salmeterol did not inhibit also the increase in sputum eosinophils percentage 24 h after allergen inhalation (E%, median: 22.7 and 15%, after placebo and after salmeterol respectively, p=n.s. between two post-allergen sputum samples). Also, the increase in blood eosinophils and both sputum and serum ECP at 24 h after allergen challenge was not affected by salmeterol pre-treatment. In conclusion, 1 week treatment with salmeterol causes a loss of its protective effect on allergen-induced airway bronchoconstriction, and does not prevent the subsequent increase in sputum and serum eosinophilic markers.

Tolerance to the protective effect of salmeterol in mild untreated asthmatics

The aim of this study was to assess the distribution of the occurrence of tolerance to the protective effect of salmeterol on allergen challenge in a large sample of asthmatic subjects. We investigated 53 subjects (45 male and eight female), mean age 24+/-8.2 years, with mild intermittent asthma, in stable phase of the disease, never previously treated with regular beta2-agonists. All subjects with a previous positive early airway response (EAR) to a screening allergen challenge underwent, in double blind randomized, cross-over manner, three further allergen challenges: after placebo (T0), after a single dose (50 microg) of inhaled salmeterol (T1), and after regular treatment with inhaled salmeterol (50 microg bid) for 1 week (T2). All subjects showed an EAR after placebo treatment (T0), and were completely protected against EAR by the single dose of salmeterol (T1). After 1-week regular treatment with salmeterol (T2). 24 out of 53 subjects (45%) were still protected, whereas 29 subjects (55%) showed a significant EAR. The distribution of the response to allergen challenge, which was quite homogeneous at T0 and T1, showed considerable heterogeneity at T2. Tolerance to the protective effect of salmeterol on allergen challenge can be observed in a large group of previously untreated mild asthmatic subjects. This phenomenon is heterogeneously distributed, with some subjects still showing a complete protection similar to that obtained after a single dose of salmeterol and others showing a response similar to that obtained after placebo. The reason of this heterogeneity needs to be elucidated.

Ozone exposure increases eosinophilic airway response induced by previous allergen challenge

We investigated whether exposure to ozone (O(3)) 24 hours after an allergen challenge test would increase airway eosinophilia induced by allergen in subjects with mild asthma with late airway response. Twelve subjects with mild atopic asthma participated in a randomized, single-blind study. Subjects underwent allergen challenge 24 hours before a 2 hour exposure to O(3) (0.27 ppm) or filtered air. Pulmonary function was monitored during the allergen challenge and after the exposure to O(3) or air. Six hours later, induced sputum was collected. After 4 weeks, the experiment was repeated with the same subjects. Allergen induced a comparable late airway response in both challenges. O(3) exposure induced a significant decrease in FVC, FEV(1), and vital capacity, and was associated with a significant increase in total symptom score compared with air exposure. The percentage of eosinophils, but not the percentage of neutrophils, in induced sputum was significantly higher after exposure to O(3) than after exposure to air (p = 0.04). These results indicate that O(3) exposure after a late airway response elicited by allergen challenge can potentiate the eosinophilic inflammatory response induced by the allergen challenge itself in subjects with mild atopic asthma. This observation may help explain the synergistic effect of air pollution and allergen exposure in the exacerbation of asthma.

Natural exposure to pollen reduces the threshold but does not change the pattern of response to the allergen in allergic subjects

It is known that exposure to seasonal allergen in sensitized asthmatics increases non-specific bronchial responsiveness, but it is controversial if exposure to seasonal allergen influences the presence and the severity of the late asthmatic response (LAR) to allergen. Fifteen asthmatic subjects sensitized to grass pollen performed a specific bronchial provocative test (sBPT) with Phleum pratensis extract before and during the pollen season. Changes of methacholine were also assessed. Allergen PD20FEV1 significantly decreased during the pollen season with respect to outside (allergen PD20FEV1, geometric mean: 0.10 vs. 0.23 biological units; P < 0.05), but the pattern of specific airway response did not change. Particularly, a consistent LAR was observed in three subjects outside the pollen season and in two subjects during the pollen season. Seven subjects with isolated early asthmatic response (EAR) outside the season did not show LAR after allergen inhalation during the pollen season. However, four of five subjects with slight LAR outside the pollen season (deltaFEV1% between 15 and 20%) lost LAR during season. Methacholine sensitivity increased slightly but significantly from outside to during the pollen season. This increase was greater in subjects with LAR outside the pollen season. The natural exposure to pollen induces an increase in bronchial sensitivity to allergen in sensitized subjects, but it does not induce LAR in subjects without LAR outside the pollen season.