The Journal of Allergy and Clinical Immunology
Volume 102, Issue 6 , Pages 927-934, December 1998

Effect of rush immunotherapy on airway inflammation and airway hyperresponsiveness after bronchoprovocation with allergen in asthma☆☆☆★

Tokyo and Kanagawa, Japan

Received 18 May 1998; received in revised form 17 July 1998; accepted 3 August 1998.

Article Outline

Abstract 

Background: Rush immunotherapy (RIT) has been shown to be effective in allergic asthma. Objective: We investigated the mechanisms of RIT on the basis of cytokine production by T-cell lines and airway inflammation and responsiveness. Methods: Subjects were 8 patients with house dust mite–allergic asthma treated with dust mite extract RIT for 6 months and 6 RIT-untreated control patients. IL-5 production by Dermatophagoides farinae –specific T-cell lines, eosinophil percentages, and eosinophil cationic protein (ECP) in induced sputum and airway responsiveness to allergen and histamine were evaluated before and after treatment. Changes in eosinophil percentages and ECP in induced sputum and responsiveness to histamine 24 hours after allergen inhalation were also studied. Results: After 6 months of RIT, percentages of total eosinophils (43.0% ± 6.90% to 16.8% ± 2.48%; P < .01), percentages of EG2+ eosinophils (32.6% ± 6.39% to 19.7% ± 4.68%; P < .01) and ECP (362.7 ± 125.3 ng/mL to 26.2 ± 5.15 ng/mL; P < .05) decreased in induced sputum, and IL-5 production by T-cell lines decreased (617 ± 93.2 pg/mL to 200.0 ± 34.1 pg/mL; P < .01). RIT decreased both early- and late-phase bronchoconstriction (early phase: 33.2% ± 3.46% to 25.4% ± 1.42%; P < .03; late phase: 16.2% ± 3.52% to 6.2% ± 1.96%; P < .03) and suppressed increases in the percentages of total (61.8% ± 4.89% to 42.0% ± 4.67%; P < .01) and EG2-positive eosinophils (55.54% ± 7.21% to 36.5% ± 6.43%; P < .01) and ECP (685.6 ± 217.0 ng/mL to 85.4 ± 23.4 ng/mL; P < .05) in induced sputum after allergen inhalation. RIT also decreased airway responsiveness to dust mite (1:303.7 ± 123.7 wt/vol to 1:65.0 ± 13.2 wt/vol; P < .03) and to histamine before (397.1 ± 206.9 μg/mL to 1391.3 ± 283.3 μg/mL; P < .03) and after allergen inhalation (139.2 ± 36.5 μg/mL to 629.1 ± 196.3 μg/mL; P < .03). Conclusion: RIT decreases airway inflammation and airway hyperresponsiveness before and after bronchial provocation with allergen, possibly by inhibiting both allergen-specific T-cell– and mast cell-dependent pathways. RIT is an effective antiinflammatory treatment in allergic asthma. (J Allergy Clin Immunol 1998;102:927-34.)

Keywords:  Asthma, rush immunotherapy, T H2 cell, mast cell, IL-5, eosinophil, airway inflammation, airway hyperresponsiveness, late asthmatic response

Abbreviations:  DM: , Dust mite, EAR: , Early asthmatic response, ECP: , Eosinophil cationic protein, LAR: , Late asthmatic response, PEF: , Peak expiratory flow, RIT: , Rush immunotherapy, TH : , T helper

 

Allergen-specific immunotherapy is effective against allergic diseases; however, its precise mechanism of action is not completely understood. Although a recent metaanalysis of 20 double-blind, placebo-controlled studies showed that immunotherapy significantly improves the control of asthma, other reports suggest that immunotherapy is not effective.1, 2, 3, 4

Bronchial provocation with allergens in patients with sensitized asthma is useful for studying asthma.5 Exposure of sensitized patients to allergen decreases FEV1 in less than 1 hour. This early asthmatic response (EAR) results from mast-cell degranulation induced by the cross-linking of allergen-specific IgE bound to high-affinity IgE receptors on the surface of mast cells. EAR characteristically resolves in less than 1 to 2 hours and is followed by a longer late asthmatic response (LAR) in approximately one half of patients with allergic asthma. The LAR has been suggested to be associated with the recruitment of eosinophils into the airway by a mast cell- and CD4+ T-cell–dependent activation pathway, which further exacerbates airway inflammation and hyperresponsiveness.6 These events in patients with asthma suggest that the LAR provides a useful model for investigating chronic airway inflammation observed during natural aeroallergen exposure and for evaluating the efficacy of treatments.

CD4+ T cells can be divided into 3 subsets on the basis of their production of cytokines: T helper 0(TH0 ), TH1 , and TH2 cells.7, 8 TH1 cells produce mostly IFN-γ, and TH2 cells produce mostly IL-4 and IL-5. Analysis of bronchoalveolar lavage fluid and bronchial biopsy specimens from patients with sensitized asthma has shown that allergen-specific CD4+ T cells produce mostly TH2 -type cytokines such as IL-4, IL-5, and IL-13.9 Therefore inhibition of cytokine production by allergen-specific TH2 cells and of mediator release by mast cells may be essential in the treatment of allergic asthma.

The purpose of this study was to evaluate the effect of allergen rush immunotherapy (RIT) on asthma symptoms, cytokine production by allergen-specific T–cell lines, airway inflammation, and airway responsiveness in patients with allergic asthma. We also investigated the effects of RIT on allergen-induced exacerbation of airway inflammation and airway responsiveness after bronchoprovocative challenge with allergen.

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METHODS 

Subjects 

Sixteen nonsmoking patients with active allergic asthma were selected on the basis of (1) positive cutaneous reactions to house dust mite extract, (2) high levels of house dust- and Dermatophagoides farinae -specific IgE in sera, (3) baseline FEV1 more than 70% of the predicted value, (4) increased bronchial responsiveness to inhaled histamine, and (5) no treatment other than rescue β2 -adrenergic drugs and slow-release theophylline for at least 3 months. No subjects had used inhaled or oral steroids before or during the study period or had had respiratory infections in the 4 weeks before enrollment or at the end of the study period. Medications were withheld for at least 12 hours before each examination visit. Plasma concentrations of theophylline in patients receiving this drug were measured before every study and were confirmed to be less than 5 μg/mL. Informed consent was obtained before the study.

Study design 

This study was performed with a randomized and parallel design. After a 4-week run-in period, the subjects were either additionally treated with allergen RIT or continued to be treated with bronchodilators for 6 months. Asthma symptoms, peak expiratory flow (PEF), and results of blood analysis were monitored. Sputum induction with hypertonic saline inhalation and airway responsiveness to histamine were evaluated within 2 weeks before the beginning and end of the study period. D farinae- specific T-cell lines were established from PBMCs, and IL-5 production stimulated by allergen was analyzed before and after 5 months of treatment. In addition, bronchoprovocation with dust mite extract was carried out at the beginning and end of the study period. Numbers of eosinophils and eosinophil cationic protein (ECP) concentration in the blood were determined before and 24 hours after allergen challenge.

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RIT 

RIT was performed with dust mite extract according to the protocol described by Nagata et al10 with slight modification. One milligram of dust mite extract containing 9.8 ng of the major allergens Der 1 and Der 2, of which 5.4 ng was of D farinae (Torii Pharmaceutical Co, Tokyo, Japan), was used.11 All patients were hospitalized during RIT, and a histamine-1 receptor antagonist was administered during treatment to reduce systemic reactions, as reported previously.12 The initial concentration of the injection was a 1/10-diluted solution of the threshold concentration by the skin test titration; 3 to 6 subcutaneous injections were given daily at 1- to 2-hour intervals. The dose increment was withheld when the local reaction exceeded 8 cm in diameter, and the maximum dose was administered before day 7. After patients were discharged, they received the maintenance dose once each week at the outpatient clinic for 2 months, then once every other week for 6 months.

Clinical measurements 

A daily record was kept of asthma symptoms, including breathlessness and wheezing on a scale of 0 to 9 (0, no symptoms; 1, breathlessness or wheezing; 3, mild asthma; 6, moderate asthma; 9, severe asthma), cough on a scale of 0.5 to 1 (0.5, infrequent cough; 1, frequent cough), and sleep disturbance on a scale of 0 to 12 (0, slept well through the night; 4, slept most of the night despite dyspnea; 8, slept with difficultly because of asthma; 12, kept awake most of the night by asthma). The severity of symptoms was compared on the basis of the sums of weekly scores for the month. Morning PEF was recorded each day as the best of 3 successive trials with a Mini-Wright peak flow meter (Clement Clark International Ltd, Harlow, UK).

Establishment of D farinae-specific T-cell lines and measurement of IL-5 

D farinae -specific T-cell lines were established before and after 5 months of treatment. PBMCs were cultured with D farinae extract. To establish T-cell lines, cells were stimulated once each week for 4 weeks with 10 μg/mL of D farinae in the presence of irradiated autologous PBMCs and 4 ng/mL recombinant human IL-2. The T-cell lines were tested for specificity with a 3-day proliferation assay performed in 96-well flat-bottomed plates in tissue culture medium supplemented with either 10 μg/mL of D farinae or 10 μg/mL of purified protein derivates and irradiated PBMCs (5 × 104 ). The T-cell lines were used at least 7 days after the last stimulation, and cells were rested for 24 hours before allergen stimulation. Cells (5 × 105 ) were cultured with 10 μg/mL of D farinae and irradiated PBMCs (5 × 105 ) as antigen-presenting cells for 16 hours. The supernatants were harvested, and IL-5 was measured with commercial ELISA kits (R & D Systems, Minneapolis, Minn).

Inhalation challenge test 

For the allergen inhalation challenge test, baseline spirometry was performed, after which patients inhaled 0.9% saline, followed by dilutions of dust mite extract from the lowest concentration with an ultrasonic nebulizer (Devilbiss, Somerset, Pa). The FEV1 was measured 5 and 10 minutes after each inhalation. If the FEV1 had not fallen by at least 20% from the postsaline value, allergen inhalation was continued until the FEV1 had decreased by at least 20% of the postsaline value.

Bronchial responsiveness to histamine was also measured. Subjects inhaled double increased concentrations of histamine for 2 minutes by tidal breathing until the FEV1 decreased by more than 20% of the baseline value. Results are expressed as the provocative concentration causing a 20% decrease in FEV1 (PC20 ). Both inhalation tests were performed at the start of the study and after 6 months of therapy.

Sputum induction and analysis 

Sputum induction was performed before and after 6 months of treatment, as described previously.13 Briefly, medications were stopped for at least 12 hours, after which sputum was induced by inhalation of increasing concentrations of hypertonic saline (0.9%, 1.8%, 3%, 4%, and 5%) until an adequate volume of sputum was collected. Patients were encouraged to cough deeply after each inhalation. Cell plugs in sputum were separated from saliva and treated with Wright-Giemsa stain so that the inflammatory cells could be counted. Slides were also stained with a mouse monoclonal anti-human antibody directed against ECP (EG2+) by the method recommended by the manufacturer (Pharmacia AB Diagnostics, Uppsala, Sweden). The percentages of total and EG2+ eosinophils were determined by counting 900 cells under a light microscope. The remaining sputum was measured and diluted 10-fold with saline solution. Diluted sputum was vortexed and centrifuged for 10 minutes at 3000 rpm at room temperature. The supernatant was collected and stored at –40°C, and ECP concentrations were measured with radioimmunoassay (Pharmacia AB Diagnostics).14

Peripheral blood analysis 

The differential leukocyte count, eosinophil count, and ECP concentration were determined in samples of peripheral blood. Because serum levels of allergen-specific IgE antibody decrease and levels of IgG4 antibody (considered a blocking antibody) increase after immunotherapy, changes in the levels of both antibodies were measured with a CAPsystem, as described previously.15

Statistical analysis 

A paired t test and Bonferroni’s correction for multiple comparison were used for statistical analysis. Data are expressed as mean ± SEM, and P values less than .05 were considered significant.

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RESULTS 

Eight patients who were receiving RIT and 6 control patients completed the study; 2 control patients dropped out of the study because of respiratory infections within 4 weeks of the end of the study. Characteristics of patients completing the study are summarized in Table I.

Table I. Patient characteristics
Patients (no)Age (y)SexIgE (IU/mL)Der f-IgE (IU/mL)Duration (y)% Predicted FEV1TreatmentDM (wt/vol)Maintenance dose
BeforeAt 6 mowt/volmL
RIT-treated subjects
122M172371587.4T,β1:1001:1001:100.15
224M18601801884.1β1:1001:301:100.30
321M6711651680.2T,β1:3001:301:100.15
419F1455781883.5T,β1:3001:1001:100.20
527M227382584.5β1:301:301:100.15
622M126301878.0T,β1:10001:1001:100.20
730M487156177.8β1:3001:301:100.15
841F363722172.3T,β1:3001:1001:100.15
Mean25.8 670. 194.516.581.0 1:303.71:65.0
SEM2.5 227.622.22.51.72 1:123.71:13.2
RIT-untreated subjects
927M1870120389.6T1:10001:1000
1024F289151679.5T,β1:1001:50
1128M12433285.5T,β1:501:100
1220M1540116480.4T,β1:1001:50
1333M19130172.4T,β1:301:50
1426F460681082.5T,β1:1001:500
Mean26.3 745.763.76.081.7 1:230.01:291.7
SEM1.8 309.818.62.42.38 1:154.51:158.9

DM , Dust mite threshold concentration to decrease FEV1 by at least 20%; T , theophylline; β , inhaled β-agonist.

Clinical efficacy of RIT 

The characteristics of the 8 patients receiving RIT and the 6 remaining RIT-untreated control subjects are presented in Table I. RIT was completed in each of the 8 patients without adverse systemic reactions. Symptom scores improved significantly after RIT: from 16.63 ± 2.24 before treatment to 6.50 ± 3.35 after 1 month, 2.18 ± 0.88 after 3 months, and 1.00 ± 0.42 after 6 months (P < .03). However, symptom scores in control subjects did not change significantly: 11.33 ± 1.82 at the start of the study, 8.67 ± 1.91 after 1 month, 9.00 ± 2.67 after 3 months, and 10.17 ± 2.14 after 6 months.

In RIT-treated subjects, morning PEF increased significantly from 471.2 ± 27.3 L/min to 496.2 ± 27.4 L/min at 1 month, 512.5 ± 24.2 L/min at 3 months, and 506.2 ± 25.2 L/min at 6 months (P < .03). However, in control subjects, PEF did not change significantly throughout the study period: 484.3 ± 30.5 L/min at the start of the study and 491.1 ± 26.8 L/min at 6 months. The number of peripheral eosinophils (525 ± 116.1/μL to 362 ± 62.5/μL) and serum ECP concentration (23.6 ± 8.7 ng/mL to 15.7 ± 3.2 ng/mL) did not change significantly in RIT-treated subjects or in untreated subjects (648 ± 168.4/μL to 524 ± 89.4/μL for eosinophils and 24.8 ± 6.6 ng/mL to 26.4 ± 4.8 ng/mL for ECP) during the study period.

Although the levels of total IgE (670 ± 228 IU/mL to 879 ± 200 IU/mL), D farinae- specific IgE (484.3 ± 30.5 IU/mL to 491.1 ± 26.8 IU/mL), and total IgG4 (0.397 ± 0.084 IU/mL to 0.289 ± 0.104 IU/mL) did not change significantly, the levels of D farinae- specific IgG4 antibody were significantly higher than baseline (0.35 ± 0.05 IU/mL) 2 weeks from the start of RIT (1.73 ± 0.30 IU/mL; P < .01).

Change in IL-5 production from D farinae-specific T-cell lines 

Although IL-5 production by D farinae- specific T-cell lines was significantly decreased (617 ± 93.2 pg/mL to 200.0 ± 34.1 pg/mL; P < .01; Fig 1), IFN-γ production was not increased with RIT (data not shown).

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  • Fig. 1. 

    IL-5 production by D farinae- specific T-cell lines before and after 5 months in RIT-treated and untreated control patients. T-cell lines (5 × 105 ) were stimulated with 10 μg/mL of D farinae allergen with irradiated PBMCs (5 × 105 ) as antigen-presenting cells. Culture supernatants were harvested 16 hours later, and IL-5 was measured with ELISA.

IL-5 production by T-cell lines established from control subjects (651 ± 134.6 pg/mL to 607 ± 199.8 pg/mL) did not change significantly.

Effects of RIT on airway inflammation and airway responsiveness 

Eosinophilic airway inflammation was observed in all subjects with asthma at the start of the study. Although the percentages of eosinophils (30.8% ± 3.95% to 29.9% ± 3.14%), EG2+ eosinophils (39.9% ± 5.99% to 38.9 ± 3.54%), and the ECP concentration (388.3 ± 84.6 ng/mL to 321.3 ± 71.2 ng/mL) had not changed significantly after 6 months in sputum from control subjects, the percentages of eosinophils (43.0% ± 6.90% to 16.8% ± 2.48%; P < .01), EG2+ eosinophil (32.6% ± 6.39% to 19.7% ± 4.68%; P < .01), and the ECP concentration (362.7 ± 125.3 ng/mL to 26.2 ± 5.2 ng/mL; P < .05) had decreased significantly in induced sputum after 6 months of RIT (Fig 2).

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  • Fig. 2. 

    Percentages of (A ) total eosinophils, (B ) EG2+ eosinophils, and (C ) ECP concentration in induced sputum before and after 6 months in RIT-treated and untreated control patients. Induced sputum was obtained before (baseline ) and 24 hours after allergen challenge (postallergen ).

The threshold concentration of dust mite extract was significantly increased (1:303.7 ± 123.7 wt/vol to 1:65.0 ± 13.2 wt/vol; P < .03; Table I), and the airway responsiveness to histamine was significantly improved (397.1 ± 206.9 μg/mL to 1391.3 ± 283.3 μg/mL; P < .03) only in RIT-treated patients after 6 months of treatment (Fig 3).

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  • Fig. 3. 

    Airway responsiveness to histamine before and after 6 months in RIT-treated and untreated control patients. PC20 was analyzed before (baseline ) and 24 hours after allergen challenge (postallergen ).

Airway responsiveness to allergen (1:230.0 ± 154.5 wt/vol to 1:291.7 ± 158.9 wt/vol) and histamine (241.3 ± 61.1 μg/mL to 252.3 ± 45.0 μg/mL) did not change significantly in control subjects (Table I and Fig 3).

Effect of RIT on respiratory function (FEV1) after allergen challenge 

Changes in FEV1 were measured until 24 hours after inhalation challenge before and after 6 months of treatment. Although a high dose of allergen was administered to induce EAR after 6 months of RIT (Table I), the percentage of fall in FEV1 from baseline values at EAR (33.2% ± 3.46% to 25.4% ± 1.42%; P < .03) and at LAR (16.2% ± 3.52% to 6.19% ± 1.96%; P < .03) was significantly attenuated (Fig 4).

  • View full-size image.
  • Fig. 4. 

    Percent fall in FEV1 after bronchoprovocation with allergen before and after 6 months in RIT-treated and untreated control patients. At the start of the study, EAR was induced by allergen challenge in all subjects, and LAR was induced in 4 of 6 control subjects and in 6 of 8 subjects later treated with RIT. These rates of induction of EAR and LAR did not change after 6 months of treatment.

No significant fall in FEV1 at EAR (32.3% ± 8.21% to 32.9% ± 5.92%) and at LAR (14.4% ± 3.65% to 15.9% ± 5.79%) was observed in control subjects.

Airway inflammation and airway responsiveness after allergen challenge 

Allergen inhalation resulted in significant increases in the percentages of total and EG2+ eosinophils and ECP concentration in induced sputum 24 hours after inhalation challenge in both patient groups before enrollment. In control subjects, the percentages of eosinophils (30.8% ± 3.95% to 41.1% ± 4.40%; P < .01), EG2+ eosinophils (39.9% ± 5.99% to 58.3% ± 6.72%; P < .05), and the ECP concentration (388.3 ± 84.6 ng/mL to 630.8 ± 98.3 ng/mL; P < .03) increased significantly after allergen challenge; however, the degrees of increase did not differ significantly from those after 6 months (eosinophil percentage, 29.9% ± 3.14% to 39.5% ± 2.36%; P < .03; EG2+ eosinophil percentage, 38.9% ± 3.54% to 54.7% ± 7.35%; P < .05; and ECP concentration, 321.2 ± 71.2 ng/mL to 561.5 ± 158.3 ng/mL; P < .05; Fig 2). In contrast, increases in the percentages of eosinophils (61.8% ± 4.89% to 42.0% ± 4.67%; P < .01) and EG2+ eosinophils (55.5% ± 7.21% to 36.5% ± 6.43%; P < .01) and the ECP concentration (685.6 ± 217.0 ng/mL to 85.4 ± 23.4 ng/mL; P < .05) were significantly less 24 hours after allergen challenge in RIT-treated patients (Fig 2).

Although airway responsiveness to histamine increased significantly 24 hours after allergen challenge in control subjects, both at the start of the study and after 6 months (PC20 , 115.0 ± 19.2 μg/mL and 91.2 ± 24.7 μg/mL), airway responsiveness after 6 months of RIT (629.1 ± 196.3 μg/mL) was significantly improved than that before treatment (139.2 ± 36.5 μg/mL; P < .03; Fig 3).

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DISCUSSION 

Our results demonstrate that RIT improves clinical symptoms and PEF and decreases airway inflammation and airway responsiveness to both allergen and histamine. RIT also decreased IL-5 production by allergen-specific T cells established from peripheral blood, attenuated early and late phase bronchoconstrictive responses after allergen inhalation, and inhibited allergen-induced increases in the percentage of total and EG2+ eosinophils and ECP concentration in induced sputum. In addition, RIT decreased airway responsiveness to histamine after bronchoprovocation with allergen.

A recent metaanalysis of 20 double-blind, placebo-controlled studies showed that immunotherapy significantly improves the control of asthma, but other reports suggest that immunotherapy is not effective.1, 2, 3, 4 Although the number of patients in our study was limited, we clearly demonstrated that allergen RIT is effective against mild asthma. There are several reasons for the clear effect of RIT in this study. First, we selected young subjects with mild asthma. Second, we selected patients sensitized solely to house dust mite. Third, although RIT was performed, a high maintenance dose of allergen continued to be administered.

Asthma is characterized by chronic airway inflammation with recruitment of several different cell populations (including T cells, mast cells, and eosinophils) into the airway.16 Although the pathogenesis of airway inflammation has not been completely elucidated, it may be initiated by TH2 cells and mast cells in allergic asthma.6 Therefore the most effective treatment for allergic asthma might be to suppress the function of both allergen-specific TH2 cells and mast cells.

Cross-linking of high-affinity IgE receptors on mast cells by allergen triggers the release of chemical mediators (such as histamine, leukotrienes, and thromboxane) that cause bronchoconstriction and the release of cytokines, including IL-4, IL-5, and TNF-α.17 Direct evidence of the importance of mast cells in initiating the allergic reaction was reported by Kung et al,18 who showed that fewer eosinophils infiltrated the airway after allergen challenge in sensitized mast cell–deficient mice W/Wv rather than in their congenic normal littermates W/W+ .

In this study we found that RIT inhibited allergen-induced EAR, possibly by suppressing the release of mediators from mast cells. Although the precise mechanism by which mediator release from mast cells is inhibited is not completely understood, the increase in D farinae- specific IgG4 antibodies after RIT may be involved. Another possibility was recently suggested by the study of Shalit and Levi-Schaffer,19 who demonstrated that challenge of mast cells with increasing amounts of antigen in vitro desensitizes only for a specific antigen but not for a nonallergic stimulus, such as compound 48/80.

Analysis of human T-cell clones from sensitized subjects has demonstrated that allergen-specific CD4+ T cells of the TH2 phenotype are involved in allergen-specific reactions.6, 17 A decrease in TH2 -type cytokine production has been reported in patients receiving conventional immunotherapy or RIT.20, 21, 22, 23 In fact, we have demonstrated in this study that IL-5 production by dust mite (D farinae)- specific T-cell lines established from PBMCs is significantly reduced after RIT. Because IL-5 favors eosinophil differentiation, activation, and survival by suppressing apoptosis, a decrease in IL-5 production by allergen-specific T cells may help decrease airway inflammation and airway hyperresponsiveness before and after induction by allergen inhalation.

Analysis of induced sputum is a noninvasive technique for investigating inflammatory changes in asthma that correlate with findings of bronchoalveolar lavage fluid and bronchial biopsy examinations.24 Increases in the number of eosinophils and ECP concentration in induced sputum after allergen inhalation indicate the usefulness of this method for analyzing changes in allergen-induced airway inflammation.25 Because successful immunotherapy inhibits allergen-induced inflammatory cell recruitment into the target organ, we have studied the effect of RIT on airway inflammation by analyzing induced sputum in allergic asthma.26, 27, 28, 29, 30 In the present study we found that RIT significantly decreased the percentages of total and EG2+ eosinophils and the ECP concentration in induced sputum both before and after bronchoprovocation with allergen. These results strongly suggest that allergen RIT suppresses airway inflammation caused by both mast cell- and T-cell–induced recruitment and activation of eosinophils in the airway.

Airway hyperresponsiveness is a characteristic feature of asthma.16 Although several factors are involved in the pathophysiologic features of airway hyperresponsiveness, ongoing airway inflammation may play an important role in inducing, maintaining, and enhancing airway hyperresponsiveness. In our study, RIT decreased airway responsiveness to histamine and decreased the percentage of active eosinophils in induced sputum, a finding that indicates that eosinophilic airway inflammation is closely associated with airway hyperresponsiveness. Furthermore, RIT significantly suppressed the increase in airway hyperresponsiveness to histamine after LAR. These results suggest that RIT reduces airway hyperresponsiveness by decreasing airway inflammation in the resting state and after allergen inhalation. Recently, remodeling of the airway that includes the thickness of basement membrane and hypertrophy of airway smooth muscle has been reported to be another important component of airway hyperresponsiveness.31 Interestingly, recent reports provide evidence that short-term use of inhaled glucocorticosteroids significantly reduces the thickness of the basement membrane.32 Furthermore, increased expression of tenascin, a component of extracellular matrix glycoprotein in patients with chronic asthma, is significantly reduced by inhaled corticosteroids.33 Because RIT decreases both airway inflammation and airway responsiveness, continuation of RIT might help reduce airway remodeling. Further studies of the long-term effects of RIT on airway remodeling should be performed.

In summary, our results support the concept that airway inflammation is closely associated with airway responsiveness and that successful RIT improves both airway inflammation and airway responsiveness, possibly by inhibiting both IL-5 production by allergen-specific T cells and mediator release by mast cells. Therefore we conclude that allergen RIT is an effective antiinflammatory treatment in the management of allergic asthma.

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Acknowledgements 

The authors thank Dr Kenta Kawazu, Dr Masatsugu Kurokawa, Dr Kiyoko Wada, Dr Masahide Miyamoto, and Miss Tomoko Akabane for their technical assistance.

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☆ From a the First Department of Internal Medicine, Showa University, Tokyo; and b the Department of Immunology and Medicine, St Mariannna University, Kanagawa.

☆☆ Reprint requests: Kenji Minoguchi, MD, PhD, First Department of Internal Medicine, Showa University, School of Medicine, 1-5-8, Hatanodai, Shinagawa-ku, Tokyo 142, Japan.

★ 0091-6749/98 $5.00 + 0  1/1/93729

PII: S0091-6749(98)70330-6

The Journal of Allergy and Clinical Immunology
Volume 102, Issue 6 , Pages 927-934, December 1998

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