Bronchial reactivity increases soon after the immediate response in dual-responding asthmatic subjects

Inhibition of mast cell tryptase by inhaled APC 366 attenuates allergen-induced late-phase airway obstruction in asthma

BACKGROUND

APC 366, a selective inhibitor of mast cell tryptase, has been shown to inhibit antigen-induced early asthmatic response (EAR), late asthmatic response (LAR), and bronchial hyperresponsiveness (BHR) in a sheep model of allergic asthma.

OBJECTIVE

The purpose of this study was to investigate the effects of APC 366 on antigen-induced EAR, LAR, and BHR in mild atopic asthmatics not on any anti-inflammatory therapy.

METHODS

Sixteen mild atopic asthmatics, each with a demonstrable antigen-induced EAR, LAR, and BHR to histamine, were recruited into this randomized, double-blinded, crossover study. APC 366 (5 mg)/placebo was administered by aerosol inhalation 3 times per day on treatment days 1 through 4. Allergen challenge was carried out on day 4. Histamine challenge was performed the following morning, 1 hour after final dosing.

RESULTS

Subjects were shown to have a significantly smaller overall mean area under the curve for the LAR (P =.012) and mean maximum fall in FEV(1) for the LAR (P =.007) after pretreatment with APC 366 in comparison with placebo. No significant effects on BHR were demonstrable. Although the EAR was reduced by 18% after treatment with APC 366 in comparison with placebo, this was not statistically significant.

CONCLUSION

Short-term repeated administration of APC 366 significantly reduced the magnitude of antigen-induced LAR in atopic asthmatics, which supports the role of mast cell tryptase in the pathophysiology of the LAR.

Mechanisms of occupational asthma

BACKGROUND

The pathogenesis and the pathologic alterations of occupational asthma are similar to those of nonoccupational asthma. Occupational asthma may therefore represent a useful model of "human asthma" to investigate mechanisms and pathophysiology of asthma in general. In an occupational setting the cause and onset of asthma may be easily identified, and the natural history may be examined in follow-up studies. The mechanisms involved in occupational asthma include genetic predisposition, immunologically mediated responses, as well as nonspecific airway inflammation. In particular, high molecular weight (eg, grain dust, flour) and some low molecular weight sensitizers (eg, acid anhydrides and platinum halide salts) have been shown to induce occupational asthma through an immunoglobulin E (IgE)-dependent mechanism, while cell-dependent immunologic mechanisms are likely to be more relevant for occupational asthma induced by other low molecular weight sensitizers (eg, toluene diisocyanate and plicatic acid contained in western red cedar). The pathology of the airway mucosa of occupational asthma is remarkably similar to the pathology of nonoccupational asthma, ie, characterized by infiltration and accumulation of eosinophils, mast cells, and activated lymphocytes along with subepithelial fibrosis. In this article, the most relevant mechanisms are discussed with particular reference to the similarities and discrepancies between occupational and nonoccupational asthma.

Bronchial allergen challenge in subjects with low levels of allergic sensitization to indoor allergens

BACKGROUND

Low skin reactivity to common inhalant allergens is frequently found in asymptomatic individuals as well as in patients with respiratory complaints. However, most studies on bronchial allergen challenge concern patients with high levels of allergic sensitization. The present study was directed to bronchial reactions after allergen challenge in subjects with low skin reactivity to Dermatophagoides pteronyssinus or cat dander.

METHODS

Titrated intracutaneous skin tests, skin prick tests, specific IgE assays, histamine release on washed leukocytes, and bronchial histamine and allergen-challenge tests were performed in 20 subjects with an intracutaneous skin test threshold for cat dander (Felis domesticus) or D. pteronyssinus above 0.1 BU/ml (mean wheal diameter in skin prick test with 10000 BU/ml: 4.4mm). Ten of the 20 patients had specific IgE below the detection limit in at least one of the three IgE assays which were done. Fifteen patients had a specific IgE level below 2 kU/I in all three tests. As a positive control group, the same parameters were studied in seven moderately sensitized patients with an intracutaneous skin test threshold below 0.1 BU/ml (mean wheal diameter with 10000 BU/ml: 7.2mm).

RESULTS

The 20 subjects with low levels of allergic sensitization had an early decrease in FEV1 of 8.6% (P<0.01) and a mean late decrease of 6.3% (P<0.05). There was a trend for decrease in PC20 histamine 24h after allergen challenge (-0.4 doubling doses, P=0.09).

CONCLUSIONS

In this group of subjects with low levels of allergic sensitization, a statistically significant early and late decrease in FEV1 was found. However, the decrease in lung function was small and unnoticed by most patients. The increase in nonspecific bronchial hyperresponsiveness after bronchial allergen challenge did not reach statistical significance in the study group. The results indicate that allergen exposure in patients with low levels of allergic sensitization may lead to airways changes in the absence of acute symptoms.

Selective airway responsiveness in asthma

Hyperresponsiveness of airway smooth muscle accounts for the susceptibility of asthmatic subjects to diverse bronchoconstrictor agents. It is widely presumed that hyperresponsiveness is not spasmogen selective. Hence, inhalation of methacholine is used routinely for clinical assessment of asthma and for evaluation of anti-asthma drugs. Comparative studies employing multiple spasmogens have revealed hyperresponsiveness to be markedly spasmogen selective. Because of this pronounced heterogeneity of hyperresponsiveness, sensitivity to methacholine cannot provide a reliable index of responsiveness. Development of exceptional hyperresponsiveness to bradykinin and to peptidoleukotrienes during allergic and other reactions could warrant the development of specific antagonists for asthma therapy. These issues are discussed here by Brian O'Connor, Simon Crowther, John Costello and John Morley.

Increase in non-specific bronchial hyperresponsiveness as an early marker of bronchial response to occupational agents during specific inhalation challenges

BACKGROUND

Specific bronchial reactivity to occupational agents may decline after exposure in the workplace ceases leading to falsely negative specific inhalation challenges. A study was carried out to assess prospectively whether increases in nonspecific bronchial hyperresponsiveness could be useful in detecting the bronchial response to occupational agents during specific inhalation challenges.

METHODS

Specific inhalation challenges were performed in 66 subjects with possible occupational asthma due to various agents. After a control day the subjects were challenged with the suspected agent for up to two hours on the first test day. Those subjects who did not show an asthmatic reaction were rechallenged on the next day for 2-3 hours. The provocative concentration of histamine causing a 20% fall (PC20) in the forced expiratory volume in one second (FEV1) was assessed at the end of the control day as well as six hours after each challenge that did not cause a > or = 20% fall in FEV1. The subjects who had a significant (> or = 3.1-fold) reduction in PC20 value at the end of the second challenge day were requested to perform additional specific inhalation challenges.

RESULTS

The first test day elicited an asthmatic reaction in 25 subjects. Of the other 41 subjects five (12%, 95% confidence interval (CI) 4% to 26%) exhibited a > or = 3.1-fold fall in the PC20 value after the inhalation challenge and developed an asthmatic reaction during the second (n = 3) or third (n = 2) challenge exposure. The offending agents included persulphate (n = 1), wood dust (n = 2), isocyanate (n = 1), or amoxycillin (n = 1). These five subjects had left their workplace for a longer period (mean (SD) 21 (14) months) than those who reacted after the first specific inhalation challenge (8 (11) months).

CONCLUSIONS

The increase in non-specific bronchial hyperresponsiveness after a specific inhalation challenge can be an early and sensitive marker of bronchial response to occupational agents, especially in subjects removed from workplace exposure for a long time. Non-specific bronchial hyperresponsiveness should be systematically assessed after specific inhalation challenges in the absence of changes in airway calibre.

Airway responsiveness to allergen is increased 24 hours after exercise challenge

Although exercise is one of the most ubiquitous triggers of acute bouts of asthma, the changes in airway responsiveness before and after exercise are not well defined. Specifically, the effect of the changes in airway responsiveness induced by exercise has not been studied on subsequent allergen exposure. To test whether the reactivity to allergen is altered by preceding exercise and to define possible factors determining it, we subjected 24 children with atopic asthma to the relevant allergen challenge on two occasions: one as a control without a preceding procedure and the other 24 hours after exercise challenge. Mean postallergen maximal percent falls in forced expiratory volume in 1 second from baseline (delta FEV1) of the whole group were higher after the exercise challenge compared with those of control in both early (< 1 hour) and late (3 to 10 hours) phases. The changes of postallergen maximal delta FEV1 between the control and post-exercise allergen challenges were not related to the early bronchial response to the preceding exercise challenge. Late asthmatic responses to exercise developed in six children, and the changes in both early and late phases were significantly higher in these children, compared with those without late asthmatic responses. Furthermore, the changes were well correlated with the magnitude of the late-phase response to preceding exercise in the group as a whole. It is concluded that an increased airway responsiveness to allergen occurs 24 hours after exercise in some patients with asthma. As the changes are related to a late bronchial response to exercise, late asthmatic response to exercise, when it occurs, may be associated with increased asthmatic symptoms for as long as 24 hours after exercise.

Effect of ozone exposure on antigen-induced airway hyperresponsiveness in guinea pigs

Airway hyperresponsiveness can be induced by several stimuli including antigen and ozone, both of which may be present in the air of polluted cities. Though the effect of ozone on the bronchoconstrictor response to antigen has been well described, the combined effect of these stimuli on airway hyperresponsiveness has not yet been studied. Sensitized guinea pigs with or without ozone exposure for 1 h at 3 ppm, 18 h prior to study, were challenged with a dose-response curve to histamine (0.01-1.8 micrograms/kg, iv) followed by an antigen challenge (ovalbumin, 50 micrograms/kg, iv), and then by a second histamine dose-response curve 1 h later. Airway responses were measured as the increase in pulmonary insufflation pressure. In sensitized guinea pigs, the histamine ED50 significantly decreased after antigen challenge, demonstrating the development of airway hyperresponsiveness. Sensitized guinea pigs exposed to ozone showed airway hyperresponsiveness to histamine when compared with nonexposed animals, and such hyperresponsiveness was further enhanced after antigen challenge. We conclude that in this guinea pig model of acute allergic bronchoconstriction both antigen challenge and ozone induce airway hyperresponsiveness, while ozone exposure does not modify the development of antigen-induced hyperresponsiveness.

Bronchial responsiveness is not always increased after allergen challenge

Increased bronchial responsiveness has been reported at various time points following allergen challenge (AC), and may be related to the magnitude of the late response (LAR). We have studied 20 mild asthmatics, who were known to develop a late asthmatic response to inhalation of house dust mite extract (fall of > 15% from post-diluent baseline FEV1 from 2 to 7h after AC). The provocation concentration of methacholine causing a 20% fall in FEV1 (PC20 FEV1) was measured before and 24 h after challenge with house dust mite extract (HDM). The mean (SEM) change in log(PC20) was 0.08 (0.09) mg ml-1, and was not significant (P = 0.38; paired t-test). The change in PC20 for each subject was not significantly correlated with the size of LAR (r = -0.33; P > 0.05), but was significantly correlated with the absolute change from baseline FEV1 at 24 h (r = 0.67; P < 0.01). Our subjects had a high baseline responsiveness, when compared with previous studies. We suggest they may have been approaching a maximally responsive state prior to study, and allergen challenge may have had little effect in further increasing responsiveness. Exposure to allergen in late responders is not necessarily followed by an increase in non-specific bronchial responsiveness.

Relationships among allergen-induced early and late phase airway obstructions, bronchial hyperreactivity, and inflammation in conscious, unrestrained guinea pigs

The relationship among allergen-induced early asthmatic reactions (EARs) and late asthmatic reactions (LARs), early (between EAR and LAR) and late (after LAR) changes in bronchial reactivity to histamine and infiltration of inflammatory cells into the airways were investigated with a new model of chronically instrumented, unrestrained, and ovalbumin-sensitized guinea pigs. Two different provocation strategies were examined. With the use of stepwise increasing allergen concentrations, all 21 animals responded with an EAR, which in 15 animals (71%) was followed by an LAR. By inhalation of a single allergen concentration for up to 15 minutes, 11 of 14 animals showed an EAR, which in 10 animals (71%) was followed by an LAR. One animal did not respond, whereas the remaining two showed only an LAR. At 6 hours (after the EAR) and 24 hours (after the LAR) after allergen provocation, a significant bronchial hyperreactivity (BHR) toward histamine aerosol was observed in the dual responding animals (both protocols), but not significant changes were observed in animals with a single EAR or a single LAR. Significant correlations were found between the initial increase in airway obstruction after allergen provocation and the severity of the EAR and LAR, as well as the early and late BHR; in addition, a significant correlation was found between the early and late BHR. In contrast, the severity of the LAR did not correlate with the BHR at 6 hours and 24 hours. At 6 hours, there was a marked tendency to an increase in the number of eosinophils and a significant increase in the number of neutrophils in the bronchoalveolar lavage. At 24 hours after provocation, the number of eosinophils and neutrophils was significantly enhanced. These data suggest that early activation of mast cells and/or inflammatory leukocytes may determine the development of the LAR, as well as the early and late BHR, although there appears to be no causal relationship between the BHR at both time points and the severity of the LAR. The relationships among allergen-induced EAR and LAR, early and late BHR, and airway inflammation observed in this new guinea pig model are strikingly similar to those observed in patients with asthma.

Inhibition of antigen-induced airway hyperresponsiveness by a thromboxane A2 receptor antagonist (AA-2414) in Ascaris suum-allergic dogs

We studied changes in airway responsiveness to acetylcholine (ACh) after antigen inhalation in Ascaris suum (A. suum)-allergic dogs. Airway responsiveness was determined by obtaining a dose-response curve of lung resistance plotted against increasing concentrations of ACh aerosol before and after inhalation of A. suum antigen. To determine the role of thromboxane A2 (TXA2) in the airway response, we tested the effect of a TXA2 receptor antagonist, AA-2414, in A. suum-allergic dogs. The procedure was repeated in each dog at an interval of 2 weeks to evaluate the effect of AA-2414 in a crossover manner. The dogs showing an airway response to antigen showed an increase in airway responsiveness to ACh 2, 4 and 6 h after antigen inhalation. The increase in airway responsiveness was significantly inhibited by administration of AA-2414 (5 mg/kg, i.v.) before antigen inhalation. These results suggest that TXA2 may be involved in antigen-induced airway hyperresponsiveness (AHR) in dogs.

Circadian variation of bronchial caliber and antigen-induced late asthmatic response

To study whether circadian variation of bronchial caliber participates in causing late asthmatic response (LAR), house-dust inhalation was made at 10 AM and 6 PM on separate days in 6 house-dust-sensitive asthmatic children aged 8 to 13 years. Bronchial obstruction was assessed through measurements of FEV1 at 4-h intervals from 24 h before to 24 h after the inhalation. The LAR, which is a 15 percent or greater decrease in FEV1 from the value at the same hour of the previous day, occurred 4 h or later after the inhalation in all challenges. The mean (+/- SD) time to the occurrence of the lowest FEV1 (maximum LAR) following the morning inhalation was 14.7 +/- 2.1 h versus 10.0 +/- 2.2 h following the evening inhalation (p < 0.05). Regardless of the hour of inhalation, FEV1 after the inhalation was lowest or near-lowest at 2 AM in all. Therefore, the maximum LAR was indistinguishable from the trough of further amplified circadian variation in FEV1 following the inhalation. These findings suggest that the downward arm of circadian variation may partially participate in causing the LAR.

Effect of a peptide leukotriene receptor antagonist, ONO-1078, on guinea-pig models of asthma

Peptide leukotrienes have been suggested to play an important role in bronchial asthma. As antigen-induced bronchoconstrictions, airway hyperreactivity, and pulmonary eosinophil accumulation are characteristics of the pathology of asthma, we investigated the effect of a peptide leukotriene receptor antagonist, ONO-1078, on these responses using guinea-pig models of asthma. Oral administration of ONO-1078 (3 mg/kg) significantly inhibited slow-reacting substance of anaphylaxis-mediated bronchoconstriction induced by i.v. administered ovalbumin. ONO-1078 (30-100 mg/kg), when administered orally both 1 h before and 4 h after ovalbumin challenge, significantly reduced immediate- and late-phase asthmatic responses, with peak responses occurring immediately and 5-11 h after challenge with inhaled ovalbumin. Oral administration of ONO-1078 significantly reduced the airway hyperreactivity (10-30 mg/kg) and the pulmonary eosinophil accumulation (30-100 mg/kg) observed 4 and 24 h after ovalbumin challenge, respectively. These results suggest that ONO-1078 may be of therapeutic use for bronchial asthma.

Increase in non-specific bronchial responsiveness after repeated inhalation of low doses of allergen

The development of bronchial hyperresponsiveness (BHR) in asthma is considered to be caused by inflammation of the airway. In IgE-mediated allergy BHR is related to the occurrence of late phase reactions. We have previously shown that exposure to low doses of allergen can cause isolated late reactions. These findings are potentially of clinical importance, since exposure to low, subclinical allergen doses may lead to bronchial inflammation and increasing bronchial responsiveness without necessarily causing immediate bronchoconstriction. This study was performed to investigate whether repeated exposure to low doses of allergen could induce a change in BHR. The trial comprised two groups of five and eight patients with a history of allergic asthma. They were submitted to a series of allergen inhalations for 5-7 days. They were given the same low allergen dose (1-10 biological units) each day. Before and after the allergen exposure period histamine challenges were performed. After the week of allergen inhalation the bronchial responsiveness was increased in 11 of 13 patients.

Asthma

There is an active inflammatory process in the airways of patients with asthma, even when the patients are asymptomatic. Some of the types of cells involved in this process possess the necessary biologic activities to produce many of the pathophysiologic features of asthma, but the underlying mechanisms have not yet been elucidated. Reducing the severity of the inflammatory process appears to be a reasonable goal of therapy, with potential long-range implications for the morbidity of asthma. Whether this theoretical benefit will be realized awaits further observation.

Is asthma curable?

The information reviewed here supports the concept that asthma is potentially curable. Reports of complete, durable remission of asthma can no longer be regarded as fortuitous occurrences, unrepresentative of asthma in general. Systematic studies of anti-inflammatory drug therapy designed to explore possible induction or remission of asthma clearly are warranted. Studies of aggressive anti-inflammatory drug therapy of asthma at the onset, to avoid establishment of chronic asthma, also are desirable. The current goals of therapy of asthma have been revised to include reduction of airway hyperreactivity with topical anti-inflammatory drugs, in addition to relief of current symptoms. This approach may provide valuable resistance to exacerbations in response to antigen exposures, infections, exercise, or irritants. Pathophysiologic mechanisms apparently essential to the establishment and perpetuation of chronic asthma have been identified. These processes may be vulnerable to eradication by combination therapy with existing pharmacologic agents such as cyclosporin A or FK-506 (to suppress cytokine production), gold, methotrexate, and other anti-inflammatory drugs, alone or in combination. Equally important, the vigorous anti-inflammatory therapy may be necessary only long enough to achieve a resolution of the chronic pulmonary inflammation. Systematic studies of the use of these agents to induce partial, or complete, stable remissions of asthma should be performed. In the past, remissions of asthma in children with neoplasia and the other patients presented herein were complete, durable, and welcome, but they were largely unexpected and unpredictable. For the future, there is increasing reason to believe that predictable pharmacologically induced remission of asthma will be feasible.

Antigen-induced hyperresponsiveness to methacholine in ventilated, anesthetized guinea pigs

Guinea pigs were actively sensitized to ovalbumin and exposed 2-3 weeks later to an aerosol of ovalbumin or saline. Changes in lung function were assessed 0.5, 1, 6, 24 and 72 h later by measuring the peak increase in pulmonary inflation pressure induced by i.v. methacholine during constant-volume ventilation. Responses to methacholine were significantly potentiated at 0.5, 1, 6 and 24 h but not at 72 h following exposure to antigen. Hyperresponsiveness to methacholine was maximal at 0.5-1 h and, in terms of magnitude, comparable to the early increase in airway reactivity found in mild asthmatics after allergen challenge. Whether the hyperresponsiveness to methacholine induced by antigen in the guinea pig can be attributed solely to an increase in airway reactivity or is due, at least in part, to decreased lung compliance requires further study.

Increase in airway responsiveness and effect of deep inhalation on airway caliber in allergen-induced asthma. Relationship to the late-phase response

The airway responsiveness to methacholine (MCh) and the effect of deep inhalation (DI) on airway caliber were determined in 18 asthmatic patients at baseline and 3 and 24 h after an allergen inhalation challenge. The dose of MCh causing a 20% fall of FEV1 (PD20) was used as an index of airway responsiveness; the ratio of forced expiratory flow at 40% of FVC from maximal and partial flow/volume curves (MEF40M/P) was used to assess the effect of DI on airway caliber. Thirteen patients showed a dual asthmatic response (DAR) to allergen, 5 patients an isolated early-phase asthmatic response (EAR). In the DAR patients, 3 h after allergen challenge, when the early-phase response had resolved and the late-phase response had yet to develop, MChPD20 (geometric mean) was reduced from 202 to 71 micrograms (P less than 0.001) whereas MEF40M/P at the MCh end point was unchanged (p greater than 0.4). Twenty-four hours after allergen challenge, when late-phase response had developed, MChPD20 was further reduced to 51 micrograms (p less than 0.02), and this reduction was accompanied by a decrease of MEF40M/P at the MCh end point (p less than 0.01). In the EAR patients, neither MChPD20 nor MEF40M/P was significantly changed at any time during the study. We conclude that most of the increase in airway responsiveness that follows acute exposure to allergen precedes the late-phase response and is not determined by the same mechanisms that impair the ability of the lung to dilate airways with a DI.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevation of tissue kallikrein and kinin in the airways of asthmatic subjects after endobronchial allergen challenge

Bronchial tissue kallikrein is the major kininogenase activity in the airways of asthmatic subjects. The relationship of IgE-mediated events to its release and/or activation is unknown, however, and is the subject of this report. Seven subjects with mild atopic asthma underwent endobronchial challenge with relevant aeroallergen. Baseline pre-allergen lavage and sequential post-challenge lavages were collected over an approximate 10-minute time course. Individual aliquots were analyzed separately and compared with saline control lavages performed in a separate lobe. In five of the seven subjects, an increase in tissue kallikrein activity, measured by cleavage of the synthetic substrate Val-Leu-Arg-pNA, was identified in the post-challenge lavages. The antigenic identity of the enzymatic activity was confirmed as a tissue kallikrein in each case by immunoblotting. Tissue kallikrein activity was highly correlated with the appearance of immunoreactive histamine and kinin (p = 0.0001). High molecular weight kininogen influx and cleavage was detected in the post-challenge samples by immunoblotting and paralleled the detection of kinin in BAL fluid. Two of the subjects, despite clinical profiles similar to those of the five positive responders, failed to react to endobronchial challenge. Saline control lavages contained detectable kallikrein, kinin, and histamine in two subjects; in each case, however, this was significantly less than in the post-allergen samples. The results demonstrate a close association between immediate type hypersensitivity events in the lower airway and the appearance of active kallikrein, kininogen substrate, and the liberation of kinin.

The relationship between airway responsiveness measured before and after the allergen-induced late asthmatic response

Single blind allergen (Ag) and saline solution bronchial challenges were performed on two successive study days in ten asthmatic subjects. Histamine challenges were performed before, at approximately 2 h (or after resolution of the immediate bronchial response [IR]), and 24 h after saline solution or Ag inhalation. Specific airway conductance (SGaw) was measured after delivery of challenge agents until a 50 percent fall in SGaw was observed. The SGaw was monitored over 8 h for immediate and late asthmatic responses (LAR). Results were expressed as provocative concentrations eliciting a 50 percent decrease in SGaw (SGawPC50HIS). No significant changes from baseline SGaw or SGawPC50HIS were demonstrated after saline solution. Eight subjects (dual reactors) exhibited both an IR and LAR after Ag and two had isolated IRs. Of the eight dual reactors, five had greater than 50 percent decreases in SGawPC50HIS immediately after resolution of the IR and six exhibited such decrements 24 h after Ag provocation. Mean baseline SGawPC50HIS (N = 10) on the Ag challenge day was 3.2 +/- 4.59 mg/ml and decreased to 0.92 +/- 4.56 mg/ml at 102 to 187 minutes after Ag (p = 0.0009) and was significantly decreased from baseline at 1.47 +/- 3.8 mg/ml 24 h after Ag (p = 0.0004). One of the two patients with isolated IR also showed an early onset increase in airway responsiveness (EOR). There was a significant correlation between the percentage of fall from baseline in SGawPC50HIS immediately after the IR and that at 24 h after Ag (r = 0.811, p = 0.005). There was no significant correlation between the decrease in SGawPC50HIS after the IR and the magnitude of the LAR. These data suggest that (1) the early events occurring prior to the LAR may determine changes in airway responsiveness observed at 24 h after Ag challenge, and (2) the EAR to histamine is not exclusively associated with the LAR.

Increased numbers of mast cells in bronchial mucosa after the late-phase asthmatic response to allergen

We examined the characteristics of allergen-induced inflammation of the bronchial mucosa in asthmatic patients. Studies were carried out 4 h (eight patients) and 24 h (nine patients) after allergen inhalation challenge; 10 patients were not challenged and served as control subjects. We found that in the control group the ratio of degranulating to granulated mast cells was higher in patients with than in patients without late-phase response. In patients studied 4 h after allergen challenge the total number of mast cells was not significantly different from that in control subjects; the ratio of degranulating to granulated mast cells was increased similarly in patients with and without late-phase response. Among patients studied 24 h after allergen challenge, those who had developed the late-phase response had an increased (p less than 0.05) number of mast cells as compared with patients who had not developed the late-phase response, the number of mast cells was significantly correlated with the severity of the late-phase response (r = 0.80; p less than 0.001). The numbers of eosinophils and mononuclear cells and the morphologic abnormalities of bronchial structure (altered ratio of cylindrical to goblet cells, thickening of the basement membrane, and edema and angiectasis of lamina propria) were similar in the different groups of patients. We conclude that the inflammatory events leading to the development of the late-phase asthmatic response to allergen represent a stimulus for an increase in the number of mast cells in the bronchial mucosa.

Dissimilarity in methacholine and adenosine 5'-monophosphate responsiveness 3 and 24 h after allergen challenge

Bronchial hyperresponsiveness (BHR) to methacholine and adenosine 5'-monophosphate (AMP) was studied in 15 allergic asthmatic patients before and 3 and 24 h after allergen challenge with house dust mite (HDM). Subjects attended the clinic on 3 consecutive days. On the first day a control solution was inhaled, and methacholine or AMP challenge was performed 3 h later. The next day HDM was inhaled, and 3 and 24 h later methacholine or AMP challenge was performed again. There were no significant difference in FEV1 baseline value between any of the study days. PD20 HDM, percentage decrease in FEV1, and AUC for both the EAR and LAR were not significantly different in the methacholine and AMP studies. After HDM challenge, PC20 methacholine decreased significantly from a geometric mean (+/- SEM) starting value of 1.39 +/- 0.63 mg/ml to 0.30 +/- 0.78 mg/ml (p less than 0.001) at 3 h and to 0.22 +/- 0.75 mg/ml (p less than 0.001) at 24 h. The magnitude of the decrease in PC20 methacholine at 3 h correlated with the severity of the late asthmatic reaction (LAR) as measured by the percentage fall in FEV1 and area under the curve (AUC) (r = -0.60 and r = 0.55; p less than 0.05). A significant decrease was observed in the PC20 AMP at 3 h, from a geometric mean value of 12.2 +/- 0.96 mg/ml after challenge with the control solution to 4.47 +/- 0.99 mg/ml (p less than 0.05) after HDM challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

Late-phase asthmatic reaction to inhaled allergen is associated with early recruitment of eosinophils in the airways

To determine whether a link exists between the recruitment of inflammatory cells in the airways and the development of the late-phase asthmatic reaction, we studied with bronchoalveolar lavage 54 asthmatic patients either at baseline (10 patients) or 4 h (11 patients), 24 h (13 patients), and 72 h (20 patients) after allergen inhalation challenge. Among the patients studied 4 h after allergen challenge, five were known to have a late-phase asthmatic response and showed a significant increase in the number and percentage of eosinophils in bronchoalveolar lavage compared with either patients without late-phase response (p less than 0.05) or unchallenged patients (p less than 0.01). Both the number and the percentage of eosinophils in bronchoalveolar lavage were also increased (p less than 0.05) in patients without a late-phase asthmatic reaction studied 24 h but not in those studied 4 h after allergen challenge. The numbers and the percentages of macrophages, neutrophils, or lymphocytes did not differ significantly among the different groups of patients. Of the patients studied 4 and 24 h after allergen challenge, only those with a late-phase asthmatic response showed an increased airway responsiveness to methacholine 1 h before bronchoalveolar lavage. We conclude that the development of the late-phase asthmatic response to allergen inhalation challenge and the allergen-induced increase in airway responsiveness are associated with an early recruitment of eosinophils in the airways.

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.

The effect of repetitive exercise on airway temperatures

To determine if a relationship exists between intra-airway thermal events and the reduction in pulmonary mechanics that occur in asthmatics when they perform repetitive exercise, we recorded intrathoracic airstream temperatures in seven subjects during and after two identical bouts of cycle ergometry performed 30 min apart. From these data, global and regional thermal energy exchanges were calculated. Inspired air conditions, work loads, and minute ventilations were held constant for both trials. Pulmonary mechanics were measured prior to and serially after each challenge. As expected, the second provocation produced a smaller response than did the first. In association with these mechanical changes, the second challenge also produced less airway cooling and slower rewarming in the central airways. Hence, repetitive exercise trials performed over short intervals attenuate the essential thermal gradients necessary to produce obstruction. To the extent that these differences in intra-airway temperature reflect changes in perfusion, our data raise the possibility that the responsivity of the bronchial microcirculation of asthmatics may be altered by repetitive exercise.

The effect of two months of treatment with inhaled budesonide on bronchial responsiveness to histamine and house-dust mite antigen in asthmatic children

We studied the effect of 2 months of treatment with budesonide (BUD) (Pulmicort), an inhaled corticosteroid, on the bronchial hyperresponsiveness to house-dust mite antigen (BHR-HDM) and to histamine (BHR-H). We also investigated whether BUD started 20 to 24 h after the development of a late asthmatic reaction (LAR) would influence the antigen-induced increase in nonspecific bronchial hyperresponsiveness to BHR-H. Thirty-one children with mild asthma who were atopic to HDM were randomized double blind into two parallel groups. Fifteen patients inhaled 0.2 mg BUD three times a day. Sixteen inhaled placebo in a similar way. Treatment began 20 to 24 h after antigen exposure and continued for 2 months. BHR-H and BHR-HDM were measured prior to and at the end of treatment. BHR-H was also determined 3 days after each antigen provocation. In the children receiving BUD, mean BHR-H and mean BHR-HDM were decreased approximately twofold after 2 months. No increase in BHR-H was observed after 3 days in the BUD group, irrespective of whether a LAR occurred. In patients in whom BUD treatment was withheld after the second antigen provocation, the protective effect of BHR-H was abolished. We conclude that 2 months of treatment with an inhaled corticosteroid causes a decrease in BHR-H and BHR-HDM. When an inhaled corticosteroid is administered 20 to 24 h after antigen provocation, It may protect against the antigen-induced increase in BHR-H. After treatment is discontinued, the protective effect wears off rapidly.

Effect of a thromboxane A2 synthetase inhibitor (OKY-046.HCl) on airway hyperresponsiveness in guinea pigs

We studied the effect of (E)-3-[p-(1H-imidazol-1-ylmethyl)phenyl]-2-propenoic acid hydrochloride monohydrate (OKY-046.HCl), a specific thromboxane (TX) A2 synthetase inhibitor, on airway hyperresponsiveness of guinea pigs. OKY-046.HCl (30-100 mg/kg, intraduodenally (i.d.) or orally (p.o.)) suppressed dose dependently the airway hyperresponsiveness to acetylcholine (ACh) induced by formyl-methionyl-leucyl-phenylalanine (FMLP), platelet activating factor (PAF) and repetitive antigen. OKY-046.HCl (100 mg/kg) also inhibited the increase in TXB2 in bronchoalveolar lavage fluid (BALF) induced by FMLP, PAF and antigen. Aspirin 10 or 30 mg/kg i.d. or p.o.) suppressed the airway hyperresponsiveness induced by FMLP and PAF but not by antigen. Azelastine (10 mg/kg i.d.) was ineffective on PAF- and antigen-induced airway hyperresponsiveness. TXA2 mimetic drugs caused airway hyperresponsiveness that was not inhibited by OKY-046.HCl (30 mg/kg i.v.). Furthermore, OKY-046.HCl showed no effect on propranolol- and physostigmine-induced airway hyperresponsiveness which did not accompany TXB2 generation in BALF. The number of eosinophils in BALF increased after FMLP exposure, an effect which was not inhibited by OKY-046.HCl. These results suggest that OKY-046.HCl inhibits airway hyperresponsiveness by suppressing TXA2 generation. We suggest that OKY-046.HCl will be a new antiasthmatic drug.

Effect of inhaled frusemide on the early response to antigen and subsequent change in airway reactivity in atopic patients

The purpose of this study was to investigate whether inhaled frusemide was able to inhibit the increase in nonspecific bronchial reactivity that occurs after the early response to allergen exposure in subjects with allergic rhinitis or asthma (or both). Ten symptom free patients initially underwent a challenge with methacholine, to determine the dose of methacholine that caused a 15% fall in FEV1 (PD15 FEV1 meth) and a challenge with a specific allergen, to determine the concentration of allergen that caused a fall in FEV1 of at least 15%. On two further occasions they inhaled allergen concentration that had caused the greater than or equal to 15% fall in FEV1 preceded by inhaled frusemide (40 mg frusemide in 4 ml buffered saline) or placebo (4 ml of diluent solution), according to a randomised, double blind, crossover design. All allergen studies were separated by at least seven days. A methacholine challenge was performed two hours after the allergen challenge, a time when the early response to allergen had completely resolved. Frusemide inhibited the early response to antigen, causing mean (95% confidence interval) protection of 87.6% (96-80%) for the maximum fall in FEV1. The increase in non-specific airway reactivity that occurred after antigen when this was preceded by placebo was reduced by frusemide. The mean (95% CI) difference in PD15 values between the placebo and the frusemide days was 1.73 (2.30-1.16) doubling doses of methacholine. These results confirm that frusemide is highly effective in preventing the early response to allergen, and show that it inhibits the increase in reactivity to methacholine that follows the early response.

Antigen challenge induces pulmonary airway eosinophil accumulation and airway hyperreactivity in sensitized guinea-pigs: the effect of anti-asthma drugs

1. Guinea-pigs were sensitized with 3 injections of ovalbumin (OA) (1 or 10 micrograms per animal) using Al(OH)3 and pertussis vaccine as adjuvants at two week intervals. 2. Sensitized guinea-pigs were challenged with an aerosol of OA (0.1%) over a one hour period and both airway reactivity and cellular content of bronchoalveolar lavage (BAL) fluid were assessed at intervals for up to 7 days. 3. Guinea-pigs sensitized with 1 microgram of ovalbumin responded to an aerosol of OA with increased pulmonary airway eosinophilia, which was evident 1 day after challenge and was present for up to 7 days. Airway hyperreactivity was not detectable in these animals. 4. Guinea-pigs sensitized with 10 micrograms of ovalbumin responded to an aerosol of OA with increased pulmonary airway neutrophilia and eosinophilia and with increased airway reactivity which was maximal between 8 and 24 h after exposure to OA. 5. Depletion of circulating platelets or neutrophils, by use of selective antisera, did not alter either the magnitude of eosinophilia or the intensity of airway reactivity in sensitized guinea-pigs (10 micrograms) exposed to an aerosol of OA. 6. Pretreatment of sensitized guinea-pigs (10 micrograms) for 6 days with AH 21-132, aminophylline, dexamethasone or ketotifen inhibited pulmonary airway eosinophilia, but did not diminish airway hyperreactivity. Neither eosinophil accumulation nor development of airway hyperreactivity was influenced by treatment with mepyramine or salbutamol over a 6 day period before OA inhalation. 7. Although eosinophilia may occur in association with increased airway reactivity in this animal model, there is no evidence of a causal relationship.

Model of bronchial hyperreactivity after active anaphylactic shock in conscious guinea pigs

A model of bronchial hyperreactivity at various times after an active anaphylactic shock in conscious guinea pigs is described. The bronchial inflammation was quantified in parallel by determination of the number of mononuclear cells, neutrophils, and eosinophils in bronchoalveolar lavage (BAL) fluids. The guinea pigs were sensitized by an intramuscular (i.m.) injection of a large dose of ovalbumin in Freund's complete adjuvant. The administration of ovalbumin (to induce anaphylactic shock) and of histamine to investigate bronchial hyperreactivity was by aerosol. The bronchial hyperreactivity to histamine was observed 3-6 hr after the anaphylactic shock. In the BAL fluid a decrease (1-3 hr) and then an increase (24-48 hr) in the number of mononuclear cells was found as well as an increase in neutrophils (3-48 hr) and in eosinophils (6-48 hr). The hyperreactivity was not correlated with changes in one category of cell in the BAL fluid. This model constitutes one simple test for investigating bronchial hyperreactivity in conscious guinea pigs. Further work is needed to try to determine the possible inflammatory parameters responsible for the hyperreactivity.

Prednisone pretreatment leads to histaminic airway hyporeactivity soon after resolution of the immediate allergic response

We assessed the effect of prednisone pretreatment (50 mg/day for three days) on the development of the early increase in histamine reactivity that occurs soon after resolution of the immediate response in allergic humans. Four allergic subjects who were known to develop only isolated immediate responses upon Kentucky bluegrass inhalation, as well as four mild allergic asthmatic subjects known to develop typical dual phase responses, were evaluated. All testing was done more than nine weeks after the grass pollen season had ended. Allergen inhalation produced an immediate response in all subjects. However, upon resolution of the immediate response to allergen in these pretreated subjects, the PC200His in all dual responding asthmatics and in three of the four isolated immediate responders had substantially increased above baseline values. We conclude that prednisone pretreatment leads to histaminic hyporeactivity soon after resolution of the immediate allergic response in both dual responding asthmatics and isolated immediate responders. It would seem that this prednisone effect is independent of its potential influence on the influx of inflammatory cells into diseased airways.

Rhinovirus upper respiratory infection increases airway hyperreactivity and late asthmatic reactions

Although viral upper respiratory infections (URIs) provoke wheezing in many asthma patients, the effect of these illnesses on the airway response to inhaled antigen is not established. The following study evaluated the effect of an experimental rhinovirus (RV) illness on airway reactivity and response to antigen in 10 adult ragweed allergic rhinitis patients. Preinfection studies included measurements of airway reactivity to histamine and ragweed antigen. Furthermore, the patients were also evaluated for late asthmatic reactions (LARs) to antigen (a 15% decrease in forced expiratory volume of the first second approximately 6 h after antigen challenge). 1 mo after baseline studies, the patients were intranasally inoculated with live RV16. All 10 patients were infected as evidenced by rhinovirus recovery in nasal washings and respiratory symptoms. Baseline FEV1 values were stable throughout the study. During the acute RV illness, there was a significant increase in airway reactivity to both histamine and ragweed antigen (P = 0.019 and 0.014, respectively). Before RV inoculation, only 1 of the 10 subjects had an LAR after antigen challenge. However, during the acute RV illness, 8 of 10 patients had an LAR (P less than 0.0085 compared with baseline); the development of LARs was independent of changes in airway reactivity and the intensity of the immediate response to antigen. Therefore, we found that not only does a RV respiratory tract illness enhance airway reactivity, but it also predisposes the allergic patient to develop LARs, which may be an important factor in virus-induced bronchial hyperresponsiveness.

Corticosteroids and cromolyn sodium as modulators of airway inflammation

Heightened airway reactivity is a cardinal feature of asthma and correlates with many clinical features of the illness, such as the acute response to bronchodilator drugs, the magnitude of diurnal fluctuations in lung function, and the amount of therapy required to control symptoms. Data have accumulated indicating that a reduction in airway reactivity can decrease asthma morbidity, and many advocate treating asthmatic patients prophylactically to prevent acute exacerbations from developing, rather than responding to them after they have occurred. This approach is particularly effective if it is used when the airways are being exposed to stimuli to which they are sensitive. A number of drugs have been purported to reduce airway reactivity, but the most convincing evidence supports the effects of cromolyn and inhaled and oral steroids. Although each type of drug has its own advantages and disadvantages and different modes of action, the common denominator is believed to be a reduction in the state of airway inflammation.

Immediate anaphylactic bronchoconstriction induces airway hyperreactivity in anaesthetized guinea-pigs

1. The possible acute occurrence of airway hyperreactivity after immediate-type bronchial anaphylaxis has been investigated in anaesthetized guinea-pigs actively sensitized to ovalbumin (OA). 2. Aerosol challenge (OA 10 mg ml-1, 5 s) provoked immediate bronchoconstriction which was substantially, although incompletely, reversed by isoprenaline (Iso) infusion (1 microgram kg-1 min-1) for 10 min). 3. Bronchoconstrictor responses to 5-hydroxytryptamine (5-HT) were enhanced in challenged animals when compared to those in non-challenged animals that had also received Iso. This was seen as a leftward shift in the location of the dose-response curve for the bronchoconstrictor effect of 5-HT (dose-ratio 2.45, 95% confidence limits 1.77-3.38; P less than 0.01). This phenomenon was associated with pulmonary infiltration of polymorphonuclear leukocytes, which was not modified by Iso treatment. 4. Iso infusion alone caused a slight enhancement of airway reactivity seen as a small leftward shift of the dose-response curve for the bronchoconstrictor effect of 5-HT (dose-ratio 1.51, 95% confidence limits 1.07-2.13; P less than 0.05). 5. These results support a causal relationship between acute pulmonary inflammation and airway hyperreactivity in an animal model of human allergic asthma.

The inflammatory theory of asthma

In summary, these observations suggest a model for asthma which is summarized in Table III. Initially, mast cells and possibly other bronchial cells, e.g., alveolar macrophages, are activated either in an IgE-dependent or, in intrinsic asthma, in an IgE-independent fashion. These cells release two sets of mediators which may be either preformed or newly synthesized. One set of mediators is responsible for the immediate bronchospastic response. This bronchospasm is transient, readily reversible, and not associated with either airway inflammation or bronchial hyperreactivity. The second set of mediators, however, promote chemotaxis and activation of neutrophils and eosinophils. The subsequent bronchial inflammation causes damage and desquamation of the respiratory epithelium. The increased exposure of irritant receptors results in hyperreactive airways. In addition, these inflammatory cells induce mast cell degranulation and recurrent bronchospasm. Thus, after the initial exposure to allergen, a vicious cycle of inflammation, hyperreactivity and recurrent mast cell degranulation develops, ultimately leading to the pathological picture of chronic asthma.