Airway eosinophils from actively sensitized guinea pigs exhibit enhanced superoxide anion release in response to antigen challenge

Role of nitric oxide and superoxide in allergen-induced airway hyperreactivity after the late asthmatic reaction in guinea-pigs

1. In the present study, the roles of nitric oxide (NO) and superoxide anions (O2(-)) in allergen-induced airway hyperreactivity (AHR) after the late asthmatic reaction (LAR) were investigated ex vivo, by examining the effects of the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) and superoxide dismutase (SOD) on the responsiveness to methacholine of isolated perfused guinea-pig tracheae from unchallenged (control) animals and from animals 24 h after ovalbumin challenge. 2. At 24 h after allergen challenge, the animals developed AHR in vivo, as indicated by a mean 2.63 +/- 0.54 fold (P < 0.05) increase in sensitivity to histamine inhalation. 3. Compared to unchallenged controls, tracheal preparations from the ovalbumin-challenged guinea-pigs displayed a significant 1.8 fold (P < 0.01) increase in the maximal response (E(max)) to methacholine, both after intraluminal (IL) and extraluminal (EL) administration of the agonist. No changes were observed in the sensitivity (pEC(50)) to the agonist. Consequently, the DeltapEC(50) (EL-IL), as a measure of epithelial integrity, was unchanged. 4. In the presence of L-NAME (100 microM, IL), tracheae from control guinea-pigs showed a 1.6 fold (P < 0.05) increase in the E(max) of IL methacholine. By contrast, the E(max) of IL methacholine was significantly decreased in the presence of 100 u ml(-1) EL SOD (54% of control, P < 0.01). 5. Remarkably, the increased responsiveness to IL methacholine at 24 h after allergen challenge was reversed by L-NAME to control (P < 0.01), and a similar effect was observed with SOD (P < 0.01). 6. The results indicate that both NO and O2(-) are involved in the tracheal hyperreactivity to methacholine after the LAR, possibly by promoting airway smooth muscle contraction through the formation of peroxynitrite.

Effects of endogenous superoxide anion and nitric oxide on cholinergic constriction of normal and hyperreactive guinea pig airways

In a guinea pig model of allergic asthma, we have recently established that a deficiency of nitric oxide (NO) contributes to the increased ex vivo responsiveness of isolated perfused tracheae to methacholine after the early asthmatic reaction at 6 h after inhalational challenge of the animals with ovalbumin aerosol. Because this deficiency could be caused by a reaction of NO with enhanced levels of inflammation-induced superoxide anion (O-2), we examined the effect of endogenous O-2 on the regulation of methacholine-induced constriction by NO of intact perfused tracheal tube preparations from unchallenged (control) guinea pigs and from animals 6 h after ovalbumin challenge. In the presence of the NO synthase (NOS) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME; 100 microM), tracheae obtained from unchallenged guinea pigs showed a 1.7-fold increase in the maximal response to intraluminally applied methacholine (p < 0.05). By contrast, the maximal airway response to methacholine was significantly decreased in the presence of the O-2 scavenger superoxide dismutase (SOD; 100 U/ml), by approximately 45% (p < 0.01). The SOD-induced decrease in responsiveness to methacholine was reversed by L-NAME. Tracheal preparations obtained at 6 h after allergen challenge showed a 1. 8-fold increased responsiveness to intraluminally applied methacholine compared with controls (p < 0.001), which was not further enhanced in the presence of L-NAME. SOD had neither an effect on the increased responsiveness nor did it restore the potentiating effect of L-NAME. These results indicate that (1) in normoreactive tracheal preparations, the regulatory role of NO is partially counteracted by endogenous O-2, and ( 2) the deficiency of NO in hyperreactive tracheae obtained at 6 h after ovalbumin challenge is not caused by its reaction with O-2, but rather to decreased cNOS activity. De Boer J, Pouw FMH, Zaagsma J, Meurs H. Effects of endogenous superoxide anion and nitric oxide on cholinergic constriction of normal and hyperreactive guinea pig airways.

The regulation of pulmonary immunity

No evidence has emerged which suggests that the principles of immunity derived from studies on cells from other body sites are contradicted in the lung and its associated lymphoid tissue. What is clear, however, is that the environment dictates the types of cells, their relationship to one another, and what perturbing events will set in motion either the development of an "active" immune response or tolerance. Investigating mechanisms for the development of lung immunity has increased our understanding of how human diseases develop and is continuing to suggest new ways to manipulate pulmonary immune responses. Demonstration that lung cells regulate both nonspecific inflammation and immunity through the expression of adhesion molecules and the secretion of cytokines offers hope for ways to design more effective vaccines, enhance microbial clearance in immunosuppressed hosts, and to suppress manifestations of immunologically mediated lung disease. Important lung diseases targeted for intensive research efforts in the immediate future are tuberculosis, asthma, and fibrotic lung disease. Perhaps even the common cold might be conquered. Considering the pace of current research on lung immunity, it may not be too ambitious to predict that these diseases may be conquered in the next decade.

Role of interleukin-5 in enhanced migration of eosinophils from airways of immunized guinea-pigs

1. Platelet activating factor (PAF), leukotriene B4 (LTB4) and interleukin-5 (IL-5) are potent chemoattractants for guinea-pig eosinophils, which may be involved in eosinophil recruitment and up-regulation in allergic diseases. Eosinophils from the bronchoalveolar lavage fluid (BALF) of ovalbumin-sensitized guinea-pigs were collected 24 h after antigen provocation and migration induced by PAF, LTB4 and rhIL-5 was studied. 2. Total BALF content and distribution of eosinophils were greater in immunized, ovalbumin-challenged guinea-pigs (5.0 +/- 0.8 x 10(6)/guinea-pig; 12 +/- 1%) than in immunized, saline-challenged animals (3.0 +/- 0.7 x 10(6)/guinea-pig; 7 +/- 1%). 3. The chemoattraction of eosinophils isolated on a metrizamide gradient was studied in micro-Boyden chambers, results being expressed as the number of migrating cells (mean +/- s.e. mean). PAF and LTB4-induced migration of eosinophils from immunized and OA-challenged guinea-pigs were significantly enhanced, as compared to immunized and saline-challenged animals (170 +/- 36 vs 35 +/- 9 migrating eosinophils for 10 nM PAF; 271 +/- 60 vs 110 +/- 19 for 1 nM LTB4). 4. The IL-5 antibody TRFK-5, in vivo, reduced eosinophil recruitment in BALF of antigen-challenged immunized animals as well as the enhanced responsiveness of eosinophils from the challenged animals, suggesting a role for IL-5 in the priming of eosinophils in vivo. 5. In contrast to TRFK-5, nedocromil sodium reduced to a similar extent eosinophil, macrophage and lymphocyte recruitment into the BALF of antigen-challenged, but failed to down-regulate the enhanced responsiveness of eosinophils from the challenged animals. 6. The increased eosinophil content in lungs from antigen-challenged guinea-pigs is thus selectively reduced by the anti-IL-5 antibody, which also attenuates the concomitant enhancement of the eosinophil responsiveness, supporting the concept that IL-5 is essential for recruitment and priming of eosinophils in vivo. In contrast, nedocromil sodium reduced non-selectively the total cell recruitment to the airways,but failed to attenuate the enhanced responsiveness of those eosinophils which migrated, indicating that its effects involve a different target.

Release of monokines by pulmonary macrophages following antigen challenge in sensitized guinea pigs

Guinea pigs were passively sensitized with immune serum to ovalbumin (OA), control serum, or saline. Twenty-four hours later, they inhaled aerosols of OA (2% in saline), saline, or lipopolysaccharide (LPS). Following anesthesia, bronchoalveolar lavage (BAL) was performed at 30, 60, 90 and 120 min postinhalation. Alveolar macrophages (AM) were isolated from the BAL fluid and incubated (18 h) in medium alone or with zymosan (1 mg/ml). Supernatants were collected and levels of interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) determined by bioassays. Unstimulated AM from animals that inhaled OA, saline, or LPS secreted similar amounts of IL-1 at 30, 60, and 90 min postinhalation. Zymosan (1 mg/ml) significantly increased IL-1 secretion by AM collected at 60 and 90 min from OA-sensitized animals that inhaled OA or saline. AM from guinea pigs sensitized to OA that inhaled OA or LPS secreted significantly increased amounts of IL-6 at 30, 60, 90, and 120 min postchallenge compared to saline sensitized controls. In all groups, AM from LPS-treated animals secreted large amounts of TNF-alpha at all sampling times postchallenge; AM from OA-sensitized and challenged animals secreted increasing amounts of TNF-alpha with time postchallenge, spontaneously and in response to zymosan. By contrast, AM from saline sensitized and challenged guinea pigs did not release detectable amounts of TNF-alpha spontaneously and secreted very low amounts in the presence of zymosan. These findings show that antigen challenge results in a rapid activation of AM isolated from BAL and suggest AM may initiate the development of inflammatory processes associated with antigen challenge.

Effect of the selective thromboxane A2 receptor antagonist, S-1452, on antigen-induced sustained bronchial hyperresponsiveness

Long-lasting bronchial hyperresponsiveness to i.v. acetylcholine was observed in actively sensitized guinea-pigs after aerosol ovalbumin exposure. The response became significant at 7 h post-challenge and persisted for at least 120 h compared to the response of unsensitized animals. Pretreatment of animals with the specific thromboxane A2 receptor antagonist, S-1452 (calcium (1R,2S,3S,4S)-(5Z)-7-(((phenylsulfonyl)amino)bicyclo[2.2.1] hept-2-yl)hept-5-enoate dihydrate), almost completely inhibited the onset of bronchial hyperresponsiveness, as assessed at 24 and 120 h post-challenge. However, it was ineffective when administered at 1 h post-challenge or 2 h before assessment of bronchial responsiveness. Lung vascular injury occurred transiently immediately after antigen challenge, the kinetics of injury being associated with those for the production of thromboxane B2 in bronchoalveolar lavage fluid. The vascular injury was dramatically suppressed by pretreatment with S-1452. These findings suggest that acutely generated thromboxane A2 plays an important role in the pathogenesis of antigen-induced long-lasting bronchial hyperresponsiveness, probably by producing vascular damage in the lungs.

Effect of formoterol on superoxide anion generation from bronchoalveolar lavage cells after antigen challenge in guinea pigs

It is well known that antigen challenge of sensitized subjects can induce an immediate and late asthmatic response, airway eosinophilia, and hyperreactivity. Using our modified guinea pig asthma model, we investigated the superoxide anion generation from eosinophils and macrophages recovered from bronchoalveolar lavage (BAL) 24 h after antigen (ovalbumin) challenge. We also investigated the effect of formoterol, a new long-acting selective beta 2-agonist, on these functions. Antigen challenge increased the total cell counts and the ratio of eosinophils in BAL. Eosinophils and macrophages were collected using discontinuous density centrifugation. Antigen challenge enhanced superoxide anion generation from eosinophils, from 5.39 +/- 1.08 to 13.19 +/- 1.95 nmol 60 min after phorbol myristate acetate (PMA) (1 ng/ml) activation, and 0.22 +/- 0.49 to 3.34 +/- 1.67 nmol 40 min after platelet-activating factor (PAF) (10(-6) M) activation. Formoterol treatment before antigen challenge prevented these enhancements. Superoxide anion generation from macrophages was also enhanced by antigen challenge, from 6.57 +/- 0.76 to 10.66 +/- 0.88 nmol 60 min after PMA activation, and 4.20 +/- 1.17 to 6.63 +/- 0.64 nmol 60 min after PAF activation. Formoterol, however, failed to inhibit enhancement of superoxide anion generation from macrophages. These results show antigen challenge of sensitized guinea pigs induces an increase of eosinophils and macrophages in BAL and enhances the functional characteristics of both cells. Formoterol had inhibitory effects on the enhancement of superoxide anion generation from eosinophils but did not have this effect on macrophages.