Biomedical subjects
Publications and source records attributed to W M Abraham.
Using disulphide cysteine-based inhibitors as lead structures, this communication describes our strategy for identifying more stable, potent antagonists of the alpha4beta1 integrin. These studies ultimately discovered potent, low molecular weight inhibitors based on D-thioproline-L-tyrosine.
The leukocyte integrin very late antigen-4 (alpha(4)beta(1), CD49d/CD29) is an adhesion receptor that plays an important role in allergic inflammation and contributes to antigen-induced late responses (LAR) and airway hyperresponsiveness (AHR). In this study, we show that single doses of a new small-molecule, tight-binding inhibitor of alpha(4), BIO-1211, whether given by aerosol or intravenously, either before or 1.5 h after antigen challenge blocks allergen- induced LAR and post-antigen-induced AHR in allergic sheep. Multiple treatments with doses of BIO-1211 that were ineffective when given singly, were protective. BIO-1211 also provided dose-dependent inhibition of the early airway response (EAR) to antigen. In conjunction with the functional protection against the antigen-induced LAR and AHR, sheep treated with BIO-1211 before challenge showed significantly reduced: (1) numbers of eosinophils in bronchoalveolar lavage (BAL), (2) BAL levels of the inflammatory marker tissue kallikrein, and (3) numbers of inflammatory cells (lymphocytes, eosinophils, metachromatic staining cells, and neutrophils) in bronchial biopsies obtained after challenge when compared with corresponding biopsies after vehicle treatment. More importantly, we show for the first time that an inhibitor of alpha(4) was able to reverse post-antigen-induced AHR, thereby decreasing the time of recovery from the normal period of > 9 d to 3 d. Our results show that effective inhibition of antigen-induced airway responses can be achieved with single doses of a potent small-molecule inhibitor of alpha(4) and that such agents may be used therapeutically, as well as prophylactically, to alleviate allergen- induced inflammatory events. These data provide further support and extend the evidence for the role of alpha(4) integrins in the pathophysiologic events that follow airway antigen challenge.
Airway mucus is a complex mixture of secretory products that provides a multifaceted defense against pulmonary infection. Mucus contains antimicrobial peptides (e.g., defensins) and enzymes (e.g., lysozyme) although the contribution of these to airway sterility has not been tested in vivo. We have previously shown that an enzymatically active, heme-containing peroxidase comprises 1% of the soluble protein in sheep airway secretions, and it has been hypothesized that this airway peroxidase may function as a biocidal system. In this study, we show that sheep airway peroxidase is identical to milk lactoperoxidase (LPO) and that sheep airway secretions contain thiocyanate (SCN(-)) at concentrations necessary and sufficient for a functional peroxidase system that can protect against infection. We also show that airway LPO, like milk LPO, produces the biocidal compound hypothiocyanite (OSCN(-)) in vitro. Finally, we show that in vivo inhibition of airway LPO in sheep leads to a significant decrease in bacterial clearance from the airways. The data suggest that the LPO system is a major contributor to airway defenses. This discovery may have significant implications for chronic airway colonization seen in respiratory diseases such as cystic fibrosis.
Emerging evidence suggests that mast cell tryptase is a therapeutic target for the treatment of asthma. The effects of this serine protease are associated with both pathophysiologic pulmonary responses and pathologic changes of the asthmatic airway. In this study, the tryptase inhibitor 1,5-bis-[4-[(3-carbamimidoyl-benzenesulfonylamino)-methyl]-p henoxy]-pentane (AMG-126737) was evaluated for its pharmacologic effects against allergen-induced airway responses. AMG-126737 is a potent inhibitor of human lung mast cell tryptase (Ki = 90 nM), with greater than 10- to 200-fold selectivity versus other serine proteases. Intratracheal administration of AMG-126737 inhibited the development of airway hyperresponsiveness in allergen-challenged guinea pigs with an ED50 of 0.015 mg/kg. In addition, the compound exhibited oral activity in the guinea pig model. The in vivo activity of AMG-126737 was confirmed in a sheep model of allergen-induced airway responses, where the compound inhibited early and late phase bronchoconstriction responses and the development of airway hyperresponsiveness. These results support the proposed role of tryptase in the pathology of asthma and suggest that AMG-126737 has potential therapeutic utility in this pulmonary disorder.
Integrin alpha4beta1 mediates leukocyte recruitment, activation, mediator release, and apoptosis inhibition, and it plays a central role in inflammatory pathophysiology. High-affinity, selective inhibitors of alpha4beta1, based on the Leu-Asp-Val (LDV) sequence from the alternatively spliced connecting segment-1 (CS-1) peptide of cellular fibronectin, are described that employ a novel N-terminal peptide "cap" strategy. One inhibitor, BIO-1211, was approximately 10(6)-fold more potent than the starting peptide and exhibited tight-binding properties (koff = 1.4 x 10(-4) s-1, KD = 70 pM), a remarkable finding for a noncovalent, small-molecule inhibitor of a protein receptor. BIO-1211 was also 200-fold selective for the activated form of alpha4beta1, and it stimulated expression of ligand-induced epitopes on the integrin beta1 subunit, a property consistent with occupancy of the receptor's ligand-binding site. Pretreatment of allergic sheep with a 3-mg nebulized dose of BIO-1211 inhibited early and late airway responses following antigen challenge and prevented development of nonspecific airway hyperresponsiveness to carbachol. These results show that highly selective and potent small-molecule antagonists can be identified to integrins with primary specificity for peptide domains other than Arg-Gly-Asp (RGD); they confirm the generality of integrins as small molecule targets; and they validate alpha4beta1 as a therapeutic target for asthma.
The purpose of this study was to determine whether aerosolized INS316 (UTP) stimulates lung mucociliary clearance (MCC) in sheep and, if so, to compare its effects with INS365, a novel P2Y(2)-receptor agonist. In the first series of studies, we used a previously described roentgenographic technique to measure tracheal mucus velocity (TMV), an index of MCC, before and for 4 h after aerosolization of INS316 (10(-1) M and 10(-2) M) and INS365 (10(-1) M and 10(-2) M), or normal saline in a randomized crossover fashion (n = 6). In a second series of studies, we compared the ability of these agents to enhance total lung clearance. For these tests, the clearance of inhaled technetium-labeled human serum albumin was measured serially over a 2-h period after aerosolization of 10(-1) M concentration of each agent (n = 7). Aerosolization of both P2Y(2)-receptor agonists induced significant dose-related increases in TMV (P < 0.05) compared with saline. The greatest increase in TMV was observed between 15 and 30 min after drug treatment. The highest dose (10(-1) M) of INS316 produced a greater overall stimulation of TMV than did INS365 (10(-1) M). Both compounds, compared with saline, induced a significant increase in MCC (P < 0.05) within 20 min of treatment. This enhancement in MCC began to plateau at 60 min. Although the response to INS316 started earlier, there was no significant difference between the clearance curves for the two compounds. We conclude that inhaled P2Y(2)-receptor agonists can increase lung MCC in sheep and that for P2Y(2)-receptor stimulation TMV accurately reflects changes in whole lung MCC.
Antigen challenge can elicit an allergic inflammatory response in the airways that involves eosinophils, basophils, and neutrophils and that is expressed physiologically as a late airway response (LAR) and airway hyperresponsiveness (AHR). Although previous studies have suggested that E-selectin participates in these allergic airway responses, there is little information concerning the role of L-selectin. To address this question, we examined the effects of administering an L-selectin-specific monoclonal antibody, DU1-29, as well as three small molecule selectin binding inhibitors, on the development of early airway responses (EAR), LAR and AHR in allergic sheep undergoing airway challenge with Ascaris suum antigen. Sheep treated with aerosol DU1-29 before antigen challenge had a significantly reduced LAR and did not develop postchallenge AHR. No protective effect was seen when sheep were treated with a nonspecific control monoclonal antibody. Treatment with DU1-29 also reduced the severity of the EAR to antigen. Similar results were obtained with each of the three small molecule selectin inhibitors at doses that depended on their L-, but not necessarily E-selectin inhibitory capacity. The inhibition of the EAR with one of the inhibitors, TBC-1269, was associated with a reduction in histamine release. Likewise, treatment with TBC-1269 reduced the number of neutrophils recovered in bronchoalveolar lavage (BAL) during the time of LAR and AHR. TBC-1269, given 90 min after antigen challenge also blocked the LAR and the AHR, but this protection was lost if the treatment was withheld until 4 h after challenge, a result consistent with the proposed time course of L-selectin involvement in leukocyte trafficking. These are the first data indicating that L-selectin may have a unique cellular function that modulates allergen-induced pulmonary responses.
Tissue kallikrein (TK) is secreted by serous cells of tracheobronchial submucosal glands and plays a role in allergic airway responses. To better understand the regulation of TK, we used primary cultures of submucosal gland cells that release TK upon stimulation. Media from cultures stimulated with chymase (10(-7) M) showed increased TK activity (0.50 +/- 0.22 mU/ml mean +/- standard error) in comparison with the control group (0.08 +/- 0.02 mU/ml). The increased TK activity was significantly correlated with increases in the levels of the serous cell marker, secretory leukoprotease inhibitor. Anion exchange chromatography of the conditioned culture media showed that TK activity eluted as a broad peak between 1.6 and 1.8 M NaCl, unlike the reported elution (0.3 to 0.6 M NaCl) of kallikreins from other tissues, suggesting that secreted bronchial TK was bound to a negatively charged molecule. Hyaluronidase digestion increased TK activity in both pre- and post-chymase-stimulated culture media, whereas no such change was seen after samples were digested with heparinase or chondroitinase ABC. Further, after hyaluronidase digestion of media, TK eluted from an anion exchange column between 0.3 and 0.6 M NaCl. Enzymatic detection of TK after nondenaturing gel electrophoresis showed that hyaluronidase digestion also reduced the electrophoretic heterogeneity of TK to a single band, whereas adding back hyaluronic acid (HA) to hyaluronidase-digested samples restored the original heterogeneity. Finally, TK activity bound to HA-Sepharose and could be eluted with HA. These studies show that primary cultures of ovine submucosal gland cells secrete TK in a regulated fashion, and that secreted TK binds to HA. This binding reduces TK enzymatic activity; therefore, factors that affect HA turnover could modify the TK activity in the airway lumen. These events could be important in the regulation of kinin-mediated airway inflammation.
Secretory leukocyte protease inhibitor (SLPI) is a naturally occurring protein of human airways that exhibits broad spectrum inhibitory activity against mast cell and leukocyte serine proteases implicated in asthma pathology. To assess the potential therapeutic utility of SLPI in this disorder, its effects on antigen-induced pulmonary responses were evaluated. In Ascaris-sensitized sheep, SLPI (3 mg) administered by aerosol daily for 4 days, with the final dose 0.5 h before antigen challenge, reduced the areas under the curve for early- and late-phase bronchoconstriction (73 and 95%, respectively; p <.05 versus control responses). SLPI also inhibited the development of airway hyperresponsiveness to carbachol (84%, p <. 05 versus control response) measured 24 h after antigen challenge. In ovalbumin-sensitized guinea pigs, intratracheal administration of SLPI daily for 3 days, with the final dose 1 h before antigen challenge, inhibited the development of airway hyperresponsiveness to histamine with an ED50 of <0.05 mg/kg. Prolonged pharmacodynamic activity of SLPI was observed in both species. In a murine model of atopic asthma, SLPI inhibited leukocyte influx into the airways after chronic allergen challenge. SLPI administered to sheep by the predosing protocol described above also prevented the antigen-induced decrease of tracheal mucus velocity (p <.05). In addition, a single aerosol administration of SLPI (30 mg) to sheep 1 h after antigen challenge inhibited the subsequent late-phase bronchoconstriction and development of hyperresponsiveness and reversed the stimulated decrease in tracheal mucus velocity. These results suggest that SLPI may provide therapeutic intervention against the pathophysiology of asthma and its underlying pathology.
Protease inhibition by secretory leukocyte protease inhibitor (SLPI) is accelerated by the sulfated polysaccharides. The nature of the SLPI-polysaccharide interaction, explored with affinity chromatography, indicated that this interaction was sensitive to the charge and type of polysaccharide. Dextran and chondroitin had the lowest affinity for SLPI, followed by dermatan, heparan, and dextran sulfates. While heparin bound SLPI tightly, the highest affinity heparin chains unexpectedly contained a lower level of sulfation than more weakly interacting chains. Heparin oligosaccharides, prepared using heparin lyase I were SLPI-affinity fractionated. Surprisingly, undersulfated heparin oligosaccharides bound SLPI with the highest affinity, suggesting the importance of free hydroxyl groups for high affinity interaction. Isothermal titration calorimetry was used to determine the thermodynamics of SLPI interaction with a low molecular weight heparin, an undersulfated decasaccharide and a tetrasaccharide. The studies showed 12-14 saccharide units, corresponding to molecular weight of approximately 4,800, were required for a 1:1 (SLPI:heparin) binding stoichiometry. Furthermore, an undersulfated decasaccharide was able to bind SLPI tightly (Kd approximately 13 nM), resulting in its activation and the inhibition of neutrophil elastase and pancreatic chymotrypsin. The in vitro assessment of heparin and the decasaccharide and tetrasaccharide using stopped-flow kinetics suggested that heparin was the optimal choice to study SLPI-based in vivo protease inhibition. SLPI and heparin were co-administered by inhalation in therapy against antigen-induced airway hyperresponsiveness in a sheep bronchoprovocation model. Heparin, in combination with SLPI demonstrated in vivo efficacy reducing early and late phase bronchoconstriction. Heparin also increased the therapeutic activity of SLPI against antigen-induced airway hyperresponsiveness.
In a previous study, a single dose of zileuton (10 mg/kg, po) given 2 h before antigen challenge, had a minimal effect on the antigen-induced early airway response (EAR), although it was effective in blocking the late airway response (LAR). Because our previous data indicated that 5-lipoxygenase (5-LO) products contribute to the severity of the antigen-induced EAR in these animals, we hypothesized that the lack of effect of zileuton on the EAR may have had to do with inadequate tissue levels. Therefore, in this study, we determined if multiple dosing with zileuton, which theoretically could improve tissue levels, would provide protection against the antigen-induced EAR as well as the LAR. Each sheep was used in each of the three trials (> or = 15 days apart), the order of which was randomized. For trial 1, the sheep were treated with zileuton (10 mg/kg in 0.1% methylcellulose, p.o.) once a day for 4 days; for trials 2, the sheep were treated with zileuton (10 mg/kg, p.o.) for 2 days; and, for trial 3, the animals were treated with vehicle (0.1% methylcellulose) for 4 days as in trial 1. In all trials, antigen challenge followed 1 h after the last treatment. In the placebo trial, antigen challenge resulted in characteristic EAR (407 +/- 102%, increase over baseline) and LAR (335 +/- 75%, increase over baseline). The antigen-induced effects were completely blocked by the 4-day treatment (EAR = 24 +/- 3%; LAR = 17 +/- 3%, P < 0.05 vs. placebo). In the 2-day trial, the immediate increase in R1, after antigen challenge was only partially blocked (EAR = 163 +/- 16%, P < 0.10 vs. placebo and P < 0.05 vs. 4-day trial), but the late response was completely blocked (24 +/- 3%). The protection against the EAR obtained with the 4-day treatment was significantly better (P < 0.05) than that obtained with the 2-day treatment. The results of this study show that multiple dosing with the 5-LO inhibitor, zileuton, provides protection against the antigen-induced EAR as well as LAR. The effect on the EAR is dependent on the treatment time, with dosing 4 days before antigen challenge providing a more significant effect than either dosing 2 days before challenge (this study) or on the same day as antigen challenge as was seen by us previously. This effect may be related to increased tissue levels of the drug.
The purpose of this study was to compare the effectiveness of an eight day treatment with clinically relevant doses of a fixed combination of the beta 2 mimetic reproterol hydrochloride and disodium cromoglycate with each agent given alone against antigen-induced early (EAR) and late airway responses (LAR) as well as post-antigen-induced airway hyperresponsiveness (AHR) in allergic sheep. Animals were treated in a randomized fashion with either the inhaled combination (n = 6), reproterol hydrochloride alone (n = 6), disodium cromoglycate alone (n = 6), or placebo (n = 8). Treatments (two puffs from a metered dose inhaler) were given three times a day for 7 days and once on the 8th day 1 h before airway challenge with Ascaris suum antigen. In the placebo trial, antigen challenge resulted in EAR and LAR as measured by increases in specific lung resistance; these changes were followed 24h later by AHR to inhaled carbachol. With respect to the placebo trial, treatment with reproterol hydrochloride reduced the EAR (P < 0.05) and blocked the LAR (P < 0.05), but had no effect on the post-challenge AHR. Treatment with disodium cromoglycate also reduced the EAR (P < 0.05), blocked the LAR (P < 0.05), and blocked the post-antigen-induced AHR (P < 0.05). Treatment with the fixed combination reduced the EAR (P < 0.05), blocked the LAR (P < 0.05), and blocked the post-antigen-induced AHR (P < 0.05). Comparison of the different agents indicated that the fixed combination gave significantly increased protection against the EAR than either agent alone, gave slightly better (P < 0.05) protection against the late response than cromolyn sodium and gave better protection against post-antigen-induced AHR than reproterol hydrochloride alone. These results suggest that a fixed combination of a beta 2-mimetic and disodium cromoglycate provides some increased protection against antigen-induced airway responses when compared to either agent alone in a controlled laboratory setting.
Inhaled heparin prevents antigen-induced bronchoconstriction and inhibits anti-immunoglobulin E-mediated mast cell degranulation. We hypothesized that the antiallergic action of heparin may be molecular weight dependent. Therefore, we studied the effects of three different low-molecular-weight fractions of heparin [medium-, low-, and ultralow-molecular-weight heparin (MMWH, LMWH, ULMWH, respectively)] on the antigen-induced acute bronchoconstrictor response (ABR) and airway hyperresponsiveness (AHR) in allergic sheep. Specific lung resistance was measured in 22 sheep before and after airway challenge with Ascaris suum antigen, without and after pretreatment with inhaled fractionated heparins at doses of 0.31-5.0 mg/kg. Airway responsiveness was estimated before and 2 h postantigen as the cumulative provocating dose of carbachol in breath units that increased specific lung resistance by 400%. All fractionated heparins caused a dose-dependent inhibition of ABR and AHR. ULMWH was the most effective fraction, with the inhibitory dose causing 50% protection (ID50) against ABR of 0.5 mg/kg, whereas ID50 values of LMWH and MMWH were 1.25 and 1.8 mg/kg, respectively. ULMWH was also the most effective fraction in attenuating AHR; the ID50 values for ULMWH, LMWH, and MMWH were 0.5, 2.5, and 4.7 mg/kg, respectively. These data suggest that 1) fractionated low-molecular-weight heparins attenuate antigen-induced ABR and AHR; 2) there is an inverse relationship between the antiallergic activity of heparin fractions and molecular weight; and 3) ULMWH is the most effective fraction preventing allergic bronchoconstriction and airway hyperresponsiveness.
Airway inflammation characterized by neutrophils and free elastase contributes to allergic mucociliary dysfunction. Glucocorticosteroids are the most important anti-inflammatory agents used in the treatment of asthma, but their effect on allergic mucociliary dysfunction is not known. Therefore, we assessed both the prophylactic and therapeutic effects of the glucocorticosteroid budesonide on antigen-induced mucociliary dysfunction in sheep. Tracheal mucus velocity (TMV), a marker of mucociliary clearance, was measured by using a roentgenographic technique. When budesonide was administered either 30 min before or 1 h after airway challenge with Ascaris suum, the antigen-induced fall in TMV at 6 h was prevented. The effects on TMV at 8 and 24 h after challenge were also determined when budesonide and, for comparative purposes, alpha1-protease inhibitor were given 6 h after antigen challenge. Budesonide treatment improved TMV at 8 h, but TMV was not significantly different from antigen alone at 24 h. Treatment with alpha1-protease inhibitor, however, caused only a significant reversal of the antigen-induced fall in TMV at 24 h after challenge; this indicates a more prolonged effect than budesonide. Our results suggest that antiproteases may have a potential role as a therapeutic approach to mucociliary dysfunction in asthma and provide evidence for another means by which glucocorticosteroids contribute to the control of the disease.
Pyocyanin (Pyo) and 1-hydroxyphenazine (1-HP) are extracellular products of Pseudomonas aeruginosa. To test whether these products were capable of producing an inflammatory response in the airways, combinations of Pyo and 1-HP at concentrations of 10(-4) and 10(-5) M were instilled into sheep airways, and indexes of inflammation were assessed by bronchoalveolar lavage (BAL) 24 h later. Challenge with the phenazines caused a significant dose-dependent increase in the number of cells and neutrophils recovered by BAL. Control challenges produced no such changes. The lung neutrophilia was accompanied by an increased concentration of albumin in BAL. The increases in BAL neutrophils and albumin could be blocked by treating the sheep with the 5-lipoxygenase inhibitor zileuton. Neither 1-HP nor Pyo was chemotactic to neutrophils when tested in vitro, but when alveolar macrophages (AM) were cultured in vitro in the presence of both Pyo and 1-HP (1 microM), the supernatants caused neutrophil chemotaxis. Analysis of AM culture supernatants incubated with the combination of pigments showed significant increases in leukotriene B4 and interleukin-8, and blocking these mediators separately or together reduced AM supernatant-induced neutrophil chemotaxis. We conclude that local instillation of Pyo and 1-HP can initiate an inflammatory response in the airways of sheep in vivo. This effect can be explained, in part, by the release of chemotactic factors produced by AM.
ML 3000 is a dual inhibitor of cyclooxygenase (COX) and 5-lipoxygenase (5-LO), two enzymes that contribute to the airway inflammation in asthma. When administered as an aerosol at a dose of 100 mg, 0.5 h before antigen challenge in allergic sheep, ML 3000 provided significant inhibition against the early bronchial response (EAR, mean 33% protection, P<0.05), completely blocked the late antigen-induced bronchoconstriction (LAR, mean 81% protection, P<0. 05) and the airway hyperresponsiveness (AHR, P<0.05) to aerosolized carbachol that occurs 24 h after antigen challenge in this model. Consistent with this functional protection was a small but significant reduction in the percentage of neutrophils recovered in bronchoalveolar lavage (BAL) at 8 h and 24 h after challenge. These findings are similar to previous data obtained in this animal model with other 5-LO inhibitors (blockade of the LAR and AHR) and COX inhibitors (blockade of AHR). These results suggest that aerosol administration of a dual inhibitor of COX and 5-LO may have beneficial effects in the treatment of allergic airway disease.
Previous experiments indicated that MIF-A3, a peptidoglycolipid extracted from Mycobacterium avium serovar 2 (Mycobacterium paratuberculosis 18), inhibits the killing of Candida albicans by activated bovine peripheral blood-derived macrophages and murine thioglycollate-elicited peritoneal macrophages in vitro. Subsequent in vitro data from our laboratory indicated that this reduction in killing may be related to the ability of MIF-A3 to scavenge reactive oxygen species (ROS). In this study we examined this hypothesis directly by determining if MIF-A3 reduced exogenous H2O2-induced candidacidal activity. When Candida albicans was incubated with H2O2 (4 mM) alone, colony-forming units/ml x 10(4) (CFU/ml) were 0.4 +/- 0.1 (mean +/- SE, n = 4) as compared to 11.3 +/- 2.0 CFU/ml in control (untreated) cultures (p < .05). The addition of catalase at concentrations > or = 6.8 U/ml, completely blocked the fungicidal effect of H2O2. However, reducing the amount of catalase from 6.8 U/ml to 3.4 U/ml resulted in a loss of scavenging activity, which was associated with a 50% increase in H2O2-mediated killing. Substituting MIF-A3 (400 micrograms/ml) for catalase, also reduced H2O2-induced fungicidal activity. In the absence of MIF-A3, H2O2 reduced Candida albicans to less than 10(3) CFU/ml. However, in the presence of MIF-A3 the CFU/ml of Candida albicans increased 7.5-fold. Based on concentration-response curves of H2O2 inhibition vs. increasing amounts of catalase we determined that the relative inhibitory capacity of the MIF-A3 (400 micrograms/ml) was approximately 1.0 U/ml "catalase equivalents." These findings provide direct evidence that MIF-A3 can scavenge H2O2, and reduce H2O2-induced killing of Candida albicans.
Antigen-induced bronchoconstriction is associated with impairment of mucociliary clearance with a time course that is consistent with the initial influx of neutrophils into the airway. In this study we tested the hypothesis that elastase released from activated neutrophils contributes to the acute (0 to 6-hr) antigen-induced mucociliary dysfunction. Tracheal mucous velocity CTMV), an index of mucociliary function, was measured with a roentgenographic technique before and serially after airway challenge with Ascaris suum antigen alone, or after pretreatment with aerosolized alpha1-protease inhibitor (alpha1-PI, 10 mg) or the specific neutrophil elastase inhibitor ICI 200,355 (10 mg). Antigen alone significantly decreased TMV. Treatment with either alpha1-PI or ICI 200,355, given either at 30 min before antigen challenge or 1 h after challenge, significantly attenuated the antigen-induced reduction in TMV at 6 h after challenge, whereas sheep treated with inactivated alpha1-PI were not protected from this antigen-induced event. Inhalation of ovine elastase (obtained from stimulated neutrophils) significantly decreased TMV, and this effect was also blocked by pretreatment with alpha1-PI. Both alpha1-PI and ICI 200,355 inhibited the activity of elastase obtained from stimulated ovine neutrophils. To verify that the neutrophil numbers and elastase activity increased in sheep airways after antigen challenge, nine animals underwent bronchoalveolar lavage (BAL) at 2 h and 4 h after instillation of A. summ antigen. Four hours after challenge, the number of neutrophils had increased by 50-fold, and free elastase activity in lavage fluid had increased. These data indicate that the antigen-induced impairment of mucociliary clearance is partly dependent on increased elastase activity, and that elastase inhibitors may be useful in protecting against mucociliary dysfunction.