Responsiveness to histamine in human sensitized airway smooth muscle

Models to study airway smooth muscle contraction in vivo, ex vivo and in vitro: implications in understanding asthma

Asthma is a chronic obstructive airway disease characterised by airway hyperresponsiveness (AHR) and airway wall remodelling. The effector of airway narrowing is the contraction of airway smooth muscle (ASM), yet the question of whether an inherent or acquired dysfunction in ASM contractile function plays a significant role in the disease pathophysiology remains contentious. The difficulty in determining the role of ASM lies in limitations with the models used to assess contraction. In vivo models provide a fully integrated physiological response but ASM contraction cannot be directly measured. Ex vivo and in vitro models can provide more direct assessment of ASM contraction but the loss of factors that may modulate ASM responsiveness and AHR, including interaction between multiple cell types and disruption of the mechanical environment, precludes a complete understanding of the disease process. In this review we detail key advantages of common in vivo, ex vivo and in vitro models of ASM contraction, as well as emerging tissue engineered models of ASM and whole airways. We also highlight important findings from each model with respect to the pathophysiology of asthma.

Airway smooth muscle in asthma: just a target for bronchodilation?

Airway smooth muscle (ASM) has long been recognized as the main cell type responsible for bronchial hyperresponsiveness. It has, thus, been considered as a target for bronchodilation. In asthma, however, there is a complex relationship between ASM and inflammatory cells, such as mast cells and T lymphocytes. Moreover, the increased ASM mass in asthmatic airways is one of the key features of airway remodeling. This article aims to review the main concepts about the 3 possible roles of ASM in asthma: (1) contractile tone, (2) inflammatory response, and (3) remodeling.

Airway smooth muscle as a model for new investigative drugs in asthma

Bronchial asthma as such exists because airway smooth muscle (ASM) contracts excessively in response to various stimuli. After several decades during which research was mainly focused on airway inflammation, increasing attention is now being paid to a possible abnormal behaviour of ASM. Thus, ASM is regarded as a major target for anti-asthma treatments. This review first describes the mechanisms of ASM contraction and airway hyperresponsiveness, through cellular, animal and human models. The developments of new drugs targeting extra and/or intracellular pathway of ASM contraction are discussed.

Omalizumab decreases nonspecific airway hyperresponsiveness in vitro

BACKGROUND

In asthmatic patients, both symptoms and hyperresponsiveness are related to immunoglobulin E (IgE) concentration in serum. The anti-IgE monoclonal antibody omalizumab improved the control of asthma, but its effect on airway hyperresponsiveness is controversial. Passive sensitization reproduced in vitro a bronchial hyperresponsiveness, an increase in IgE bearing cells, and a mast cell degranulation. This study was designed to examine the effect of omalizumab on passive sensitization-induced hyperresponsiveness, alterations in IgE positive inflammatory cells and mast cell degranulation within the bronchial wall.

METHODS

Proximal (3-5 mm diameter) and distal (0.5-1.5 mm diameter) human bronchi dissected out from 10 lung specimens were incubated in normal or asthmatic serum containing various concentrations of omalizumab. Contractile responses to histamine or Dermatophagoides pteronyssinus (D. pter) were recorded using an organ bath system and expressed as percentage of maximal contractile response to acetylcholine (ACh). Immunohistochemistry was performed using monoclonal antibodies directed against IgE or tryptase. Mast cells were classified as fully granulated (type I), partly (type II) or largely degranulated (type III).

RESULTS

The specific bronchial hyperresponsiveness to D. pter and the nonspecific bronchial hyperresponsiveness to histamine following passive sensitization were significantly inhibited by omalizumab in both distal and proximal airways. Passive sensitization-induced increase in IgE positive cells was also abolished by omalizumab in a concentration dependent manner. Mast cell degranulation which was inhibited by omalizumab was positively correlated with the contractile response to D. pter.

CONCLUSIONS

Omalizumab blocks specific and nonspecific bronchial hyperresponsiveness. Anti-IgE also decreases IgE bearing cell number and mast cell degranulation.

Airway smooth muscle as a regulator of immune responses and bronchomotor tone

The traditional view of airway smooth muscle (ASM) in asthma, as a purely contractile tissue, seems to be inadequate. Compelling evidence now suggests that ASM plays an important role in regulating bronchomotor tone, in perpetuating airway inflammation, and in remodeling of the airways. This article reviews three distinct functions of ASM cells: the process of excitation-contraction coupling, with a particular focus on the role of cytokines in modulating calcium responses; the processes of smooth muscle cell proliferation and migration; and the synthetic and immunomodulatory function of ASM cells. This article also discusses how altered synthetic function contributes to airway remodeling.

The high-affinity IgE receptor (FcepsilonRI): a critical regulator of airway smooth muscle cells?

The airway smooth muscle (ASM) has been typically described as a contractile tissue, responding to neurotransmitters and inflammatory mediators. However, it has recently been recognized that ASM cells can also secrete cytokines and chemokines and express cell adhesion molecules that are important for the perpetuation and modulation of airway inflammation. Recent progress has revealed the importance of IgE Fc receptors in stimulating and modulating the function of these cells. In particular, the high-affinity receptor for IgE (FcepsilonRI) has been identified in primary human ASM cells in vitro and in vivo within bronchial biopsies of atopic asthmatic individuals. Moreover, activation of this receptor has been found to induce marked increases in the intracellular calcium concentrations and T helper 2 cytokines and chemokines release. This and other evidence discussed in this review provide an emerging view of FcepsilonR/IgE network as a critical modulator of ASM cell function in allergic asthma.

Inhibition of Rho-kinase normalizes nonspecific hyperresponsiveness in passively sensitized airway smooth muscle preparations

Currently, little is known about mechanisms underlying passive sensitization-induced nonspecific airway hyperresponsiveness. We sought to determine whether the nonspecific airway hyperresponsiveness observed after passive sensitization involves an increased role of Rho-kinase in airway smooth muscle contraction. In addition, the contribution of Rho-kinase to specific allergen-induced airway smooth muscle contraction was studied. Guinea pig tracheal smooth muscle preparations were incubated for 16 h, in the presence of serum obtained from nonsensitized guinea pigs or atopic serum obtained from actively ovalbumin-sensitized guinea pigs. After incubation, the contribution of Rho-kinase to histamine-, methacholine- or ovalbumin-induced isometric contractions was determined, using the specific Rho-kinase inhibitor Y-27632. Maximal contractions induced by histamine and methacholine were significantly increased in passively sensitized preparations, without a change in potency (-logEC50). In control preparations, Y-27632 reduced the potency of both agonists, without affecting maximal contraction. Remarkably, the increased agonist responsiveness induced by passive sensitization was fully normalized by Y-27632. Treatment with Y-27632 also reduced ovalbumin-induced contraction in these preparations. This study shows that the nonspecific airway smooth muscle hyperresponsiveness as well as the specific allergen responsiveness induced by passive sensitization are dependent on Rho-kinase. The complete inhibition by Y-27632 of the passive sensitization-induced increased responsiveness toward histamine and methacholine indicates a pivotal role of Rho-kinase in this process.

TGF-beta potentiates airway smooth muscle responsiveness to bradykinin

The molecular mechanisms by which bradykinin induces excessive airway obstruction in asthmatics remain unknown. Transforming growth factor (TGF)-beta has been involved in regulating airway inflammation and remodeling in asthma, although it is unknown whether TGF-beta can modulate bradykinin-associated bronchial hyperresponsiveness. To test whether TGF-beta directly modulates airway smooth muscle (ASM) responsiveness to bradykinin, isolated murine tracheal rings were used to assess whether TGF-beta alters ASM contractile responsiveness to bradykinin. Interestingly, we found TGF-beta-treated murine rings (12.5 ng/ml, 18 h) exhibited increased expression of bradykinin 2 (B(2)) receptors and became hyperreactive to bradykinin, as shown by increases in maximal contractile responses and receptor distribution. We investigated the effect of TGF-beta on bradykinin-evoked calcium signals since calcium is a key molecule regulating ASM excitation-contraction coupling. We reported that TGF-beta, in a dose- (0.5-10 ng/ml) and time- (2-24 h) dependent manner, increased mRNA and protein expression of the B(2) receptor in cultured human ASM cells. Maximal B(2) receptor protein expression that colocalized with CD44, a marker of membrane cell surface, occurred after 18 h of TGF-beta treatment and was further confirmed using fluorescence microscopy. TGF-beta (2.5 ng/ml, 18 h) also increased bradykinin-induced intracellular calcium mobilization in fura-2-loaded ASM cells. TGF-beta-mediated enhancement of calcium mobilization was not attenuated with indomethacin, a cyclooxygenase inhibitor. These data demonstrate for the first time that TGF-beta may play a role in mediating airway hyperresponsiveness to bradykinin seen in asthmatics by enhancing ASM contractile responsiveness to bradykinin, possibly as a result of increased B(2) receptor expression and signaling.

Increased airway responsiveness, allergy-type-I skin responses and systemic anaphylaxis in a humanized-severe combined immuno-deficiency mouse model

BACKGROUND

In patients with allergic bronchial asthma, a strong relationship between elevated serum IgE antibody titres and the development of increased airway responsiveness (AR) has been demonstrated. To further elucidate the relationship between human (hu) IgE and development of increased AR, we developed an in vivo model utilizing immuno-compromised severe combined immuno-deficiency (SCID) mice.

METHODS

SCID mice were either reconstituted with peripheral blood mononuclear cells (PBMC) from non-atopic, healthy or atopic individuals sensitized against house dust mite allergen (Der p), or passively sensitized with plasma from non-atopic, healthy or atopic individuals.

RESULTS

In both systems, atopic hu-SCID mice developed increased AR. The following results suggest that these responses were mediated via IgE antibodies: increased AR did not occur after transfer of either PBMC or IgE-negative plasma from non-atopic individuals; increased AR occurred simultaneous with increased serotonin release detected 15 min after allergen-aerosol challenge in bronchoalveolar lavage fluid; and increased AR required at least two allergen-aerosol challenges. SCID mice reconstituted with serum containing anti-Der p IgE antibodies developed positive immediate-type skin test responses to intradermal injection of Der p as well as anti-hu-IgE antibody. In addition, IgE binding to skin mast cells was demonstrated by immunohistochemistry. Furthermore, intravenous challenge of hu anti-Der p positive SCID mice with Der p resulted in systemic anaphylaxis.

CONCLUSION

These data provide evidence that passive immunization of SCID mice with hu IgE alters AR and that T cells and eosinophils were not a requirement for the development of increased AR in this model.

TNF-[alpha] modulates murine tracheal rings responsiveness to G-protein-coupled receptor agonists and KCl

Although the mechanisms that underlie airway hyperresponsiveness in asthma are complex and involve a variety of factors, evidence now suggests that intrinsic abnormalities in airway smooth muscle (ASM) may play an important role. We previously reported that TNF-alpha, a cytokine involved in asthma, augments G-protein-coupled receptor (GPCR) agonist-evoked calcium responses in cultured ASM cells. Here we have extended our previous studies by investigating whether TNF-alpha also modulates the contractile and relaxant responses to GPCR activation using cultured murine tracheal rings. We found that in tracheal rings treated with 50 ng/ml TNF-alpha, carbachol-induced isometric force was significantly increased by 30% compared with those treated with diluent alone (P < 0.05). TNF-alpha also augmented KCl-induced force generation by 70% compared with rings treated with diluent alone (P < 0.01). The enhancing effect of TNF-alpha on carbachol-induced isometric force generation was completely abrogated in the tracheal rings obtained from TNF-alpha receptor (TNFR)1-deficient mice and in control rings treated with a TNF-alpha mutant that solely activates TNFR2. TNF-alpha also attenuated relaxation responsiveness to isoproterenol but not to PGE2 or forskolin. TNF-alpha modulatory effects on GPCR-induced ASM responsiveness were completely abrogated by pertussis toxin, an inhibitor of Gialpha proteins. Taken together, these data suggest that TNF-alpha may participate in the development of airway hyperresponsiveness in asthma via the modulation of ASM responsiveness to both contractile and beta-adrenoceptor GPCR agonists.

Contractile responses to adenosine, R-PIA and ovalbumen in passively sensitized guinea-pig isolated airways

1. Responses to adenosine, R-PIA and ovalbumen were examined in guinea-pig isolated superfused tracheal spirals to determine the effects of passive sensitization by overnight incubation in serum from ovalbumen (OA)-sensitized or non-sensitized guinea-pigs. 2. Tissues incubated with serum from non-sensitized and OA-sensitized guinea-pigs contracted (0.07+/-0.02 and 0.04+/-0.01 g, respectively) to adenosine (300 micro M) whereas non-incubated or Krebs-incubated tissues produced no contractions to adenosine or ovalbumen (10 micro g). Ovalbumen caused substantial contractions (0.40+/-0.09 g) after OA-sensitized serum incubation and significantly (P<0.05) smaller contractions (0.08+/-0.03 g) after non-sensitized serum incubation. Tracheae from guinea-pigs actively sensitized to ovalbumen 14-21 days beforehand also contracted to adenosine, R-PIA (3 micro M) and ovalbumen. 3. The A(1)/A(2) adenosine receptor antagonist, 8-phenyltheophylline (8-PT, 3 micro M), failed to antagonize these contractions, suggesting that A(1)/A(2) adenosine receptors were not involved. 4. Unlike adenosine, R-PIA (3 micro M) produced contractions in non-incubated (0.23+/-0.04 g) or Krebs-incubated (0.15+/-0.04 g) tracheae, as well as after passive and active sensitization. None of these responses were blocked by 8-PT. 5. The A(3) receptor agonist, IB-MECA, in the presence of 8-PT produced small contractions in passively sensitized tracheae (10 micro M, 0.02+/-0.003 g) and, in larger doses (100 micro M and 1 mM), contracted actively sensitized tracheae. 6. In actively sensitized trachea, the A(3) receptor antagonist, MRS-1220 (100 nM), significantly (P<0.05) attenuated adenosine contractions in the presence of 8-PT from 0.23+/-0.07 g to 0.07+/-0.03 g. 7. These results show that passive, like active sensitization, reveals bronchoconstrictions to adenosine of isolated tracheae. The insensitivity to 8-PT blockade, the antagonism by MRS-1220, and the fact that the A(3) receptor agonist, IB-MECA, mimics this response, suggest involvement of A(3) receptors. R-PIA, however, has a different profile of adenosine receptor activity.

Passive sensitization of human airways induces mast cell degranulation and release of tryptase

BACKGROUND

This study was designed to examine the effect of passive sensitization (PS) on human bronchial mast cells. PS with asthmatic serum induces a hyper-responsiveness to nonspecific agonists, and immunoglobulin (Ig)E binding mainly on mast cells.

METHODS

Bronchi dissected out from 19 lung specimens were incubated in normal or asthmatic serum. Immunohistochemistry was performed using monoclonal antibodies (MoAbs) directed against tryptase, chymase, or c-kit. Mast cells were classified as fully granulated (type I), partly (type II) or largely degranulated (type III). Tryptase was measured in supernatant using ELISA. Contractile response was recorded in a separated set of experiments using an organ bath system.

RESULTS

PS decreased both tryptase positive cells (47.9 +/- 10.0 vs. 26.7 +/- 4.8 cell/mm2, P = 0.003) and chymase positive cells (26.1 +/- 3.3 vs. 14.9 +/- 1.8 cell/mm2, P = 0.01), but did not alter the number of c-kit positive cell. PS decreased the proportion of type I (55.4 vs. 28.9%, P < 0.0001) and, concomitantly increased that of types II (23.2 vs. 41.0%, P < 0.0001) and III (21.4 vs. 30.1%, P = 0.04). Following PS, tryptase concentration significantly increased and the magnitude of histamine response, was correlated with the amount of type II mast cells.

CONCLUSION

PS of human isolated bronchi induces a mast cell degranulation related to in vitro hyper-responsiveness, along with a tryptase release.

Modulation of calcium homeostasis as a mechanism for altering smooth muscle responsiveness in asthma

Airway hyperresponsiveness remains a defining characteristic of asthma. Traditional views assert that airway smooth muscle is an important structural effector cell in the bronchi that modulates bronchomotor tone induced by contractile agonists. New evidence, however, suggests that abnormalities in airway smooth muscle functions, induced by variety of extracellular stimuli, may play an important role in the development of airway hyperresponsiveness. Studies using isolated bronchial preparations or cultured cells show that inflammatory mediators and cytokines may alter calcium homeostasis in airway smooth muscle and render the cells nonspecifically hyperreactive to agonists.

Mechanisms of airway remodeling. Airway smooth muscle

The airway smooth muscle cell can contract; relax; participate in allergic and inflammatory responses by expressing adhesion molecules, releasing cytokines, and producing matrix proteins and proteases; and, as has been reported, undergo migration. These properties enable the muscle cell to be a key component in the airway wall remodeling that accompanies persistent asthma. Evidence is emerging that identifies the pivotal steps in the signal transduction pathways that lead to the excessive proliferation of the muscle observed in vitro in airway smooth muscle cells from subjects with asthma. The contractile, biochemical, and growth characteristics of muscle from allergic subjects are different from those of nonallergic subjects. In addition, the allergic response impacts on the extracellular matrix in which the muscle is embedded, by altering the profile of matrix proteins released. Once the relationships between allergy and inflammation of the smooth muscle and its extracellular matrix are better defined, opportunities to prevent or reverse airway remodeling will become available.

Immune mechanisms of smooth muscle hyperreactivity in asthma

Asthma is characterized by bronchial hyperresponsiveness to a variety of bronchospasmogenic stimuli. To study the pathophysiologic mechanisms underlying the increased sensitivity and degree of maximal airway narrowing, various in vivo and in vitro models have been developed with methods of active and passive sensitization. These studies indicated a major role for alterations in the smooth muscle itself rather than neural dysfunction or airway inflammation as the underlying cause for the development of bronchial hyperresponsiveness. During the last years smooth muscle cells were found to exhibit not only the "classical" contractile phenotype but also a proliferative-synthetic phenotype, which is capable of producing proinflammatory cytokines, chemotaxins, and growth factors. Allergic sensitization can alter both contractile and secretory functions, thereby indicating that the smooth muscle cell could contribute directly to the persistence of airway inflammation in asthma. A better understanding of the changes within the smooth muscle cells and of the mechanisms that lead to their induction could contribute to the development of novel therapeutic approaches for the treatment of asthma.

Serum immunoglobulin E levels predict human airway reactivity in vitro

BACKGROUND

Airway hyperresponsiveness to non-specific stimuli is one characteristic feature of airway diseases such as bronchial asthma and chronic bronchitis. Until now, studies aiming to demonstrate a relationship between in vivo conditions associated with airway hyperreactivity and in vitro airway responsiveness have been inconclusive.

OBJECTIVE

Since serum immunoglobulin (Ig) E is believed to be one determinant of airway reactivity in vivo, we studied whether in vitro airway reactivity in lung resection material from patients with elevated levels of serum IgE was increased as compared with patients with undetectable IgE. By this approach, we aimed to elucidate the role of circulating IgE for bronchial smooth muscle reactivity in vitro.

METHODS

Bronchial rings from nine patients with total serum IgE levels above 200 U/mL and 10 patients with total serum IgE levels below 10 U/mL were passively sensitized, i.e. incubated overnight with buffer or sensitizing serum containing high levels of total IgE (> 250 U/mL). Afterwards, contractile responses to histamine were assessed in the organ bath.

RESULTS

Histamine responsiveness was significantly increased in airways obtained from patients with IgE levels above 200 U/mL as compared with airways from patients with IgE levels below 10 U/mL (P < 0.05). Passive sensitization of bronchi from patients with low IgE significantly increased histamine responsiveness, as compared with non-sensitized controls from the same patients (P < 0.05). In contrast, passive sensitization of airways from patients with elevated IgE did not further increase responsiveness. There was no difference in histamine reactivity between non-passively sensitized and passively sensitized tissue preparations from patients with IgE above 200 U/mL and passively sensitized tissues from patients with IgE below 10 U/mL.

CONCLUSION

Our findings reveal that elevated levels of serum IgE predict airway hyperresponsiveness to histamine in vitro. At the same time, they indicate that the in vitro model of passive sensitization, in addition to its ability to induce allergen responses, also mimics conditions of non-specific airway hyperreactivity, which are relevant under in vivo conditions.

The role of leukotrienes in the regulation of tone and responsiveness in isolated human airways

Cysteinyl-leukotrienes and histamine are the major determinants of inherent tone in isolated human bronchi, which is mainly the result of a balance of continual production and release of contractile mediator, in particular cysteinyl-leukotrienes and to a lesser extent histamine, and on the other side bronchodilating prostanoids. Cysteinyl-leukotrienes are also powerful constrictors of isolated human airways through direct interaction with Cys-LT1 receptors on airway smooth muscle, and with a potency 1,000-fold higher than histamine. On stimulation inflammatory cells such as eosinophils and mst cells produce and release significantly increased amounts of leukotrienes leading to smooth muscle contration in vitro. In isolated human airways, leukotrienes are the most important mediators of allergen and adenosine-induced contractile responses. The induction of allergen responses in passively sensitized airways is not only related to an increased release of leukotrienes and histamines, but also to an enhanced responsiveness of the airway smooth muscle, particularly to LTC4. Studies in isolated human airways in vitro have demonstrated that understanding the regulation of human airway tone and airway reactivity are closely linked to the understanding of baseline and stimulated production of and smooth muscle responsiveness to leukotrienes in vitro and in vivo.

Human isolated airway contraction: interaction between air pollutants and passive sensitization

Although there is epidemiological evidence that an increase in allergic diseases such as asthma may be linked to air pollution, there is little experimental data to address this issue. The aim of this study was thus to investigate the interaction between passive sensitization and exposure to pollutants in human isolated airways. We have examined (1) the effect of a preexposure to pollutants on the contraction of sensitized bronchi to a specific antigen, and (2) the effect of passive sensitization on the contraction to nonspecific agonists in bronchi preexposed to pollutants. In tissues sensitized by incubation in sera from asthmatic patients, preexposure to 0.3 microM acrolein (an aldehyde) for 10 min or 20 min significantly increased the maximal contractile response to the antigen Dermatophagoides pteronyssinus (D. pter.) by 20.5 +/- 6.5 and 34.9 +/- 7.4%, respectively. Similarly, preexposure to ozone (1 ppm for 20 min) increased the response to D. pter. by 25.3 +/- 11.3%. On the other hand, passive sensitization increased the contractile response to carbachol or histamine of bronchial rings preexposed to 0.3 microM acrolein for 10 min by 33.5 +/- 6.2% and 32.5 +/- 5.1%, respectively. This study provides a proof of principle in vitro for a combined effect of immunological sensitization and exposure to pollutants, i.e., passive sensitization and exposure to pollutants act in a synergistic manner on human bronchial smooth muscle reactivity in response to both specific antigen and nonspecific agonists.

Mast cell tryptase as a mediator of hyperresponsiveness in human isolated bronchi

BACKGROUND

Although the role of mediators and cytokines produced by mast cells is well established in asthmatic bronchial inflammation, the contribution of mast cell-derived proteases to the development of hyperresponsiveness remains unclear. There have been reports indicating that tryptase alters the mechanical activity of animal airway smooth muscle or spontaneously sensitized human isolated airways.

OBJECTIVE

The aim of this study was to analyse the effect of purified mast cell tryptase on non-sensitized human isolated bronchi.

METHODS

Both central and peripheral bronchi, dissected from lung specimens obtained at thoracotomy, were studied in terms of both mechanical activity i.e. isometric contraction in response to a variety of agonists and distribution of inflammatory cells i.e. immunohistochemistry.

RESULTS

In both proximal and distal bronchi, the reactivity to histamine was significantly increased by a previous incubation in the presence of 1 microg/mL of tryptase (increase in maximal force, DeltaFmax was 12.1 +/- 3.8%, and 8.8 +/- 3.1%, respectively). This effect of tryptase on histamine-induced contraction was completely abrogated in the presence of the protease inhibitor benzamidine (100 micromol/L). Histological examination of specimens exposed to tryptase demonstrated an increase in mast cell number within the subepithelial tissue whereas mast cell numbers in the epithelial layer concomittently decreased.

CONCLUSION

These results indicate that human mast cell tryptase alters the contractile response of non-sensitized human isolated bronchi and that this alteration is accompanied by a change in the mast cell distribution within the airway wall.

Tryptase mediates hyperresponsiveness in isolated guinea pig bronchi

Hyperresponsiveness of airway smooth muscle to allergens and environmental factors has long been associated with the pathophysiology of asthma. Tryptase, a serine protease of lung mast cells, has been implicated as one of the mediators involved in the induction of hyperresponsiveness. As a consequence, tryptase inhibitors have become the subject of study as potential novel therapeutic agents for asthma. Secretory leukocyte protease inhibitor (SLPI) is a naturally occurring protein of human airways which exhibits anti-tryptase activity. To assess the potential therapeutic utility of SLPI in asthma, its effects were evaluated using in vitro and ex vivo models of airway hyperresponsiveness and compared with the effects of the small molecule tryptase inhibitor APC-366. Our results demonstrate that SLPI inhibits tryptase-mediated hyperresponsiveness in vitro and attenuates the hyperresponsiveness observed in airway smooth muscle from antigen-sensitized animals subjected to antigen exposure. The small molecule tryptase inhibitor APC-366 has a similar inhibitory effect. Thus, tryptase appears to be a significant contributor to the development of hyperresponsiveness in these models. To the extent that tryptase contributes to the development and progression of asthma, SLPI may possess therapeutic potential in this disease setting.

Mechanisms of immune sensitization of human bronchus

Bronchial hyperresponsiveness (BHR), the increased sensitivity to a wide variety of stimuli that narrow the airways, is a central abnormality in patients with asthma, and is frequently observed in patients with chronic obstructive pulmonary disease. In the study of the underlying mechanisms of BHR, various animal models have been employed, using methods of active and passive immunization. These studies have led to a changed understanding of smooth muscle hyperreactivity, questioning both the past paradigm of altered neural activity and the modern concepts of inflammation as the single most factor determining BHR, and emphasizing the particular importance of the end organ- the smooth muscle cell. More recently, passive sensitization of human airways has been used by several investigators to describe the mechanisms of allergic sensitization and to study the role of functional abnormalities of human airway smooth muscle, which may represent the key to understanding human BHR, and thus lead to novel treatment approaches for the future.

Inhibition of human airway sensitization by a novel monoclonal anti-IgE antibody, 17-9

We investigated the effect of a novel mouse IgG2b nonanaphylactogenic anti-human IgE antibody, 17-9, on allergen and histamine responses in passively sensitized human airways in vitro to determine the specific contribution of IgE to the sensitization process. Bronchial rings were sensitized with serum containing high levels of allergen-specific IgE (Dermatophagoides farinae), or with a hapten-specific chimeric humanized IgE (JW8). There was a concentration-dependent contraction of serum-sensitized bronchial rings to D. farinae (517 +/- 188 mg tension at 10 U/ml, n = 8) that was not observed in nonsensitized controls. This response was practically abolished when tissues were sensitized in the presence of 100 microg/ml anti-IgE antibody 17-9 (54 +/- 20 mg). In tissues sensitized with the anti-NIP IgE, JW8, there was a concentration-dependent contraction to the specific antigen NIP-BSA (560 +/- 154 mg at 0.3 microg/ml, n = 5) that was not observed in nonsensitized control subjects and that was substantially inhibited when 17-9 was present in the sensitization buffer (124 +/- 109 mg). The inhibition with 17-9 was specific, as pretreatment with a non-IgE-specific IgG2b antibody did not affect allergen responses. Potency and maximal contractions to histamine in serum-sensitized tissues were significantly elevated compared with nonsensitized controls; this was not affected by the presence of 17-9 during sensitization (pEC50 = 5.1 +/- 0.2 versus 5.0 +/- 0.3 in tissues sensitized in the absence of 17-9). In tissues sensitized with JW8 there was no significant increase in responsiveness to histamine. We conclude that allergen responses in sensitized human airways are dependent on IgE levels in the sensitizing serum while nonspecific (hyper)responsiveness depends on serum factors other than IgE. Nonanaphylactogenic anti-human IgE antibodies effectively inhibit allergen responses of human airways in vitro but may not affect other factors inducing hyperresponsiveness.

Immunoglobulin E-induced passive sensitization of human airways: an immunohistochemical study

In vivo, IgE production is related to bronchial hyperresponsiveness and, in vitro, passive sensitization of human airways with asthmatic serum containing a high concentration of IgE enhances the contractile response to a variety of agonists. However, cell types implicated in this IgE sensitization are not fully determined. The aim of this study was to determine IgE-bearing cells during passive sensitization with special reference to mast cells. Peripheral bronchi were dissected out from 10 lung specimens obtained at thoracotomy and processed into glycolmethacrylate resin. Sections, each 2 microm thick, were passively sensitized by incubation for 2 h at 37 degrees C in either buffer supplemented with monoclonal IgE or asthmatic serum with a high concentration of IgE (> or = 1,000 IU/ml). Immunohistochemistry was performed using monoclonal antibodies directed against the epsilon chain, and markers of the various IgE-bearing cells (e.g., AA1, antichymase). The number of IgE-bearing cells was significantly higher in passively sensitized specimens as compared with nonsensitized specimens (6.63 +/- 1.71 versus 4.29 +/- 1.35/mm2; p = 0.013, n = 10). Mast cells represented 65% of IgE-bearing cells, 41.6 and 23.4% for TC and T subtypes, respectively. These results indicate that mast cell is the main cell type involved in IgE-induced passive sensitization. The involvement of mast cell-derived tryptase in the mechanisms of IgE-related hyperresponsiveness should be further examined.

Airway smooth muscle in asthma

One of the factors that may contribute to the exaggerated airway narrowing in asthma is an abnormality of the airway smooth muscle. This abnormality could take the form of an increase in the amount of muscle or an alteration in its pharmacological reactivity. The former could be due to either hypertrophy (an increase in individual muscle cell size) or hyperplasia (an increase in cell number). Changes in pharmacological reactivity that could be relevant to altered airway calibre could result from an increase in contraction or alternatively, a decrease in relaxation. Based on available evidence, the increase in smooth muscle bulk is probably the consequence of both hyperplasia and hypertrophy and several growth factors, inflammatory mediators and cytokines have been implicated. Asthmatic airway tissue is rarely available for in vitro pharmacological studies and evidence for enhanced contraction is limited. Recent evidence suggests that an abnormality in beta adrenoceptor function may contribute to impairment of relaxation, but further work needs to be done. Passive sensitization of non-asthmatic airways in vitro provides a good model for the study of the mechanisms underlying airway hyperresponsiveness, and will be the subject of more intensive study in the future.

Effect of guinea-pig purified immunoglobulin G1 on the responsiveness of tracheal, aortic, vas deferens and ileum smooth muscles

BACKGROUND

Smooth muscles hyperresponsiveness is a common feature in anaphylaxis and allergic diseases.

OBJECTIVE

The aim of the present work was to investigate the effect of in vitro passive sensitization with highly purified immunoglobulin G1 (IgG1) on the responsiveness of tracheal, aortic, vas deferens and ileum smooth muscles.

METHODS

Firstly, IgG1, obtained from actively sensitized BFA guinea-pigs, was purified by Protein A-Sepharose column and characterized by enzyme-linked immunosorbent assay (ELISA) and immunoelectrophoresis analysis. Concentration-response curves to spasmogens (acetylcholine for trachea and vas deferens, noradrenaline for aorta and histamine for ileum) were established before and after in vitro passive sensitization with IgG1.

RESULTS

Contractile responses and maximal contractions were significantly enhanced after passive sensitization for all the organs. Maximal contractions were significantly increased in the trachea (+46.7%), aorta (+51%), vas deferens (+114.2%) and ileum (+117.2%). At the end of the experiments, the application of the sensitizing antigen induced a significant Schultz-Dale reaction of the smooth muscles.

CONCLUSION

The present results show that the in vitro application of purified IgG1 can produce non-specific smooth muscle hyperreactivity and hypersensitivity. So, IgG1 can be considered as the main factor involved in the genesis of sensitization-induced hyperresponsiveness, and probably play a great role in hyperreactivity observed during allergic diseases and anaphylaxis.

Biphasic increase in cytosolic free calcium induced by bradykinin and histamine in cultured tracheal smooth muscle cells: is the sustained phase artifactual?

The effects of bradykinin (BK) and histamine on intracellular Ca2+ ([Ca2+]i) were studied in fura-2-loaded guinea-pig tracheal smooth muscle cells in culture. BK, at 10 nM, and histamine, at 100 microM, induced a rise in [Ca2+]i which was inhibited by the B2 antagonist Hoe 140 and by the H1 antagonist triprolidine, respectively. This rise in [Ca2+]i is biphasic, consisting of a rapid transient phase followed by a sustained phase. The transient phase, induced by either BK or histamine, was strongly inhibited by thapsigargin, a microsomal Ca(2+)-ATPase inhibitor, usually used to deplete certain intracellular Ca(2+)-stores. Ni2+ (4 mM) did not affect the transient phase but abolished the sustained phase when cells were stimulated by BK, further supporting the fact that the transient phase was only dependent on intracellular Ca2+ pools. The sustained phase was partially (for BK) and completely (for histamine) inhibited by 30 microM Mn2+. This effect could be completely reversed by the addition of DTPA, a cell-impermeant chelator of Mn2+, indicating that the Mn2+ exerted its effect extracellularly. The presence of 1 mM probenecid (an inhibitor of a membrane organic anion transporter that extrudes fura-2) drastically inhibited the sustained phase by more than 77% for BK and 88% for histamine. Our results suggest that the effects of BK and histamine on airway smooth muscle cells are mediated via bradykinin B2 receptors and histamine H1 receptors, respectively whose activation allows the rapid transient rise in [Ca2+]i from thapsigargin-sensitive intracellular Ca2+ pools. The sustained phase is proposed to be drastically influenced by an acceleration of fura-2 extrusion during the increase of [Ca2+]i via a probenecid-sensitive mechanism.

Sensitization decreases relaxation in human isolated airways

Passively sensitized human isolated airways provide an opportunity to study some aspects of bronchial hyperresponsiveness in vitro. Since it has been suggested that excessive airway narrowing could be due to impaired relaxation, we examined the effect of a variety of agents producing relaxation via different mechanisms, i.e., verapamil and lemakalim (a calcium channel antagonist and a potassium channel opener, respectively) and isoproterenol, forskolin, and dibutyryl cAMP (modulators of the beta-adrenoceptor signal transduction pathway). Human bronchial rings, obtained at thoracotomy, were passively sensitized by incubation in serum from atopic asthmatic patients, and control rings were incubated in serum from nonatopic subjects. We also studied bronchial rings from five spontaneously sensitized human lung specimens. Responses to the relaxant compounds were measured isometrically. Passive sensitization significantly decreased the efficacy of verapamil in maximally contracted tissues from 60 +/- 10 to 45 +/- 7% of the maximal carbachol response (n = 6, p < 0.05) and that of lemakalim from 51 +/- 16 to 38 +/- 14% (n = 7, p < 0.05) in tissues at baseline tone. Similarly, spontaneously sensitized tissues relaxed less to lemakalim (64 +/- 6% of the maximal response to isoproterenol, n = 5, p < 0.05) than did nonsensitized tissues (80 +/- 4%). Sensitization did not alter responses to isoproterenol, forskolin, and dibutyryl cAMP. We conclude that sensitization of human isolated airways reduces relaxation responses that depend upon activation of ion channels but not those that depend upon activation of beta-adrenoceptors and transduction processes directly coupled to these receptors.

Effect of passive sensitization on the mechanical activity of human isolated bronchial smooth muscle induced by substance P, neurokinin A and VIP

1. The effect of passive sensitization on the mechanical activity of human isolated bronchial smooth muscle induced by the following neuropeptides substance P (SP), neurokinin A (NKA) and vasoactive intestinal peptide (VIP) was studied both in the absence and in the presence of the neutral endopeptidase (NEP) inhibitor, phosphoramidon. 2. Cumulative concentration-response curves (CCRC) to these neuropeptides were constructed in human passively sensitized isolated bronchial rings and compared to those in paired controls. Passively sensitized human isolated bronchial rings were tissues incubated overnight in serum from asthmatic patients atopic to Dermatophagoides pteronyssinus and paired controls were tissues originating from the same lung specimens but incubated overnight in serum from healthy donors. 3. In the absence of phosphoramidon, passive sensitization significantly increased the amplitude of the contractile responses to SP and NKA including that to the maximal concentration given from 50 +/- 5% to 76 +/- 6% (n = 5, P < 0.05) and from 70 +/- 7% to 101 +/- 6% (n = 5, P < 0.05) of the maximal response to acetylcholine, respectively. Passive sensitization significantly shifted to the left the CCRC for both tachykinins as measured by the geometric means dose-ratios which were 8.5 (95% confidence limits (CL): 3.1-13.9) and 7.3 (95% CL: 4.2-10.3) for SP and NKA, respectively. 4. In the presence of phosphoramidon (10 microM), passive sensitization still increased significantly the amplitude of the contractile responses to SP and NKA including that to the maximal concentration given from 74 +/- 4% to 115 +/- 7% (n = 5, P<0.05) and from 104 +/- 9% to 146 +/- 16% (n = 5, P<0.05)of the maximal response to acetylcholine, respectively. Passive sensitization still significantly shifted to the left the CCRC for both tachykinins as measured by the dose-ratios which were 9.0 (95% CL:4.3-13.6) and 5.4 (95% CL: 2.9-7.9) for SP and NKA, respectively.5. The relaxant response to the maximal concentration of VIP given in tissues precontracted with histamine (0.5 mM) was significantly reduced by passive sensitization from 41 +/- 4% to 25 +/- 3% (n = 5,P <0.05) of the amplitude of the precontraction in the absence of phosphoramidon and from 72 +/- 1%to 49 +/- 4% (n = 5, P<0.05) in the presence of phosphoramidon (10 microM). Passive sensitization significantly shifted to the right the CCRC for VIP as measured by the dose-ratios which were 10.4(95% CL: 6.6-14.1) and 6.4 (95% CL: 3.0-9.8) in the absence and in the presence of phosphoramidon,respectively.6. We conclude that passive sensitization enhances the mechanical response to neuropeptides which contract human isolated bronchial smooth muscle and reduces that to a neuropeptide which relaxes it.The mechanism of passive sensitization-induced changes in the mechanical activity appears to be independent of a decrease in NEP activity since these changes persist in the presence of the NEP inhibitor, phosphoramidon.