Relationship between mediator release from human lung mast cells in vitro and in vivo

Targeted inhibition of allergen-induced histamine production by neutrophils

Histamine is a critical inflammatory mediator in allergic diseases. We showed in a previous work that neutrophils from allergic patients produce histamine in response to allergens to which the patients were sensitized. Here, we investigate the molecular mechanisms involved in this process using peripheral blood neutrophils. We challenged these cells in vitro with allergens and analyzed histamine release in the culture supernatants. We also explored the effect of common therapeutic drugs that ameliorate allergic symptoms, as well as allergen-specific immunotherapy. Additionally, we examined the expression of histidine decarboxylase and diamine oxidase, critical enzymes in the metabolism of histamine, under allergen challenge. We show that allergen-induced histamine release is dependent on the activation of the phosphoinositide 3-kinase, mitogen-activated protein kinase p38, and extracellular signal-regulated kinase 1/2 signaling pathways. We also found a contribution of the phosphatase calcineurin to lesser extent. Anti-histamines, glucocorticoids, anti-M3-muscarinic receptor antagonists, and mainly β₂ -receptor agonists abolished the allergen-dependent histamine release. Interestingly, allergen-specific immunotherapy canceled the histamine release through the downregulation of histidine decarboxylase expression. Our observations describe novel molecular mechanisms involved in the allergen-dependent histamine release by human neutrophils and provide new targets to inhibit histamine production.

A novel inhaled Syk inhibitor blocks mast cell degranulation and early asthmatic response

Spleen tyrosine kinase (Syk) is essential for signal transduction of immunoreceptors. Inhibition of Syk abrogates mast cell degranulation and B cell responses. We hypothesized that Syk inhibition in the lung by inhaled route could block airway mast cells degranulation and the early asthmatic response without the need of systemic exposure. We discovered LAS189386, a novel Syk inhibitor with suitable properties for inhaled administration. The aim of this study was to characterize the in vitro and in vivo profile of LAS189386. The compound was profiled in Syk enzymatic assay, against a panel of selected kinases and in Syk-dependent cellular assays in mast cells and B cells. Pharmacokinetics and in vivo efficacy was assessed by intratracheal route. Airway resistance and mast cell degranulation after OVA challenge was evaluated in an ovalbumin-sensitized Brown Norway rat model. LAS189386 potently inhibits Syk enzymatic activity (IC50 7.2 nM), Syk phosphorylation (IC50 41 nM), LAD2 cells degranulation (IC50 56 nM), and B cell activation (IC50 22 nM). LAS189386 inhibits early asthmatic response and airway mast cell degranulation without affecting systemic mast cells. The present results support the hypothesis that topical inhibition of Syk in the lung, without systemic exposure, is sufficient to inhibit EAR in rats. Syk inhibition by inhaled route constitutes a promising therapeutic option for asthma.

Mast cell mediators cause early allergic bronchoconstriction in guinea-pigs in vivo: a model of relevance to asthma

One feature of allergic asthma, the EAR (early allergic reaction), is not present in the commonly used mouse models. We therefore investigated the mediators involved in EAR in a guinea-pig in vivo model of allergic airway inflammation. Animals were sensitized using a single OVA (ovalbumin)/alum injection and challenged with aerosolized OVA on day 14. On day 15, airway resistance was assessed after challenge with OVA or MCh (methacholine) using the forced oscillation technique, and lung tissue was prepared for histology. The contribution of mast cell mediators was investigated using inhibitors of the main mast cell mediators [histamine (pyrilamine) and CysLTs (cysteinyl-leukotrienes) (montelukast) and prostanoids (indomethacin)]. OVA-sensitized and challenged animals demonstrated AHR (airway hyper-responsiveness) to MCh, and lung tissue eosinophilic inflammation. Antigen challenge induced a strong EAR in the sensitized animals. Treatment with a single compound, or indomethacin together with pyrilamine or montelukast, did not reduce the antigen-induced airway resistance. In contrast, dual treatment with pyrilamine together with montelukast, or triple inhibitor treatment, attenuated approximately 70% of the EAR. We conclude that, as in humans, the guinea-pig allergic inflammation model exhibits both EAR and AHR, supporting its suitability for in vivo identification of mast cell mediators that contribute to the development of asthma. Moreover, the known mast cell mediators histamine and leukotrienes were major contributors of the EAR. The data also lend further support to the concept that combination therapy with selective inhibitors of key mediators could improve asthma management.

The role of dendritic cells and regulatory T cells in the regulation of allergic asthma

Airways hyperresponsiveness (AHR) is one of the major clinical features of allergic airways disease including allergic asthma, however the immunological mechanisms leading to the induction and regulation of this disorder are not fully understood. In this review we will summarise the evidence of a number of studies, principally in murine models of AHR, suggesting a central role for respiratory tract dendritic cells (RTDC) in the induction of AHR through the generation of lung-homing, allergen-specific effector T cells. We will also summarise the evidence supporting a role for regulatory T cells in the attenuation of AHR and will propose that, as a counterpoint to their capacity to induce AHR, RTDC may also play a role in the attenuation of AHR through the generation of regulatory T cells (T(reg)). A better understanding of the relationship between the physiological and immunological responses to allergen-induced AHR attenuation, and particularly the role of RTDC and T(reg) in this process, will be essential for the development of new treatments and therapies.

Identification with MRI of the pleura as a major site of the acute inflammatory effects induced by ovalbumin and endotoxin challenge in the airways of the rat

Inflammatory effects in the rat lung have been investigated, non-invasively by MRI, at early time points (3 and 6 h) after ovalbumin (OA) or endotoxin (LPS) challenges. Six hours after challenge with OA, a strong, even inflammatory signal was present around the periphery of the lung in a region corresponding to the pleura. Histological analysis confirmed the presence of marked edema associated with the pleural cavity of OA-treated animals. Lower levels of pleural edema were observed in MRI and histological evaluation of LPS-treated animals and no abnormality was observed in actively sensitized and naïve, saline-treated groups. Diffuse edematous signals were detected in the lung 3 and 6 h after challenge with OA or LPS; the signal volumes were larger at both time points following OA instillation. Bronchoalveolar lavage (BAL) fluid analysis performed 6 h after challenge revealed increased levels of protein and greater cellular activation in OA- than in LPS-treated animals. Furthermore, increased levels of peribronchial edema were found by histology 6 h after OA. BAL fluid and histological assessments demonstrated that the inflammatory signals were due to edema and not mucus as no significant changes in BAL mucin concentrations or differences in goblet cells were identified between OA or LPS challenge and their respective vehicle groups. Our data show that MRI is able to detect, non-invasively, inflammatory signals in both the lung and the pleura in spontaneously breathing animals, highlighting its potential to study the consequences of pulmonary insults on both sites.

Effect of salbutamol on nasal symptoms and mast cell degranulation induced by adenosine 5' monophosphate nasal challenge

BACKGROUND

In addition to its well-known functional agonism at the level of beta(2) adrenergic receptors on airways smooth muscle cells, salbutamol appears to have additional protective effects, possibly through an inhibition of mast cell activation.

OBJECTIVE

The aim of this study is to provide the first evidence in vivo of inhibition of human mast cell activation by salbutamol.

METHODS

Nine atopic subjects received placebo and salbutamol (5 mg/mL) 15 min before an adenosine 5' monophosphate (AMP) nasal provocation in a double-blind crossover study design. The nasal lavage was collected from these subjects prior to or 3, 5, 15 or 30 min after the AMP nasal challenge, and concentrations of histamine and tryptase in the nasal lavage were measured.

RESULTS

AMP nasal provocation produced considerable sneezing and induced a transient increase in histamine and tryptase release with peak values achieved at 3 min after the challenge in all the subjects studied. Compared with placebo, salbutamol significantly attenuated the release of histamine and tryptase induced by AMP challenge (P=0.048 and 0.020, respectively). Moreover, the AMP-induced sneezing was also inhibited by pre-treatment with salbutamol (P=0.004).

CONCLUSIONS

Intranasal salbutamol attenuates nasal symptoms and inhibits histamine and tryptase release caused by AMP nasal provocation thus supporting the hypothesis that salbutamol may play an additional protective role in the airways by inhibiting mast cell activation.

The effects of Ma-Xing-Gan-Shi-Tang on respiratory resistance and airway leukocyte infiltration in asthmatic guinea pigs

Ma-Xing-Gan-Shi-Tang (MXGST), a traditional Chinese medicine, has been used in treatment of the bronchial asthma for several centuries. However, the therapeutic mechanisms of this Chinese medicine are still far from clear. To understand the mechanism of anti-asthmatic property of MXGST, a guinea pig model of allergic asthma was used to investigate the effects of MXGST on Dermatophagoides pteronyssinus-induced early and late asthmatic responses and airway inflammation, and examine direct beta2-adrenoceptor agonist activity in guinea-pig isolated trachea. Administration of MXGST (10 g/kg) extracts significantly inhibited the antigen induced immediate asthmatic responses (IAR) in actively sensitized guinea pig. MXGST caused concentration-dependent relaxation in strips of guinea pig trachea contracted with carbachol, and ICI-118551, a selective beta2-adrenoceptor antagonist, significantly inhibit the relaxation caused by MXGST. Furthermore, examination of bronchoalveolar lavage fluid (BALF) revealed that MXGST significantly inhibited the increase in neutrophil in the airway at 1, 6 and 24 hr after antigen challenge. Histopathologic examination results showed that MXGST suppressed the neutrophil infiltration into lung tissue. In conclusion, we suggest that the anti-asthmatic effects of MXGST are mainly due to its stimulation of beta2-adrenoceptors on bronchial smooth muscle and its anti-inflammatory ability to inhibit the neutrophil into the airway. The precise mechanism of action of MXGST in asthma remains to be elucidated.

Mediator involvement in antigen-induced bronchospasm and microvascular leakage in the airways of ovalbumin sensitized Brown Norway rats

1. To determine which mediators are involved in antigen-induced bronchospasm and microvascular leakage in the airways of ovalbumin sensitised Brown Norway rats we investigated the effect of a histamine H(1) receptor antagonist, mepyramine, a 5-HT receptor antagonist, methysergide, and a cys-leukotriene-1 receptor antagonist, montelukast. 2. Ovalbumin at 1 mg kg(-1) i.v. caused a significant increase in microvascular leakage in the airways and at 3 mg kg(-1) i.v. caused a significant increase in airways resistance. 3. Histamine (1 mg kg(-1) i.v.), 5-HT (0.1 mg kg(-1) i.v.) and leukotriene D(4) (LTD(4), 50 microg kg(-1) i.v.) caused a significant increase in microvascular leakage in the airways. 4. Mepyramine (1 mg kg(-1) i.v.), methysergide (0.1 mg kg(-1) i.v.), or montelukast (30 mg kg(-1) i.v.) inhibited histamine, 5-HT or LTD(4) -induced microvascular leakage respectively. 5. Methysergide (0.1 mg kg(-1) i.v.) reduced ovalbumin-induced microvascular leakage in the trachea and at 0.3 mg kg(-1) i.v. inhibited bronchospasm (38 and 58%, respectively). Montelukast (30 mg kg(-1) p.o.) reduced ovalbumin-induced microvascular leakage in airway tissue to basal levels (78%) and inhibited ovalbumin-induced bronchospasm (50%). Mepyramine (3 mg kg(-1) i.v.) had no effect on ovalbumin-induced leakage or bronchospasm. 6. A combination of all three compounds (mepyramine, methysergide and montelukast) reduced ovalbumin-induced microvascular leakage in airway tissue to basal levels (70 - 78%) and almost completely inhibited bronchospasm (92%). 7. Antigen-induced bronchospasm appears to equally involve the activation of 5-HT and cys-leukotriene-1 receptors whereas ovalbumin-induced microvascular leakage appears to be predominantly mediated by cys-leukotriene-1 receptors.

Effect of San-Ao-Tang on immediate and late airway response and leukocyte infiltration in asthmatic guinea pigs

San-Ao-Tang (SAT), a traditional Chinese medicines, has been used to treat patients with the bronchial asthma for several centuries. However, the therapeutic mechanisms of this Chinese medicine are still far from clear. To understand the mechanism of antiasthmatic property of SAT, a guinea pig model of allergic asthma was used to investigate the effects of SAT on Dermatophagoides pteronyssinus-induced immediate and late asthmatic responses and airway inflammation. Our results showed that administration of SAT (10 g/kg) extracts significantly inhibited the antigen induced immediate asthmatic responses (IAR) in actively sensitized guinea pig. Examination of bronchoalveolar lavage fluid (BALF) revealed that SAT significantly inhibited the increase in neutrophil in the airway at 1, 2, 4, 6, 8 hr after antigen challenge. Histopathologic examination showed SAT suppressed the neutrophil infiltration into lung tissue. These results suggest that the antiasthmatic effect of SAT be mainly due to its bronchodilator effect and its ability to inhibit the neutrophil into the airway. The precise mechanism of action of SAT in asthma remains to be elucidated.

In vitro responses to antigen stimulation: comparison between human lung parenchyma resected from asthmatic patients and non-asthmatic patients

BACKGROUND

The airway of asthmatic patients is hyperresponsive to various stimuli in vivo. There are, however, only a few reports that compared the in vivo responsiveness of asthmatic patients and non-asthmatic subjects to those of lung parenchyma in vitro.

OBJECTIVES

To compare the contractile response, release of various chemical mediators, and responsiveness to drugs in samples of lung parenchyma excised from asthma patients with those of non-asthmatic subjects.

METHODS

Human lung parenchymal strips were subjected to passive sensitization with sera of 5+ RAST titer to mites. The strip was suspended in a magnus bath containing a buffer solution. Parenchymal contraction was induced by PGF2 alpha. After washing, the baseline concentrations of thromboxane B2 (TXB2), leukotriene (LT), and histamine were measured in each bath and then contraction was induced by the addition of a mite antigen. The concentrations of TXB2, LT, and histamine were measured after contraction. The inhibitory effects of TXA2 synthetase inhibitor (DP-1904) and TXA2 receptor antagonist (AA-2414) were also evaluated in both tissue samples.

RESULTS

There were no significant differences between lung parenchymal tissues of asthmatic and non-asthmatic patients with regard to PGF2 alpha-induced contraction, antigen-induced contraction, release of chemical mediators, and the response to drugs.

CONCLUSION

Unlike the response in vivo, there are no differences in the response to stimuli in vitro between lung parenchymal tissues of asthmatic and non-asthmatic patients.

[Comparison of the effect of subcutaneous injection of adrenaline and terbutaline in asthma crisis in infants]

BACKGROUND

Edema of the mucous membranes lining the airways is a major factor of airway obstruction in asthma. Stimulation of both alpha and beta-adrenergic receptors is thus logically useful to reduce edema through vasoconstriction and to cause smooth muscle relaxation. The aim of this work was to compare the effects of subcutaneous epinephrine vs terbutaline for treating acute attack of asthma in infants.

PATIENTS AND METHODS

Fifty-four infants aged less than 30 months admitted for acute asthma attacks were included in this study. None had previous cardiovascular or definite pulmonary disease and none had tachycardia above 200/min. The patients were randomly given subcutaneous epinephrine, 10 micrograms/kg (n = 28) or subcutaneous terbutaline at the same dosage (n = 26).

RESULTS

Improvement in accessory muscle use, oxygen saturation, PaO2 and PCO2 was similar in both groups. The respiratory rate was significantly improved after administration of epinephrine (P = 0.05). No adverse effects were seen in either drug.

CONCLUSION

Subcutaneous administration of epinephrine is as effective as terbutaline in treating acute attack of asthma in infants. This drug, easy to use and of low-cost, could be the treatment of choice in developing countries.

Time course study for airway inflammation and responsiveness by repeated provocation of aeroantigen in guinea pigs

To investigate the mechanisms of airway hyperresponsiveness (AHR), we examined the time course for asthmatic responses (including immediate asthmatic response (IAR), late asthmatic response (LAR), and AHR), airway inflammation (including edema in the airway, accumulation of inflammatory cells in bronchoalveolar lavage fluid (BALF), and mediator release including histamine and thromboxane A2 (TXA2) in BALF after the repeated provocation of aeroantigen in sensitized guinea pigs. Furthermore, we examined the effect of S-1452, a TXA2 receptor antagonist, on the antigen-induced airway obstruction and AHR in guinea pigs. We found that IAR occurred 1 min after every antigen inhalations. LAR was observed every 4 h after the inhalation of antigen without 1st or 2nd challenge. AHR was initially observed 4 h after the 5th inhalation of antigen, and then AHR was observed at every time measured even after the 6th provocation. The water content of the airway increased after the 2nd antigen inhalation. A number of leukocytes, especially eosinophils in BALF, was observed 30 min after the 2nd antigen inhalation. Desquamation of epithelia was observed 30 min after the 5th antigen inhalation. TXB2 and histamine in BALF were detected after the first antigen inhalation. These results suggest that LAR is caused by repeated airway inflammation such as eosinophilia and mediator release including TXA2. AHR may appear with the damages of lung tissue such as desquamation of epithelia. Oral administration of S-1452 (1 and 10 mg/kg) significantly inhibited LAR and AHR, assessed after the 6th antigen challenge. The present findings suggest that repeated antigen challenge causes airway inflammation and leads to the onset of LAR and AHR when became chronic. Furthermore, persistent generated TXA2 plays an important role in the pathogenesis of antigen-induced late-phase obstruction and AHR.

Bronchoconstriction and eosinophil recruitment in guinea pig lungs after platelet activating factor administration

Using a forced expiratory maneuver to measure flow volume loops, we evaluated the ability of platelet activating factor (PAF) to induce acute bronchospasm and in histological changes associated with bronchial asthma in guinea pigs. We determined both the dose-response curve and the time course of PAF-induced bronchoconstriction. Eight guinea pigs with weights ranging from 350 to 450 g were anesthetized, tracheotomized, and then paralyzed with gallamine. Baseline pulmonary function tests (PFT) were done. Different doses (25, 50, 100, 200, and 500 ng/kg) of PAF were injected through the jugular vein, and serial PFTs were done at 30 sec, 2, 5, and 20 min after each dose of PAF. Acetylcholine provocation testing was done following the 200 ng/kg dose of PAF. The PFTs included a forced expiratory maneuver, airway opening pressure (PaO), and total lung compliance (TLC). After all PFTs were completed, cell counts were done on fluid obtained from bronchoalveolar lavage (BAL) and the lungs were removed for histological study. Eight other guinea pigs were used as controls. The results showed that with increasing doses of PAF from 25 ng/kg to 200 ng/kg, all lung function parameters, including vital capacity, peak flow, MFEF 75%, MFEF 50%, MFEF 25%, and total lung compliance, gradually decreased. However, a further increase of the dose of PAF up to 500 ng/kg did not result in continued worsening of PFTs. The most severe bronchoconstriction occurred 30 sec after PAF was injected, and it gradually resolved thereafter. PAF injection also induced a severe inflammatory reaction of the airway and lung tissue, characterized by congestion, edema, inflammatory cell (especially lymphocytes and eosinophils) infiltration, and desquamation of bronchial epithelial cells. In conclusion, in the guinea pig model, PAF can induce acute reversible bronchospasm and bronchial hyperreactivity, as well as the typical histological changes of bronchial asthma.

Role of macrophages in pulmonary late-phase reaction in guinea pigs

To examine the role of macrophages in pulmonary late-phase reaction (LPR), macrophages were reduced in sensitized guinea pigs by an intravenous injection of liposome-encapsulated dichloromethylene diphosphonate (Cl2MDP). Macrophage reduction was evaluated by bronchoalveolar lavage (BAL) fluid analysis. In Cl2MDP liposome-treated animals, the number of macrophages in BAL fluid significantly decreased by 56% compared with PBS liposome-treated animals (1.6 +/- 0.1 vs. 3.6 +/- 0.4 x 10(6) cells, p < 0.01). The number of neutrophils, eosinophils, or lymphocytes in BAL fluid showed no significant changes in these two groups. Both PBS and Cl2MDP liposome-treated sensitized guinea pigs were challenged with an inhalation of antigen, and respiratory resistance (Rrs) was measured. PBS liposome-treated animals (control) exhibited both immediate (IPR) and late (LPR) increases in Rrs. The maximal increases in Rrs at IPR and LPR were 217 +/- 19 and 187 +/- 20% of baseline values, respectively (n = 9). On the other hand, Cl2MDP liposome-treated animals showed an immediate increase in Rrs (IPR); however, the late increase in Rrs (LPR) was significantly suppressed (p < 0.05). The maximal increases in Rrs at IPR and LPR were 200 +/- 13 and 134 +/- 11% of baseline values, respectively (n = 8). In Cl2MDP liposome-treated animals, the numbers of macrophages and neutrophils in BAL fluid 4 hr after antigen challenge decreased by 45% and 54%, respectively, compared with PBS liposome-treated animals (p < 0.05). In Cl2MDP liposome-treated animals, neutrophil chemotactic activity in BAL fluid 4 hr after antigen challenge decreased by 59% compared with PBS liposome-treated animals (p < 0.05). These results suggest that macrophages play an important role in the development of pulmonary LPR through the induction of neutrophil accumulation in the airways.

The effect of a thromboxane A2 receptor antagonist BAY-u-3405 on experimental allergic reactions

The effect of a novel thromboxane A2 receptor antagonist, BAY-u-3405, on experimental allergic airway and skin reactions was studied in vivo. At doses of 3-30 mg/kg BAY-u-3405 clearly inhibited the U-46619-induced increase in respiratory resistance (Rrs) in guinea pigs. BAY-u-3405 at doses of 3 and 30 mg/kg inhibited the aerosolized antigen-induced biphasic increase in respiratory resistance in guinea pigs. Moreover, BAY-u-3405 inhibited repeated aeroantigen-induced airway hyperactivity and airway inflammation in mice. In IgE antibody-mediated biphasic skin reactions in mice, both immediate and late-phase reactions were inhibited by 10 mg/kg of BAY-u-3405. These results demonstrate the efficacy of BAY-u-3405 on the antigen-induced late-phase reactions in the airway and skin in guinea pigs and mice, and antigen-induced airway hyperactivity in mice.

TNF alpha-induced activation of eosinophil oxidative metabolism and morphology--comparison with IL-5

Human dermal mast cells are capable of releasing cytokines, particularly preformed TNF alpha, upon appropriate stimulation. Mast cell activation in vivo was shown to be associated with an influx and activation of inflammatory cells, initially PMN (polymorphonuclear neutrophilic granulocytes) then eosinophils. In order to learn more about the mechanisms by which TNF alpha is capable of activating eosinophils, in the present study the effect of TNF alpha on morphology and function of highly purified normal eosinophils (> or = 95%) was examined. As estimated by transmission and scanning electron microscopy, TNF alpha-stimulated eosinophils appeared to be strictly adherent and flattened exhibiting a characteristic "hemispheric" shape. TNF alpha induced a dose-dependent, long-lasting production of reactive oxygen species as measured by lucigenin-dependent chemiluminescence (CL), even at a concentration of 0.001 U/ml. The maximal response upon stimulation with TNF alpha, however, was significantly lower than optimal effects induced by IL-5. TNF alpha-induced responses were completely inhibited by cytochalasin B and staurosporin, and partially blocked by pertussis toxin. Separation of eosinophils by discontinuous density gradients revealed the existence of at least two hypodense eosinophil populations with a distinct susceptibility to stimulation with TNF alpha. Based on functional assay systems, in contrast to a significant extracellular, only a small intracellular H2O2 production was detected. Accordingly, H2O2 production, detected by an ultrastructural technique, was observed only on the outer surface of the plasma membrane in the contact zones in between adjacent cells. Extracellular as well as intracellular production of H2O2 was completely inhibited by cytochalasin B. TNF alpha-induced activation of eosinophils is most probably mediated by binding to the 55 kD and the 75 kD TNF-receptor since both receptor molecules could be detected by FACS analysis and immune electron microscopy using receptor-specific antibodies. However, in contrast to its effect on eosinophil oxidative response, TNF alpha did not induce the release of significant concentrations of eosinophil cationic protein or eosinophil peroxidase in supernatants of cytokine-stimulated eosinophils, as detected by functional as well as immunological assay systems. These results clearly indicate that TNF alpha represents a potent eosinophil-activating cytokine which may be of relevance in the allergic inflammatory response.

CR 2039, a new bis-(1H-tetrazol-5-yl)phenylbenzamide derivative with potential for the topical treatment of asthma

The pharmacological activity of CR 2039 (4-(1H-tetrazol-5-yl)-N-(4-[1H-tetrazol-5-yl]phenylbenzam ide)) a newly discovered antiallergic compound is described. CR 2039 administered i.m. or i.v. inhibited rat passive cutaneous anaphylaxis (PCA) with an ED50 of 0.1 mg/kg and a potency about 15 times higher than that of disodium cromoglycate (DSCG). CR 2039 i.m., by aerosol or as dry powder insufflation, gave dose-related significant protection against IgE-dependent bronchial anaphylaxis induced by aerosolized antigen in anesthetized guinea-pigs. In conscious guinea-pigs CR 2039 given i.m. delayed dose dependently (ED50, 17 mg/kg) the onset of bronchoconstriction induced by aerosolized antigen, while DSCG was ineffective up to 100 mg/kg. The protection was accompanied by significant inhibition of the vascular permeability provoked by antigen challenge in all airway segments except trachea. CR 2039 (10-100 mg/kg i.v.) inhibited the microvascular permeability changes in a model of allergic conjunctivitis in sensitized guinea-pigs. CR 2039 inhibited dose dependently guinea-pig lung cAMP-phosphodiesterase with an IC50 of 50 microM.

Elevated levels of peripheral-blood, naturally occurring aliphatic polyamines in bronchial asthmatic patients with active symptoms

The levels of peripheral-blood, naturally occurring aliphatic polyamines, such as putrescine, spermidine, and spermine, from 21 bronchial asthmatic patients (11 atopics and 10 nonatopics) were measured by postcolumn derivatization high-performance liquid chromatography analysis. None of the patients, except the 44-year-old woman in the case report below, were given prednisolone, and they were instructed to take only regular medication during the tests. Blood was drawn from the patients in a fasting state, and the polyamine levels were compared between the times when they were free of asthmatic symptoms and when they had mild spontaneous attacks. Nine (5 atopics and 4 nonatopics), 6 (3 atopics and 3 nonatopics), and 4 (3 atopics and 1 nonatopic) out of 20 patients, when they had relatively mild asthmatic attacks, showed higher putrescine, spermidine, and spermine levels, respectively, than those of normal healthy control subjects. The levels of peripheral blood polyamines from a 44-year-old atopic bronchial asthmatic woman, who was admitted to the hospital with severe asthmatic attacks, were measured serially, and the putrescine and spermidine levels were found to be elevated during the asthmatic attacks, returning to normal levels in parallel with the clinical course. These data may suggest a role for naturally occurring aliphatic polyamines in bronchial asthma.

Substance P and beta-endorphin-like immunoreactivity in lavage fluids of subjects with and without allergic asthma

Six atopic subjects with grass pollen allergy and six nonallergic healthy volunteers were enrolled into this study. Substance P-like immunoreactivity (SP-LIR) and beta-endorphin-like immunoreactivity (beta E-LIR) were determined in bronchoalveolar lavage (BAL) and nasal lavage (NAL) fluids before and after allergen (grass pollen) provocation. A significant increase in the baseline concentration of SP-LIR and beta E-LIR was seen in BAL of allergic subjects. In NAL of allergic subjects an increased baseline concentration of SP-LIR was found (beta E-LIR not detectable). After allergen provocation there was a rise of SP-LIR and beta E-LIR in BAL fluids of allergic subjects immediately after provocation. In NAL fluids of allergic subjects allergen challenge resulted in a rise of SP-LIR within 10 minutes. Allergen provocation did not influence SP-LIR and beta E-LIR concentration in BAL and NAL in nonallergic controls. The demonstrated higher baseline levels of SP-LIR and beta E-LIR as well as the increase after provocation in the BAL and NAL of allergic subjects but not in nonallergic controls support the hypothesis that these neuropeptides contribute to allergic reactions in airways of humans.

Cyclosporin A in asthma therapy: a pharmacological rationale

Lymphocytes play a central role in immunological reactions and control the mobilisation and recruitment into lung tissue of eosinophils and mast cells. Since cyclosporin A can profoundly influence lymphocyte activation, it is appropriate to consider this drug as a novel anti-asthma therapy. Inhalation of low doses of cyclosporin A strongly inhibits the influx of inflammatory cells into the airways during acute allergic reactions, even though associated bronchospasm and airway hyper-reactivity are undiminished. It is suggested that cyclosporin A will be an effective anti-asthma therapy with an anti-asthma profile resembling that of established glucocorticosteroids.

A23187-induced pulmonary gas trapping and inflammation in the guinea pig

A brief A23187 aerosol exposure produced prolonged airway obstruction with granulocyte accumulation in conscious guinea pigs. Aminophylline, atropine, pyrilamine, salbutamol, SC-41930 (a leukotriene B4 antagonist) and WEB 2086 (a platelet activating factor antagonist) were administered intravenously (i.v.) to evaluate their ability to prevent these changes. Inhaled salbutamol was also assessed. Aminophylline, atropine, and salbutamol (i.v. and aerosol) inhibited A23187-induced gas trapping (p less than 0.01). However, pyrilamine, SC-41930 and WEB 2086 did not influence this airway obstructive effect. Only atropine, inhaled salbutamol and SC-41930 inhibited the cell influx (p less than 0.01), while pyrilamine potentiated the inflammation (p less than 0.05). We conclude that A23187 produces a sustained bronchospasm and an intense granulocyte accumulation. The treatment agents tested differ considerably in their ability to alter A23187-induced airway obstruction and inflammation.

Comparative protective effect of the inhaled beta 2-agonist salbutamol (albuterol) on bronchoconstriction provoked by histamine, methacholine, and adenosine 5'-monophosphate in asthma

We have investigated the ability of salbutamol to protect against bronchoconstriction induced by methacholine, histamine, and adenosine 5'-monophosphate (AMP) in nine subjects with asthma. In a double-blind, placebo-controlled study, salbutamol, 2.5 mg administered by nebulization, increased the geometric mean provocation concentrations of methacholine, histamine, and AMP required to produce a 20% decrease in FEV1 from 0.3 to 2.2, 0.4 to 3.8, and 4.0 to 106.7 mg/ml after placebo and active treatment, respectively (p less than 0.01). Thus, this dose of beta 2-adrenoceptor agonist displaced the concentration-response curves for methacholine, histamine, and AMP to the right in a parallel fashion by 8.8 (0.6 to 29.3)-, 10.3 (1.4 to 33)-, and 26.6 (1.5 to 76.6)-fold, respectively, the difference between the results for AMP and those for histamine and methacholine being statistically significant (p less than 0.01). For six of the nine subjects studied, salbutamol displaced the concentration-response curve for AMP to the right by greater than 50-fold. There was no correlation between bronchodilatation and protection against bronchoconstriction induced by any of the agonists. We conclude that salbutamol protects against bronchoconstriction provoked by methacholine and histamine by functional antagonism, whereas with AMP, an additional activity is demonstrable, possibly involving inhibition of mast cell-mediator release.

Evidence that neutrophils do not participate in the late-phase airway response provoked by ovalbumin inhalation in conscious, sensitized guinea pigs

Inhalation of ovalbumin by conscious, sensitized guinea pigs induced two phases of airway obstruction measured at 2 h (EAR) and at 17 h (LAR), respectively. In addition to causing airway obstruction, allergen challenge induced an accumulation in the bronchial lumen of eosinophil and neutrophil polymorphonuclear leukocytes at 17 h. Intraperitoneal injection of guinea pigs with a specific rabbit anti-guinea pig neutrophil serum 24 h before challenge reduced the number of circulating neutrophils by 94% and the airway neutrophilia after challenge by 90%, but it had no effect on the magnitude of either the EAR or the LAR. The observation that the LAR was not effected by neutropenia supports previous conclusions derived from experiments using the anti-allergic drugs, cromolyn sodium and nedocromil sodium, and the beta 2-adrenoceptor stimulant, albuterol, that, although there is a temporal relationship between neutrophil accumulation in the airways and the peak of the LAR, this polymorphonuclear leukocyte does not play a central role in the pathophysiologic processes that give rise to the late-phase response to guinea pig airways.

The inhibitory effect of azelastine hydrochloride on histamine- and allergen-induced bronchoconstriction in atopic asthma

We have examined the effect of azelastine, a new H1 histamine receptor antagonist, against bronchoconstriction induced by histamine and allergen. Twelve mild, atopic asthmatics each underwent two histamine and two allergen concentration-response inhalation challenges 4 hr after treatment with either 8.8 mg of azelastine or a matched placebo. Following azelastine the dose of histamine required to provoke a 20% fall in FEV1 (PD20 histamine) rose, from a geometric mean of 0.31 mg/ml to greater than 13.2 mg/ml. Azelastine also significantly inhibited allergen-induced bronchoconstriction, the PD20 allergen rising from 9.3 cumulative breath units (c.b.u.) to greater than 47.9 c.b.u., a greater than 5-fold increase. We conclude that azelastine effectively inhibits both histamine and allergen-induced bronchoconstriction, with considerably greater potency against histamine.

H1-antihistamines and calmodulin antagonists inhibit the ionophore A23187-induced eicosanoid formation by human leukocytes

The effects of the H1-antihistamines astemizole, oxatomide and pyrilamine, of the calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), on the ionophore A23187 (5 mumol/l)-induced release of cysteinyl-leukotrienes (LT) and thromboxane (TX) B2 from mixed human leukocytes were investigated in comparison to those of the cyclooxygenase inhibitor indomethacin and the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA). In contrast to pyrilamine both astemizole and oxatomide inhibited the release of cysteinyl-LT and TXB2 with IC50 values between 4 and 23 mumol/l. Both astemizole and oxatomide were about twice as effective in inhibiting cysteinyl-LT release as compared to TXB2 release. Similar to astemizole and oxatomide the calmodulin antagonists trifluoperazine and W-7 inhibited the eicosanoid release. W-7 was, however, clearly less effective and in contrast to trifluoperazine no difference was observed in its potency to inhibit cysteinyl-LT or TXB2 release. The H1-antihistamines, astemizole and oxatomide as well as the calmodulin antagonists did not cause intracellular retention of the eicosanoids tested. The reference compounds indomethacin and NDGA proved to be the most potent inhibitors. The results demonstrate that the therapeutic antihistamines astemizole and oxatomide as well as the classical calmodulin antagonists trifluoperazine and W-7 are able to inhibit eicosanoid formation.

The effect of an increase in inhaled allergen dose after terfenadine on the occurrence and magnitude of the late asthmatic response

We have attempted to use a potent and selective histamine H1-receptor antagonist terfenadine to allow a larger dose of allergen to be administered to previous single early responders to investigate if an increased dose of allergen could induce a late asthmatic response. Pre-treatment with 180 mg of terfenadine enabled a geometric mean increase in allergen dose of 4.12-fold to be inhaled by eight atopic subjects with mild asthma, who initially were classified as single early responders, with maximal fall in FEV1 3-8 hr after allergen challenge (Lmax) of less than 15% from baseline value. The magnitude of early asthmatic response was similar to that obtained on the control day when allergen challenge was performed in the absence of terfenadine. Two subjects were converted to dual responders with Lmax of 23.1 and 24.3%, which occurred with a 32- and 65-fold increase in allergen dose respectively, and a 6- and 4.9-fold decrease in non-specific airways responsiveness measured as the cumulative provocative concentration of methacholine that caused a 20% fall in FEV1 from baseline. The remaining six subjects failed to achieve an Lmax of greater than 10% even with a 1.29-2.66-fold increase in allergen dose. For the group as a whole an increase in allergen dose was associated with an increase in overall bronchoconstrictor response 3-8 hr after challenge. These results indicate that it is possible to induce a late asthmatic response in a subject who previously demonstrated only an early response by increasing the dose of allergen inhaled.

Adenosine as a pro-inflammatory mediator in asthma

Adenosine, which may be formed by all cells during relative energy or oxygen deficit, may act as an autocoid by modifying the function of other cells in the local environment. In asthmatic, but not normal, subjects, inhalation of adenosine causes a marked bronchoconstriction which may be reduced by the purinoceptor antagonist theophylline, sodium cromoglycate, nedocromil sodium, histamine, H1-antagonists and cyclo-oxygenase inhibitors. Repeated exposure to adenosine induces a state of tachyphylaxis and cross-tachyphylaxis with exercise-induced bronchoconstriction but not with that provoked by allergen. Although the mechanisms by which adenosine induces changes in airways function are not clear, it is suggested that it has an indirect effect, possibly by up-regulating bronchoconstrictor factors already present in asthma such as mast cell mediator release or neuronal reflexes.

Effect of nedocromil sodium on early and late phase responses to allergen challenge in the guinea-pig

We have developed a model of asthma in conscious guinea-pigs in which inhalation challenge with specific allergen induces both early and late phase reductions in specific airways conductance. Analysis of cells removed from the airways by bronchoalveolar lavage showed the presence of a neutrophilia, which reached a maximum at 17 hours, and an eosinophilia which developed more slowly, still increasing at 72 hours. Nedocromil sodium inhaled before challenge inhibited both the early and late phase responses. In contrast, the beta-adrenoceptor stimulant, salbutamol, inhibited only the early phase. When inhaled 6 hours after challenge, i.e. between the early and late phase responses, the late phase bronchoconstriction was prevented by nedocromil sodium but only partially by salbutamol. Evidence that the neutrophilia was not functionally associated with the late response was gained from the observations that it was inhibited by both nedocromil sodium and salbutamol, whereas only nedocromil sodium blocked the late phase airways response. When administered 6 hours after challenge, nedocromil sodium reduced eosinophil accumulation at 72 hours in parallel with inhibiting a secondary late response at this time. These results demonstrate that nedocromil sodium is able to prevent both early and late phase reductions in airways function in an animal model of allergic asthma. Whereas inhibition of the early response may reflect an effect on mast cell mediator release, the effects of nedocromil sodium on the late response and on eosinophil accumulation are strongly suggestive of an anti-inflammatory effect within the lung.

Allergy or inflammation? From neuropeptide stimulation of human skin mast cells to studies on the mechanism of the late asthmatic response

This short review examines two examples of studies into the mechanisms of allergic responses which have particular relevance to inflammation research. The first is the ability of human skin mast cells, but not those derived from lung, adenoids, tonsils or intestine, to release histamine in response to stimulation by neuropeptides including substance P, vasoactive intestinal polypeptide (VIP) and somatostatin. The neuropeptide activation site does not appear to be a classical tachykinin receptor but rather a binding site of low affinity and low specificity capable of interacting with neuropeptides and compounds with similar physicochemical characteristics. In contrast to IgE-dependent activation, neuropeptide stimulation of skin mast cells induces a rapid release of histamine with minimal generation of PGD2 and LTC4. This pseudo-allergic reaction is thought to underlie the weal and flare response in the skin and may have a role in urticaria. The second example describes studies to elucidate the mechanisms of the late asthmatic response by use of a guinea-pig model. As in man, both early and late phase responses in the guinea-pig are inhibited by sodium cromoglycate whereas only the early response is inhibited by the beta-adrenoceptor stimulant drug salbutamol. Examination of bronchoalveolar fluid has shown a temporal relationship between an airways neutrophilia and the late response. However, pharmacological manipulation and the use of an anti-neutrophil serum has shown that these events are not interdependent. The role of the airways eosinophilia requires further investigation.

The effect of cromolyn sodium and albuterol on early and late phase bronchoconstriction and airway leukocyte infiltration after allergen challenge of nonanesthetized guinea pigs

We describe the effects of the antiallergic drug cromolyn sodium and the beta 2-selective adrenoceptor agonist albuterol against early and late phase changes in specific airways conductance (sGaw) and leukocyte infiltration into the airways after allergen challenge of nonanesthetized guinea pigs. Inhalation of ovalbumin by sensitized guinea pigs induced three phases of airways obstruction: an early asthmatic response (EAR) peaking at 2 h, a late response (LAR) peaking at 17 h, and a further late response (LLAR) being observed at 72 h. The LAR was accompanied by a 13-fold rise in neutrophils and a four-fold rise in eosinophils recovered by bronchoalveolar lavage (BAL) at 17 h. By 72 h, the BAL content of neutrophils had returned to near normal, whereas eosinophil numbers had risen to 6.7-fold above baseline. Inhalation of an aerosolized solution of cromolyn, 10 mg/ml, 15 min before challenge inhibited both the EAR and LAR and the influx of neutrophils into the airways at 17 h but had no effect on eosinophil accumulation. Inhalation of cromolyn at 6 h, i.e., after the completion of the EAR, inhibited the LAR, the LLAR, and the rise in eosinophils at 72 h but did not reduce the influx of neutrophils at 17 h. Administration of cromolyn at both 15 min before and 6 h after challenge inhibited all changes in sGaw and reduced the accumulation of neutrophils at 17 h and the influx of eosinophils at 72 h. In contrast, inhalation of albuterol, 0.1 mg/ml, 15 min before allergen provocation blocked the EAR and the rise in BAL neutrophils at 17 h but did not inhibit the LAR. Inhalation of albuterol at 6 h partially reversed the LAR but had no effect on either the LLAR or cellular changes. Given at both times, albuterol inhibited the EAR and neutrophil accumulation at 17 h and partially reversed the LAR but produced no other effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced bronchoalveolar lavage mast cells histamine releasability in allergic dogs with and without airway hyperresponsiveness

To determine if mast cells from the airway lumen of Basenji-greyhound (BG) dogs differ functionally from mast cells of control dogs, we compared spontaneous release and A 23187-induced and C5-induced histamine release from bronchoalveolar lavage (BAL) fluid of 14 BG and five allergic and five nonallergic control dogs. No dog received antigen, agonist, or therapeutic aerosols for 4 weeks before BAL. The fluid recovered was centrifuged, and the number of mast cells was quantitated. Aliquots containing equal numbers of mast cells were incubated with A 23187 or C5 for 30 minutes, and histamine release was measured by an automated fluorometric method. Spontaneous release, A 23187-induced release, C5-induced release, and total histamine content per mast cell were calculated. The total amount of histamine per mast cell was not significantly different in BGs and allergic and nonallergic control dogs. Mast cells obtained by BAL released histamine to A 23187 and C5 in a dose-related manner. Spontaneous histamine release and A 23187-induced histamine release was significantly greater in BGs and allergic control dogs compared to nonallergic control dogs. C5-induced histamine release was significantly greater in BGs than in allergic as well as nonallergic control dogs. These data suggest that BAL mast cell histamine releasability must be defined with respect to each stimulus and that mast cells obtained from BAL from control dogs differ with respect to histamine releasability from mast cells of allergic dogs with and without airway hyperresponsiveness. This study suggests that mast cells obtained from BAL can be used to study mast cell function in the control and the allergic state.

Early and late-phase bronchoconstriction after allergen challenge of nonanesthetized guinea pigs. I. The association of disordered airway physiology to leukocyte infiltration

We describe a guinea pig model of asthma in which animals were sensitized and challenged by inhalation of aerosolized ovalbumin. Challenge was performed under cover of mepyramine (10 mg/kg) to allow a high enough concentration of ovalbumin to elicit consistent late responses. Airway resistance and thoracic gas volume of conscious guinea pigs was assessed by whole body plethysmography before and at regular intervals for as long as 72 h after challenge. At the same time points, cellular changes in the lung were assessed by both examination of cells recovered by bronchoalveolar lavage (BAL) and lung histology. There were no significant changes in specific airway conductance (SGaw), BAL cell content or lung histology in animals challenged with saline control. Challenge with 2% ovalbumin caused an early fall in SGaw, which peaked at 2 h and amounted to a 43.7 +/- 4.1% fall from baseline. This was followed by 2 late responses, the first reaching maximum at 17 h with a 46.9 +/- 4.5% decrease in SGaw from baseline and the second at 72 h with a 39.0 +/- 3.5% fall in SGaw. Examination of BAL fluid revealed a 7-fold increase in neutrophils at 6 h and a 17-fold increase at 17 h, after which numbers decreased to baseline. Eosinophilia developed more slowly, being insignificant at 6 h and 6-fold at 17 h; by 72 h, eosinophils constituted 48.9 +/- 6.9% of the total cells recovered. No changes in mononuclear cells or lymphocytes were observed. Histologic examination of the lung revealed a progressive eosinophil infiltration of the airways, but not alveoli or vascular bed. Electron microscopy showed degranulation of eosinophils recovered by BAL and discharge of mucus from goblet cells in the trachea. Because these changes are similar to those that occur after allergen challenge in human asthma, we suggest that this represents a useful animal model in which to study the mechanism of early and late bronchoconstriction responses.

Mediator release in an isolated airway segment in subjects with asthma

To determine if mediator release would occur in the airways of human subjects after exposure to a hyperosmolar stimulus, we challenged isolated airway segments in vivo with 900 mosmol sodium chloride using a specially designed double-balloon catheter. In order to determine if differences in mediator concentrations correlated with airway responsiveness or with atopy, we studied 3 separate groups: 6 atopic, asthmatic subjects; 6 atopic, nonasthmatic subjects; and 6 nonatopic, nonasthmatic normal subjects. In addition, to determine if the presence of the catheter itself was a stimulus, we studied 6 atopic, asthmatic subjects after exposure to isotonic sodium chloride alone (sham exposure). Lavage specimens were assayed for PGD2, PGF2 alpha, PGE2, TxB2, LTC4, and LTB4 by radioimmunoassay and for histamine by the modified single isotope enzymatic assay. The histamine concentration of the baseline lavage samples (bronchoalveolar lavage and isolated airway segment lavage) for the subjects with asthma were significantly greater than for the atopic or normal subjects (p less than 0.05). There was a significant negative correlation between histamine concentration in the lavage samples and the airway responsiveness of the subjects (r = -0.53, p less than 0.0001). There was a marked correlation among the concentrations of histamine, PGD2, PGF2 alpha, and TxB2 in all the lavage fluids for the subjects with asthma (p less than 0.03 for all comparisons and p less than 0.0001 for overall concordance). As a result of hyperosmolar challenge, there was a significant increase in the concentration of histamine, PGD2, and PGF2 alpha in the subjects with asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a cyclo-oxygenase inhibitor, flurbiprofen, and an H1 histamine receptor antagonist, terfenadine, alone and in combination on allergen induced immediate bronchoconstriction in man

The effect of flurbiprofen, a potent cyclo-oxygenase inhibitor, on histamine and methacholine reactivity was assessed in seven atopic subjects with asthma. Flurbiprofen 150 mg daily for three days displaced the histamine-FEV1 concentration-response curve to the right by 1.5 doubling doses, whereas no effect was observed on the response to methacholine. Subsequently the effects of flurbiprofen and terfenadine, a specific H1 histamine receptor antagonist, on allergen induced bronchoconstriction were studied in seven atopic but non-asthmatic subjects. The subjects inhaled the concentration of grass pollen allergen that had previously been shown to produce a 20% fall in FEV1 on separate occasions after prior treatment with placebo, flurbiprofen 150 mg daily for three days, terfenadine 180 mg three hours before challenge, and the combination of flurbiprofen and terfenadine. After placebo, allergen challenge caused a mean (SEM) maximum fall in FEV1 of 37.6% (2.6%) after 20 (3.7) minutes, followed by a gradual recovery to within 15% of baseline at 60 minutes. Terfenadine reduced the maximum allergen provoked fall in FEV1 to 21.5% (2.2%) and reduced the area under the time-response curve (AUC) by 50% (6%). Flurbiprofen alone reduced the mean maximum fall in FEV1 to 29.6% (3.2%) and reduced the AUC by 26%. The effect of the combination of flurbiprofen and terfenadine did not differ significantly from that of terfenadine alone. We conclude that histamine and prostaglandins contribute to immediate allergen induced bronchoconstriction and that a complex interaction occurs between the two classes of mediators.

Asthma management--a new dimension

This report describes a consensus on current asthma management in the UK, indicates areas of clinical concern and provides a rationale for improved therapy.

Asthma: emerging concepts and potential therapies

Asthma is a disease of the airways that results in reversible airflow obstruction. Recent investigations have suggested that airway inflammation is associated with increased airway responsiveness and worsening of asthmatic symptoms. The role that mast cell mediators might play in the production of asthma has been investigated by use of newer analytical techniques and by use of fiberoptic bronchoscopy with lavage to obtain lower respiratory tract fluid and cells. In addition, new investigational compounds that interfere with the synthesis or action of inflammatory mediators have been tested. Developing lines of investigation suggest that chronic activation of inflammatory cells may be important in the pathogenesis of asthma.

Two types of human mast cells that have distinct neutral protease compositions

Two human mast cell types were identified by immunohistochemical techniques in skin, lung, and small intestine. One type contains the neutral proteases, tryptase and chymotryptic proteinase, and is termed the TC mast cell. The second type contains only tryptase and is termed the T mast cell. Both types are fixed better by Carnoy's fluid than by formalin. The percentage of mast cells accounted for by the T type was 12 in skin; 98 in mucosa and 13 in submucosa of small intestine; and 77 in bronchial/bronchiolar subepithelium, about 97 in bronchial/bronchiolar epithelium, and 93 in alveoli of lung. Dispersed lung cells contained 90% T mast cells. The mean area of TC mast cells (76 micron2) was slightly larger than that of T mast cells (66 micron2); however, there was such extensive overlap that individual mast cells belonging to different types could not be distinguished on the basis of size. The recognition of human mast cell types with distinct protease compositions suggests a higher level of complexity of human mast cell-mediated reactions than heretofore appreciated.