Platelet-activating factor. A potent chemotactic and chemokinetic factor for human eosinophils

The role of eosinophils in asthma

During recent years it has become apparent that the eosinophil may represent a powerful effector cell in the pathogenesis of asthma, particularly in the late asthmatic response. It can be stimulated by a number of stimuli among which PAF appears to be one of the most effective. The eosinophil is a source for a variety of proinflammatory and toxic products with profound effect in the lungs and airways. These eosinophil products mimic some of the features of asthma and the strong association of the eosinophil with asthma has led to the suggestion that asthma would be better classified as "chronic desquamating eosinophilic bronchitis." Although the evidence known to date is persuasive many questions still remain unanswered and await further investigation. Future therapeutic approaches in asthma may aim at interrupting the mechanisms leading to eosinophil bronchial accumulation and activation.

Production of paf-acether by human epidermal cells

The production of the inflammatory mediator paf-acether (paf) from human epidermal cells was investigated in vitro. Human epidermal cells, freshly isolated from normal skin or in culture, were incubated in Tyrode's buffer containing 0.25% lipid-free bovine serum albumin in the presence of 2 microM calcium ionophore A23187, at 37 degrees C, for 1 to 60 min. Paf production slightly began at the first min of stimulation, was significant after 10 min, reached a maximum at 20 min (251 +/- 25 pg/l X 10(6) cells, mean +/- 1 SD), and decreased thereafter. About 50% of the paf amount produced by epidermal cells was recovered in supernatants. Addition of the non-acetylated paf precursor 1-O-octadecyl-sn-glycero-3-phosphocholine, i.e., lyso-paf, at 0.1 microM to epidermal cells during A23187-stimulation did not alter this production. In contrast, addition of acetyl-coenzyme A at 0.1 mM enhanced paf production by 5 times. The material produced by epidermal cells was identical to synthetic paf because: 1) the aggregation of aspirin-treated and ADP-insensitive washed rabbit platelets it induced was inhibited by BN 52021, an antagonist of the paf putative receptor; 2) the factor was inactivated by phospholipase A2 but was insensitive to lipase from Rhizopus arrhizus; 3) it exhibited the same retention time as synthetic paf during standard and reverse-phase (RP) high-pressure liquid chromatography (HPLC) elution. The paf precursors, i.e., lyso-paf and 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine, were also detected in epidermal cells, stimulated with A23187 or not. As determined by RP-HPLC analysis and confirmed by gas chromatography analysis, these precursors and the paf produced by epidermal cells exhibited more than 90% of a hexadecyl chain at the sn-1 position of the molecule. The present results demonstrate the synthesis and release of paf by normal human epidermal cells. Paf production within the epidermis might account for the development of cutaneous inflammation and the pathogenesis of many skin disorders.

Mucosal dysfunction and damage induced by platelet activating factor (PAF)

The effect of PAF on human nasal mucosa was investigated in vitro. Normal paranasal sinus mucosa was obtained from the ethmoid sinuses by surgical procedure and incubated in the form of tissue culture. Ciliary movement was viewed under an inverted microscope and recorded on video tapes, and its activity was measured photoelectrically. Morphological alterations were examined by light and electron microscopy. PAF inhibited ciliary activity of human nasal mucosa, in a time and a dose dependent manner, at concentrations from 10(-6)M to 10(-10)M, while no significant change was observed at 10(-11) M. Lyso-PAF exhibited minimal effect on the mucosa at a concentration of 10(-6) M. Morphological alterations of the epithelial layer of the mucosa such as edema, cell exfoliation and desquamation were found to increase across time. Ultrastructural alterations were observed prior to inhibition of ciliary activity. These data indicate the cytotoxic effect of PAF on human paranasal sinus mucosa.

PAF metabolism in resident and activated alveolar macrophages: role of protein kinase C

Platelet-activating factor (PAF) metabolism was studied in resident and activated alveolar macrophages. Macrophages were obtained from normal Sprague-Dawley rats and from rats previously injected with complete Freund's adjuvant. Macrophages were attached and stimulated for 90 min. Then, cell PAF was extracted and quantitated by thin-layer chromatography. We found that in both resident and activated macrophages, calcium ionophore A23187 was a potent stimulus for PAF production while phorbol myristate acetate (PMA) was not. PMA and ionophore acted synergistically to increase PAF content in resident macrophages. This synergism was not observed in activated macrophages. To examine if this difference between resident and activated macrophages was due to a difference in PAF degradation, we assayed acetylhydrolase, the PAF-degrading enzyme. We found that ionophore stimulated acetylhydrolase activity in activated macrophages, but not in resident macrophages. Furthermore, PMA potentiated the ionophore effect in activated macrophages. This synergism was less obvious in resident cells. We conclude that PAF metabolism is different in activated and resident alveolar macrophages. Protein kinase C may play an important role in acetylhydrolase regulation in these cells.

Quantitation of mast cells and eosinophils in the bronchial mucosa of symptomatic atopic asthmatics and healthy control subjects using immunohistochemistry

We have used fiberoptic bronchoscopy to obtain endobronchial biopsies in which mast cells and eosinophils were enumerated using monoclonal antibodies directed against mast cell tryptase (AA1) and the eosinophil cationic protein (EG2). Eleven symptomatic atopic asthmatics treated with beta 2-agonists alone and six normal subjects were studied. Over a period of 2 wk prior to bronchoscopy, patients recorded asthma symptom scores, bronchodilator usage, and twice-daily peak expiratory flow. Five days before bronchoscopy, methacholine responsiveness was assessed. Two biopsies were taken from the subcarinae, one of which was processed into araldite for immunostaining by the streptavidin biotin immunoperoxidase method and the other into Spurr resin for electron microscopy. The number of AA1 staining mast cells present in the bronchial mucosa was not significantly different in the epithelium or submucosa between the asthmatic and the normal subjects. However, in the biopsies from asthmatics, there were significantly greater numbers of EG2-staining eosinophils in the epithelium (median, 1.2/mm versus zero; p less than 0.005) and in the submucosa (median, 50/mm2 versus 1/mm2; p less than 0.001). Electron microscopy showed morphologic features of mast cell and eosinophil degranulation in the asthmatics. No correlation could be established between mast cell or eosinophil numbers and indices of disease activity of PC20 methacholine, which points to the complexity of mechanisms responsible for the symptoms and the airway hyperresponsiveness of asthma.

IL-5 enhances the in vitro adhesion of human eosinophils, but not neutrophils, in a leucocyte integrin (CD11/18)-dependent manner

In an attempt to explain the preferential accumulation of eosinophils at sites of allergic tissue reactions, we have studied the effects of interleukin-5 (IL-5) on the adherence of human eosinophils and neutrophils to plasma-coated glass (PCG) or human microvascular endothelial cells (HMVEC). IL-5 was compared with IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF) and platelet-activating factor (PAF), since all these agents have biological properties associated with eosinophil activation and/or survival in vitro. IL-5, IL-3 and GM-CSF induced a time-dependent increase in adherence of normal density eosinophils to PCG optimal at 60 min, whereas the effect of PAF was greater at 15 min. Similar results were obtained with neutrophils, with the exception that IL-5 had minimal and non-significant effects on this cell type. Unstimulated eosinophils and neutrophils also adhered to PCG or HMVEC, but in low numbers. Preincubation of eosinophils with IL-5, GM-CSF or PAF resulted in dose-dependent increases in the numbers of adherent cells to PCG. IL-3 had a smaller but significant effect on enhanced eosinophil adhesion to PCG, while IL-2 and lyso-PAF were ineffective. Neutrophils gave similar levels of baseline and stimulated adhesion to PCG as eosinophils, IL-5 again had no significant stimulatory effect. IL-5 also increased eosinophil, but not neutrophil, adherence to HMVEC in a concentration-dependent manner. Preincubation with the protein synthesis inhibitor cycloheximide had no effect on IL-5-, GM-CSF- or PAF-stimulated eosinophil adhesion. The contribution of the CD11/18 leucocyte integrins to IL-5- and PAF-induced eosinophil hyperadherence was investigated by inhibition experiments utilizing monoclonal antibodies (mAb). Enhanced adhesion to PCG (by PAF) or HMVEC (by IL-5) was inhibited by (ranked in order of potency) anti-CR3 alpha = common beta-chain greater than LFA-1 alpha. Anti-p150,95 alpha had no measurable effect. Baseline adhesion by unstimulated eosinophils was not significantly influenced by prior incubation with these mAb. Using flow cytometry, IL-5 and IL-3 were found to up-regulate cosinophil but not neutrophil CR3 expression. These findings demonstrate that IL-5 enhances cosinophil, but not neutrophil, adherence reactions, by a mechanism dependent, at least in part, on the CD11/18 family of adhesion glycoproteins.

PAF-induced bronchial hyperresponsiveness in the rabbit: contribution of platelets and airway smooth muscle

1. Aerosol administration of platelet activating factor (PAF) to normal rabbits induced an enhanced airway responsiveness to inhaled histamine, 6 and 24 h after exposure. Following exposure to bovine serum albumin (BSA) as the carrier molecule for PAF, there was an increase in airway responsiveness to histamine 6 h after challenge, although by 24 h this was not significantly different from the responsiveness of airways to histamine before BSA. 2. PAF-induced bronchial hyperresponsiveness at 24 h was associated with a substantial increase in the number of neutrophils and mononuclear cells and a small, but significant increase in the number of eosinophils in the lungs as assessed by bronchoalveolar lavage. BSA exposure failed to alter the total number of cells in the lungs, although there was a significant increase in the number of neutrophils in the bronchoalveolar lavage fluid. 3. Selective platelet depletion with a guinea-pig anti-rabbit platelet serum inhibited PAF-induced bronchial hyperresponsiveness. In addition, there was an attenuation of PAF-induced airway inflammation in animals rendered thrombocytopenic. 4. The contractile potency to histamine, methacholine and carbachol was similar in intrapulmonary bronchi taken from rabbits exposed to an aerosol of BSA or PAF. Furthermore, the relaxant potency to the non-selective beta-adrenoceptor agonist isoprenaline, was unaltered in PAF-treated rabbits. In contrast, there was a 2.58 fold reduction in the relaxant potency to theophylline in rabbits exposed to PAF compared with rabbits exposed to BSA. 5. These results suggest that in the rabbit, PAF-induced bronchial hyperresponsiveness at 24 h is associated with airways inflammation and is dependent upon platelet activation, but is not related to changes in airway smooth muscle function.

Platelet activating factor does not cause a reproducible increase in bronchial responsiveness in normal man

The reproducibility of acute effects of inhaled PAF on airway calibre, circulating neutrophil count and any subsequent increase in bronchial responsiveness has been studied in six normal subjects and compared to the effects of inhaled lyso-PAF, the inactive precursor and metabolite of PAF. PAF caused acute bronchoconstriction and a transient fall in neutrophil count on two separate occasions in five out of six subjects (minimum percentage of baseline values (mean): first PAF challenge; sGaw 69%, Vmax30 72%; neutrophil count 70%; second PAF challenge; sGaw 61%, Vmax30 74%, neutrophil count 63%). In one subject inhaled PAF caused bronchoconstriction and a transient fall in neutrophil count once, but a second challenge resulted in no detectable changes. There was no significant increase in bronchial responsiveness to methacholine in any subject studied on five occasions over a 2-week period following each PAF challenge. Challenge with lyso-PAF did not cause acute effects or any subsequent changes in bronchial responsiveness. These findings demonstrate that any effects of inhaled PAF on bronchial responsiveness in normal man are small and probably not of clinical significance. It would also be inappropriate to use this human model to study the mechanisms of bronchial hyperresponsiveness or for the preliminary assessment of potential new anti-asthma drugs.

Anaphylactic challenge causes eosinophil accumulation in bronchoalveolar lavage fluid of guinea pigs. Modulation by betamethasone, phenidone, indomethacin, WEB 2086, and a novel antiallergy agent, SCH 37224

Eosinophil infiltration into bronchoalveolar areas of the lung has been assessed in guinea pigs sensitized to ovalbumin (OA) and then challenged with the aerosolized antigen. Cell content, histamine, and guinea pig albumin (GPA) have been measured in bronchoalveolar lavage (BAL) fluid from these animals. Extensive eosinophil accumulation resulted from sensitization followed by OA challenge; monocytes that initially accounted for greater than 80% of the BAL cells remained essentially constant, and neutrophils comprised less than 3% of the population throughout. Eosinophils were elevated at 3 h, peaked with a fivefold increase at 24 h, and remained elevated for at least 7 days. Histopathologic changes observed in lungs taken from sensitized guinea pigs 24 h after OA challenge confirm this eosinophilia. Increased histamine and GPA were detected only at 5 min. Oral treatment with betamethasone (ED50 = 0.4 mg/kg), phenidone (ED50 = 15 mg/kg), Sch 37224 (ED50 = 0.5 mg/kg), and WEB 2086 (ED50 = 4 mg/kg) decreased eosinophil accumulation in the BAL fluid, indicating roles for 5-lipoxygenase products and PAF in this multimediator-dependent model of allergic inflammation. On the other hand, 4 mg/kg of indomethacin increased total cells with no effect on eosinophils, precluding a major role for cyclooxygenase products. Sch 37224, an antileukotriene agent and an orally active novel antiallergy agent in sheep, guinea pigs, and humans, is as potent as betamethasone at blocking eosinophil infiltration, suggesting that it may also suppress human pulmonary inflammation.

The requirement for platelets in allergen-induced late asthmatic airway obstruction. Eosinophil infiltration and heightened airway responsiveness in allergic rabbits

In these studies, we have used an allergic rabbit model to investigate the role of platelets in the late asthmatic response (LAR) by depleting platelets with a guinea pig antirabbit platelet antiserum (APAS). Allergen exposure of immunized rabbits pretreated with normal guinea pig serum (NGPS) to serve as a control resulted in an early- and late-phase obstructive airway response that persisted for 6 h. When the immunized animals were pretreated with APAS, the magnitude of the LAR in terms of dynamic compliance was reduced by 86.2% (p less than 0.03), but there was no difference in the early response curve. Allergen challenge of animals treated with NGPS resulted in an increased bronchial responsiveness to inhaled histamine: PD50 Cdyn geometric mean +/- SEM before, 2.36 mg/ml (3.43-1.64); after, 0.60 mg/ml (0.67-0.54) (p less than 0.01). PD50 RL before, 1.78 mg/ml (2.4-1.32); after, 0.58 mg/ml (0.81-0.47) (p less than 0.05). In contrast, when animals were treated with APAS, there was a significant inhibition of allergen-induced airway hyperresponsiveness to inhaled histamine: PD50 Cdyn geometric mean +/- SEM before, 1.42 mg/ml (2.06-0.98); after, 1.10 mg/ml (1.41-0.86) (p less than 0.4). PD50 RL before, 1.62 mg/ml (2.22-1.39); after, 1.05 mg/ml (1.35-0.82) (p greater than 0.4). Analysis of bronchoalveolar lavage fluid revealed an increase in the number of neutrophils and eosinophils after allergen exposure in control animals (p less than 0.01). However, in animals rendered thrombocytopenic, the number of eosinophils, but not neutrophils, was significantly reduced (p less than 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Mucosal inflammation in asthma

Over the past decade, it has become increasingly recognized that airways inflammation is one of the major components of asthma. Until recently, measurements of bronchial responsiveness and mediators of allergic reactions were the only methods of studying pathogenetic mechanisms in asthma. With improved diagnostic procedures such as fiberoptic bronchoscopy, it has become possible to investigate these mechanisms and the resulting inflammatory changes in situ. BAL has highlighted the presence of mast cells and eosinophils and has given proof of their mediator participation in airways inflammation and hyperresponsiveness. Endobronchial biopsies have so far yielded results that are similar to those obtained from postmortem studies, although it appears that there are varying degrees of inflammation in living asthmatics. Even in mild disease, the histopathologic features of bronchial asthma are consistent with chronic inflammation. Indirect evidence obtained from allergen challenge leading to increased bronchial hyperresponsiveness during LAR, and direct evidence of inflammatory cells and their mediators in the airway mucosa and lumen after allergen challenge argue for an active role of cells in bringing about inflammatory changes. At present, however, it is not possible to relate precisely the findings obtained by bronchoscopy to the clinical presentation and progression of asthma. Cell activation with production of potent mediators of inflammation may be more relevant to inflammation than the simple presence of these cells in the airways. Almost all the inflammatory cells present in the bronchial wall and lumen have been implicated in the pathogenesis of mucosal inflammation in asthma, but with our current state of knowledge, none can be singled out as the most important contributor. The mast cell was the first to be investigated in depth, and despite the accumulation of large amounts of data concerning its ultrastructure and function, it remains uncertain to what extent this cell is involved in inflammatory responses. Thus, while its main role appears to be that of initiator of allergen-induced responses, the eosinophil has attracted more attention as a proinflammatory cell rather than as an antiinflammatory cell with a capacity to be selectively recruited from the circulation in response to IgE-dependent signals. The eosinophil secretes potent mediators that cause damage to the bronchial epithelium and lead to bronchoconstriction. The role of other cells is at present not as well defined.(ABSTRACT TRUNCATED AT 400 WORDS)

The presence of platelet-activating factor associated with eosinophil and/or neutrophil accumulations in the pleural fluids

Platelet-activating factor (PAF) has been reported to play a role in the inflammatory reaction, but the mechanism of PAF in humans is still unclear. We examined the presence of PAF in pleural fluids from 23 patients with pleural effusion and in all cases detected PAF associated with eosinophil and/or neutrophil infiltrations. The amounts of PAF in pleural fluids were, respectively, 340, 50 to 170, and 1,250 to 2,130 fmol/ml for a patient with eosinophilic pneumonia, those with pneumothorax (n = 9), and empyema (n = 3). In contrast, patients with tuberculous pleuritis (n = 2), lung edema (n = 3), or malignant disease (n = 5) had no detectable amounts of pleural fluid PAF (less than or equal to 10 fmol/ml). The amount of PAF showed a close correlation with the numbers of eosinophils and neutrophils in the pleural fluids. Furthermore, PAF was mostly detected in the cellular fractions, and the molecular species of PAF from the patients with empyema were almost consistent with those of PAF generated by human blood neutrophils. These results indicate that neutrophils and, presumably, eosinophils were the cellular source of PAF in the pleural fluids in the pathologic state of inflammation.

Effect of Staphylococcus aureus delta-toxin on human granulocyte functions and platelet-activating-factor metabolism

The production of delta-toxin is supposed to be responsible for various pathophysiological effects during infection with Staphylococcus aureus. We compared the effects of delta-toxin with the structurally related bee venom toxin melittin on granulocyte functions and inflammatory mediator release. Delta-toxin and melittin induced a rapid Ca2+ influx, as was shown by fluorescence detection. Furthermore, oxygen radical production, as determined by luminol-enhanced chemiluminescence, was triggered by delta-toxin (0.15 to 15 micrograms/ml), whereas melittin showed only marginal effects. Release of lysozyme and beta-glucuronidase was observed only at high concentrations of 15 micrograms of melittin and delta-toxin per ml. Preincubation (15 min) of neutrophils with both toxins resulted in the formation of 3H-platelet-activating factor (3H-PAF) from 3H-lyso-PAF. After 5 min of incubation, the exogenously added lyso-PAF was converted to PAF (delta-toxin, 80 +/- 2%; melittin, 27 +/- 12% of total radioactivity; n = 3, mean +/- standard error of the mean) and 1-O-alkyl-2-acyl-glycerophosphorylcholine (alkyl-acyl-GPC) (corresponding values, 20 +/- 3% and 51 +/- 14% of total radioactivity). The newly generated PAF was rapidly metabolized to lyso-PAF and alkyl-acyl-GPC during the subsequent incubation period of 60 min. In the absence of any toxin, no formation of PAF from lyso-PAF was observed. Further studies indicated that the metabolism of PAF into lyso-PAF and alkyl-acyl-GPC was inhibited in the presence of delta-toxin. Melittin had no significant effects on PAF metabolism. Neither delta-toxin nor melittin modulated the uptake of PAF and lyso-PAF significantly. Our data provide evidence that delta-toxin has an effect on the activity of neutrophil granulocytes with regard to its proinflammatory capacity.

The effect of platelet-activating factor on IgE binding to, and IgE-dependent biological properties of, human eosinophils

This study investigated the effect of platelet-activating factor (PAF), leukotriene B4 (LTB4) histamine and formyl-methionyl-leucyl-phenylalanine (FMLP) on immunoglobulin E (IgE) binding and IgE-dependent cytotoxicity of human normal density eosinophils. The binding of a native myeloma IgE to normal human eosinophils was measured by flow cytometry using a fluorescein-conjugated polyclonal anti-IgE antibody. Preincubation with PAF (optimal at 10(-7)M), but not lyso-PAF or FMLP, gave dose-dependent increases in IgE binding. PAF and LTB4 gave significant increases in IgE binding after 5 min preincubation (P less than 0.05); the effect was further enhanced at 30 min (P less than 0.01). This was further confirmed using the rosette assay where PAF and LTB4, but not lyso-PAF or FMLP, gave dose- and time-dependent increases in IgE eosinophil rosettes. Eosinophil cytotoxicity for schistosomula of Schistosoma mansoni, incubated with immune serum, was also significantly enhanced (P less than 0.01) by PAF in a dose-dependent fashion (optimal at 10(-8) M). Schistosomula coated with FPLC-purified IgE fractions were susceptible to killing by normal density eosinophils, and this was enhanced with PAF (10(-8)M), LTB4 (10(-7)M) and histamine (10(-5)M) but not with FMLP (10(-7)M) or lyso-PAF. IgE-dependent cytotoxicity was confirmed by the removal of contaminating IgG from IgE-rich fractions, and by the abolishment of IgE-dependent cytotoxicity after IgE adsorption. These results suggest that PAF (and to a lesser extent LTB4 and histamine) increase IgE binding, IgE-dependent adherence and cytotoxicity of normal human eosinophils. Although IgE receptors have not been identified, the data support current concepts that certain biological properties of eosinophils may be IgE associated.

Effect of bacterial products on neutrophil migration in vitro

Chronic bronchial inflammation is associated with migration of large numbers of granulocytes into the bronchial tree. A study was designed to find out whether products of bacteria commonly isolated in chronic bronchial infection stimulate neutrophil migration in vitro. Neutrophils from healthy donors were studied by a modified Boyden chamber technique. Bacterial culture filtrates stimulated neutrophil migration over a wide dilution range and the chemotactic activity was heat stable. Culture filtrates derived from Pseudomonas aeruginosa, Streptococcus pneumoniae, and Haemophilus influenzae were significantly chemokinetic and directionally chemotactic, whereas filtrates from Staphylococcus aureus were only chemotactic. Gel filtration of S aureus and P aeruginosa culture filtrates yielded high, medium, and low molecular weight fractions showing chemotactic activity. S pneumoniae and H influenzae yielded fractions with only low molecular weight chemotactic activity. Neutrophil chemotactic responses, occurring in response to all bacterial species tested, appear to represent a defence mechanism by the host. Chemoattractant activity may, however, contribute to bronchial damage mediated by products released from continuously attracted, activated neutrophils.

The effects of activated eosinophils and neutrophils on guinea pig airway epithelium in vitro

Epithelial shedding is a characteristic feature of asthmatic airways and has been attributed to eosinophil products. We have examined the interaction of purified intraperitoneal guinea pig eosinophils with or without platelet-activating factor (PAF, 10(-7) M) or lyso-PAF (10(-7) M) with guinea pig tracheal epithelium in vitro. At 0, 4, 14, and 24 h, the percentage of ciliation of the tracheal circumference (CTC) was measured by light microscopy and the ciliary beat frequency (CBF) by photometry. PAF-activated eosinophils (50 x 10(6) cells/ml) disrupted the epithelium, mean CBF and CTC being reduced by 77.8 +/- 5.8% (mean +/- SEM; P less than 0.001 versus control) and 94.2 +/- 1.4% (P less than 0.001) over 24 h, respectively. PAF (10(-7) M) alone had no significant effect. Lyso-PAF with eosinophils (50 x 10(6) cells/ml) also reduced mean CBF and CTC but to a lesser extent. Eosinophils alone also led to a reduction of 36.2 +/- 11.4% in mean CBF and 53.0 +/- 15.5% in CTC, but these changes were not significant. The PAF antagonist, WEB 2086 (10(-6) M), significantly inhibited the mean CBF and CTC reduction due to PAF-activated eosinophils by 61.5 +/- 17.2% (P less than 0.01) and 20.8 +/- 6.5% (P less than 0.05), respectively. In addition, catalase (1,125 U/ml) partially inhibited the mean CBF and CTC reduction induced by PAF-activated eosinophils. Intraperitoneal neutrophils (PMN) (50 x 10(6) cells/ml) also disrupted epithelium but to a lesser extent (24-h reduction: 34.2 +/- 12.7% for mean CBF and 60.2 +/- 13.2% for CTC, respectively). Stimulation with PAF (10(-7) M) had no further effect. Marked exfoliation of the epithelial layer was observed after 14 h of incubation with activated eosinophils. We concluded the PAF-activated eosinophils are capable of grossly disrupting ciliated epithelium and may contribute to epithelial damage observed in asthma.

Inhibition of neutrophil and eosinophil induced chemotaxis by nedocromil sodium and sodium cromoglycate

1. Neutrophils and eosinophils infiltrate the airways in association with the allergen-induced late phase asthmatic reaction. Mobilization of these cells takes place via lipid-like and protein-like chemotactic factors. In this study platelet-activating factor (PAF), leukotriene B4 (LTB4), zymosan-activated serum (ZAS) and N-formyl-methionyl-leucyl-phenylalanine (FMLP) were used as illustrative examples of both groups. Chemotaxis was studied in human neutrophils and eosinophils. The inhibitory effects of nedocromil sodium and sodium cromoglycate were evaluated. 2. All chemotactic factors tested attracted neutrophils with the following rank order of activity: ZAS greater than PAF identical to FMLP identical to LTB4. Eosinophils were only mobilized by PAF, LTB4 and ZAS with the following rank order of activity: ZAS greater than PAF greater than LTB4. 3. Nedocromil sodium and sodium cromoglycate were equally active as the PAF antagonist BN 52021 in inhibiting the PAF-induced chemotaxis of neutrophils (IC50 approximately 10(-8) M). Both drugs were also equally active in inhibiting the chemotaxis of neutrophils induced by ZAS (IC50 approximately 10(-7)-10(-6) M), FMLP (IC50 approximately 10(-7) M) and LTB4 (IC50 approximately 10(-6) M). 4. Nedocromil sodium significantly inhibited the chemotaxis of eosinophils induced by PAF (IC50 approximately 10(-6) M) and LTB4 (IC50 approximately 10(-7) M). The inhibitory potency of BN 52021 was similar to that of nedocromil sodium on the PAF-induced chemotaxis of eosinophils. Sodium cromoglycate was incapable of eliciting significant inhibition of these chemotactic responses. However, sodium cromoglycate significantly inhibited the chemotaxis of eosinophils induced by ZAS (IC50 approximately 10(-7) M), whereas nedocromil sodium was ineffective.

Comparison of leukotriene B4-induced neutrophil migration through different cellular barriers

Migration of neutrophils across epithelial or endothelial barriers in response to chemotactic stimuli occurs in inflammation and host defense. Leukotriene B4 (LTB4) may be synthesized by and certainly induces chemotaxis of neutrophils. To better understand the interaction between LTB4, neutrophils, and endothelium and epithelium, we compared the effects of LTB4 on human peripheral blood neutrophil migration through filters alone and on human umbilical vein endothelial (HUVE) cells and three different epithelial cell types, Madin-Darby canine kidney (MDCK) cells, human colon carcinoma (T84) cells, and rat type II alveolar cells, cultured on these filters. Significant LTB4-stimulated neutrophil migration occurred at the lowest (1 nM) dose and in the shortest period of time (15 min) across endothelial cells vs. all three epithelial cell types, and interestingly, vs. filters alone. Dose-response experiments (1-100 nM) indicated that at equimolar LTB4 concentrations neutrophil migration across endothelium was two- to threefold greater than that observed across filters alone and the three epithelial barriers. At higher LTB4 concentrations (100 nM), the degree of neutrophil migration through the three epithelial barriers was equivalent to that observed for filters alone. Overall, the data indicate that the various cellular barriers play an active role in inflammatory processes by regulating the transmigration of neutrophils in response to certain inflammatory chemotactic stimuli.

Release of leukotriene C4 (LTC4) from human eosinophils following adherence to IgE- and IgG-coated schistosomula of Schistosoma mansoni

The release of leukotriene C4 (LTC4) from human low-density eosinophils following adherence to live or formalin-fixed schistosomula of Schistosoma mansoni coated with parasite-specific IgE or IgG obtained from pooled human anti-S. mansoni serum has been studied. IgE-rich fractions were obtained after fractionation of pooled immune sera on fast-protein liquid chromatography (FPLC; polyanion SI-17 column) and were identified by parasite-specific RAST. Contaminating IgG was removed by adsorption on a Staphylococcus aureus-protein A affinity column. IgG-rich FPLC fractions were identified by a specific ELISA assay. IgG-dependent activities were confirmed by protein A adsorption. Low-density eosinophils adhered to live and formalin-fixed schistosomula coated with specific antisera and released 11.7 +/- 2.7 and 16.5 +/- 3.5 pmoles of LTC4/10(6) cells, respectively. LTC4 release induced by A23187 (5 x 10(-6) M) from the same cells was 80 +/- 24 pmoles/10(6) cells and 9.9 +/- 1 pmoles/10(6) cells in the presence of Sepharose particles (CNBr-activated 4B beads) covalently coated with normal human IgG. Fixed schistosomula coated with FPLC-purified IgE and IgG gave 7.6 +/- 0.4 and 6.0 +/- 0.1 pmoles of LTC4 per 10(6) low-density eosinophils, respectively. The same IgE- and IgG-rich fractions induced eosinophil-mediated cytotoxicity of live schistosomula in vitro. Removal of IgE by an anti-IgE affinity column abolished both the IgE-dependent release of LTC4 and the in vitro killing of larvae. Conversely, IgG-dependent activities were abolished by protein A, but not anti-IgE, adsorption. Normal density eosinophils generated undetectable amounts of LTC4 when incubated with IgE-coated schistosomula, whereas with IgG-coated larvae 4.6 pmoles/10(6) cells were obtained. Following preincubation with platelet-activating factor (PAF) (10(-7) M) and leukotriene B4 (LTB4) (10(-7) M), normal density eosinophils released LTC4 when in contact with larvae coated with antigen-specific IgE. Lyso-PAF had no effect in any of the systems tested. The synthetic chemotactic tripeptide formyl-methionyl-leucyl-phenylalanine (FMLP) had no influence on IgE-dependent release of LTC4 from eosinophils. In contrast, FMLP (10(-7) M) enhanced the IgG-dependent LTC4 release, with PAF and LTB4 also showing a small enhancing effect. None of these agents substantially altered the release potential of low-density eosinophils in either IgE- or IgG-dependent events. Thus the results presented here indicate that in an IgE-dependent system, human low-density eosinophils can be induced to adhere to and kill IgE-coated helminthic targets and release biologically relevant amounts of LTC4.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium-ionophore-induced formation of platelet-activating factor and leukotrienes by horse eosinophils: a comparative study

Horse eosinophils preincubated with 3H-labelled acetate and stimulated with the Ca2+ ionophores ionomycin or A23187 form a radioactive compound, which we have shown to be 1-O-alkyl-2-[3H]acetyl-sn-glycero-3-phosphocholine (platelet-activating factor). We could detect no 1-O-acyl-2-[3H]acetyl-glycero-3-phosphocholine in the radioactive fraction. The formation of platelet-activating factor was strongly correlated to the generation of leukotriene C4, the main arachidonate metabolite in horse eosinophils, suggesting that platelet-activating factor and leukotriene C4 have a common precursor pool (1-O-alkyl-2-arachidonyl-glycero-3-phosphocholine) and a common regulation of synthesis. Even though both ionomycin and A23187 are described as Ca2+ ionophores, they have a series of significantly different effects on the eosinophils with respect to formation of platelet-activating factor and leukotriene C4. While A23187 induces an asymptotic maximum of mediator formation at concentrations higher than 20 microM, ionomycin expressed a narrow optimum at 2 microM. The effects of exogenous pH on the release of mediators also differ strongly between the two ionophores: for A23187 the effects are the same for both mediators but when ionomycin is used as stimulant, generation of platelet-activating factor and leukotriene C4 are affected differently.

Effects of inhaled PAF in humans on circulating and bronchoalveolar lavage fluid neutrophils. Relationship to bronchoconstriction and changes in airway responsiveness

We have compared the effect of inhaled platelet activating factor (PAF) on circulating neutrophils with its ability to induce bronchoconstriction and bronchial hyperresponsiveness in humans. Human volunteers inhaled PAF, given as six successive inhalations 15 min apart, followed by bronchoalveolar lavage (BAL) 4 h later. The mean density and volume of circulating neutrophils were measured by metrizamide gradients and flow cytometry, respectively. PAF caused a decrease in Vp20 of 38.2 +/- 4.5% at 5 min after the first inhalation (p less than 0.001). This was associated with a fall in the peripheral blood neutrophil count from 3.15 +/- 0.3 to 1.1 +/- 0.3 x 10(6) per ml (p less than 0.001), followed by a rebound neutrophilia (p less than 0.01). The mean density of peripheral blood neutrophils fell significantly at 15 min (p less than 0.02), with a return to baseline values despite further PAF inhalations; this was associated with an increase in neutrophil volume (n = 4; p less than 0.05). The numbers of neutrophils (x 10(5] in BAL fluid after PAF were significantly greater than after inhalation of lyso-PAF: 7.1 +/- 1.4 (n = 7) versus 1.3 +/- 0.3 (n = 5, p less than 0.01); eosinophil counts did not change significantly. The PC40 (the concentration of methacholine needed to cause a fall in Vp30) decreased from 17.1 (GSEM 1.40) to 8.7 (1.44) mg/ml (n = 12, p less than 0.02) 3 days after PAF. Inhaled lyso-PAF was inactive in all these respects.(ABSTRACT TRUNCATED AT 250 WORDS)

Eosinophil accumulation in pulmonary airways of guinea-pigs induced by exposure to an aerosol of platelet-activating factor: effect of anti-asthma drugs

1. Exposure of guinea-pigs to aerosols of platelet activating factor (PAF) (0.01 to 100 micrograms ml-1) induced a dose-dependent increased incidence of eosinophils in bronchoalveolar lavage fluid (BAL) at 48 h. Total leucocyte numbers and the percentages of lymphocytes and neutrophils were unchanged in BAL fluid. 2. Increased numbers of eosinophils were detected in BAL 1 h after exposure to PAF but eosinophilia was not maximal until 48 h. One week after exposure to PAF, the percentage of eosinophils in BAL was within the normal range. 3. Depletion of circulating platelets or neutrophils by intravenous injection of specific antisera did not modify accumulation of eosinophils in the airway lumen following inhalation of PAF (10 micrograms ml-1). 4. PAF-induced pulmonary airway eosinophil accumulation was inhibited by treatment with SDZ 64-412, a selective PAF-antagonist, whether the compound was administered before, or 30 min after, inhalation of PAF. 5. Pulmonary airway eosinophil accumulation due to inhaled PAF (10 micrograms ml-1) was inhibited by prior treatment with aminophylline, cromoglycate, ketotifen, dexamethasone and AH 21-132. 6. Pulmonary airway eosinophil accumulation due to inhaled PAF (10 micrograms ml-1) was not inhibited by prior treatment with indomethacin, salbutamol or mepyramine.

Prevention of non-specific airway hyperreactivity after allergen challenge in guinea-pigs by the PAF receptor antagonist SDZ 64-412

1. Allergen challenge by aerosol in sensitized guinea-pigs elicited non-specific airway hyperreactivity assessed by reactivity to i.v. histamine or acetylcholine. Airway hyperreactivity to histamine persisted for at least 48 h and was accompanied by pulmonary eosinophilia as determined by bronchoalveolar lavage cell analysis. 2. Airway hyperreactivity was independent of vagal reflex mechanisms since it was not abrogated by bilateral vagotomy. 3. The novel platelet-activating factor (PAF) receptor antagonist SDZ 64-412 inhibited the development of airway hyperreactivity, as measured 24 h after aerosol allergen challenge, when given as a single treatment orally 2 h before allergen challenge. The PAF receptor antagonist WEB 2086 as well as methylprednisolone and ketotifen also showed efficacy in preventing development of airway hyperreactivity. 4. Neither the two PAF antagonists nor ketotifen had any effect on bronchoalveolar lavage (BAL) eosinophil numbers. Methylprednisolone was the only substance which readily prevented eosinophil recruitment in addition to airway hyperreactivity. 5. We conclude that allergen-induced airway hyperreactivity in guinea-pigs is inhibited by prophylactic anti-asthma drugs and specific PAF receptor antagonists, thus demonstrating a pivotal role of PAF in this response. There was a lack of correlation between airway hyperreactivity and the presence of BAL eosinophils.

Generation of platelet activating factor (PAF) by a human lung epithelial cell line

A human lung epithelial cell line (ATC-CCL-185) was cultured in nutrient Ham-F12 medium. Cells in monolayers were stimulated with either ionophore A23187 (1 microM) or phorbol myristate acetate (PMA, 0.2 microM) for various periods of time. Samples were analysed by HPLC and the presence of platelet activating factor (PAF) was detected by bioassay of the release of [3H]serotonin from rabbit platelets undergoing aggregation. The ATC-CCL 185 cells were found to synthesize PAF following activation with either PMA or ionophore. Ionophore at 1 microM was found to be more potent than PMA at 0.2 microM in the induction of PAF synthesis (congruent to 80 ng/mg protein). The synthesis of PAF through ionophore stimulation reached a maximum at 5 min, whereas PMA stimulation peaked at 15-20 min. PMA induced approximately one third the level of PAF synthesis by the ionophore. The PAF synthesized by these CCL185 cells was found to be mainly associated with the cell membrane with less than 10% released into the medium. Release of PAF into cell supernatant was dependent on the presence of bovine serum albumin (BSA). In the absence of BSA, a large portion (approximately 90%) of PAF was found to be cell associated, and only 60% when BSA concentration reached greater than or equal to 0.2%. These results demonstrate the ability of this lung epithelial cell line to synthesis PAF thus, suggesting that epithelial cells might participate in the process of inflammatory lung diseases, through the generation of this important mediator.

The role of platelet activating factor in allergic respiratory disease

1. Platelet activating factor (PAF) is an ether-linked phospholipid capable of eliciting many of the factors of the allergic response including bronchoconstriction, mucosal oedema, eosinophil infiltration and bronchial hyperresponsiveness. 2. A wide range of selective PAF receptor antagonists have now been described which have been reported to reduce many aspects of allergen-induced inflammatory responses in experimental animals. 3. Early clinical studies have indicated that some of these drugs are also effective PAF antagonists in man, but no controlled studies have been reported using these compounds in patients with allergic asthma. 4. The gingkolide mixture BN 52063 has recently been reported to inhibit allergen-induced cutaneous inflammation in man; a response which has certain pathological similarities to allergen-induced late-onset airways obstruction in the lung. 5. Therefore, drugs antagonizing the actions of PAF may well lead to a better understanding of and may be a novel therapeutic approach for allergic respiratory disorders.

A new approach to the treatment of asthma

Asthma is a chronic inflammatory condition. The previous emphasis on bronchodilator therapy, which does not treat the underlying inflammation, may be misplaced. Earlier introduction of antiinflammatory agents, such as corticosteroids or cromolyn sodium, is strongly recommended. Effective suppression of airway inflammation reduces the need for bronchodilator therapy and may reduce the morbidity and, perhaps, mortality of asthma.

YM461, a PAF antagonist, blocks antigen-induced late airway responses and airway hyperresponsiveness in allergic sheep

We examined the effect of an orally active antagonist, YM461, of platelet activating factor (PAF) on antigen-induced early and late airway responses and on the development of airway hyperresponsiveness 24 h after challenge in allergic sheep. Early and late airway responses were determined by measuring specific lung resistance (SRL) before and periodically after challenge. Airway responsiveness was determined from the slopes of dose-response curves of SRL vs. increasing doses of carbachol aerosol. The sheep were challenged with Ascaris suum antigen once after vehicle treatment (control) and once 1 h after oral administration of 3 or 10 mg/kg YM461 (each trial was greater than or equal to 14 days apart). Airway responsiveness to carbachol was determined 1-3 days prior to and 24 h after antigen challenge. In control 1 and control 2 trials antigen challenge caused significant peak early (288 and 292%, respectively) and peak late (103 and 124%, respectively) increases over baseline in SRL. SRL returned to baseline 24 h after challenge but the sheep developed airway hyperresponsiveness as indicated by the 2.6-fold increases in the slopes of the carbachol dose-response curves in the control trials. YM461, 3 and 10 mg/kg p.o., significantly inhibited the late responses (66 and 82%, respectively) and blocked the development of airway hyperresponsiveness at 24 h. The early responses were not significantly reduced in either trial. These results suggest that PAF contributes to the antigen-induced late airway responses and associated airway hyperresponsiveness in allergic sheep.

Bronchial hyperresponsiveness in asthmatic children. Correlation with macrophages and eosinophils in broncholavage fluid

Bronchial responsiveness assessed by histamine bronchial challenge testing in 22 children with chronic stable asthma was compared with the number of inflammatory cells per milliliter of broncholavage fluid obtained by fiberoptic bronchoscopy. Hyperresponsiveness was closely correlated with increased counts of eosinophils and macrophages and with the ratio of eosinophils to macrophages. There was no correlation of neutrophil or lymphocyte counts with bronchial hyperresponsiveness and none of the cell types was correlated with airway obstruction. Our findings support the hypotheses that macrophages may be important in the development of bronchial hyperresponsiveness in children with asthma and that they may modulate bronchial responsiveness both directly and by recruitment of eosinophils.

Chemotactic responsiveness of eosinophils isolated from patients with inflammatory skin diseases

We determined the chemotactic responsiveness of peripheral eosinophilic granulocytes (eosinophils) isolated from patients with inflammatory dermatoses and healthy volunteers. Ten patients with atopic dermatitis, five patients with drug reactions, ten patients with psoriasis, and fourteen healthy volunteers were studied. Well characterized chemotaxins, the complement split product C5a, leukotriene B4 (LTB4), platelet activating factor (PAF), and N-formyl-methionyl-leucyl-phenylalanine (FMLP), were used as chemoattractants. Eosinophils from healthy volunteers showed strong migratory responses towards C5a and PAF but responded poorly to LTB4 and FMLP. When patients were grouped by disease severity, eosinophil chemotactic responses to PAF were significantly enhanced in severely affected patients (p less than 0.05); this was not true with C5a, LTB4 or FMLP. This enhanced eosinophil chemotaxis to PAF was not related to a specific disease. No correlation between eosinophil chemotactic activity and peripheral blood eosinophil count was observed. The increased responsiveness of circulating eosinophils towards PAF may be related to altered receptor expression during cutaneous inflammation.

Density heterogeneity of eosinophil leucocytes: induction of hypodense eosinophils by platelet-activating factor

We have examined the induction of hypodense eosinophils by platelet-activating factor (PAF), a mediator which may be involved in eosinophil activation in allergic diseases. Guinea-pig eosinophils were incubated with buffer or PAF and applied to continuous Percoll density gradients. Cellular density ranged from 1.0142 to 1.1369 g/ml. Peak eosinophil density in control was 1.0887 +/- 0.0008 g/ml (mean +/- SEM), and 91.1 +/- 1.4% of eosinophils were distributed between 1.0810 and 1.1000 g/ml. Preincubation of eosinophils with PAF(10(-7) M) resulted in a time-dependent and non-cytolytic increase of the number of hypodense eosinophils, with peak densities after incubation for 1 hr and 2 hr of 1.0834 +/- 0.0014 (n = 4, P less than 0.05) and 1.0755 +/- 0.0007 g/ml (n = 6, P less than 0.01), respectively. After incubation for 2 hr, 82.0 +/- 4.9% (n = 6) eosinophils showed a density lower than 1.080 g/ml. Lyso-PAF, the inactive precursor and metabolite of PAF, at a concentration of 10(-7) M had no effect on cell density. The specific PAF receptor antagonist WEB 2086 (10(-6) M) inhibited the PAF-induced density shift by 87.0 +/- 5.3%. Our results demonstrate that a single mediator is able to induce the formation of hypodense eosinophils. We conclude that the appearance of hypodense eosinophils in allergic diseases such as asthma may occur, at least in part, in response to inflammatory mediators which activate these cells.

Platelet-activating factor causes goblet cell depletion in the conjunctiva

Platelet-activating factor (PAF) (1-O-hexadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine) produced dose-dependent depletion of the goblet cell population associated with the conjunctival epithelium. Reductions in goblet cell numbers did not correspond to leukocyte infiltration and were consistent with a direct effect of PAF. In contrast, LTD4 and LTE4 did not affect the goblet cell population although they caused massive eosinophil infiltration into the conjunctival epithelium. Histamine also produced conjunctival goblet cell depletion, but this appeared secondary to eosinophil degranulation and resultant epithelial desquamation. In addition to goblet cell expulsion, PAF produced an increase in conjunctival microvascular permeability over an identical dose-range. PAF-induced leukocyte emigration was small or absent and comprised a neutrophil infiltrate which exhibited no clear dose-dependent relationship. Lyso-PAF produced effects only at the highest dose employed where pathological changes and a distinct increase in conjunctival microvascular permeability were evident. Lyso-PAF- and PAF-induced increases in conjunctival microvascular permeability were virtually abolished by the PAF antagonist CV-6209. The pronounced inhibitory activity of CV-6209 suggests that high doses of lyso-PAF may either weakly stimulate conjunctival PAF receptors or that there may be sufficient conversion of lyso-PAF to biologically active levels of PAF.

Evidence for two platelet activating factor receptors on eosinophils: dissociation between PAF-induced intracellular calcium mobilization degranulation and superoxides anion generation in eosinophils

We have compared platelet activating factor (PAF)-induced eosinophil peroxidase (EPO) release and intracellular calcium mobilization with superoxide anion (.O2-) generation from guinea pig eosinophils. EPO release and Ca2+ mobilization occurred at lower concentrations of PAF (EC50 values of 1.3 nM and 11.5 nM, respectively) while .O2- production was observed at higher concentrations (EC50 of 31.7 microM). Receptor characterization with the competitive PAF antagonist, WEB 2086, gave pA2 values of 8.5 and 8.3 for EPO enzyme release and rise in [Ca2+]i, respectively, and 5.8 for the .O2- production. In addition, PAF-induced degranulation and elevation of [Ca2+]i were dependent on extracellular Ca2+ whereas PAF-stimulated .O2- generation was dependent on the presence of extracellular Mg2+ ions. These results suggest the existence either of two subtypes of the PAF receptor or a single receptor that can exist in one of two affinity states on guinea pig eosinophils.

Evidence of PAF-acether metabolic pathway activation in antigen challenge of upper respiratory airways

Lyso-PAF-acether and PAF-acether (formerly platelet-activating factor) were detected in nasal secretions from patients with hay fever who underwent local antigen challenge. Lyso-PAF release was observed in 12 of 13 patients, with a maximum (p less than 0.001) 5 min after stimulation and a progressive decrease during the first hour. PAF was detected in the 5-min postchallenge nasal washings from two of 13 subjects. After HPLC, this mediator was found in four of seven postchallenge nasal washings submitted to this procedure, with a peak 5 min and 10 min after provocation. Histamine analysis revealed a significant (p less than 0.001) but time-limited (5 min) release in nasal secretion. The pattern of immunoreactive leukotriene C4 showed a maximal peak (p less than 0.01) 5 min after allergen provocation, with raised levels for 20 min. Nasal stimulation with nebulized saline solution or grass pollens in healthy subjects and in patients suffering from allergic rhinitis caused by Dermatophagoides pteronyssinus was followed by no local mediator release. These data indicate that, in addition to histamine and peptide-leukotrienes, lyso-PAF and PAF are released in nasal secretions after local antigen stimulation in patients with hay fever, with a preponderance of lyso-PAF response. On the basis of these results, it is conceivable that these ether-phospholipids may be involved in allergic inflammation of human nasal airways.

New concepts in the pathogenesis of bronchial hyperresponsiveness and asthma

Recent studies have suggested that inflammation may play an important role in the characteristic bronchial hyperresponsiveness and symptoms of chronic asthma. The mechanisms by which inflammatory cells, mediators, and nerves interact to produce the features of asthma are still uncertain, however. Although mast cells play an important role in the immediate response to allergen (and probably exercise), pharmacologic evidence argues against a critical role in the late response or bronchial hyperresponsiveness in which other cells, such as macrophages and eosinophils, may play a more important role. Many mediators have been implicated in asthma, but only PAF causes a prolonged increase in bronchial responsiveness. PAF attracts eosinophils into tissues and potently activates these cells, which may lead to epithelial damage, a key feature of asthmatic airways. PAF is also a potent inducer of microvascular leakage in airways, which may result in submucosal edema and plasma exudation into the airway lumen in the future. PAF antagonists will reveal whether PAF plays an important role in the eosinophilic inflammation of asthma. Neural mechanisms may also make an important contribution. Inflammatory mediators may influence neurotransmitter release from airway nerves, and neurotransmitters may be proinflammatory. Neural control is complex and cholinergic, adrenergic, and NANC mechanisms may contribute to bronchial hyperresponsiveness. Many neuropeptides, which may be the transmitters of NANC nerves, have been identified in airways. Neuropeptides in airway sensory nerves, such as substance P, have potent proinflammatory effects and, if these are released by an axon reflex, may amplify the inflammatory response in asthma. Since asthma may be chronic eosinophilic bronchitis, it is logical that the primary treatment should involve drugs that suppress this inflammatory response. At present, corticosteroids appear to be the most effective therapy; they have potent effects against eosinophils and macrophages (but not on mast cells) and reduce bronchial hyperresponsiveness and symptoms. By contrast, bronchodilators, such as beta-agonists, although they reduce symptoms, do not reduce the chronic inflammatory response or bronchial hyperresponsiveness and may mask the underlying inflammation. New therapies should be directed toward controlling eosinophil infiltration and activation in airways.

Effect of inhaled leukotriene B4 alone and in combination with prostaglandin D2 on bronchial responsiveness to histamine in normal subjects

The effect of intradermal injection of leukotriene B4 alone and in combination with prostaglandin D2 and E2 and the effect of inhaled leukotriene B4 in combination with prostaglandin D2 were studied in six non-asthmatic men. The intradermal injection of leukotriene B4 (1 microgram) alone caused no immediate or late response in five of the six subjects but greatly potentiated the flare response to intradermal prostaglandin D2 (0.5 microgram) and E2 (0.5 microgram) in all subjects. In contrast, inhaled prostaglandin D2 (6 micrograms) alone and in combination with inhaled leukotriene B4 (12 micrograms) caused no change in the response to inhaled histamine, measured 30 minutes and three and six hours after the inhalation. These findings provide no support for the suggestion that leukotriene B4 has an important role in causing bronchial hyperresponsiveness. The possibility that higher doses of inhaled leukotriene B4 may alter bronchial responsiveness cannot, however, be ruled out.

Differential sensitivities of purified human eosinophils and neutrophils to defined chemotaxins

Functions of eosinophils and neutrophils isolated from normal human blood were determined by measuring chemotactic migration and release of beta-glucuronidase. Four well-characterized chemotaxins, the complement fragment C5a, formyl-methionyl-leucyl-phenylalanine (FMLP), platelet-activating factor (PAF), and leukotriene B4 (LTB4) were used as stimuli. Neutrophils showed remarkable chemotactic responses to all four chemotaxins. In contrast, eosinophils showed a significant chemotactic response to C5a and PAF, but only weak responses to FMLP and LTB4. Using these chemotaxins we found the following order of chemotactic potency (maximal number of migrated cells): C5a = LTB4 greater than FMLP greater than PAF for neutrophils and PAF = C5a greater than LTB4 = FMLP for eosinophils. Neutrophils elicited a significant beta-glucuronidase release when stimulated by C5a and FMLP, whereas only small amounts were released with PAF and LTB4. On the other hand, an amount of beta-glucuronidase released from eosinophils comparable to that from neutrophils was elicited only with C5a. FMLP, LTB4, and PAF caused the release of small percentages of beta-glucuronidase. The important cellular functions of eosinophils and neutrophils, chemotaxis and enzyme release, are thought to be controlled by differential responsiveness to stimuli.

Recombinant interferon-gamma primes alveolar macrophages cultured in vitro for the release of leukotriene B4 in response to IgG stimulation

The capacity of interferon-gamma to regulate the generation and release of leukotriene B4 (LTB4) from human alveolar macrophages of normal nonsmoking individuals was evaluated. When alveolar macrophages were incubated for 60 min with heat aggregated IgG (HAIgG), they generated and released 5.7 +/- 1.7 ng of LT B4 per 10(6) cells compared to 1.9 +/- 0.4 ng from cells incubated with buffer alone, P = 0.02. When alveolar macrophages were preincubated with interferon-gamma for 24 h before activation for 60 min with heat-aggregated IgG, the soluble IgG aggregates became a significantly more effective stimulus for LTB4 release, 17.0 +/- 3.9 ng/10(6) cells, P = 0.001, compared to cells incubated in the absence of interferon-gamma and challenged with HAIgG. Interferon-gamma did not alter the response to A23187. This effect of interferon-gamma was both time and dose dependent; it also was specific since neither interferon-alpha nor interferon-beta had a regulatory effect on the release of LTB4 from cells in response to challenge with HAIgG. Preincubation of the alveolar macrophages with interferon-gamma augmented the density of IgG1 receptors by 81.5 +/- 17.3%; neither interferon-alpha nor interferon-beta effected this parameter. Furthermore, monomeric IgG1 blocked HAIgG induced LTB4 release from alveolar macrophages primed with interferon-gamma. Therefore, at least one of the mechanisms by which interferon-gamma primes alveolar macrophages for the production and release of LTB4 in response to stimulation by aggregates of IgG is that of increasing the number of receptors for this stimulus.