Activation of the Prostaglandin E2 receptor EP2 prevents house dust mite-induced airway hyperresponsiveness and inflammation by restraining mast cells' activity.

BACKGROUND: Prostaglandin E2 (PGE2 ) has been proposed to exert antiasthmatic effects in patients, to prevent antigen-induced airway pathology in murine models, and to inhibit mast cells (MC) activity in vitro. OBJECTIVE: To assess in a murine model whether the protective effect of PGE2 may be a consequence of its ability to activate the E-prostanoid (EP)2 receptor on airway MC. METHODS: Either BALB/c or C57BL/6 mice were exposed intranasally (i.n.) to house dust mite (HDM) aeroallergens. Both strains were given PGE2 locally (0.3 mg/kg), but only BALB/c mice were administered butaprost (EP2 agonist: 0.3 mg/kg), or AH6809 (EP2 antagonist; 2.5 mg/kg) combined with the MC stabilizer sodium cromoglycate (SCG: 25 mg/kg). Airway hyperresponsiveness (AHR) and inflammation, along with lung MC activity, were evaluated. In addition, butaprost's effect was assessed in MC-mediated passive cutaneous anaphylaxis (PCA) in mice challenged with 2,4-dinitrophenol (DNP). RESULTS: Selective EP2 agonism attenuated aeroallergen-caused AHR and inflammation in HDM-exposed BALB/c mice, and this correlated with a reduced lung MC activity. Accordingly, the blockade of endogenous PGE2 by means of AH6809 worsened airway responsiveness in sensitive BALB/c mice, and such worsening was reversed by SCG. The relevance of MC to PGE2 -EP2 driven protection was further highlighted in MC-dependent PCA, where butaprost fully prevented MC-induced ear swelling. Unlike in BALB/c mice, PGE2 did not protect the airways of HDM-sensitized C57BL/6 animals, a strain in which we showed MC to be irrelevant to aeroallergen-driven AHR and inflammation. CONCLUSIONS & CLINICAL RELEVANCE: The beneficial effect of both exogenous and endogenous PGE2 in aeroallergen-sensitized mice may be attributable to the activation of the EP2 receptor, which in turn acts as a restrainer of airway MC activity. This opens a path towards the identification of therapeutic targets against asthma along the 'EP2 -MC-airway' axis.

Evaluation of the expression of P-selectin, ICAM-1, and TNF-alpha in bacteria-free lesional skin of atopic dogs with low-to-mild inflammation.

Canine atopic dermatitis (AD) is a pruritic skin condition that shares many clinical and pathophysiological features with its human counterpart. A major therapeutic challenge of AD is the control of the skin inflammatory process. A detailed knowledge of the pro-inflammatory molecules involved in cell recruitment in AD would allow for a better control of the disease. We thus have studied the protein expression of P-selectin, ICAM-1 and TNF-alpha in the lesional and non-lesional skin of atopic dogs that had been treated for bacterial infections. Despite a low-to-mild inflammatory process, P-selectin protein was clearly upregulated in the lesional skin areas when compared with non-lesional skin (four-fold average increase). This P-selectin upregulation was accompanied by signs of functional changes such as increased cell margination, and membrane-associated protein expression. Although the expression of ICAM-1 and TNF-alpha was not enhanced in the lesional versus the non-lesional skin, there was a trend towards a correlated upregulation of both molecules. Further studies will help elucidate the significance of the substantial overexpression of P-selectin in canine AD, in particular in a scenario where bacterial antigens are not contributing as pro-inflammatory stimuli.

Cardiotoxicity of histamine and the possible role of histamine in the arrhythmogenesis produced by certain antihistamines.

Since 1990 it has repeatedly been reported that some histamine H1 receptor antagonists (e.g. terfenadine and astemizole) are able to produce ventricular arrhythmias (e.g. torsade de pointes) when they are given at dosages above the therapeutic range and/or administered together with cytochrome P-450 3A4 inhibitors, such as ketoconazole or erythromycin. Although the mechanism by which these arrhythmias are produced remains unclear, the recently reported ability of these drugs to block outward K+ currents has been suggested as the cause of their arrhythmogenic effects. Alternatively, we have observed that some H1 antihistamines, including terfenadine and astemizole, are able to release histamine from guinea-pig cardiac mast cells. Thus, we have proposed that the liberated histamine, acting through an H2 receptor-stimulating mechanism, can prolong the action potential duration and hence induce arrhythmogenic effects. This paper describes experimental observations supporting the hypothesis that some H1 antihistamines can induce severe cardiac arrhythmias via the local release of histamine.

Prediction of the disposition of propafenone in humans and dogs from pharmacokinetic parameters in other animal species.

Most allometric studies performed until now have considered results obtained by different authors. The parameters mentioned in these studies reflect experiments made under very different conditions and have been calculated by assembling these heterogeneous data reported in the literature. In this paper, we present an allometric study of propafenone carried out in eight animal species, all treated and handled under the same conditions, and taking into account their weight to calculate different pharmacokinetic parameters. Propafenone plasma concentration-time data were analyzed by a model-independent method, and the pharmacokinetic parameters (Y) were correlated with body weight (B) using linear regression analysis by the equation Y = aBx. In addition, human and dog pharmacokinetic parameters were predicted from the results obtained in the other seven species and compared with the experimentally observed values. We demonstrated that these predictions are subject to great error when drugs with extensive metabolism, such as propafenone, are considered.

Canine cutaneous mast cells dispersion and histamine secretory characterization.

In view of the high incidence of canine cutaneous atopic disease and the relevance of mast cells to its pathogenesis, it was considered important to isolate firstly cutaneous mast cells from normal dog skin and to assess the histamine secretory activity, as this can be further used as a tool for the study of canine skin mast cell pharmacology in cutaneous atopy. The procedure for canine dermal mast cell dispersion following a skin enzymatic digestion (as for previous human skin mast cell dispersion methods) is described in detail. The number of canine cutaneous mast cells yielded per gram of skin was 2.31 +/- 0.21 x 10(5) representing 1.00% of the total cutaneous cells. The total histamine content per mast cell is 4.93 +/- 0.39 pg. Net histamine release owing to stimulation by calcium ionophore A23187 (1 microM) and concanavalin A (1 mg ml-1) was respectively 32.17 +/- 3.56% and 20.39 +/- 2.41% of the total amount per cell. Viability and reactivity to both stimuli of dispersed cutaneous mast cells were similar to the results found in humans. The present study allows further research on the role of mast cells immunopharmacology in allergy by investigation of cells isolated from canine skin in naturally occurring or experimentally induced atopy in the dog to be undertaken.

Comparative study of histamine release from skin mast cells dispersed from atopic, ascaris-sensitive and healthy dogs.

Atopic dermatitis results from the interaction between allergen and allergen-specific IgE bound to the mast cell surface receptors. This process triggers mast cell degranulation and accounts at least for early phase reaction. Furthermore, there is increasing in vitro and in vivo evidence that IgE has the ability to induce overexpression of the Fc epsilonRI receptor on the mast cell plasma membrane. In order to study the potential effect of an increase in serum IgE on mast cell activity, the histamine releasability of mature mast cells isolated from the skin of atopic, ascaris-sensitive and healthy dogs was analyzed. No histamine release was detected upon the immunological stimulation of cells that were not previously sensitized with atopic or ascaris-sensitive dog serum. However, when passively sensitized, skin mast cells were challenged with either Asc SI antigen or anti-IgE, the mast cell histamine release increased in a stimulus concentration-dependent manner. The amount of histamine released was significantly higher in response to anti-IgE than in response to Asc SI antigen. However. the difference in the percentage of mast cell histamine release between atopic (26.3+/-2.8%) and non-atopic (30.9+/-1.7%) dogs was not statistically significant, similar to what occurred when ascaris-sensitive (12.8+/-1.6%) and non-sensitive (13.2+/-1.7%) dogs were compared. Although these results could suggest that there is either little or no increase in the density of IgE receptors in atopic or ascaris-hypersensitive dogs versus controls, we strongly consider either the possibility that the digestion procedure might affect cell behaviour in vitro or that an underlying increase of receptors poorly affects the release of granule-stored mediators but influences mast cell activity in a different manner.

IgE enhances Fc epsilon RI expression and IgE-dependent TNF-alpha release from canine skin mast cells.

The role of IgE on mast cell (MC) activation is well known. Recent studies have demonstrated that IgE also has the ability to up-regulate the high affinity IgE receptor (Fc epsilon RI) on the surface of human and murine MC, leading to an increased production of cytokines and chemokines. In the present study, we have examined the influence of IgE levels on Fc epsilon RI expression, and its consequences on TNF-alpha production from canine skin MC. Mature MC were enzymatically dispersed from the skin biopsies of 6-8 dogs and were cultured for up to 5 days in medium supplemented with recombinant canine stem cell factor (SCF) (6 ng/ml), in the presence of increasing serum IgE concentrations (ranging from 0 to 80 microg/ml). Subsequently, skin MC were activated with anti-IgE, and TNF-alpha concentration was assessed 5h post-activation by a cytotoxic bioassay. Fc epsilon RI receptors were identified in MC surface by flow cytometry. MC cultured for up to 5 days in the presence of high serum IgE concentration (8 microg/ml) produced twice the quantity of TNF-alpha than MC cultured in the absence of serum IgE, in response to stimulation with anti-IgE. Moreover, the percentage of Fc epsilon RI-positive skin cells was found to be approximately double in cells cultured with serum IgE compared to that cultured in the absence of IgE, following saturation of IgE receptors. These results suggest that, as found in human and murine MC, IgE may induce an up-regulation of the Fc epsilon RI density and an enhancement in the secretory activity of canine skin MC. This study could be of great interest in designing new therapeutic strategies for controlling MC activation in inflammatory and allergic processes.

Stem cell factor enhances IgE-mediated histamine and TNF-alpha release from dispersed canine cutaneous mast cells.

Stem cell factor (SCF), the c-kit receptor ligand, plays a critical role in mast cell (MC) development and differentiation. In addition, SCF has recently been found to both modulate and induce MC activation. To investigate the effect of SCF on canine cutaneous MC function, we have characterized the ability of SCF to modulate the release by mature canine MC of preformed (histamine) and newly generated (TNF-alpha) mediators. Mature MC were isolated from skin and cultured in the absence or presence of exogenous SCF (6 ng/ml) for up to 5 days and then challenged with anti-IgE (1 microg/ml) alone for 30 min or with a combination of SCF (50 ng/ml) and anti-IgE. SCF alone failed to trigger either histamine or TNF-alpha release at any time. However, we observed that SCF used as a co-stimulus significantly potentiated histamine and TNF-alpha release in canine MC activated through Fc epsilon RI regardless of whether or not SCF was added to the medium during culturing. Thus, the mean histamine release (%) and TNF-alpha production (pg/ml) were found to be significantly higher if cells were maintained in culture in SCF-supplemented medium compared with cells cultured in the absence of exogenous SCF. We also observed that MC responsiveness to immunological stimulation increased with culture time, the percentage of histamine released being higher in cells cultured for at least 3 days when compared to freshly isolated MC. Taken together these findings suggest that canine skin MC releasability can be enhanced independently either through prolonged incubation with SCF and/or through anti-IgE and SCF co-stimulation.

Comparative morphofunctional study of dispersed mature canine cutaneous mast cells and BR cells, a poorly differentiated mast cell line from a dog subcutaneous mastocytoma.

The dog mastocytoma BR cell line provides us with a permanent source of canine mast cells, allowing a characterization of secretory mediators that exert important effects in canine allergic and nonallergic diseases and in physiological processes. We studied the ultrastructural characteristics and histamine releasing activity after immunological and non-immunological stimuli of the dog mastocytoma BR cell line, and compared the cell line to normal skin mast cells enzymatically isolated from healthy dogs. The histamine content of BR cells was 0.04 +/- 0.002 pg/cell, approximately 100-fold less than that found in canine skin mast cells. Non-immunologic stimuli induced similar concentration-dependent histamine release from skin mast cells and BR cells: 29.3 +/- 0.9% vs. 12.7 +/- 0.7% (calcium ionophore A23187), 23.3 +/- 0.7% vs. 18.8 +/- 0.7% (substance P) and 12.5 +/- 0.3% vs. 12.1 +/- 0.9% (compound 48/80), respectively. Immunologic stimulation, however, was only effective on canine skin mast cells, causing 30.9 +/- 1.7%, 27.7 +/- 0.6% and 12.2 +/- 0.9% histamine release in response to anti-canine IgE, concanavalin A, and antigen Asc S 1, respectively. The absence of functional IgE receptors in BR cells was confirmed by the lack of response to anti-IgE and antigen Asc S 1 following passive sensitization with dog atopic serum and dog antigen sensitized serum. We conclude that BR cells are able to release histamine after non-immunologic stimulation in a similar manner to canine skin mast cells, but that there are morphological and functional differences possibly due to different states of maturity or differentiation. For this reason the study of the highly homogeneous BR cells could offer insights into dog mast cell biology in contexts where freshly isolated cells cannot be used because of low purity and recovery.

[Bronchial mucoepidermoid carcinoma]. / Carcinoma mucoepidermoide bronquial.

We submit the case of a child afflicted with a mucoepidermoid bronchial tumor. The patient is a boy, aged seven, who after undergoing antibiotic treatment for six weeks because of a fever and atelectasia-condensation in the right lower lobe showed no signs of clinical improvement and was sent to our department to undergo further study and treatment. A bronchoscopy performed shows a polypoid mass that partially blocks the main bronchial tube a few milimiters under the access to the right upper lobe. A biopsy is carried out and the anatomopathological test shows there is a low degree epidermoid carcinoma. We decide to perform a lobectomy which for the tumor location and the lung condition has to be medium and lower right. We proceed to remove the adenopaty of hilium not affected by the tumor. The postoperative period develops without incidents. A check-up bronchoscopy performed three months later shows two polypoid masses in the right bronchial tube which, once a biopsy is performed, proved to be granulation tissue. Twelve months after undergoing surgery, the patient's condition is good, there is no evidence of tumor relapse and the breathing capacity is adequate, though there is an obstructive restrictive pattern in the espirometry. Even taking into consideration that lung tumors are extremely unusual, the epidermoid carcinoma is the one which most frequently occurs. The tumor's low malignancy is a sign that points to a good prognosis. Performing conservative surgery by means of bronchoplasty should be taken into account so as to keep the sequelae on the lung condition to a minimum, even though in this case the tumor location made it impossible.

Mucosal mast cells mediate motor response induced by chronic oral exposure to ovalbumin in the rat gastrointestinal tract.

We previously demonstrated that oral chronic exposure to ovalbumin (OVA) causes intestinal hypermotility in Sprague-Dawley rats. In this study, the objective was to determine the mechanism of action of OVA and the role of mucosal mast cells in the regulation of motor activity in this model. Rats were orally exposed to OVA during 6 weeks. Intestinal mucosal mast cells (IMMCs) were counted and rat mast cell protease II (RMCPII) measured in duodenum, jejunum, ileum and colon. Anti-OVA IgE, IgG, and IL-4 were measured in serum. Eosinophils and IgE(+) cells were counted in jejunum. In an additional study rats were treated with the mast cell stabilizer ketotifen and mast cell number, RMCPII concentration and motor activity in vitro were evaluated. OVA exposed rats showed an increase in mucosal mast cell number and in RMCPII content in small intestine and colon. However, variables of a Th(2) type response were not affected by exposure to OVA: (i) neither OVA specific IgE nor IgG were found; (ii) IL-4 did not increase and, (iii) the number of eosinophils and IgE(+) cells was identical in the exposed and unexposed groups. These results brought us to hypothesize a possible non-Ig-mediated action of OVA on mast cells. Ketotifen significantly diminished the response to OVA: Ketotifen reduced the number of mast cells and the RMCPII content and blocked increased intestinal contractility. In addition ketotifen modified motor response in both OVA exposed and unexposed animals giving evidence of the importance of mast cells in intestine motor activity driving.

The role of mast cells in atopy: what can we learn from canine models? A thorough review of the biology of mast cells in canine and human systems.

Mast cell research has largely focused on the role of these cells in the early phase of allergic reactions. However, their involvement may well extend beyond this stage, and even reach across nonallergic conditions. Mast cells from different sources have helped advance our knowledge of their biology. Although in vitro and in vivo research in this area has mainly focused on humans, such studies are limited by the extent to which cells from certain human tissues and/or human patients can be collected or studied. While rodents also provide valuable models with which to further our understanding of the behaviour of mast cells and their contribution to allergy, reported differences between human and murine mast cells, and, in some instances, the limitations of in vivo rodent models of mast cell-mediated allergic conditions, preclude their use. In this review, we introduce a relatively unknown mast cell population, that of the dog. Canine mast cells display many phenotypic and functional similarities with their human counterparts, and dogs develop spontaneous and induced allergic diseases that share clinical and pathophysiological features with the human condition. Therefore, the use of canine cells can shed light on the general role of mast cells, particularly in relation to allergic diseases given the potential of in vivo dog models within this field. Here we provide a detailed review of the data reported from in vitro and in vivo studies of canine mast cells, and compare them with results obtained in human systems. We also highlight direct evidence of the mast cell contribution to canine atopy. We conclude that the dog offers useful in vitro and in vivo models in which to investigate mast cell behaviour, and that its use should be considered when undertaking studies aimed either at elucidating the role of mast cells in health and disease, or at prescreening novel therapies prior to entry into man.

Sensitization of naive beagles by intradermal injection of an ascaris antigen: induction of a model of skin allergy.

Ascaris suum-hypersensitive beagles represent a unique model of skin allergy. Despite its suitability, the need to test numerous dogs prior to the selection of natural positive responders causes many complications. We hypothesized that the model could be induced in adult beagles by primary sensitization. Ten dogs were included in an intradermal sensitization program using ascaris antigen and were thereafter tested for cutaneous reaction. After 2 weeks, 60% developed a positive reaction that lasted for months. We therefore present a straightforward method to establish the Ascaris canine model of allergy that will extend its availability for research in cutaneous allergy immunomodulation.

Effect of H1- and H2-receptor antagonists on the hemodynamic changes induced by the intravenous administration of ketamine in sevoflurane-anesthetized cats.

OBJECTIVE: The anesthetic ketamine has been reported to cause both an increase of the plasma histamine concentration, notably in cats, and a cardiovascular depression. The latter has been described in humans and in other species. However the relevance of the histamine fluctuation for the ketamine-induced hemodynamic changes has not been determined. SUBJECTS AND TREATMENT: We studied the contribution of histamine to the hemodynamic effects induced by IV ketamine (7 mg/kg) in 12 sevoflurane anesthetized cats, of which half had been pre-treated with combined H(1)- and H(2) -receptor antagonists. METHODS: The mean arterial pressure (MAP) and the heart rate (HR) from both untreated (group C) and pre-treated (group AH) cats were recorded before and after the ketamine administration. The plasma histamine concentration was also measured. RESULTS: Plasma histamine fluctuations in the control and the antihistamine-treated group followed a similar pattern (no statistical differences); an initial rise that peaked 2 min after ketamine injection (from 0.63 +/- 0.11 ng/ml to 2.22 +/- 0.69 ng/ml in the C group, and from 0.71 +/- 0.10 ng/ml to 1.09 +/- 0.28 ng/ml in the AH group) followed by an immediate decrease in plasma concentrations. As for the hemodynamic variables under analysis, in the control group ketamine administration was followed by an early 30.3 +/- 8.1% reduction (p < 0.005) in the MAP with no associated changes in the HR. In the antihistamine pre-treated group, ketamine caused a further decrease of the MAP (41.7 +/- 2.3%), and a significant (p < 0.01) 11.6 +/- 2.9% reduction of the HR. CONCLUSION: Ketamine in anesthetized cats triggers histamine release and induces cardiovascular depression. The depression is more pronounced under the blockade of histamine activity through histamine receptor antagonists.

Antinerve growth factor treatment prevents intestinal dysmotility in Trichinella spiralis-infected rats.

Nerve growth factor (NGF) could be involved in the development of hyperalgesia as well as in nervous remodeling consequence of inflammation. Both dysmotility and increase of visceral sensitivity have been described in functional gastrointestinal disorders such as irritable bowel syndrome. Trichinella spiralis-infected rats show an exacerbated spontaneous motility and a significant increase of the excitatory response to cholecystokinin (CCK), both associated with a reversible inflammatory process and the hypertrophy of the muscle layers. In this study we determined the intestinal expression of NGF mRNA by polymerase chain reaction and NGF by enzyme-linked immunosorbent assay. We implanted serosal strain gauge transducers on duodenum, jejunum, and ileum of anesthetized Sprague-Dawley rats to record circular muscle contractions. The experimental protocol included the evaluation of intestinal spontaneous motor activity (SMA), the response to CCK-8, and the ascending contraction induced by electrical mucosal stimulation. This protocol was performed in healthy and infected nontreated rats, in healthy rats with an NGF antibody treatment (1.6 mg/rat i.p.), and in infected rats with the same treatment applied at 0 or 3 days postinfection. NGF and NGF mRNA levels in the bowel were increased during inflammation. Although anti-NGF treatments did not prevent or reverse inflammatory response, the treatment was effective in preventing the motor alterations induced by the T. spiralis infection, i.e., inhibited increased SMA, reversed altered response to CCK, and reversed in part exacerbated response to electrical stimulation.

In vitro inhibitory effect of rupatadine on histamine and TNF-alpha release from dispersed canine skin mast cells and the human mast cell line HMC-1.

OBJECTIVE AND DESIGN: To examine the inhibitory potential of rupatadine, a new H1-antihistamine and anti-PAF agent, on histamine and TNF-alpha release. Comparison with an H1-antihistamine (loratadine) and a PAF-antagonist (SR-27417A). MATERIAL: Dispersed canine skin mast cells were used to assess the effect of the drugs tested on FcepsilonRI-dependent and -independent histamine release; the human HMC-1 cell line was used to study TNF-alpha release. TREATMENT AND METHODS: Before stimulation mast cell populations were treated with increasing concentrations of rupatadine, loratadine and SR-27417A. Histamine and TNF-alpha release were measured following 15-30 min and 3 h activation, respectively. RESULTS: The IC50 for rupatadine in A23187, concanavalin A and anti-IgE induced histamine release was 0.7+/-0.4 microM, 3.2+/-0.7 microM and 1.5+/-0.4 microM, respectively whereas for loratadine the IC50 was 2.1+/-0.9 microM, 4.0+/-1.3 M and 1.7+/-0.5 microM. SR-27417A exhibited no inhibitory effect. Rupatadine, loratadine and SR-27417A inhibited TNF-alpha release with IC50 2.0+/-0.9 microM, 2.1+/-1.1 M and 4.3+/-0.6 microM, respectively. CONCLUSIONS: Rupatadine and loratadine showed similar inhibitory effect on histamine and TNF-alpha release, whereas SR-27417A only exhibited inhibitory effect against TNF-alpha.

Assessment of proliferative activity of canine dermal mast cells by bromodeoxyuridine and proliferating cell nuclear antigen labelling.

Cutaneous mast cells from skin biopsies of three healthy dogs and three dogs with atopic dermatitis were assessed for their proliferative potential using bromodeoxyuridine and proliferating cell nuclear antigen labelling. Mast cells isolated from the skin of two healthy dogs were also studied using bromodeoxyuridine labelling. Mast cells in skin biopsy specimens and mast cells isolated from the skin of healthy dogs did not incorporate bromodeoxyuridine. Two mast cells expressing proliferating cell nuclear antigen were seen around two superficial vessels in the dermis of one atopic dog. Epidermal cells, glandular epithelial cells, fibroblasts and endothelial cells incorporated bromodeoxyuridine and showed positive staining for proliferating cell nuclear antigen. These results suggest that canine mature mast cells do not proliferate in the dermis.

Mast cells induce upregulation of P-selectin and intercellular adhesion molecule 1 on carotid endothelial cells in a new in vitro model of mast cell to endothelial cell communication.

It is suggested that mast cells contribute to cell recruitment in inflammation through the upregulation of endothelial adhesion molecules. P-selectin and intercellular adhesion molecule(ICAM)-1 are two key adhesion molecules that have been associated indirectly with mast cell activity. The canine C2 mastocytoma cell line and primary cultures of canine carotid endothelial cells were used to establish a new in vitro model to help study the interaction between mast cells and endothelial cells. Carotid endothelial cells were incubated with mast cell mediators to uncover their effect on endothelial ICAM-1 and P-selectin expression. To assess the relative contributions of tumour necrosis factor (TNF)-alpha and histamine to such effect, an H1 antihistamine and a TNF-alpha blocking antibody were used. Prior to activation by mast cell mediators, P-selectin was expressed only within the cytoplasm, and ICAM-1 was constitutively expressed on the surface of the canine carotid endothelial cells. Both adhesion molecules were enhanced significantly and strongly upon mast cell activation at various time points. Unstored TNF-alpha was fully responsible for ICAM-1 upregulation. P-selectin was up-regulated by both preformed and newly synthesized mast cell mediators, but neither histamine nor TNF-alpha accounted for such an effect. Therefore,a new model is proposed in which the pro-inflammatory effect of mast cells on endothelial cells can be studied in vitro. In this model, it has been demonstrated that only TNF-alpha accounts for the overexpression of ICAM-1 induced by mast cells, and that mast cells up-regulate P-selectin expression through a histamine-independent mechanism.