Mast Cell Histamine Release Research Articles

Sparassis crispa suppresses mast cell-mediated allergic inflammation: Role of calcium, mitogen-activated protein kinase and nuclear factor-κB

Allergic inflammatory disease such as food allergy, asthma and atopic dermatitis are increasing worldwide. In this study, we investigated the effect of water extract of Sparassis crispa (WESC) Fr. (Aphyllophoromycetideae) on mast cell-mediated allergic inflammation and the possible mechanisms of action. WESC inhibited compound 48/80-induced systemic anaphylaxis and serum histamine release in mice. WESC decreased immunoglobulinE (IgE)-mediated passive cutaneous anaphylaxis. Additionally, WESC reduced histamine release and intracellular calcium in human mast cells activated by phorbol 12-myristate 13-acetate (PMA) and calcium ionophore A23187. WESC decreased PMA and A23187-stimulated expression of pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α, inlerleukin (IL)-6 and IL-1β. The inhibitory effect of WESC on pro-inflammatory cytokines was nuclear factor-κB, extracellular signal-regulated kinase and p38 mitogen-activated protein kinase-dependent. Our results suggest potential therapeutic application of WESC in allergic inflammatory diseases.

Enhancing effects of trichloroethylene and tetrachloroethylene on type I allergic responses in mice

Trichloroethylene (TCE) and tetrachloroethylene (perchloroethylene; PCE) are commonly identified as environmental contaminants of groundwater. Previously, we investigated the enhancing effects of TCE and PCE on antigen-induced histamine release and inflammatory mediator production in rat mast cells. In this study, to examine the potential effect of TCE and PCE on antigen-induced histamine release from mouse mast cells, mouse bone marrow-derived mast cells (BMMC) were sensitized with anti-dinitrophenol (DNP) monoclonal IgE antibody and then stimulated with DNP-BSA containing with TCE or PCE. Both TCE and PCE significantly enhanced antigen-induced histamine release from BMMC. Next we investigated the effects of TCE and PCE on the passive cutaneous anaphylaxis (PCA) reaction in vivo using ICR mice. TCE and PCE significantly enhanced the PCA reaction in a dose-dependent manner. In addition, we examined the enhancing effects of ingesting small amount of TCE and PCE in drinking water on antigen-stimulated allergic responses. After the ICR mice had ingested TCE or PCE in their drinking water for 2 or 4 weeks, we performed the PCA reaction. Both TCE and PCE ingestion enhanced the PCA reaction in a dose-dependent manner for 4 weeks. These results suggest that exposure to TCE and PCE leads to the augmentation of type I allergic responses in many species.

Clinical and investigative assessment of patients with positive versus negative autologous serum skin test: A study of 80 south Indian patients

Background:Chronic urticaria (CU) is defined as urticaria persisting daily as or almost daily for more than 6 weeks and affecting 0.1% of the population. Mast cell degranulation and histamine release is of central importance in the pathogenesis of CU. About 40-50% of the patients with chronic idiopathic urticaria demonstrate an immediate wheal and flare response to intra-dermal injected autologous serum. This led to the concept of autoimmune urticaria.Aims:To determine the occurrence, clinical features, associated clinical conditions, comorbidities of autoimmune urticaria and to compare this with chronic spontaneous urticaria. This study aimed to find the frequency of autologous serum skin test (ASST) positive patients among patients with CU and to identify the clinical and laboratory parameters associated with positive ASST.Materials and Methods:Prospective correlation study was done on 80 chronic urticaria patients, more than 6 weeks duration, attending outpatient department of dermatology during a period of November 2007 to January 2010. Patients were subjected to ASST, complete blood count, urine routine examination, liver function tests, renal function tests, thyroid function tests, H. pylori antibody tests, C3 and C4 complement level estimation, antinuclear antibody, and urine analysis.Results:ASST was positive in 58.75% and negative in 41.25% of the patients, respectively. Out of 33 patients with history of angioedema, 9 (27.3%) patients were in ASST negative group and 24 were in positive group, this was statistically significant. Both groups showed no statistically significant difference for epidemiological details.Conclusion:ASST is considered a screening test for an autoimmune urticaria, which decreases the rate of diagnosis of “idiopathic” form of chronic urticaria. Patients with an autoimmune urticaria have more severe urticaria, more prolonged duration, more frequent attacks, and angioedema. Identification of autoimmune urticaria may permit the use of an immunotherapy in severe disease unresponsive to anti-histamine therapy.

Amaranthus spinosus Linn. inhibits mast cell-mediated anaphylactic reactions

The current study characterizes the mechanism by which the Amaranthus spinosus (Amaranthaceae) decreases mast cell-mediated anaphylactic reactions. Anaphylaxis is a typical hypersensitivity Type I reaction, sharing common mechanisms with asthma in its early and late phases. Mast cells are key as effector cells in hypersensitivity Type I reactions. A. spinosus has been traditionally used in the treatment of allergic bronchitis and asthma, but its role in mast cell-mediated anaphylactic reactions has not fully been investigated. This report investigated the potential effects of the ethyl acetate fraction of A. spinosus leaves (EAFAS) against a Compound 48/80 (potent secretagogue)-induced systemic anaphylactic shock paradigm in a mouse model. In addition, rat peritoneal mast cells (RPMC) were used in in vitro studies to investigate the effect of EAFAS on Compound 48/80-induced peritoneal mast cell degranulation and histamine release. When administration by the oral route—1 h before Compound 48/80 injection—EAFAS (at dose from 0.001–1 g/kg) completely inhibited the induced anaphylactic shock. EAFAS at concentrations ranging 0.25–1 mg/ml dose-dependently attenuated rates of mast cell degranulation and histamine release from RPMC that were evoked by Compound 48/80. The results of the present investigation indicated that EAFAS stabilizes the mast cell lipid bilayer membrane, thereby preventing the perturbation of membrane and the release of histamine. As a result of these anti-degranulating and anti-histaminic effects, it can be suggested that EAFAS may have a potential use in the prophylaxis and management of anaphylactic reactions.

Acetylsalicylic acid potentiates passive systemic anaphylaxis in mice

Acetylsalicylic acid (ASA) is a nonsteroidal anti-inflammatory drug that can cause mast cell dependent diseases in sensitive individuals. ASA induced asthma is believed to be related to an overproduction of cysteinyl leukotriene C4 (LTC4) secondary to cyclooxygenase inhibition. It remains to be elucidated whether and by which mechanisms ASA may also influence systemic anaphylactic reactions. In order to clarify if ASA modulates passive systemic anaphylaxis (PSA), Balb/c mice were pre-treated with ASA, sensitized with anti-TNP-BSA intravenously followed by intravenous challenge with TNP-BSA. The temperature profile was assessed for 70 min. Levels of mast cell mediators in the sera (histamine, serotonin, LTC4) were determined by ELISA. Additionally murine bone marrow-derived cultured and peritoneal mast cells were incubated in vitro with ASA, loaded with IgE, stimulated with anti-IgE and histamine release was assessed. ASA aggravated the symptoms of PSA; the maximum temperature drop for ASA pre-treated mice was 5.1 ± 0.4 versus 3.7 ± 0.5 in the control (p = 0.004). In line with exacerbated hypothermia, elevated amounts of mast cell mediators were found in mouse sera. LTC4 was enhanced and most interestingly, increases in the preformed mediators histamine and serotonin were likewise detected. Contrary to these findings the histamine release of mast cells incubated with ASA in vitro was reduced. Together, ASA potentiates PSA probably by enhancing the degranulation of mast cells in vivo, thereby increasing the availability of anaphylactic mediators. Since ASA suppresses mast cell activation in vitro, the environment surrounding the mast cells dictate most likely changes in the releasability of these effector cells upon ASA treatment. Our findings emphasize the importance of in vivo models to study anaphylaxis as only in vivo experiments can unravel the complex interplay of different cells and tissue factors.

Anti-allergic activity of German chamomile (Matricaria recutita L.) in mast cell mediated allergy model

Chamomile is most popular used medicinal plant and extensively consumed as a tea or tisanes. Traditionally this plant was used for treatment of many ailments such as allergy disorders and inflammatory mediated diseases. We investigated the effects of anti-allergic activity of Matricaria recutita L. on mast cell mediated allergic models. The protective effect of methanol extract of Matricaria recutita against compound 48/80 induced anaphylaxis and pruritis models for acute phase of hypersensitivity reactions were carried out. The late phase hypersensitivity reactions by compound 48/80 induced mast cell degranulation and histamine release from blood along with serum nitric oxide (NO), rat peritoneal fluid nitric oxide (NO) and bronchoalveolar fluid nitric oxide (NO) levels were measured. The methanol extract of Matricaria recutita L. showed inhibitory effects on anaphylaxis induced by compound 48/80 and significant dose dependent anti-pruritis property was observed by inhibiting the mast cell degranulation. Mast cell membrane stabilization activity was also observed in compound 48/80 induced mast cell activation. Dose dependent reduction in the histamine release, along with decreased release of serum, rat peritoneal and BAL fluid nitric oxide (NO) levels were observed. These results suggest that the methanol extract of Matricaria recutita showed potent anti-allergic activity by inhibition of histamine release from mast cells.

Effect of ryanodine on histamine release from rat peritoneal mast cells induced by anti-IgE.

Ryanodine strongly inhibited histamine release from rat peritoneal mast cells induced by anti-IgE. Ryanodine also inhibited Ca(2+)-mobilization from the intracellular Ca(2+)-store as well as histamine release in mast cells activated by anti-IgE. These results suggest that the effect of ryanodine on histamine release from rat mast cells might be due to the inhibition of Ca2+ release from the intracellular Ca2+ store.

Mast Cell Degranulating Peptide: A Multi-functional Neurotoxin

This review discusses our present knowledge of the structure and activities of the mast cell degranulating peptide (MCDP). This peptide is a basic, 22 amino acid residue component of honey bee venom with striking immunological and pharmacological activities. MCDP is a potent anti-inflammatory agent, but at low concentrations it is a strong mediator of mast cell degranulation and histamine release. MCDP is also an epileptogenic neurotoxin, an avid blocker of the potassium channels and can cause a significant lowering of the blood pressure in rats. Some of the biological activities of MCDP appear to have distinct mechanisms and may represent a good illustration of the structure-function relationship.

Inhibition of anaphylaxis like reaction and mast cell activation by Sitagliptin

Mast cells stimulation activates degranulation process resulting in releasing of mediators, such as histamine. In this study, the effect of aqueous extract of sitagliptin, a selective dipeptidylpeptidase-4 inhibitor, on the mast cell-mediated allergic response was studied with the possible mechanisms of action, focusing on the histamine release and pro-inflammatory cytokine secretion in mast cells. Sitagliptin produced dose dependent inhibition in compound 48/80-induced systemic reactions. In addition, sitagliptin attenuated IgE-mediated skin allergic reaction. Sitagliptin dose-dependently reduced compound 48/80- and IgE-induced histamine release from mast cells. Sitagliptin decreased the secretion of pro-inflammatory cytokines, tumor necrosis factor-α, in mast cells. So, the finding of this study provides evidence that sitagliptin inhibits mast cell derived allergic reactions, and involvement of pro-inflammatory cytokine secretion in such effects.

Inhibitory Effects of Genistein and Water Extracts of Various Herbs on Histamine Release

Water extracts of eighteen herbal materials and genistein were used to investigate their effects on compound 48/80-induced histamine release in rat peritoneal mast cells (RPMCs). The inhibition effects of histamine release by the water extracts of Ulmus pumila Linne (UP), Lonicera japonica Thunberg (LJT), Angelica gigas Nakai (AGN), Cordyceps militaris (CM), Rehmannia glutinosa Liboschitz (RGL), Liriope platyphylla Wang et Tang (LPWT), Zizyphus jujuba var. inermis Rehder (ZJ) were evaluated by a dose-response assay. LPWT, ZJ, and genistein showed dose-dependent decrease in histamine release at the concentrations of 1 to 1,000 mg/mL, and the inhibition percentage reached up to 31.0, 35.9, and 46.2%, respectively. UP, LJT, AGN, CM, and RGL significantly decreased histamine release at 1 to 100 μg/mL. Among the various combinations, mixture of UP and genistein showed an enhanced inhibition on histamine release.

Case Scenario: Self-extraction of Intrathecal Pump Medication with a Concomitant Intrathecal Granulomatous Mass

Case Scenario: Self-extraction of Intrathecal Pump Medication with a Concomitant Intrathecal Granulomatous Mass

Immunomodulatory properties of a lemon-quince preparation (Gencydo®) as an indicator of anti-allergic potency

Gencydo®, a combination of lemon (Citrus limon) juice and aqueous quince (Cydonia oblonga) extract has been used traditionally in anthroposophical medicine for treating patients with allergic rhinitis or asthma. Because there are no reports about the mode of action, we investigated the anti-allergic effects of this preparation in vitro by using cell lines and primary cells in various biological and immunological endpoints. The release of soluble mediators from basophilic cells, mast cells and lung epithelial cells, which are essential for the initiation of early- and late-phase allergic reactions, was analyzed in relation to the synthetic anti-allergic drugs azelastine and dexamethasone. In addition, the impact of Gencydo® on the viability and activation of GM-CSF-activated eosinophil granulocytes was investigated. Gencydo® reduced the degranulation and histamine release of IgE-activated basophilic cells and mast cells and inhibited the IgE- and PMA/A23187-induced increases in IL-8, TNF-α and GM-CSF production in mast cells. The effects were comparable to that of the used concentration of azelastine and dexamethasone. Furthermore, Gencydo® partially blocked eotaxin release from human bronchial epithelial cells, but has no impact on the viability and activation of GM-CSF-activated eosinophil granulocytes. In conclusion, these results give a rational base for the topical use of Gencydo® in treatment of allergic disorders through the down regulation of soluble mediators, which are essential for the initiation and maintenance of allergic reactions.

TRPM8 mediates cold and menthol allergies associated with mast cell activation

Exposure to low temperatures often causes allergic responses or urticaria. Similarly, menthol, a common food additive is also known to cause urticaria, asthma, and rhinitis. However, despite the obvious clinical implications, the molecular mechanisms responsible for inducing allergic responses to low temperatures and menthol have not been determined. Because a non-selective cation channel, transient receptor potential subtype M8 (TRPM8) is activated by cold and menthol, we hypothesized that this channel mediates cold- and menthol-induced histamine release in mast cells. Here, we report that TRPM8 is expressed in the basophilic leukemia mast cell line, RBL-2H3, and that exposure to menthol or low temperatures induced Ca 2+ influx in RBL-2H3 cells, which was reversed by a TRPM8 blocker. Furthermore, menthol, a TRPM8 agonist, induced the dose-dependent release of histamine from RBL-2H3 cells. When TRPM8 transcripts were reduced by siRNA (small interfering RNA), menthol- and cold-induced Ca 2+ influx and histamine release were significantly reduced. In addition, subcutaneous injection of menthol evoked scratching, a typical histamine-induced response which was reversed by a TRPM8 blocker. Thus, our findings indicate that TRPM8 mediates the menthol- and cold-induced allergic responses of mast cells, and suggest that TRPM8 antagonists be viewed as potential treatments for cold- and menthol-induced allergies.

Treatment of mast cells with carbon dioxide suppresses degranulation via a novel mechanism involving repression of increased intracellular calcium levels

Intranasal noninhaled delivery of carbon dioxide (CO₂) is efficacious in the symptomatic treatment of seasonal allergic rhinitis. The goal of this study was to determine whether and how 100% CO₂ inhibits mast cell degranulation, thereby possibly contributing to the reduction of symptoms in seasonal allergic rhinitis. Peritoneal mast cells isolated from rats and labelled with sulforhodamine-B (SFRM-B) were used to determine whether CO₂ treatment could block mast cell degranulation and histamine release in response to 48/80. In addition, the effect of CO₂ on intracellular calcium levels in unstimulated and stimulated mast cells was determined by fluorescent microscopy. Treatment with 48/80 caused >90% of mast cells containing SFRM-B to degranulate, resulting in a marked decrease in the fluorescent intensity within the mast cells, and simultaneously causing a significant increase in histamine release. Significantly, the stimulatory effect of 48/80 on fluorescent intensity and histamine levels was greatly inhibited (>95%) to near control levels by pretreatment with 100% CO₂. Treatment with 48/80 also caused a robust transient increase in intracellular calcium, whereas pretreatment with CO₂ repressed the increase in calcium (>70%) in response to 48/80. Results from this study provide the first evidence of a unique regulatory mechanism by which CO₂ inhibits mast cell degranulation and histamine release by repressing stimulated increases in intracellular calcium. Thus, our data provide a plausible explanation for the reported therapeutic benefit of noninhaled intranasal delivery of 100% CO₂ to treat allergic rhinitis.

Expression and release of IL‐29 by mast cells and modulation of mast cell behavior by IL‐29

The role of interleukin (IL)-29 in innate immunity has been recognized recently, and it is regarded as a potent bioactive molecule. However, little is known about its role in the pathogenesis of allergy. Because mast cells are recognized as primary effector cells of allergy, we investigated the potential relationship between IL-29 and mast cells in this study. To examine the expression of IL-29 in mast cells and the influence of IL-29 on mast cell mediator release and accumulation. Expression of IL-29 in mast cells was determined by double-labeling immunohistochemistry and flow cytometry analysis. Mast cell cell-line was cultured to examine the mediator release, and mouse peritoneal model was employed to observe the mast cell accumulation. Large proportions of mast cells expressing IL-29 were localized in human tissue including the colon, tonsil and lung. Mast cells can release substantial quantity of IL-29 upon challenge with proteolytic allergens. Extrinsic IL-29 provoked IL-4 and IL-13 release from mast cell line P815 cells through PI3K/Akt and (JAK)/STAT3 signaling pathways, but failed to induce mast cell histamine release from human mast cells. Extrinsic IL-29 also induced mast cell infiltration in mouse peritoneum by a CD18- and ICAM1-dependent mechanism. Mast cell-derived IL-29 has the potential to be involved in the pathogenesis of allergic inflammation.

Serum total tryptase levels are increased in patients with active chronic urticaria

We have demonstrated previously mast cell histamine release upon incubation with chronic urticaria (CU) sera, presumably by degranulation. To explore total and mature tryptase in order to assess whether any increase in total tryptase levels is due in part to mast cell degranulation or to mast cell burden. We also wanted to explore differences between the autoimmune groups called idiopathic (serum unable to activate basophils), and to correlate total and mature tryptase levels with different urticaria features. We measured total and mature tryptase serum levels in 81 CU patients, 16 atopic donors and 21 healthy control sera. We assessed autoimmunity by measuring the CD63 expression in normal basophil donors upon incubation with CU sera. We found significantly higher levels of total tryptase in the sera of CU patients (6.6 ±4.1 μg/L) than in sera from healthy non-atopic subjects (4.4 ±2.8 μg/L) and from atopic subjects (4.5 ±1.7 μg/L). Mature tryptase levels were undetectable (<1 ng/mL). Total tryptase levels in the autoimmune urticaria group were significantly higher (9.8 ±5.4 μg/L) than the idiopathic urticaria group (4.4 ±2.2 μg/L). A significant difference in total tryptase was found between symptomatic patients (7.3 ±4.1 μg/L) compared with asymptomatic ones (5.7 ±4.1 μg/L) at the time of venesection. No difference was found in mature tryptase levels either. Total elevated tryptase levels are not accompanied by an elevated mature tryptase levels, as might be expected if the serum levels reflected mast cell degranulation.

Mitochondrial signaling for histamine releases in laser‐irradiated RBL‐2H3 mast cells

The low power laser irradiation (LPLI) can promote the wound healing, but the mechanism is still not fully understood. We have found in our previous work that the LPLI induces mast cells to release the histamine and thus suggested that the increased histamine release is probably one of the causes for promoting the wound healing since mast cells have been found to play positive roles in the process of wound healing. This study aims to explore the mechanism of histamine release in RBL-2H3 mast cells under laser irradiations. The wavelength effect of laser irradiations, the permeability function of mitochondrial membrane, the Bcl-2 effect, the cytosolic alkalinization and the increment of intracellular Ca(2+) ([Ca(2+)](i)), on histamine release in RBL-2H3 cells were studied, respectively, with the corresponding fluorescence probes. The action bands of laser irradiations were consistent with the absorption bands of cytochrome c oxidase, suggesting that cytochrome c oxidase is the photoacceptor. After laser irradiation, (1) the cytochrome c releases from mitochondrial to cytosol reflecting an increased permeability of mitochondrial membrane, (2) the cytosolic alkalinization appears, (3) [Ca(2+)](i) increases, and (4) finally the enhancement of histamine release occurs. When Bcl-2 was used to inhibit the permeability of mitochondrial membrane these cellular signaling from (1) to (4) were all suppressed obviously. As a photoacceptor, cytochrome c oxidase absorbs incident photons and initiates the mitochondrial signaling. When the signals are transferred from the mitochondrial to the cytosol, the cytosolic alkalinization appears leading to the opening of a Ca(2+) channel on the membrane, the transient receptor potential vanilloid (TRPV), and an increment of [Ca(2+)](i). The increased [Ca(2+)](i) consequently mediates an enhanced histamine release. Such a responding chain is a suggested mechanism to understand the histamine release in RBL-2H3 cells under laser irradiations.

Antipruritic activity of extracts of Humulus scandens, the combinations of bioactive flavonoids

The antipruritic effects of the ethanol fractions of Humulus scandens on the 4-AP (4-aminopyridine)-induced and chloroquine-induced scratching in ICR mice were examined. The 40% ethanol fractions of H. scandens suppressed both the 4-AP- and chloroquine-induced scratching behavior, which significantly inhibited degranulation of rat peritoneal mast cell and antigen-stimulated histamine release. Further studies proved that the 40% ethanol fractions of H. scandens decreased the content of IL4 in serum of chloroquine-induced scratching ICR mice. The results suggest that the 40% ethanol fractions of H. scandens has antipruritic effects on both antihistamine-resistant and -sensitive pruritus.

Lipopolysaccharide fromPorphyromonas GingivalisStimulates Rat Mast Cells to Cysteinyl Leukotriene Generation and Upregulates Toll-like Receptor −2 and −4 Expression

Mast cells are found in all tissues of the oral cavity and it is suggested that they take part in the development of oral inflammation. As Porhyromonas gingivalis is widely recognized as a major pathogen in the development and progression of gingivitis and periodontitis, the aim of our study is to determine the effect of P. gingivalis lipopolysaccharide (LPS) on mast cell degranulation, cysteinyl leukotriene (cysLT) generation, and migration, as well as Toll-like receptor (TLR)-2 and -4 expression. Experiments were carried out in vitro on rat peritoneal mast cells. LPS-induced mast cell histamine release was estimated by a spectrofluorometric method and cysLT generation by ELISA test. Mast cell migration in response to this antigen was examined according to Boyden's modified method and TLR expression was determined by flow cytometry. We found that P. gingivalis LPS did not induce mast cell degranulation and histamine release. However, activation of mast cells with this bacterial antigen resulted in generation and release of significant amounts of cysLTs. We also documented that LPS from P. gingivalis did not stimulate mast cell migration, even in the presence of laminin, whereas it strongly upregulated TLR2 and TLR4 expression on mast cells. Observations that P. gingivalis LPS activates mast cells to generate and release proinflammatory mediators such as cysLTs and modulates TLR2 and TLR4 expression indicates that these cells might be involved in the emergency of inflammatory processes evolved in response to P gingivalis infection.

Bepotastine besilate, a highly selective histamine H 1 receptor antagonist, suppresses vascular hyperpermeability and eosinophil recruitment in in vitro and in vivo experimental allergic conjunctivitis models

To elucidate the ocular pharmacological properties of bepotastine besilate, a selective histamine H 1 receptor antagonist, when compared with other histamine H 1 receptor antagonists, using guinea pig allergic conjunctivitis models and in vitro models of eosinophil recruitment and mast cell membrane stabilization. Conjunctival vascular hyperpermeability was studied in guinea pigs passively sensitized with anti-ovalbumin antiserum or following subconjunctival injection of histamine. Modulation of eosinophil recruitment was evaluated for both platelet-activating factor (PAF)-induced eosinophil infiltration in guinea pigs and leukotriene B 4-induced in vitro chemotaxis of guinea pig peritoneal eosinophils. Membrane-stabilizing effects of bepotastine also were studied with rat peritoneal mast cells stimulated with the ionophore A23187. Histamine H 1 receptor antagonists including bepotastine besilate were topically administered before ovalbumin, histamine or PAF challenges for in vivo experiments or were added directly to mast cell and eosinophil medium in vitro. Bepotastine besilate significantly inhibited conjunctival vascular hyperpermeability in a dose-dependent manner with maximal effect for bepotastine besilate 1.5%. In separate in vivo experiments, bepotastine besilate 1.0% was significantly more effective than levocabastine 0.025% in the passive sensitization model or olopatadine 0.1% in the histamine-induced hyperpermeability model. Bepotastine besilate 1.0% further suppressed PAF-induced eosinophil infiltration into conjunctival tissue more effectively than ketotifen 0.05%. Chemotaxis of guinea pig peritoneal eosinophils and histamine release from rat peritoneal mast cells in vitro were also inhibited by addition of bepotastine. Olopatadine had a weak effect as compared to that of bepotastine on eosinophil chemotaxis and no effect on mast cell histamine release in our study conditions. Bepotastine besilate was more potent than olopatadine, ketotifen, or levocabastine in reducing vascular hyperpermeability in various animal models of allergic conjunctivitis. Mast cell function and eosinophil chemotaxis were also inhibited in vitro with bepotastine, suggesting bepotastine acts as an inhibitor of allergic response through multiple mechanisms: histamine H 1 receptor antagonism, mast cell stabilization, and inhibition of eosinophil migration to ocular inflammatory sites.