Mucosal Mast Cell Activation Research Articles

S1789 Altered Jejunal Tight Junction Signalling Correlates With Mucosal Mast Cell Activation and Symptom Severity in Diarrhea-Prone Irritable Bowel Syndrome Patients

S1789 Altered Jejunal Tight Junction Signalling Correlates With Mucosal Mast Cell Activation and Symptom Severity in Diarrhea-Prone Irritable Bowel Syndrome Patients

A Cyclooxygenase-2 Selective Inhibitor Worsens Respiratory Function and Enhances Mast Cell Activity in Ovalbumin-Sensitized Mice

Background Cyclooxygenase (COX)-2 activity has been said to have a protective effect in asthmatic patients as a result of prostaglandin E 2 production. In order to elucidate the mechanisms involved, we evaluated the impact of selective inhibition of COX-2 with rofecoxib during ovalbumin (OVA) challenge, assessing mast cell activity and airway response in a murine model of asthma. Material and methods Mice were sensitized to OVA (10 μg injected intraperitoneally) and further challenged with 0.5% intranasal OVA. Half the sensitized animals were treated orally with rofecoxib (15 mg/kg/d during the challenge phase). Lung function was measured by whole body plethysmography before and after exposure to OVA. The severity of airway inflammation was evaluated by means of a scoring system. Finally, the serum level of mouse mast cell protease (mMCP)-1 was determined as an indicator of mucosal mast cell activity. Results Sensitized mice treated with rofecoxib exhibited 2.4-fold greater airway hyperresponsiveness than did vehicle-treated mice at a methacholine concentration of 100 mg/mL. A clear trend toward worsening airway inflammation in the presence of rofecoxib was observed, although the difference between rofecoxibtreated and vehicle-treated animals was not significant. These changes were accompanied by a significant increase in mucosal mast cell activity. Conclusions Selective pharmacological inhibition of COX-2 during the challenge phase worsens airway function in the OVA-induced murine model of acute asthma. We suggest that this effect might be at least partially explained by the increase in airway mast cell activity.

Un inhibidor selectivo de la ciclooxigenasa-2 empeora la función respiratoria y fomenta la actividad de los mastocitos en ratones sensibilizados a la ovalbúmina

Background Cyclooxygenase (COX)-2 activity has been said to have a protective effect in asthmatic patients as a result of prostaglandin E 2 production. In order to elucidate the mechanisms involved, we evaluated the impact of selective inhibition of COX-2 with rofecoxib during ovalbumin challenge, assessing mast cell activity and airway response in a murine model of asthma. Material and methods Mice were sensitized to ovalbumin (10 μg injected intraperitoneally) and further challenged with 0.5% intranasal ovalbumin. Half the sensitized animals were treated orally with rofecoxib (15 mg/kg/d during the challenge phase). Lung function was measured by whole body plethysmography before and after exposure to ovalbumin. The severity of airway inflammation was evaluated by means of a scoring system. Finally, the serum level of mouse mast cell protease-1 was determined as an indicator of mucosal mast cell activity. Results Sensitized mice treated with rofecoxib exhibited 2.4-fold greater airway hyperresponsiveness than did vehicle-treated mice at a methacholine concentration of 100 mg/ml. A clear trend toward worsening airway inflammation in the presence of rofecoxib was observed, although the difference between rofecoxib-treated and vehicle-treated animals was not significant. These changes were accompanied by a significant increase in mucosal mast cell activity. Conclusions Selective pharmacological inhibition of COX-2 during the challenge phase worsens airway function in the ovalbumin -induced murine model of acute asthma. We suggest that this effect might be at least partially explained by the increase in airway mast cell activity.

IgE-induced degranulation of mucosal mast cells is negatively regulated via nicotinic acetylcholine receptors

The autonomic nervous system is known to mediate mast cell activation. We investigated expression of nicotinic acetylcholine receptors (nAChRs) in mucosal-type mast cells and their contribution to the regulation of mast cell activation. Expression of mRNA of nAChR α4, α7, and β2 subunits were detected in specially differentiated mucosal-type murine bone marrow-derived mast cells (mBMMCs). Pretreatment with non-specific nAChRs agonists, acetylcholine, nicotine and epibatidine and a specific α7 subunit agonist GTS-21 significantly inhibited antigen-induced degranulation of mBMMCs in a dose-dependent manner and GTS-21-induced inhibition was significantly blocked by α7 subunit antagonist, α-bungarotoxin. Furthermore, confocal microscopy also demonstrated surface binding of α-bungarotoxin on mBMMCs. Our findings indicate that mucosal mast cell activation may be negatively regulated mainly through nAChR α7 subunit, suggesting that nAChRs are involved in neuronal-mucosal mast cell interactions.

MUCOSAL MAST CELL PROTEASES ARE INVOLVED IN COLONIC PERMEABILITY ALTERATIONS AND SUBSEQUENT BACTERIAL TRANSLOCATION IN ENDOTOXEMIC RATS

LPS-induced endotoxemia is associated with gut immune stimulation, mucosal inflammation, colonic paracellular permeability (CPP) alteration, and it promotes bacterial translocation (BT). Gut permeability increase linked to LPS promotes mucosal barrier dysfunction resulting to BT. However, the mechanisms involved in these alterations remain unknown. We aimed to evaluate the role of colonic mucosal mast cells and luminal serine protease activity (PA) in the alterations of CPP and BT induced by LPS. Rats receiving doxantrazole, a mast cell stabilizer, combined or not with LPS from Escherichia coli and CPP as well as BT were evaluated after each treatment. Mucosal mast cell activation was assessed by histological methods and by rat mast cell protease 2 level measurement in colonic content. Colonic luminal PA and mucosal inflammation (myeloperoxidase activity) were biochemically determined. In addition, the ability of luminal contents to act on CPP was evaluated in vitro in Ussing chambers. Peripheral administration of LPS promoted mast cell degranulation and increased CPP, BT, mucosal myeloperoxidase activity as well as rat mast cell protease 2 levels, and PA in colonic content. LPS-induced CPP increase and BT were prevented by doxantrazole. In vitro, exposure of the apical side of colonic tissues with supernatants from colonic contents of LPS-treated rats increased CPP. This effect was blocked by the serine protease inhibitor soybean trypsin inhibitor. Our data bring evidence of a key role of mucosal mast cells in LPS-induced increase of CPP and BT through the release of serine proteases into the colonic lumen.

Activated Mucosal Mast Cells Differentiate Eosinophilic (Allergic) Esophagitis From Gastroesophageal Reflux Disease

To evaluate the utility of activated mucosal mast cells (MC) in the differential diagnosis of eosinophilic esophagitis (EE) and gastroesophageal reflux disease (GERD). Intraepithelial eosinophils and MC were quantified in esophageal biopsies from 25 children with EE, 22 children with GERD and 22 controls. MCs were identified by immunohistochemistry for MC tryptase, whereas MC activation status was evaluated by immunohistochemistry for immunoglobulin E (IgE) and by electron microscopy. Esophageal biopsies from patients with EE showed higher intraepithelial eosinophil counts (55 +/- 27.5 vs 6.9 +/- 9.7, P < 0.0001) and MC counts (26.3 +/- 12.7 vs 7.8 +/- 8.9, P < 0.0001) than those from patients with GERD. Almost all EE biopsies (24 of 25 patients; 96%) contained IgE-bearing cells compared with 9 of 22 (41%) GERD biopsies (P < 0.001). GERD biopsies with intraepithelial eosinophil counts >7/high-power field (suggesting an allergic component) contained IgE-bearing cells in 6 of 7 (86%) cases compared to 3 of 15 (20%) cases with eosinophil counts <7/h.p.f (P < 0.01). No intraepithelial eosinophils, MC or IgE-positive cells were present in controls. Electron microscopy confirmed the presence of intraepithelial MC and changes in cytoplasmic granules indicative of MC and eosinophil activation. Intraepithelial MC counts and IgE-bearing cells may help to differentiate EE and GERD and to define a subset of GERD patients in which an allergic component is present. The findings support a role for a MC-mediated hypersensitivity reaction in the pathogenesis of EE.

Mast Cell Stabilizer Ketotifen [4-(1-Methyl-4-piperidylidene)-4H-benzo[4,5]cyclohepta[1,2-b]thiophen-10(9H)-one Fumarate] Prevents Mucosal Mast Cell Hyperplasia and Intestinal Dysmotility in Experimental Trichinella spiralis Inflammation in the Rat

Trichinella spiralis infection in rats induces hypermotility and an abnormal response to cholecystokinin (CCK) similar to motor disturbances observed in irritable bowel syndrome. Mast cell hyperplasia is also characteristic of this experimental model. The aim of our study was to correlate mast cell activity with the development of dysmotility and to demonstrate whether the mast cell stabilizer ketotifen [4-(1-methyl-4-piperidylidene)-4H-benzo[4,5]cyclohepta[1,2-b]thiophen-10(9H)-one fumarate] could prevent the development of intestine hypermotility. Sprague-Dawley rats were infected with T. spiralis and, 5 days after infection, treated with the mast-cell stabilizer ketotifen (10 mg/kg/day). Twelve days after infection, intestinal spontaneous motor activity and response to CCK were evaluated by means of strain-gauge transducers. Immunohistochemistry for rat mast cell protease II (RMCPII), cyclooxygenase (COX)-2, and inducible nitric-oxide synthase (iNOS) was performed in intestinal specimens. In addition, RMCPII and myeloperoxidase were determined in serum. Infected control rats showed hypermotility, mast cell hyperplasia, increased RMCPII levels, increased myeloperoxidase, and overexpression of COX-2 and iNOS. In contrast, ketotifen-treated rats showed spontaneous intestinal motility and CCK response similar to the noninfected control rats. Mast cell hyperplasia and RMCPII were reduced in ketotifen-treated rats. Inflammatory parameters were less modified by ketotifen, but those animals that received the longest ketotifen treatment showed a slight amelioration in these parameters. These results indicate that mast cells are implicated in the development of hypermotility. The treatment with ketotifen prevented hypermotility and mast cell hyperplasia and diminished mucosal mast cell activity.

Effects of Transforming Growth Factor-Beta and Formula Feeding on Systemic Immune Responses to Dietary β-Lactoglobulin in Allergy-Prone Rats

Early nutritional events have the potential to affect health outcomes in later life including the development of allergy. Food allergy is usually the first manifestation of allergy. Breast-feeding has been associated with a protective effect against the development of allergy, but the evidence is contradictory and the mechanisms involved are not clear. We hypothesize that milk cytokines, such as transforming growth factor beta (TGF-beta), play a role in regulating immune responses to dietary antigens. Using a rat pup model of gastrostomy feeding, the immune response profile, at weaning and post-weaning, of allergy-prone Brown Norway rats fed formula supplementation with TGF-beta was assessed. We show that feeding formula to allergy-prone rat pups results in increased total IgE immunoglobulin, beta-lactoglobulin (BLG) IgG1 antibody, and mucosal mast cell activation, as measured by serum rat mast cell protease II (RMCPII) levels in the gut. Supplementation of formula with physiological levels of TGF-beta down-regulated the BLG IgG1 response as well as total IgE and mucosal mast cell activation. Supplementation of formula also resulted in an increase in Th1 cytokines, interleukin (IL)-18, IL-12p40, IL-12p35, and interferon gamma (IFN-gamma) and an increase in IL-10. In conclusion, TGF-beta supplementation of formula moved the immune response profile of allergy prone (Th2 type) rat pups toward a Th1 profile in the suckling period. Importantly, this immune profile persisted after weaning when TGF-beta was no longer present in the diet.

IL-18 with IL-2 protects against Strongyloides venezuelensis infection by activating mucosal mast cell–dependent type 2 innate immunity

C57BL/6 (B6) and B6 background STAT6−/− mice pretreated with IL-18 plus IL-2 showed prominent intestinal mastocytosis and rapidly expelled implanted adult worms of the gastrointestinal nematode Strongyloides venezuelensis. In contrast, identically pretreated mast cell–deficient W/Wv mice failed to do so. Thus, activated mucosal mast cells (MMC) are crucial for parasite expulsion. B6 mice infected with S. venezuelensis third-stage larvae (L3) completed parasite expulsion by day 12 after infection, whereas IL-18−/− or IL-18Rα −/− B6 mice exhibited marked impairment in parasite expulsion, suggesting a substantial contribution of IL-18–dependent MMC activation to parasite expulsion. Compared with IL-18−/− or IL-18Rα −/− mice, S. venezuelensis L3–infected STAT6−/− mice have poorly activated MMC and sustained infection; although their IL-18 production is normal. Neutralization of IL-18 and IL-2 further reduces expulsion in infected STAT6−/− mice. These results suggest that collaboration between IL-18–dependent and Th2 cell–dependent mastocytosis is important for prompt parasite expulsion.

Heightened Responses to Stressors in Patients with Inflammatory Bowel Disease

Several studies suggest that stressful situations (stressors) worsen the course of inflammatory bowel disease (IBD), but the mechanism is not known. Based on several lines of evidence, we hypothesized that psychosocial stress activates the brain-gut axis (BGA) and mucosal mast cells (MC), and activated MC produce proinflammatory cytokines. To test this hypothesis, we determined whether stressor-induced activation of BGA is exaggerated in IBD patients. Stress was induced in 15 IBD patients who were in remission (inactive IBD) and in seven controls by a widely used stressor, the cold pressor test (CPT), daily for five consecutive days. Induction of stress was confirmed objectively by measurement of stress hormones (serum cortisol and ACTH), and hemodynamic parameters and subjectively by questionnaire. Activation of the BGA by this stressor was assessed by evaluating colonic mucosal MC histology and degranulation, using electron microscopy (EM). The effects of the stressor on the intestinal mucosa were assessed by changes in inflammatory cell histology, epithelial mitochondria (EM), and oxidative tissue injury (assays for protein oxidation). In both study groups, the stressor resulted in (1) increased levels of stress hormones, (2) the expected changes in hemodynamic parameters, (3) activation and degranulation of MC, (4) mitochondrial damage to epithelial cells, and (5) mucosal protein oxidation. These changes were more marked in IBD patients. The heightened response to the stressors and the greater epithelial damage in IBD patients suggests that stress-induced activation of the BGA and of mucosal MC is important in the initiation and/or flare up of IBD.

New targets for allergic rhinitis--a disease of civilization.

Allergic rhinitis is an inflammatory disorder of the nasal mucosa, mediated by TH2 lymphocytes, which is linked to atopy and whose prevalence is increasing in association with a Western lifestyle. The production of allergen-specific IgE, activation of mucosal mast cells and the recruitment and activation of effector leukocytes provides potential therapeutic targets, including selective inhibition of cytokines, adhesion molecules and signalling pathways. Blockade of IgE, using monoclonal antibodies and vaccine strategies, is a new approach for interrupting the allergic cascade, whereas the use of recombinant mutated allergens, peptides and DNA oligonucleotides will lead to improved efficacy and reduced side effects of immunotherapy to induce tolerance.

Neuroendocrine control of intestinal mucosal mast cells under physiological conditions.

Mast cells are involved in the pathogenesis of both allergies to food and inflammatory bowel disorders. In addition, there are several lines of evidence suggesting that mucosal mast cells also respond to intraluminal stimuli. Our aim was to identify neuroendocrine stimuli that could modify mucosal mast cell activity in the rat. Anaesthetized rats were prepared for duodenal perfusion and mast cell activation was measured by analysis of RMCP II concentration in the duodenal perfusate. Either buffered saline solution or a 5% ovalbumin hydrolysate (OVH) solution was infused into the duodenum. Subdiaphragmatic vagotomy or afferent ablation by intraluminal treatment with capsaicin diminished RMCP II concentration in basal conditions and significantly reduced the response to OVH, which in control animals induced a three-fold increase of the protease. The noradrenergic blockers phentholamine and propranolol significantly diminished RMCP II concentration in basal conditions and completely blocked the response to OVH. Intravenous infusion of cholecystokinin-related peptides also induced a response of mast cells. However, the response was different depending on the peptide. CCK-8 induced a slight increase of RMCP II, whereas both CCK-33 and gastrin induced a significant decrease in mast cell activity. These results show that intraluminal content modulates mucosal mast cell activity by complex mechanisms involving both nervous and endocrine pathway.

A blockade of complement activation prevents rapid intestinal ischaemia-reperfusion injury by modulating mucosal mast cell degranulation in rats.

We attempted to define the putative role of complement activation in association with mucosal mast cell (MMC) degranulation in the pathogenesis of rapid intestinal ischaemia-reperfusion (I/R) injury. We prepared complement activity-depleted rats by the administration of the anti-complement agent K-76COOH and the serine-protease inhibitor FUT-175. Autoperfused segments of the jejunum were exposed to 60 min of ischaemia, followed by reperfusion for various time periods, and the epithelial permeability was assessed by the 51Cr-EDTA clearance rate. The number of MMC was immunohistochemically assessed. In control rats, the maximal increase in mucosal permeability was achieved by 30-45 min of reperfusion. This increase was significantly attenuated by the administration of either K-76COONa alone or in combination with FUT-175. In contrast, the administration of carboxypeptidase inhibitor (CPI), which prevents the inactivation of complement-derived anaphylatoxins such as C5a, significantly enhanced the increase in I/R-induced mucosal permeability. These findings were confirmed morphologically by light microscopy and scanning electron microscopy. In addition, the I/R-induced mucosal injury was accompanied by a marked decrease in the number of MMC, and administration of K-76COOH significantly inhibited this change. These results indicate that complement activation and the generation of complement-derived anaphylatoxins are key events in I/R-induced mucosal injury. It is likely that intestinal I/R-induced mucosal injury may be partially mediated by MMC activation associated with the complement activation.

Role of mast cells in chronic stress induced colonic epithelial barrier dysfunction in the rat

BACKGROUND AND AIMSStress may be an important factor in exacerbating inflammatory bowel disease but the underlying mechanism is unclear. Defective epithelial barrier function may allow uptake of luminal antigens that...

Role of Complement Activation and Mast Cell Degranulation in the Pathogenesis of Rapid Intestinal Ischemia/Reperfusion Injury in Rats

The aim of this study is to define the putative role of complement activation and mucosal mast cell (MMC) degranulation in the pathogenesis of rapid ischemia-reperfusion (I/R) injury. We prepared complement activity-depleted rats by the administration of the anti-complementary agent K-76COONa. To assess the role of MMC degranulation, we used the MMC stabilizer MAR-99 and genetically mast cell-deficient Ws/Ws rats. Autoperfused segments of the jejunum were exposed to 60 min of ischemia, followed by 60 min reperfusion. The epithelial permeability was assessed by ⁵¹Cr-EDTA clearance rate, and the number of MMC was immunohistochemically assessed. I/R treatment induced a marked increase in mucosal permeability and MMC degranulation. The treatment with K-76COONa and MAR-99 significantly attenuated these changes. Furthermore, in Ws/Ws rats the increase in mucosal permeability and MMC degranulation was significantly attenuated. These findings indicate the role of complement activation and MMC activation in the pathogenesis of rapid intestinal I/R injury. A regulation of the complement activation and MMC degranulation may be one of the clinical strategies for prevention of I/R-induced mucosal injury.

Delayed expulsion of the nematode Trichinella spiralis in mice lacking the mucosal mast cell-specific granule chymase, mouse mast cell protease-1.

Expulsion of gastrointestinal nematodes is associated with pronounced mucosal mast cell (MMC) hyperplasia, differentiation, and activation, accompanied by the systemic release of MMC granule chymases (chymotrypsin-like serine proteases). The beta-chymase mouse mast cell protease-1 (mMCP-1) is expressed predominantly by intraepithelial MMCs, and levels in the bloodstream and intestinal lumen are maximal at the time of worm expulsion in parasitized mice. To address the in vivo functions of MMC-specific beta-chymases, we have generated transgenic mice that lack the mMCP-1 gene. They were backcrossed onto a congenic BALB/c background to investigate the response to nematode infection. The deletion of the mMCP-1 gene is associated with significantly delayed expulsion of Trichinella spiralis and increased deposition of muscle larvae in BALB/c mice despite the presence of normal and sometimes increased numbers of MMCs. Neither worm fecundity nor worm burdens were altered in Nippostrongylus-infected mMCP-1(-/)- BALB/c mice. These data demonstrate, for the first time, that the ablation of an MMC-derived effector molecule compromises the expulsion process.

Suppressed T helper 2 immunity and prolonged survival of a nematode parasite in protein-malnourished mice.

Protein malnutrition may increase susceptibility to gastrointestinal parasitic infections, possibly as a result of impaired intestinal and/or systemic T helper 2 (Th2) effector responses induced by down-regulation of Th2 cytokines and/or up-regulation of Th1 cytokines. To test this hypothesis, female BALB/c mice (n = 18/diet) were fed a control (24%), marginal (7%), or deficient (3%) protein diet and given a challenge infection with Heligmosomoides polygyrus. The 3% mice had higher worm burdens at 1, 2, and 4 weeks postchallenge infection (pci), lower increases in serum IgE, reduced intestinal eosinophilia, and depressed mucosal mast cell proliferation and activation at 1-2 weeks pci. To determine whether these suppressed effector responses resulted from altered spleen and mesenteric lymph node (MLN) cytokine production, cells were restimulated in vitro with parasite antigen and cytokine concentrations were measured. Deficient MLN cells secreted significantly less IL-4 and more IFN-gamma at 1-2 weeks pci than did control MLN cells. Deficient spleen cells also secreted more IFN-gamma at 2 weeks pci compared with control spleen cells. From reverse transcription-PCR analyses, the 3% mice also had lower IL-4 mRNA level in spleen and MLN at 1-2 weeks pci. Our study supports the hypothesis that protein malnutrition increases the survival of a nematode parasite by decreasing gut-associated IL-4 (Th2) and increasing IFN-gamma (Th1) within 2 weeks pci, leading to reduced intestinal and systemic Th2 effector responses.

Chronic stress impairs rat growth and jejunal epithelial barrier function: role of mast cells.

We examined the impact of chronic stress on rat growth rate and intestinal epithelial physiology and the role of mast cells in these responses. Mast cell-deficient (Ws/Ws) rats and +/+ littermate controls were submitted to water avoidance stress or sham stress, 1 h/day, for 5 days. Seven hours after the last sham or stress session, jejunal segments were mounted in Ussing chambers, in which secretion and permeability were measured. Body weight (as a growth index) and food intake were determined daily. Stress increased baseline jejunal epithelial ion secretion (indicated by short-circuit current), ionic permeability (conductance), and macromolecular permeability (horseradish peroxidase flux) in +/+ rats, but not in Ws/Ws rats, compared with nonstressed controls. Stress induced weight loss and reduced food intake similarly in the groups. In +/+ rats, these parameters remained altered 24-72 h after the cessation of stress. Modulation of stress-induced mucosal mast cell activation may help in the management of certain intestinal conditions involving epithelial pathophysiology.

Vagus-mediated activation of mucosal mast cells in the stomach: Effect of ketotifen on gastric mucosal lesion formation and acid secretion induced by a high dose of intracisternal TRH analogue

TRH analogue, RX 77368, injected intracisternally (i.c.) at high dose (3 μg/rat) produces gastric mucosal lesion formation through vagal-dependent pathway. The gastric mucosal hyperemia induced by i.c. RX 77368 was shown to be mediated by muscarinic vagal efferent fibres and mast cells. Furthermore, electrical vagal stimulation was observed to induce gastric mucosal mast cell degranulation. The aim of the study was to assess the influence of ketotifen, a mast cell stabilizer, on RX 77368-induced gastric lesion formation and gastric acid secretion. RX 77368 (3 μg, i.c.) or vehicle (10 μL, i.c.) was delivered 240 min prior to the sacrifice of the animals. Ketotifen or vehicle (0.9% NaCl, 0.5 mL) was injected intraperitoneally (i.p.) at a dose of 10 mg.kg –1 30 min before RX 77368 injection. The extent of mucosal damage was planimetrically measured by a video image analyzer (ASK Ltd., Budapest) device. In the gastric acid secretion studies, the rats were pretreated with ketotifen (10 mg.kg –1, i.p.) or vehicle (0.9% NaCl, 0.5 mL, i.p.), 30 min later pylorus-ligation was performed and RX 77368 (3 μg, i.c.) or vehicle (0.9% NaCl, 10 μL, i.c.) was injected. The rats were killed 240 min after i.c. injection, and the gastric acid secretion was measured through the titration of gastric contents with 0.1 N NaOH to pH 7.0. RX 77368 (3 μg, i.c.) resulted in a gastric mucosal lesion formation involving 8.2% of the corpus mucosa ( n = 7). Ketotifen elicited an 85% inhibition on the development of mucosal lesions ( n = 7, P < 0.001) whereas ketotifen alone had no effect on the lesion formation in the mucosa ( n = 7). The RX 77368 induced increase of gastric acid secretion was not influenced by ketotifen pretreatment in 4-h pylorus-ligated animals. Central vagal activation induced mucosal lesion formation is mediated by the activation of mucosal mast cells in the stomach. Mast cell inhibition by ketotifen does not influence gastric acid secretion induced by i.c. TRH analogue in 4-h pylorus-ligated rats.

Role of mucosal mast cells in early vascular permeability changes of intestinal DTH reaction in the rat.

Previously, it was shown that depletion and stabilization of the mucosal mast cell around the time of challenge were very effective in reducing delayed-type hypersensitivity (DTH) reactions in the small intestine of the rat. The role of mucosal mast cells in the early component of intestinal DTH reaction was further investigated in this study. In vivo small intestinal vascular leakage and serum levels of rat mast cell protease II (RMCP II) were determined within 1 h after intragastric challenge of rats that had been sensitized with dinitrobenzene 5 days before. A separate group of rats was used to study vasopermeability in isolated vascularly perfused small intestine after in vitro challenge. To investigate the effects of mast cell stabilization on the early events of the DTH reaction, doxantrazole was used. The influence of sensory nerves was studied by means of neonatal capsaicin-induced depletion of sensory neuropetides. Within 1 h after challenge, a significant increase in vascular permeability was found in vivo as well as in vitro. This was associated with a DTH-specific increase in RMCP II in the serum, indicating mucosal mast cell activation. In addition, doxantrazole treatment and caspaicin pretreatment resulted in a significant inhibition of the DTH-induced vascular leakage and an increase in serum RMCP II. These findings are consistent with an important role for mucosal mast cells in early vascular leakage changes of intestinal DTH reactions. In addition, sensory nervous control of mucosal mast cell activation early after challenge is demonstrated.