Macrophage engulfment of mucosal mast cells in rats treated with dexamethasone

Dexamethasone effects in the Strongyloides venezuelensis infection in a murine model

The aim of this study was to investigate the immunomodulatory effects of glucocorticoids on the immune response to Strongyloides venezuelensis in mice. Balb/c mice were infected with S. venezuelensis and treated with Dexamethasone (Dexa) or vehicle. Dexa treatment increased circulating blood neutrophil numbers and inhibited eosinophil and mononuclear cell accumulation in the blood, bronchoalveolar, and peritoneal fluid compared with control animals. Moreover, Dexa decreased tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin-3 (IL-3), IL-4, IL-5, IL-10, and IL-12 production in the lungs and circulating immunoglobulin G1 (IgG1), IgG2a, and IgE antibody levels while increasing the overall parasite burden in the feces and intestine. Dexa treatment enhanced the fertility of female nematodes relative to untreated and infected mice. In summary, the alterations in the immune response induced by Dexa resulted in a blunted, aberrant immune response associated with increased parasite burden. This phenomenon is similar to that observed in S. stercoralis-infected humans who are taking immunosuppressive or antiinflammatory drugs, including corticosteroids.

Differential corticosterone responses to stress in the lung in two strains of Flinders rats

BACKGROUND

Acute stress affects a variety of organs and cellular systems. These include the hypothalamic-pituitary-adrenal (HPA) axis, corticotropin-releasing factor (CRF), mast cells and nerves. Flinders-sensitive (FSL) rat strains have hypercholinergic responses and are more sensitive than Flinders-resistant rats (FRL) to anaphylaxis.

OBJECTIVE

To investigate the effects of acute water avoidance stress (1 h) on FSL and FRL tracheal epithelial tissue.

METHODS

We measured short circuit current (I(sc)) as a measure of tracheal response, and the effect of substance P (SP) on tracheal epithelium in Ussing chambers. Electron microscopy was performed to assess mast cell activation.

RESULTS

Both strains showed increased I(sc) responses to stress, inhibited by prior injection of the CRF receptor 1 and 2 antagonist, alpha-helical CRF-(9-41). No increases in conductance were seen. Stress responses were accompanied by electron microscopic morphologic evidence for mast cell degranulation, which was not completely inhibited by alpha-helical CRF-(9-41) pre-treatment. Stress primed the epithelium for an enhanced response to SP in FSL, but this again was not inhibited by alpha-helical CRF-(9-41). FRL had 2.5 times the corticosterone response of FSL.

CONCLUSION

Acute stress affects the tracheal epithelium, not accompanied by changes in ion permeability, but associated with mast cell degranulation. Because blunted HPA axis responses are associated with vulnerability to inflammation, this may partially explain the findings. These stress effects on the lung have a genetic basis associated with relative corticosterone responses, are complex and only in part mediated by CRF.

Mast cells and nerves tickle in the tummy: implications for inflammatory bowel disease and irritable bowel syndrome

Mast cells are well known as versatile cells capable of releasing and producing a variety of inflammatory mediators upon activation and are often found in close proximity of neurons. In addition, inflammation leads to local activation of neurons resulting in the release neuropeptides, which also play an important immune modulatory role by stimulation of immune cells. In intestinal disorders like inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), the number of mast cells is known to be much higher than in the normal intestine. Moreover, both these disorders are also reported to be associated with alterations in neuropeptide content and in neural innervation. Mutual association between mast cells and enteric nerves has been demonstrated to be increased in pathophysiological conditions and contribute to spreading and amplification of the response in IBD and IBS. In this review the focus lies on studies appointed to the direct interaction between mast cells and nerves in IBD, IBS, and animal models for these disorders so far.

TNF-alpha is crucial for the development of mast cell-dependent colitis in mice

Inflammatory bowel disease (IBD) describes chronic inflammatory conditions of the gastrointestinal tract, and TNF-alpha plays a pivotal role in mediating the response. The proinflammatory cytokine TNF-alpha is rapidly released by mast cells after degranulation. In the present study, we hypothesized TNF-alpha to be an important player in our recently described mast cell-dependent murine model for IBD. The effect of neutralizing anti-TNF-alpha MAb was studied on colonic hypersensitivity in mice induced by a skin application of dinitrofluorobenzene (DNFB) followed by an intrarectal challenge with dinitrobenzene sulfonic acid. Features of the colonic hypersensitivity response included diarrhea, mast cell infiltration and activation, infiltration of inflammatory cells in the colon, colonic patch hypertrophy, and increased mast cell-derived TNF-alpha levels in the colon. Anti-TNF-alpha MAb could effectively abrogate diarrhea in DNFB-sensitized mice 72 h after the challenge. The numbers of colonic patches and total tissue damage scores were reduced by anti-TNF-alpha MAb treatment in DNFB-sensitized mice 72 h after the challenge. Mast cell infiltration and activation remained unaffected by neutralizing anti-TNF-alpha MAb. Treatment with the corticosteroid dexamethasone, a frequently used therapeutic treatment in IBD, resulted in a reduction of diarrhea, cellular infiltration, and total tissue damage scores to the same extent as anti-TNF-alpha MAb. Additionally, dexamethasone treatment could also reduce total TNF-alpha levels in the colon, mast cell numbers, and mast cell activation in both vehicle- and DNFB-sensitized mice 72 h after the challenge. These findings suggest that TNF-alpha can play an instrumental role in causing inflammatory responses in the present murine model for IBD downstream from mast cell activation.

Role of bradykinin in gastric vasodilation caused by hypertonic saline and acid back diffusion

Protective vasodilation in response to tissue injury and acid back diffusion is associated with release of bradykinin in the rat stomach. We hypothesized that bradykinin might be involved in mechanisms behind such vasodilation via influence on mast cells and sensory neurons. Acid back diffusion after mucosal barrier disruption with hypertonic saline evoked degranulation of mast cells in the rat stomach wall. Acid back diffusion was also associated with increased luminal release of histamine and gastric blood flow in normal rats, but not in mast cell-deficient rats. Bradykinin (BK(2)) receptor blockade inhibited degranulation of submucosal mast cells in the stomach and attenuated gastric vasodilation both in response to acid back diffusion and after stimulation of sensory neurons with capsaicin. Gastric vasodilation caused by mucosal injury with hypertonic saline alone was associated with degranulation of mucosal mast cells. These events were unaffected by inhibition of prostaglandin synthesis, whereas bradykinin (BK(2)) receptor blockade was associated with abolished vasodilation and inhibition of mucosal mast cell degranulation. We conclude that bradykinin is involved in gastric vasodilation caused by hypertonic injury alone via influence on mast cells, and by acid back diffusion via influence on both sensory neurons and mast cells.

Histamine is involved in gastric vasodilation during acid back diffusion via activation of sensory neurons

Protective vasodilation during acid back diffusion into the rat gastric mucosa depends on activation of sensory neurons and mast cell degranulation with histamine release. We hypothesized that these two mediator systems interact and that histamine partly exerts its effect via sensory nerves. Gastric blood flow (GBF) and luminal histamine were measured in chambered stomachs, and mast cell numbers were assessed by morphometry. Ablation of sensory neurons and depletion of mast cells were produced by pretreatment with capsaicin or dexamethasone, respectively. Mucosal exposure to 1.5 M NaCl and then to pH 1.0 saline in ablated and control rats caused increased luminal histamine and reduced numbers of mast cells. Enterochromaffin-like cell marker pancreastatin remained unchanged. Only control rats responded with an increase in GBF. Capsaicin stimulation (640 microM) of the undamaged mucosa induced identical increase in GBF and unchanged mast cell mass in normal and dexamethasone-treated rats. Increase in GBF after topical exposure to histamine (30 mM) in rats pretreated with capsaicin or a calcitonin gene-related peptide (CGRP)(1) antagonist human CGRP(8-37) or exposed to the calcium pore blocker ruthenium red was less than one-half of that in control rats. These data suggest that mast cell-derived histamine is involved in gastric vasodilatation during acid back diffusion partly via sensory neurons.

Treatment of mildly to moderately active ulcerative colitis with a tryptase inhibitor (APC 2059): an open-label pilot study

BACKGROUND

Mast cells isolated from the colonic mucosa in active ulcerative colitis appear to be partially degranulated, suggesting the release of tryptase.

AIM

To investigate the safety and activity of APC 2059, a highly specific tryptase inhibitor, in the treatment of ulcerative colitis.

METHODS

This was an open-label, Phase 2, multicentre pilot study in patients with mildly to moderately active ulcerative colitis, with a disease activity index of 6-9 on a 12-point scale. Fifty-six adults received 20 mg APC 2059 subcutaneously twice daily and 53 completed 28 days of treatment. The primary end-point was response, defined as a final disease activity index of < or = 3. Supplementary analyses were also performed.

RESULTS

Sixteen (29%) of 56 patients responded. Five (9%) showed complete remission (disease activity index=0). Twenty-seven (49%) improved, with a final disease activity index of < or = 3 or a four-point reduction. Improvement or normalization in each category of the disease activity index was as follows: stool frequency, 64%; bleeding, 64%; endoscopy, 50%; physicians' rating, 63%. There were no significant relationships between outcome and pharmacokinetics. The most common adverse events were related to the injection site (32.1%).

CONCLUSIONS

In this pilot study, the tryptase inhibitor APC 2059 was safe and there was evidence of activity in the treatment of ulcerative colitis.

Pharmacological modulation of allergic inflammation in the rat airways and association with mast cell heterogeneity

Administration of ovalbumin by aerosol to sensitised rats produced a rapid (15 min) protein exudation in different airway tissues, as determined by Evans blue staining. This was associated with marked mast cell degranulation determined by histological examination, with there being no difference between mucosal and connective tissue mast cells. A 5-day administration regimen with compound 48/80 selectively depleted connective tissue mast cell (positive to berberine staining) without modifying ovalbumin-induced plasma protein extravasation. Treatment of rats with dexamethasone (1 mg/kg, -12 h) or nor-dihydroguaiaretic acid (30 mg/kg i.p., -30 min) significantly reduced ovalbumin-induced protein extravasation and preserved mucosal mast cell morphology. Indomethacin (4 mg/kg i.v., -30 min) exerted no effect on either parameter. In conclusion, we propose the mucosal mast cell as a target cell responsible at least partly for the inhibitory actions of known anti-inflammatory drugs. We suggest an involvement of endogenous leukotriene(s), but not prostanoid(s), in mucosal mast cell activation/degranulation.

Mast cells are involved in the gastric hyperemic response to acid back diffusion via release of histamine

Acid back diffusion into the rat stomach mucosa leads to gastric vasodilation. We hypothesized that histamine, if released from the rat mucosa under such conditions, is mast cell derived and involved in the vasodilator response. Gastric blood flow (GBF) and luminal histamine were measured in an ex vivo chamber. Venous histamine was measured from totally isolated stomachs. Mucosal mast cells (MMC), submucosal connective tissue mast cells (CTMC), and chromogranin A-immunoreactive cells (CgA IR) were assessed morphometrically. After mucosal exposure to 1.5 M NaCl, the mucosa was subjected to saline at pH 5.5 (control) or pH 1.0 (H(+) back diffusion) for 60 min. H(+) back diffusion evoked a marked gastric hyperemia, increase of luminal and venous histamine, and decreased numbers of MMC and CTMC. CgA IR cells were not influenced. Depletion of mast cells with dexamethasone abolished (and stabilization of mast cells with ketotifen attenuated) both hyperemia and histamine release in response to H(+) back diffusion. GBF responses to H(+) back diffusion were attenuated by H(1) and abolished by H(3) but not H(2) receptor blockers. Our data conform to the idea that mast cells are involved in the gastric hyperemic response to acid back diffusion via release of histamine.

Endogenous corticosteroids modulate Clostridium difficile toxin A-induced enteritis in rats

We examined the role of glucocorticoids in acute inflammatory diarrhea mediated by Clostridium difficile toxin A. Toxin A (5 microg) or buffer was injected in rat ileal loops, and intestinal responses were measured after 30 min to 4 h. Ileal toxin A administration increased plasma glucocorticoids after 1 h, at which time the toxin-stimulated secretion was not significant. Administration of the glucocorticoid analog dexamethasone inhibited toxin A-induced intestinal secretion and inflammation and downregulated toxin A-mediated increase of macrophage inflammatory protein-2. Adrenalectomy followed by replacement with glucocorticoids at various doses suggested that intestinal responses to toxin A were related to circulating levels of glucocorticoids. Administration of the glucocorticoid receptor antagonist RU-486 enhanced toxin A-mediated intestinal secretion and inflammation. We conclude that C. difficile toxin A causes increased secretion of endogenous glucocorticoids, which diminish the intestinal secretory and inflammatory effects of toxin A.

Senescent jejunal mast cells and eosinophils in the mouse preferentially translocate to the spleen and draining lymph node, respectively, during the recovery phase of helminth infection

Because mice infected with Trichinella spiralis experience a pronounced, but transient, mastocytosis and eosinophilia in their intestine, this disease model was used to follow the fate of senescent T cell-dependent mast cells (MCs) and eosinophils. Very few MCs or eosinophils undergoing apoptosis were found in the jejunum during the resolution phase of the infection, even though apoptotic MCs were common in the large intestine. Although the mesenteric draining lymph nodes contained large numbers of apoptotic eosinophils, MCs were rarely found at this location. During the recovery phase, large numbers of MCs were present in the spleen, and many of these cells possessed segmented nuclei. These splenic MCs were not proliferating. Although MCs from the jejunum and spleen of noninfected mice failed to express mouse MC protease (mMCP) 9, essentially all of the MCs in the jejunal submucosa and spleen of T. spiralis-infected mice expressed this serine protease during the recovery phase. The MCs in the jejunum expressed mMCP-9 before any mMCP-9-containing cells could be detected in the spleen. The fact that mMCP-9-containing MCs were detected in splenic blood vessels as these cells began to disappear from the jejunum supports the view that many jejunal MCs translocate to the spleen during the recovery phase of the infection. During this translocation process, some senescent jejunal MCs undergo nuclear segmentation. These studies reveal for the first time different exit and disposal pathways for T cell-dependent eosinophils and MCs after their expansion in the jejunum during a helminth infection.

Role of intestinal mast cells in modulating gastrointestinal pathophysiology

OBJECTIVE

This article reviews the current understanding of the pathophysiologic role of intestinal mast cells.

DATA SOURCE

Up to date English language publications on mast cell characteristics, heterogeneity and functions were used. Recent articles were used to develop and extend novel concepts about the role of intestinal mast cells.

STUDY SELECTION

Reference sources were selected because of their pertinence to the pathophysiological effects of mast cells in intestinal hypersensitivity. Recent publications on the following topics were emphasized: mast cell proteases in intestinal anaphylaxis; effects of nitric oxide in gastrointestinal pathophysiology; involvement of cytokines derived from mast cells in tissue damage and repair.

RESULTS

Mast cells are clearly implicated in the pathology of intestinal disease. Growing evidence suggests physiological roles for mast cells in the protection of tissues from inflammatory damage, and in intestinal maturation. Mast cells can release cytokines, such as tumour necrosis factor-alpha and interleukin-10, which were originally thought to contribute to inflammatory damage, but which may also have anti-inflammatory properties. Interestingly, mast cell function can be regulated by nitric oxide, and mast cells themselves are sources of this important mediator. Nitric oxide has protective as well as detrimental effects in the intestine.

CONCLUSIONS

Intestinal mast cells have physiologic regulatory effects in addition to their pathologic effects. However, relatively little is known about the mechanisms of these regulatory effects. Mast cells are likely in an ongoing fluctuating balance between physiological functions and pathological effects in normal individuals. Poorly known factors can create an imbalance and lead to pathologic reactions.

Disruption of intestinal barrier function associated with experimental colitis: possible role of mast cells

The objective was to characterize changes in barrier and transport function in an experimental model of colitis, and to determine whether mast cells contribute to these changes. Colitis was induced in rats with intracolonic 2,4,6-trinitrobenzenesulfonic acid (TNBS, 30 mg) in 50% ethanol. Controls received 0.9% saline or the ethanol vehicle alone. In vivo loop perfusion was used to assess colonic water flux (in microliter.cm-1.h-1) and lumen-to-blood 51Cr-labeled EDTA clearance (% administered dose) after TNBS. Myeloperoxidase (MPO) was used as an index of granulocyte influx. TNBS or its vehicle caused a marked decrease in water absorption and an increase in permeability at 4 h after administration compared with saline. Neither dexamethasone (anti-inflammatory control) nor doxantrazole (mast cell stabilizer) was able to attenuate these early changes likely caused by the vehicle. In contrast, at later times, TNBS (but not its vehicle) also increased 51Cr-EDTA permeability and decreased water absorption; both effects were significantly attenuated by dexamethasone or doxantrazole. These drugs also significantly reduced TNBS-induced MPO accumulation and release of rat mast cell protease II. We conclude that experimental colitis is associated with severe defects in intestinal transport and barrier functions and that mast cells may contribute to the pathogenesis of these changes.

Role of neutrophils and mast cells in acute indomethacin-induced small bowel injury in the rat

The aim of this study was to determine whether the injury to the rat jejunum during the first 4.5 h exposure to indomethacin is due to an influx of neutrophils or degranulation of resident mast cells. Indomethacin and vehicle both caused changes in villous morphology (length, width, etc.) while only indomethacin injured the small bowel, as indicated by increased histological lesion score and 51Cr-ethylene diamine tetraacetate (EDTA) flux across the intestinal epithelium. Immunohistochemical staining showed the same small increase in neutrophil density (predominantly in the submucosa) following exposure to vehicle as following exposure to indomethacin. Chronic oral administration of indomethacin for 48 h did cause increased tissue neutrophil density compared to that in vehicle-fed controls. Mast cell depletion (using dexamethasone) did not alter either the indomethacin-induced increase in 51Cr-EDTA clearance or the increase in neutrophil density caused by the vehicle and by indomethacin. However, the lesion score following exposure to indomethacin was significantly lower in mast-cell-depleted animals than in control animals. We conclude that the acute phase of indomethacin-induced intestinal injury is not associated with neutrophil influx. Increased neutrophils seen after chronic indomethacin may result from injury rather than be causative. Mast cells appear to exacerbate the initial stages of indomethacin-induced intestinal injury.

The effect of dexamethasone on resistance of older lambs to infection with Nematodirus battus

Old lambs (8 months of age) infected with 50,000 L3 of Nematodirus battus had larvae developing normally in their tissues on day 4 post-infection (P.I.), but by day 8 P.I. there were only 4105 +/- 1044 worms left in the alimentary tract. Some of these worms contained crystals in their intestine. Eight-month-old lambs treated with dexamethasone and infected with 50,000 L3 of N. battus contained a mean worm burden of 7878 +/- 1262 on 18 days P.I. Untreated 8-month-old lambs similarly infected were virtually worm free by day 18 P.I. Peripheral eosinophilia became elevated in the untreated lambs over the course of infection and, at post-mortem, the tissue mast cell and eosinophil counts were much higher than in the dexamethasone treated group. Although the phenomenon of age resistance is thought to have a strong immunological component, there may also be other physiological factors, resulting in fewer nematodes and lower fecundity of the worms.

Mast cells in the brain: evidence and functional significance

For the past two decades the brain has been considered to be an immune-privileged site that excludes circulating cells from the parenchyma. New evidence indicates that some hematocytes reside in the brain, while others traffic through it. Mast cells belong to both of these functional types. Moreover, the appearance of mast cells in the CNS can be triggered behaviorally. After a brief period of courtship, for example, there is a marked increase in mast cells in the medial habenula of sexually active doves compared with controls. Exposure to gonadal steroids that occur endogenously or that are administered exogenously increases both the number of mast cells and their state of activation in the brain. These results show that hematopoietic cells can provide targeted delivery of neuromodulators to specific regions of the brain, thereby influencing neural-endocrine interactions.

Role of histamine in a rat model of colitis

We examined the possible involvement of mast cells in a rat model of colitis, by monitoring levels of histamine at various times after inducing inflammation with intrarectal trinitrobenzene sulfonic acid in 50% ethanol. The ability of a histamine H1 antagonist, diphenhydramine, to modify colitis was also assessed. As expected, trinitrobenzene sulfonic acid in 50% ethanol induced a sustained colitis. Myeloperoxidase levels in macroscopically damaged tissue peaked at one week, and declined thereafter. In contrast, tissue histamine levels were normal at one week, then increased in damaged tissue to approximately four times normal levels at four weeks. Indices of inflammation were markedly suppressed at one week by diphenhydramine, while tissue histamine levels were unaffected. Chronic colitis in rats is thus apparently accompanied by a local mast cell hyperplasia or influx. Moreover, antagonism of a major mast cell mediator, histamine, significantly reduces the severity of inflammation in this model.

Neutrophil infiltration does not contribute to the ulcerogenic effects of indomethacin in the rat gastric antrum

We have previously suggested (Trevethick et al., Gut 34, 156-160) that indomethacin-induced ulceration of the rat gastric antrum may be a neutrophil-dependent process. Accordingly, in this study we have used an anti-neutrophil serum (ANS) to investigate the effects of neutrophil depletion on this pathology. In animals pretreated with the ANS to induce a nearly total neutropaenia, indomethacin-induced increases in blood neutrophilia and cell infiltration into the gastric antrum (assessed as LTB4 release ex vivo) were eliminated. In marked contrast, however, ANS pretreatment affected neither the area of mucosa damaged nor the microscopic characteristics or distribution of the lesions. These results suggest that, in contrast to the published reports examining indomethacin-induced ulceration of the gastric fundus, neutrophil infiltration is not involved in the pathogenesis of indomethacin-induced ulceration of the rat gastric antrum.

Fasting or dexamethasone treatment reduce protease content in rat lung mast cells and modulation of histamine synthesis by H3 receptors

The sensitivity of mast cells to H3-receptor modulation was studied in rat lung under various hormonal conditions. The heterogeneity of mast cell sub-populations in rat lung was assessed by the tissue content of rat mast cell protease I (RMCP I) and rat mast cell protease II (RMCP II). After 24 h fasting, concentrations of RMCP I were unchanged whereas the concentration of RMCP II was significantly reduced by 49%. The [3H]histamine (HA) synthesis was concomitantly decreased by 35%. In addition, the modulation of [3H]HA synthesis by the H3 receptor agonist, (R)alpha-methylHA and by the antagonist, thioperamide, observed in control rats, was lost in fasted rats. Single and repeated administrations of dexamethasone did not influence RMCPI concentrations, but decreased the concentrations of RMCP II with a parallel decrease in [3H]HA synthesis. The inhibitory effect of (R)alpha-methylHA on [3H]HA synthesis was also reduced. These results suggest that a subpopulation of RMCP II-containing mast cells, very sensitive to environmental factors, could be the mast cells synthesizing HA in an H3-receptor-dependent manner.

Dose-response studies of depletion and repopulation of rat intestinal mucosal mast cells after irradiation

The effects of radiation on gut mucosal mast cells (MMC) and tissue eosinophils were examined. Groups of rat were given single doses of whole-body irradiation from 0.5 to 5 Gy. Serum rat mast cell protease II (RMCPII) concentration showed a significant dose-dependent fall after 1 Gy on day 3 and 1.5 Gy on day 7. MMC counts and tissue RMCPII values on day 7 decreased significantly by 70% after 1 Gy and were undetectable with larger doses. Rat with normal and expanded MMC populations were irradiated or given anaphylaxis. Serum RMCPII concentrations did not change after irradiation, but there was a 10-fold increase in RMCPII after anaphylaxis. Tissue eosinophils in jejunum were 50% of control at 7 days after 2 Gy, and this effect was progressively more marked with higher doses. Similar effects on MMC and eosinophils were demonstrated in ileum, ascending colon and rectum. After 4.5 Gy, repopulation of the gut with MMC did not occur until week 3-4 postirradiation and MMC counts were still 50% below those of controls at 5 weeks postirradiation. Counts of tissue eosinophils 5 weeks after 4.5 Gy irradiation had returned to control levels in jejunum but were still significantly depleted in colon. These experiments show that the high radiosensitivity of rat intestinal MMC is dose dependent, similar at four different levels in the gastrointestinal tract and does not lead to immediate release of granule protease; repopulation with MMC does not begin until at 3 weeks postirradiation.

Developmental changes in intestinal globule leukocytes of normal rats

The changes in the number, distribution, and ultrastructure of globule leukocytes (GL) during postnatal development were investigated in the intestinal epithelium of non-infected healthy rats. Intestinal GL were abundant in normal newborn rats even in the absence of infection. They subsequently decreased markedly to the adult level by the fourth week. Ultrastructurally, morphological variations suggesting maturation of the cells were observed in the GL during development. These changes could be noted neither in the mucosal mast cells (MMC) nor in the granular intra-epithelial lymphocytes. Morphological differences between GL and other cells were evident in adult animals. Most notably, paracrystalline structures were found exclusively in the granules of the GL. Immunohistochemically, both the GL and MMC were stained with anti-serotonin, but not with anti-IgE. Degranulation of GL in developing rats was caused by repeated intraperitoneal administration of dexamethasone. Neither GL nor MMC were affected by compound 48/80. These results indicate that (1) the GL and MMC are derived from a common ancestral cell toward the end of embryonic development, (2) the immature GL migrate from the lamina propria into the epithelium to differentiate, mature, and proliferate, and (3) the immature GL have specific functions during the neonatal period.

Mucosal damage during intestinal anaphylaxis in the rat. Effect of betamethasone and disodium cromoglycate

In this study, two antiallergic compounds, betamethasone and disodium cromoglycate were tested in an animal model of intestinal anaphylaxis. Rats, immunized with Nippostrongylus brasiliensis, were challenged intravenously with whole worm antigen or saline. Antigen challenge resulted in significant abnormalities: epithelial damage with shorter villi, decreased activity of digestive enzymes, decreased levels of mucosal histamine, a mast cell mediator, and increased blood uptake of [51Cr]EDTA from the lumen. Low-dose betamethasone, 24 and 48 hr before antigen, was not effective in preventing the effects: villus damage and increased [51Cr]EDTA uptake were seen, although mucosal mast cell numbers were significantly reduced by the drug. High-dose betamethasone completely prevented intestinal anaphylaxis: villus height, digestive function, and [51Cr]EDTA recovery in antigen-challenged animals were not significantly different from controls. Mucosal histamine levels and mast cells were significantly reduced in the high dose betamethasone group. Oral disodium cromoglycate did not prevent the abnormalities but provided a slight beneficial effect.

Colonic mucosal mast cell distribution at line of demarcation of active ulcerative colitis

We examined the distribution of colonic mucosal mast cells in 25 patients with active ulcerative colitis, with a clear line of demarcation separating active inflammation from normal mucosa. Biopsies, at least one adjacent to the line of demarcation, one in inflamed mucosa, and one above were obtained during colonoscopy. Eight patients had elevated mast cells throughout the colon, and 12 had increased numbers at the line of demarcation of disease. Mean numbers of mast cells from these patients were 6.3 (+/- 2.1 SD) in active inflammation, 19.5 (+/- 7.1 SD) at the line of demarcation, and 15.8 (+/- 8.4 SD) in normal mucosa. Histologic inflammation decreased as mast cells increased. The accumulation of mast cells at the visible line of demarcation between normal and abnormal mucosa suggests mast cells play a critical role in either accelerating the process of inflammation or in suppressing continued extension of the disease.