Intestinal Mucosal Mast Cells Research Articles

Nutritional Support for Adaptation to Radiation-Induced Suppression of Mucosal Immunity in the Intestine of the Rat

Appropriate enteral nutrition provided immediately after injury or trauma to the gastrointestinal tract may limit or reverse damage to the mucosal barrier. In this regard, diets containing amino acids, such as arginine and glutamine, or fish oil have been identified as beneficial. This report assesses the role of amino acids as "essential nutrients" in the repair of intestinal mucosa damaged by gamma radiation. Rats were used experimentally to test the hypothesis that the recovery of the immune responses in the intestinal mucosa, which are suppressed by radiation, can be improved by feeding an elemental amino acid diet, referred to hereafter as the diet, immediately after irradiation. The objective was to assess the impact of the diet on the expression of type I hypersensitivity or anaphylaxis in the jejunal mucosa. The local expression of this immunological response, which involves several radiosensitive cell types, was studied in rats immunized by oral infection with the nematode parasite, Trichinella spiralis. Rats that recover from infection become immunized and their small intestine undergoes anaphylaxis when subsequently challenged with parasite-derived antigen. This hypersensitivity response is expressed, in part, as Cl- secretion and can be observed in vitro or in vivo. When challenge is provided by a secondary inoculum of infective T. spiralis larvae, Cl- secretion is accompanied by fluid secretion and by the rapid expulsion of the parasite from the intestine. Immunized rats maintained on a stock diet and exposed to 7 Gy of total-abdominal irradiation from a cobalt-60 gamma-ray source failed to express antigen-induced Cl- secretion fully for up to 14 days postirradiation, and rejection of the parasite was suppressed for at least 30 days postirradiation. The suppression of immune responsiveness is associated with the disappearance of intestinal mucosal mast cells, which normally trigger the anaphylactic response. When rats are maintained on the diet after irradiation, the capacity to reject the parasite remains suppressed. However, the ability to express anaphylaxis-mediated Cl- secretion returns by 3 days postirradiation. The quick, diet-supported recovery of antigen-induced Cl- secretion occurs despite the continued absence of mast cells. Although the recovery of anaphylaxis-mediated responses suppressed by irradiation is only partial, our experimental results underscore the potential for enhancing the recovery process through nutritional support.

Release of the mucosal mast cell granule chymase, rat mast cell protease-II, during anaphylaxis is associated with the rapid development of paracellular permeability to macromolecules in rat jejunum.

The soluble granule chymase, rat mast cell protease-II (RMCP-II), is abundantly expressed in intestinal mucosal mast cells (MMC) but its function is not known. One hypothesis is that RMCP-II degrades the epithelial basement membrane and promotes the loss of enterocytes typically associated with type I hypersensitivity reactions in the rat. To test this hypothesis more directly, ex vivo perfusion of the cranial mesenteric artery and jejunal lumen was used to monitor the anaphylactic release of RMCP-II and its effects on mucosal permeability and epithelial integrity. Within 2 min of intravascular challenge with soluble adult Nippostrongylus brasiliensis worm antigen there was a 1,000-fold (P < 0.02) increase in the concentration of RMCP-II in the vascular perfusate from the jejunum of Nippostrongylus-sensitized rats but not the controls. Similarly, translocation of RMCP-II into the gut lumen increased 10-fold (P < 0.02) after 2 min only in worm antigen-challenged immune rats. Using an identical protocol, but incorporating Evans blue-labeled human serum albumin (EB-HSA) in the vascular perfusate, the timing of the release of RMCP-II into the two compartments was very similar to the first experiment and furthermore the translocation of EB-HSA increased 18-fold (P < 0.05) after 4 min in sensitized rats challenged with worm antigen. To examine the effects of RMCP-II more directly 1 mg of the highly purified chymase was introduced into the cranial mesenteric artery in ex vivo perfused normal rats. A significant (P < 0.05) 70-fold increase in concentration of RMCP-II in jejunal perfusate occurred after 6 min. In a repeat dose-response experiment, infusion of 0.375, 0.75, or 1.5 mg of RMCP-II, together with EB-HSA, established that the cumulative amounts of RMCP-II and EB-HSA translocated from the vasculature to the gut lumen in each perfusion (during the 10-min period of RMCP-II infusion) were significantly correlated. Analysis of intestinal perfusates by SDS-PAGE and by Western blotting using monoclonal anti-RMCP-II antibody confirmed that there was a concomitant translocation of both the protease and EB-HSA into the gut lumen. Histological evaluation of the mucosa failed to reveal any significant morphological change in any of the experiments. The rapid development of macromolecular leak, its association with the translocation of RMCP-II, and the absence of gross epithelial lesions, suggest for the first time that a mast cell granule chymase increases epithelial permeability via a paracellular route and implies that the substrate may be a protein, or proteins, in the epithelial junctional complex.

Electrical stimulation of the vagus nerve modulates the histamine content of mast cells in the rat jejunal mucosa

Mast cells are best known for their participation in allergic reactions. However, a number of recent studies suggest that mast cells are subject to nervous control. In the gut mucosa, mast cells are intimately associated with nerves, and the psychologically conditioned release of RMCP II (a mucosal mast cell-derived mediator) has been reported. These data suggest the potential for CNS regulation of intestinal mucosal mast cells. In this study, we stimulated the cervical vagi and found an increased histamine content in mucosal mast cells, without apparent degranulation. Furthermore, these changes could be prevented by subdiaphragmatic vagotomy. These data support the potential for intestinal mucosal mast cell regulation by the central nervous system and suggest modulation of mast cells without degranulation.

Proteinases of rat mast cells. Peritoneal but not intestinal mucosal mast cells express mast cell proteinase 5 and carboxypeptidase A.

Six basic proteins of 26 to 38 kDa with isoelectric points (pI) > or = 8.5 were abundant in proteins separated by two-dimensional SDS-PAGE from adult rat peritoneal mast cells (MC). One was identified previously as rat mast cell proteinase (RMCP) 1, a chymase of 26 to 28 kDa, pI > 9.0. Microsequence analyses showed that two polypeptides of about 29 and 30 kDa had NH2 terminal amino acid sequences homologous to mouse MC proteinase 5 (MCP-5), whereas the amino terminals of the 33, 35, and 36 kDa proteins were homologous to MC carboxypeptidase A (MC-CPA). Rabbit Abs produced against synthetic peptides of the identified NH2 terminal sequences were used in immunoblot studies. At least three proteins reacted with Abs to MC-CPA, whereas Abs to MCP-5 detected three adjacent polypeptides, rather than just the two identified by using microsequence analysis. Removal of oligosaccharide side chains using peptide:N-glycosidase F reduced the heterogeneity of each set of three polypeptides (MCP-5 and MC-CPA) to a band of each protein of a lower M(r). The serine proteinase inhibitor [3H]diisopropylfluorophosphate ([3H]DFP) bound to a proteinase of 30 to 35 kDa, which is probably MC tryptase (pI < or = 6.0). Immunoblot analysis of proteins from intestinal mucosal mast cells showed RMCP-2, but not RMCP-1, MCP-5, or MC-CPA. This is the first report of MCP-5 in the rat and of clearly distinguishable glycosylated forms of MC CPA. These proteinases appear to be restricted in their distribution to selected MC populations, but little is known about their functions.

Stem Cell Factor Contributes to Intestinal Mucosal Mast Cell Hyperplasia in Rats Infected With Nippostrongylus brasiliensis or Trichinella spiralis, but Anti-Stem Cell Factor Treatment Decreases Parasite Egg Production During N brasiliensis Infection

We assessed the effects of the c-kit ligand, stem cell factor (SCF), in the jejunal mucosal mast cell hyperplasia that occurs during infection with the intestinal nematodes, Nippostrongylus brasiliensis or Trichinella spiralis in rats. Compared with vehicle-treated rats, rats treated with SCF (25 micrograms/kg/d, intravenous [i.v.] for 14 days) during N brasiliensis infection exhibited significantly higher levels of the rat mucosal mast cell (MMC)-associated protease, rat mast cell protease II (RMCP II) in the jejunum and serum on day 8 of infection, but not on days 10 or 15 of infection. By contrast, in comparison to rats treated with normal sheep IgG, rats treated with a polyclonal sheep antirat SCF antibody exhibited markedly decreased numbers of jejunal MMCs, levels of jejunal RMCP II, and serum concentrations of RMCP II during infection with either nematode, particularly at the earlier intervals of infection (< or = day 10). Taken together, these findings indicate that SCF importantly contributes to MMC hyperplasia and/or survival during N brasiliensis or T spiralis infection in rats, but that levels of endogenous SCF are adequate to sustain near maximal MMC hyperplasia during infection with these nematodes. Notably, treatment of rats with SCF somewhat increased, and treatment with anti-SCF significantly decreased, parasite egg production during N brasiliensis infection. This finding raises the interesting possibility that certain activities of intestinal MMCs may contribute to parasite fecundity during infection with this nematode.

Effects of subdiaphragmatic vagotomy on mucosal mast cell densities in stomach and jejunum of rats.

There is increasing evidence for the innervation of intestinal mucosal mast cells (IMMC), including both microanatomical and functional data.1 Some of this work suggests peptidergic or cholinergic nerve-induced activation of mast cells. For example, Bani-Sacchi et al., reported a decrease in the stainability of IMMC in the ileum after field stimulation of isolated intestines.2 This was accompanied by an increased release of acetylcholine and histamine, and was depressed by atropine and tetrodotoxin.

Strongyloides venezuelensis infection in Syrian golden hamster, Mesocricetus auratus, with reference to the phenotype of intestinal mucosal mast cells

Syrian golden hamster, Mesocricetus auratus, was found to be a moderately susceptible host for the intestinal helminth, Strongyloides venezuelensis. After infection by subcutaneous inoculation with 3000 infective larvae (L3), about 20% of them became adult worms in the small intestine, and, after a stable infection up to day 20, adult worms were slowly and gradually expelled towards day 45. Before infection, mast cells in the jejunum were about 30/10 villus crypt units and over 80% of them were formalin-resistant and berberine sulphate-fluorescence positive. After infection with S. venezuelensis, the number of intestinal mast cells gradually increased with time and about a half of them were formalin-sensitive and berberine sulphate fluorescence-negative. Intraepithelial migration of mast cells was never seen before and after infection. Heterogeneity of mucosal mast cells in terms of granular proteoglycans was further confirmed by the determination of critical electrolyte concentration. In spite of the heterogeneity of proteoglycans, enzyme-histochemical study revealed that practically all mucosal mast cells of Syrian golden hamsters were positive for chymase but negative for tryptase. Mast cells in the skin and tongue were also positive for chymase but negative for tryptase. Together with our previous study on mucosal mast cells of other rodents, phenotypic variances of mucosal mast cells seem to be closely related to the protective capacity against the genus Strongyloides.

Mucosal mast cell proliferation following normal and heterotopic infections of the nematode Nippostrongylus brasiliensis in rats

Infections of intestinal nematodes induce the T cell-dependent proliferation of intestinal mucosal mast cells (MMC). To examine whether nematode-induced MMC proliferation is affected by the site of infestation, adult-stage nematode Nippostrongylus brasiliensis (NB) was transplanted into the normal infection site, the duodenum, or into heterotopic sites, the peritoneal cavity (i.p.) or subcutaneous tissue (s.c.), of rats. Two weeks after duodenal inoculation, MMC numbers in the small intestine had increased 6.5-fold. In contrast, i.p. and s.c. inoculation induced only slight increases of intestinal MMC. After i.p. inoculation, worm granulomas developed in the connective tissues adhering to stomach and duodenum, and large numbers of mast cells appeared around the granulomas. The majority of the latter mast cells showed histochemical features similar to MMC: they were formalin sensitive, berberine sulfate-, alcian blue+/safranine-, and rat mast cell protease (RMCP) II+. After s.c. inoculation, worm granulomas developed at the inoculation site, but the number of mast cells around the granulomas was not significantly increased. These results suggest that intense proliferation of MMC or MMC-like cells is induced only by the infections on mucosa or in mucosa-associated tissues.

Morphological and functional characteristics of peritoneal mast cells from young rats.

To study why neonatal and young rats are resistant to the effects of some secretagogues, such as compound 48/80 and 2.5-S nerve growth factor, we examined peritoneal mast cells from 14-15-day-old rats (young rats) and compared them to peritoneal mast cells from adults. Peritoneal mast cells from young rats contain approximately one-tenth of the amount of histamine observed in adult peritoneal mast cells. However, both cell populations contained similar low levels of the mucosal mast cell-associated protease rat mast cell protease II. Histochemical analysis of peritoneal mast cells from young rats using safranin O and berberine sulphate suggested that only a portion of the granules of these cells contained heparin. At an ultrastructural level the young rat peritoneal mast cell contains relatively few granules. The majority of mast cells from young rats have a bilobed or indented nucleus which is only rarely observed in adult cells. Functionally, the young rat peritoneal mast cell demonstrates a significantly reduced histamine release in response to the connective tissue mast cell-specific secretagogues compound 48/80 and 2.5-S nerve growth factor. In contrast, the percent histamine release in response to the neurotransmitter substance P, which degranulates both connective tissue mast cells and intestinal mucosal mast cells, was similar in the adult cells and the young rat cells. This study demonstrates substantial differences between the young rat and adult peritoneal mast cells which may explain the ability of very young animals to withstand large doses of certain secretagogues.

Different susceptibility to the IL‐3 induced‐protective effects between Strongyloides ratti and Nippostrongylus brasiliensis in C57BL/6 mice

Repetitive administration of recombinant IL-3 induced protection against Strongyloides ratti but not against Nippostrongylus brasiliensis in C57BL/6 mice. Numbers of S. ratti were negligible from day 4 to day 6 post-infection in mice injected with IL-3, whereas N. brasiliensis burdens were almost equal from day 4 to day 6 between mice injected with IL-3 or with medium. Mice treated with IL-3 and then concurrently infected with S. ratti and N. brasiliensis were protected from intestinal S. ratti but not from N. brasiliensis. The numbers of intestinal mucosal mast cells were increased by the repetitive IL-3 treatment on one day after the final injection and was augmented by subsequent infection with both nematodes.

Mucosal mast cells and the expulsive mechanisms of mice against Strongyloides venezuelensis

Khan A. I., Horii Y., Tiuria R., Sato Y. and Nawa Y. 1993. Mucosal mast cells and the expulsive mechanisms of mice against Strongyloides venezuelensis. International Journal for Parasitology 23: 551–555. The possible importance of mucosal mast cells in the expulsive mechanisms of mice against Strongyloides venezuelensis was examined. After a primary infection by subcutaneous inoculation with various doses into C57BL/6 mice, about 50% of the initial dose of infective larvae (L 3) became adult worms and, regardless of the dose of infection, they were completely expelled by Day 12 with similar kinetics. Intestinal mastocytosis at the time of expulsion was comparable among groups given different doses of infection. A kinetic study after infection with 2000 L 3 in C57BL/6 mice revealed that mastocytosis started from Day 8, rapidly reached a peak on Day 12, and then gradually decreased. The strongest mastocytosis was observed in the upper one sixth of the small intestine where the majority of adult worms parasitized. Over 80% of mast cells induced by the infection were located in the intestinal epithelial layer. When mast cell-deficient W/W v and their normal littermate + / + mice were infected with 1000 L 3, expulsion was significantly delayed in W/W v mice, though adult worms were eventually expelled by Day 18 in W/W v mice. Delayed expulsion as well as defective mast cell responses of W/W v mice were completely restored by bone marrow grafting 10 weeks prior to infection. These results show that, like S. ratti infection, intestinal mucosal mast cells are important in causing expulsion of S. venezuelensis.

Repeated antigen challenge in rats induces a mucosal mast cell hyperplasia

Background: A link between mast cells and a number of intestinal diseases has been suggested. Treatment of adult rats with connective tissue mast cell degranulating agents has been shown to induce an intestinal mucosal mast cell hyperplasia. We have examined the hypothesis that repeated systemic antigen challenge would similarly up-regulate the mucosal mast cell population. Methods: Animals were primed with 10 μg of albumin and challenged twice weekly with 3, 30, or 300 μg of ovalbumin, subcutaneously, for 4 weeks. The mast cell numbers were assessed histologically. In addition, measurements were made of tissue/mast cell-mediator content. Results: Repeatedly challenged animals that received 30-μg doses of soluble ovalbumin developed a mucosal mast cell hyperplasia in the duodenum 2 weeks after the cessation of treatment. No change in connective tissue mast cell numbers was observed. Repeated administration of 300 μg of antigen did not induce a mucosal mast cell hyperplasia. No significant difference between the mucosal mast cell numbers in antigen-challenged and control animals was observed when animals were treated concurrently with the mast cell-stabilizing agent disodium cromoglycate. Conclusions: Repeated antigen challenge at doses that induce mast cell activation is associated with an increase in the number of mucosal mast cells.

Further Studies on the Effect of Nitrogen Dioxide on Mast Cells: The Effect of the Metabolite, Nitrite

To evaluate the relationship between atmospheric nitrogen dioxide exposure and the development of allergic diseases, the effects of nitrite as a chemical product of inhaled nitrogen dioxide on mast cell functions were investigated. We have studied nitrite-induced histamine release from two functionally distinct mast cell populations, namely peritoneal mast cells (PMC) and intestinal mucosal mast cells (IMMC) of Nippostrongylus brasiliensis-infected rats. High concentrations of nitrite alone (10, 20, and 50 mM) induced histamine release from IMMC, but not from PMC. Moreover, histamine release from PMC and IMMC stimulated with sensitizing antigen was significantly enhanced by pretreatment with 50 mM nitrite or nitrate. No differences in histamine release from nitrite-treated and control PMC were seen below 1 mM. To investigate the effect of nitrite on tumor cell cytotoxic activity, PMC were incubated with various concentrations of nitrite. Pretreatment with 5 and 50 miss nitrite markedly depressed tumor necrosis factor (TNF)-α-dependent natural cytotoxicity of PMC for the tumor target WEHI-164. Thus, high concentrations of nitrite enhanced mast cell histamine release, but depressed TNF-ct-dependent cytotoxicity. However, low concentrations of nitrite (<1 mM) that would normally be produced by short-term atmospheric exposure to nitrogen dioxide may have no significant effects on mast cell functions.

In vitro translation of mRNA from rat peritoneal and intestinal mucosal mast cells.

We isolated RNA from in vivo-derived rat peritoneal (PMC) and intestinal mucosal mast cells (IMMC) and assessed the in vitro translation products of these two mast cell types using rabbit reticulocyte lysate and wheat germ systems. The translated polypeptides were analyzed by one- and two-dimensional gel electrophoresis. Fluorographic analyses established that polypeptides with a spectrum of molecular size and pI were produced by both PMC and IMMC. Immunoprecipitation studies with anti-rat mast cell protease (RMCP) I antibodies detected a band at 31 kD from products of PMC RNA assessed by one-dimensional electrophoresis, whereas anti-RMCP II antibodies precipitated a band of 27 kD from products of IMMC RNA. This is the first report of translation products of IMMC and of the translated precursors of RMCP I and RMCP II.

Mucosal mast cell responses to experimental Metagonimus yokogawai infection in rats.

Intestinal mucosal mast cell (MMC) responses were studied in rats experimentally infected with Metagonimus yokogawai (Digenea: Heterophyidae). Twenty Sprague-Dawley rats were fed each 2,500 metacercariae isolated from the sweetfish and sacrificed on the week 1, 2, 3 and 4 post-infection (PI). Recovery of worms was performed from the small intestine of each rat. To visualize the MMCs, duodenal and jejunal (upper, middle and lower) tissue sections were made and stained with alcian blue/safranine-0. The average worm recovery rates were 16.2% and 13.8% on the week 1 and week 2, respectively, but they decreased rapidly to 4.1% and 4.2% on the week 3 and week 4 PI, respectively, which indicate spontaneous worm expulsion after the week 2. The MMC number in the infected rats was, compared with uninfected controls, significantly increased in the whole small intestine, through the whole period of observation. The peak level of mastocytosis was observed on the week 3 PI. It is strongly suggested that MMCs might be involved in the expulsion process of flukes from the rat intestine.

Prostaglandins inhibit inflammatory mediator release from rat mast cells

Background: Mast cells have been implicated in the pathogenesis of gastric ulceration. It is possible that prostaglandins exert cytoprotective effects by inhibiting the release of proulcerogenic mediators from mast cells. Methods: The effects of three prostaglandins on the release of platelet-activating factor, tumor necrosis factor, and histamine from rat mast cells (peritoneal and intestinal mucosal) activated with calcium ionophore or antigen were assessed. Results: Upon stimulation with either agonist, intestinal mucosal and peritoneal mast cells released significant quantities of platelet-activating factor. Preincubation for 5 minutes with misoprostol, prostaglandin (PG)E2, 16,16-dimethyl PGE2, ketotifen, or PF-5901 concentration-dependently reduced ionophore-stimulated platelet-activating factor release; significant effects were observed with picomolar to nanomolar concentrations of the prostaglandins and micromolar concentrations of the other compounds. Tumor necrosis factor release from peritoneal and mucosal mast cells was also significantly inhibited by the prostaglandins in picomolar to nanomolar concentrations. Misoprostol and PGE2 at concentrations of 5–50 nmol/L significantly inhibited histamine release from peritoneal mast cells stimulated with ionophore but did not affect histamine release stimulated by antigen. Conclusions: These results show potent inhibitory effects of prostaglandins on the release of pro-ulcerogenic inflammatory mediators from mast cells. Such effects may contribute to the protective and anti-inflammatory effects of prostaglandins in the gastrointestinal tract and elsewhere.

Steroid-Induced Depletion of Mucosal Mast Cells and Eosinophils in Intestine of Athymic Nude Rats

In conventional rats, we have previously demonstrated that corticosteroid treatment caused macrophage engulfment and destruction of intestinal mucosal mast cells and eosinophils by 24 h without evidence of local tissue destruction, inflammation or secretion of rat mast cell protease II. As the growth and survival of these cells appear to be dependent on factors derived from T lymphocytes, we examined the response in congenitally athymic rnu/rnu rats and euthymic rnu/+ rats 35 days after parasitic infection. Rats were injected intraperitoneally with 1 mg dexamethasone and sections of jejunum were examined at 0, 7, 13 and 24 h. The numbers of mucosal mast cells significantly decreased in both groups and became less than 30% of the original values at 24 h. Tissue mast cell protease decreased similarly. However, protease in serum did not increase and there were no inflammatory changes at any time. The numbers of eosinophils also rapidly decreased and became less than 20% at 24 h in both rnu/rnu and rnu/+ rats. By electron microscopy, we saw granular changes (fusion) in mast cells and nuclear changes (apoptosis) in eosinophils by 7 h after corticosteroid in athymic rats. Macrophage engulfment of these cells was observed at 7 and 13 h. Our results suggest that inflammatory cell depletion by macrophages is not dependent on suppression of typical thymus-derived T lymphocytes, and may be due either to direct effects of steroids on the cells themselves, or indirectly upon cells other than T cells which normally supply maintenance and growth factors for them.

Nerve remodelling during intestinal inflammation.

The intestinal mucosa contains a dense nerve network and many inflammatory cells, and these may interact through the exchange of regulatory molecules. Evidence suggests that intestinal mucosal mast cells are innervated, and it is known that the density of this cell type changes significantly in nematode-infected rats. Recent data indicates that rat jejunal mucosal nerves remodel after Nippostrongylus brasiliensis infection, with degenerative and regenerative phases during the acute and recovery stages of inflammation. Seven weeks postinfection there is a net increase in the density and number per villus of mucosal nerves. These changes suggest that mucosal nerves exhibit structural plasticity in inflamed tissues, which must impact on interactions between the enteric nervous system and other mucosal elements in disease.

Isolation and degranulation of mucosal mast cells from the small intestine of parasitized sheep

The isolation of mucosal mast cells and globule leucocytes from the small intestine of sheep immunized with Trichostrongylus colubriformis is described. Sheep mast cell protease was released from these cells in a dose-dependent fashion after incubation with soluble protein from T. colubriformis larvae. Release also occurred with other T. colubriformis antigens whereas non-parasite antigens at comparable protein concentrations evinced only a minimal response. Mucosal mast cells prepared from worm-free sheep also produced a similar minimal response. This is the first report describing the release of sheep mast cell protease from isolated sheep intestinal mucosal mast cells after addition of specific parasite antigens.

Transcriptional regulation of the mucosal mast cell-specific protease gene, MMCP-2, by interleukin 10 and interleukin 3.

Although transcription of mast cell (MC) secretory granule neutral protease genes has been shown to distinguish MC subclasses in mucosal and serosal environments, the specific cytokines that regulate the expression of these genes have not been determined. To examine cytokine-mediated gene regulation, bone marrow-derived MC (BMMC) differentiated in vitro were obtained by culturing mouse bone marrow progenitor cells in the presence of WEHI-3 cell-conditioned medium, concanavalin A-stimulated splenocyte-conditioned medium (BMMCC), or recombinant (r) interleukin (IL)-3 (BMMCIL-3). All three populations of BMMC expressed the serosal MC-specific transcripts that encode mouse MC serine protease (MMCP)-5, MMCP-6, and MC carboxypeptidase A. However, only BMMCC contained MMCP-2 mRNA, a late expressed gene selectively transcribed by intestinal mucosal MC that proliferate during helminthic infestation in response to the T cell-derived cytokines IL-3, IL-4, and IL-10. When BMMCIL-3 were exposed to rIL-10 in the presence of either rIL-3 or rIL-4, they expressed MMCP-2 mRNA. Not only was the transcription of the MMCP-2 gene in BMMC dependent on continuous exposure of the cells to rIL-10, but the level of MMCP-2 mRNA in these cells could be down-regulated by rIL-3. These studies comparing the effects of two cytokines on the transcriptional regulation of secretory granule protease genes in MC demonstrate that rIL-10 induces BMMCIL-3 to express the mucosal MC protease MMCP-2, that rIL-3 attenuates the rIL-10-induced expression of this gene, and that transcription of the MMCP-2 gene is reversed in the absence of rIL-10.