Number, fixation properties, dye-binding and protease expression of duodenal mast cells: comparisons between healthy subjects and patients with gastritis or Crohn’s disease

Summary There is an accumulation of evidence to suggest that mast cells may play a key role in gastrointestinal inflammation. We have investigated the numbers and heterogeneity in staining properties of mast cells in biopsies of the duodenum of normal subjects (n = 10), and of normal duodenum from patients with Crohn’s disease of the ileum and/or colon (n = 7) or with Helicobacter-associated gastritis of the antrum/corpus (n = 6). In normal donors, two subsets of mast cells, one located in the duodenal mucosa and the other in the submucosa, were clearly distinguished by their morphology and dye-binding properties. Whereas submucosal mast cells stained metachromatically with Toluidine Blue after neutral formalin fixation and emitted a yellow fluorescence after staining with Berberine sulphate, those in the mucosa were invisible using these stains. In patients with gastritis or Crohn’s disease, there were marked changes in the numbers of mucosal mast cells compared with control subjects, even though the duodenal biopsies were from apparently uninvolved tissue. Gastritis was associated with increased mucosal mast cell numbers (controls: 187 ± 23 cells mm−2; gastritis: 413 ± 139 cells mm−2; p = 0.0004), but mean mucosal mast cell counts in the uninvolved duodenum of Crohn’s patients were actually decreased (34 ± 30 cells mm−2, p = 0.0147). The clear differentiation between mucosal and submucosal mast cells on the basis of metachromasia with Toluidine Blue was not seen in biopsies from the patients with gastritis or Crohn’s disease. Previous studies which have suggested that there are no distinct mucosal and submucosal mast cell subsets in the human intestine may, therefore, have been affected by the use of tissue from diseased subjects. Heterogeneity in the expression of mast cell tryptase and chymase was seen by immunohistochemistry using specific antibodies, but the relative numbers of mast cell subsets were critically dependent on the methods used. Using a sensitive staining procedure, the majority of mucosal mast cells stained positively for chymase as well as for tryptase, an observation confirmed by immunoelectron microscopy and immunoabsorption studies. Our findings suggest that early stages in intestinal inflammation may be reflected in changes in mast cell numbers and in their staining properties, and call for a reappraisal of mast cell heterogeneity in the human intestinal tract This revised version was published online in November 2006 with corrections to the Cover Date.     

Histochemistry and morphology of porcine mast cells

Summary Mast cells have been described extensively in rodents and humans but not in pigs, and the objective of this study was to characterize porcine mast cells by histochemistry and electron microscopy. Carnoy's fluid proved to be a good fixative but fixation with neutral buffered formalin blocked staining of most mast cells. Alcian Blue stained more mast cells than did Toluidine Blue (pH 0.5), although Alcian Blue also stained goblet cells. In pigs, unlike rodents, the Alcian Blue method did not distinguish between mast cells in the intestinal mucosa and those in the connective tissue of the intestinal submucosa, tongue and skin. Mast cells were significantly larger in adult pigs than in piglets; in adult pigs and piglets, mast cells in the intestinal mucosa were significantly larger than those in submucosal connective tissue, and they were more varied in shape in piglets and adults. Granules in mast cells in the intestinal mucosa stained less intensely than those in mast cells in connective tissue of tongue, skin and intestinal submucosa. Mast cells in the connective tissue of the tongue, skin and intestinal submucosa fluoresced strongly when stained with berberine sulphate or with a mixture of berberine sulphate and Acridine Orange, but mast cells in the intestinal mucosa did not. All mast cells reacted positively in an enzyme-histochemical method previously used to detect human tryptase but not in a method previously used to detect human chymase. Mast cells in the medulla of thymus stained similarly to mast cells in the intestinal mucosa. Ultrastructural differences between mast cells were not detected.     

Bovine mast cells: distribution, density, heterogeneity, and influence of fixation techniques

Mast cells can be distinguished according to various characteristics: rodent mast cells have been subtyped by histochemical criteria, whereas canine and human mast cells have been classified according to their proteases. Comparisons of mast cells from different species have therefore resulted in contradictory and confusing opinions on mast cell heterogeneity. Thus, it is essential to obtain species-specific data on mast cell density and heterogeneity. The present study was carried out to determine the physiological distribution of mast cell numbers and types in bovines according to tissue location, staining, and fixation methods. Samples were fixed in formalin or Carnoy’s fluid. The average number of mast cells was determined by using a metachromatic staining method. Protease content of mast cells was examined with a double-enzyme-immunohistochemical staining technique. Three mast cell subtypes were distinguished: T-, TC-, and C-mast cells. The T-mast cell was the predominant subtype in nearly all investigated organs and tissue locations. Only tryptase-positive mast cells could be demonstrated in bovine skin and uterus. No chymase activity was found in these organs, regardless of the fixation type. A larger number of mast cells was observed after fixation in Carnoy’s fluid. The three different mast cell subtypes were only demonstrated in formalin-fixed tissue; chymase-positive mast cells were not found after fixation in Carnoy’s fluid. Increasing experimental data suggest that mast cell subtypes have different functions in promoting and modulating inflammation and in remodeling the extracellular matrix. Since mast cell tryptase and chymase have different functional properties, these results may clarify the different reaction patterns observed in various organs and species.     

Chymotrypsin- and trypsin-type serine proteases in rat mast cells: properties and functions

Two of the major enzymes present in and released from rat mast cells are chymotrypsin-type serine protease (chymase) and trypsin-type serine protease (tryptase), and these have been postulated to be important in the inflammatory reactions. There have been no clear data regarding the trypsin-type protease in rat mast cells. Tryptase was recently purified from rat peritoneal mast cells with an associated protein (trypstatin) that inhibited the protease activity above pH 7.5. Chymase was also purified from rat peritoneal cells by employing a one-step method involving hydrophobic chromatography on octyl-Sepharose 4B or arginine-Sepharose 4B. The properties of chymase and tryptase were described in relation to substrate specificity and their relative sensitivity to inhibitors. It was found that proteolytic activities of these enzymes were modulated by naturally occurring substances, such as phosphoglycerides, long-chain fatty acids, and trypstatin. There is as yet little evidence for the physiological roles of these enzymes in the inflammatory reaction. It has been found that the specific, low-molecular-weight inhibitor of chymase, chymostatin, and that of tryptase, leupeptin, inhibit histamine release induced by addition of anti-rat IgE to mast cells. However, the inhibitors with molecular weights of more than 6000 were found to have no effect in this process. The data suggest that chymase and tryptase in mast cell granules play a crucial or significant role in the process of degranulation.     

Activation of paracrine TGF-beta1 signaling upon stimulation and degranulation of rat serosal mast cells: a novel function for chymase.

As a source of transforming growth factor beta1 (TGF-beta1), mast cells have been implicated as potential effector cells in many pathological processes. However, the mechanisms by which mast cells express, secrete, and activate TGF-beta1 have remained vague. We show here by means of RT-PCR, immunoblotting, and immunocytochemistry that isolated rat peritoneal mast cells synthesize and store large latent TGF-beta1 in their chymase 1-containing secretory granules. Mast cell stimulation and degranulation results in rapid secretion of the latent TGF-beta1, which is converted by chymase 1 into an active form recognized by the type II TGF-beta serine/threonine kinase receptor (TbetaRII). Thus, mast cells secrete active TGF-beta1 by a unique secretory mechanism in which latent TGF-beta1 and the activating enzyme chymase 1 are coreleased. The activation of latent TGF-beta1 specifically by chymase was verified using recombinant human latent TGF-beta1 and recombinant human chymase. In isolated TbetaRI- and TbetaRII-expressing peritoneal macrophages, the activated TGF-beta1 induces the expression of the plasminogen activator inhibitor 1 (PAI-1), whereas in the mast cells, the levels of TbetaRI, TbetaRII, and PAI-1 expression were below detection. Selective stimulation of mast cells in vivo in the rat peritoneal cavity leads to rapid overexpression of TGF-beta1 in peritoneal mast cells and of TbetaRs in peritoneal macrophages. These data strongly suggest that mast cells can act as potent paracrine effector cells both by secreting active TGF-beta1 and by enhancing its response in target cells.     

In situ detection of the mast cell proteases chymase and tryptase in human lung tissue using light and electron microscopy

Scroll-rich, "mucosal" mast cells are the predominant human lung mast cell type. It has been proposed that these mast cells store tryptase but are mostly chymase deficient. We present a detailed immunolocalisation study of chymase and tryptase in lung specimens of eight patients. Using monoclonal antibody B7 in a conventional tissue processing method for light microscopy, chymase-positive mast cells were much fewer than tryptase-positive ones. However, they approached the number of tryptase-positive cells when optimised processing was used. Two different monoclonal antibodies, B7 and CC1, were used to visualise chymase in purified lung mast cells of two patients using ultrastructural immunogold labelling. Immunoabsorption controls demonstrated a reactivity of B7 with both tryptase and chymase, but indicated specificity of CC1 for chymase. On the ultrastructural level, all of more than 1,400 lung mast cells evaluated labelled for chymase. Reactivity was seen in cytoplasmic granules, cytoplasm and vesicles, but not elsewhere. Tryptase labelling using monoclonal antibody G3 was also present in all mast cells detected, and was retained in altered granules (=activated mast cells), where B7 labelling was sparse. The average labelling density was approximately sixfold higher than for chymase. In summary, chymase may be more abundant in human lung mast cells than hitherto thought.     

用免疫荧光标记对人组织中肥大细胞亚型的分选与形态观察

方法:利用中性蛋白酶成分、特征性酶抗体的免疫荧光染色和流式细胞仪确定分选肥大细胞亚型,以激光扫描共聚焦显微镜显示肥大细胞内分泌颗粒。结果:三种免疫表型被确定:肥大细胞的类胰蛋白酶阳性(MCT)、类糜蛋白酶阴性;类糜蛋白酶阳性(MCC)、类胰蛋白酶阴性和类胰蛋白酶阳性、类糜蛋白酶阳性(MCTC)。肥大细胞内分泌颗粒分散或聚集存在,分泌颗粒突起分泌或以分散的方式释放。分泌颗粒大范围释放后,肥大细胞的形态结构发生了改变。结论:利用肥大细胞的特征性酶抗体、免疫荧光标记和流式细胞仪可将人组织中的肥大细胞分选纯化为三种亚型;以共聚焦显微镜显示肥大细胞含有丰富的分泌颗粒,它说明肥大细胞具备了为人体I型变态反应提供快速反应的物质基础。     

Chymase and tryptase in dog mastocytoma cells: asynchronous expression as revealed by enzyme cytochemical staining

Mast cell populations can be distinguished by differences in the content and substrate specificity of their two major cytoplasmic granule proteases, the chymases and the tryptases. To explore the origins of differences in the types of proteases present in mast cells, we used a double cytochemical staining technique to reveal both chymase and tryptase in cells from four lines of dog mast cell tumors containing both enzymes. We expected that if chymase and tryptase were expressed together during cell development the relative staining intensity of chymase compared to tryptase would be constant among different cells of each tumor. Instead, we found substantial variation in the relative intensity of chymase and tryptase staining among cells of a given mastocytoma line, each of which contained cells presumed to be monoclonal in origin but heterogeneous with respect to cell development. The overall staining intensity for chymase or tryptase correlated with the amount of protease activity in extracts of tumor homogenates. Staining specificity was established by use of selective inhibitors and competitive substrates and was tested on various types of dog cells obtained by bronchoalveolar lavage. The results suggest that active chymase and tryptase may be expressed differently during mast cell differentiation and support the possibility of a close developmental relationship between mast cells differing in protease phenotype. Moreover, the success of the staining procedures applied to mastocytoma cells suggests that they may be of general utility in phenotyping of mast cells according to the protease activities present in their granules.     

Identification of a cathepsin G-like proteinase in the MCTC type of human mast cell

Human mast cells can be divided into two subsets based on serine proteinase composition: a subset that contains the serine proteinases tryptase and chymase (MCTC), and a subset that contains only tryptase (MCT). In this study we examined both types of mast cells for two additional proteinases, cathepsin G and elastase, which are the major serine proteinases of neutrophils. Because human mast cell chymase and cathepsin G are both chymotrypsin-like proteinases, the properties of these enzymes were further defined to confirm their distinctiveness. Comparison of their N-terminal sequences showed 30% nonidentity over the first 35 amino acids, and comparison of their amino acid compositions demonstrated a marked difference in their Arg/Lys ratios, which was approximately 1 for chymase and 10 for cathepsin G. Endoglycosidase F treatment increased the electrophoretic mobility of chymase on SDS gels, indicating significant N-linked carbohydrate on chymase; no effect was observed on cathepsin G. Immunoprecipitation and immunoblotting with specific antisera to each proteinase revealed little, if any, detectable cross-reactivity. Immunocytochemical studies showed selective labelling of MCTC type mast cells by cathepsin G antiserum in sections of human skin, lung, and bowel. No labeling of mast cells by elastase antiserum was detected in the same tissues, or in dispersed mast cells from lung and skin. A protein cross-reactive with cathepsin G was identified in extracts of human skin mast cells by immunoblot analysis. This protein had a slightly higher Mr (30,000) than the predominant form of neutrophil cathepsin G (Mr 28,000), and could not be separated from chymase (Mr 30,000) by SDS gel electrophoresis because of the size similarity. Using casein, a protein substrate hydrolyzed at comparable rates by chymase and cathepsin G, it was shown that about 30% of the caseinolytic activity in mast cell extracts was sensitive to inhibitors of cathepsin G that had no effect on chymase. Hydrolytic activity characteristic of elastase was not detected in these extracts. These studies indicate that human MCTC mast cells may contain two different chymotrypsin-like proteinases: chymase and a proteinase more closely related to cathepsin G, both of which are undetectable in MCT mast cells. Neutrophil elastase, on the other hand, was not detected in human mast cells by our procedures.     

Rat mast cell tryptase

Rat mast cell tryptase is located largely if not totally in the cell's secretory granules. When the active site reagent [3H]diisopropyl fluorophosphate was used to label tryptase and chymase simultaneously, the ratio of tryptase:chymase active sites was determined to be 0.05. In comparison to chymase and tryptase in other species and chymase in the rat, rat tryptase is poorly bound to the granule matrix as evidenced by (1) its release parallel to histamine on induction of secretion and (2) its appearance in the supernatant when isolated granules were stripped of their membranes with hypotonic medium. Tryptase on release from the granule is moderately stable at a pH of 5.0 but unstable at pH 7.5, the pH that the enzyme encounters on secretion from the cell. These several properties indicate that the role of rat mast cell tryptase extracellularly is likely to differ greatly from that of chymase.     

Distribution, Histochemical and Enzyme Histochemical Characterization of Mast Cells in Dogs

This study describes the distribution, proteoglycan properties and protease activity of mast cells from 15 different dog organs. In beagles and mixed breed dogs, staining with Alcian Blue-Safranin O revealed mast cells in all the organs examined. However, their numbers varied and they demonstrated unique localization patterns within some of these organs. Berberine sulphate fluorescence-positive mast cells were observed in the submucosa, muscularis and serosa of the intestines, as well as the tongue and liver (within the connective tissue). Mast cells within the intestinal mucosa were negative for, or demonstrated weak, berberine sulphate staining. Heterogeneity of mast cells in terms of the proteoglycans contained within their granules was further confirmed by determination of critical electrolyte concentrations (CECs). The CECs of mast cells within the connective tissue of several organs, including the intestines (submucosal and muscularis-serosal layers) were all greater than 1.0 M. The results from CEC experiments together with berberine staining indicate that heparin was contained within their granules. Relative to the CECs of mast cells in other organs, mast cells in the intestinal mucosa exhibited lower CECs, suggesting that the proteoglycans within their granules were of lower charge density and/or molecular weight. Although mast cells were classified into two groups by proteoglycans within the granules, enzyme histochemical analysis in beagles revealed three subtypes of mast cells: chymase (MC(C)), tryptase (MC(T)) and dual positive (MC(TC)) cells. There was no correlation between the proteoglycan content and enzyme properties of the mast cell granules.     

Mucosal mast cells of the rat intestine: a re-evaluation of fixation and staining properties, with special reference to protein blocking and solubility of the granular glycosaminoglycan

Mucosal mast cells of the gastrointestinal tract constitute a separate cell line within the mast cell system of the rat, differing in several respects from the classical connective tissue mast cells and, unlike the latter, requiring special fixation techniques for their demonstration. We have examined some histochemical properties of mucosal mast cells of the duodenum and compared them with connective tissue mast cells of the tongue or skin. The results indicate that the structural integrity of the granules of both types of mast cell is partly dependent on ionic linkages between glycosaminoglycan and protein. The so far unidentified glycosaminoglycan of mucosal mast cells appears to be more soluble than the heparin of connective tissue mast cells. The strongly fluorescent binding of Berberine to the granules of connective tissue mast cells and, depending on their content, of heparin is absent from mucosal mast cells, confirming previous findings which suggested that they contain a glycosaminoglycan with a lower degree of sulphation. Aldehyde fixation by routine procedures reversibly blocks the cationic dye binding of mucosal mast cell granules. The dye binding groups may be unmasked by trypsination or by long staining times of the order of several days. The results suggest that the blocking of staining by aldehydes is caused by a diffusion barrier of a protein nature. Mucosal and connective tissue mast cells thus differ with respect to the spatial arrangement of glycosaminoglycan and protein in their granules. As a result of the study a modified method for the demonstration of mucosal mast cells in tissue sections is described, based on normal formaldehyde fixation and staining in Toluidine Blue for a long time. It has some advantages over previous methods and preserves the structure of mucosal and connective tissue mast cells equally well.     

Human mast cell chymase cleaves pro-IL-18 and generates a novel and biologically active IL-18 fragment

Increased release of IL-18 in the skin causes atopic dermatitis (AD)-like skin lesions, suggesting a role of IL-18 in the pathogenesis of AD. Caspase-1 is a well-known activator of IL-18, but caspase-1 knockout mice still have biologically active IL-18. Normal human keratinocyte constitutively produces pro-IL-18, but it is unable to activate it, suggesting the existence of an alternative pathway for IL-18 in the skin. Dermal accumulation of mast cells is commonly observed in AD patients and in experimental mouse models of AD. Connective tissue mast cells contain high amounts of chymase and tryptase in their cytoplasmic granules. In the present study, we demonstrated that activation of IL-18 is a novel function of human mast cell chymase. Human mast cell chymase rapidly cleaves recombinant pro-IL-18 at 56-phenylalanine and produces a biologically active IL-18 fragment that is smaller than any other reported IL-18-derived species. The human mast cell chymase and the novel IL-18-derived active peptide may be novel therapeutic targets in AD- and IL-18-associated diseases.     

Distribution, density and heterogeneity of canine mast cells and influence of fixation techniques

 The present study was carried out to determine the physiological distribution of mast cell numbers and types in the dog according to tissue location, staining and fixation methods. Tissue samples from stomach, duodenum, lung, lymph node, skin and uterus were evaluated. Samples were fixed in formalin as well as in Carnoy’s fluid. The average number of mast cells was determined using a metachromatic staining method. Protease content of mast cells was examined with a double enzyme-immunohistochemical staining technique, using a histochemical reaction for chloroacetate esterase to detect chymase activity and an immunohistochemical staining method for the detection of tryptase. Canine mast cells can be subdivided into formalin-sensitive and -resistant mast cells. Three subtypes were identified according to their content of the mast cell-specific proteases tryptase (T) and chymase (C): T-, TC- and C-mast cells. Significant differences regarding the distribution of mast cell subtypes as well as the influence of the fixation method can be observed. This underlines the fact that data regarding mast cell heterogeneity from other species, obtained by different fixation methods, are not comparable. This fact has to be taken into consideration when evaluating mast cell subtypes under pathological conditions. Accepted: 29 January 1998     

胃促胰酶和肥大细胞在豚鼠过敏性休克死亡的应用

目的:建立豚鼠过敏性休克模型,研究胃促胰酶和肥大细胞在过敏性休克诊断上的应用。方法:20只清洁级豚鼠随机分为10只实验组和10只对照组,应用混合人血清构建的过敏模型,ELISA方法测定豚鼠血清Ig E含量,免疫组化染色观察胃促胰酶在喉头、气管、肺、胃、肠的表达,肥大细胞特殊染色计数肥大细胞。结果:实验组豚鼠有70%发生过敏性休克死亡,实验组豚鼠血清中Ig E的含量显著高于对照组豚鼠(P0.05),实验组豚鼠于喉头、气管、肺胃促胰酶的表达高于对照组(P0.05),实验组豚鼠于喉头、气管、肺、胃的肥大细胞总数高于对照组豚鼠(P0.05),肺组织观察到肥大细胞脱颗粒。结论:胃促胰酶和肥大细胞可以为过敏性休克死亡的法医学鉴定提供参考。     

Granule Associated Serine Proteases of Hematopoietic Cells – An Analysis of Their Appearance and Diversification during Vertebrate Evolution

Serine proteases are among the most abundant granule constituents of several hematopoietic cell lineages including mast cells, neutrophils, cytotoxic T cells and NK cells. These proteases are stored in their active form in the cytoplasmic granules and in mammals are encoded from four different chromosomal loci: the chymase locus, the met-ase locus, the T cell tryptase and the mast cell tryptase locus. In order to study their appearance during vertebrate evolution we have performed a bioinformatic analysis of related genes and gene loci from a large panel of metazoan animals from sea urchins to placental mammals for three of these loci: the chymase, met-ase and granzyme A/K loci. Genes related to mammalian granzymes A and K were the most well conserved and could be traced as far back to cartilaginous fish. Here, the granzyme A and K genes were found in essentially the same chromosomal location from sharks to humans. However in sharks, no genes clearly identifiable as members of the chymase or met-ase loci were found. A selection of these genes seemed to appear with bony fish, but sometimes in other loci. Genes related to mammalian met-ase locus genes were found in bony fish. Here, the most well conserved member was complement factor D. However, genes distantly related to the neutrophil proteases were also identified in this locus in several bony fish species, indicating that this locus is also old and appeared at the base of bony fish. In fish, a few of the chymase locus-related genes were found in a locus with bordering genes other than the mammalian chymase locus and some were found in the fish met-ase locus. This indicates that a convergent evolution rather than divergent evolution has resulted in chymase locus-related genes in bony fish.     

Tryptase and chymase are angiogenic in vivo in the chorioallantoic membrane assay

Human mast cells (MCs) are divided in two types depending on the expression of tryptase and chymase in their granules. Literature data indicate that both tryptase and chymase are angiogenic, but there is currently no evidence of their direct angiogenic activity in vivo. In this study, we have investigated the capacity of tryptase and chymase to promote vasoproliferation in chick embryo chorioallantoic membrane (CAM), a well established in vivo assay to study angiogenesis and anti-angiogenesis. The results showed that both tryptase and chymase stimulate angiogenesis and that the response is similar to that obtained with vascular endothelial growth factor (VEGF), a well-known angiogenic cytokine, and confirm the angiogenic activity of these two proteases stored in MC granules.     

Mast cell proteoglycans modulate the secretagogue, proteoglycanase, and amidolytic activities of dog mast cell chymase.

Chymase, a potent secretagogue for airway gland serous cells, is stored in secretory granules and released from mast cells together with proteoglycans. To investigate the hypothesis tha tproteoglycans modulate chymase-induced effects, we studied the influence of proteoglycans purified from dog mastocytoma cells on chymase-induced secretion from cultured bovine airway gland serous cells. Heparin proteoglycans reduced the chymase-induced secretory response, whereas glycosaminoglycans and chondroitin sulfate proteoglycans had less of an effect. Chymase released together with proteoglycans from activated mast cells caused secretion comparable to that caused by purified chymase reconstituted with purified proteoglycans. Despite partial inhibition by exocytosed proteoglycans, the secretagogue activity of chymase remains substantial compared to that of histamine. However, proteoglycans virtually abolished chymase-induced degradation of the products of serous cell secretion. Although the secretagogue and proteoglycanase activities of chymase are inhibited by most classes of mast cell granule-associated glycans, the amidolytic activity of chymase toward tripeptide 4-nitroanilide substrates is augmented. These findings suggest that mast cell proteoglycans modulate the secretagogue, proteoglycanase, and peptidase activity of chymase, and the results predict that the extent of this modulation in vivo depends on the nature of the proteoglycans with which chymase is released from mast cells.