Apposition of fibroblasts to mast cells and lymphocytes in normal human lung and in cryptogenic fibrosing alveolitis. Ultrastructure and cell perimeter measurements

Development of Adaptive Immunity and Its Role in Lung Remodeling

Asthma is characterized by airflow limitations resulting from bronchial closure, which can be either reversible or fixed due to changes in airway tissue composition and structure, also known as remodeling. Airway remodeling is defined as increased presence of mucins-producing epithelial cells, increased thickness of airway smooth muscle cells, angiogenesis, increased number and activation state of fibroblasts, and extracellular matrix (ECM) deposition. Airway inflammation is believed to be the main cause of the development of airway remodeling in asthma. In this chapter, we will review the development of the adaptive immune response and the impact of its mediators and cells on the elements defining airway remodeling in asthma.

The controversial role of mast cells in fibrosis

Fibrosis is a medical condition characterized by an excessive deposition of extracellular matrix compounds such as collagen in tissues. Fibrotic lesions are present in many diseases and can affect all organs. The excessive extracellular matrix accumulation in these conditions can often have serious consequences and in many cases be life-threatening. A typical event seen in many fibrotic conditions is a profound accumulation of mast cells (MCs), suggesting that these cells can contribute to the pathology. Indeed, there is now substantialv evidence pointing to an important role of MCs in fibrotic disease. However, investigations from various clinical settings and different animal models have arrived at partly contradictory conclusions as to how MCs affect fibrosis, with many studies suggesting a detrimental role of MCs whereas others suggest that MCs can be protective. Here, we review the current knowledge of how MCs can affect fibrosis.

Neuroinflammatory Mechanisms of Connective Tissue Fibrosis: Targeting Neurogenic and Mast Cell Contributions

Significance: The pathogenesis of fibrogenic wound and connective tissue healing is complex and incompletely understood. Common observations across a vast array of human and animal models of fibroproliferative conditions suggest neuroinflammatory mechanisms are important upstream fibrogenic events. Recent Advances: As detailed in this review, mast cell hyperplasia is a common observation in fibrotic tissue. Recent investigations in human and preclinical models of hypertrophic wound healing and post-traumatic joint fibrosis provides evidence that fibrogenesis is governed by a maladaptive neuropeptide-mast cell-myofibroblast signaling pathway. Critical Issues: The blockade and manipulation of these factors is providing promising evidence that if timed correctly, the fibrogenic process can be appropriately regulated. Clinically, abnormal fibrogenic healing responses are not ubiquitous to all patients and the identification of those at-risk remains an area of priority. Future Directions: Ultimately, an integrated appreciation of the common pathobiology shared by many fibrogenic connective tissue conditions may provide a scientific framework to facilitate the development of novel antifibrotic prevention and treatment strategies.

Cellular interactions in the pathogenesis of interstitial lung diseases

Interstitial lung disease (ILD) encompasses a large and diverse group of pathological conditions that share similar clinical, radiological and pathological manifestations, despite potentially having quite different aetiologies and comorbidities. Idiopathic pulmonary fibrosis (IPF) represents probably the most aggressive form of ILD and systemic sclerosis is a multiorgan fibrotic disease frequently associated with ILD. Although the aetiology of these disorders remains unknown, in this review we analyse the pathogenic mechanisms by cell of interest (fibroblast, fibrocyte, myofibroblast, endothelial and alveolar epithelial cells and immune competent cells). New insights into the complex cellular contributions and interactions will be provided, comparing the role of cell subsets in the pathogenesis of IPF and systemic sclerosis.

Distinct cell populations contribute to the complex pathogenesis of IPF and systemic sclerosis-associated ILDhttp://ow.ly/AjFaz

CADM1 is a key receptor mediating human mast cell adhesion to human lung fibroblasts and airway smooth muscle cells

Background

Mast cells (MCs) play a central role in the development of many diseases including asthma and pulmonary fibrosis. Interactions of human lung mast cells (HLMCs) with human airway smooth muscle cells (HASMCs) are partially dependent on adhesion mediated by cell adhesion molecule-1 (CADM1), but the adhesion mechanism through which HLMCs interact with human lung fibroblasts (HLFs) is not known. CADM1 is expressed as several isoforms (SP4, SP1, SP6) in HLMCs, with SP4 dominant. These isoforms differentially regulate HLMC homotypic adhesion and survival.

Objective

In this study we have investigated the role of CADM1 isoforms in the adhesion of HLMCs and HMC-1 cells to primary HASMCs and HLFs.

Methods

CADM1 overexpression or downregulation was achieved using adenoviral delivery of CADM1 short hairpin RNAs or isoform-specific cDNAs respectively.

Results

Downregulation of CADM1 attenuated both HLMC and HMC-1 adhesion to both primary HASMCs and HLFs. Overexpression of either SP1 or SP4 isoforms did not alter MC adhesion to HASMCs, whereas overexpression of SP4, but not SP1, significantly increased both HMC-1 cell and HLMC adhesion to HLFs. The expression level of CADM1 SP4 strongly predicted the extent of MC adhesion; linear regression indicated that CADM1 accounts for up to 67% and 32% of adhesion to HLFs for HMC-1 cells and HLMCs, respectively. HLFs supported HLMC proliferation and survival through a CADM1-dependent mechanism. With respect to CADM1 counter-receptor expression, HLFs expressed both CADM1 and nectin-3, whereas HASMCs expressed only nectin-3.

Conclusion and Clinical Relevance

Collectively these data indicate that the CADM1 SP4 isoform is a key receptor mediating human MC adhesion to HASMCs and HLFs. The differential expression of CADM1 counter-receptors on HLFs compared to HASMCs may allow the specific targeting of either HLMC-HLF or HLMC-HASMC interactions in the lung parenchyma and airways.

The mast cell stabilizer ketotifen reduces joint capsule fibrosis in a rabbit model of post-traumatic joint contractures

OBJECTIVES

Using a rabbit model of post-traumatic joint contractures, we investigated whether treatment with a mast cell stabilizer after joint injury would lessen the molecular manifestations of joint capsule fibrosis.

METHODS

Surgical joint injury was used to create stable post-traumatic contractures of the knee in skeletally mature New Zealand white rabbits. Four groups of animals were studied: a non-operated control group (n = 8), an operated contracture group (n = 13) and two operated groups treated with the mast cell stabilizer, ketotifen, at doses of 0.5 mg/kg (n = 9) and 1.0 mg/kg (n = 9) twice daily. Joint capsule fibrosis was assessed by quantifying the mRNA and protein levels of α-SMA, tryptase, TGF-β1, collagen I and collagen III. Significance was tested using an ANOVA analysis of variance.

RESULTS

The protein and mRNA levels of α-SMA, TGF-β1, tryptase and collagen I and III were significantly elevated in the operated contracture group compared to control (p < 0.01). In both ketotifen-treated groups, protein and mRNA levels of α-SMA, TGF-β1 and collagen I were significantly reduced compared to the operated contracture group (p < 0.01).

CONCLUSIONS

These data suggest an inflammatory pathway mediated by mast cell activation is involved in joint capsule fibrosis after traumatic injury.

Activated MCTC mast cells infiltrate diseased lung areas in cystic fibrosis and idiopathic pulmonary fibrosis

Background

Although mast cells are regarded as important regulators of inflammation and tissue remodelling, their role in cystic fibrosis (CF) and idiopathic pulmonary fibrosis (IPF) has remained less studied. This study investigates the densities and phenotypes of mast cell populations in multiple lung compartments from patients with CF, IPF and never smoking controls.

Methods

Small airways, pulmonary vessels, and lung parenchyma were subjected to detailed immunohistochemical analyses using lungs from patients with CF (20 lung regions; 5 patients), IPF (21 regions; 7 patients) and controls (16 regions; 8 subjects). In each compartment the densities and distribution of MC_T and MC_TC mast cell populations were studied as well as the mast cell expression of IL-6 and TGF-β.

Results

In the alveolar parenchyma in lungs from patients with CF, MC_TC numbers increased in areas showing cellular inflammation or fibrosis compared to controls. Apart from an altered balance between MC_TC and MC_T cells, mast cell in CF lungs showed elevated expression of IL-6. In CF, a decrease in total mast cell numbers was observed in small airways and pulmonary vessels. In patients with IPF, a significantly elevated MC_TC density was present in fibrotic areas of the alveolar parenchyma with increased mast cell expression of TGF-β. The total mast cell density was unchanged in small airways and decreased in pulmonary vessels in IPF. Both the density, as well as the percentage, of MC_TC correlated positively with the degree of fibrosis. The increased density of MC_TC, as well as MC_TC expression of TGF-β, correlated negatively with patient lung function.

Conclusions

The present study reveals that altered mast cell populations, with increased numbers of MC_TC in diseased alveolar parenchyma, represents a significant component of the histopathology in CF and IPF. The mast cell alterations correlated to the degree of tissue remodelling and to lung function parameters. Further investigations of mast cells in these diseases may open for new therapeutic strategies.

Mast cells in lung inflammation

Mast cells play an important role in the lung in both health and disease. Their primary role is to initiate an appropriate program of inflammation and repair in response to tissue damage initiated by a variety of diverse stimuli. They are important for host immunity against bacterial infection and potentially in the host immune response to non small cell lung cancer. In situations of ongoing tissue damage, the sustained release of numerous pro-inflammatory mediators, proteases and cytokines, contributes to the pathophysiology of lung diseases such as asthma and interstitial lung disease. A key goal is the development of treatments which attenuate adverse mast cell function when administered chronically to humans in vivo. Such therapies may offer a novel approach to the treatment of many life-threatening diseases.

Ultrastructural changes in lung tissue after acute lead intoxication in the rat

Pulmonary toxicity of lead was studied in rats after an intraperitoneal administration of lead acetate at a dose of 25 mg/kg. Three consecutive days of treatment increased lead content in the whole blood to 2.1 µg/dl and in lung homogenate it attained 9.62 µg/g w.w. versus control values of 0.17 µg/dl and 0.78 µg/g w.w., respectively. At the ultrastructural level, the effects of lead toxicity were observed in lung capillaries, interstitium, epithelial cells and alveolar lining layer. Accumulation of aggregated platelets, leucocytic elements and monocytes was found within capillaries. Interstitium comprised a substantial number of collagen, elastin filaments and lipofibroblasts. Lamellar bodies of type II pneumocytes contained phospolipid lamellae, which stratified into an irregular arrangement. Pulmonary alveoli were filled with macrophages. The extracellular lining layer of lung alveoli was partially destroyed. This study provided evidence that acute lead intoxication affects the whole lung parenchyma and by impairing production of the surfactant might disturb the regular respiratory function.

Adenosine potentiates human lung mast cell tissue plasminogen activator activity

We investigated whether adenosine, a potent contributor to the regulation of pulmonary function, can modulate human lung mast cell (HLMC) fibrinolytic activity. Tissue plasminogen activator (tPA) activity and tPA transcript expression levels from a human mast cell line (HMC-1) and HLMC were monitored following adenosine application. Adenosine potentiated mast cell tPA activity and tPA gene expression in a dose-dependent manner. Adenosine effects were abolished in the presence of adenosine deaminase. HMC-1 cells and HLMC predominantly expressed adenosine A(2A) and A(2B) receptor transcripts (A(2B) ≈ A(2A) > A(3) >> A(1)). Pharmacological and signaling studies suggest that the A(2A) receptor is the major subtype accounting for adenosine-induced mast cell tPA activity. Finally, the supernatant from HMC-1 cells and HLMC treated with adenosine (for 24 h) significantly increased fibrin clot lysis, whereas ZM241385, an A(2A) receptor antagonist, abolished this effect. To our knowledge, this study provides the first data to demonstrate the potentiating effect of adenosine on mast cell tPA activity and fibrin clot lysis.

The analysis of tryptase in serum of sarcoidosis patients

Sarcoidosis is a systemic granulomatous disease of unknown etiology characterized by activation of macrophages and T lymphocytes. Relatively little is known about the role of mast cells and their mediators in the pathogenesis of sarcoidosis. Tryptase is an enzyme produced by activated mast cells, regarded as a marker of mast cell activation. To analyse tryptase concentrations in serum of sarcoidosis patients in an attempt to define the role of tryptase and mast cells in the pathogenesis of sarcoidosis and to evaluate the potential of tryptase as marker of disease severity. Quantitative analysis of tryptase concentrations was performed in serum of patients with stable sarcoidosis (n = 12), progressive sarcoidosis (n = 23) and controls (n = 13). Patients enrolled in the study had been monitored at Siena Regional Referral Centre for Sarcoidosis from onset for at least 12 months. Significantly higher concentrations of tryptase were found in peripheral blood of sarcoidosis patients (6.08 +/- 3.98 microg/l) than controls (2.96 +/- 1.75microg/l; p = 0.012). Patients with progressive disease showed the highest tryptase concentrations in serum. Tryptase and mast cells may be involved in the immunopathogenesis of sarcoidosis and further studies are required to understand if tryptase may represent a marker of sarcoidosis severity.

MMP dependence of fibroblast contraction and collagen production induced by human mast cell activation in a three-dimensional collagen lattice

Mast cell-fibroblast interactions may contribute to fibrosis in asthma and other disease states. Fibroblast contraction is known to be stimulated by coculture with the human mast cell line, HMC-1, or by mast cell-derived agents. Matrix metalloproteinases (MMPs) can also mediate contraction, but the MMP-dependence of mast cell-induced fibroblast contractility is not established, and the consequences of mast cell activation within the coculture system have not been fully explored. We demonstrate that activation of primary human mast cells (pHMC) with IgE receptor cross-linking, or activation of HMC-1 with C5a, enhanced contractility of human lung fibroblasts in a three-dimensional collagen lattice system. This enhanced contractility was inhibited by the pan-MMP antagonist, batimastat, and was transferrable in the conditioned medium of activated mast cells. Exogenously added MMPs promoted gel contraction by mediating the proteolytic activation of latent transforming growth factor-beta (TGF-beta). Consistent with this, fibroblast contraction induced by mast cell activation was enhanced by addition of excess latent TGF-beta to the cultures. Batimastat inhibited this response, suggesting that MMPs capable of activating latent TGF-beta were released following mast cell activation in coculture with fibroblasts. Collagen production was also stimulated by activated mast cells in an MMP-dependent manner. MMP-2 and MMP-3 content of the gels increased in the presence of activated mast cells, and inhibition of these enzymes blocked the contractile response. These findings demonstrate the MMP dependence of mast cell-induced fibroblast contraction and collagen production.

c-Kit immunophenotyping and metalloproteinase expression profiles of mast cells in interstitial lung diseases

Diverse interstitial lung diseases (ILD) demonstrate mesenchymal infiltration by an abundance of activated mast cells whose role in parenchymal fibrogenesis remains unclear. Since mast cells differentiate in a dynamic, tissue-specific manner via signals transduced by c-Kit receptor, we examined the effect of ILD microenvironments on c-Kit expression and metalloproteinase phenotypes of mesenchymal mast cell populations. Immunohistochemical and flow cytometric analyses characterized surface expression of c-Kit on mast cells in tissues obtained from patients with idiopathic pulmonary fibrosis, systemic sclerosis, sarcoidosis, and lymphangioleiomyomatosis, thus identifying a unique immunophenotype not shared by normal lung mast cells. Isolation of c-Kit+/FcepsilonRI+/CD34- mast cells via immunocytometric sorting of heterogeneous cell populations from mechanically disaggregated lung tissues permitted analysis of gene expression patterns by two-step real-time polymerase chain reaction. Transcriptional profiling identified expression of c-Kit and the neutral serine proteases, tryptase and chymase, establishing the identity of sorted populations as mature mast cells. Mast cells harvested from ILD tissues demonstrated characteristic metalloproteinase phenotypes which included expression of matrix metalloproteinase (MMP)-1 and a disintegrin and metalloproteinase (ADAM)-9, -10, and -17. Immunohistochemical co-localization guided by gene profiling data confirmed expression of chymase, MMP-1, and ADAM-17 protein in subpopulations of mast cells in remodelling interstitium. Gene profiling of harvested mast cells also showed increased transcript copy numbers for TNFalpha and CC chemokine receptor 2, which play critical roles in lung injury. We conclude that ILD microenvironments induce unique c-Kit receptor and metalloproteinase mast cell phenotypes.

T cell proliferation by direct cross-talk between OX40 ligand on human mast cells and OX40 on human T cells: comparison of gene expression profiles between human tonsillar and lung-cultured mast cells

Mast cells (MCs) are the primary effector cells in allergic reactions and have also been found to activate T cells and to reside in close physical proximity to T cells. However, the molecular mechanisms involved in the MC-T cell interaction remain unclear. We hypothesized that human tonsillar MCs, which locate in the interfollicular areas, might interact with T cells. Thus, we first established a culture system of human tonsillar MCs and then compared gene expression profiles of tonsillar MCs with that of lung MCs before and after aggregation of FcepsilonRI by using high-density oligonucleotide probe arrays. Here we show that resting tonsillar MCs, when compared with lung MCs, revealed significantly higher expression levels for CC chemokines (CCL3 and 4), which recruit T cells, and for TNFR superfamilies (OX40 ligand and 4-1BB ligand), which induce proliferation of T cells. After aggregation of FcepsilonRI, not only tonsillar MCs but also lung MCs up-regulated the expression of these molecules. We confirmed that T cell proliferation is induced in direct cross-talk by the MC surface molecule OX40 ligand. These results suggest that human MCs may play important roles in adaptive immunity through the T cell responses.

Pathogenetic mechanisms in usual interstitial pneumonia/idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive, usually fatal, form of interstitial lung disease characterized by failure of alveolar re-epithelialization, persistence of fibroblasts/myofibroblasts, deposition of extracellular matrix, and distortion of lung architecture which ultimately results in respiratory failure. Clinical IPF is associated with a histopathological pattern of usual interstitial pneumonia (UIP) on surgical lung biopsy. Therapy for this disease with glucocorticoids and other immunomodulatory agents is largely ineffective and recent trials of newer anti-fibrotic agents have been disappointing. While the inciting event(s) leading to the initiation of scar formation in UIP remain unknown, recent advances in our understanding of the mechanisms underlying both normal and aberrant wound healing have shed some light on pathogenetic mechanisms that may play significant roles in this disease. Unlike other fibrotic diseases of the lung, such as those associated with collagen vascular disease, occupational exposure, or chemotherapeutic agents, UIP is not associated with a significant inflammatory response; rather, dysregulated epithelial-mesenchymal interactions predominate. Identification of pathways crucial to fibrogenesis might offer potentially novel therapeutic targets to slow or halt the progression of IPF. This review focuses on evolving concepts of cellular and molecular mechanisms in the pathogenesis of UIP/IPF.

The differentiation and function of myofibroblasts is regulated by mast cell mediators

Myofibroblasts are fibroblasts that express certain features of smooth muscle differentiation. Increased numbers of myofibroblasts and mast cells are frequently found together in a wide variety of settings, such as normal wound repair and scleroderma skin, which suggests that mediators produced by the mast cells could play a role in the regulation of myofibroblast differentiation and function. We used a human mast cell line, HMC-1, to determine if mast cells can induce normal human dermal fibroblasts to differentiate into functional myofibroblasts in vitro. We monitored the differentiation process by assaying two properties of the myofibroblast phenotype: expression of alpha-smooth muscle actin and functional capacity to contract a collagen matrix. In both a simple coculture system and in a skin-equivalent culture system, HMC-1 cells induced alpha-smooth muscle actin expression by fibroblasts. HMC-1 cells also stimulated fibroblast contraction of collagen gels, and the relative amount of contraction was dependent upon the number of HMC-1 cells present. To characterize the individual contributions made by specific mast cell products, we examined the effects of histamine, tumor necrosis factor alpha, and tryptase. Histamine induced a clear increase in alpha-smooth muscle actin expression, but it did not appear to stimulate fibroblast contraction. Tumor necrosis factor alpha had no effect in either assay. Purified human tryptase induced alpha-smooth muscle actin expression, and blocking the proteolytic activity of tryptase with specific inhibitors reduced that response. Tryptase inhibitors also eliminated the ability of HMC-1 cells to stimulate fibroblast contraction, suggesting that tryptase secreted by the HMC-1 cells may be one of the active mast cell mediators.

Structural examination of tryptase-, and VIP-positive mast cells in the common bile duct of patients with lithiasis

The morphology of tryptase-, and vasoactive intestinal polypeptide (VIP)-positive mast cells was examined immunohistochemically in 38 common bile ducts collected from patients with secondary chronic cholangitis and varying degrees of inflammatory activity. Mast cells numbers in chronic exacerbated and chronic sclerotic cholangitis were significantly higher as compared with those in controls (72.4 cells/mm2 and 25.2 cells/mm2 vs. 5.9 cells/mm2; p < 0.0001, Student's t test). The increased number of tryptase-positive mast cells in chronic exacerbated cholangitis correlated with the severeness of inflammatory infiltration. In cases of chronic exacerbated cholangitis, the increased number of mast cells was detected in conjunction with active fibroplasia. In chronic sclerotic cholangitis mast cells were lower in number as compared with exacerbated cholangitis and were observed in relation with inactive fibrosis. Numerous VIP-positive mast cells were found in all patients with cholangitis. Ultrastructural immunocytochemistry showed tryptase positivity to be localized over either electron-dense or particulate granules with a mean diameter of 0.261+/-0.073 microm or 0.171+/-0.053 microm, respectively. VIP positivity was formed as a finely or coarsely granular pattern over larger electron-dense granules of 0.475+/-0.14 microm in diameter. Tryptase-positive mast cells were located mainly in and around surface and glandular epithelium. The involvement of tryptase- and VIP-positive mast cells in inflammation, fibrosis and epithelial reactions in the common bile duct is discussed.

Effect of heparin and related glycosaminoglycan on PDGF-induced lung fibroblast proliferation, chemotactic response and matrix metalloproteinases activity

Fibroblast migration, proliferation, extracellular matrix protein synthesis and degradation are the key events in various biological and pathological processes in pulmonary fibrosis. In addition, biopsy specimens from the lungs of patients with pulmonary fibrosis show increased numbers of mast cells which have metachromatic granules containing heparin, histamine and proteases. Little is known about how these products influence pulmonary fibrosis. In the present study, we investigated the effect of heparin and related glycosaminoglycans on PDGF-induced lung fibroblast proliferation and chemotactic response in vitro. In addition, we examined the effect of heparin on both the induction of matrix metalloproteinases (MMPs) and MMPs activity in lung fibroblasts in vitro. Heparin, de-N-sulphated heparin but not heparan sulphate inhibited PDGF-induced lung fibroblast proliferation. In contrast, only heparin inhibited PDGF-stimulated human lung fibroblast chemotaxis. Negatively charged poly-L-glutamic acid had no effect on either fibroblast proliferation or chemotaxis. Thus the negative charge alone cannot account for the ant-proliferative and anti-chemotactic effects of heparin. Furthermore, heparin and heparan sulphate also had no inhibitory effect on induction of MMPS, including MMP-1 (interstitial collagenase), MMP-2 (gelatinase A) and MMP-9 (gelatinase B). Only heparin inhibited both MMP-1 and MMP-2/MMP-9 activity. Additionally, tissue inhibitor of metalloproteinase type 1 (TIMP-1) and type 2 (TIMP-2) inhibited PDGF-stimulated human lung fibroblast chemotaxis. The ability of heparin to inhibit fibroblast chemotaxis may account for the inhibitory effect of heparin on MMP activity. The above results suggested that heparin and related glycosaminoglycans differentially regulate PDGF-induced lung fibroblast proliferation, chemotaxis and MMPs activity and further that these effects may have a key role in extracellular matrix remodeling in inflammatory lung disease.

Mast cell tryptase stimulates human lung fibroblast proliferation via protease-activated receptor-2

Mast cells play a potentially important role in fibroproliferative diseases, releasing mediators including tryptase that are capable of stimulating fibroblast proliferation and procollagen synthesis. The mechanism by which tryptase stimulates fibroblast proliferation is unclear, although recent studies suggest it can activate protease-activated receptor (PAR)-2. We therefore investigated the role of PAR-2 in tryptase-induced proliferation of human fetal lung and adult lung parenchymal and airway fibroblasts and, for comparative purposes, adult dermal fibroblasts. Tryptase (0.7-70 mU/ml) induced concentration-dependent increases in proliferation of all fibroblasts studied. Antipain, bis(5-amidino-2-benzimidazolyl)methane, and benzamidine inhibited tryptase-induced fibroblast proliferation, demonstrating that proteolytic activity is required for the proliferative effects of tryptase. RT-PCR demonstrated the presence of PAR-2 mRNA, and immunohistochemical staining localized PAR-2 to the cell surface of lung fibroblasts. In addition, specific PAR-2 activating peptides, SLIGKV and SLIGRL, mimicked the proliferative effects of tryptase. In contrast, human dermal fibroblasts only weakly stained with the PAR-2 antibody, PAR-2 mRNA was almost undetectable, and fibroblasts did not respond to PAR-2 activating peptides. These results suggest that tryptase induces lung, but not dermal, fibroblast proliferation via activation of PAR-2 and are consistent with the hypothesis that the release of tryptase from activated mast cells may play an important role in the fibroproliferative response observed in asthma, chronic obstructive pulmonary disease, and patients with pulmonary fibrosis.

Mast Cell Expression of Gelatinases A and B Is Regulated by kit Ligand and TGF-β

Our prior work shows that cultured BR cells derived from dog mastocytomas secrete the 92-kDa proenzyme form of gelatinase B. We provided a possible link between mast cell activation and metalloproteinase-mediated matrix degradation by demonstrating that α-chymase, a serine protease released from secretory granules by degranulating mast cells, converts progelatinase B to an enzymatically active form. The current work shows that these cells also secrete gelatinase A. Furthermore, gelatinases A and B both colocalize to α-chymase-expressing cells of canine airway, suggesting that normal mast cells are a source of gelatinases in the lung. In BR cells, gelatinase B and α-chymase expression are regulated, whereas gelatinase A expression is constitutive. Progelatinase B mRNA and enzyme expression are strongly induced by the critical mast cell growth factor, kit ligand, which is produced by fibroblasts and other stromal cells. Induction of progelatinase B is blocked by U-73122, Ro31-8220, and thapsigargin, implicating phospholipase C, protein kinase C, and Ca2+, respectively, in the kit ligand effect. The profibrotic cytokine TGF-β virtually abolishes the gelatinase B mRNA signal and also attenuates kit ligand-mediated induction of gelatinase B expression, suggesting that an excess of TGF-β in inflamed or injured tissues may alter mast cell expression of gelatinase B, which is implicated in extracellular matrix degradation, angiogenesis, and apoptosis. In summary, these data provide the first evidence that normal mast cells express gelatinases A and B and suggest pathways by which their regulated expression by mast cells can influence matrix remodeling and fibrosis.

Stem cell factor in nasal polyposis and allergic rhinitis: increased expression by structural cells is suppressed by in vivo topical corticosteroids

BACKGROUND

Mast cells are increased in nasal polyp (Np) and allergic rhinitis (AR) tissue and are suppressed by topical corticosteroid treatment. Stem cell factor (SCF), a mast cell growth and survival factor, may explain these phenomena.

OBJECTIVE

We investigated structural cell gene expression and production of SCF in nasal tissues in patients who had received and who had not received in vivo intranasal corticosteroid therapy.

METHODS

Northern blot analyses for messenger RNA and ELISA for biologically active SCF protein from cultured Np epithelial cells and fibroblasts were performed. Immunostaining for SCF in cultured and tissue nasal structural cells in the presence or absence of steroid treatment was also performed.

RESULTS

We detected significant expression of SCF mRNA and protein by cultured Np epithelial cells and Np fibroblasts; Np fibroblast SCF supported the differentiation of mast cells in vitro. There were more immunoreactive SCF-positive Np epithelial cells in patients with AR than in control subjects (97.2 +/- 2.8 vs 45.6 +/- 22.0%; p < 0.0001). SCF that could be immunostained was significantly diminished overall in Np structural cells in the group given in vivo steroid treatment, with a modest (trend to significant) effect on any given cell type analyzed. In vitro treatment with budesonide of SCF-producing fibroblasts demonstrated inhibition of unstimulated, primary Np fibroblasts but not of IL-1-stimulated fibroblasts or transformed cell lines.

CONCLUSIONS

Human Np and AR tissue structural cells express and produce increased SCF. Our in vitro studies suggest that intranasal steroids blunt SCF expression in Nps, an effect that may be responsible for a decrease in mast cells and symptoms.

Mast cell tryptase stimulates the synthesis of type I collagen in human lung fibroblasts

Mast cell activation is a characteristic feature of chronic inflammation, a condition that may lead to fibrosis as a result of increased collagen synthesis by fibroblasts. We have investigated the potential of tryptase, the major protease of human mast cells, to stimulate collagen synthesis in the human lung fibroblast cell line MRC-5. Tryptase was isolated from human lung tissue by ion-exchange and affinity chromatography. At concentrations of 18 and 36 mU/ml, tryptase stimulated both an increase in cell numbers, and a fivefold increase in DNA synthesis as determined by methyl-[3H]thymidine incorporation. Similar concentrations of tryptase resulted in a 2.5-fold increase in collagen synthesis as determined both by incorporation of [3H]proline into collagen, and by assay of hydroxyproline concentrations in the supernatants. There was also a twofold increase in collagenolytic activity in the culture medium after tryptase treatment, indicating that the increase in collagen synthesis was not a consequence of decreased collagenase production. All of these actions of tryptase were reduced in the presence of the protease inhibitors leupeptin and benzamidine hydrochloride, indicating a requirement for an active catalytic site. SDS-PAGE and autoradiographic analysis of the [3H]collagen produced by the cells revealed it to be predominantly type I collagen. Our findings suggest that the release of tryptase from activated mast cells may provide a signal for abnormal fibrosis in inflammatory disease.

Mast cells induce T-cell adhesion to human fibroblasts by regulating intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression

The capacity of mast cell products to mediate T-cell adhesion to fibroblasts was explored using heterotypic coculture systems or by exposing fibroblasts to mast-cell-conditioned media (MCCM), prepared by degranulating mast cells with calcium ionophore. Experimental results indicated that fibroblasts exposed to MCCM for 24 h bound fivefold more T cells than control fibroblasts. Binding was inhibited with intercellular adhesion molecule-1 (ICAM-1) or vascular cell adhesion molecule-1 (VCAM-1) neutralizing antibodies. Enzyme-linked immunosorbent assay and fluorescence-activated cell sorter analysis revealed that fibroblasts exposed to MCCM markedly increased ICAM-1 and VCAM-1 surface expression by 4 h, with levels maximal at 16 h and returning toward baseline by 48 h. A dose-dependent response of ICAM-1 and VCAM-1 expression was noted using serial dilutions of MCCM or by altering the ratio of degranulated mast cells cocultured with fibroblasts. Similar results were obtained using human fibroblasts derived from the dermis, synovium, and lung, although lung fibroblasts were generally less responsive. Northern analysis confirmed that MCCM regulated ICAM-1 and VCAM-1 expression at the mRNA level. In summary, mast cell products stimulated fibroblast surface expression, steady-state mRNA levels, and functional expression of ICAM-1 and VCAM-1. Experimental data suggest that mast-cell-derived tumor necrosis factor-alpha may be in large part responsible for these observations, although further studies using human mast cells will be required. Using a skin-equivalent organotypic coculture model with fibroblasts admixed with mast cells, we observed increased ICAM-1 expression in both keratinocytes and fibroblasts after activation of the mast cells.

Spindle cell and pleomorphic lipoma: an ultrastructural study

Spindle cell and pleomorphic lipoma are rare benign tumors of adipose tissue. Their histogenesis is poorly understood and pleomorphic lipoma has not previously been studied ultrastructurally. This study describes the morphology and ultrastructure of 6 cases of spindle cell and pleomorphic lipoma. Both spindle cell and pleomorphic lipomas showed similar ultrastructural features with an interrupted basal lamina, occasional non-membrane-bound lipid vacuoles and abundant rER. In all the cases mast cells were conspicuous and were intimately related to both spindle and pleomorphic cells. It is proposed that both the spindle and pleomorphic multinucleated cells that characterize these tumors are prelipoblastic mesenchymal cells. The possible significance of an interaction between these cells and mast cells is discussed.

Relationship between cells obtained by bronchoalveolar lavage and survival in idiopathic pulmonary fibrosis

BACKGROUND

The relationship between cell types in bronchoalveolar lavage (BAL) fluid and the clinical course of patients with idiopathic pulmonary fibrosis (IPF) has been the subject of several studies. However, the results of these studies are not conclusive. The aim of this study was to investigate the relationship between the absolute and relative cell numbers in BAL fluid from patients with IPF and their survival.

METHODS

Results obtained from the initial BAL fluid analyses of all histologically proven cases of IPF (n = 49) were selected retrospectively. Cox's proportional hazards survival analysis was used for estimating the relationship between absolute and relative cell numbers and survival.

RESULTS

A negative relationship was found between both the absolute numbers and percentages of eosinophils in BAL fluid samples and survival. No such relationship was demonstrated for the absolute numbers or the percentages of any other cell type.

CONCLUSIONS

Although this study has restrictions, these findings suggest a negative relationship between the absolute numbers and percentages of eosinophils in BAL fluid samples and survival in patients with IPF.

Tryptase immunoreactive mast cell hyperplasia in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), the most common cause of chronic lung disease in prematurely born infants, is histologically characterized by various degrees of airway and alveolar septal fibrosis. Tryptase, a serine protease specific to mast cells, has been shown to have potent fibroblast mitogenic properties and in addition has been shown to be increased in adult fibrotic lung disorders. Based on this analogy, the distribution of pulmonary mast cells exhibiting tryptase immunoreactivity was investigated by immunoperoxidase staining in autopsy specimens of infants dying with BPD. Morphologically normal lung specimens from similarly aged infants dying of sudden infant death syndrome (SIDS) served as controls. Tryptase-positive mast cell counts were performed at 250x from at least 10 random fields in bronchial, peribronchiolar, and alveolar regions. Compared to controls, in lung sections exhibiting typical histologic features of long-standing BPD, tryptase positive cells were significantly increased in bronchial (23.9 +/- 3.6 vs 14.4 +/- 2.3) and peribronchiolar (15.3 +/- 3.2 vs 4.63 +/- 0.6) regions compared to controls (P < 0.05, Student's t test). In particular, alveolar regions exhibiting moderate to severe degrees of septal fibrosis exhibited a dramatic increase in the number of tryptase-positive cells (9.83 +/- 1.89 vs 0.34 +/- 0.18, P = 0.003). These findings of a tryptase-positive mast cell hyperplasia in BPD suggest potential roles of mast cells as well as tryptase in the pathogenesis of this disease.

Messages and handshakes: cellular interactions in pulmonary fibrosis

A better understanding of early cellular events following pulmonary injury may permit the identification of those patterns of response which are destined to progress to fibrosis. Interactions between inflammatory, fibroblastic and epithelial cells appear to play crucial roles in fibrogenesis. Intercellular communication may be via "messages" delivered by soluble mediators or "handshakes" at sites of cell-to-cell contact. In this review, we question the validity of some prevailing concepts about the importance of growth factor secretion by alveolar macrophages; examine the possible role of activated T-lymphocytes in regulating macrophage production of mediators; and hypothesise that whereas fibroblast proliferation may primarily be stimulated by macrophage-derived cytokines, accumulation of collagen may be regulated by growth factors expressed by injured alveolar epithelial cells.

Atopy as a risk factor for cryptogenic fibrosing alveolitis

In a case-control study of occupational and environmental causes of cryptogenic fibrosing alveolitis we recently observed a higher prevalence of self-reported symptoms of wheeze, rhinitis or conjunctivitis in cases than in controls. To determine objectively whether this was due to a higher prevalence of atopy amongst cases of CFA, we have measured skin sensitivity to common allergens (D. Pteronyssinus, grass pollen, and cat fur), eosinophil counts and total Immunoglobulin E (IgE) in venous blood in the 22 surviving CFA cases from that study who were willing to provide a blood sample, and in one matched control per case. At least one positive skin test was recorded in 13 cases and six controls, the matched odds of one or more positive test being significantly increased in cases by a ratio of 8.0 (95% confidence interval 1.01-64, P = 0.05). Geometric mean eosinophil counts and IgE levels were also increased amongst cases by factors of 1.6 (95% CI 0.96-2.6) and 1.9 (0.9-3.8) respectively, although these differences were not significant. Differences in skin sensitivity, eosinophil counts, and IgE levels all tended to be more obvious in the 13 case control pairs in which the case was not taking steroids or other immunosuppressive treatment. We conclude that cases of CFA showed increased skin sensitivity to common allergens, and had evidence of increased IgE and eosinophilia in peripheral blood. These findings suggest that atopy may be an important determinant of susceptibility to CFA.

The riddle of the mast cell: kit(CD117)-ligand as the missing link?

Tissue mast cells are multifunctional immune cells and have been implicated in allergic and inflammatory reactions. However, while the role of allergen binding to surface IgE via the high-affinity Fc epsilon receptor on mast cells is well understood, major questions in mast-cell biology remain to be answered. In particular, it is largely unknown which stimuli lead to the differentiation of human mast cells from their precursor cells and how the maturing cells localize (or home) and acquire effector functions within the microvasculature. A potential solution is suggested by Peter Valent in this viewpoint. The emerging concept is that a single tissue hormone, the ligand of the c-kit tyrosine kinase receptor (CD117), provides a key signal in multiple aspects of mast-cell differentiation and function.

The nature of atypical multinucleated stromal cells: a study of 37 cases from different sites

The morphology, immunophenotype and ultrastructure of atypical multinucleated stromal cells in 37 specimens from different anatomical sites were compared. Overall, cellular morphology was similar between sites but nuclear features, immunophenotype and ultrastructure varied and reflected that of adjacent normal mononuclear stromal cells. It is concluded that the atypical multinucleated stromal cells represent a reactive change in the indigenous stromal cells. In all the cases mast cells were seen as a prominent component of the inflammatory infiltrate and many of them were intimately related to the atypical stromal cells. It is suggested that reactive stromal cell changes may relate to an interaction with mast cells.

New perspectives on basic mechanisms in lung disease. 1. Lung injury, inflammatory mediators, and fibroblast activation in fibrosing alveolitis

It is over 25 years since Scadding first defined the term fibrosing alveolitis. It has since been established that complex mechanisms underlie its pathogenesis, including epithelial and endothelial injury, vascular leakage, production of inflammatory cells and their mediators, and fibroblast activation. Only through a detailed knowledge of how these cellular and molecular events are interlinked will we learn how to combat this disease, which is notoriously resistant to present treatments. So far the only therapeutic advances have been refinements in immunosuppression, and even these treatments are frequently disappointing. We believe that future advances in treatment will come from the development of agents that protect endothelial and epithelial cells from further injury and agents that can inhibit release of inflammatory mediators. A better knowledge of the mechanisms of collagen gene activation and the biochemical pathways of collagen production may also allow the identification of vulnerable sites at which new treatments may be directed. A combined approach to modifying appropriate parts of both the inflammatory component and the fibroblast/collagen component should provide a new stimulus to research. Further epidemiological studies are also needed to identify the environmental causes of lung injury that initiate the cascade of events leading to interstitial fibrosis.