Human synovial mast cells. I. Ultrastructural in situ and in vitro immunologic characterization

Autoantibodies to IgE can induce the release of proinflammatory and vasoactive mediators from human cardiac mast cells

Mast cells are multifunctional immune cells with complex roles in tissue homeostasis and disease. Cardiac mast cells (HCMCs) are strategically located within the human myocardium, in atherosclerotic plaques, in proximity to nerves, and in the aortic valve. HCMCs express the high-affinity receptor (FcεRI) for IgE and can be activated by anti-IgE and anti-FcεRI. Autoantibodies to IgE and/or FcεRI have been found in the serum of patients with a variety of immune disorders. We have compared the effects of different preparations of IgG anti-IgE obtained from patients with atopic dermatitis (AD) with rabbit IgG anti-IgE on the release of preformed (histamine and tryptase) and lipid mediators [prostaglandin D₂ (PGD₂) and cysteinyl leukotriene C₄ (LTC₄)] from HCMCs. Functional human IgG anti-IgE from one out of six AD donors and rabbit IgG anti-IgE induced the release of preformed (histamine, tryptase) and de novo synthesized mediators (PGD₂ and LTC₄) from HCMCs. Human IgG anti-IgE was more potent than rabbit IgG anti-IgE in inducing proinflammatory mediators from HCMCs. Human monoclonal IgE was a competitive antagonist of both human and rabbit IgG anti-IgE. Although functional anti-IgE autoantibodies rarely occur in patients with AD, when present, they can powerfully activate the release of proinflammatory and vasoactive mediators from HCMCs.

Mast Cells as a Double Edged Sword in Immunity: Disorders of Mast Cell Activation and Therapeutic Management. Second of Two Parts

Mast cells (MCs) bear many receptors that allow them to respond to a variety of exogenous and endogenous stimuli. However, MC function is dual since they can initiate pathological events or protect the host against infectious challenges. The role of MCs in disease will be analyzed in a broad sense, describing cellular and molecular mechanisms related to their involvement in auto-inflammatory diseases, asthma, autoimmune diseases and cancer. On the other hand, their protective role in the course of bacterial, fungal and parasitic infections will also be illustrated. As far as treatment of MC-derived diseases is concerned, allergen immunotherapy as well as other attempts to reduce MC-activation will be outlined according to the recent data. Finally, in agreement with current literature and our own data polyphenols have been demonstrated to attenuate type I allergic reactions and contact dermatitis in response to nickel. The use of polyphenols in these diseases will be discussed also in view of MC involvement.

Persistence of Mast Cell-Positive Synovitis in Early Rheumatoid Arthritis Following Treatment With Conventional Synthetic Disease Modifying Anti-Rheumatic Drugs

Mast cells (MCs) are immune cells infiltrating the synovial membrane and implicated in the pathogenesis of Rheumatoid Arthritis (RA). Their infiltration in the synovia of early RA patients has been shown to be associated with systemic inflammation, disease activity and autoantibody positivity. Here, we analyzed their presence in matched synovial samples obtained by ultrasound-guided synovial biopsies pre- and post-treatment with conventional synthetic Disease Modifying Anti-Rheumatic Drugs (csDMARDs) (n=20). Upon IHC staining, patients were classified as MC+ve/-ve based on the presence/absence of CD117+ synovial MCs. At baseline, MC+ve patients had significantly higher synovial inflammation, inflammatory markers, disease activity and a higher prevalence of lympho-myeloid aggregates. Synovial biopsies after 6 months of treatment with csDMARDs showed a significant reduction of synovitis scores, but only a partial reduction of MC numbers. Accordingly, 45% of patients (9/20) were MC+ve after treatment, in association with significantly higher degree of synovitis and higher proportion lympho-myeloid aggregates. Finally, significantly lower patients with MC+ve synovitis at 6 months reached Low Disease Activity (LDA), while the association of MCs with disease activity was independent from lymphoid aggregates, after adjustment for BMI and age. Overall, this study confirms the relevance of MCs as part of the inflammatory infiltrate in the synovia of RA patients, warranting further investigations in larger cohorts to clarify their role in disease progression and response to treatment and their relevance as prognostic markers and potential therapeutic targets.

HIV gp120 Induces the Release of Proinflammatory, Angiogenic, and Lymphangiogenic Factors from Human Lung Mast Cells

Human lung mast cells (HLMCs) express the high-affinity receptor FcεRI for IgE and are involved in chronic pulmonary diseases occurring at high frequency among HIV-infected individuals. Immunoglobulin superantigens bind to the variable regions of either the heavy or light chain of immunoglobulins (Igs). Glycoprotein 120 (gp120) of HIV-1 is a typical immunoglobulin superantigen interacting with the heavy chain, variable 3 (V_H3) region of human Igs. The present study investigated whether immunoglobulin superantigen gp120 caused the release of different classes of proinflammatory and immunoregulatory mediators from HLMCs. The results show that gp120 from different clades induced the rapid (30 min) release of preformed mediators (histamine and tryptase) from HLMCs. gp120 also caused the de novo synthesis of cysteinyl leukotriene C₄ (LTC₄) and prostaglandin D₂ (PGD₂) from HLMCs. Incubation (6 h) of HLMC with gp120 induced the release of angiogenic (VEGF-A) and lymphangiogenic (VEGF-C) factors from HLMCs. The activating property of gp120 was mediated through the interaction with IgE V_H3⁺ bound to FcεRI. Our data indicate that HIV gp120 is a viral superantigen, which induces the release of different proinflammatory, angiogenic, and lymphangiogenic factors from HLMCs. These observations could contribute to understanding, at least in part, the pathophysiology of chronic pulmonary diseases in HIV-infected individuals.

Heterogeneity of Human Mast Cells With Respect to MRGPRX2 Receptor Expression and Function

Mast cells and their mediators play a role in the control of homeostasis and in the pathogenesis of several disorders. The concept of rodent mast cell heterogeneity, initially established in the mid-1960s has been extended in humans. Human mast cells isolated and purified from different anatomic sites can be activated via aggregation of cell surface high affinity IgE receptors (FcεRI) by antigens, superantigens, anti-IgE, and anti-FcεRI. MAS-related G protein-coupled receptor-X2 (MRGPRX2) is expressed at high level in human skin mast cells (MCs) (HSMCs), synovial MCs (HSyMCs), but not in lung MCs (HLMCs). MRGPX2 can be activated by neuropeptide substance P, several opioids, cationic drugs, and 48/80. Substance P (5 × 10⁻⁷ M – 5 × 10⁻⁶ M) induced histamine and tryptase release from HSMCs and to a lesser extent from HSyMCs, but not from HLMCs and human cardiac MCs (HHMCs). Morphine (10⁻⁵ M – 3 × 10⁻⁴ M) selectively induced histamine and tryptase release from HSMCs, but not from HLMCs and HHMCs. SP and morphine were incomplete secretagogues because they did not induce the de novo synthesis of arachidonic acid metabolites from human mast cells. In the same experiments anti-IgE (3 μg/ml) induced the release of histamine and tryptase and the de novo synthesis of prostaglandin D₂ (PGD₂) from HLMCs, HHMCs, HSyMCs, and HSMCs. By contrast, anti-IgE induced the production of leukotriene C₄ (LTC₄) from HLMCs, HHMCs, HSyMCs, but not from HSMCs. These results are compatible with the heterogeneous expression and function of MRGPRX2 receptor on primary human mast cells isolated from different anatomic sites.

Mast Cells in Early Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by inflammation of the synovial membrane, with thickening of the synovial layer, cellular hyperplasia, and infiltration of immune cells. Mast cells (MCs) are cells of the innate immunity present in healthy synovia and part of the cellular hyperplasia characterizing RA synovitis. Although their presence in synovia has been well described, the exact functions and the correlation of MCs with disease development and progression have been debated, particularly because of contradictory data obtained in animal models and from patients with longstanding disease. Here, we present a revision of the literature on MCs in RA, including the most recent observations obtained from patients with early RA, indicating MCs as relevant markers of disease severity in early RA.

Superantigenic Activation of Human Cardiac Mast Cells

B cell superantigens, also called immunoglobulin superantigens, bind to the variable regions of either the heavy or light chain of immunoglobulins mirroring the lymphocyte-activating properties of classical T cell superantigens. Protein A of Staphylococcus aureus, protein L of Peptostreptococcus magnus, and gp120 of HIV are typical immunoglobulin superantigens. Mast cells are immune cells expressing the high-affinity receptor for IgE (FcεRI) and are strategically located in the human heart, where they play a role in several cardiometabolic diseases. Here, we investigated whether immunoglobulin superantigens induced the activation of human heart mast cells (HHMCs). Protein A induced the de novo synthesis of cysteinyl leukotriene C₄ (LTC₄) from HHMCs through the interaction with IgE V_H3⁺ bound to FcεRI. Protein L stimulated the production of prostaglandin D₂ (PGD₂) from HHMCs through the interaction with κ light chains of IgE. HIV glycoprotein gp120 induced the release of preformed (histamine) and de novo synthesized mediators, such as cysteinyl leukotriene C₄ (LTC₄), angiogenic (VEGF-A), and lymphangiogenic (VEGF-C) factors by interacting with the V_H3 region of IgE. Collectively, our data indicate that bacterial and viral immunoglobulin superantigens can interact with different regions of IgE bound to FcεRI to induce the release of proinflammatory, angiogenic, and lymphangiogenic factors from human cardiac mast cells.

Human mast cells and basophils-How are they similar how are they different?

Mast cells and basophils are key contributors to allergies and other inflammatory diseases since they are the most prominent source of histamine as well as numerous additional inflammatory mediators which drive inflammatory responses. However, a closer understanding of their precise roles in allergies and other pathological conditions has been marred by the considerable heterogeneity that these cells display, not only between mast cells and basophils themselves but also across different tissue locations and species. While both cell types share the ability to rapidly degranulate and release histamine following high-affinity IgE receptor cross-linking, they differ markedly in their ability to either react to other stimuli, generate inflammatory eicosanoids or release immunomodulating cytokines and chemokines. Furthermore, these cells display considerable pharmacological heterogeneity which has stifled attempts to develop more effective anti-allergic therapies. Mast cell- and basophil-specific transcriptional profiling, at rest and after activation by innate and adaptive stimuli, may help to unravel the degree to which these cells differ and facilitate a clearer understanding of their biological functions and how these could be targeted by new therapies.

Mast cells in early rheumatoid arthritis associate with disease severity and support B cell autoantibody production

OBJECTIVES

Mast cells (MCs) are involved in the pathogenesis of rheumatoid arthritis (RA). However, their contribution remains controversial. To establish their role in RA, we analysed their presence in the synovium of treatment-naïve patients with early RA and their association and functional relationship with histological features of synovitis.

METHODS

Synovial tissue was obtained by ultrasound-guided biopsy from treatment-naïve patients with early RA (n=99). Immune cells (CD3/CD20/CD138/CD68) and their relationship with CD117⁺MCs in synovial tissue were analysed by immunohistochemistry (IHC) and immunofluorescence (IF). The functional involvement of MCs in ectopic lymphoid structures (ELS) was investigated in vitro, by coculturing MCs with naïve B cells and anticitrullinated protein antibodies (ACPA)-producing B cell clones, and in vivo in interleukin-27 receptor alpha (IL27ra)-deficient and control mice during antigen-induced arthritis (AIA).

RESULTS

High synovial MC counts are associated with local and systemic inflammation, autoantibody positivity and high disease activity. IHC/IF showed that MCs reside at the outer border of lymphoid aggregates. Furthermore, human MCs promote the activation and differentiation of naïve B cells and induce the production of ACPA, mainly via contact-dependent interactions. In AIA, synovial MC numbers increase in IL27ra deficient mice, in association with ELS and worse disease activity.

CONCLUSIONS

Synovial MCs identify early RA patients with a severe clinical form of synovitis characterised by the presence of ELS.

A systematic review on the role of eicosanoid pathways in rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis is characterized by the production of eicosanoids, cytokines, adhesion molecules, infiltration of T and B lymphocytes in the synovium and oxygen reduction accompanied by the cartilage degradation. Eicosanoids are responsible for the progressive destruction of cartilage and bone, however neither steroids, nor the non steroidal anti-inflammatory drugs (NSAIDs), cannot slow down cartilage and bone destruction providing only symptomatic improvement. The current rheumatoid arthritis treatment options include mainly the use of disease-modifying anti-rheumatic drugs, the corticosteroids, the NSAIDs and biological agents.

METHODS

PubMed, Cochrane, and Embase electronic database were used as the main sources for extracting several articles, reviews, original papers in English for further review and analysis on the implication of arachidonic acid metabolites with rheumatoid arthritis and different strategies of targeting arachidonic acid metabolites, different enzymes or receptors for improving the treatment of rheumatoid arthritis patients.

RESULTS

We first focused on the role of individual prostaglandins and leukotrienes, in the inflammatory process of arthritis, concluding with an outline of the current clinical situation of rheumatoid arthritis and novel treatment strategies targeting the arachidonic acid pathway.

CONCLUSIONS

Extended research is necessary for the development of these novel compounds targeting the eicosanoid pathway, by increasing the levels of anti-inflammatory eicosanoids (PGD₂,15dPGJ₂), by inhibiting the production of pro-inflammatory eicosanoids (PGE₂, LTB₄, PGI₂) involved in rheumatoid arthritis or also by developing dual compounds displaying both the COX-2 inhibitor/TP antagonist activity within a single compound.

Mast cells in rheumatoid arthritis: friends or foes?

Mast cells are tissue-resident cells of the innate immunity, implicated in the pathogenesis of many autoimmune diseases, including rheumatoid arthritis (RA). They are present in synovia and their activation has been linked to the potentiation of inflammation in the course of RA. However, recent investigations questioned the role of mast cells in arthritis. In particular, animal models generated conflicting results, so that many of their pro-inflammatory, i.e. pro-arthritogenic functions, even though supported by robust experimental evidence, have been labelled as redundant. At the same time, a growing body of evidence suggests that mast cells can act as tunable immunomodulatory cells. These characteristics, not yet fully understood in the context of RA, could partially explain the inconsistent results obtained with experimental models, which do not account for the pro- and anti-inflammatory functions exerted in more chronic heterogeneous conditions such as RA. Here we present an overview of the current knowledge on mast cell involvement in RA, including the intriguing hypothesis of mast cells acting as subtle immunomodulatory cells and the emerging concept of synovial mast cells as potential biomarkers for patient stratification.

Are Mast Cells MASTers in Cancer?

Prolonged low-grade inflammation or smoldering inflammation is a hallmark of cancer. Mast cells form a heterogeneous population of immune cells with differences in their ultra-structure, morphology, mediator content, and surface receptors. Mast cells are widely distributed throughout all tissues and are stromal components of the inflammatory microenvironment that modulates tumor initiation and development. Although canonically associated with allergic disorders, mast cells are a major source of pro-tumorigenic (e.g., angiogenic and lymphangiogenic factors) and antitumorigenic molecules (e.g., TNF-α and IL-9), depending on the milieu. In certain neoplasias (e.g., gastric, thyroid and Hodgkin's lymphoma) mast cells play a pro-tumorigenic role, in others (e.g., breast cancer) a protective role, whereas in yet others they are apparently innocent bystanders. These seemingly conflicting results suggest that the role of mast cells and their mediators could be cancer specific. The microlocalization (e.g., peritumoral vs intratumoral) of mast cells is another important aspect in the initiation/progression of solid and hematologic tumors. Increasing evidence in certain experimental models indicates that targeting mast cells and/or their mediators represent a potential therapeutic target in cancer. Thus, mast cells deserve focused consideration also as therapeutic targets in different types of tumors. There are many unanswered questions that should be addressed before we understand whether mast cells are an ally, adversary, or innocent bystanders in human cancers.

Dietary Supplements for Arthritis and other Inflammatory Conditions: Key Role of Mast Cells and Benefit of Combining Anti-Inflammatory and Proteoglycan Products

Arthritis is estimated to affect over 30% of all adults and all the available drugs add considerable morbidity and mortality of their own. A recent therapeutic approach targets the mast cells that are currently considered critical in a variety of inflammatory diseases, especially arthritis. Mast cells could be activated by many immune and neural triggers, as well as by many food substances and drugs leading to secretion of numerous vasoactive and inflammatory molecules. Recent studies have shown that mast cells can be inhibited by certain naturally occurring flavonoids, such as quercetin, and the sulfated proteoglycan chondroitin sulfate. Glucosamine and chondroitin are present in many dietary supplements, but neither the source nor the purity of the active substances is listed; moreover, these formulations do not permit sufficient absorption, due to the high molecular weight and negative charge. Moreover, a common source of chondroitin sulfate is cow trachea with the risk of spongioform encephalopathy (mad cow disease). A new series of dietary supplements (Algonot-Plus®) are based on published scientific evidence and combine quercetin, glucosamine sulfate and chondroitin sulfate of high purity in formulations that include kernel olive oil to increase absorption of the inhibitory substances.

Ability of Interleukin-33- and Immune Complex-Triggered Activation of Human Mast Cells to Down-Regulate Monocyte-Mediated Immune Responses

OBJECTIVE

Mast cells have been implicated in the pathogenesis of rheumatoid arthritis (RA). In particular, their activation by interleukin-33 (IL-33) has been linked to the development of arthritis in animal models. The aim of this study was to evaluate the functional responses of human mast cells to IL-33 in the context of RA.

METHODS

Human mast cells were stimulated with IL-33 combined with plate-bound IgG or IgG anti-citrullinated protein antibodies (ACPAs), and their effects on monocyte activation were evaluated. Cellular interactions of mast cells in RA synovium were assessed by immunofluorescence analysis, and the expression of messenger RNA (mRNA) for mast cell-specific genes was evaluated in synovial biopsy tissue from patients with early RA who were naive to treatment with disease-modifying antirheumatic drugs.

RESULTS

IL-33 induced the up-regulation of Fcγ receptor type IIa and enhanced the activation of mast cells by IgG, including IgG ACPAs, as indicated by the production of CXCL8/IL-8. Intriguingly, mast cell activation triggered with IL-33 and IgG led to the release of mediators such as histamine and IL-10, which inhibited monocyte activation. Synovial mast cells were found in contact with CD14+ monocyte/macrophages. Finally, mRNA levels of mast cell-specific genes were inversely associated with disease severity, and IL-33 mRNA levels showed an inverse correlation with the levels of proinflammatory markers.

CONCLUSION

When human mast cells are activated by IL-33, an immunomodulatory phenotype develops, with human mast cells gaining the ability to suppress monocyte activation via the release of IL-10 and histamine. These findings, together with the presence of synovial mast cell-monocyte interactions and the inverse association between the expression of mast cell genes at the synovial level and disease activity, suggest that these newly described mast cell-mediated inhibitory pathways might have a functional relevance in the pathogenesis of RA.

Lipid droplets in activated mast cells - a significant source of triglyceride-derived arachidonic acid for eicosanoid production

Mast cells are potent effectors of immune reactions and key players in various inflammatory diseases such as atherosclerosis, asthma, and rheumatoid arthritis. The cellular defense response of mast cells represents a unique and powerful system, where external signals can trigger cell activation resulting in a stimulus-specific and highly coordinated release of a plethora of bioactive mediators. The arsenal of mediators encompasses preformed molecules stored in cytoplasmic secretory granules, as well as newly synthesized proteinaceous and lipid mediators. The release of mediators occurs in strict chronological order and requires proper coordination between the endomembrane system and various enzymatic machineries. For the generation of lipid mediators, cytoplasmic lipid droplets have been shown to function as a major intracellular pool of arachidonic acid, the precursor for eicosanoid biosynthesis. Recent studies have revealed that not only phospholipids in mast cell membranes, but also triglycerides in mast cell lipid droplets are a substrate source for eicosanoid formation. The present review summarizes current knowledge about mast cell lipid droplet biology, and discusses expansions and challenges of traditional mechanistic models for eicosanoid production.

A myofibroblast-mast cell-neuropeptide axis of fibrosis in post-traumatic joint contractures: an in vitro analysis of mechanistic components

Previous studies have implicated a myofibroblast-mast cell-neuropeptide axis of fibrosis in pathologic joint capsules from post-traumatic contractures. The hypothesis to be tested is that joint capsule cells (JC) from human elbows with post-traumatic contractures and their interactions with mast cells (MC) and neuropeptides in the microenvironment underlie the pathogenesis of contractures. The hypothesis was tested using an in vitro collagen gel contraction model. The JC were isolated from human elbow capsules and mixed with neutralized PureCol collagen I. The gels were treated in various ways, including addition of MC (HMC-1), the neuropeptide substance P (SP), an NK1 receptor (SP receptor) antagonist RP67580 and the mast cell stabilizer ketotifen fumarate (KF). The collagen gels were released from the wells and gel size (contraction) was measured optically at multiple time points. The JC contracted collagen gels in a dose-dependent manner. This was enhanced in the presence of MC and increased further with SP. Increasing concentrations of the SP receptor antagonist, RP67580 or the mast cell stabilizer, KF decreased the magnitude of contraction. These observations identify putative mechanistic components of a myofibroblast-mast cell-neuropeptide axis of fibrosis in the joint capsules in post-traumatic contractures and potential prophylactic or therapeutic interventions.

Impact of Mast Cells in Rejection of Allografts

Mast cells in the tissue are located close to nerves in and around the small vessels where they orchestrate important immune response after antigen recognition through Toll-like receptors. Mast cells can activate T and B lymphocytes and dendritic cells and have been postulated to act directly within tissue allografts and/or to induce indirect effects via inflammatory mediator release, therefore they have been shown to play an indispensable role in allograft tolerance. Major limitation in the success of transplantation is the immune response of the recipient to the donor tissue. The failure of tissue grafting is caused by an inflammatory reaction called rejection. Mast cells play a role during immune response and are elicited with transplanted allograft and also may exhibit their immune-regulatory effects directly through secretion of modulatory cytokines and activation of metabolic pathways. However, the role of mast cells in transplantation is poorly understood. The most severe rejection episodes have been found in patients with an increased number of mast cells. Mast cell mediators which can activate latent forms of TGF-β or increase angiotensin II levels are capable of inducing fibrosis through various mechanisms, activating fibroblasts and inducing collagen synthesis. Mast cells are also implicated in regulatory T-cell functions and are required to sustain peripheral tolerance via Treg, therefore there is an interaction between mast cells and Treg cells. Treg create IL-9 in enhancing mast cell growth and Chemotaxis, suggesting that Treg and mast cells form a functional unit that mediates graft tolerance. In this study we concentrate our attention on the role of mast cells in rejection of allografts and try to understand the role of mast cell-related immune mechanisms in organ transplantation.

Activation of human synovial mast cells from rheumatoid arthritis or osteoarthritis patients in response to aggregated IgG through Fcγ receptor I and Fcγ receptor II

OBJECTIVE

Substantial evidence suggests that human synovial mast cells (MCs) are involved in the pathogenesis of rheumatoid arthritis (RA). A plausible pathway for the activation of synovial MCs is through IgG receptors, given the prevalence of circulating IgG isotype autoantibodies and synovial immune complexes in patients with RA. However, IgG receptor expression on human synovial MCs remains uncharacterized. The aim of this study was to identify which IgG receptor(s) on synovial MCs are responsible for MC activation in immune complexes.

METHODS

Synovial tissue specimens were obtained from patients with RA or patients with osteoarthritis (OA) who were undergoing joint replacement surgery, and synovial MCs were enzymatically dispersed. Cultured synovium-derived MCs were generated by culturing synovial cells with stem cell factor, and receptor expression was analyzed using fluorescence-activated cell sorting. Mediators released from MCs were measured using enzyme immunoassays or enzyme-linked immunosorbent assays.

RESULTS

Primary synovial MCs and cultured synovium-derived MCs obtained from both patients with RA and patients with OA expressed Fcε receptor I (FcεRI), FcγRI, and FcγRII but not FcγRIII. Cultured synovium-derived MCs induced degranulation and the production of prostaglandin D2 and tumor necrosis factor α (TNFα) through FcγRI. The aggregation of FcγRII caused histamine release from cultured MCs but not from primary MCs. Histamine release induced by aggregated IgG was significantly inhibited by neutralizing anti-FcγRI monoclonal antibody and anti-FcγRII monoclonal antibody.

CONCLUSION

With regard to the FcR expression profile, synovial MCs from patients with RA and patients with OA were similar. FcγRI was responsible for producing abundant TNFα from synovial MCs in response to aggregated IgG. Immune complexes may activate synovial MCs through FcγRI and FcγRII.

Prostaglandins and rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, autoimmune, and complex inflammatory disease leading to bone and cartilage destruction, whose cause remains obscure. Accumulation of genetic susceptibility, environmental factors, and dysregulated immune responses are necessary for mounting this self-reacting disease. Inflamed joints are infiltrated by a heterogeneous population of cellular and soluble mediators of the immune system, such as T cells, B cells, macrophages, cytokines, and prostaglandins (PGs). Prostaglandins are lipid inflammatory mediators derived from the arachidonic acid by multienzymatic reactions. They both sustain homeostatic mechanisms and mediate pathogenic processes, including the inflammatory reaction. They play both beneficial and harmful roles during inflammation, according to their site of action and the etiology of the inflammatory response. With respect to the role of PGs in inflammation, they can be effective mediators in the pathophysiology of RA. Thus the use of agonists or antagonists of PG receptors may be considered as a new therapeutic protocol in RA. In this paper, we try to elucidate the role of PGs in the immunopathology of RA.

Inhibition of interleukin-1beta-induced matrix metalloproteinases 1 and 13 production in human osteoarthritic chondrocytes by prostaglandin D2

OBJECTIVE

To investigate the effects of prostaglandin D2 (PGD2) on interleukin-1beta (IL-1beta)-induced matrix metalloproteinase 1 (MMP-1) and MMP-13 expression in human chondrocytes and the signaling pathways involved in these effects.

METHODS

Chondrocytes were stimulated with IL-1 in the presence or absence of PGD2, and expression of MMP-1 and MMP-13 proteins was evaluated by enzyme-linked immunosorbent assay. Messenger RNA (mRNA) expression and promoter activity were analyzed by real-time reverse transcription-polymerase chain reaction and transient transfections, respectively. The role of the PGD2 receptors D prostanoid receptor 1 (DP1) and chemoattractant receptor-like molecule expressed on Th2 cells (CRTH2) was evaluated using specific agonists and antibody-blocking experiments. The contribution of the cAMP/protein kinase A (PKA) pathway was determined using cAMP-elevating agents and PKA inhibitors.

RESULTS

PGD2 decreased in a dose-dependent manner IL-1-induced MMP-1 and MMP-13 protein and mRNA expression as well as their promoter activation. DP1 and CRTH2 were expressed and functional in chondrocytes. The effect of PGD2 was mimicked by BW245C, a selective agonist of DP1, but not by 13,14-dihydro-15-keto-PGD2, a selective agonist of CRTH2. Furthermore, treatment with an anti-DP1 antibody reversed the effect of PGD2, indicating that the inhibitory effect of PGD2 is mediated by DP1. The cAMP-elevating agents 8-Br-cAMP and forskolin suppressed IL-1-induced MMP-1 and MMP-13 expression, and the PKA inhibitors KT5720 and H89 reversed the inhibitory effect of PGD2, suggesting that the effect of PGD2 is mediated by the cAMP/PKA pathway.

CONCLUSION

PGD2 inhibits IL-1-induced production of MMP-1 and MMP-13 by chondrocytes through the DP1/cAMP/PKA signaling pathway. These data also suggest that modulation of PGD2 levels in the joint may have therapeutic potential in the prevention of cartilage degradation.

Mast cell activation is characterized by upregulation of a functional anaphylatoxin C5a receptor

BACKGROUND

Mast cells (MC) are key effector cells of allergic diseases and resistance to helminthic parasites and induce or amplify diverse innate and adaptive immune responses. The signals controlling MC mobilization during inflammation are not fully understood.

RESULTS

Since anaphylatoxins are attractive candidates as MC chemoattractants, we investigated expression and function of anaphylatoxin receptors in murine MC. Precursor cell-derived MC cultured with IL-3 in the presence or absence of SCF did not express significant amounts of surface C5a receptor (C5aR) or C3a receptor (C3aR). MC required approximately 4 h of stimulation with Ag (DNP-albumin, following preincubation with IgE anti-DNP), ionomycin, or PMA to enable a strong chemotactic response towards C5a, paralleled by a distinct C5aR upregulation. Likewise, C5a induced intracellular calcium fluxes solely in activated MC. In contrast, C3a proved to be a weak MC chemotaxin and unable to increase intracellular calcium. Primary peritoneal MC did not express detectable amounts of anaphylatoxin receptors, however, similar to precursor cell-derived MC, stimulation with Ag or ionomycin for 4 h induced a prominent surface expression of C5aR whereas C3aR remained undetectable.

CONCLUSION

Collectively, our results suggest that Ag-dependent as well as -independent activation induces an inflammatory MC phenotype which is distinguished by neoexpression of a functional C5aR as a novel effector mechanism in MC-mediated pathogenesis.

Age alters the ability of substance P to sensitize joint nociceptors in guinea pigs

Pain perception is altered during senescence and it is thought that this could in part be due to changes in peripheral pain sensing processes. The present study examined the effect of substance P (SP) (10(-10)-10(-8) mol; 0.1 mL bolus close intraarterial) on knee joint afferent mechanosensitivity in young (2- to 5-mo-old) and aged (17- to 36-mo-old) Dunkin-Hartley guinea pigs. Single unit electrophysiological recordings were made from knee joint primary afferent nerves in response to normal (nonnoxious) and painful (noxious) rotation of the joint. In young and old animals, local application of SP had a sensitizing effect on joint afferents in response to movements made in the normal working range of the knee. With noxious hyper-rotation of the joint, SP was able to increase afferent firing rate in young but not in old animals. These data demonstrate a lack of SP-mediated sensitization of joint nociceptors during senescence and suggest a peripheral deficiency in joint nociception with respect to age.

Mast cells in the pathogenesis of rheumatic diseases and as potential targets for anti-rheumatic therapy

Increasing evidence suggests that mast cells (MCs), in addition to acute allergic reactions, are involved in the pathogenesis of chronic inflammatory diseases and in particular in rheumatoid arthritis (RA). MCs reside in connective tissues and in synovial tissue of joints. They produce an array of proinflammatory mediators, tissue destructive proteases, and cytokines, most prominently tumor necrosis factor-alpha, which is one of the key cytokines in the pathogenesis of RA. MCs may also participate in the development of secondary or amyloid A amyloidosis, as the partial degradation of the serum amyloid A (SAA) protein by MCs leads to the generation of a highly amyloidogenic N-terminal fragment of SAA. MCs may contribute to the pathogenesis of connective tissue diseases, scleroderma, vasculitic syndromes, and systemic lupus erythematosus, although the data available are limited. Inhibition of the most important growth factor receptor of human MCs, c-Kit, by the selective tyrosine kinase inhibitor imatinib mesylate, induces apoptosis of synovial tissue MCs. As MCs are long-lived cells, induction of their apoptosis could be a feasible approach to inhibit their functions. Preliminary findings suggest that a drug that inhibits c-Kit could have anti-rheumatic activity in the treatment of patients with RA and spondyloarthropathies.

Synovial mast cells: role in acute and chronic arthritis

Mast cells reside in the normal synovium and increase strikingly in number in rheumatoid arthritis and other joint diseases. Given the broad spectrum of activity of this lineage, it has for decades been considered probable that mast cells are involved in the pathophysiology of synovitis. Recent work in murine arthritis has substantiated this suspicion, showing that mast cells can contribute importantly to the initiation of inflammatory arthritis. However, the role of the greatly expanded population of synovial mast cells in established arthritis remains unknown. Here we review the current understanding of mast cell function in acute arthritis and consider the potentially important influence of this cell on key processes within the chronically inflamed synovium, including leukocyte recruitment and activation, fibroblast proliferation, angiogenesis, matrix remodeling, and injury to collagen and bone. We also consider recent evidence supporting an immunomodulatory or anti-inflammatory role for mast cells as well as pharmacologic approaches to the mast cell as a therapeutic target in inflammatory arthritis.

The role of mast cells in atopy: what can we learn from canine models? A thorough review of the biology of mast cells in canine and human systems

Mast cell research has largely focused on the role of these cells in the early phase of allergic reactions. However, their involvement may well extend beyond this stage, and even reach across nonallergic conditions. Mast cells from different sources have helped advance our knowledge of their biology. Although in vitro and in vivo research in this area has mainly focused on humans, such studies are limited by the extent to which cells from certain human tissues and/or human patients can be collected or studied. While rodents also provide valuable models with which to further our understanding of the behaviour of mast cells and their contribution to allergy, reported differences between human and murine mast cells, and, in some instances, the limitations of in vivo rodent models of mast cell-mediated allergic conditions, preclude their use. In this review, we introduce a relatively unknown mast cell population, that of the dog. Canine mast cells display many phenotypic and functional similarities with their human counterparts, and dogs develop spontaneous and induced allergic diseases that share clinical and pathophysiological features with the human condition. Therefore, the use of canine cells can shed light on the general role of mast cells, particularly in relation to allergic diseases given the potential of in vivo dog models within this field. Here we provide a detailed review of the data reported from in vitro and in vivo studies of canine mast cells, and compare them with results obtained in human systems. We also highlight direct evidence of the mast cell contribution to canine atopy. We conclude that the dog offers useful in vitro and in vivo models in which to investigate mast cell behaviour, and that its use should be considered when undertaking studies aimed either at elucidating the role of mast cells in health and disease, or at prescreening novel therapies prior to entry into man.

Human umbilical cord blood-derived mast cells: a unique model for the study of neuro-immuno-endocrine interactions

Findings obtained using animal models have often failed to reflect the processes involved in human disease. Moreover, human cultured cells do not necessarily function as their actual tissue counterparts. Therefore, there is great demand for sources of human progenitor cells that may be directed to acquire specific tissue characteristics and be available in sufficient quantities to carry out functional and pharmacological studies. Acase in point is the mast cell, well known for its involvement in allergic reactions, but also implicated in inflammatory diseases. Mast cells can be activated by allergens, anaphylatoxins, immunoglobulin-free light chains, superantigens, neuropeptides, and cytokines, leading to selective release of mediators. These could be involved in many inflammatory diseases, such as asthma and atopic dermatitis, which worsen by stress, through activation by local release of corticotropin-releasing hormone or related peptides. Umbilical cord blood and cord matrix-derived mast cell progenitors can be separated magnetically and grown in the presence of stem cell factor, interleukin-6, interleukin-4, and other cytokines to yield distinct mast cell populations. The recent use of live cell array, with its ability to study such interactions rapidly at the single-cell level, provides unique new opportunities for fast output screening of mast cell triggers and inhibitors.

The critical role of mast cells in allergy and inflammation

Mast cells are well known for their involvement in allergic and anaphylactic reactions, but recent findings implicate them in a variety of inflammatory diseases affecting different organs, including the heart, joints, lungs, and skin. In these cases, mast cells appear to be activated by triggers other than aggregation of their IgE receptors (FcepsilonRI), such as anaphylatoxins, immunoglobulin-free light chains, superantigens, neuropeptides, and cytokines leading to selective release of mediators without degranulation. These findings could explain inflammatory diseases, such as asthma, atopic dermatitis, coronary inflammation, and inflammatory arthritis, all of which worsen by stress. It is proposed that the pathogenesis of these diseases involve mast cell activation by local release of corticotropin-releasing hormone (CRH) or related peptides. Combination of CRH receptor antagonists and mast cell inhibitors may present novel therapeutic interventions.

Arthritis and pain. Neurogenic origin of joint pain

Arthritis pain affects millions of people worldwide yet we still have only a limited understanding of what makes our joints ache. This review examines the sensory innervation of diarthroidal joints and discusses the neurophysiological processes that lead to the generation of painful sensation. During inflammation, joint nerves become sensitized to mechanical stimuli through the actions of neuropeptides, eicosanoids, proteinase-activated receptors and ion channel ligands. The contribution of immunocytes to arthritis pain is also reviewed. Finally, the existence of an endogenous analgesic system in joints is considered and the reasons for its inability to control pain are postulated.

Distinct expression of mast cell tryptase and protease activated receptor-2 in synovia of rheumatoid arthritis and osteoarthritis

The objective of this study is to examine the differential expression of mast cell tryptase and its receptor, protease-activated receptor-2 (PAR-2), in the synovium and synovial fluid of patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Biochemical and immunohistochemical analyses were performed to determine whether the trypsin-like protease in the synovium is identical to mast cell tryptase. The effects of mast cell tryptase on the proliferation of synovial fibroblast-like cells (SFCs) and the release of IL-8 thereof were evaluated by the [3H]-thymidine incorporation and ELISA, respectively. The trypsin-like protease in the synovium of RA patients was identical to human mast cell tryptase, which was composed of two subunits: 33 and 34 kDa. The 33- and 34-kDa proteins are different glycosylated forms of the 31-kDa protein, which was unglycosylated. Mast cell tryptase activity in RA synovial fluid was significantly higher than that in OA synovial fluid, while their activities and expression in the synovium were similar. Expression of PAR-2 mRNA in the synovium was higher in RA than in OA. Mast cell tryptase containing the unglycosylated 31-kDa subunit was the predominant form in synovial fluid. RA patients had higher amounts of this subunit in their synovial fluid than OA patients. Mast cell tryptase and PAR-2 activating peptide stimulated the proliferation of SFCs and release of IL-8 from these cells. Mast cell tryptase secretion into RA synovial fluid is higher than OA synovial fluid. Mast cell tryptase in synovial fluid stimulates the proliferation of SFCs and the release of pro-inflammatory cytokines via PAR-2, which may contribute to exacerbation of synovitis in RA.

The role of joint nerves and mast cells in the alteration of vasoactive intestinal peptide (VIP) sensitivity during inflammation progression in rats

The present study examined the peripheral effects of vasoactive intestinal peptide (VIP) on rat knee joint blood flow during acute and chronic inflammation. The involvement of joint nerves and synovial mast cells on these effects was also investigated. Prior to blood flow assessment, animals were deeply anaesthetised with ethyl carbamate (urethane; 2 mg kg(-1) i.p.). Local application of VIP (10(-13)-10(-9) mol) onto the capsular surface of normal rat knee joints caused a dose-dependent increase in synovial perfusion with an ED50 of 1.2 x 10(-11) mol. The dilator effect of the peptide was transient with the maximal response occurring approximately 1 min after drug administration. VIP-induced vasodilatation was blocked by co-administration of the VIP receptor antagonist VIP(6-28) (10(-9) mol). The inhibitory effect of the antagonist was consistent across the entire VIP dose range (P=0.01). The vasoresponsiveness to VIP was significantly attenuated in acutely inflamed joints; however, surgical denervation of acutely inflamed knees re-established the vasodilator effect of the neuropeptide. Topical application of VIP to 1- and 3-week adjuvant monoarthritic knees produced a hyperaemic response, which was not significantly different from normal (P=0.06 and 0.73 for 1- and 3-week adjuvant treated joints, respectively). Stabilisation of synovial mast cells by disodium cromoglycate (cromolyn) pretreatment did not alter the vasoresponsiveness to VIP in acute or chronically inflamed joints. The vasodilatatory effect of VIP is lost during acute knee joint inflammation and this abrogated effect is neurally dependent. In the chronic phase of knee joint inflammation, VIP-mediated hyperaemia recovers to normal levels. Synovial mast cells do not influence the vasomotor effects of exogenously applied VIP in inflamed knee joints.

Simultaneous labeling of mast cell proteases and protease mRNAs at the bone-implant interface of aseptically loosened hip implants

Human mast cells (MC) exhibit two distinct phenotypes based on the protease content of their secretory granules. MC(TC) cells express tryptase, chymase, cathepsin G, and mast cell carboxypeptidase, while MC(T) cells express only tryptase. Both mast cell phenotypes were assessed near regions of osteolysis in uninfected failed joint implants by immunohistochemistry with antibodies to tryptase and chymase, and by in situ hybridization with anti-sense RNA probes for the respective mRNA molecules. Specimens from the interface membrane of 32 aseptically loosened total hip implants were studied, 28 of which had mast cells of the MC(TC) type. Most of these mast cells were aligned along the bone-prosthesis interface adjacent to loosened implants, suggesting involvement in the chronic inflammatory response that leads to bone resorption. Further ultrastructural evidence of mast cells in tissues from failed joint interface membranes was shown by transmission electron microscopy, and detection by staining after magnetic activated cell sorting. The presence of MC at the periprosthetic interface of eroded bone suggests MC degranulation and activity are associated with osteolysis in failed joint prostheses.

Cheongyeolsaseuptang inhibits production of TNF-alpha, IL-6 and IL-8 as well as NF-kappa B activation in human mast cells

Traditional Korean medicine, Cheongyeolsaseuptang (CYSST) has been widely applied as a treatment of rheumatoid arthritis (RA) in Korea. However, its effect in experimental models remains unknown. Recent reports suggest that in patients with RA, synovial mast cells increase in number and show signs of activation and production of cytokines. In this study, we investigated the effect of CYSST on production of cytokines by activated human mast cell line, HMC-1. When CYSST (1mg/ml) was added, the production of tumor necrosis factor-alpha, interleukin (IL)-6, and IL-8 was significantly inhibited about 37, 33.6, and 48%, respectively on phorbol 12-myristate 13-acetate (PMA) plus calcium ionophore A23187-stimulated HMC-1 cells. In addition, CYSST inhibited PMA plus A23187-induced activation of nuclear factor-kappaB. These findings may help understanding the mechanism of action of this medicine leading to control activated mast cells on inflammatory condition like RA.

Mast cells and mast cell mediators as targets of dietary supplements

OBJECTIVE

To review the increasing amount of data that support or dispel the use of dietary supplements in the treatment of inflammatory conditions that involve mast cells, such as allergies, arthritis, and chronic pelvic pain syndrome.

DATA SOURCES

A search was conducted in MEDLINE for natural substances, dietary supplements, flavonoids, and proteoglycans for their in vitro or in vivo effects on allergic and inflammatory conditions.

STUDY SELECTION

Studies were selected for inclusion because of the impact factor of the journal, the definitive nature of the findings, the soundness of the study design, and the expert opinion of the authors.

RESULTS

Dietary supplements include a large group of products, such as vitamins, minerals, plant, or animal extracts, as well as herbal preparations that are often called medicinal herbs. Many of the available dietary supplements contain a multitude of ingredients, the source and/or purity of which is seldom disclosed; some of these may have biologic effects of their own or may interact with other supplements or drugs, often leading to adverse effects. The most well-documented evidence published to date is on the inhibitory action of natural compounds, especially flavonoids, on mast cells and allergic symptoms. Some flavonoids have weak inhibitory activity, whereas others may have no benefit or may be detrimental. Sulfated proteoglycans could provide synergistic action but require formulations with increased absorption.

CONCLUSIONS

Combining the most active flavonoids with proteoglycans could be helpful in atopic and inflammatory conditions. However, a complete list of active ingredients and their source, purity, and exact concentration should be a requirement for nutraceuticals to standardize, compare, and promote their safe use.

Critical role of mast cells in inflammatory diseases and the effect of acute stress

Mast cells are not only necessary for allergic reactions, but recent findings indicate that they are also involved in a variety of neuroinflammatory diseases, especially those worsened by stress. In these cases, mast cells appear to be activated through their Fc receptors by immunoglobulins other than IgE, as well as by anaphylatoxins, neuropeptides and cytokines to secrete mediators selectively without overt degranulation. These facts can help us better understand a variety of sterile inflammatory conditions, such as multiple sclerosis (MS), migraines, inflammatory arthritis, atopic dermatitis, coronary inflammation, interstitial cystitis and irritable bowel syndrome, in which mast cells are activated without allergic degranulation.

The Oriental Medicine 'Cool-Cool (Cool-X-A)' Inhibits Inflammatory Cytokine Production and Migration in Mast Cells

Plant medications have been applied to treat pains from various types of arthritis in Korea. Rheumatoid arthritis (RA) is well known to be a chronic autoimmune/inflammatory disease that leads to progressive joint damage and cartilage destruction. Accumulation and activation of mast cells have been demonstrated in rheumatoid synovial tissue. Because infiltrated mast cells and their mediators may contribute to the initiation and progression of the inflammatory process and matrix degradation of RA, we tested the inhibitory effects of "Cool-Cool" (CC, Cool-X-A), an Oriental medication, on the production and migration of major inflammatory cytokines in mast cells. CC was treated in vitro before activation of human mast cell line (HMC-1) with phorbol 12-myristate 13-acetate, and the cytotoxicity of CC was assessed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide assay. CC had no cytotoxic effects on HMC-1 cell viability. The inhibitory effects on cytokine production were monitored by enzyme-linked immunosorbent assay and reverse transcriptase-polymerase chain reaction (RT-PCR). CC inhibited not only the secretion but also the expression of TNF-alpha and IL-8 in HMC-1 cells. CC also suppressed migration of mast cells induced by stem cell factor. These findings may help in understanding the mechanism of action of this herbal medication, leading to the control of mast cells in inflammatory conditions like RA.

Mast cell deficient W/W(v) mice lack stress-induced increase in serum IL-6 levels, as well as in peripheral CRH and vascular permeability, a model of rheumatoid arthritis

Corticotropin releasing hormone (CRH) and interleukin-6 (IL-6) are implicated in inflammatory diseases triggered by stress. Acute restraint stress increases serum IL-6 in the blood, but its source is not known. Our current study was carried out in order to determine the contribution of mast cells to stress-induced IL-6 release and to investigate skin CRH and vascular permeability in mice. W/W(v) mast cell deficient and their wild type control +/+ mice were stressed in a plexiglass restraint chamber for 60 or 120 min. Serum corticosterone and IL-6 levels were measured. Other mice were injected with (99)Tchnetium gluceptate ((99)Tc) and its extravastion, indicating vascular permeability, was determined along with CRH levels in the skin and knee joints. Acute stress increased serum IL-6 in mice, but was greatly inhibited in W/W(v) mast cell deficient mice. Vascular permeability to (99)Tc, as well as local CRH levels, were also increased by stress, but not in W/W(v) mice. Findings from our current study suggest a link between mast cells and stress-related skin and joint inflammation and may explain initial events in psoriatic and rheumatoid arthritis.

Mast cells in Wallerian degeneration: morphologic and ultrastructural changes

The morphologic and ultrastructural changes of mast cells were followed in degenerating distal and regenerating proximal stumps of frog brachial nerve during Wallerian degeneration. Quantitative analysis included determination of both number and size of mast cells. The mast cell response to injury consisted of an early and a late phase. In the early phase, there was an increase in mast cell numbers in the proximal site of the lesion and a release of Alcian blue material consistent with mediator release. This phase of mast cell activation may be related, through the secretion of biogenic agents such as heparin and histamine, to the increase of endoneurial vessel size and vascular permeability, providing access for macrophages and mast cell precursors. The later phase, which peaked at 40 days after transection in the degenerating distal stump, consisted in the degranulation of the mast cells. These mast cells, closely associated with macrophages and degenerating Schwann cells, released secretory granules into the endoneurial microenvironment. These degranulating mast cells, through the released acid hydrolases, may contribute along with macrophages and Schwann cells, to the degradation of myelin debris. At the same time, mast cells appeared filled with granular content in the regenerating proximal segment. Therefore, we suggest that mast cells in peripheral nerves may play an important role in nerve degenerating and regenerating mechanisms through the secretion of diffusible molecules.

Treatment of mastocytosis: pharmacologic basis and current concepts

Mastocytosis is a rare, heterogeneous disorder characterized by a marked increase in mast cell density in various tissues. Mast cells from different human tissues are heterogeneous. So far, there is no cure for systemic mastocytosis. Conventional therapy is based on agents that antagonize mediators released from mast cells, drugs that inhibit the release of mediators and agents that modulate mast cell proliferation. This pharmacologic approach is satisfactory in the majority of patients with indolent mastocytosis. At the beginning of the new millennium, the therapy of severe forms of aggressive mastocytosis remains a challenge for students of this intriguing disorder.

The activation of synovial mast cells: modulation of histamine release by tryptase and chymase and their inhibitors

Mast cells have been implicated as having pivotal roles in arthritis, but little is known of the processes leading to the activation of synovial mast cells or their potential for pharmacological control. We have investigated the ability of tryptase and chymase, and inhibitors of these major mast cell proteases to modulate the activation of mast cells from human synovial tissue. The tryptase inhibitor drug N-(1-hydroxy-2-naphthoyl)-L-arginyl-L-prolinamide hydrochloride (APC366) inhibited immunoglobulin E (IgE)-dependent histamine release in a dose-dependent manner, with about 70% inhibition being achieved at a dose of 300 microM. Histamine release stimulated by calcium ionophore A23187 was also inhibited by this compound. The chymase inhibitor chymostatin inhibited IgE-dependent histamine release by approximately 60% at 1 microg/ml. Tryptase at concentrations of 3.0 microg/ml and greater stimulated histamine release from synovial cells, which was dependent on catalytic activity, whereas chymase had little effect on these cells. The activation of mast cells by tryptase may represent an amplification process in the synovium. The mast cell stabilising properties of inhibitors of tryptase and chymase could be of therapeutic value in arthritis.

Tumor necrosis factor alpha promotes the expression of stem cell factor in synovial fibroblasts and their capacity to induce mast cell chemotaxis

OBJECTIVE

To investigate the expression of the stroma cell product stem cell factor (SCF) in synovial fibroblasts (SFB) in patients with rheumatoid arthritis (RA) and osteoarthritis (OA), and to analyze the capacity of SFB to induce mast cell (MC) chemotaxis.

METHODS

Synovial tissue was obtained from 29 patients with RA and 25 patients with OA. Tissue was dispersed by enzymatic digestion using collagenase. SFB were grown in serial passage and exposed to tumor necrosis factor alpha (TNFalpha) or control medium. Expression of SCF in cultured SFB was analyzed by reverse transcription-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), and immunostaining. The ability of SFB (supernatants) to induce MC migration was analyzed using a double-chamber chemotaxis assay and the human mast cell line HMC-1. In situ expression of SCF in synovial tissue from patients with RA (n = 6) and OA (n = 6) was examined by double immunohistochemistry using antibodies against SCF and the fibroblast-specific antibody AS02.

RESULTS

In both RA and OA, cultured SFB were found to express SCF messenger RNA, as assessed by RT-PCR. In addition, the SCF protein was detectable in cell lysates and supernatants of SFB by ELISA. Incubation of SFB with TNFalpha resulted in an increased expression and release of SCF. Recombinant human SCF (rHuSCF) and SFB supernatants induced significant migration of HMC-1 cells above control levels. In addition, exposure of SFB to TNFalpha led to an increased migration of HMC-1, and a blocking anti-SCF antibody inhibited the rHuSCF- and SFB-induced migration of HMC-1. In situ double immunostaining revealed expression of SCF in AS02-positive SFB in the synovium of patients with RA.

CONCLUSION

Our results show that SFB (in RA and OA) express SCF and induce MC chemotaxis. Furthermore, TNFalpha was found to augment SCF expression in SFB. It is hypothesized that these cellular interactions play an important role in MC accumulation and related events in RA.

Synovial tissue analysis in rheumatoid arthritis

In rheumatoid arthritis, synovial tissue is easily accessible for systematic analysis. Blind needle biopsy is a simple and safe procedure, but is restricted to smaller tissue samples. Arthroscopic biopsy is also safe but is more complicated as it allows access to most sites in the joint and provides adequate tissue for extensive laboratory investigations. Synovial tissue analysis has been successfully applied to studies of disease mechanisms, response to treatment and prognosis. The immuno-histological features in synovial tissue have consistently reflected disease status. Synovial tissue analysis has been particularly informative in the study of novel therapeutic agents.

Tryptase-chymase double-positive human mast cells express the eotaxin receptor CCR3 and are attracted by CCR3-binding chemokines

Eosinophils, basophils, and Th2 cells express the chemokine receptor CCR3, which binds eotaxin, RANTES, and some other chemokines. Using immunohistochemistry and flow cytometry, we demonstrate that CCR3 is also expressed by a variable proportion of human mast cells in gut, skin, and lung tissue. By contrast, with the same anti-CCR3 antibody (B711), CCR3 was poorly if at all detectable on human Th2 cells in vitro and in vivo. Eotaxin neither induced histamine release from purified human mast cells nor increased anti-IgE-stimulated histamine secretion. However, both eotaxin and RANTES elicited mast cell migration in vitro with a similar efficacy. High percentages of CCR3-expressing mast cells were present in the skin and in the intestinal submucosa; much lower percentages were found in the intestinal mucosa and in lung interstitium. Double immunostaining with anti-CCR3 and anti-chymase antibody showed that the vast majority of CCR3-expressing mast cells in the various tissues examined were tryptase-chymase double-positive. Therefore, tryptase-chymase double-positive mast cells express CCR3 and are attracted by CCR3-binding chemokines, eotaxin, and RANTES. Our findings indicate that these chemokines may play an important role in the differentiation and/or migration of this mast cell subset in connective tissues, as well as in sites of allergic inflammation.

Stem Cell Factor Is Localized in, Released from, and Cleaved by Human Mast Cells

Stem cell factor (SCF) is the most important cytokine regulating human mast cell growth and functions. The immunogold technique showed SCF in the secretory granules of skin mast cells and in lung parenchymal mast cells (HLMC). Immunoreactive SCF (iSCF) was detected in cell lysates of HLMC, but not in basophils; iSCF and histamine were detected in supernatants of HLMC 3 min after challenge with anti-FcεRI or anti-IgE, and iSCF in supernatants rapidly declined after 30 min, whereas histamine remained unchanged for 120 min. HPLC and electrospray mass spectrometry (ES/MS) analysis of recombinant human SCF1–166 (18,656.9 ± 0.9 Da) treated with chymase showed a polypeptide of 17,977.1 ± 0.6 Da and a minor component of 697.4 ± 0.1 Da generated by specific cleavage at Phe159. SCF1–166 and SCF1–159 similarly activated HLMC, potentiated anti-IgE-induced activation of these cells, and stimulated HLMC chemotaxis. SCF159–166 had no effect on mast cells. Western blot analysis of supernatants of anti-IgE-activated HLMC incubated with recombinant human SCF1–166 showed that SCF1–166 was rapidly cleaved to SCF1–159 and SCF1–144. Experiments with supernatants of anti-IgE-activated HLMC incubated with SCF1–166 yielded similar results. In conclusion, SCF is stored in mast cell secretory granules and is immunologically released by human mast cells. SCF1–166 is rapidly and specifically cleaved to SCF1–159 by chymase, which retains its biological effect on mast cells. SCF is also cleaved by other proteases to several SCF species whose possible biological activities remain to be established.

The anti-IgE/anti-FcepsilonRIalpha autoantibody network in allergic and autoimmune diseases

Basophil granulocytes and tissue mast cells and their mediators play a role in the pathogenesis of several immune and inflammatory disorders. Human basophils and mast cells (FcepsilonRI+ cells) can be activated through immunological interaction with the IgE-FcepsilonRI network. FcepsilonRI+ cells can be triggered by cross-linking between the Fab portions of IgE and multivalent antigens (direct anaphylaxis). 'Reverse type' anaphylaxis can occur through three distinct mechanisms: antibodies against the Fcepsilon portion of IgE (anti-IgE), antibodies against epitopes of the alpha chain of FcepsilonRI (anti-FcepsilonRIalpha) and anti-IgG acting on IgG-IgE complexes bound to FcepsilonRI. Anti-IgE autoantibodies are occasionally present even in normal donors and more frequently in a variety of allergic (chronic urticaria, atopic dermatitis and bronchial asthma) and autoimmune disorders (rheumatoid arthritis, lupus erythematosus and systemic sclerosis). IgG anti-IgE from a small percentage of patients induces the release of mediators from human FcepsilonRI+ cells. Some of the anti-IgE autoantibodies present in allergic patients are non-anaphylactogenic, thus representing a possible protective mechanism preventing the association of IgE with FcepsilonRI. Anti-FcepsilonRIalpha autoantibodies also occur in a significant percentage of patients of chronic urticaria and probably non-allergic asthma and some autoimmune diseases. Although anti-IgE and anti-FcepsilonRIalpha autoantibodies, present in a percentage of patients with immune disorders, are relevant to the pathogenesis of these conditions, much remains to be learnt about their immunochemistry, their prevalence and precise role in various inflammatory diseases.

Synovial mast cell responses during clinical improvement in early rheumatoid arthritis

OBJECTIVES

To determine the synovial mast cell response in early rheumatoid arthritis (RA) during clinical improvement, and to examine for relations with clinical and histological parameters of disease activity.

METHODS

Twenty two synovial samples were obtained from six patients with RA using needle arthroscopy. The mean disease duration at baseline was eight months, and two to three further samples were obtained over a mean follow up period of 15 months during which treatment initiated clinical improvement occurred. Sections were immunostained to detect MCT and MCTC mast cells and correlations were sought between clinical and histological data.

RESULTS

The overall mean synovial mast cell density was 40.3 cells/mm2, with regional densities of 60.6 and 34.2 mast cells/mm2 in the superficial and deeper synovial layers respectively. The MCT subset predominated, outnumbering MCTC by 3:1. There was a significant correlation between the histological inflammation index and the MCT density, (r = 0.4, p < 0.05) but not the MCTC subset. The regional distribution and predominant subset of mast cells varied in individual patient's synovia over time, with a trend towards restriction of the mast cell response to the superficial synovium during clinical improvement.

CONCLUSIONS

The mast cell response in early RA is characterised by substantial expansion of predominantly MCT mast cells that correlates with histological indices of inflammation. During clinical improvement, this expansion tended to become more superficial. Taken together with previous studies of long duration RA, which implicate MCTC cells in synovial damage and disease progression, these results suggest that MCT and MCTC mast cells may possess distinct functions in the spectrum of inflammatory events occurring during RA.

Mast cell subpopulations in the synovial tissue of patients with osteoarthritis: selective increase in numbers of tryptase-positive, chymase-negative mast cells

Although there is relatively little evidence of inflammation in osteoarthritis (OA), increases in mast cell numbers and mast cell activation are prominent features of the synovial tissue. As little is known of the types of mast cells which may be involved, the numbers and distribution of mast cell subpopulations have been investigated as defined according to their content of proteases. Tissue was obtained from patients with OA undergoing total knee replacement surgery (n = 14) and from control subjects either post-mortem (n = 11) or following leg amputation for peripheral vascular disease (n = 3); a double-labelling immunocytochemical procedure with monoclonal antibodies specific for tryptase and chymase was applied to identify those mast cells which contain both tryptase and chymase (MCTC) and those with tryptase but not chymase (MCT). There was considerable variation between individual tissues and between sites of tissue sampling, but cells of the MCTC subset were predominant in the synovial layer of both groups of subjects without joint disease, accounting for some 60 per cent of all mast cells present. In tissue from OA patients, however, there appeared to have been a striking shift in the relative proportions of mast cells from the MCTC to the MCT phenotype, with many more MCT cells present in the synovial tissues of OA patients (median 53 MCT/mm2) than in tissue from post-mortem (7.5 MCT/mm2, P < 0.0001) or amputation controls (12 MCT/mm2). In contrast, numbers of synovial MCTC cells in the synovium of OA patients (20 MCTC/mm2) differed little from those in either of the control groups (both 12 MCTC/mm2). In several other conditions, the MCT cells have been linked with inflammatory events, but it seems that in OA, other factors may be operating to induce a selective expansion of this subpopulation.

Immunopharmacology of human mast cells and basophils

Human mast cells and basophils play a key role in the pathogenesis of several immunological and inflammatory disorders, not only by producing inflammatory and fibrogenic mediators, but also by directly (CD40 ligand) and indirectly secreting various cytokines and chemokines. Studies carried out to evaluate the effects of drugs that modulate the release of mediators and cytokines from these cells have contributed to clarifying the biochemical mechanism by which immunological and non-immunological stimuli activate these cells. Significant differences have been documented between human mast cells and basophils as regard the pharmacological agents that modulate the release of mediators, between mast cells isolated from different anatomical sites, and between compounds of the same class of drugs. Efforts to gain insight into the biochemical events occurring during immunological activation of mast cells and basophils could lead to the identification of new biochemical targets for therapeutic interventions in several immunological disorders.