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

Bioinformatics and system biology analysis revealed the crosstalk between COVID-19 and osteoarthritis

BACKGROUND

The global coronavirus disease 2019 (COVID-19) outbreak has significantly impacted public health. Moreover, there has been an association between the incidence and severity of osteoarthritis (OA) and the onset of COVID-19. However, the optimal diagnosis and treatment strategies for patients with both diseases remain uncertain. Bioinformatics is a novel approach that may help find the common pathology between COVID-19 and OA.

METHODS

Differentially expressed genes (DEGs) were screened by R package "limma." Functional enrichment analyses were performed to find key biological functions. Protein-protein interaction (PPI) network was constructed by STRING database and then Cytoscape was used to select hub genes. External data sets and OA mouse model validated and identified the hub genes in both mRNA and protein levels. Related transcriptional factors (TF) and microRNAs (miRNAs) were predicted with miRTarBase and JASPR database. Candidate drugs were obtained from Drug Signatures database. The immune infiltration levels of COVID-19 and OA were evaluated by CIBERSORT and scRNA-seq.

RESULTS

A total of 74 common DEGs were identified between COVID-19 and OA. Receiver operating characteristic curves validated the effective diagnostic values (area under curve > 0.7) of four hub genes (matrix metalloproteinases 9, ATF3, CCL4, and RELA) in both the training and validation data sets of COVID-19 and OA. Quantitative polymerase chain reaction and Western Blot showed significantly higher hub gene expression in OA mice than in healthy controls. A total of 84 miRNAs and 28 TFs were identified to regulate the process of hub gene expression. The top 10 potential drugs were screened including "Simvastatin," "Hydrocortisone," and "Troglitazone" which have been proven by Food and Drug Administration. Correlated with hub gene expression, Macrophage M0 was highly expressed while Natural killer cells and Mast cells were low in both COVID-19 and OA.

CONCLUSION

Four hub genes, disease-related miRNAs, TFs, drugs, and immune infiltration help to understand the pathogenesis and perform further studies, providing a potential therapy target for COVID-19 and OA.

High-Sucrose Diet Accelerates Arthritis Progression in a Collagen-Induced Rheumatoid Arthritis Model

SCOPE

High dietary sugar and sweeteners are suspected to cause the development of rheumatoid arthritis (RA) symptoms through the induction of proinflammatory cytokine release. However, the mechanisms by which increased dietary sugar affects RA etiology are not yet fully understood. The study uses a mouse model of collagen-induced RA (CIA) to investigate the relationship between excessive sugar consumption and RA risk.

METHODS AND RESULTS

RA-associated pathological features are assessed in the nonimmunized (NI) control group, the CIA-positive control group, and the CIA + high-sucrose diet (CIA+HS, 63% calories from sucrose) group. Compared with the CIA group, the CIA+HS group shows a greater increase in paw thickness and clinical scores, as well as, a higher degree of pannus formation and inflammation in the knee, ankle, and sole tissues. Moreover, the infiltration of immune cells is increased in the CIA+HS group. Although the expression of hepatic lipogenic genes, is not altered, that of toll-like receptor (TLR4) and IL-1β is considerably elevated in the CIA+HS group.

CONCLUSIONS

These findings suggest that excessive sucrose consumption causes hepatic fibrosis and inflammation, contributing to the pathophysiology of RA.

Mast Cell Involvement in the Pathogenesis of Selected Musculoskeletal Diseases

In recent years, there has been a noteworthy revival of interest in the function of mast cells (MCs) in the human body. It is now acknowledged that MCs impact a wide array of processes beyond just allergies, leading to a shift in research direction. Unfortunately, some earlier conclusions were drawn from animal models with flawed designs, particularly centered around the receptor tyrosine kinase (Kit) pathway. Consequently, several subsequent findings may have been unreliable. Thus, what is now required is a re-examination of these earlier findings. Nevertheless, the remaining data are fascinating and hold promise for a better comprehension of numerous diseases and the development of more effective therapies. As the field continues to progress, many intriguing issues warrant further investigation and analysis. For instance, exploring the bidirectional action of MCs in rheumatoid arthritis, understanding the extent of MCs' impact on symptoms associated with Ehlers-Danlos syndrome, and unraveling the exact role of the myofibroblast-mast cell-neuropeptides axis in the joint capsule during post-traumatic contractures are all captivating areas for exploration. Hence, in this review, we summarize current knowledge regarding the influence of MCs on the pathogenesis of selected musculoskeletal diseases, including rheumatoid arthritis, spondyloarthritis, psoriatic arthritis, gout, muscle and joint injuries, tendinopathy, heterotopic ossification, and Ehlers-Danlos syndrome. We believe that this review will provide in-depth information that can guide and inspire further research in this area.

IL-33-mediated activation of mast cells is involved in the progression of imiquimod-induced psoriasis-like dermatitis

BACKGROUND

Psoriasis is a chronic inflammatory dermatosis with an unclear pathogenesis. Mast cells (MCs) can serve as a bridge between innate and adaptive immunity and are involved in the regulation of the inflammatory state and immune homeostasis in diseases. MCs constitutively express interleukin-33 receptor T1/ST2 (IL-33R). IL-33 is a potent MCs activator that is actively secreted by keratinocytes in psoriasis. However, the regulatory role of MCs in psoriasis remains uncertain. Therefore, we hypothesised that IL-33 could promote MC activation to regulate psoriasis development.

METHODS

We performed experiments on wild-type (WT) and MC-deficient (Kit Wsh/Wsh) mice, established psoriasis-like mouse models using imiquimod (IMQ), and performed RNA sequencing and transcriptomic analysis of skin lesions. Exogenous administration was performed using recombinant IL-33. Validation and evaluation were performed using PSI scoring, immunofluorescence, immunohistochemistry, and qPCR.

RESULTS

We observed an upregulation in the number and activation of MCs in patients with psoriasis and in IMQ-induced psoriasis-like dermatitis. Deficiency of MCs ameliorates IMQ-induced psoriatic dermatitis at an early stage. IL-33 is increased and co-localized with MCs in the dermis of psoriasis-like lesions using immunofluorescence. Compared to WT mice, IMQ-induced Kit^Wsh/Wsh mice demonstrated a delayed response to exogenous IL-33.

CONCLUSIONS

MCs are activated by IL-33 in the early stages of psoriasis and exacerbate psoriasis-associated skin inflammation. The regulation of MC homeostasis may be a potential therapeutic strategy for psoriasis. Video Abstract.

The multifaceted role of mast cells in joint inflammation and arthritis

OBJECTIVE

To review current knowledge surrounding the role of mast cells in joint inflammation and arthritis.

METHOD

Narrative review.

RESULTS

Mast cells (MCs) are commonly observed in the synovium of the joint, particularly surrounding blood vessels and nerve endings. Some studies have reported increased MC number and degranulation in patients with osteoarthritis (OA). In two studies, MCs were the only immune cell type found in higher concentrations in synovium of OA patients compared to rheumatoid arthritis patients. Activation of MCs in OA includes signaling pathways such as immunoglobulin E/Fc epsilon Receptor 1 (IgE/FcεR1), immunoglobulin G/Fc gamma receptor (IgG/FcγR), complement, and toll-like cell surface receptor-mediated signaling, resulting in context-dependent release of either pro-inflammatory and/or anti-inflammatory mediators within the joint. Activation of MCs results in the release of pro-inflammatory mediators that ultimately contribute to inflammation of the synovium, bone remodeling, and cartilage damage. However, some studies have proposed that MCs can also exhibit anti-inflammatory effects by secreting mediators that inactivate pro-inflammatory cytokines such as interleukin 6 (IL-6).

CONCLUSIONS

MCs may play a role in mediating synovial inflammation and OA progression. However, the mechanisms governing MC activation, the downstream pro- and/or anti-inflammatory effects, and their impact on osteoarthritis pathogenesis remains to be elucidated and requires extensive further study. Furthermore, it is important to establish the pathways of MC activation in OA to determine whether MCs exhibit varying phenotypes as a function of disease stage. Ultimately, such research is needed before understanding whether MCs could be targeted in OA treatments.

Human Lung Mast Cells: Therapeutic Implications in Asthma

Mast cells are strategically located in different compartments of the lung in asthmatic patients. These cells are widely recognized as central effectors and immunomodulators in different asthma phenotypes. Mast cell mediators activate a wide spectrum of cells of the innate and adaptive immune system during airway inflammation. Moreover, these cells modulate the activities of several structural cells (i.e., fibroblasts, airway smooth muscle cells, bronchial epithelial and goblet cells, and endothelial cells) in the human lung. These findings indicate that lung mast cells and their mediators significantly contribute to the immune induction of airway remodeling in severe asthma. Therapies targeting mast cell mediators and/or their receptors, including monoclonal antibodies targeting IgE, IL-4/IL-13, IL-5/IL-5Rα, IL-4Rα, TSLP, and IL-33, have been found safe and effective in the treatment of different phenotypes of asthma. Moreover, agonists of inhibitory receptors expressed by human mast cells (Siglec-8, Siglec-6) are under investigation for asthma treatment. Increasing evidence suggests that different approaches to depleting mast cells show promising results in severe asthma treatment. Novel treatments targeting mast cells can presumably change the course of the disease and induce drug-free remission in bronchial asthma. Here, we provide an overview of current and promising treatments for asthma that directly or indirectly target lung mast cells.

IL-31 and IL-33 in rheumatoid arthritis patients

Objective – to investigate clinical and diagnostic significance of IL-31 and IL-33 determination in patients with rheumatoid arthritis (RA).

Material and methods. 154 patients with a reliable diagnosis of RA were examined. Serum levels of IL-31 and IL-33 were studied using multiplex xMAP technology on Bio-PlexTM 200 System analyzer (BIO-RAD, USA). The upper limit of the norm in the study of 20 healthy donor sera was (M+3σ): IL-31 – 15.08 pg/ml, IL-33 – 3.40 pg/ml.

Results. IL-31 (Me (25th; 75th percentile) – 13.75 (5.63; 308.52) and 6.10 (2.87; 8.62) pg/ml (p<0.001), IL-33 – 18.86 (7.45; 65.95) and 0.52 (0.17; 0.78) pg/ml (p><0.001) levels were observed in RA patients in comparison with the control group. An increase in IL-33 concentration (more than 3.40 pg/ml) was observed in 87.0% of patients, and IL-31 (more than 15.08 pg/ml) in 48.1% of patients with RA. An increase in IL-33 alone was observed in 42.2% (65 of 154 patients) with RA, while an isolated increase in IL-31 concentration was observed in only 2 (1.3%) patients. Simultaneous hyperproduction of IL-33 and IL-31 occurred in 69 (44.9%) patients. We revealed positive correlation of clinical and laboratory parameters of RA with cytokine concentration: SDAI correlated with IL-33 (r=0.36; p><0.05); CRP – with IL-31 (r=0.49; p><0,05) and IL-33 (r=0.40; p><0.05). Conclusion. Concentrations of IL-31 and IL-33 are elevated in RA patients and correlate with the indices of inflammatory activity of the disease.>< 0.001), IL-33 – 18.86 (7.45; 65.95) and 0.52 (0.17; 0.78) pg/ml (p<0.001) levels were observed in RA patients in comparison with the control group. An increase in IL-33 concentration (more than 3.40 pg/ml) was observed in 87.0% of patients, and IL-31 (more than 15.08 pg/ml) in 48.1% of patients with RA. An increase in IL-33 alone was observed in 42.2% (65 of 154 patients) with RA, while an isolated increase in IL-31 concentration was observed in only 2 (1.3%) patients. Simultaneous hyperproduction of IL-33 and IL-31 occurred in 69 (44.9%) patients. We revealed positive correlation of clinical and laboratory parameters of RA with cytokine concentration: SDAI correlated with IL-33 (r=0.36; p><0.05); CRP – with IL-31 (r=0.49; p><0,05) and IL-33 (r=0.40; p><0.05). Conclusion. Concentrations of IL-31 and IL-33 are elevated in RA patients and correlate with the indices of inflammatory activity of the disease.>< 0.001) levels were observed in RA patients in comparison with the control group. An increase in IL-33 concentration (more than 3.40 pg/ml) was observed in 87.0% of patients, and IL-31 (more than 15.08 pg/ml) in 48.1% of patients with RA. An increase in IL-33 alone was observed in 42.2% (65 of 154 patients) with RA, while an isolated increase in IL-31 concentration was observed in only 2 (1.3%) patients. Simultaneous hyperproduction of IL-33 and IL-31 occurred in 69 (44.9%) patients. We revealed positive correlation of clinical and laboratory parameters of RA with cytokine concentration: SDAI correlated with IL-33 (r=0.36; p<0.05); CRP – with IL-31 (r=0.49; p><0,05) and IL-33 (r=0.40; p><0.05). Conclusion. Concentrations of IL-31 and IL-33 are elevated in RA patients and correlate with the indices of inflammatory activity of the disease.>< 0.05); CRP – with IL-31 (r=0.49; p< ,05) and IL-33 (r=0.40; p<0.05)

Conclusion. Concentrations of IL-31 and IL-33 are elevated in RA patients and correlate with the indices of inflammatory activity of the disease.

Growth stimulation expressed gene 2 (ST2): Clinical research and application in the cardiovascular related diseases

As an interleukin (IL)-1 receptor family member, scientists found that when circulating soluble growth stimulation expressed gene 2 (sST2) is low, its ligand, IL-33, will bind to ST2L to exert protective effects on various types of cells. On the other hand, competitive binding of IL-33 occurs when sST2 concentrations are increased, followed by a reduction in the amount available for cell protection. Based on this mechanism, the usage of sST2 is to identify the population of high-risk patients with cardiovascular disease. In recent years, the role of serum sST2 in the occurrence, diagnosis, prognosis, and treatment of cardiovascular diseases has been gradually accepted by doctors. This manuscript systemically reviews the biological functions and applications of sST2 in disease diagnosis and treatment, especially for cardiovascular diseases. In clinical testing, since IL-33 can negatively impact sST2 measurement accuracy, the properties of current assay kits have been summarized and discussed to provide a clear view of the clinical chemistry results. Although sST2 is a promising biomarker, there are few quantitative approaches available for clinical testing. In this context, a mass spectrometry (MS)-based approach might be an option, as this is a powerful analytical tool to distinguish structurally related molecules in the matrix and decrease false-positive results in clinical testing. Moreover, approaches developed based on MS would be an ideal way to further study sST2 standardization.

Utilizing mast cells in a positive manner to overcome inflammatory and allergic diseases

Mast cells (MCs) are immune cells widely distributed in the body, accompanied by diverse phenotypes and functions. Committed mast cell precursors (MCPs) leave the bone marrow and enter the blood circulation, homing to peripheral sites under the control of various molecules from different microenvironments, where they eventually differentiate and mature. Partly attributable to the unique maturation mechanism, MCs display high functional heterogeneity and potentially plastic phenotypes. High plasticity also means that MCs can exhibit different subtypes to cope with different microenvironments, which we call “the peripheral immune education system”. Under the peripheral immune education system, MCs showed a new character from previous cognition in some cases, namely regulation of allergy and inflammation. In this review, we focus on the mucosal tissues, such as the gastrointestinal tract, to gain insights into the mechanism underlying the migration of MCs to the gut or other organs and their heterogeneity, which is driven by different microenvironments. In particular, the immunosuppressive properties of MCs let us consider that positively utilizing MCs may be a new way to overcome inflammatory and allergic disorders.

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.

CLP1 is a Prognosis-Related Biomarker and Correlates With Immune Infiltrates in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic, heterogeneous autoimmune disease with a high disability rate that seriously affects society and individuals. However, there is a lack of effective and reliable diagnostic markers and therapeutic targets. In this study, we identified diagnostic markers of RA based on RNA modification and explored its role as well as degree of immune cell infiltration. We used the gene expression profile data of three synovial tissues (GSE55235, GSE55457, GSE77298) from the Gene Expression Omnibus (GEO) database and the gene of 5 RNA modification genes (including m6A, m1A, m5C, APA, A-1), combined with cluster analysis, identified four RNA modifiers closely related to RA (YTHDC1, LRPPRC, NOP2, and CLP1) and five immune cells namely T cell CD8, CD4 memory resting, T cells regulatory (Tregs) Macrophages M0, and Neutrophils. Based on the LASSO regression algorithm, hub genes and immune cell prediction models were established respectively in RA and a nomogram based on the immune cell model was built. Around 4 key RNA modification regulator genes, miRNA-mRNA, mRNA-TF networks have been established, and GSEA-GO, KEGG-GSEA enrichment analysis has been carried out. Finally, CLP1 was established as an effective RA diagnostic marker, and was highly positively correlated with T cells follicular helper (Tfh) infiltration. On the other hand, highly negatively correlated with the expression of mast cells. In short, CLP1 may play a non-negligible role in the onset and development of RA by altering immune cell infiltration, and it is predicted to represent a novel target for RA clinical diagnosis and therapy.

Mast Cells as Important Regulators in Autoimmunity and Cancer Development

Mast cells are an essential part of the immune system and are best known as important modulators of allergic and anaphylactic immune responses. Upon activation, mast cells release a multitude of inflammatory mediators with various effector functions that can be both protective and damage-inducing. Mast cells can have an anti-inflammatory or pro-inflammatory immunological effect and play important roles in regulating autoimmune diseases including rheumatoid arthritis, type 1 diabetes, and multiple sclerosis. Importantly, chronic inflammation and autoimmunity are linked to the development of specific cancers including pancreatic cancer, prostate cancer, colorectal cancer, and gastric cancer. Inflammatory mediators released from activated mast cells regulate immune responses and promote vascular permeability and the recruitment of immune cells to the site of inflammation. Mast cells are present in increased numbers in tissues affected by autoimmune diseases as well as in tumor microenvironments where they co-localize with T regulatory cells and T effector cells. Mast cells can regulate immune responses by expressing immune checkpoint molecules on their surface, releasing anti-inflammatory cytokines, and promoting vascularization of solid tumor sites. As a result of these immune modulating activities, mast cells have disease-modifying roles in specific autoimmune diseases and cancers. Therefore, determining how to regulate the activities of mast cells in different inflammatory and tumor microenvironments may be critical to discovering potential therapeutic targets to treat autoimmune diseases and cancer.

Bioinformatics-based study to identify immune infiltration and inflammatory-related hub genes as biomarkers for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease whose principal pathological change is aggressive chronic synovial inflammation; however, the specific etiology and pathogenesis have not been fully elucidated. We downloaded the synovial tissue gene expression profiles of four human knees from the Gene Expression Omnibus database, analyzed the differentially expressed genes in the normal and RA groups, and assessed their enrichment in functions and pathways using bioinformatics methods and the STRING online database to establish protein-protein interaction networks. Cytoscape software was used to obtain 10 hub genes; receiver operating characteristic (ROC) curves were calculated for each hub gene and differential expression analysis of the two groups of hub genes. The CIBERSORT algorithm was used to impute immune infiltration. We identified the signaling pathways that play important roles in RA and 10 hub genes: Ccr1, Ccr2, Ccr5, Ccr7, Cxcl5, Cxcl6, Cxcl13, Ccl13, Adcy2, and Pnoc. The diagnostic value of these 10 hub genes for RA was confirmed using ROC curves and expression analysis. Adcy2, Cxcl13, and Ccr5 are strongly associated with RA development. The study also revealed that the differential infiltration profile of different inflammatory immune cells in the synovial tissue of RA is an extremely critical factor in RA progression. This study may contribute to the understanding of signaling pathways and biological processes associated with RA and the role of inflammatory immune infiltration in the pathogenesis of RA. In addition, this study shows that Adcy2, Cxcl13, and Ccr5 have the potential to be biomarkers for RA treatment.

IL-10 in Mast Cell-Mediated Immune Responses: Anti-Inflammatory and Proinflammatory Roles

Mast cells (MCs) play critical roles in Th2 immune responses, including the defense against parasitic infections and the initiation of type I allergic reactions. In addition, MCs are involved in several immune-related responses, including those in bacterial infections, autoimmune diseases, inflammatory bowel diseases, cancers, allograft rejections, and lifestyle diseases. Whereas antigen-specific IgE is a well-known activator of MCs, which express FcεRI on the cell surface, other receptors for cytokines, growth factors, pathogen-associated molecular patterns, and damage-associated molecular patterns also function as triggers of MC stimulation, resulting in the release of chemical mediators, eicosanoids, and various cytokines. In this review, we focus on the role of interleukin (IL)-10, an anti-inflammatory cytokine, in MC-mediated immune responses, in which MCs play roles not only as initiators of the immune response but also as suppressors of excessive inflammation. IL-10 exhibits diverse effects on the proliferation, differentiation, survival, and activation of MCs in vivo and in vitro. Furthermore, IL-10 derived from MCs exerts beneficial and detrimental effects on the maintenance of tissue homeostasis and in several immune-related diseases including contact hypersensitivity, auto-immune diseases, and infections. This review introduces the effects of IL-10 on various events in MCs, and the roles of MCs in IL-10-related immune responses and as a source of IL-10.

Regulation of osteoclastogenesis by mast cell in rheumatoid arthritis

Background

In the pathogenesis of rheumatoid arthritis (RA), the role of mast cells has not been revealed clearly. We aimed to define the inflammatory and tissue-destructive roles of mast cells in rheumatoid arthritis (RA).

Methods

Serum and synovial fluid (SF) concentration levels of tryptase, chymase, and histamine were quantified using ELISA. After activating mast cells using IL-33, the production of TNF-α, IL-1β, IL-6, IL-17, RANKL, and MMPs was determined using real-time PCR and ELISA. Osteoclastogenesis was assessed in CD14+ monocytes from peripheral blood and SF, which were cultured with IL-33-activated mast cells, by counting TRAP-positive multinucleated cells.

Results

The concentration levels of serum tryptase, chymase, and histamine and SF histamine were higher in patients with RA than in controls. FcεR1 and c-kit-positive mast cells were higher in RA synovium than in osteoarthritic (OA) synovium. Stimulation of mast cells by IL-33 increased the number of trypatse+chymase− and tryptase+chymase+ mast cells. IL-33 stimulation also increased the gene expression levels of TNF-α, IL-1β, IL-6, IL-17, RANKL, and MMP-9 in mast cells. Furthermore, IL-33 stimulated human CD14+ monocytes to differentiate into TRAP+ multinucleated osteoclasts. When CD14+ monocytes were co-cultured with mast cells, osteoclast differentiation was increased. Additionally, IL-33-activated mast cells stimulated osteoclast differentiation. The inhibition of intercellular contact between mast cells and monocytes using inserts reduced osteoclast differentiation.

Conclusions

IL-33 increased inflammatory and tissue-destructive cytokines by activation of mast cells. Mast cells stimulated osteoclast differentiation in monocytes. Mast cells could stimulate osteoclastogenesis indirectly through production of tissue-destructive cytokines and directly through stimulation of osteoclast precursors.

Higher PGD2 production by synovial mast cells from rheumatoid arthritis patients compared with osteoarthritis patients via miR-199a-3p/prostaglandin synthetase 2 axis

We previously reported that synovial mast cells (MCs) from patients with rheumatoid arthritis (RA) produced TNF-α in response to immune complexes via FcγRI and FcγRIIA. However, the specific functions of synovial MCs in RA remain unclear. This study aimed to elucidate those functions. Synovial tissues and fluid were obtained from RA and osteoarthritis (OA) patients undergoing joint replacement surgery. Synovium-derived, cultured MCs were generated by culturing dispersed synovial cells with stem cell factor. We performed microarray-based screening of mRNA and microRNA (miRNA), followed by quantitative RT-PCR-based verification. Synovial MCs from RA patients showed significantly higher prostaglandin systhetase (PTGS)1 and PTGS2 expression compared with OA patients' MCs, and they produced significantly more prostaglandin D₂ (PGD₂) following aggregation of FcγRI. PGD₂ induced IL-8 production by human group 2 innate lymphoid cells, suggesting that PGD₂-producing MCs induce neutrophil recruitment into the synovium of RA patients. PTGS2 mRNA expression in RA patients' MCs correlated inversely with miRNA-199a-3p expression, which down-regulated PTGS2. RA patients' synovial fluid contained significantly more PGD₂ compared with OA patients' fluid. Synovial MCs might regulate inflammation in RA through hyper-production of PGD₂ following FcRγ aggregation. Our findings indicate functional heterogeneity of human MCs among diseases.

IL-33 and Superantigenic Activation of Human Lung Mast Cells Induce the Release of Angiogenic and Lymphangiogenic Factors

Human lung mast cells (HLMCs) express the high-affinity receptor FcεRI for IgE and are strategically located in different compartments of human lung, where they play a role in several inflammatory disorders and cancer. Immunoglobulin superantigens (e.g., protein A of Staphylococcus aureus and protein L of Peptostreptococcus magnus) bind to the variable regions of either the heavy (V_H3) or light chain (κ) of IgE. IL-33 is a cytokine expressed by epithelial cells that exerts pleiotropic functions in the lung. The present study investigated whether immunoglobulin superantigens protein A and protein L and IL-33 caused the release of inflammatory (histamine), angiogenic (VEGF-A) and lymphangiogenic (VEGF-C) factors from HLMCs. The results show that protein A and protein L induced the rapid (30 min) release of preformed histamine from HLMCs. By contrast, IL-33 did not induce the release of histamine from lung mast cells. Prolonged incubation (12 h) of HLMCs with superantigens and IL-33 induced the release of VEGF-A and VEGF-C. Preincubation with IL-33 potentiated the superantigenic release of histamine, angiogenic and lymphangiogenic factors from HLMCs. Our results suggest that IL-33 might enhance the inflammatory, angiogenic and lymphangiogenic activities of lung mast cells in pulmonary disorders.

Neuroimmune connections between corticotropin-releasing hormone and mast cells: novel strategies for the treatment of neurodegenerative diseases

Corticotropin-releasing hormone is a critical component of the hypothalamic–pituitary–adrenal axis, which plays a major role in the body’s immune response to stress. Mast cells are both sensors and effectors in the interaction between the nervous and immune systems. As first responders to stress, mast cells can initiate, amplify and prolong neuroimmune responses upon activation. Corticotropin-releasing hormone plays a pivotal role in triggering stress responses and related diseases by acting on its receptors in mast cells. Corticotropin-releasing hormone can stimulate mast cell activation, influence the activation of immune cells by peripheral nerves and modulate neuroimmune interactions. The latest evidence shows that the release of corticotropin-releasing hormone induces the degranulation of mast cells under stress conditions, leading to disruption of the blood-brain barrier, which plays an important role in neurological diseases, such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, autism spectrum disorder and amyotrophic lateral sclerosis. Recent studies suggest that stress increases intestinal permeability and disrupts the blood-brain barrier through corticotropin-releasing hormone-mediated activation of mast cells, providing new insight into the complex interplay between the brain and gastrointestinal tract. The neuroimmune target of mast cells is the site at which the corticotropin-releasing hormone directly participates in the inflammatory responses of nerve terminals. In this review, we focus on the neuroimmune connections between corticotropin-releasing hormone and mast cells, with the aim of providing novel potential therapeutic targets for inflammatory, autoimmune and nervous system diseases.

Association between IL-33 and other inflammatory factors in patients with rheumatoid arthritis and in fibroblast-like synoviocytes in vitro

IL-33 is a member of the IL-1 family of cytokines whose role remains controversial in rheumatoid arthritis (RA). The present study was performed to evaluate the correlation of IL-33 with other cytokines and chemokines in serum and the synovia, and to explore the nature of the association. The concentration of IL-33 in samples from 96 patients with RA was analyzed. The response of fibroblast-like synoviocytes (FLSs) to treatment with different concentrations of IL-33 was assessed in vitro. IL-33 was indicated to exhibit an association with multiple cytokines and chemokines in synovial fluid with an inverted-U-shaped trend, including IL-6, IL-1β, IL-8, MIG and IP-10, but not in the serum. Furthermore, in vitro experiments confirmed that IL-33 also exerted a U-type dose-dependent regulatory effect on FLS function. In addition, the data-points do not exactly follow the U-shaped curve fit in most cases, therefore, the applicability of this mathematical model in clinical practice is limited.

Anti-Tumorigenic Activities of IL-33: A Mechanistic Insight

Interleukin-33 (IL-33) is an epithelial-derived cytokine that can be released upon tissue damage, stress, or infection, acting as an alarmin for the immune system. IL-33 has long been studied in the context of Th2-related immunopathologies, such as allergic diseases and parasitic infections. However, its capacity to stimulate also Th1-type of immune responses is now well established. IL-33 binds to its specific receptor ST2 expressed by most immune cell populations, modulating a variety of responses. In cancer immunity, IL-33 can display both pro-tumoral and anti-tumoral functions, depending on the specific microenvironment. Recent findings indicate that IL-33 can effectively stimulate immune effector cells (NK and CD8⁺ T cells), eosinophils, basophils and type 2 innate lymphoid cells (ILC2) promoting direct and indirect anti-tumoral activities. In this review, we summarize the most recent advances on anti-tumor immune mechanisms operated by IL-33, including the modulation of immune checkpoint molecules, with the aim to understand its potential as a therapeutic target in cancer.

Blocking Interleukin-33 Alleviates the Joint Inflammation and Inhibits the Development of Collagen-Induced Arthritis in Mice

Rheumatoid arthritis (RA) is considered a systemic chronic inflammatory joint disease characterized by chronic synovitis and cartilage and bone destruction. Interleukin-33 (IL-33) is a proinflammatory cytokine which is highly expressed in the synovium of RA patients and the joints of mice with collagen-induced arthritis (CIA) and exacerbates CIA in mice. However, the role of the IL-33-neutralizing antibody in the murine model of CIA remains unclear. In the present study, CIA mice were given intraperitoneally with polyclonal rabbit anti-murine IL-33 antibody (anti-IL-33) or normal rabbit IgG control after the first signs of arthritis. Administration of anti-IL-33 after the onset of disease significantly reduced the severity of CIA and joint damage compared with controls treated with normal rabbit IgG. Anti-IL-33 treatment also significantly decreased the serum levels of interferon-γ(IFN-γ),IL-6, IL-12, IL-33, and tumor necrosis factor-α (TNF-α). Moreover, anti-IL-33 treatment significantly downregulated the production of IFN-γ, IL-6, IL-12, IL-33, and TNF-α in ex vivo-stimulated spleen cells. Together, our results indicate that the IL-33-neutralizing antibody may provide a therapeutic strategy for RA by inhibiting the release of proinflammatory cytokines.

Visfatin and Rheumatoid Arthritis: Pathogenetic Implications and Clinical Utility

Objective:

Analysis and generalization of data related to visfatin involvement in the pathogenesis of inflammation at various stages of rheumatoid arthritis.

Data Synthesis:

Visfatin is an adipocytokine which has also been identified in non-adipose tissues. It influences directly on the maturation of B cells, which are involved in autoantibody production and T cell activation. Visfatin can promote inflammation via regulation of pro-inflammatory cytokines including TNF, IL-1β and IL-6. The concentration of circulating visfatin in rheumatoid arthritis patients is higher compared to healthy individuals. Several studies suggest that visfatin level is associated with rheumatoid arthritis activity, and its elevation may precede clinical signs of the relapse. In murine collagen-induced arthritis, visfatin levels were also found to be elevated both in inflamed synovial cells and in joint vasculature. Visfatin blockers have been shown to confer fast and long-term attenuation of pathological processes; however, most of their effects are transient. Other factors responsible for hyperactivation of the immune system can participate in this process at a later stage. Treatment of rheumatoid arthritis with a combination of these blockers and inhibitors of other mediators of inflammation can potentially improve treatment outcomes compared to current therapeutic strategies. Recent advances in the treatment of experimental arthritis in mice as well as the application of emerging treatment strategies obtained from oncology for rheumatoid arthritis management could be a source of novel adipokine-mediated anti-rheumatic drugs.

Conclusion:

The ongoing surge of interest in anticytokine therapy makes further study of visfatin highly relevant as it may serve as a base for innovational RA treatment.

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.

Roles of mast cells in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory arthritis, and the complex interaction and activation of innate and adaptive immune cells are involved in RA pathogenesis. Mast cells (MCs) are one of the tissue-resident innate immune cells, and they contribute to RA pathogenesis. In the present review, the evidence of the pathologic role of MC in RA is discussed based on human and animal data. In addition, the potential role of MC in RA pathogenesis and the research area that should be focused on in the future are suggested.

Future Needs in Mast Cell Biology

The pathophysiological roles of mast cells are still not fully understood, over 140 years since their description by Paul Ehrlich in 1878. Initial studies have attempted to identify distinct "subpopulations" of mast cells based on a relatively small number of biochemical characteristics. More recently, "subtypes" of mast cells have been described based on the analysis of transcriptomes of anatomically distinct mouse mast cell populations. Although mast cells can potently alter homeostasis, in certain circumstances, these cells can also contribute to the restoration of homeostasis. Both solid and hematologic tumors are associated with the accumulation of peritumoral and/or intratumoral mast cells, suggesting that these cells can help to promote and/or limit tumorigenesis. We suggest that at least two major subsets of mast cells, MC1 (meaning anti-tumorigenic) and MC2 (meaning pro-tumorigenic), and/or different mast cell mediators derived from otherwise similar cells, could play distinct or even opposite roles in tumorigenesis. Mast cells are also strategically located in the human myocardium, in atherosclerotic plaques, in close proximity to nerves and in the aortic valve. Recent studies have revealed evidence that cardiac mast cells can participate both in physiological and pathological processes in the heart. It seems likely that different subsets of mast cells, like those of cardiac macrophages, can exert distinct, even opposite, effects in different pathophysiological processes in the heart. In this chapter, we have commented on possible future needs of the ongoing efforts to identify the diverse functions of mast cells in health and disease.

Novel Therapeutic Approaches in Rheumatoid Arthritis: Role of Janus Kinases Inhibitors

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Rheumatoid Arthritis (RA) is a chronic inflammatory disease characterized by synovial inflammation and hyperplasia, autoantibody production, cartilage and bone destruction and several systemic features. Cardiovascular, pulmonary, psychological, and muscle involvement are the main comorbidities of RA and are responsible for the severity of the disease and long-term prognosis.

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Pharmacological treatment of rheumatic diseases has evolved remarkably over the past years. In addition, the widespread adoption of treat to target and tight control strategies has led to a substantial improvement of outcomes, so that drug-free remission is nowadays a realistic goal in the treatment of RA. However, despite the availability of multiple therapeutic options, up to 40% of patients do not respond to current treatments, including biologics. Small-molecule therapies offer an alternative to biological therapies for the treatment of inflammatory diseases. In the past 5 years, a number of small-molecule compounds targeting Janus Kinases (JAKs) have been developed. Since JAKs are essential for cell signaling in immune cells, in particular controlling the response to many cytokines, their inhibitors quickly became a promising class of oral therapeutics that proved effective in the treatment of RA.

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ofacitinib is the first Janus Kinase (JAK) inhibitor approved for the treatment of RA, followed more recently by baricitinib. Several other JAK inhibitors, are currently being tested in phase II and III trials for the treatment of a different autoimmune diseases. Most of these compounds exhibit an overall acceptable safety profile similar to that of biologic agents, with infections being the most frequent adverse event. Apart from tofacitinib, safety data on other JAK inhibitors are still limited. Long-term follow-up and further research are needed to evaluate the general safety profile and the global risk of malignancy of these small molecules, although no clear association with malignancy has been reported to date.

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Here, we will review the main characteristics of JAK inhibitors, including details on their molecular targets and on the clinical evidences obtained so far in the treatment of RA.

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.

IL-33 and MRGPRX2-Triggered Activation of Human Skin Mast Cells-Elimination of Receptor Expression on Chronic Exposure, but Reinforced Degranulation on Acute Priming

Clinically relevant exocytosis of mast cell (MC) mediators can be triggered by high-affinity IgE receptor (FcεRI)-aggregation (allergic route) or by the so-called pseudo-allergic pathway elicited via MAS-related G protein-coupled receptor-X2 (MRGPRX2). The latter is activated by drugs and endogenous neuropeptides. We recently reported that FcεRI-triggered degranulation is attenuated when human skin mast cells are chronically exposed to IL-33. Here, we were interested in the regulation of the MRGPRX2-route. Chronic exposure of skin MCs to IL-33 basically eliminated the pseudo-allergic/neurogenic route as a result of massive MRGPRX2 reduction. This downregulation seemed to partially require c-Jun N-terminal Kinase (JNK), but not p38, the two kinases activated by IL-33 in skin MCs. Surprisingly, however, JNK had a positive effect on MRGPRX2 expression in the absence of IL-33. This was evidenced by Accell^®-mediated JNK knockdown and JNK inhibition. In stark contrast to the dampening effect upon prolonged exposure, IL-33 was able to prime for increased degranulation by MRGPRX2 ligands when administered directly before stimulation. This supportive effect depended on p38, but not on JNK activity. Our data reinforce the concept that exposure length dictates whether IL-33 will enhance or attenuate secretion. IL-33 is, thus, the first factor to acutely enhance MRGPRX2-triggered degranulation. Finally, we reveal that p38, rarely associated with MC degranulation, can positively affect exocytosis in a context-dependent manner.

Yin-Yang of IL-33 in Human Skin Mast Cells: Reduced Degranulation, but Augmented Histamine Synthesis through p38 Activation

Mast cells (MCs) are the principal effector cells of IgE-mediated allergy. IL-33 is released by resident skin cells as alarmin upon tissue damage or allergen contact. Owing to their pronounced receptor expression, MCs are important targets of IL-33 action, but consequences for skin MCs are ill-defined, especially upon chronic exposure to IL-33. Mimicking the inflammatory milieu of skin disorders, we found that persistent exposure to IL-33 (over a 5-week period) strengthened skin MC numbers through accelerated cell-cycle progression and restriction of apoptosis. Conversely, IL-33 attenuated degranulation and FcεRI expression, potentially as a feedback to chronic "alarmin" exposure. Interestingly, the negative impact on histamine release was counterbalanced by amplified histamine production. Considering the clinical significance of histamine and scarce information on its regulation, we explored the molecular underpinnings. IL-33 induced swift phosphorylation of p38 and JNK (but not of ERK1/2 or AKT), and stimulated histidine decarboxylase expression. Combining pharmacological inhibition and kinase elimination by Accell-facilitated RNA interference in skin MCs revealed a p38-dependent, but JNK-independent mechanism. Collectively, IL-33 exerts multifaceted effects on cutaneous MCs at a post-maturation stage. The IL-33-skin MC axis may contribute to and balance inflammation in chronic skin disorders.

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.

The Pleiotropic Immunomodulatory Functions of IL-33 and Its Implications in Tumor Immunity

Interleukin-33 (IL-33) is a IL-1 family member of cytokines exerting pleiotropic activities. In the steady-state, IL-33 is expressed in the nucleus of epithelial, endothelial, and fibroblast-like cells acting as a nuclear protein. In response to tissue damage, infections or necrosis IL-33 is released in the extracellular space, where it functions as an alarmin for the immune system. Its specific receptor ST2 is expressed by a variety of immune cell types, resulting in the stimulation of a wide range of immune reactions. Recent evidences suggest that different IL-33 isoforms exist, in virtue of proteolytic cleavage or alternative mRNA splicing, with potentially different biological activity and functions. Although initially studied in the context of allergy, infection, and inflammation, over the past decade IL-33 has gained much attention in cancer immunology. Increasing evidences indicate that IL-33 may have opposing functions, promoting, or dampening tumor immunity, depending on the tumor type, site of expression, and local concentration. In this review we will cover the biological functions of IL-33 on various immune cell subsets (e.g., T cells, NK, Treg cells, ILC2, eosinophils, neutrophils, basophils, mast cells, DCs, and macrophages) that affect anti-tumor immune responses in experimental and clinical cancers. We will also discuss the possible implications of diverse IL-33 mutations and isoforms in the anti-tumor activity of the cytokine and as possible clinical biomarkers.

Immune-modulation via IgD B-cell receptor suppresses allergic skin inflammation in experimental contact hypersensitivity models despite of a Th2-favoured humoral response

Atopic dermatitis (AD) and allergic contact dermatitis (ACD) are common skin inflammatory conditions. B and T cells are strongly implicated in allergic contact hypersensitivity (CHS) conditions. Activation of IgD B-cell receptor (BCR) by anti-IgD stimulation depletes mature B cells and modulates T-helper cell type 1/2 (Th1/2) responses in vivo. It is not known whether these effects by anti-IgD exacerbates or ameliorates chronic skin inflammations. This study investigated the effects of anti-IgD and B-cell depleting anti-CD20 antibody on skin inflammation in CHS murine models. Chronic CHS were induced by challenges with allergens trimellitic anhydride (TMA) or 2,4 dinitrochlorobenzene (DNCB). Mice were treated with an anti-IgD or anti-CD20 at various time-points following allergen challenges. This study revealed that early therapeutic treatments with anti-IgD at 4 h after allergen challenge significantly reduced skin inflammation in both TMA- and DNCB-induced CHS models (P < 0.05). In contrast, anti-CD20 treatment exacerbated skin inflammation in DNCB-induced CHS despite of an extensive B cell depletion (P < 0.05). Anti-IgD treatment depleted mature CD19⁺IgD⁺ B cells but enhanced allergen-specific IgM and total IgE productions, suggesting a Th2-favoured humoral response. Anti-IgD reduced neutrophilic infiltrations but increases accumulation of mast cells in dermal tissues. The anti-inflammatory effects of anti-IgD were supported by evidence of an increase in the percentage of regulatory B cells and T cells. Collectively, this study demonstrates that immune-modulation by anti-IgD treatment suppresses Th2-mediated allergic skin inflammation in murine models despite a skew toward a Th2-favvoured humoral response and therefore may present a novel treatment for chronic human AD and ACD.

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.

Effects of Tocilizumab Therapy on Serum Interleukin-33 and Interleukin-6 Levels in Patients With Rheumatoid Arthritis

Objectives

This study aims to examine the effects of tocilizumab therapy on serum levels of interleukin (IL)-33 and IL-6 in rheumatoid arthritis (RA) patients.

Patients and methods

Interleukin-33 and IL-6 levels in serum samples from 83 RA patients (10 males, 73 females; mean age 51.9 years; range, 26 to 77 years) and 12 healthy controls (2 males, 10 females; mean age 52.2 years; range, 39 to 62 years) were compared by cross-sectional, case control analysis. Of the RA patients, 40 received 24 weeks of tocilizumab therapy and were assigned to the prospective cohort. These 40 patients were then divided into two subgroups as responders and non-responders according to the American College of Rheumatology (ACR) 20. The remaining 43 RA patients did not receive tocilizumab therapy. Serum cytokine levels were analyzed at baseline and after 24 weeks of tocilizumab therapy in these patients.

Results

Interleukin-33 and IL-6 concentrations were significantly higher in RA patients than in healthy controls (p<0.001 for both). Serum IL-33 levels in RA patients showed a significant correlation with rheumatoid factor titer (r=0.660, p<0.001), and IL-6 levels showed a significant correlation with high-sensitivity C-reactive protein levels (Spearman's rank correlation coefficient=0.482, p<0.001). Serum IL-33 levels decreased significantly after 24 weeks of tocilizumab therapy (p<0.001); this was particularly marked in ACR20 responders (p<0.001). However, the decrease in non-responders was not significant (p=0.066). Changes in serum IL-6 levels after 24 weeks of tocilizumab therapy were not significant in either ACR20 responders or non-responders.

Conclusion

Serum IL-33 levels in RA patients receiving tocilizumab therapy decreased significantly, particularly in ACR20 responders. Thus, IL-33 may be a useful marker for monitoring responses to tocilizumab therapy.

Histamine Release from Mast Cells and Basophils

Mast cells and basophils represent the most relevant source of histamine in the immune system. Histamine is stored in cytoplasmic granules along with other amines (e.g., serotonin), proteases, proteoglycans, cytokines/chemokines, and angiogenic factors and rapidly released upon triggering with a variety of stimuli. Moreover, mast cell and basophil histamine release is regulated by several activating and inhibitory receptors. The engagement of different receptors can trigger different modalities of histamine release and degranulation. Histamine released from mast cells and basophils exerts its biological activities by activating four G protein-coupled receptors, namely H1R, H2R, H3R (expressed mainly in the brain), and the recently identified H4R. While H1R and H2R activation accounts mainly for some mast cell- and basophil-mediated allergic disorders, the selective expression of H4R on immune cells is uncovering new roles for histamine (possibly derived from mast cells and basophils) in allergic, inflammatory, and autoimmune disorders. Thus, the in-depth knowledge of mast cell and basophil histamine release and its biologic effects is poised to uncover new therapeutic avenues for a wide spectrum of disorders.

The dual regulation of substance P-mediated inflammation via human synovial mast cells in rheumatoid arthritis

BACKGROUND

Neural pathways are thought to be directly involved in the pathogenesis of rheumatoid arthritis (RA). Although synovial mast cells (MCs) are activated by substance P (SP), the role of MCs in neural pathways in RA remains unknown. The aims of this study were to investigate 1) whether tachykinins are produced by synovial MCs and whether production differs in RA and osteoarthritis (OA) patients, and 2) what is the responsible receptor for SP in synovial MCs.

METHODS

Synovial tissues were obtained from patients with RA or OA undergoing joint replacement surgery. Cultured synovium-derived MCs were generated by culturing dispersed synovial cells with stem cell factor. SP expression was investigated using immunofluorescence and enzyme immunoassays. Mas-related gene X2 (MrgX2) expression was reduced in human MCs using a lentiviral shRNA silencing technique.

RESULTS

SP expression was localized around the cell membrane in 41% (median) of the MCs in synovium from RA but in only 7% of that from OA, suggesting the activation of MCs. Synovial MCs expressed tachykinin (TAC) 1 mRNA, the expression of which was upregulated by the aggregation of FcɛRI or the addition of aggregated IgG. However, the released SP appeared to be rapidly degraded by MC chymase. Synovial MCs were activated with SP through MrgX2 to release histamine without producing proinflammatory cytokines.

CONCLUSIONS

Activated synovial MCs may rapidly degrade SP, which may downregulate the SP-mediated activation of synoviocytes in RA. On the other hand, SP activates MCs to induce inflammatory mediators, suggesting the dual regulation of SP-mediated inflammation by MCs in RA.

Influence of IL-6, IL-33, and TNF-α on human mast cell activation: Lessons from single cell analysis by flow cytometry

BACKGROUND

Mechanisms that govern priming and degranulation of human mast cells (MCs) remain elusive. Besides, most of our knowledge is based on experiments from which data only reflect an average of all stimulated cells. This study aims at investigating the effects of proinflammatory cytokines IL-6, IL-33, and TNF-α on IgE-dependent and IgE-independent activation of individual MCs.

METHODS

MCs were derived from CD34⁺ progenitors isolated from 50 mL whole blood from 4 healthy controls and 5 birch pollen allergic patients. Passively sensitized MCs were preincubated with IL-6, IL-33, or TNF-α and stimulated with anti-IgE/birch pollen allergen or substance P, the latter being a ligand for the G-protein-coupled MRGPRX2-receptor. Activation-i.e., upregulation of CD203c-and anaphylactic degranulation-i.e., appearance of CD63-were measured using flow cytometry.

RESULTS

Preincubation with IL-33 demonstrated upregulated CD203c density without degranulation. Subsequent IgE-dependent stimulation (anti-IgE/birch pollen allergen) resulted in higher appearance of CD63 as compared to cells without preincubation, indicating IL-33 to exert a priming effect (P = 0.04). IL-6 only increased allergen-specific responses but to a lesser extent than IL-33. Combination of IL-33/IL-6 had a synergistic effect, demonstrating more degranulation in response to allergen. TNF-α had no effect on IgE-mediated activation, nor synergistic effects with IL-33. Stimulation with substance P resulted in degranulation that could not be enhanced by preincubation.

CONCLUSIONS

In conclusion, IL-33, and in a lesser extent IL-6, prime individual MCs for subsequent IgE-mediated activation. Moreover, this priming effect is synergistic. In contrast, none of the cytokines had a priming effect on MRGPRX2-mediated activation of MCs. © 2017 International Clinical Cytometry Society.

Bidirectional Mast Cell-Eosinophil Interactions in Inflammatory Disorders and Cancer

Human mast cells (MCs) and eosinophils were first described and named by Paul Ehrlich. These cells have distinct myeloid progenitors and differ morphologically, ultrastructurally, immunologically, biochemically, and pharmacologically. However, MCs and eosinophils play a pivotal role in several allergic disorders. In addition, these cells are involved in autoimmune disorders, cardiovascular diseases, and cancer. MCs are distributed throughout all normal human tissues, whereas eosinophils are present only in gastrointestinal tract, secondary lymphoid tissues, and adipose tissue, thymus, mammary gland, and uterus. However, in allergic disorders, MCs and eosinophils can form the "allergic effector unit." Moreover, in several tumors, MCs and eosinophils can be found in close proximity. Therefore, it is likely that MCs have the capacity to modulate eosinophil functions and vice versa. For example, interleukin 5, stem cell factor, histamine, platelet-activating factor (PAF), prostaglandin D2 (PGD2), cysteinyl leukotrienes, and vascular endothelial growth factors (VEGFs), produced by activated MCs, can modulate eosinophil functions through the engagement of specific receptors. In contrast, eosinophil cationic proteins such as eosinophil cationic protein and major basic protein (MBP), nerve growth factor, and VEGFs released by activated eosinophils can modulate MC functions. These bidirectional interactions between MCs and eosinophils might be relevant not only in allergic diseases but also in several inflammatory and neoplastic disorders.

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.

Are Basophils and Mast Cells Masters in HIV Infection?

The World Health Organization AIDS epidemic update estimates that more than 37 million people are living with HIV infection. Despite the unprecedented success of antiretroviral treatments, significant challenges remain in the fight against HIV. In particular, how uninfected cells capture HIV and transmit virions to target cells remains an unanswered question. Tissue mast cells and peripheral blood basophils can be exposed to virions or HIV products during infection. Several HIV proteins (i.e., envelope glycoproteins gp120 and gp41, Tat, and Nef) can interact with distinct surface receptors expressed by human basophils and mast cells and modulate their functional responses at different levels. Additionally, several groups have provided evidence that human mast cells can be infected in vitro, as well as in vivo, by certain strains of HIV. Recently, it has been demonstrated that basophils purified from healthy donors and intestinal mast cells can efficiently capture HIV on their cell surface and, cocultured with CD4+ T cells, they can transfer the virus to the cocultured cells leading to infection. Direct contact between human basophils or intestinal mast cells and CD4+ T cells can mediate viral trans-infection of T cells through the formation of viral synapses. Thus, basophils and mast cells can provide a cellular basis for capturing and then spreading viruses throughout the body. Collectively, these findings suggest that human basophils and mast cells play a complex and possibly distinct role in HIV infection, warranting further investigations.

Serum IL-33, a new marker predicting response to rituximab in rheumatoid arthritis

BACKGROUND

Recent works have suggested a possible link between interleukin (IL)-33 and B-cell biology. We aimed to study the possible association between serum IL-33 detection and response to rituximab (RTX) in rheumatoid arthritis (RA) patients in different cohorts with an accurate enzyme-linked immunosorbent assay (ELISA).

METHODS

Serum IL-33, rheumatoid factor (RF), anti-cyclic citrullinated peptide (anti-CCP), and high serum immunoglobulin (Ig)G levels were assessed in 111 RA patients receiving a first course of 2 g RTX (cohort 1) in an observational study and in 74 RA patients treated with the same schedule in routine care (cohort 2). Univariate and multivariate analyses identified factors associated with a European League Against Rheumatism (EULAR) response at 24 weeks.

RESULTS

At week 24, 84/111 (76%) and 54/74 (73%) patients reached EULAR response in cohorts 1 and 2, respectively. Serum IL-33 was detectable in only 33.5% of the patients. In the combined cohorts, the presence of RF or anti-CCP (odds ratio (OR) 3.27, 95% confidence interval (CI) 1.13-9.46; p = 0.03), high serum IgG (OR 2.32, 95% CI 1.01-5.33; p = 0.048), and detectable serum IL-33 (OR 2.40, 95% CI 1.01-5.72; p = 0.047) were all associated with RTX response in multivariate analysis. The combination of these three factors increased the likelihood of response to RTX. When serum IL-33 detection was added to seropositivity and serum IgG level, 100% of the patients with the three risk factors (corresponding to 9% of the population) responded to RTX (OR versus patients with none of the three risk factors 29.61, 95% CI 1.30-674.79; p = 0.034).

CONCLUSION

Detectable serum IL-33 may predict clinical response to RTX independently of, and synergistically with, auto-antibodies and serum IgG level.

TRIAL REGISTRATION

NCT01126541 ; 18 May 2010.

Expansion of Th17 Cells by Human Mast Cells Is Driven by Inflammasome-Independent IL-1β

Mast cells (MC) are most well known for their role in innate immune responses. However, MC are increasingly recognized as important regulators of adaptive immune responses, especially in setting the outcome of T cell responses. In this study we determined the effect of MC on cytokine production by naive and memory human Th cells. CD4⁺ T cells were cultured with MC supernatant or control medium, after which cytokine production by T cells was determined. Supernatant of activated MC specifically increased the number of IL-17-producing T cells. This enhancement of Th17 cell number was specifically observed for the memory CD4⁺ T cell population and not for the naive CD4⁺ T cell population. The effect of MC was inhibited for ∼80% by blocking Abs to IL-1β and the rIL-1R antagonist anakinra. Importantly, secretion of active IL-1β by MC was independent of caspase activity, indicating that Th17 cell expansion by MC occurred through inflammasome-independent IL-1β. Together, these studies reveal a role for human MC in setting the outcome of T cell responses through release of caspase-independent IL-1β, and provide evidence for a novel contribution of MC in boosting the Th17 axis in mucosal immune responses.

Connective Tissue Degeneration: Mechanisms of Palmar Fascia Degeneration (Dupuytren's Disease)

Dupuytren's disease is a connective tissue disorder of the hand causing excessive palmar fascial fibrosis with associated finger contracture and disability. The aetiology of the disease is heterogeneous, with both genetic and environmental components. The connective tissue is abnormally infiltrated by myofibroblasts that deposit collagen and other extracellular matrix proteins. We describe the clinical profile of Dupuytren's disease along with current therapeutic schemes. Recent findings on molecular and cellular parameters that are dysregulated in Dupuytren's disease, which may contribute to the onset of the disease, and the role of resident inflammation promoting fibrosis, are highlighted. We review recent literature focusing on non-myofibroblast cell types (stem cell-like cells), their pro-inflammatory and pro-fibrotic role that may account for abnormal wound healing response.