Mast cells contribute to initiation of autoantibody-mediated arthritis via IL-1

Sinapic acid-pullulan based inflammation responsive nanomicelles for the local treatment of experimental inflammatory arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder of joints. It is one of the major causes of disability and morbidity worldwide. Administration of conventional drugs through the systemic route restricts the bioavailability of drugs, systemic toxicity, and reduced efficacy. We have introduced Rebamipide (Reb)-loaded Sinapic acid (SA)-Pullulan (PL) nanomicelles (Reb@SA-PL NMs), a nanotechnology based drug delivery system for the treatment of inflammatory arthritis. PL is a polysaccharide obtained from the fungus Aureobasidium pullulans, and SA is a bioactive polyphenol found in various plants. Both are classified by US-FDA Generally Recognised as Safe (GRAS) materials. Reb@SA-PL NMs found to be cytocompatible. Subsequently, intra-articular administration of Reb@SA-PL NMs enhances the anti-arthritic potential compared to free Reb drug in collagen-induced experimental inflammatory arthritis rat model. Reb@SA-PL NMs reduced the expression of RANKL receptor and Nf-κB. Reb@SA-PL NMs reverses the breakdown of type II collagen, MMP-13, and inhibits the pro-inflammatory markers. Reb@SA-PL NMs prevented bone erosion, cartilage degradation, joint oedema, and synovial inflammation. The results of the study demonstrated that Reb@SA-PL NMs, an enzyme-responsive drug delivery system, has excellent potential for alleviating inflammatory arthritis by blocking MMP-13 and RANKL.

Dietary omega-3 fatty acids modulate the production of platelet-derived microvesicles in an in vivo inflammatory arthritis model

PURPOSE

The aim of this study was to investigate the effects of different ω-3 polyunsaturated fatty acid (PUFA) enriched diets, including a novel renewable plant source of ω-3 fatty acids (Buglossoides arvensis), on the development and progression of rheumatoid arthritis (RA).

METHODS

RA was induced in mice consuming experimental diets using the K/BxN model. The experimental diets consisted of either a western control diet (control), diets containing B. arvensis oil or fish oil. The effects of the diets on platelets, platelet microvesicles (PMVs), and inflammatory markers such as clinical index, ankle thickness and cytokine/chemokine release were measured.

RESULTS

While ω-3 PUFA-enriched diets did not prevent the development of arthritis in the K/BxN model, a significant decrease in ankle swelling was observed compared to the control group. Platelets isolated from mice consuming either low content of B. arvensis oil or fish oil diets exhibited significantly decreased PMVs production compared to mice consuming the control diet.

CONCLUSION

Our study provides insight into the contribution of ω-3 PUFA supplementation in modulating the pro-inflammatory phenotype of platelets in RA pathology. Furthermore, our study suggests that low concentrations of dietary B. arvensis oil may have similar anti-inflammatory potential seen with dietary fish oil supplementation.

Unmasking the NLRP3 inflammasome in dendritic cells as a potential therapeutic target for autoimmunity, cancer, and infectious conditions

Proper and functional immune response requires a complex interaction between innate and adaptive immune cells, which dendritic cells (DCs) are the primary actors in this coordination as professional antigen-presenting cells. DCs are armed with numerous pattern recognition receptors (PRRs) such as nucleotide-binding and oligomerization domain-like receptors (NLRs) like NLRP3, which influence the development of their activation state upon sensation of ligands. NLRP3 is a crucial component of the immune system for protection against tumors and infectious agents, because its activation leads to the assembly of inflammasomes that cause the formation of active caspase-1 and stimulate the maturation and release of proinflammatory cytokines. But, when NLRP3 becomes overactivated, it plays a pathogenic role in the progression of several autoimmune disorders. So, NLRP3 activation is strictly regulated by diverse signaling pathways that are mentioned in detail in this review. Furthermore, the role of NLRP3 in all of the diverse immune cells' subsets is briefly mentioned in this study because NLRP3 plays a pivotal role in modulating other immune cells which are accompanied by DCs' responses and subsequently influence differentiation of T cells to diverse T helper subsets and even impact on cytotoxic CD8+ T cells' responses. This review sheds light on the functional and therapeutic role of NLRP3 in DCs and its contribution to the occurrence and progression of autoimmune disorders, prevention of diverse tumors' development, and recognition and annihilation of various infectious agents. Furthermore, we highlight NLRP3 targeting potential for improving DC-based immunotherapeutic approaches, to be used for the benefit of patients suffering from these disorders.

A bioactive and biodegradable vitamin C stearate-based injectable hydrogel alleviates experimental inflammatory arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory joint disorder affecting nearly 1% of the global population. In RA, synovial joints are infiltrated by inflammatory mediators and enzymes, leading to articular cartilage deterioration, joint damage, and bone erosion. Herein, the 9-aminoacridine-6-O-stearoyl-L-ascorbic acid hydrogel (9AA-SAA hydrogel) was formulated by the heat-cool method and further characterized for surface charge, surface morphology, rheology, and cytocompatibility. Furthermore, we evaluated the therapeutic efficacy of the 9AA-SAA hydrogel, an enzyme-responsive drug delivery system with on-and-off switching capabilities based on disease severity against collagen-induced experimental arthritis in Wistar rats. The anti-inflammatory action of the US FDA-approved drug 9-aminoacridine (9AA) was revealed which acted through nuclear receptor subfamily 4 group A member 1 (NR4A1), an anti-inflammatory orphan nuclear receptor that inhibits nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB). Furthermore, we have explored the role of ascorbic acid, an active moiety of 6-O-stearoyl-L-ascorbic acid (SAA), in promoting the production of collagen production through ten-eleven translocation-2 (TET2) upregulation. Targeting through NR4A1 and TET2 could be the probable mechanism for the treatment of experimental arthritis. The combination of 9AA and ascorbic acid demonstrated enhanced therapeutic efficacy in the 9AA-SAA hydrogel, significantly reducing the severity of experimental arthritis. This approach, in contrast to existing treatments with limited effectiveness, presents a promising and more effective strategy for RA treatment by mitigating inflammation in experimental arthritis.

IL-18 receptor-α signalling pathway contributes to autoantibody-induced arthritis via neutrophil recruitment and mast cell activation

OBJECTIVES

The interleukin (IL)-18 signalling pathway is involved in animal models of collagen-induced arthritis, but the role of this pathway in autoantibody-induced arthritis is poorly understood. An autoantibody-induced arthritis model, K/BxN serum transfer arthritis, reflects the effector phase of arthritis and is important in innate immunity including neutrophils and mast cells. This study aimed to investigate the role of the IL-18 signalling pathway in autoantibody-induced arthritis using IL-18 receptor (IL-18R) α-deficient mice.

METHODS

K/BxN serum transfer arthritis was induced in IL-18Rα-/- and wild-type B6 (controls) mice. The severity of arthritis was graded, and histological and immunohistochemical examinations were performed on paraffin-embedded ankle sections. Total Ribonucleic acid (RNA) isolated from mouse ankle joints was analysed by real-time reverse transcriptase-polymerase chain reaction.

RESULTS

IL-18 Rα-/- mice had significantly lower arthritis clinical scores, neutrophil infiltration, and numbers of activated, degranulated mast cells in the arthritic synovium than in controls. IL-1β, which is indispensable for the progression of arthritis, was significantly downregulated in inflamed ankle tissue in IL-18 Rα-/- mice.

CONCLUSIONS

IL-18/IL-18Rα signalling contributes to the development of autoantibody-induced arthritis by enhancing synovial tissue expression of IL-1β and inducing neutrophil recruitment and mast cell activation. Therefore, inhibition of the IL-18Rα signalling pathway might be a new therapeutic strategy for rheumatoid arthritis.

Bioactivity-Guided Fraction from Viscera of Abalone, Haliotis discus hannai Suppresses Cellular Basophils Activation and Anaphylaxis in Mice

Basophils and mast cells are specialized effector cells in allergic reactions. Haliotis discus hannai (abalone), is valuable seafood. Abalone male viscera, which has a brownish color and has not been previously reported to show anti-allergic activities, was extracted with acetone. Six different acetone/hexane fractions (0, 10, 20, 30, 40, and 100%) were obtained using a silica column via β-hexosaminidase release inhibitory activity-guided selection in phorbol myristate acetate and a calcium ionophore, A23187 (PMACI)-induced human basophils, KU812F cells. The 40% acetone/hexane fraction (A40) exhibited the strongest inhibition of PMACI-induced-β-hexosaminidase release. This fraction dose-dependently inhibited reactive oxygen species (ROS) production and calcium mobilization without cytotoxicity. Western blot analysis revealed that A40 down-regulated PMACI-induced MAPK (ERK 1/2, p-38, and JNK) phosphorylation, and the NF-κB translocation from the cytosol to membrane. Moreover, A40 inhibited PMACI-induced interleukin (IL)-1β, IL-6, and IL-8 production. Anti-allergic activities of A40 were confirmed based on inhibitory effects on IL-4 and tumor necrosis factor alpha (TNF-α) production in compound (com) 48/80-induced rat basophilic leukemia (RBL)-2H3 cells. A40 inhibited β-hexosaminidase release and cytokine production such as IL-4 and TNF-α produced by com 48/80-stimulated RBL-2H3 cells. Furthermore, it's fraction attenuated the IgE/DNP-induced passive cutaneous anaphylaxis (PCA) reaction in the ears of BALB/c mice. Our results suggest that abalone contains the active fraction, A40 is a potent therapeutic and functional material to treat allergic diseases.

Mast cell-mediated immune regulation in health and disease

Mast cells are important components of the immune system, and they perform pro-inflammatory as well as anti-inflammatory roles in the complex process of immune regulation in health and disease. Because of their strategic perivascular localization, sensitivity and adaptability to the microenvironment, and ability to release a variety of preformed and newly synthesized effector molecules, mast cells perform unique functions in almost all organs. Additionally, Mast cells express a wide range of surface and cytoplasmic receptors which enable them to respond to a variety of cytokines, chemicals, and pathogens. The mast cell's role as a cellular interface between external and internal environments as well as between vasculature and tissues is critical for protection and repair. Mast cell interactions with different immune and nonimmune cells through secreted inflammatory mediators may also turn in favor of disease promoting agents. First and forefront, mast cells are well recognized for their multifaceted functions in allergic diseases. Reciprocal communication between mast cells and endothelial cells in the presence of bacterial toxins in chronic/sub-clinical infections induce persistent vascular inflammation. We have shown that mast cell proteases and histamine induce endothelial inflammatory responses that are synergistically amplified by bacterial toxins. Mast cells have been shown to exacerbate vascular changes in normal states as well as in chronic or subclinical infections, particularly among cigarette smokers. Furthermore, a potential role of mast cells in SARS-CoV-2-induced dysfunction of the capillary-alveolar interface adds to the growing understanding of mast cells in viral infections. The interaction between mast cells and microglial cells in the brain further highlights their significance in neuroinflammation. This review highlights the significant role of mast cells as the interface that acts as sensor and early responder through interactions with cells in systemic organs and the nervous system.

Activated mast cells in periprosthetic joint infection-associated tissue

Background

Periprosthetic joint infection (PJI) is a devastating complication of total joint arthroplasty surgery. Increased densities of activated mast cells have been predicted to be present in PJI compared to non-infectious arthroplasty failure based on analysis of transcriptomic data, but their presence in PJI-associated periprosthetic tissues has not been visually confirmed.

Objective

This preliminary study investigated the presence and activation status of mast cells in periprosthetic tissues associated with PJI.

Methods

Periprosthetic tissues from five PJI cases and three arthroplasty failures due to instability and one due to stiffness were immunohistochemically stained using tryptase and microscopically evaluated to enumerate mast cells and evaluate overall activation status within tissue samples. Mast cell activation was evidenced by the release of tryptase into the extracellular space surrounding mast cells.

Results

Mast cells were found in all samples, with average cellular densities of 22 and 26 cells/mm2 tissue in PJI and uninfected samples, respectively (p, 0.6610). Apparent mast cell activation and degranulation was readily observed throughout each of the five PJI samples studied, but not in any of the uninfected samples studied.

Conclusion

While preliminary, these findings provide evidence for a role of mast cells in the immune response in PJI. Additional investigation of the role of mast cells during arthroplasty failure is warranted, providing a better understanding of underlying biology and informing potential diagnostic and treatment targets.

Crosstalk of Mast Cells and Natural Killer Cells with Neurons in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a major comorbidity of cancer. Multiple clinical interventions have been studied to effectively treat CIPN, but the results have been disappointing, with no or little efficacy. Hence, understanding the pathophysiology of CIPN is critical to improving the quality of life and clinical outcomes of cancer patients. Although various mechanisms of CIPN have been described in neuropathic anti-cancer agents, the neuroinflammatory process involving cytotoxic/proinflammatory immune cells remains underexamined. While mast cells (MCs) and natural killer (NK) cells are the key innate immune compartments implicated in the pathogenesis of peripheral neuropathy, their role in CIPN has remained under-appreciated. Moreover, the biology of proinflammatory cytokines associated with MCs and NK cells in CIPN is particularly under-evaluated. In this review, we will focus on the interactions between MCs, NK cells, and neuronal structure and their communications via proinflammatory cytokines, including TNFα, IL-1β, and IL-6, in peripheral neuropathy in association with tumor immunology. This review will help lay the foundation to investigate MCs, NK cells, and cytokines to advance future therapeutic strategies for CIPN.

High Heme and Low Heme Oxygenase-1 Are Associated with Mast Cell Activation/Degranulation in HIV-Induced Chronic Widespread Pain

An overwhelming number of people with HIV (PWH) experience chronic widespread pain (CWP) throughout their lifetimes. Previously, we demonstrated that PWH with CWP have increased hemolysis and attenuated heme oxygenase 1 (HO-1) levels. HO-1 degrades reactive, cell-free heme into antioxidants like biliverdin and carbon monoxide (CO). We found that high heme or low HO-1 caused hyperalgesia in animals, likely through multiple mechanisms. In this study, we hypothesized that high heme or low HO-1 caused mast cell activation/degranulation, resulting in the release of pain mediators like histamine and bradykinin. PWH who self-report CWP were recruited from the University of Alabama at Birmingham HIV clinic. Animal models included HO-1-/- mice and hemolytic mice, where C57BL/6 mice were injected intraperitoneally with phenylhydrazine hydrochloride (PHZ). Results demonstrated that plasma histamine and bradykinin were elevated in PWH with CWP. These pain mediators were also high in HO-1-/- mice and in hemolytic mice. Both in vivo and in vitro (RBL-2H3 mast cells), heme-induced mast cell degranulation was inhibited by treatment with CORM-A1, a CO donor. CORM-A1 also attenuated mechanical and thermal (cold) allodynia in hemolytic mice. Together, the data suggest that mast cell activation secondary to high heme or low HO-1 seen in cells and animals correlates with elevated plasma levels of heme, histamine, and bradykinin in PWH with CWP.

Profiling the Immune Response to Periprosthetic Joint Infection and Non-Infectious Arthroplasty Failure

Arthroplasty failure is a major complication of joint replacement surgery. It can be caused by periprosthetic joint infection (PJI) or non-infectious etiologies, and often requires surgical intervention and (in select scenarios) resection and reimplantation of implanted devices. Fast and accurate diagnosis of PJI and non-infectious arthroplasty failure (NIAF) is critical to direct medical and surgical treatment; differentiation of PJI from NIAF may, however, be unclear in some cases. Traditional culture, nucleic acid amplification tests, metagenomic, and metatranscriptomic techniques for microbial detection have had success in differentiating the two entities, although microbiologically negative apparent PJI remains a challenge. Single host biomarkers or, alternatively, more advanced immune response profiling-based approaches may be applied to differentiate PJI from NIAF, overcoming limitations of microbial-based detection methods and possibly, especially with newer approaches, augmenting them. In this review, current approaches to arthroplasty failure diagnosis are briefly overviewed, followed by a review of host-based approaches for differentiation of PJI from NIAF, including exciting futuristic combinational multi-omics methodologies that may both detect pathogens and assess biological responses, illuminating causes of arthroplasty failure.

Caffeic Acid Modified Nanomicelles Inhibit Articular Cartilage Deterioration and Reduce Disease Severity in Experimental Inflammatory Arthritis

Inflammation plays an important role in the development of rheumatoid arthritis (RA). NR4A1 is an anti-inflammatory orphan nuclear receptor involved in protection from inflammatory stimuli in RA. In this study we have explored the anti-inflammatory potential of the FDA-approved drug 9-aminoacridine (9AA) and the natural compound caffeic acid (CA) conjugated to nanomicelles for the treatment of RA. We have synthesized methoxy polyethylene glycol polycaprolactone block copolymer (mPEG-b-PCL) by ring opening polymerization of ε-caprolactone. Then, we conjugated the hydrophilic caffeic acid (CA) with mPEG-b-PCL micelles via Steglich esterification and incorporated the 9AA drug. These nanomicelles were formulated by the solvent evaporation method with a size distribution around 190 nm and showed maximum drug loading capacity along with sustained drug release behavior. Furthermore, we tested the therapeutic potential of the formulated 9AA-encapsulated CA-conjugated nanomicelles (9AA-NMs) against an experimental RA model. We observed promising results which showed alleviation of arthritic symptoms by reducing inflammation, joint damage, bone erosion, and swelling. Further, collagen destruction was significantly reduced in articular cartilage, as shown by safranin-O and toluidine blue staining. The protective mechanism might be due to the simultaneous inhibition of NF-κB by 9AA and CA, whereas the activation of NR4A1 by 9AA leads to the suppression of HIF-1α. This combined therapeutic effect of 9AA and CA has enhanced the therapeutic efficacy of 9AA-NM and markedly reduced the severity of inflammatory arthritis. Unlike existing drugs for pain management and with limited efficacy, 9AA-NM exerted a disease-relevant activation/blockade that alleviated inflammation and exhibited marked therapeutic efficacy against RA.

Mast Cells and Interleukins

Mast cells play a critical role in inflammatory diseases and tumor growth. The versatility of mast cells is reflected in their ability to secrete a wide range of biologically active cytokines, including interleukins, chemokines, lipid mediators, proteases, and biogenic amines. The aim of this review article is to analyze the complex involvement of mast cells in the secretion of interleukins and the role of interleukins in the regulation of biological activities of mast cells.

Sex Differences in Mast Cell-Associated Disorders: A Life Span Perspective

Mast cells are critical innate immune effectors located throughout the body that are crucial for host defense mechanisms via orchestrating immune responses to a variety of host and environmental stimuli necessary for survival. The role of mast cells in brain development and behavior, meningeal function, and stress-related disorders has also been increasingly recognized. While critical for survival and development, excessive mast cell activation has been linked with an increasing number of inflammatory, stress-associated, and neuroimmune disorders including allergy/anaphylaxis, autoimmune diseases, migraine headache, and chronic pain disorders. Further, a strong sex bias exists for mast cell-associated diseases with females often at increased risk. Here we review sex differences in human mast cell-associated diseases and animal models, and the underlying biological mechanisms driving these sex differences, which include adult gonadal sex hormones as well the emerging organizational role of perinatal gonadal hormones on mast cell activity and development.

Nonhematopoietic IRAK1 drives arthritis via neutrophil chemoattractants

IL-1 receptor-activated kinase 1 (IRAK1) is involved in signal transduction downstream of many TLRs and the IL-1R. Its potential as a drug target for chronic inflammatory diseases is underappreciated. To study its functional role in joint inflammation, we generated a mouse model expressing a functionally inactive IRAK1 (IRAK1 kinase deficient, IRAK1KD), which also displayed reduced IRAK1 protein expression and cell type-specific deficiencies of TLR signaling. The serum transfer model of arthritis revealed a potentially novel role of IRAK1 for disease development and neutrophil chemoattraction exclusively via its activity in nonhematopoietic cells. Consistently, IRAK1KD synovial fibroblasts showed reduced secretion of neutrophil chemoattractant chemokines following stimulation with IL-1β or human synovial fluids from patients with rheumatoid arthritis (RA) and gout. Together with patients with RA showing prominent IRAK1 expression in fibroblasts of the synovial lining, these data suggest that targeting IRAK1 may be therapeutically beneficial. As pharmacological inhibition of IRAK1 kinase activity had only mild effects on synovial fibroblasts from mice and patients with RA, targeted degradation of IRAK1 may be the preferred pharmacologic modality. Collectively, these data position IRAK1 as a central regulator of the IL-1β-dependent local inflammatory milieu of the joints and a potential therapeutic target for inflammatory arthritis.

The protective effects of NE 52-QQ57 against interleukin-33-induced inflammatory response in activated synovial mast cells

Cytokines-mediated immunity is essential for the pathological development of rheumatoid arthritis (RA). Inhibition of signaling has suggested a potential remedial approach to RA. G protein-coupled receptor 4 (GPR4) has been proven to possess a broad range of physiological functions, but its function in synovial mast cells and RA is less reported. In this study, the protective effects of NE 52-QQ57, a GPR4 antagonist, against interleukin (IL)-33-challenged inflammatory response in activated synovial mast cells were investigated. We report that IL-33 amplified GPR4 expression in HMC-1 mast cells. The GPR4 antagonist NE 52-QQ57 alleviated IL-33-caused secretions of IL-17, interferon-γ, and tumor necrosis factor-α in HMC-1 mast cells. Furthermore, we note that NE 52-QQ57 reduced IL-33-induced expressions of matrix metalloproteinase-2 (MMP-2) and MMP-9. Also, NE 52-QQ57 inhibited cyclooxygenase 2 and prostaglandin E2 expression in IL-33-challenged cells. Also, NE 52-QQ57 ameliorated IL-33-induced oxidative stress by reducing mitochondrial reactive oxygen species and 4-hydroxynonenal. Mechanistically, NE 52-QQ57 mitigated IL-33-induced activation of the p38/nuclear factor-κB signaling pathway. We conclude that targeting GPR4 might be a promising strategy for RA treatment.

The Interactions Between Autoinflammation and Type 2 Immunity: From Mechanistic Studies to Epidemiologic Associations

Autoinflammatory diseases are a group of clinical syndromes characterized by constitutive overactivation of innate immune pathways. This results in increased production of or responses to monocyte- and neutrophil-derived cytokines such as interleukin-1β (IL-1β), Tumor Necrosis Factor-α (TNF-α), and Type 1 interferon (IFN). By contrast, clinical allergy is caused by dysregulated type 2 immunity, which is characterized by expansion of T helper 2 (Th2) cells and eosinophils, as well as overproduction of the associated cytokines IL-4, IL-5, IL-9, and IL-13. Traditionally, type 2 immune cells and autoinflammatory effectors were thought to counter-regulate each other. However, an expanding body of evidence suggests that, in some contexts, autoinflammatory pathways and cytokines may potentiate type 2 immune responses. Conversely, type 2 immune cells and cytokines can regulate autoinflammatory responses in complex and context-dependent manners. Here, we introduce the concepts of autoinflammation and type 2 immunity. We proceed to review the mechanisms by which autoinflammatory and type 2 immune responses can modulate each other. Finally, we discuss the epidemiology of type 2 immunity and clinical allergy in several monogenic and complex autoinflammatory diseases. In the future, these interactions between type 2 immunity and autoinflammation may help to expand the spectrum of autoinflammation and to guide the management of patients with various autoinflammatory and allergic diseases.

Sargahydroquinoic acid isolated from Sargassum serratifolium as inhibitor of cellular basophils activation and passive cutaneous anaphylaxis in mice

Basophils and mast cells are characteristic effector cells in allergic reactions. Sargahydorquinoic acid (SHQA), a compound isolated from Sargassum serratifolium (marine alga), possesses various biochemical properties, including potent antioxidant activities. The objective of the present study was to investigate inhibitory effects of SHQA on the activation of human basophilic KU812F cells induced by phorbol myristate acetate and A23187 (PMACI), a calcium ionophore. Furthermore, we confirmed the inhibitory effects of SHQA on the activation of rat basophilic leukemia (RBL)-2H3 cells induced by compound 48/80 (com 48/80), bone marrow-derived mast cells (BMCMCs) induced by anti-dinitrophenyl(DNP)-immunoglobulin E (IgE)/DNP-bovine serum albumin (BSA), DNP/IgE and on the reaction of passive cutaneous anaphylaxis (PCA) mediated by IgE. SHQA reduced PMACI-induced intracellular reactive oxygen species (ROS) and calcium levels. Western blot analysis revealed that SHQA downregulated the activation of ERK, p38, and NF-κB in a dose-dependent manner. Moreover, SHQA suppressed the production and gene expression of various cytokines, including interleukin (IL)-1 β, IL-4, IL-6, and IL-8 in PMACI-induced KU812F cells and IL-4 and tumor necrosis factor (TNF)- α in com 48/80-induced RBL-2H3 cells. It also determined the inhibition of PMACI, com 48/80- and IgE/DNP-induced degranulation by reducing the release of β -hexosaminidase. Furthermore, it attenuated the IgE/DNP-induced PCA reaction in the ears of BALB/c mice. These results suggest that SHQA isolated from S. serratifolium is a potential therapeutic functional food material for inhibiting effector cell activation in allergic reactions and anaphylaxis in animal model.

Molecular and Cellular Heterogeneity in Rheumatoid Arthritis: Mechanisms and Clinical Implications

Rheumatoid arthritis is an autoimmune disease that exhibits significant clinical heterogeneity. There are various treatments for rheumatoid arthritis, including disease-modifying anti-rheumatic drugs (DMARDs), glucocorticoids, non-steroidal anti-inflammatory drugs (NSAIDs), and inflammatory cytokine inhibitors (ICI), typically associated with differentiated clinical effects and characteristics. Personalized responsiveness is observed to the standard treatment due to the pathophysiological heterogeneity in rheumatoid arthritis, resulting in an overall poor prognosis. Understanding the role of individual variation in cellular and molecular mechanisms related to rheumatoid arthritis will considerably improve clinical care and patient outcomes. In this review, we discuss the source of pathophysiological heterogeneity derived from genetic, molecular, and cellular heterogeneity and their possible impact on precision medicine and personalized treatment of rheumatoid arthritis. We provide emphasized description of the heterogeneity derived from mast cells, monocyte cell, macrophage fibroblast-like synoviocytes and, interactions within immune cells and with inflammatory cytokines, as well as the potential as a new therapeutic target to develop a novel treatment approach. Finally, we summarize the latest clinical trials of treatment options for rheumatoid arthritis and provide a suggestive framework for implementing preclinical and clinical experimental results into clinical practice.

IL-1β-driven osteoclastogenic Tregs accelerate bone erosion in arthritis

IL-1β is a proinflammatory mediator with roles in innate and adaptive immunity. Here we show that IL-1β contributes to autoimmune arthritis by inducing osteoclastogenic capacity in Tregs. Using mice with joint inflammation arising through deficiency of the IL-1 receptor antagonist (Il1rn-/-), we observed that IL-1β blockade attenuated disease more effectively in early arthritis than in established arthritis, especially with respect to bone erosion. Protection was accompanied by a reduction in synovial CD4+Foxp3+ Tregs that displayed preserved suppressive capacity and aerobic metabolism but aberrant expression of RANKL and a striking capacity to drive RANKL-dependent osteoclast differentiation. Both Il1rn-/- Tregs and wild-type Tregs differentiated with IL-1β accelerated bone erosion upon adoptive transfer. Human Tregs exhibited analogous differentiation, and corresponding RANKLhiFoxp3+ T cells could be identified in rheumatoid arthritis synovial tissue. Together, these findings identify IL-1β-induced osteoclastogenic Tregs as a contributor to bone erosion in arthritis.

Mast Cells in the Skin: Defenders of Integrity or Offenders in Inflammation?

Mast cells (MCs) are best-known as key effector cells of immediate-type allergic reactions that may even culminate in life-threatening anaphylactic shock syndromes. However, strategically positioned at the host–environment interfaces and equipped with a plethora of receptors, MCs also play an important role in the first-line defense against pathogens. Their main characteristic, the huge amount of preformed proinflammatory mediators embedded in secretory granules, allows for a rapid response and initiation of further immune effector cell recruitment. The same mechanism, however, may account for detrimental overshooting responses. MCs are not only detrimental in MC-driven diseases but also responsible for disease exacerbation in other inflammatory disorders. Focusing on the skin as the largest immune organ, we herein review both beneficial and detrimental functions of skin MCs, from skin barrier integrity via host defense mechanisms to MC-driven inflammatory skin disorders. Moreover, we emphasize the importance of IgE-independent pathways of MC activation and their role in sustained chronic skin inflammation and disease exacerbation.

The central role of IL-33/IL-1RL1 pathway in asthma: From pathogenesis to intervention

Interleukin-33 (IL-33), a member of the IL-1 family, and its cognate receptor, Interleukin-1 receptor like-1 (IL-1RL1 or ST2), are susceptibility genes for childhood asthma. In response to cellular damage, IL-33 is released from barrier tissues as an 'alarmin' to activate the innate immune response. IL-33 drives type 2 responses by inducing signalling through its receptor IL-1RL1 in several immune and structural cells, thereby leading to type 2 cytokine and chemokine production. IL-1RL1 gene transcript encodes different isoforms generated through alternative splicing. Its soluble isoform, IL-1RL1-a or sST2, acts as a decoy receptor by sequestering IL-33, thereby inhibiting IL1RL1-b/IL-33 signalling. IL-33 and its receptor IL-1RL1 are therefore considered as putative biomarkers or targets for pharmacological intervention in asthma. This review will provide an overview of the genetics and biology of the IL-33/IL-1RL1 pathway in the context of asthma pathogenesis. It will discuss the potential and complexities of targeting the cytokine or its receptor, how genetics or biomarkers may inform precision medicine for asthma targeting this pathway, and the possible positioning of therapeutics targeting IL-33 or its receptor in the expanding landscape of novel biologicals applied in asthma management.

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.

Neuronal interleukin-1 receptors mediate pain in chronic inflammatory diseases

Chronic pain is a major comorbidity of chronic inflammatory diseases. Here, we report that the cytokine IL-1β, which is abundantly produced during multiple sclerosis (MS), arthritis (RA), and osteoarthritis (OA) both in humans and in animal models, drives pain associated with these diseases. We found that the type 1 IL-1 receptor (IL-1R1) is highly expressed in the mouse and human by a subpopulation of TRPV1⁺ dorsal root ganglion neurons specialized in detecting painful stimuli, termed nociceptors. Strikingly, deletion of the Il1r1 gene specifically in TRPV1⁺ nociceptors prevented the development of mechanical allodynia without affecting clinical signs and disease progression in mice with experimental autoimmune encephalomyelitis and K/BxN serum transfer–induced RA. Conditional restoration of IL-1R1 expression in nociceptors of IL-1R1–knockout mice induced pain behavior but did not affect joint damage in monosodium iodoacetate–induced OA. Collectively, these data reveal that neuronal IL-1R1 signaling mediates pain, uncovering the potential benefit of anti–IL-1 therapies for pain management in patients with chronic inflammatory diseases.

The prospects for targeting FcR as a novel therapeutic strategy in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by synovial membrane hyperplasia, infiltration of inflammatory cells and bone tissue destruction. Although there have been many measures taken for RA therapy in recent years, they are not sufficiently safe or effective. Thus, it is very important to develop new drugs and slow down damage to other healthy organs in the case of RA. Lately, immunoglobulin Fc receptors (FcRs), such as the IgG Fc receptor (FcγR), IgA Fc receptor (FcαR), and IgD Fc receptor (FcδR), have been found to be involved in inducing or suppressing arthritis. FcRs interacting with immune complexes (ICs) are a key factor in the etiopathogenesis of RA. Therefore, an increasing number of methodsfor the targeted treatment of RA with FcRs are emerging, such as recombinant soluble FcγRs, recombinant multimeric Fc fragments and monoclonal antibodies, and have been demonstrated to significantly improve RA symptoms. Simultaneously, certain kinases involved in the downstream signaling of FcRs can also be a target for the treatment of RA, such as Syk and Btk inhibitors. An overview of these FcRs is provided in this review, including a description of FcR-related functions, signaling pathways, and potential FcR-targeting molecules for RA therapy. To date, the initial results of those developed FcR-targeting molecules have been promising. With this, FcRs might offer a better alternative to RA medication. Additionally, further pharmacological characterization and a better understanding of the unique mechanisms of FcR-targeting molecules are necessary.

Mast cells as a unique hematopoietic lineage and cell system: From Paul Ehrlich's visions to precision medicine concepts

The origin and functions of mast cells (MCs) have been debated since their description by Paul Ehrlich in 1879. MCs have long been considered 'reactive bystanders' and 'amplifiers' in inflammatory processes, allergic reactions, and host responses to infectious diseases. However, knowledge about the origin, phenotypes and functions of MCs has increased substantially over the past 50 years. MCs are now known to be derived from multipotent hematopoietic progenitors, which, through a process of differentiation and maturation, form a unique hematopoietic lineage residing in multiple organs. In particular, MCs are distinguishable from basophils and other hematopoietic cells by their unique phenotype, origin(s), and spectrum of functions, both in innate and adaptive immune responses and in other settings. The concept of a unique MC lineage is further supported by the development of a distinct group of neoplasms, collectively referred to as mastocytosis, in which MC precursors expand as clonal cells. The clinical consequences of the expansion and/or activation of MCs are best established in mastocytosis and in allergic inflammation. However, MCs have also been implicated as important participants in a number of additional pathologic conditions and physiological processes. In this article, we review concepts regarding MC development, factors controlling MC expansion and activation, and some of the fundamental roles MCs may play in both health and disease. We also discuss new concepts for suppressing MC expansion and/or activation using molecularly-targeted drugs.

Notch signalling drives synovial fibroblast identity and arthritis pathology

The synovium is a mesenchymal tissue composed mainly of fibroblasts with a lining and sublining that surrounds the joints. In rheumatoid arthritis (RA), the synovial tissue undergoes marked hyperplasia, becomes inflamed and invasive and destroys the joint^1,2. Recently, we and others found that a subset of fibroblasts located in the sublining undergoes major expansion in RA and is linked to disease activity^3,4,5. However, the molecular mechanism by which these fibroblasts differentiate and expand in RA remains unknown. Here, we identified a critical role for NOTCH3 signaling in the differentiation of perivascular and sublining CD90(THY1)+ fibroblasts. Using single cell RNA-sequencing and synovial tissue organoids, we found that NOTCH3 signaling drives both transcriptional and spatial gradients in fibroblasts emanating from vascular endothelial cells outward. In active RA, NOTCH3 and NOTCH target genes are markedly upregulated in synovial fibroblasts. Importantly, genetic deletion of Notch3 or monoclonal antibody-blockade of NOTCH3 signaling attenuates inflammation and prevents joint damage in inflammatory arthritis. Our results indicate that synovial fibroblasts exhibit positional identity regulated by endothelium-derived Notch signaling and that this stromal crosstalk pathway underlies inflammation and pathology in inflammatory arthritis.

The Role of Mast Cells in Bone Metabolism and Bone Disorders

Mast cells (MCs) are important sensor and effector cells of the immune system that are involved in many physiological and pathological conditions. Increasing evidence suggests that they also play an important role in bone metabolism and bone disorders. MCs are located in the bone marrow and secrete a wide spectrum of mediators, which can be rapidly released upon activation of mature MCs following their differentiation in mucosal or connective tissues. Many of these mediators can exert osteocatabolic effects by promoting osteoclast formation [e.g., histamine, tumor necrosis factor (TNF), interleukin-6 (IL-6)] and/or by inhibiting osteoblast activity (e.g., IL-1, TNF). By contrast, MCs could potentially act in an osteoprotective manner by stimulating osteoblasts (e.g., transforming growth factor-β) or reducing osteoclastogenesis (e.g., IL-12, interferon-γ). Experimental studies investigating MC functions in physiological bone turnover using MC-deficient mouse lines give contradictory results, reporting delayed or increased bone turnover or no influence depending on the mouse model used. By contrast, the involvement of MCs in various pathological conditions affecting bone is evident. MCs may contribute to the pathogenesis of primary and secondary osteoporosis as well as inflammatory disorders, including rheumatoid arthritis and osteoarthritis, because increased numbers of MCs were found in patients suffering from these diseases. The clinical observations could be largely confirmed in experimental studies using MC-deficient mouse models, which also provide mechanistic insights. MCs also regulate bone healing after fracture by influencing the inflammatory response toward the fracture, vascularization, bone formation, and callus remodeling by osteoclasts. This review summarizes the current view and understanding of the role of MCs on bone in both physiological and pathological conditions.

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.

Paradigm Shifts in Mast Cell and Basophil Biology and Function: An Emerging View of Immune Regulation in Health and Disease

The physiological role of the mast cell and basophil has for many years remained enigmatic. In this chapter, we briefly summarize some of the more recent studies that shed new light on the role of mast cells and basophils in health and disease. What we gain from these studies is a new appreciation for mast cells and basophils as sentinels in host defense and a further understanding that dysregulation of mast cell and basophil function can be a component of various diseases other than allergies. Perhaps the most important insight reaped from this work is the increasing awareness that mast cells and basophils can function as immunoregulatory cells that modulate the immune response in health and disease. Collectively, the recent knowledge provides new challenges and opportunities toward the development of novel therapeutic strategies to augment host protection and modify disease through manipulation of mast cell and basophil function.

Mast Cells as a Double-Edged Sword in Immunity: Their Function in Health and Disease. First of Two Parts

Mast cells (MCs) have recently been re-interpreted in the context of the immune scenario in the sense that their pro-allergic role is no longer exclusive. In fact, MCs even in steady state conditions maintain homeostatic functions, producing mediators and intensively cross-talking with other immune cells. Here, emphasis will be placed on the array of receptors expressed by MCs and the variety of cytokines they produce. Then, the bulk of data discussed will provide readers with a wealth of information on the dual ability of MCs not only to defend but also to offend the host. This double attitude of MCs relies on many variables, such as their subsets, tissues of residency and type of stimuli ranging from microbes to allergens and food antigens. Finally, the relationship between MCs with basophils and eosinophils will be discussed.

Revisit of autoimmunity to glucose-6-phosphate isomerase in experimental and rheumatoid arthritis

Rheumatoid arthritis (RA) is an inflammatory disorder characterized by synovial inflammation in multiple joints. Autoantibodies (Abs) are the hallmark of RA, and as disease-specific and diagnostic markers, rheumatoid factor and anti-citrullinated protein antibody (ACPA) are produced pre-clinically, but their pathogenic roles in RA remain elusive. In this review, we focus on one of the candidate autoantigens in RA; glucose-6-phosphate isomerase (GPI). The arthritogenic role of GPI has been confirmed in two different mouse models: the K/BxN- and GPI-induced arthritis models. Both anti-GPI Abs and citrullinated-GPI peptide Abs have been detected in human RA. Studies conducted in these rodent models have confirmed that the pathogenesis of arthritis involves the localization of autoantigens not only in the joints but also in the circulation. In this review, we revisit and summarize the arthritogenic relevance of GPI in animal RA models and in human RA, and extend the discussion to joint-specific inflammation.

Dendritic cells, T cells and their interaction in rheumatoid arthritis

Dendritic cells (DCs) are the key professional antigen-presenting cells which bridge innate and adaptive immune responses, inducing the priming and differentiation of naive to effector CD4+ T cells, the cross-priming of CD8+ T cells and the promotion of B cell antibody responses. DCs also play a critical role in the maintenance of immune homeostasis and tolerance. DC-T cell interactions underpin the generation of an autoimmune response in rheumatoid arthritis (RA). Here we describe the function of DCs and review evidence for DC and T cell involvement in RA pathogenesis, in particular through the presentation of self-peptide by DCs that triggers differentiation and activation of autoreactive T cells. Finally, we discuss the emerging field of targeting the DC-T cell interaction for antigen-specific immunotherapy of RA.

Antibody-dependent and -independent mechanisms of inflammatory arthritis

Inflammatory arthritis encompasses a set of common diseases characterized by immune-mediated attack on joint tissues. Most but not all affected patients manifest circulating autoantibodies. Decades of study in human and animal arthritis have identified key roles for autoantibodies in immune complexes and through direct modulation of articular biology. However, joint inflammation can arise because of pathogenic T cells and other pathways that are antibody-independent. Here we review the evidence for these parallel tracks, in animal models and in humans, to explore the range of mechanisms engaged in the pathophysiology of arthritis and to highlight opportunities for targeted therapeutic intervention.

Importance of Fc Receptor γ-Chain ITAM Tyrosines in Neutrophil Activation and in vivo Autoimmune Arthritis

Activating Fcγ receptors associated with Fc receptor γ-chain (FcRγ) are critical for mediating neutrophil effector functions in immune complex-mediated autoimmune diseases. FcRγ contains ITAM tyrosines and the in vivo role of these tyrosines has not been defined in neutrophils and arthritis. In this study, the in vivo functions of FcRγ ITAM tyrosines were characterized using wild type and ITAM tyrosine mutant (Y65F/Y76F) transgenic mice crossed to an FcRγ-deficient genetic background. FcRγ-deficient neutrophils showed undetectable cell surface expression of the activating Fcγ receptor IV, defective immune complex-induced superoxide production, degranulation and spreading. Although the re-expression of both the wild type and the ITAM tyrosine mutant (Y65F/Y76F) FcRγ could restore activating Fcγ receptor expression of FcRγ-deficient neutrophils, only the wild type transgenic form could mediate Fcγ receptor-dependent effector functions. In contrast, neutrophils carrying ITAM tyrosine mutant FcRγ were unable to produce superoxide, mediate degranulation and perform active spreading. In addition, our results confirmed the protection of FcRγ-deficient mice from autoimmune arthritis. Importantly, the presence of the wild type FcRγ transgene, in contrast to the ITAM tyrosine mutant transgene, partially reversed autoimmune arthritis development. The reversing effect of the wild type transgene was even more robust when animals carried the wild type transgene in a homozygous form. Collectively, FcRγ ITAM tyrosines play a critical role in the induction of neutrophil effector responses, the initiation and progression of an autoantibody-induced experimental arthritis in vivo, indicating a signaling, rather than just a receptor stabilizing function of the molecule.

Mast cells as sources of cytokines, chemokines, and growth factors

Mast cells are hematopoietic cells that reside in virtually all vascularized tissues and that represent potential sources of a wide variety of biologically active secreted products, including diverse cytokines and growth factors. There is strong evidence for important non-redundant roles of mast cells in many types of innate or adaptive immune responses, including making important contributions to immediate and chronic IgE-associated allergic disorders and enhancing host resistance to certain venoms and parasites. However, mast cells have been proposed to influence many other biological processes, including responses to bacteria and virus, angiogenesis, wound healing, fibrosis, autoimmune and metabolic disorders, and cancer. The potential functions of mast cells in many of these settings is thought to reflect their ability to secrete, upon appropriate activation by a range of immune or non-immune stimuli, a broad spectrum of cytokines (including many chemokines) and growth factors, with potential autocrine, paracrine, local, and systemic effects. In this review, we summarize the evidence indicating which cytokines and growth factors can be produced by various populations of rodent and human mast cells in response to particular immune or non-immune stimuli, and comment on the proven or potential roles of such mast cell products in health and disease.

Berberine suppresses IL-33-induced inflammatory responses in mast cells by inactivating NF-κB and p38 signaling

Berberine (BBR) possesses many pharmacological characteristics including anti-inflammation, anti-allergy, anti-angiogenesis and anti-tumor. However, the effects and mechanisms of BBR on IL-33-induced mast cell inflammatory responses are kept unknown. To investigate these, rat peritoneal mast cells (RPMCs) were isolated from the peritoneal cavity and cultured with BBR treatment in combination IL-33 stimulation. Firstly, cytotoxic effect of BBR on RPMCs was detected by MTT assay. Then, IL-33-induced cytokine production and the expression of ST2 receptor, were evaluated by ELISA and real-time PCR, respectively. In addition, NF-κB and MAPK signaling involved in IL-33-mediated mast cell activation were assessed by Western blot, which also was confirmed using the signal transduction inhibitors. Simultaneously, the effect of BBR on IL-33-activated enhancement of IgE-mediated mast cell responses was analyzed. Lastly, SD rats were used to explore the effect of BBR on IL-33-induced inflammation in vivo. BBR treatment significantly reduced IL-33-stimulated cytokine production in RPMCs, such as IL-6, TNF-α, IL-13 and MCP-1, but had little effect in ST2 expression. BBR modulated IL-33 signaling via suppressing IL-33-induced NF-ΚB transcription and p38 phosphorylation, but not ERK and JNK. Additionally, BBR also hampered the combined effects of IL-33 and IgE-mediated mast cell activation. Decreased cytokine production followed BBR treatment in vitro was consistent with that in vivo, where BBR injection i.p. into rats obviously inhibited IL-33-induced plasma cytokine levels. These findings demonstrated that BBR suppressed IL-33-mediated inflammation in mast cells by inactivating NF-κB and p38 signaling, suggesting its potential application for the treatment of allergic inflammation.

Lineage-Specific Analysis of Syk Function in Autoantibody-Induced Arthritis

Autoantibody production and autoantibody-mediated inflammation are hallmarks of a number of autoimmune diseases. The K/BxN serum-transfer arthritis is one of the most widely used models of the effector phase of autoantibody-induced pathology. Several hematopoietic lineages including neutrophils, platelets, and mast cells have been proposed to contribute to inflammation and tissue damage in this model. We have previously shown that the Syk tyrosine kinase is critically involved in the development in K/BxN serum-transfer arthritis and bone marrow chimeric experiments indicated that Syk is likely involved in one or more hematopoietic lineages during the disease course. The aim of the present study was to further define the lineage(s) in which Syk expression is required for autoantibody-induced arthritis. To this end, K/BxN serum-transfer arthritis was tested in conditional mutant mice in which Syk was deleted in a lineage-specific manner from neutrophils, platelets, or mast cells. Combination of the MRP8-Cre, PF4-Cre, or Mcpt5-Cre transgene with floxed Syk alleles allowed efficient and selective deletion of Syk from neutrophils, platelets, or mast cells, respectively. This has also been confirmed by defective Syk-dependent in vitro functional responses of the respective cell types. In vivo studies revealed nearly complete defect of the development of K/BxN serum-transfer arthritis upon neutrophil-specific deletion of Syk. By contrast, Syk deletion from platelets or mast cells did not affect the development of K/BxN serum-transfer arthritis. Our results indicate that autoantibody-induced arthritis requires Syk expression in neutrophils, whereas, contrary to prior assumptions, Syk expression in platelets or mast cells is dispensable for disease development in this model.

Targeting IgG in Arthritis: Disease Pathways and Therapeutic Avenues

Rheumatoid arthritis (RA) is a polygenic and multifactorial syndrome. Many complex immunological and genetic interactions are involved in the final outcome of the clinical disease. Autoantibodies (rheumatoid factors, anti-citrullinated peptide/protein antibodies) are present in RA patients' sera for a long time before the onset of clinical disease. Prior to arthritis onset, in the autoantibody response, epitope spreading, avidity maturation, and changes towards a pro-inflammatory Fc glycosylation phenotype occurs. Genetic association of epitope specific autoantibody responses and the induction of inflammation dependent and independent changes in the cartilage by pathogenic autoantibodies emphasize the crucial contribution of antibody-initiated inflammation in RA development. Targeting IgG by glyco-engineering, bacterial enzymes to specifically cleave IgG/alter N-linked Fc-glycans at Asn 297 or blocking the downstream effector pathways offers new avenues to develop novel therapeutics for arthritis treatment.

A time-course microarray data analysis reveals consistent dysregulated genes and upstream microRNAs in autoantibody-mediated arthritis

Background

The purpose of this study is to identify key genes and microRNAs (miRNAs) involved in autoantibody-mediated arthritis (AMA).

Methods

A time-course microarray data (ID: GSE27492) of peripheral blood leukocytes, ankle tissue, and synovial fluid from K/BxN mouse serum-transferred mice were downloaded from Gene Expression Omnibus. Those samples were collected at days 0, 1, 3, 7, 12, and 18 after serum injection. Limma of R was employed to identify differentially expressed genes (DEGs) in samples collected at days 1–18 compared with those collected at day 0. Consistent DEGs were obtained by taking the interaction of DEGs from different time points, followed by functional enrichment analysis. MiRNAs were screened out and constructed into regulatory network with DEGs using Cytoscape.

Results

In total, 17 consistent DEGs were obtained, including downregulated Ephx1 and upregulated AF251705, Adam8, Arg1, Basp1, Ccl2, Ccl7, Ccl9, Ccr2, Clec4a2, Clec4d, Cxcl1, Fabp5, Fcgr1, Gp49a, Il1rn, and Saa3. Those DEGs were associated with biological processes of immune response, inflammatory response, and defense response; chemokine signaling pathway; cytokine-cytokine receptor interaction; and NOD-like receptor signaling pathway. Additionally, 202 miRNAs were identified to have a regulatory effect on 9 of the 17 DEGs. Notably, miR-944, miR-374a, and miR374b were found to regulate the expression of Cxcl1, Ccl7, and Ccl2. Clec4d was targeted by 78 miRNAs.

Conclusions

Our study reveals that 17 DEGs and 202 miRNAs may be associated with autoimmune disorder in the progression of AMA, which could guide future researches.

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.

Mechanisms of Autoantibody-Induced Pathology

Autoantibodies are frequently observed in healthy individuals. In a minority of these individuals, they lead to manifestation of autoimmune diseases, such as rheumatoid arthritis or Graves' disease. Overall, more than 2.5% of the population is affected by autoantibody-driven autoimmune disease. Pathways leading to autoantibody-induced pathology greatly differ among different diseases, and autoantibodies directed against the same antigen, depending on the targeted epitope, can have diverse effects. To foster knowledge in autoantibody-induced pathology and to encourage development of urgently needed novel therapeutic strategies, we here categorized autoantibodies according to their effects. According to our algorithm, autoantibodies can be classified into the following categories: (1) mimic receptor stimulation, (2) blocking of neural transmission, (3) induction of altered signaling, triggering uncontrolled (4) microthrombosis, (5) cell lysis, (6) neutrophil activation, and (7) induction of inflammation. These mechanisms in relation to disease, as well as principles of autoantibody generation and detection, are reviewed herein.

Megakaryocytes compensate for Kit insufficiency in murine arthritis

The growth factor receptor Kit is involved in hematopoietic and nonhematopoietic development. Mice bearing Kit defects lack mast cells; however, strains bearing different Kit alleles exhibit diverse phenotypes. Herein, we investigated factors underlying differential sensitivity to IgG-mediated arthritis in 2 mast cell-deficient murine lines: KitWsh/Wsh, which develops robust arthritis, and KitW/Wv, which does not. Reciprocal bone marrow transplantation between KitW/Wv and KitWsh/Wsh mice revealed that arthritis resistance reflects a hematopoietic defect in addition to mast cell deficiency. In KitW/Wv mice, restoration of susceptibility to IgG-mediated arthritis was neutrophil independent but required IL-1 and the platelet/megakaryocyte markers NF-E2 and glycoprotein VI. In KitW/Wv mice, platelets were present in numbers similar to those in WT animals and functionally intact, and transfer of WT platelets did not restore arthritis susceptibility. These data implicated a platelet-independent role for the megakaryocyte, a Kit-dependent lineage that is selectively deficient in KitW/Wv mice. Megakaryocytes secreted IL-1 directly and as a component of circulating microparticles, which activated synovial fibroblasts in an IL-1-dependent manner. Transfer of WT but not IL-1-deficient megakaryocytes restored arthritis susceptibility to KitW/Wv mice. These findings identify functional redundancy among Kit-dependent hematopoietic lineages and establish an unanticipated capacity of megakaryocytes to mediate IL-1-driven systemic inflammatory disease.

Interleukin-33 as a marker of disease activity in rheumatoid factor positive polyarticular juvenile idiopathic arthritis

OBJECTIVE

To investigate clinical usefulness of serum interleukin (IL)-33 levels as an indicator of disease activity in juvenile idiopathic arthritis (JIA).

METHODS

We measured serum levels of IL-33 in 39 patients with JIA, including 7 patients with rheumatoid factor positive poly-JIA (RF + poly-JIA), 8 patients with RF negative poly-JIA (RF-poly-JIA), 20 patients with oligoarticular JIA (Oligo-JIA), 4 patients with enthesitis-related arthritis (ERA) and 30 age-matched healthy controls. Furthermore, we determined their correlation with measures of disease activity.

RESULTS

Serum IL-33 levels in patients with RF + poly-JIA were significantly elevated compared to those in patients with RF-poly-JIA, oligo-JIA and HC. Serum IL-33 levels in patients with RF-poly-JIA, oligo-JIA and ERA were not elevated compared to those in HC. Serum IL-33 levels in RF + poly-JIA patients normalized in remission phase. Serum IL-33 levels correlated positively with RF in patients with RF + poly-JIA.

CONCLUSIONS

These results indicate that serum IL-33 levels in RF + poly-JIA patients correlated with disease activity, suggesting a potential role of IL-33 as a promising indicator of disease activity.

bIgG time for large eaters: monocytes and macrophages as effector and target cells of antibody-mediated immune activation and repression

The mononuclear phagocytic system consists of a great variety of cell subsets localized throughout the body in immunological and non-immunological tissues. While one of their prime tasks is to detect, phagocytose, and kill intruding microorganisms, they are also involved in maintaining tissue homeostasis and immune tolerance toward self through removal of dying cells. Furthermore, monocytes and macrophages have been recognized to play a critical role for mediating immunoglobulin G (IgG)-dependent effector functions, including target cell depletion, tissue inflammation, and immunomodulation. For this, monocyte and macrophage populations are equipped with a complex set of Fc-receptors, enabling them to directly interact with pro- or anti-inflammatory IgG preparations. In this review, we will summarize the most recent findings, supporting a central role of monocytes and macrophages for pro- and anti-inflammatory IgG activity.

Serglycin proteoglycans limit enteropathy in Trichinella spiralis-infected mice

BACKGROUND

Serglycin proteoglycans are essential for maturation of secretory granules and for the correct granular storage of cationic proteases in hematopoietic cells, e.g. mast cells. However, little is known about the in vivo functions of serglycin proteoglycans during infection. Here we investigated the potential role of serglycin proteoglycans in host defense after infection with the nematode Trichinella spiralis.

RESULTS

Twelve days post infection lack of serglycin proteoglycans caused significantly increased enteropathy. The serglycin-deficient mice showed significantly increased intestinal worm burden, reduced recruitment of mast cells to the intestinal crypts, decreased levels of the mast cell proteases MCPT5 and MCPT6 in intestinal tissue, decreased serum levels of TNF-α, IL-1β, IL-10 and IL-13, increased levels of IL-4 and total IgE in serum, and increased intestinal levels of the neutrophil markers myeloperoxidase and elastase, as compared to wild type mice. At five weeks post infection, increased larvae burden and inflammation were seen in the muscle tissue of the serglycin-deficient mice.

CONCLUSIONS

Our results demonstrate that the serglycin-deficient mice were more susceptible to T. spiralis infection and displayed an unbalanced immune response compared to wild type mice. These findings point to an essential regulatory role of serglycin proteoglycans in immunity.

K/BxN Serum-Transfer Arthritis as a Model for Human Inflammatory Arthritis

The K/BxN serum-transfer arthritis (STA) model is a murine model in which the immunological mechanisms occurring in rheumatoid arthritis (RA) and other arthritides can be studied. To induce K/BxN STA, serum from arthritic transgenic K/BxN mice is transferred to naive mice and manifestations of arthritis occur a few days later. The inflammatory response in the model is driven by autoantibodies against the ubiquitously expressed self-antigen, glucose-6-phosphate isomerase (G6PI), leading to the formation of immune complexes that drive the activation of different innate immune cells such as neutrophils, macrophages, and possibly mast cells. The pathogenesis further involves a range of immune mediators including cytokines, chemokines, complement factors, Toll-like receptors, Fc receptors, and integrins, as well as factors involved in pain and bone erosion. Hence, even though the K/BxN STA model mimics only the effector phase of RA, it still involves a wide range of relevant disease mediators. Additionally, as a murine model for arthritis, the K/BxN STA model has some obvious advantages. First, it has a rapid and robust onset of arthritis with 100% incidence in genetically identical animals. Second, it can be induced in a wide range of strain backgrounds and can therefore also be induced in gene-deficient strains to study the specific importance of disease mediators. Even though G6PI might not be an essential autoantigen, for example, in RA, the K/BxN STA model is a useful tool to understand how autoantibodies, in general, drive the progression of arthritis by interacting with downstream components of the innate immune system. Finally, the model has also proven useful as a model wherein arthritic pain can be studied. Taken together, these features make the K/BxN STA model a relevant one for RA, and it is a potentially valuable tool, especially for the preclinical screening of new therapeutic targets for RA and perhaps other forms of inflammatory arthritis. Here, we describe the molecular and cellular pathways in the development of K/BxN STA focusing on the recent advances in the understanding of the important mechanisms. Additionally, this review provides a comparison of the K/BxN STA model to some other arthritis models.