Characterization of ERK activation in human mast cells stimulated by contact with T cells

Distinction between rhinitis alone and rhinitis with asthma using interactomics

The concept of "one-airway-one-disease", coined over 20 years ago, may be an over-simplification of the links between allergic diseases. Genomic studies suggest that rhinitis alone and rhinitis with asthma are operated by distinct pathways. In this MeDALL (Mechanisms of the Development of Allergy) study, we leveraged the information of the human interactome to distinguish the molecular mechanisms associated with two phenotypes of allergic rhinitis: rhinitis alone and rhinitis in multimorbidity with asthma. We observed significant differences in the topology of the interactomes and in the pathways associated to each phenotype. In rhinitis alone, identified pathways included cell cycle, cytokine signalling, developmental biology, immune system, metabolism of proteins and signal transduction. In rhinitis and asthma multimorbidity, most pathways were related to signal transduction. The remaining few were related to cytokine signalling, immune system or developmental biology. Toll-like receptors and IL-17-mediated signalling were identified in rhinitis alone, while IL-33 was identified in rhinitis in multimorbidity. On the other hand, few pathways were associated with both phenotypes, most being associated with signal transduction pathways including estrogen-stimulated signalling. The only immune system pathway was FceRI-mediated MAPK activation. In conclusion, our findings suggest that rhinitis alone and rhinitis and asthma multimorbidity should be considered as two distinct diseases.

Targeting Mast Cells in Allergic Disease: Current Therapies and Drug Repurposing

The incidence of allergic disease has grown tremendously in the past three generations. While current treatments are effective for some, there is considerable unmet need. Mast cells are critical effectors of allergic inflammation. Their secreted mediators and the receptors for these mediators have long been the target of allergy therapy. Recent drugs have moved a step earlier in mast cell activation, blocking IgE, IL-4, and IL-13 interactions with their receptors. In this review, we summarize the latest therapies targeting mast cells as well as new drugs in clinical trials. In addition, we offer support for repurposing FDA-approved drugs to target mast cells in new ways. With a multitude of highly selective drugs available for cancer, autoimmunity, and metabolic disorders, drug repurposing offers optimism for the future of allergy therapy.

Extracellular Vesicles as Emerging Players in Intercellular Communication: Relevance in Mast Cell-Mediated Pathophysiology

Mast cells are major effector cells in eliciting allergic responses. They also play a significant role in establishing innate and adaptive immune responses, as well as in modulating tumor growth. Mast cells can be activated upon engagement of the high-affinity receptor FcεRI with specific IgE to multivalent antigens or in response to several FcεRI-independent mechanisms. Upon stimulation, mast cells secrete various preformed and newly synthesized mediators. Emerging evidence indicates their ability to be a rich source of secreted extracellular vesicles (EVs), including exosomes and microvesicles, which convey biological functions. Mast cell-derived EVs can interact with and affect other cells located nearby or at distant sites and modulate inflammation, allergic response, and tumor progression. Mast cells are also affected by EVs derived from other cells in the immune system or in the tumor microenvironment, which may activate mast cells to release different mediators. In this review, we summarize the latest data regarding the ability of mast cells to release or respond to EVs and their role in allergic responses, inflammation, and tumor progression. Understanding the release, composition, and uptake of EVs by cells located near to or at sites distant from mast cells in a variety of clinical conditions, such as allergic inflammation, mastocytosis, and lung cancer will contribute to developing novel therapeutic approaches.

Exosomes From Packed Red Cells Induce Human Mast Cell Activation and the Production of Multiple Inflammatory Mediators

Most blood transfusion-related adverse reactions involve the immunologic responses of recipients to exogenous blood components. Extracellular vesicles isolated from packed red cells can affect the recipient’s immune system. Mast cells are traditionally known as effector cells for allergic transfusion reactions. However, growing evidence supports the notion that activated mast cells might disturb host innate immunologic responses. Exosomes are a type of extracellular vesicle. To determine the effect of exosomes on mast cells, we enriched exosomes derived from volunteer plasma (EXs-nor) and packed red cells (EXs-RBCs) using ultracentrifugation and incubated them with a human mast cell line (HMC-1). We found that EXs-RBC exposure increased the expression of tryptase-1 and prostaglandin D2, the production of multiple inflammatory mediators, and the levels of Toll-like receptor-3 (TLR-3) and phospho-mitogen-activated protein kinase (MAPK) in HMC-1 cells. MAPK inhibitors (SB203580, PD98059, and SP600125) and a TLR-3/dsRNA complex inhibitor reduced the EXs-RBC-stimulated production of inflammatory mediators in HMC-1 cells, whereas the TLR-3 agonist [poly (A:U)] elevated the production of these mediators. These results indicate that EXs-RBCs activate HMC-1 cells and elicit the production of multiple inflammatory mediators, partly via the TLR-3 and MAPK pathways. Mast cells activated by EXs-RBCs exhibit complex inflammatory properties and might play a potential role in transfusion-related adverse reactions.

Recent advances in mast cell activation and regulation

Mast cells are innate immune cells that intersect with the adaptive immunity and play a crucial role in the initiation of allergic reactions and the host defense against certain parasites and venoms. When activated in an allergen- and immunoglobulin E (IgE)-dependent manner, these cells secrete a large variety of allergenic mediators that are pre-stored in secretory granules or de novo–synthesized. Traditionally, studies have predominantly focused on understanding this mechanism of mast cell activation and regulation. Along this line of study, recent studies have shed light on what structural features are required for allergens and how IgE, particularly anaphylactic IgE, is produced. However, the last few years have seen a flurry of new studies on IgE-independent mast cell activation, particularly via Mrgprb2 (mouse) and MRGPRX2 (human). These studies have greatly advanced our understanding of how mast cells exert non-histaminergic itch, pain, and drug-induced pseudoallergy by interacting with sensory neurons. Recent studies have also characterized mast cell activation and regulation by interleukin-33 (IL-33) and other cytokines and by non-coding RNAs. These newly identified mechanisms for mast cell activation and regulation will further stimulate the allergy/immunology community to develop novel therapeutic strategies for treatment of allergic and non-allergic diseases.

Lung cancer-derived extracellular vesicles: a possible mediator of mast cell activation in the tumor microenvironment

Activated mast cells are often found in the tumor microenvironment. They have both pro- and anti-tumorigenic roles, depending on the tumor type. Several lines of evidence suggest that the tumor microenvironment contains multiple soluble factors that can drive mast cell recruitment and activation. However, it is not yet clear how mast cells are activated by tumor cells. In this study, we explored whether tumor-derived microvesicles (TMV) from non-small cell lung cancer (NSCLC) cells interact with human mast cells, activate them to release cytokines, and affect their migratory ability. PKH67-labelled TMV isolated from NSCLC cell lines were found to be internalized by mast cells. This internalization was first noticed after 4 h and peaked within 24 h of co-incubation. Furthermore, internalization of TMV derived from NSCLC cell lines or from surgical lung tissue specimens resulted in ERK phosphorylation, enhanced mast cell migratory ability and increased release of cytokines and chemokines, such as TNF-α and MCP-1. Our data are thus, consistent with the conclusion that TMV have the potential to influence mast cell activity and thereby, affect tumorigenesis.

MicroRNA Involvement in Allergic and Non-Allergic Mast Cell Activation

Allergic inflammation is accompanied by the coordinated expression of numerous genes and proteins that initiate, sustain, and propagate immune responses and tissue remodeling. MicroRNAs (miRNAs) are a large class of small regulatory molecules that are able to control the translation of target mRNAs and consequently regulate various biological processes at the posttranscriptional level. MiRNA profiles have been identified in multiple allergic inflammatory diseases and in the tumor microenvironment. Mast cells have been found to co-localize within the above conditions. More specifically, in addition to being essential in initiating the allergic response, mast cells play a key role in both innate and adaptive immunity as well as in modulating tumor growth. This review summarizes the possible role of various miRNAs in the above-mentioned processes wherein mast cells have been found to be involved. Understanding the role of miRNAs in mast cell activation and function may serve as an important tool in developing diagnostic as well as therapeutic approaches in mast cell-dependent pathological conditions.

Immune synapses between mast cells and γδ T cells limit viral infection

Mast cells (MCs) are immune sentinels, but whether they also function as antigen-presenting cells (APCs) remains elusive. Using mouse models of MC deficiency, we report on MC-dependent recruitment and activation of multiple T cell subsets to the skin and draining lymph nodes (DLNs) during dengue virus (DENV) infection. Newly recruited and locally proliferating γδ T cells were the first T cell subset to respond to MC-driven inflammation, and their production of IFN-γ was MC dependent. MC-γδ T cell conjugates were observed consistently in infected peripheral tissues, suggesting a new role for MCs as nonconventional APCs for γδ T cells. MC-dependent γδ T cell activation and proliferation during DENV infection required T cell receptor (TCR) signaling and the nonconventional antigen presentation molecule endothelial cell protein C receptor (EPCR) on MCs. γδ T cells, not previously implicated in DENV host defense, killed infected targeted DCs and contributed to the clearance of DENV in vivo. We believe immune synapse formation between MCs and γδ T cells is a novel mechanism to induce specific and protective immunity at sites of viral infection.

Mast cell desensitization inhibits calcium flux and aberrantly remodels actin

Rush desensitization (DS) is a widely used and effective clinical strategy for the rapid inhibition of IgE-mediated anaphylactic responses. However, the cellular targets and underlying mechanisms behind this process remain unclear. Recent studies have implicated mast cells (MCs) as the primary target cells for DS. Here, we developed a murine model of passive anaphylaxis with demonstrated MC involvement and an in vitro assay to evaluate the effect of DS on MCs. In contrast with previous reports, we determined that functional IgE remains on the cell surface of desensitized MCs following DS. Despite notable reductions in MC degranulation following DS, the high-affinity IgE receptor FcεRI was still capable of transducing signals in desensitized MCs. Additionally, we found that displacement of the actin cytoskeleton and its continued association with FcεRI impede the capacity of desensitized MCs to evoke the calcium response that is essential for MC degranulation. Together, these findings suggest that reduced degranulation responses in desensitized MCs arise from aberrant actin remodeling, providing insights that may lead to improvement of DS treatments for anaphylactic responses.

Mitochondrial STAT3 plays a major role in IgE-antigen-mediated mast cell exocytosis

BACKGROUND

The involvement of mitochondrial oxidative phosphorylation (OXPHOS) in mast cell exocytosis was recently suggested by the finding that mitochondria translocate to exocytosis sites upon mast cell activation. In parallel, mitochondrial signal transducer and activator of transcription 3 (STAT3) was found to be involved in ATP production. However, the regulation of mitochondrial STAT3 function and its connection to mast cell exocytosis is unknown.

OBJECTIVE

We sought to explore the role played by mitochondrial STAT3 in mast cell exocytosis.

METHODS

Experiments were performed in vitro with human and mouse mast cells and rat basophilic leukemia (RBL) cells and in vivo in mice. OXPHOS activity was measured after immunologic activation. The expression of STAT3, extracellular signal-regulated kinase 1/2, and protein inhibitor of activated STAT3 in the mitochondria during mast cell activation was determined, as was the effect of STAT3 inhibition on OXPHOS activity and mast cell function.

RESULTS

Here we show that mitochondrial STAT3 is essential for immunologically mediated degranulation of human and mouse mast cells and RBL cells. Additionally, in IgE-antigen-activated RBL cells, mitochondrial STAT3 was phosphorylated on serine 727 in an extracellular signal-regulated kinase 1/2-dependent manner, which was followed by induction of OXPHOS activity. Furthermore, the endogenous inhibitor of STAT3, protein inhibitor of activated STAT3, was found to inhibit OXPHOS activity in the mitochondria, resulting in inhibition of mast cell degranulation. Moreover, mice injected with Stattic, a STAT3 inhibitor, had a significant decrease in histamine secretion.

CONCLUSION

These results provide the first evidence of a regulatory role for mitochondrial STAT3 in mast cell functions, and therefore mitochondrial STAT3 could serve as a new target for the manipulation of allergic diseases.

The role of IgE-receptors in IgE-dependent airway smooth muscle cell remodelling

Background

In allergic asthma, IgE increases airway remodelling but the mechanism is incompletely understood. Airway remodelling consists of two independent events increased cell numbers and enhanced extracellular matrix deposition, and the mechanism by which IgE up-regulates cell proliferation and extracellular matrix deposition by human airway smooth muscle cells in asthma is unclear.

Objective

Characterise the role of the two IgE receptors and associated signalling cascades in airway smooth muscle cell remodelling.

Methods

Primary human airway smooth muscle cells (8 asthmatics, 8 non-asthmatics) were stimulated with human purified antibody-activated IgE. Proliferation was determined by direct cell counts. Total collagen deposition was determined by Sircol; collagen species deposition by ELISA. IgE receptors were silenced by siRNA and mitogen activated protein kinase (MAPK) signalling was blocked by chemical inhibitors.

Results

IgE dose-dependently increased extracellular matrix and collagen deposition by airway smooth muscle cells as well as their proliferation. Specifically in cells of asthma patients IgE increased the deposition of collagen-type-I, -III, –VII and fibronectin, but did not affect the deposition of collagens type-IV. IgE stimulated collagen type-I and type-VII deposition through IgE receptor-I and Erk1/2 MAPK. Proliferation and deposition of collagens type-III and fibronectin involved both IgE receptors as well as Erk1/2 and p38 MAPK. Pre-incubation (30 minutes) with Omalizumab prevented all remodelling effects completely. We observed no changes in gelatinase activity or their inhibitors.

Conclusion & Clincal Relevance

Our study provides the molecular biological mechanism by which IgE increases airway remodelling in asthma through increased airway smooth muscle cell proliferation and deposition of pro-inflammatory collagens and fibronectin. Blocking IgE action prevents several aspects of airway smooth muscle cell remodelling. Our findings may explain the recently described reduction of airway wall thickness in severe asthma patients treated with humanised anti-IgE antibodies.

T cell-mediated modulation of mast cell function: heterotypic adhesion-induced stimulatory or inhibitory effects

Close physical proximity between mast cells and T cells has been demonstrated in several T cell mediated inflammatory processes such as rheumatoid arthritis and sarcoidosis. However, the way by which mast cells are activated in these T cell-mediated immune responses has not been fully elucidated. We have identified and characterized a novel mast cell activation pathway initiated by physical contact with activated T cells, and showed that this pathway is associated with degranulation and cytokine release. The signaling events associated with this pathway of mast cell activation have also been elucidated confirming the activation of the Ras mitogen-activated protein kinase systems. More recently, we hypothesized and demonstrated that mast cells may also be activated by microparticles released from activated T cells that are considered as miniature version of a cell. By extension, microparticles might affect the activity of mast cells, which are usually not in direct contact with T cells at the inflammatory site. Recent works have also focused on the effects of regulatory T cells (Treg) on mast cells. These reports highlighted the importance of the cytokines IL-2 and IL-9, produced by mast cells and T cells, respectively, in obtaining optimal immune suppression. Finally, physical contact, associated by OX40–OX40L engagement has been found to underlie the down-regulatory effects exerted by Treg on mast cell function.

Inhibitory effect of farnesylthiosalicylic acid on mediators release by mast cells: preferential inhibition of prostaglandin D(2) and tumor necrosis factor-α release

There is substantial evidence suggesting that the Ras inhibitor farnesylthiosalicylic acid (FTS) may modulate various aspects of immune function and inflammation in addition to its well known anti-cancer activity. In this regard, we have recently shown that FTS suppresses T lymphocyte-mediated immune responses. Mast cells (MC), the main effector cells in the elicitation of the allergic response, are known to secrete granule-associated mediators and to release prostaglandins and cytokines on FCεRI-cross-linking, thereby contributing to the pathogenesis of allergic diseases. We hypothesized that MC act as an additional target for FTS. In the present work we analyze the effects of FTS on MC degranulation, prostaglandin release, and cytokine release in vitro, and on the elicitation of IgE-mediated MC dependent cutaneous allergic inflammation in vivo. First we have established that FTS inhibited Ras activation in MC. Next, we have shown that FTS preferentially inhibited prostaglandin (PG) D(2) and tumor necrosis factor (TNF)-α release without having any significant effect on MC β-hexosaminidase secretion. In vivo administration of FTS inhibited the late phase of passive cutaneous anaphylaxis reaction. The time course of FTS-induced inhibition in vivo correlated with mediators release and not with degranulation. This data suggests that FTS may have an inhibitory effect on MC mediated allergic inflammation, and thus may be considered as a possible therapeutic modality.

Meningeal mast cells affect early T cell central nervous system infiltration and blood-brain barrier integrity through TNF: a role for neutrophil recruitment?

Mast cells contribute to the pathogenesis of experimental autoimmune encephalomyelitis, a rodent model of the human demyelinating disease multiple sclerosis. Yet their site and mode of action is unknown. In both diseases, myelin-specific T cells are initially activated in peripheral lymphoid organs. However, for disease to occur, these cells must enter the immunologically privileged CNS through a breach in the relatively impermeable blood-brain barrier. In this study, we demonstrate that a dense population of resident mast cells in the meninges, structures surrounding the brain and spinal cord, regulate basal CNS barrier function, facilitating initial T cell CNS entry. Through the expression of TNF, mast cells recruit an early wave of neutrophils to the CNS. We propose that neutrophils in turn promote the blood-brain barrier breach and together with T cells lead to further inflammatory cell influx and myelin damage. These findings provide specific targets for intervention in multiple sclerosis as well as other immune-mediated CNS diseases.