What we know (and don't know) about the biology and functions of mast cells and basophils

Differences and Similarities in the Mechanisms and Clinical Expression of Bradykinin-Mediated vs. Mast Cell-Mediated Angioedema

Angioedema (AE), transient localized swelling due to extravasated fluid, is commonly classified as mast cell mediator-induced, bradykinin-mediated or of unknown cause. AE often occurs more than once, and it is these recurrent forms of AE that are challenging for patients and physicians, and they are the ones we focus on and refer to as AE in this review. Since effective treatment depends on the causative mediator, reliable and early diagnosis is essential. Although their clinical presentations bear similarities, many forms of angioedema exhibit specific patterns of clinical appearance or disease history that may aid in diagnosis. Here, we describe the most common differences and similarities in the mechanisms and clinical features of bradykinin-mediated and mast cell mediator-induced types of angioedema. We first provide an overview of the diseases that manifest with mast cell mediator-induced versus bradykinin-mediated angioedema as well as their respective underlying pathogenesis. We then compare these diseases for key clinical features, including angioedema location, course and duration of swelling, attack frequency, prevalence and relevance of prodromal signs and symptoms, triggers of angioedema attacks, and other signs and symptoms including wheals, age of onset, and duration. Our review and comparison of the clinical profiles of different types of angioedema incorporate our own clinical experience as well as published information. Our aim is to highlight that mast cell mediator-induced and bradykinin-mediated angioedema types share common features but are different in many aspects. Knowledge of the differences in underlying pathomechanisms and clinical profiles between different types of angioedema can help with the diagnostic approach in affected patients and facilitate targeted and effective treatment.

Mast Cells and the Pancreas in Human Type 1 and Type 2 Diabetes

Mast cells are highly differentiated, widely distributed cells of the innate immune system, that are currently considered as key regulators of both innate and adaptive immunity. Mast cells play a key role in health and survival mechanisms, especially as sentinel cells that can stimulate protective immune responses. On the other hand, it has been shown that mast cells are involved in the pathogenesis of several diseases, and recently a possible pathogenetic role of mast cells in diabetes has been proposed. In this review we summarize the evidence on the increased presence of mast cells in the pancreas of subjects with type 1 diabetes, which is due to the autoimmune destruction of insulin secreting beta cells, and discuss the differences with type 2 diabetes, the other major form of diabetes. In addition, we describe some of the pathophysiological mechanisms through which mast cells might exert their actions, which could be targeted to potentially protect the beta cells in autoimmune diabetes.

The Epithelial-to-Mesenchymal Transition as a Possible Therapeutic Target in Fibrotic Disorders

Fibrosis is a chronic and progressive disorder characterized by excessive deposition of extracellular matrix, which leads to scarring and loss of function of the affected organ or tissue. Indeed, the fibrotic process affects a variety of organs and tissues, with specific molecular background. However, two common hallmarks are shared: the crucial role of the transforming growth factor-beta (TGF-β) and the involvement of the inflammation process, that is essential for initiating the fibrotic degeneration. TGF-β in particular but also other cytokines regulate the most common molecular mechanism at the basis of fibrosis, the Epithelial-to-Mesenchymal Transition (EMT). EMT has been extensively studied, but not yet fully explored as a possible therapeutic target for fibrosis. A deeper understanding of the crosstalk between fibrosis and EMT may represent an opportunity for the development of a broadly effective anti-fibrotic therapy. Here we report the evidences of the relationship between EMT and multi-organ fibrosis, and the possible therapeutic approaches that may be developed by exploiting this relationship.

Endogenous sulfur dioxide is a novel inhibitor of hypoxia-induced mast cell degranulation

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Endogenous SO₂/AAT pathway exists in mast cells (MCs).

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Endogenous SO₂ is a novel MC membrane stabilizer under hypoxic circumstance.

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MC-derived SO₂ upregulates cAMP level, thereby suppressing MC degranulation.

Introduction

Mast cell (MC) degranulation is an important step in the pathogenesis of inflammatory reactions and allergies; however, the mechanism of stabilizing MC membranes to reduce their degranulation is unclear.

Methods

SO₂ content in MC culture supernatant was measured by HPLC-FD. The protein and mRNA expressions of the key enzymes aspartate aminotransferase 1 (AAT1) and AAT2 and intracellular AAT activity were detected. The cAMP level in MCs was detected by immunofluorescence and ELISA. The release rate of MC degranulation marker β-hexosaminidase was measured. The expression of AAT1 and cAMP, the MC accumulation and degranulation in lung tissues were detected.

Objectives

To exam whether an endogenous sulfur dioxide (SO₂) pathway exists in MCs and if it serves as a novel endogenous MC stabilizer.

Results

We firstly show the existence of the endogenous SO₂/AAT pathway in MCs. Moreover, when AAT1 was knocked down in MCs, MC degranulation was significantly increased, and could be rescued by a SO₂ donor. Mechanistically, AAT1 knockdown decreased the cyclic adenosine monophosphate (cAMP) content in MCs, while SO₂ prevented this reduction in a dose-independent manner. Pretreatment with the cAMP-synthesizing agonist forskolin or the cAMP degradation inhibitor IBMX significantly blocked the increase in AAT1 knockdown-induced MC degranulation. Furthermore, in hypoxia-stimulated MCs, AAT1 protein expression and SO₂ production were markedly down regulated, and MC degranulation was activated, which were blunted by AAT1 overexpression. The cAMP synthesis inhibitor SQ22536 disrupted the suppressive effect of AAT1 overexpression on hypoxia-induced MC degranulation. In a hypoxic environment, mRNA and protein expression of AAT1 was significantly reduced in lung tissues of rats. Supplementation of SO₂ elevated the cAMP level and reduced perivascular MC accumulation and degranulation in lung tissues of rats exposed to a hypoxic environment in vivo.

Conclusion

SO₂ serves as an endogenous MC stabilizer via upregulating the cAMP pathway under hypoxic circumstance.

Environmental and Endogenous Acids Can Trigger Allergic-Type Airway Reactions

Inflammatory allergic and nonallergic respiratory disorders are spreading worldwide and often coexist. The root cause is not clear. This review demonstrates that, from a biochemical point of view, it is ascribable to protons (H+) released into cells by exogenous and endogenous acids. The hypothesis of acids as the common cause stems from two considerations: (a) it has long been known that exogenous acids present in air pollutants can induce the irritation of epithelial surfaces, particularly the airways, inflammation, and bronchospasm; (b) according to recent articles, endogenous acids, generated in cells by phospholipases, play a key role in the biochemical mechanisms of initiation and progression of allergic-type reactions. Therefore, the intracellular acidification and consequent Ca2+ increase, induced by protons generated by either acid pollutants or endogenous phospholipases, may constitute the basic mechanism of the multimorbidity of these disorders, and environmental acidity may contribute to their spread.

Immune Modulation in Asthma: Current Concepts and Future Strategies

Asthma treatment concepts have profoundly changed over the last 20 years, from standard therapeutic regimens for all patients with asthma towards individually tailored interventions targeting treatable traits ("precision medicine"). A precise and highly effective immune modulation with minimal adverse effects plays a central role in this new concept. Recently, there have been major advances in the treatment of asthma with immune-modulatory compounds. One example is the approval of several highly potent biologics for the treatment of severe asthma. New immune-modulatory strategies are expected to enter clinical practice in the future; these innovations will be especially important for patients with treatment-resistant asthma.

Pefloxacin induced changes in serotonergic innervation and mast cell number in rat salivary glands

Pefloxacin is a second-generation fluoroquinolone antibiotic. Besides its advantageous characteristics, side effects including the hypofunction of salivary glands, decreased saliva production, and peripheral neuropathy were observed during the administration of pefloxacin. The aim of this study was to investigate the changes in the number of serotonergic immunoreactive fibers and mast cells after pefloxacin treatment in the parotid and sublingual glands of rats to detect the possible neurotoxic effect of pefloxacin. The adult female rats were treated with intraperitoneal (i.p.) injection of pefloxacin for three or seven days (at a concentration of 20 mg/100g body weight) and the serotonergic innervation pattern along with the change in mast cell number were evaluated by using histochemistry and immunohistochemistry in the parotid and sublingual glands. We found that a three-day treatment significantly increased the number of immunoreactive serotonergic nerve fibers, but after a seven-day treatment the number of serotonin positive nerve fibers decreased almost to values of the control group. The alteration of mast cell number was parallel with the changes of the serotonin positive fibers during the treatment. These results suggest that pefloxacin treatment can modify the finely controlled communication between the immune- and the peripheral nervous systems, resulting neurogenic inflammatory process. The background of this process is the altered serotonergic innervation and the increased number of activated mast cells releasing different mediators for example histamine, which can finally lead to reduced number of serotonin positive nerve fibers after a seven-day treatment of pefloxacin leading to atrophy and hypofunction of the salivary glands.