Diagnostic Value of Serum Baseline Tryptase Levels in Childhood Asthma and Its Correlation with Disease Severity

Updates in diagnosis and management of paediatric mastocytosis

PURPOSE OF REVIEW

Paediatric mastocytosis is a rare clonal disorder characterized by the overproduction and organ infiltration of mast cells. Symptoms are due to mast cell mediator release. Cutaneous mastocytosis is the most common presentation in children with systemic disease being rare. Our aim is to provide a practical guideline in differentiating subtypes of paediatric mastocytosis while providing actionable recommendations on diagnosis, clinical management, follow-up and prognosis.

RECENT FINDINGS

Longitudinal cohort studies of paediatric cutaneous mastocytosis have shown spontaneous remission with favourable prognosis. Hereditary alpha-tryptasemia may coexist with mastocytosis; thus, screening for this disorder is recommended. There is an emerging role for serum tryptase in asthma endotyping and potential for using therapeutic tryptase inhibitors.

SUMMARY

Morbidity in paediatric mastocytosis typically arises from symptoms secondary to mast cell mediator release. Prognosis for nonaggressive disease is typically favourable; however, risks for anaphylaxis and psychosocial morbidity may be underestimated. Symptomatic management and anticipatory guidance may help support patients and families throughout the disease course.

Increased expressions of CD123, CD63, CD203c, and Fc epsilon receptor I on blood leukocytes of allergic asthma

Background : Altered basophil identification markers have been discovered to associate with allergic asthma (AA) in recent years. However, little is known about the expression of basophil markers in blood granulocytes. Aim: To parallel test blood basophils in peripheral blood mononuclear cell (PBMC) and granulocyte populations of patients with AA and AA combined with allergic rhinitis (ARA) Methods: The expressions of surface molecules were determined via flow cytometry. CD123 expressing cells in blood were isolated using a cell sorting technique, and mouse AA models were employed for in vivo study. Results: The numbers of CD123+HLA-DR- cells in the granulocytes of AA and ARA patients markedly increased. However, only 49.7% of CD123+HLA-DR- cells in granulocytes and 99.0% of CD123+HLA-DR- cells in PBMCs were basophils. Almost all CD123+HLA-DR- cells expressed CD63 regardless in granulocytes or PBMC. The numbers of CD63, Fc epsilon receptor I (FcεRI), and CD203c expressing cells markedly enhanced in CD123+HLA-DR- granulocytes of AA and ARA patients. Mean fluorescence intensity (MFI) of CD63 and CD203c expressions on CD123+HLA-DR- PBMC and granulocytes of AA and ARA patients dramatically elevated. House dust mite extract (HDME) and Artemisia sieversiana wild allergen extract (ASWE) enhanced the numbers of CD63+CD123+HLA-DR- granulocytes and PBMC and the MFI of CD203c expression on CD123+HLA-DR- granulocyte of AA and ARA patients. Histamine, tryptase, and PGD2 enhanced proportions of CD123+ KU812 cells. ASWE- and HDME-induced AA mice showed upregulated CD63 expression on basophils. In conclusion, upregulated expressions of CD123, CD203c, CD63, and FcεRIα in PBMC and granulocytes of patients with AA and ARA suggest that CD123+HLA-DR- cells may contribute to the development of AA and ARA.

Molecular and Immunomodulatory Actions of New Antiasthmatic Agents: Exploring the Diversity of Biologics in Th2 Endotype Asthma

Asthma is a major respiratory disorder characterised by chronic inflammation and airway remodelling. It affects about 1-8% of the global population and is responsible for over 461,000 deaths annually. Until recently, the pharmacotherapy of severe asthma involved high doses of inhaled corticosteroids in combination with β-agonist for prolonged action, including theophylline, leukotriene antagonist or anticholinergic yielding limited benefit. Although the use of newer agents to target Th2 asthma endotypes has improved therapeutic outcomes in severe asthmatic conditions, there seems to be a paucity of understanding the diverse mechanisms through which these classes of drugs act. This article delineates the molecular and immunomodulatory mechanisms of action of new antiasthmatic agents currently being trialled in preclinical and clinical studies to remit asthmatic conditions. The ultimate goal in developing antiasthmatic agents is based on two types of approaches: either anti-inflammatory or bronchodilators. Biologic and most small molecules have been shown to modulate specific asthma endotypes, targeting thymic stromal lymphopoietin, tryptase, spleen tyrosine kinase (Syk), Janus kinase, PD-L1/PD-L2, GATA-3, and CD38 for the treatment and management of Th2 endotype asthma.

Blood tryptase and thymic stromal lymphopoietin levels predict the risk of exacerbation in severe asthma

Some patients with severe asthma experience exacerbations despite receiving multiple therapy. The risk of exacerbation and heterogeneous response to treatment may be associated with specific inflammatory molecules that are responsive or resistant to corticosteroids. We aimed to identify the independent factors predictive for the future risk of exacerbation in patients with severe asthma. In this multi-center prospective observational study, 132 patients with severe asthma were enrolled and divided into exacerbation (n = 52) and non-exacerbation (n = 80) groups on the basis of exacerbation rate after a 1-year follow-up period. We found that previous history of severe-to-serious exacerbation, baseline blood eosinophil counts (≥ 291cells/μL), and serum tryptase (≤ 1448 pg/mL) and thrymic stromal lymphopoietin (TSLP) levels (≥ 25 pg/mL) independently predicted the future development of exacerbation with adjusted odds ratios (AOR) of 3.27, 6.04, 2.53 and 8.67, respectively. Notably, the patients with high blood eosinophil counts and low tryptase levels were likely to have more exacerbations than those with low blood eosinophil counts and high tryptase levels (AOR 16.9). TSLP potentially played the pathogenic role across different asthma phenotypes. TSLP and tryptase levels may be implicated in steroid resistance and responsiveness in the asthma inflammatory process. High blood eosinophil counts and low serum tryptase levels predict a high probability of future asthma exacerbation.

The emerging role of mast cell proteases in asthma

It is now well established that mast cells (MCs) play a crucial role in asthma. This is supported by multiple lines of evidence, including both clinical studies and studies on MC-deficient mice. However, there is still only limited knowledge of the exact effector mechanism(s) by which MCs influence asthma pathology. MCs contain large amounts of secretory granules, which are filled with a variety of bioactive compounds including histamine, cytokines, lysosomal hydrolases, serglycin proteoglycans and a number of MC-restricted proteases. When MCs are activated, e.g. in response to IgE receptor cross-linking, the contents of their granules are released to the exterior and can cause a massive inflammatory reaction. The MC-restricted proteases include tryptases, chymases and carboxypeptidase A3, and these are expressed and stored at remarkably high levels. There is now emerging evidence supporting a prominent role of these enzymes in the pathology of asthma. Interestingly, however, the role of the MC-restricted proteases is multifaceted, encompassing both protective and detrimental activities. Here, the current knowledge of how the MC-restricted proteases impact on asthma is reviewed.

Mast Cells and Their Progenitors in Allergic Asthma

Mast cells and their mediators have been implicated in the pathogenesis of asthma and allergy for decades. Allergic asthma is a complex chronic lung disease in which several different immune cells, genetic factors and environmental exposures influence the pathology. Mast cells are key players in the asthmatic response through secretion of a multitude of mediators with pro-inflammatory and airway-constrictive effects. Well-known mast cell mediators, such as histamine and bioactive lipids are responsible for many of the physiological effects observed in the acute phase of allergic reactions. The accumulation of mast cells at particular sites of the allergic lung is likely relevant to the asthma phenotype, severity and progression. Mast cells located in different compartments in the lung and airways have different characteristics and express different mediators. According to in vivo experiments in mice, lung mast cells develop from mast cell progenitors induced by inflammatory stimuli to migrate to the airways. Human mast cell progenitors have been identified in the blood circulation. A high frequency of circulating human mast cell progenitors may reflect ongoing pathological changes in the allergic lung. In allergic asthma, mast cells become activated mainly via IgE-mediated crosslinking of the high affinity receptor for IgE (FcεRI) with allergens. However, mast cells can also be activated by numerous other stimuli e.g. toll-like receptors and MAS-related G protein-coupled receptor X2. In this review, we summarize research with implications on the role and development of mast cells and their progenitors in allergic asthma and cover selected activation pathways and mast cell mediators that have been implicated in the pathogenesis. The review places an emphasis on describing mechanisms identified using in vivo mouse models and data obtained by analysis of clinical samples.

Mast cell disorders: From infancy to maturity

Mast cells are typically linked to immediate hypersensitivity and anaphylaxis. This review looks beyond this narrow role, focusing on how these cells have evolved and diversified via natural selection promoting serine protease gene duplication, augmenting their innate host defense function against helminths and snake envenomation. Plasticity of mast cell genes has come at a price. Somatic activating mutations in the mast cell growth factor KIT gene cause cutaneous mastocytosis in young children and systemic mastocytosis with a more guarded prognosis in adults who may also harbor other gene mutations with oncogenic potential as they age. Allelic TPSAB1 gene duplication associated with higher basal mast cell tryptase is possibly one of the commonest autosomal dominantly inherited multi-system diseases affecting the skin, gastrointestinal tract, circulation and musculoskeletal system. Mast cells are also establishing a new-found importance in severe asthma, and in remodeling of blood vessels in cancer and atherosclerotic vascular disease. Furthermore, recent evidence suggests that mast cells sense changes in oxygen tension, particularly in neonates, and that subsequent degranulation may contribute to common lung, eye, and brain diseases of prematurity classically associated with hypoxic insults. One hundred and forty years since Paul Ehrlich's initial description of "mastzellen," this review collates and highlights the complex and diverse roles that mast cells play in health and disease.

Accelerated reactivity of blood granulocytes in patients with atopic bronchial asthma out of exacerbation

Reactive oxygen species (ROS) are important in bronchial asthma (BA) pathogenesis owing to accumulation of activated granulocytes in the lungs. But the ROS-producing activity of the cells is insufficiently understood in the blood of BA patients. This study analyzes the kinetics of phagocyte respiratory burst in the blood to improve the methods of BA patients monitoring. Patients with atopic BA out of exacerbation (n=60) and healthy controls (n=43) were recruited. The time-course of respiratory response to opsonized zymosan (OZ) was recorded in the whole blood using luminol-dependent chemiluminescence (CL), and its activation kinetics (lag-time, rate, amplitude, ROS production) was calculated. The discriminative power of ROS generation kinetics was defined by Receiver Operating Characteristic (ROC) curve analysis. Standard physiological respiratory parameters of patients did not differ from the controls. More rapid response to OZ was recorded in BA patient samples versus the controls. The primed state of phagocytes in the blood of BA patients was corroborated by significant weakening formyl peptide priming effect. The adhesion of granulocytes to cultured human endothelial cells was two-fold higher in BA patients versus controls. ROC curve analysis exhibited good discriminative effectiveness of the CL kinetics to compare BA individuals with the controls. The highest power (86% sensitivity and 90% specificity) was achieved at a linear combination of the parameters. We assume that the assessment of phagocyte reactivity based on the analysis of the response kinetic profile is a good test for monitoring of the state in BA patients.