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Dysregulated mast cell-mediated inflammation and/or activation have been linked to a number of human diseases, including asthma, anaphylaxis, chronic spontaneous urticaria, and mast cell activation syndromes. As a major mast cell granule protein, tryptase is a biomarker commonly used in clinical practice to diagnose mast cell-associated disorders and -mediated reactions, but its mechanistic roles in disease pathogenesis remains incompletely understood. Here, we summarize recent advances in the understanding of human tryptase genetics and the effects that different genetic composition may have on the quaternary structure of tetrameric mature tryptases. We also discuss how these differences may impact clinical phenotypes including allergic inflammation, immediate hypersensitivity, and others seen in patients with mast cell-associated disorders. With the increased application of next-generation sequencing, we foresee that human genetic approaches will be a major focus of understanding human tryptase functions in various human mast cell disorders and in new therapeutic development., (Copyright © 2021. Published by Elsevier Ltd.)

Mastocytosis is a hematopoietic neoplasm characterized by expansion of KIT D816V-mutated clonal mast cells in various organs and severe or even life-threatening anaphylactic reactions. Recently, hereditary α-tryptasemia (HαT) has been described as a common genetic trait with increased copy numbers of the α-tryptase encoding gene, TPSAB1, and associated with an increased basal serum tryptase level and a risk of mast cell activation. The purpose of our study was to elucidate the clinical relevance of HαT in patients with mastocytosis. TPSAB1 germline copy number variants were assessed by digital polymerase chain reaction in 180 mastocytosis patients, 180 sex-matched control subjects, 720 patients with other myeloid neoplasms, and 61 additional mastocytosis patients of an independent validation cohort. α-Tryptase encoding TPSAB1 copy number gains, compatible with HαT, were identified in 17.2% of mastocytosis patients and 4.4% of the control population (P < .001). Patients with HαT exhibited higher tryptase levels than patients without HαT (median tryptase in HαT+ cases: 49.6 ng/mL vs HαT- cases: 34.5 ng/mL, P = .004) independent of the mast cell burden. Hymenoptera venom hypersensitivity reactions and severe cardiovascular mediator-related symptoms/anaphylaxis were by far more frequently observed in mastocytosis patients with HαT than in those without HαT. Results were confirmed in an independent validation cohort. The high prevalence of HαT in mastocytosis hints at a potential pathogenic role of germline α-tryptase encoding TPSAB1 copy number gains in disease evolution. Together, our data suggest that HαT is a novel emerging robust biomarker in mastocytosis that is useful for determining the individual patient´s risk of developing severe anaphylaxis., (© 2021 by The American Society of Hematology.)

PurposeCa V 3.2 signaling contributes to nociception, pruritus, gastrointestinal motility, anxiety, and blood pressure homeostasis. This calcium channel, encoded by CACNA1H, overlaps the human tryptase locus, wherein increased TPSAB1 copy number causes hereditary α-tryptasemia. Germ-line CACNA1H variants may contribute to the variable expressivity observed with this genetic trait.MethodsTryptase-encoding sequences at TPSAB1 and TPSB2, and TPSG1 and CACNA1H variants were genotyped in 46 families with hereditary α-tryptasemia syndrome. Electrophysiology was performed on tsA201 HEK cells transfected with wild-type or variant CACNA1H constructs. Effects on clinical phenotypes were interrogated in families with TPSAB1 duplications and in volunteers from the ClinSeq cohort.ResultsThree nonsynonymous variants in CACNA1H (rs3751664, rs58124832, and rs72552056) cosegregated with TPSAB1 duplications in 32/46 families and were confirmed to be in linkage disequilibrium (LD). In vitro, variant Ca V 3.2 had functional effects: reducing current densities, and altering inactivation and deactivation properties. No clinical differences were observed in association with the CACNA1H haplotype.ConclusionA previously unrecognized haplotype containing three functional CACNA1H variants is relatively common among Caucasians, and is frequently coinherited on the same allele as additional TPSAB1 copies. The variant CACNA1H haplotype, which in vitro imparts partial gain of function, does not result in detectable phenotypic differences in the heterozygous state.

Mast cells and basophils are innate immune cells with overlapping functions that contribute to anti-helminth immunity. Mast cell function during helminth infection was previously studied using mast cell-deficient Kit-mutant mice that display additional mast cell-unrelated immune deficiencies. Here, we use mice that lack basophils or mucosal and connective tissue mast cells in a Kit-independent manner to re-evaluate the impact of each cell type during helminth infection. Neither mast cells nor basophils participated in the immune response to tissue-migrating Strongyloides ratti third-stage larvae, but both cell types contributed to the early expulsion of parasitic adults from the intestine. The termination of S. ratti infection required the presence of mucosal mast cells: Cpa3 Cre mice, which lack mucosal and connective tissue mast cells, remained infected for more than 150 days. Mcpt5 Cre R-DTA mice, which lack connective tissue mast cells only, and basophil-deficient Mcpt8 Cre mice terminated the infection after 1 month with wild-type kinetics despite their initial increase in intestinal parasite burden. Because Cpa3 Cre mice showed intact Th2 polarization and efficiently developed protective immunity after vaccination, we hypothesize that mucosal mast cells are non-redundant terminal effector cells in the intestinal epithelium that execute anti-helminth immunity but do not orchestrate it.

Mouse mast cell protease 11 (mMCP-11) is the most recently identified member of the mouse mast cell tryptase family. This tryptase is preferentially produced by basophils in contrast to other members that are expressed by mast cells but not basophils. Although blood-circulating basophils have long been considered as minor and redundant relatives of tissue-resident mast cells, recent studies illustrated that basophils and mast cells play distinct roles in vivo. To explore the in vivo role of basophil-derived mMCP-11, here we prepared recombinant mMCP-11 and its protease-dead mutant. Subcutaneous injection of the wild-type mMCP-11 but not the mutant induced edematous skin swelling with increased microvascular permeability in a dose-dependent manner. No apparent infiltration of proinflammatory cells including neutrophils and eosinophils was detected in the skin lesions. The cutaneous swelling was abolished by the pretreatment of mice with indomethacin, a cyclooxygenase inhibitor, suggesting the major contribution of prostaglandins to the microvascular leakage. Of note, the cutaneous swelling was elicited even in mast cell-deficient mice, indicating that mast cells are dispensable for the mMCP-11-induced cutaneous swelling. Thus, basophil-derived mMCP-11 can induce microvascular leakage via prostaglandins in a mast cell-independent manner, and may contribute to the development of basophil-mediated inflammatory responses., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Aims: The aim of study is to investigate the effect of nifedipine on viral myocarditis in an animal model., Main Methods: Four-week-old male DBA/2 mice were inoculated with 2 pfu of encephalomyocarditis virus (EMCV) and randomized to nifedipine (n=10) or control (n=10) group. The control group was fed by regular chow and the nifedipine group contained 0.01% of nifedipine. Mast cell density was counted, and expressions of messenger RNAs of stem cell factor (SCF), matrix metalloproteinases (MMPs), pro-collagen I, mast cell proteases, tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) were evaluated by RT-PCR., Key Findings: The area of myocardial necrosis was smaller in the nifedipine vs the control group (mean+/-SD, 1.2+/-1.3% vs 3.8+/-1.8%, respectively, P<0.005). The mast cell density (count/mm(2)) was lower in the nifedipine vs the control group (mean+/-SD, 0.23+/-0.16 vs 1.08+/-0.45, respectively, P<0.0005). The expressions of MMPs, mast cell proteases, TNF-alpha, IL-6, SCF and pro-collagen I were lower in the nifedipine group than in the control group (P<0.05)., Significance: Nifedipine inhibited the activation of various participants in inflammatory and immune reactions in EMCV myocarditis.

We have previously demonstrated that mast cells were significantly increased during Newcastle disease virus (NDV) infection, but their precise role in the process is unknown. In this study, we investigated the role of mast cells in this process by using ketotifen, a mast cell membrane stabilizer. A total of 60 specific-pathogen-free chickens were randomly divided into 3 groups of 20 birds each (NDV-infected group, ketotifen-pretreated group, and the control group). The ketotifen-pretreated group was administered orally with ketotifen before NDV infection. On 12, 24, and 48 h postinfection, 5 chickens from each treatment were killed. Tissues of proventriculus were collected to quantify mast cells, the content of tryptase and histamine by cytochemistry, immunohistochemistry, and fluorescence analysis, respectively. The results showed that the population of mast cells and the content of tryptase and histamine were increased significantly in the proventriculus (P < 0.01) of infected birds compared with the control group. An acute mucosal injury was observed in the infected chickens. In contrast, among chickens pretreated with ketotifen, followed by NDV infection, the mast cells number and the content of tryptase and histamine were decreased significantly (P < 0.01). Likely as a result, the mucosal injury was remitted remarkably. The overall results of this experiment suggest that mast cells are implicated in NDV-induced mucosal injury. Inhibition of mast cell mediator release may represent a novel strategy to modulate this process.