Impact of naturally forming human α/β-tryptase heterotetramers in the pathogenesis of hereditary α-tryptasemia

Human α/β-tryptase heterotetramer, a previously hidden form of tryptase, explains some of the unusual clinical features of hereditary α-tryptasemia. α/β-Tryptase forms naturally in mast cells and, when secreted, activates clinically relevant proteins, likely impacting a variety of mast cell disorders.

Both α-tryptase and β-tryptase are preferentially expressed by human mast cells, but the purpose of α-tryptase is enigmatic, because its tetramers lack protease activity, whereas β-tryptase tetramers are active proteases. The monogenic disorder called hereditary α-tryptasemia, due to increased α-tryptase gene copies and protein expression, presents with clinical features such as vibratory urticaria and dysautonomia. We show that heterotetramers composed of 2α- and 2β-tryptase protomers (α/β-tryptase) form naturally in individuals who express α-tryptase. α/β-Tryptase, but not homotetramer, activates protease-activated receptor-2 (PAR2), which is expressed on cell types such as smooth muscle, neurons, and endothelium. Also, only α/β-tryptase makes mast cells susceptible to vibration-triggered degranulation by cleaving the α subunit of the EGF-like module–containing mucin-like hormone receptor-like 2 (EMR2) mechanosensory receptor. Allosteric effects of α-tryptase protomers on neighboring β-tryptase protomers likely result in the novel substrate repertoire of α/β-tryptase tetramers that in turn cause some of the clinical features of hereditary α-tryptasemia and of other disorders involving mast cells.

Long-Term Outcomes with Subcutaneous C1-Inhibitor Replacement Therapy for Prevention of Hereditary Angioedema Attacks

BACKGROUND

For the prevention of attacks of hereditary angioedema (HAE), the efficacy and safety of subcutaneous human C1-esterase inhibitor (C1-INH[SC]; HAEGARDA, CSL Behring) was established in the 16-week Clinical Study for Optimal Management of Preventing Angioedema with Low-Volume Subcutaneous C1-Inhibitor Replacement Therapy (COMPACT).

OBJECTIVE

To assess the long-term safety, occurrence of angioedema attacks, and use of rescue medication with C1-INH(SC).

METHODS

Open-label, randomized, parallel-arm extension of COMPACT across 11 countries. Patients with frequent angioedema attacks, either study treatment-naive or who had completed COMPACT, were randomly assigned (1:1) to 40 IU/kg or 60 IU/kg C1-INH(SC) twice per week, with conditional uptitration to optimize prophylaxis (ClinicalTrials.gov registration no. NCT02316353).

RESULTS

A total of 126 patients with a monthly attack rate of 4.3 in 3 months before entry in COMPACT were enrolled and treated for a mean of 1.5 years; 44 patients (34.9%) had more than 2 years of exposure. Mean steady-state C1-INH functional activity increased to 66.6% with 60 IU/kg. Incidence of adverse events was low and similar in both dose groups (11.3 and 8.5 events per patient-year for 40 IU/kg and 60 IU/kg, respectively). For 40 IU/kg and 60 IU/kg, median annualized attack rates were 1.3 and 1.0, respectively, and median rescue medication use was 0.2 and 0.0 times per year, respectively. Of 23 patients receiving 60 IU/kg for more than 2 years, 19 (83%) were attack-free during months 25 to 30 of treatment.

CONCLUSIONS

In patients with frequent HAE attacks, long-term replacement therapy with C1-INH(SC) is safe and exhibits a substantial and sustained prophylactic effect, with the vast majority of patients becoming free from debilitating disease symptoms.

Paired acute-baseline serum tryptase levels in perioperative anaphylaxis: An observational study

BACKGROUND

Anaphylaxis is recognized mainly through clinical criteria, which may lack specificity or relevance in the perioperative setting. The transient increase in serum tryptase has been proposed since 1989 as a diagnostic tool. Sampling for well-defined acute and baseline determinations has been recommended. We assessed the performance of four proposed algorithms with tightly controlled time frames for tryptase sampling, their robustness with inadequate sampling times, and the possible use of mature tryptase determination.

METHODS

A retrospective study was performed on 102 adult patients from the Aix-Marseille University Hospitals who had experienced a perioperative hypersensitivity reaction clinically suggesting anaphylaxis. EAACI and ICON criteria were used to diagnose anaphylaxis. Mature and total serum tryptase levels were measured.

RESULTS

Based on EAACI guidelines, clinical diagnostic criteria for anaphylaxis were found in 76 patients and lacking in 26. The most effective algorithm was the international consensus recommendation of 2012 that acute total tryptase levels should be greater than ([1.2×baseline tryptase] + 2] μg/L to be considered a clinically significant rise. In our cohort, this algorithm achieved 94% positive predictive value (PPV), 53% negative predictive value (NPV), 75% sensitivity, 86% specificity, and a Youden's index value of 0.61. A detectable acute mature tryptase level showed lower sensitivity, particularly in patients with acute total tryptase levels lower than 16 μg/L. Acute tryptase levels varied as a function of the clinical severity of anaphylaxis.

CONCLUSION

Total tryptase levels in serum discriminated between nonanaphylactic and anaphylactic events in a perioperative setting when acute and baseline levels were collected and analyzed by the consensus algorithm.

IgE-mediated mast cell activation promotes inflammation and cartilage destruction in osteoarthritis

Osteoarthritis is characterized by articular cartilage breakdown, and emerging evidence suggests that dysregulated innate immunity is likely involved. Here, we performed proteomic, transcriptomic, and electron microscopic analyses to demonstrate that mast cells are aberrantly activated in human and murine osteoarthritic joint tissues. Using genetic models of mast cell deficiency, we demonstrate that lack of mast cells attenuates osteoarthritis in mice. Using genetic and pharmacologic approaches, we show that the IgE/FcεRI/Syk signaling axis is critical for the development of osteoarthritis. We find that mast cell-derived tryptase induces inflammation, chondrocyte apoptosis, and cartilage breakdown. Our findings demonstrate a central role for IgE-dependent mast cell activation in the pathogenesis of osteoarthritis, suggesting that targeting mast cells could provide therapeutic benefit in human osteoarthritis.

Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

IL-33 with anti-FceRI Ab induces functional CD25 on human skin mast cells

Purpose

CD25 is expressed on the surface of clonal mast cells (MCs) in disorders such as mastocytosis, but not on normal MCs. IL-33, a new member of the IL-1 family of cytokines, is expressed primarily by epithelial and endothelial cells. IL-33 is released during cell necrosis, acting as “an alarmin” that can enhance T cell responses and activate MCs. We tests the hypothesis that treating MCs with IL-33 and anti-FceRI Ab induces cell-surface CD25.

Methods

MCs were dispersed from fresh surgical human skin and placed into culture with SCF (100 ng/ml) for 6–10 weeks. FACS analysis, western blotting, qRT-PCR and degranulation assays were performed, and cytokine, chemokine and sCD25 secretion was measured by ELISA.

Results

We found CD25 mRNA is expressed in primary MCs, and CD25 protein is detected within but not on the surface of resting MCs. When MCs were primed with IL-33 (10 ng/ml) and anti-FceRI Ab (10 ng/ml) for 2 days, surface CD25 was induced, as confirmed by flow cytometry and western blotting. Induction of CD25 was effectively inhibited by either anti-ST2 Ab or cyclosporine A. As C5a (10 nM) did not induce surface CD25 in combination with IL-33, degranulation of MCs is not critical for CD25 expression. MCs express CD132 mRNA and protein, and IL-33 plus anti-FceRI Ab induces CD122 mRNA. Consequently, the effect of IL-2 was examined. IL-2 (25–50 ng/ml) dose-dependently induced IL-6, IL-8, CCL4 and GM-CSF release by MCs only after priming with IL-33 and anti-FceRI Ab. Additionally, IL-33 with anti-FceRI Ab induces shedding of CD25, which can be suppressed by ADAM 17 inhibition to a greater extent than ADAM 10 inhibition.

Conclusion

Thus, polyclonal MCs from human skin, when primed, can express surface CD25 and a functional IL-2R complex.

Proposed Diagnostic Algorithm for Patients with Suspected Mast Cell Activation Syndrome

Mast cell activation (MCA) accompanies diverse physiologic and pathologic processes and is one of the more frequently encountered conditions in medicine. MCA-related symptoms are usually mild and often transient. In such cases, histamine receptor blockers and other mediator-targeting drugs can usually control MCA. In severe cases, an MCA syndrome (MCAS) may be diagnosed. However, overt MCAS is an unusual condition, and many patients referred because of suspected MCAS are diagnosed with other diseases (autoimmune, neoplastic, or infectious) unrelated to MCA or suffer from MCA-related (eg, allergic) disorders and/or comorbidities without fulfilling criteria of an overt MCAS. These considerations are important as more and more patients are informed that they may have MCA or even MCAS without completing a thorough medical evaluation. In fact, in several instances, symptoms are misinterpreted as MCA/MCAS, and other clinically relevant conditions are not thoroughly pursued. The number of such referrals is increasing. To avoid such unnecessary referrals and to prevent misdiagnoses, we here propose a diagnostic algorithm through which a clinically relevant (systemic) MCA can be suspected and MCAS can subsequently be documented or excluded. In addition, the algorithm proposed should help guide the investigating care providers to consider the 2 principal diagnoses that may underlie MCAS, namely, severe allergy and systemic mastocytosis accompanied by severe MCA. Although validation is required, we anticipate that this algorithm will facilitate the management of patients with suspected MCAS.

Adverse reactions to drugs and biologics in patients with clonal mast cell disorders: A Work Group Report of the Mast Cells Disorder Committee, American Academy of Allergy, Asthma & Immunology

Providers caring for patients with mastocytosis are tasked with the decision to consider therapeutic options. This can come with some trepidation because information available in the public domain lists numerous mast cell (MC) activators based on data that do not discriminate between primates, rodents, and MC lines; do not consider dosage; and do not take into account previous exposure and resultant clinical findings. This being said, there is support in the literature for an enhanced MC response in some patients with mastocytosis and in cases in which there is a greater incidence of adverse reactions associated with certain antigens, such as venoms and drugs. Thus this report provides a comprehensive guide for those providers who must decide on therapeutic options in the management of patients with clonal MC disease.

Effect of Lanadelumab Compared With Placebo on Prevention of Hereditary Angioedema Attacks: A Randomized Clinical Trial

IMPORTANCE

Current treatments for long-term prophylaxis in hereditary angioedema have limitations.

OBJECTIVE

To assess the efficacy of lanadelumab, a fully human monoclonal antibody that selectively inhibits active plasma kallikrein, in preventing hereditary angioedema attacks.

DESIGN, SETTING, AND PARTICIPANTS

Phase 3, randomized, double-blind, parallel-group, placebo-controlled trial conducted at 41 sites in Canada, Europe, Jordan, and the United States. Patients were randomized between March 3, 2016, and September 9, 2016; last day of follow-up was April 13, 2017. Randomization was 2:1 lanadelumab to placebo; patients assigned to lanadelumab were further randomized 1:1:1 to 1 of the 3 dose regimens. Patients 12 years or older with hereditary angioedema type I or II underwent a 4-week run-in period and those with 1 or more hereditary angioedema attacks during run-in were randomized.

INTERVENTIONS

Twenty-six-week treatment with subcutaneous lanadelumab 150 mg every 4 weeks (n = 28), 300 mg every 4 weeks (n = 29), 300 mg every 2 weeks (n = 27), or placebo (n = 41). All patients received injections every 2 weeks, with those in the every-4-week group receiving placebo in between active treatments.

MAIN OUTCOME AND MEASURES

Primary efficacy end point was the number of investigator-confirmed attacks of hereditary angioedema over the treatment period.

RESULTS

Among 125 patients randomized (mean age, 40.7 years [SD, 14.7 years]; 88 females [70.4%]; 113 white [90.4%]), 113 (90.4%) completed the study. During the run-in period, the mean number of hereditary angioedema attacks per month in the placebo group was 4.0; for the lanadelumab groups, 3.2 for the every-4-week 150-mg group; 3.7 for the every-4-week 300-mg group; and 3.5 for the every-2-week 300-mg group. During the treatment period, the mean number of attacks per month for the placebo group was 1.97; for the lanadelumab groups, 0.48 for the every-4-week 150-mg group; 0.53 for the every-4-week 300-mg group; and 0.26 for the every-2-week 300-mg group. Compared with placebo, the mean differences in the attack rate per month were -1.49 (95% CI, -1.90 to -1.08; P < .001); -1.44 (95% CI, -1.84 to -1.04; P < .001); and -1.71 (95% CI, -2.09 to -1.33; P < .001). The most commonly occurring adverse events with greater frequency in the lanadelumab treatment groups were injection site reactions (34.1% placebo, 52.4% lanadelumab) and dizziness (0% placebo, 6.0% lanadelumab).

CONCLUSIONS AND RELEVANCE

Among patients with hereditary angioedema type I or II, treatment with subcutaneous lanadelumab for 26 weeks significantly reduced the attack rate compared with placebo. These findings support the use of lanadelumab as a prophylactic therapy for hereditary angioedema. Further research is needed to determine long-term safety and efficacy.

TRIAL REGISTRATION

EudraCT Identifier: 2015-003943-20; ClinicalTrials.gov Identifier: NCT02586805.

Severity strata for POEM, PO-SCORAD, and DLQI in US adults with atopic dermatitis

BACKGROUND

Patient-Oriented Eczema Measure (POEM) is the preferred patient-reported outcome (PRO) for assessing symptoms of atopic dermatitis (AD). Dermatology Life Quality Index (DLQI) is commonly used to assess the burden of skin disease. Previous severity strata were developed for POEM and DLQI in clinical cohorts, which may be biased toward more severe disease. Severity strata were not previously examined in population-based cohorts. Patient-Oriented Scoring AD (PO-SCORAD) is another commonly used PRO for assessing AD symptoms; however, severity strata are not established.

OBJECTIVE

We sought to confirm previously developed strata for POEM and DLQI, and to develop strata for the PO-SCORAD in a population-based cohort of adults with AD.

METHODS

A cross-sectional, population-based study of 8,217 adults was performed using a structured questionnaire. A diagnosis of AD was determined using modified UK Diagnostic Criteria for AD (n = 602). AD severity was assessed using self-reported global AD severity (anchoring question), POEM, PO-SCORAD, and DLQI. Strata were selected using an anchoring approach based on patient-reported disease severity.

RESULTS

We confirmed the existing strata for DLQI (mild = 0-5, moderate = 6-10, severe = 11-30) (kappa = 0.446). However, the preferred strata for POEM was mild = 0-7, moderate = 8-19, and severe = 20-28 (kappa = 0.409) and PO-SCORAD was mild = 1-27, moderate = 28-56, severe = 57-104 (kappa = 0.444).

CONCLUSION

Existing strata for DLQI performed well in a population-based cohort of adult AD. The optimal severity strata for the POEM in our AD population varies slightly from those previously published for AD. This may suggest that different strata may be optimal in different study settings and cohorts. Finally, we proposed new strata for PO-SCORAD in adult AD.

Dual functionality of β-tryptase protomers as both proteases and cofactors in the active tetramer

Human β-tryptase, a tetrameric trypsin-like serine protease, is an important mediator of the allergic inflammatory responses in asthma. During acute hypersensitivity reactions, mast cells degranulate, releasing active tetramer as a complex with proteoglycans. Extensive efforts have focused on developing therapeutic β-tryptase inhibitors, but its unique activation mechanism is less well-explored. Tryptase is active only after proteolytic removal of the pro-domain followed by tetramer formation via two distinct symmetry-related interfaces. We show that the cleaved I16G mutant cannot tetramerize, likely due to impaired insertion of its N terminus into its "activation pocket," indicating allosteric linkage at multiple sites on each protomer. We engineered cysteines into each of the two distinct interfaces (Y75C for small or I99C for large) to assess the activity of each tetramer and disulfide-locked dimer. Using size-exclusion chromatography and enzymatic assays, we demonstrate that the two large tetramer interfaces regulate enzymatic activity, elucidating the importance of this protein-protein interaction for allosteric regulation. Notably, the I99C large interface dimer is active, even in the absence of heparin. We show that a monomeric β-tryptase mutant (I99C*/Y75A/Y37bA, where C* is cysteinylated Cys-99) cannot form a dimer or tetramer, yet it is active but only in the presence of heparin. Thus heparin both stabilizes the tetramer and allosterically conditions the active site. We hypothesize that each β-tryptase protomer in the tetramer has two distinct roles, acting both as a protease and as a cofactor for its neighboring protomer, to allosterically regulate enzymatic activity, providing a rationale for direct correlation of tetramer stability with proteolytic activity.

Human mast cells present antigen to autologous CD4+ T cells

BACKGROUND

Mast cells (MCs), the primary effector cell of the atopic response, participate in immune defense at host/environment interfaces, yet the mechanisms by which they interact with CD4⁺ T cells has been controversial.

OBJECTIVE

We used in situ-matured primary human MCs and matched CD4⁺ T cells to diligently assess the ability of MCs to act as antigen-presenting cells.

METHODS

We examined mature human skin-derived MCs using flow cytometry for expression of antigen-presenting molecules, for their ability to stimulate CD4⁺ T cells to express CD25 and proliferate when exposed to superantigen or to cytomegalovirus (CMV) antigen using matched T cells and MCs from CMV-seropositive or CMV-seronegative donors, and for antigen uptake. Subcellular localization of antigen, HLA molecules, and tryptase was analyzed by using structured illumination microscopy.

RESULTS

Our data show that IFN-γ induces HLA class II, HLA-DM, CD80, and CD40 expression on MCs, whereas MCs take up soluble and particulate antigens in an IFN-γ-independent manner. IFN-γ-primed MCs guide activation of T cells by Staphylococcus aureus superantigen and, when preincubated with CMV antigens, induce a recall CD4⁺ T_H1 proliferation response only in CMV-seropositive donors. MCs co-opt their secretory granules for antigen processing and presentation. Consequently, MC degranulation increases surface delivery of HLA class II/peptide, further enhancing stimulation of T-cell proliferation.

CONCLUSIONS

IFN-γ primes human MCs to activate T cells through superantigen and to present CMV antigen to T_H1 cells, co-opting MC secretory granules for antigen processing and presentation and creating a feed-forward loop of T-cell-MC cross-activation.

Prevention of Hereditary Angioedema Attacks with a Subcutaneous C1 Inhibitor

BACKGROUND

Hereditary angioedema is a disabling, potentially fatal condition caused by deficiency (type I) or dysfunction (type II) of the C1 inhibitor protein. In a phase 2 trial, the use of CSL830, a nanofiltered C1 inhibitor preparation that is suitable for subcutaneous injection, resulted in functional levels of C1 inhibitor activity that would be expected to provide effective prophylaxis of attacks.

METHODS

We conducted an international, prospective, multicenter, randomized, double-blind, placebo-controlled, dose-ranging, phase 3 trial to evaluate the efficacy and safety of self-administered subcutaneous CSL830 in patients with type I or type II hereditary angioedema who had had four or more attacks in a consecutive 2-month period within 3 months before screening. We randomly assigned the patients to one of four treatment sequences in a crossover design, each involving two 16-week treatment periods: either 40 IU or 60 IU of CSL830 per kilogram of body weight twice weekly followed by placebo, or vice versa. The primary efficacy end point was the number of attacks of angioedema. Secondary efficacy end points were the proportion of patients who had a response (≥50% reduction in the number of attacks with CSL830 as compared with placebo) and the number of times that rescue medication was used.

RESULTS

Of the 90 patients who underwent randomization, 79 completed the trial. Both doses of CSL830, as compared with placebo, reduced the rate of attacks of hereditary angioedema (mean difference with 40 IU, -2.42 attacks per month; 95% confidence interval [CI], -3.38 to -1.46; and mean difference with 60 IU, -3.51 attacks per month; 95% CI, -4.21 to -2.81; P<0.001 for both comparisons). Response rates were 76% (95% CI, 62 to 87) in the 40-IU group and 90% (95% CI, 77 to 96) in the 60-IU group. The need for rescue medication was reduced from 5.55 uses per month in the placebo group to 1.13 uses per month in the 40-IU group and from 3.89 uses in the placebo group to 0.32 uses per month in the 60-IU group. Adverse events (most commonly mild and transient local site reactions) occurred in similar proportions of patients who received CSL830 and those who received placebo.

CONCLUSIONS

In patients with hereditary angioedema, the prophylactic use of a subcutaneous C1 inhibitor twice weekly significantly reduced the frequency of acute attacks. (Funded by CSL Behring; COMPACT EudraCT number, 2013-000916-10 , and ClinicalTrials.gov number, NCT01912456 .).

Chronic Idiopathic Urticaria: Systemic Complaints and Their Relationship with Disease and Immune Measures

BACKGROUND

Patients with chronic idiopathic urticaria (CIU)/chronic spontaneous urticaria sometimes report systemic complaints (SCs).

OBJECTIVE

We sought to determine the frequency and characteristics of SCs among patients with CIU, as well as the association of SCs with disease measures, basophil histamine release, and serum tryptase.

METHODS

Adult patients with CIU were recruited from a university allergy clinic. Patients completed a disease symptom survey and underwent blood sampling for subsequent basophil histamine release and serum tryptase measurement.

RESULTS

A total of 155 patients with CIU were surveyed, with 103 reporting SCs with concomitant hives as follows: joint pain or swelling (55.3%), headache/fatigue (47.6%), flushing (42.7%), wheezing (30.1%), gastrointestinal complaints (26.2%), and palpitations (9.7%). Patients with SCs (CIU-SC) were compared with those with no SCs (CIU-NSC). Both groups had similar demographic characteristics (average age in 40s, majority female and white) and basophil histamine release profiles. CIU-SC had significantly greater disease duration (51.5% CIU-SC vs 30.8% CIU-NSC had >4 years duration), emergency department visits (41.7% vs 23.1% had >1 visit in the last year), CIU-related work absences (65% vs 27.5% had >1 day), oral corticosteroid use (84.5% vs 59.6%), quality-of-life impairment (76.1 vs 59.2 SkinDex score), and serum tryptase levels (5.1 ng/mL vs 3.9 ng/mL).

CONCLUSIONS

Despite similar demographic characteristics and basophil profiles as patients with CIU-NSC, patients with CIU-SC have features of greater disease burden (work absences, emergency department visits, and corticosteroid use), quality-of-life impairment, and baseline serum tryptase levels.

Advances in the Classification and Treatment of Mastocytosis: Current Status and Outlook toward the Future

Mastocytosis is a term used to denote a heterogeneous group of conditions defined by the expansion and accumulation of clonal (neoplastic) tissue mast cells in various organs. The classification of the World Health Organization (WHO) divides the disease into cutaneous mastocytosis, systemic mastocytosis, and localized mast cell tumors. On the basis of histomorphologic criteria, clinical parameters, and organ involvement, systemic mastocytosis is further divided into indolent systemic mastocytosis and advanced systemic mastocytosis variants, including aggressive systemic mastocytosis and mast cell leukemia. The clinical impact and prognostic value of this classification has been confirmed in numerous studies, and its basic concept remains valid. However, refinements have recently been proposed by the consensus group, the WHO, and the European Competence Network on Mastocytosis. In addition, new treatment options are available for patients with advanced systemic mastocytosis, including allogeneic hematopoietic stem cell transplantation and multikinase inhibitors directed against KIT D816V and other key signaling molecules. Our current article provides an overview of recent advances in the field of mastocytosis, with emphasis on classification, prognostication, and emerging new treatment options in advanced systemic mastocytosis. Cancer Res; 77(6); 1261-70. ©2017 AACR.

A humanized mouse model of anaphylactic peanut allergy

BACKGROUND

Food allergy is a growing health problem with very limited treatment options. Investigation of the immunologic pathways underlying allergic sensitization to foods in humans has been greatly constrained by the limited availability of intestinal tissue and gut-resident immune cells. Although mouse models have offered insights into pathways of food sensitization, differences between rodent and human immune physiology limit the extension of these findings to our understanding of human disease.

OBJECTIVE

We sought to develop a strategy for the generation of mice with humanized adaptive immune systems, complete with tissue engraftment by human mast cells that are competent to mount specific IgE-mediated responses and drive systemic anaphylaxis on ingestion challenge.

METHODS

Nonobese diabetic severe combined immunodeficient mice lacking the cytokine receptor common gamma chain (γc-/-) and carrying a human stem cell factor transgene were engrafted with human hematopoietic stem cells. The impact of peanut (PN) feeding and IgE neutralization on the development of immune responses, mast cell homeostasis, and anaphylactic food allergy was assessed in these animals.

RESULTS

Humanized nonobese diabetic severe combined immunodeficient common gamma chain-deficient stem cell factor (huNSG) mice exhibited robust engraftment with functional human T and B lymphocytes and human mast cells were found in significant numbers in their tissues, including the intestinal mucosa. Following gavage feeding with PN, they mounted specific antibody responses, including PN-specific IgE. When enterally challenged with PN, they exhibited mast-cell-mediated systemic anaphylaxis, as indicated by hypothermia and increases in plasma tryptase levels. Anti-IgE (omalizumab) treatment ablated this anaphylactic response.

CONCLUSIONS

huNSG mice provide a novel tool for studying food allergy and IgE-mediated anaphylaxis.

Elevated basal serum tryptase identifies a multisystem disorder associated with increased TPSAB1 copy number

Elevated basal serum tryptase levels are present in 4-6% of the general population, but the cause and relevance of such increases are unknown. Previously, we described subjects with dominantly inherited elevated basal serum tryptase levels associated with multisystem complaints including cutaneous flushing and pruritus, dysautonomia, functional gastrointestinal symptoms, chronic pain, and connective tissue abnormalities, including joint hypermobility. Here we report the identification of germline duplications and triplications in the TPSAB1 gene encoding α-tryptase that segregate with inherited increases in basal serum tryptase levels in 35 families presenting with associated multisystem complaints. Individuals harboring alleles encoding three copies of α-tryptase had higher basal serum levels of tryptase and were more symptomatic than those with alleles encoding two copies, suggesting a gene-dose effect. Further, we found in two additional cohorts (172 individuals) that elevated basal serum tryptase levels were exclusively associated with duplication of α-tryptase-encoding sequence in TPSAB1, and affected individuals reported symptom complexes seen in our initial familial cohort. Thus, our findings link duplications in TPSAB1 with irritable bowel syndrome, cutaneous complaints, connective tissue abnormalities, and dysautonomia.

Regulation of Reactive Oxygen Species and the Antioxidant Protein DJ-1 in Mastocytosis

Neoplastic accumulation of mast cells in systemic mastocytosis (SM) associates with activating mutations in the receptor tyrosine kinase KIT. Constitutive activation of tyrosine kinase oncogenes has been linked to imbalances in oxidant/antioxidant mechanisms in other myeloproliferative disorders. However, the impact of KIT mutations on the redox status in SM and the potential therapeutic implications are not well understood. Here, we examined the regulation of reactive oxygen species (ROS) and of the antioxidant protein DJ-1 (PARK-7), which increases with cancer progression and acts to lessen oxidative damage to malignant cells, in relationship with SM severity. ROS levels were increased in both indolent (ISM) and aggressive variants of the disease (ASM). However, while DJ-1 levels were reduced in ISM with lower mast cell burden, they rose in ISM with higher mast cell burden and were significantly elevated in patients with ASM. Studies on mast cell lines revealed that activating KIT mutations induced constant ROS production and consequent DJ-1 oxidation and degradation that could explain the reduced levels of DJ-1 in the ISM population, while IL-6, a cytokine that increases with disease severity, caused a counteracting transcriptional induction of DJ-1 which would protect malignant mast cells from oxidative damage. A mouse model of mastocytosis recapitulated the biphasic changes in DJ-1 and the escalating IL-6, ROS and DJ-1 levels as mast cells accumulate, findings which were reversed with anti-IL-6 receptor blocking antibody. Our findings provide evidence of increased ROS and a biphasic regulation of the antioxidant DJ-1 in variants of SM and implicate IL-6 in DJ-1 induction and expansion of mast cells with KIT mutations. We propose consideration of IL-6 blockade as a potential adjunctive therapy in the treatment of patients with advanced mastocytosis, as it would reduce DJ-1 levels making mutation-positive mast cells vulnerable to oxidative damage.

Functional angiotensin and bradykinin receptors are expressed on primary human mast cells

Purpose

The role of mast cells (MCs) has traditionally been recognized as an effector cell for IgE-mediated allergic diseases, involving ~20% of USA citizens. However, everyone has MCs, indicating their involvement in biologic and pathobiologic conditions beyond allergy. Angiotensin converting enzyme inhibitors (ACEI) and angiotensin II type 1 receptor (AT1R) blockers are used to treat cardiovascular disorders such as hypertension, while a bradykinin type 2 receptor (B2R) inhibitor is used to treat attacks of hereditary angioedema. We examined the expression and biological function of AT1R, B2R and B1R on primary human MCs.

Methods

MCs were dispersed from fresh surgical human skin obtained from CHTN, and placed into culture with SCF (100 ng/ml) for 4–8 weeks. FACS analysis, western blotting, qRT-PCR, degranulation (β-hexosaminidase release), cytokine/chemokine secretion of IL-6, IL-8 and CCL5, nitric oxide (NO) production (DAF-AM diacetate) were measured.

Results

FACS analysis and western blotting showed the AT1R and B2R are expressed on MCs. Angiotensin II (0.1–10 μM) and bradykinin (BK, 0.1–2 μM) stimulated MCs to release cytokines (1–4 ng/ml) which was inhibited by specific inhibitors. BK also stimulated the production of NO. Both the B2R and B1R are up-regulated by TNFα (10 ng/ml for 3 days), leading to enhanced activation of MCs by BK (1 μM) and desArg-LysBK (1 μM). Exposure of MCs to angiotensin II (2 μM), angiotensin (1–7)(10 μM) or ACEI (ramipril 1 μM) also enhanced cytokine secretion triggered by low concentration of BK (0.03–0.25 μM).

Conclusion

These findings suggest functional interactions of AT1R, B2R, ACE and Mas on human MCs, providing novel roles for MCs in cardiovascular, inflammatory and allergic disorders.

Biomarkers of the involvement of mast cells, basophils and eosinophils in asthma and allergic diseases

Biomarkers of disease activity have come into wide use in the study of mechanisms of human disease and in clinical medicine to both diagnose and predict disease course; as well as to monitor response to therapeutic intervention. Here we review biomarkers of the involvement of mast cells, basophils, and eosinophils in human allergic inflammation. Included are surface markers of cell activation as well as specific products of these inflammatory cells that implicate specific cell types in the inflammatory process and are of possible value in clinical research as well as within decisions made in the practice of allergy-immunology.