The potential clinical utility of serum alpha-protryptase levels

Overexpression of FcεRI on Bone Marrow Mast Cells, but Not MRGPRX2, in Clonal Mast Cell Disorders With Wasp Venom Anaphylaxis

Background

Uncertainties remain about the molecular mechanisms governing clonal mast cell disorders (CMCD) and anaphylaxis.

Objective

This study aims at comparing the burden, phenotype and behavior of mast cells (MCs) and basophils in patients with CMCD with wasp venom anaphylaxis (CMCD/WVA⁺), CMCD patients without anaphylaxis (CMCD/ANA^-), patients with an elevated baseline serum tryptase (EBST), patients with wasp venom anaphylaxis without CMCD (WVA⁺) and patients with a non-mast cell haematological pathology (NMHP).

Methods

This study included 20 patients with CMCD/WVA⁺, 24 with CMCD/ANA^-, 19 with WVA⁺, 6 with EBST and 5 with NMHP. We immunophenotyped MCs and basophils and compared baseline serum tryptase (bST) and both total and venom specific IgE in the different groups. For basophil studies, 13 healthy controls were also included.

Results

Higher levels of bST were found in CMCD patients with wasp venom anaphylaxis, CMCD patients without anaphylaxis and EBST patients. Total IgE levels were highest in patients with wasp venom anaphylaxis with and without CMCD. Bone marrow MCs of patients with CMCD showed lower CD117 expression and higher expression of CD45, CD203c, CD63, CD300a and FcεRI. Within the CMCD population, patients with wasp venom anaphylaxis showed a higher expression of FcεRI as compared to patients without anaphylaxis. Expression of MRGPRX2 on MCs did not differ between the study populations. Basophils are phenotypically and functionally comparable between the different patient populations.

Conclusion

Patients with CMCD show an elevated burden of aberrant activated MCs with a significant overexpression of FcεRI in patients with a wasp venom anaphylaxis.

Hereditary Alpha-Tryptasemia: a Commonly Inherited Modifier of Anaphylaxis

PURPOSE OF REVIEW

Hereditary alpha-tryptasemia (HαT) is an autosomal dominant genetic trait and a common cause of elevated basal serum tryptase in Western populations. It is a risk factor for severe anaphylaxis among individuals with venom allergy and an established modifier of anaphylaxis and mast cell mediator-associated symptoms among patients with systemic mastocytosis. Understanding the physiology of tryptases and how this may relate to the clinical features associated with HαT is the first step in identifying optimal medical management and targets for novel therapeutics.

RECENT FINDINGS

HαT prevalence is increased in both clonal and non-clonal mast cell-associated disorders where it augments symptoms of immediate hypersensitivity, including anaphylaxis. The unique properties of naturally occurring α/β-tryptase heterotetramers may explain certain elements of phenotypes associated with HαT, though additional mechanisms are being evaluated. This review provides an overview of the clinical and translational studies that have identified HαT as a modifier of mast cell-associated disorders and anaphylaxis and discusses mechanisms that may potentially explain some of these clinical findings.

Development and application of novel immunoassays for eosinophil granule major basic proteins to evaluate eosinophilia and myeloproliferative disorders

BACKGROUND

During eosinophil differentiation, the granule eosinophil major basic protein 1 (eMBP1) is synthesized as a 32-kDa precursor form, referred to as proMBP1, which is processed into the 14-kDa mature form of eMBP1. The prevalence of these two forms of MBP1 in most pathological conditions remains unknown.

OBJECTIVE

To develop the immunoassays that differentiate mature eMBP1 and proMBP1 and apply them to analyze their levels in biological fluids from patients with eosinophilia and hematologic disorders.

METHODS

We produced a series of monoclonal antibodies and selected pairs capable of discriminating between the two molecular forms of eMBP1. Radioimmunoassay (RIA) was performed to simultaneously quantitate the levels of mature eMBP1 and proMBP1 in secretions from patients with chronic rhinosinusitis (CRS) and sera from patients with hypereosinophilic syndrome (HES) and other myeloproliferative disorders.

RESULTS

The novel immunoassays possessed less than 1% crossreactivity between mature eMBP1 and proMBP1. Mature eMBP1, but not proMBP1, was found in nasal secretions of CRS patients. In contrast, elevated serum levels of mature eMBP1 and proMBP1 were observed in approximately 60% and 90% of HES patients, respectively, with proMBP1 present in greater quantities than mature eMBP1. Patients with several myeloproliferative disorders also showed high serum levels of proMBP1 while mature eMBP1 remained at basal levels.

CONCLUSION

The novel immunoassays successfully differentiated mature eMBP1 and proMBP1 in human biological fluids. Further studies addressing the clinical correlates of these assays will help to develop biomarkers to diagnose and monitor patients with eosinophilia and myeloproliferative disorders.

Laboratory Tests in Diagnosis of Mastocytosis: Literature Review and Case Report

Мastocytosis is a heterogeneous group of disorders characterized by abnormal growth and accumulation of mast cells (MCs) in the skin and/or other organ systems. Mastocytosis is a rare disease. The annual incidence is 5-10 cases per 1 million people. However, the majority of cases stay undiagnosed due to the lack of specific tests and a wide variety of clinical features of the disease. In mastocytosis, somatic mutations of KIT gene lead to autocrine dysregulation and constitutive c-KIT activation in the absence of its ligand SCF. Clinical symptoms of the disease are determined by MC mediator release and/or infiltration of tissues by MCs. According to the World Health Organisation classification updated in 2016 mastocytosis is divided to cutaneous mastocytosis (CM), indolent systemic mastocytosis (ISM), smoldering systemic mastocytosis (SSM), SM with an associated hematologic (non-MC-lineage) neoplasm (SMAHN), aggressive SM (ASM), MC leukemia (MCL) and MC sarcoma (MCS). The CM and ISM prognosis is excellent with (almost) normal life expectancy, unlike aggressive forms (ASM and MCL) with poor prognosis. In this paper the key aspects of clinical features and diagnostic criteria of mastocytosis are discussed. We present a case report of a patient with mastocytosis in the skin following psoralen plus ultraviolet A (PUVA) therapy with good response.

Hereditary Alpha Tryptasemia: Genotyping and Associated Clinical Features

Hereditary alpha tryptasemia is an autosomal dominant genetic trait caused by increased germline copies of TPSAB1 encoding alpha-tryptase. Individuals with this trait have elevated basal serum tryptase, and may present with associated multisystem complaints. Both basal serum tryptase levels and severity of clinical symptoms display a gene-dose relationship with TPSAB1, whereby higher tryptase levels and greater symptom severity are correlated with increasing numbers of alpha-encoding TPSAB1. As the functional effects of increased basal serum tryptase and/or altered tryptase gene expression are elucidated, greater insights will be gained into the symptoms associated with hereditary alpha tryptasemia and their potential therapy.

Long-term treatment with imatinib results in profound mast cell deficiency in Ph+ chronic myeloid leukemia

Although mast cells (MC) play an important role in allergic reactions, their physiologic role remains unknown. In mice, several models of MC-deficiency have been developed. However, no comparable human model is available. We examined the in vitro- and in vivo effects of the KIT-targeting drug imatinib on growth and development of human MC. Imatinib was found to inhibit stem cell factor (SCF)-induced differentiation of MC in long-term suspension cultures (IC50: 0.01 μM). Correspondingly, long-term treatment of chronic myeloid leukemia (CML) patients with imatinib (400 mg/day) resulted in a marked decrease in MC. In patients with continuous complete molecular response during therapy, bone marrow MC decreased to less than 5% of pre-treatment values, and also serum tryptase concentrations decreased significantly (pre-treatment: 32.0±11.1 ng/ml; post-therapy: 3.4±1.8, p<0.01). Other myeloid lineages, known to develop independently of KIT, were not affected by imatinib-therapy. Imatinib also produced a substantial decrease in MCdevelopment in mice. However, no clinical syndrome attributable to drug-induced MC-deficiency was recorded in our CML patients. Together, imatinib suppresses MC production in vitro and in vivo. However, drug-induced MC depletion is not accompanied by adverse clinical events, suggesting that MC are less relevant to homeostasis in healthy tissues than we assumed so far.

Mast cell activation syndromes: definition and classification

Mast cell activation (MCA) occurs in a number of different clinical conditions, including IgE-dependent allergies, other inflammatory reactions, and mastocytosis. MCA-related symptoms may be mild, moderate, severe, or even life-threatening. The severity of MCA depends on a number of different factors, including genetic predisposition, the number and releasability of mast cells involved in the reaction, the type of allergen, presence of specific IgE, and presence of certain comorbidities. In severe reactions, MCA can be documented by a substantial increase in the serum tryptase level above baseline. When symptoms are recurrent, are accompanied by an increase in mast cell-derived mediators in biological fluids, and are responsive to treatment with mast cell-stabilizing or mediator-targeting drugs, the diagnosis of mast cell activation syndrome (MCAS) is appropriate. Based on the underlying condition, these patients can further be classified into i) primary MCAS where KIT-mutated, clonal mast cells are detected, ii) secondary MCAS where an underlying inflammatory disease, often in the form of an IgE-dependent allergy, but no KIT-mutated mast cells, is found, and iii) idiopathic MCAS, where neither an allergy or other underlying disease, nor KIT-mutated mast cells are detectable. It is important to note that in many patients with MCAS, several different factors act together to lead to severe or even life-threatening anaphylaxis. Detailed knowledge about the pathogenesis and complexity of MCAS, and thus establishing the exact final diagnosis, may greatly help in the management and therapy of these patients.

Tryptase and histamine metabolites as diagnostic indicators of indolent systemic mastocytosis without skin lesions

BACKGROUND

Risk indicators of indolent systemic mastocytosis (ISM) in adults with clinical suspicion of ISM without accompanying skin lesions [urticaria pigmentosa (UP)] are lacking. This study aimed at creating a decision tree using clinical characteristics, serum tryptase, and the urinary histamine metabolites methylimidazole acetic acid (MIMA) and methylhistamine (MH) to select patients for bone marrow investigations to diagnose ISM.

METHODS

Retrospective data analysis of all adults, in whom bone marrow investigations were performed to diagnose ISM, was carried out.

RESULTS

In total, 142 patients were included. SM was absent in all 44 patients with tryptase <10 μg/l, in 45 of 98 (46%) patients with tryptase ≥10 μg/l and in 18 of 52 patients (35%) with tryptase >20 μg/l. Above 43 μg/l, all patients had ISM (n = 11). Male gender, insect venom anaphylaxis as presenting symptom, tryptase, MIMA, and MH were independent ISM predictors. If tryptase was ≥10 μg/l, the diagnostic accuracy of MIMA and MH was high (areas under the ROC curve 0.92).

CONCLUSIONS

In suspected patients without UP, the ISM risk is very low (if present at all) if tryptase is <10 μg/l. If tryptase is ≥10 μg/l, this risk depends on MIMA and MH, being low if these are normal, but high if these are elevated. Male gender and insect venom anaphylaxis are additional risk indicators. We recommend refraining from bone marrow examinations in suspected patients without UP if tryptase is <10 μg/l. Our results question the reliability of the minor diagnostic World Health Organization criterion of tryptase >20 μg/l.

Cutaneous manifestations in Hymenoptera and Diptera anaphylaxis: relationship with basal serum tryptase

OBJECTIVES

To compare the clinical presentation of systemic anaphylaxis to Hymenoptera and Diptera with regard to basal serum tryptase (BT) and to evaluate mastocytosis in patients with elevated tryptase.

PATIENTS AND METHODS

The medical records of 140 patients with a history of a systemic reaction to venom were retrospectively reviewed. Symptoms and severity of anaphylaxis and BT were recorded. Most patients with elevated tryptase were screened for mastocytosis: a dermatological examination with a skin biopsy was performed in 19 cases and a bone marrow biopsy in 14 cases.

RESULTS

Tryptase was elevated in 23 patients. These patients reported fewer usual skin reactions (urticaria in 26.1% of cases with raised tryptase vs. 76.1% of cases with normal tryptase), more flushing (52.2% vs. 4.3%) and frequently did not present skin reaction (26.1% vs. 9.4%). They presented a more severe reaction (mean grade of severity: 3.48 vs. 2.69). Mastocytosis was diagnosed in seven patients with elevated tryptase: indolent systemic mastocytosis in six cases and cutaneous mastocytosis without systemic involvement in one case. In five cases, mastocytosis was previously undiagnosed. Lesions of cutaneous mastocytosis, diagnosed in five patients, consisted of urticaria pigmentosa in all cases and were often inconspicuous.

CONCLUSION

These results demonstrate particular clinical features of the allergic reaction in patients with elevated BT and the higher frequency of mastocytosis in this population. In patients with a severe anaphylactic reaction without urticaria, but with flushing, tryptase should be assayed and an underlying mastocytosis should be considered.

Systematic follow-up increases incidence of anaphylaxis during adverse reactions in anesthetized patients

BACKGROUND

The incidence of hypersensitivity reactions during anesthesia is underestimated because clinical symptoms may vary and diagnosis is not obvious. Our aim was to investigate the consequences of a systematic follow-up of patients on the estimated incidence of allergic reactions during anesthesia.

METHODS

We conducted a prospective study over a 2-year period (70,000 anesthesias). When patients were suspected with hypersensitivity reactions or with unexplained adverse reactions during anesthesia, blood was sampled to measure histamine and tryptase, and then skin tests were performed 4-6 weeks later.

RESULTS

During the studied period, 39 patients were enrolled in the database. Eight were excluded because of lack of skin tests. Twenty-two patients had clinical features compatible with immediate hypersensitivity reaction, and nine had reactions rated as 'unexplained' by the attending physician. Following systematic investigation, we found 22 hypersensitivity reactions (15 patients with obvious and seven with unexplained reactions) during anesthesia. This increases the estimated incidence of hypersensitivity reactions from 1 : 4667 to 1 : 3180 anesthesias. Tryptase concentrations were increased in only 50% of these patients. In our series, positive and negative predictive values of tryptase at T(0) for the diagnosis of anaphylaxis were 100% and 60%, respectively. Latex was the major causative agent, followed by neuromuscular blocking agents and antibiotics.

CONCLUSIONS

Systematic follow-up of patients with unexplained reactions during anesthesia increases the estimated incidence of IgE-mediated hypersensitivity reactions during anesthesia by 50%.

SAFE: a multidisciplinary approach to anaphylaxis education in the emergency department

BACKGROUND

Anaphylaxis is a serious allergic reaction that is rapid in onset and may cause death. Allergists and emergency department (ED) physicians recognize the need for multidisciplinary efforts to increase public awareness of anaphylaxis, improve patient education, and enhance emergency and long-term management for the millions of Americans at risk for anaphylactic reactions.

OBJECTIVES

To provide an overview of the scientific literature documenting inconsistencies and limitations in the management of anaphylaxis in the ED, to highlight the need to enhance ED discharge instructions and patient education materials, and to introduce the SAFE system, an aid to improve the ongoing management and avoidance of factors that contribute to anaphylaxis.

METHODS

An expert panel of allergists and ED physicians was convened by the American College of Allergy, Asthma and Immunology and the American College of Emergency Physicians to develop recommendations for educational materials on anaphylaxis for ED personnel and patients.

RESULTS

The panel developed the acronym SAFE, a mnemonic device to remind physicians of the 4 basic action steps suggested for the care of a patient with anaphylaxis: (1) Seek support, (2) Allergen identification and avoidance, (3) Follow-up for specialty care, and (4) Epinephrine for emergencies.

CONCLUSION

The SAFE system is designed as a tool to raise awareness of anaphylaxis and its treatments among individuals at risk and the ED personnel charged with their care. Future studies need to examine the impact of the SAFE system in decreasing the morbidity and mortality rates associated with anaphylaxis and other severe allergic reactions.

Navigating the updated anaphylaxis parameters

: Anaphylaxis, an acute and potentially lethal multi-system clinical syndrome resulting from the sudden, systemic degranulation of mast cells and basophils, occurs in a variety of clinical scenarios and is almost unavoidable inmedical practice. Healthcare professionalsmust be able to recognize its features, treat an episode promptly and appropriately, and be able to provide recommendations to prevent future episodes. Epinephrine, administered immediately, is the drug of choice for acute anaphylaxis. The discussion provides an overview of one set of evidence-based and consensus parameters for the diagnosis and management of anaphylaxis.

Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria

Although a classification for mastocytosis and diagnostic criteria are available, there remains a need to define standards for the application of diagnostic tests, clinical evaluations, and treatment responses. To address these demands, leading experts discussed current issues and standards in mastocytosis in a Working Conference. The present article provides the resulting outcome with consensus statements, which focus on the appropriate application of clinical and laboratory tests, patient selection for interventional therapy, and the selection of appropriate drugs. In addition, treatment response criteria for the various clinical conditions, disease-specific symptoms, and specific pathologies are provided. Resulting recommendations and algorithms should greatly facilitate the management of patients with mastocytosis in clinical practice, selection of patients for therapies, and the conduct of clinical trials.

Evaluation of biologic activity of tryptase secreted from blast cells in acute myeloid leukemia

A number of autocrine and paracrine growth regulators are considered to be involved in the survival and proliferation of blast cells in acute myeloid leukemia (AML). We have recently shown that blast cells in a group of patients with AML produce and secrete the mitogenic enzyme tryptase. In the present study, we examined functional effects of tryptase in the context of AML. As assessed by 3H-thymidine uptake experiments, tryptase-containing serum from patients with AML as well as heparin-complexed recombinant tryptase were found to promote the proliferation of cultured bone marrow- and lung fibroblasts in a dose-dependent manner. A neutralizing antibody against human beta-tryptase was found to diminish these growth-stimulatory effects of serum-tryptase in all patients examined. Tryptase also induced the expression of mRNA for GM-CSF and SCF, two cytokines known to promote growth of AML cells, in cultured bone marrow fibroblasts. Neither recombinant tryptase nor tryptase-rich serum of AML patients, showed an effect on the growth of leukemic blast cells irrespective of the FAB category or expression of protease-activated receptor (PAR)-2, a putative molecular target of tryptase. Together, tryptase is secreted from AML blasts as a biologically active molecule that may exhibit paracrine rather than autocrine effects in AML.

Diagnostic Value of Tryptase in Anaphylaxis and Mastocytosis

Serum (or plasma) levels of total and mature tryptase measurements are recommended in the diagnostic evaluation of systemic anaphylaxis and systemic mastocytosis, but their interpretation must be considered in the context of a complete workup of each patient. Total tryptase levels generally reflect the increased burden of mast cells in patients with all forms of systemic mastocytosis (indolent systemic mastocytosis, smoldering systemic mastocytosis, systemic mastocytosis associated with a hematologic clonal non-mast cell disorder, aggressive systemic mastocytosis, and mast cell leukemia) and the decreased burden of mast cells associated with cytoreductive therapies in these disorders. Causes of an elevated total tryptase level other than systemic mastocytosis must be considered, however, and include systemic anaphylaxis, acute myelocytic leukemia, various myelodysplastic syndromes, hypereosinophilic syndrome associated with the FLP1L1-PDGFRA mutation, end-stage renal failure, and treatment of onchocerciasis. Mature (beta) tryptase levels generally reflect the magnitude of mast cell activation and are elevated during most cases of systemic anaphylaxis, particularly with parenteral exposure to the inciting agent.

Tryptase as Severity Marker in Drug Provocation Tests

BACKGROUND

In the absence of objective symptoms, it is difficult to assess an adverse reaction during drug provocation testing. We evaluated the value of serum tryptase levels to distinguish between positive, negative and, even more important, so-called 'hysterical' reactions (conversion symptoms). The latter are occasionally observed in drug provocation tests when the patient experiences ambiguous subjective symptoms.

METHODS

In a prospective single-center study, 303 patients underwent 785 drug provocation tests. Blood was taken for tryptase measurement on each test day before and after drug challenge, and the changes in serum tryptase levels in patients with no reactions were compared with those who experienced immediate reactions to a drug.

RESULTS

Thirty-four of 785 drug provocations were clinically judged as being positive. Despite objective symptoms, median serum tryptase values in the afternoon were even lower than baseline levels. However, this decrease was not statistically significant. In the 751 patients suffering no objective reactions, the median values of post-testing tryptase values were statistically significantly decreased as compared with pretesting values.

CONCLUSIONS

The measurement of serum tryptase levels does not appear to be helpful to differentiate mild allergic or nonallergic reactions from 'hysterical' ones. The milder decrease in the group with objective drug reactions might indicate slight mast cell activation in some patients. More severe clinical drug reactions led to stronger mast cell degranulation. Mild reactions did not increase the tryptase levels consistently.

Les mastocytoses systémiques

Systemic mastocytosis is characterized by abnormal mast cell proliferation in different organs. The 2001 consensus classification distinguishes in separate categories indolent systemic mastocytosis, systemic mastocytosis with concomitant blood disease, aggressive systemic mastocytosis and mast cell leukemia. Clinical manifestations are caused by tissue infiltration by proliferating mastocytes and by release of mediators. The principal organs affected are the skin, bones, digestive tract, liver, spleen and lymph nodes. Diagnosis of mastocytosis is based on appropriate stains (Giemsa, toluidine blue) and immunophenotype features (tryptase, CD117, also known as c-KIT and stem cell factor receptor). Serum tryptase levels reflect the total mast cell burden. Treatment must prevent release of mast cell mediators (histamine antagonists, cromolyn sodium, corticosteroids, or leukotriene-receptor inhibitors), limit bone involvement (bisphosphonates) and reduce the number of circulating mast cells (interferon, cladribine, or tyrosine kinase inhibitors). Enhanced understanding of the pathogenic mechanisms (mutation of c-kit and platelet-derived growth factor receptor alpha has led to the development of targeted treatments, including new inhibitors of tyrosine kinase and of nuclear factor Kappa B.

Elevated basal serum tryptase and hymenoptera venom allergy: relation to severity of sting reactions and to safety and efficacy of venom immunotherapy

BACKGROUND

Mastocytosis and/or elevated basal serum tryptase may be associated with severe anaphylaxis.

OBJECTIVE

To analyse Hymenoptera venom-allergic patients with regard to basal tryptase in relation to the severity of sting reactions and the safety and efficacy of venom immunotherapy.

METHODS

Basal serum tryptase was measured in 259 Hymenoptera venom-allergic patients (158 honey bee, 101 Vespula). In 161 of these (104 honey bee, 57 Vespula), a sting challenge was performed during venom immunotherapy.

RESULTS

Nineteen of the 259 patients had an elevated basal serum tryptase. Evidence of cutaneous mastocytosis as documented by skin biopsy was present in 3 of 16 patients (18.8%). There was a clear correlation of basal serum tryptase to the grade of the initial allergic reaction (P<0.0005). Forty-one of the 161 sting challenged patients reacted to the challenge, 34 to a bee sting and 7 to a Vespula sting. Thereof, 10 had an elevated basal serum tryptase, i.e. 1 (2.9%) of the reacting and 2 (2.9%) of the non-reacting bee venom (BV) allergic individuals, as compared to 3 (42.9%) of the reacting and 4 (8%) of the non-reacting Vespula venom-allergic patients. Thus, there was a significant association between a reaction to the sting challenge and an elevated basal serum tryptase in Vespula (chi2=6.926, P<0.01), but not in BV-allergic patients. Systemic allergic side-effects to venom immunotherapy were observed in 13.9% of patients with normal and in 10% of those with elevated basal serum tryptase.

CONCLUSIONS

An elevated basal serum tryptase as well as mastocytosis are risk factors for severe or even fatal shock reactions to Hymenoptera stings. Although the efficacy of venom immunotherapy in these patients is slightly reduced, most of them can be treated successfully. Based on currently available data, lifelong treatment has to be discussed in this situation.

Beta tryptase levels are not elevated in patients undergoing liver transplantation

Reperfusion syndrome during liver transplantation and anaphylaxis are clinical syndromes that share similarities in physiological responses. The liver and intestine contain a variety of immunologically active cells, including mast cells. The purpose of this study is to investigate the possibility that mast-cell degranulation occurs routinely during transplantation and thereby contributes to hemodynamic instability and coagulopathy. Beta tryptase, an enzyme released by mast cells during degranulation, is a reliable marker for mast-cell-mediated events. Six patients undergoing liver transplantation had beta tryptase levels assayed in blood immediately before and after reperfusion of the liver. No patient showed an increase in beta tryptase levels at 15 or 60 minutes after reperfusion. In conclusion, it is unlikely that clinically significant mast-cell degranulation occurs routinely in patients undergoing liver transplantation.

Indolent systemic mast cell disease: immunophenotypic characterization of bone marrow mast cells by flow cytometry

BACKGROUND

Mast cell disease has a low prevalence and is difficult to diagnose in the absence of the characteristic skin lesions that usually accompany the condition. Extracutaneous involvement is not easy to assess. There are reports in the recent literature on the use of tryptase as a reliable immunohistochemical marker as well as on the study of the immunophenotype of bone marrow mast cells. The latter is of great help for the diagnosis of systemic involvement as, after the skin, the bone marrow is the organ most commonly affected by the disease.

OBJECTIVE

We describe two cases of indolent systemic mast cell disease (SMCD) where flow cytometry was used to identify immunophenotypical characteristics of bone marrow mast cells. Recent advances in the application of this technique prove it can be a good diagnostic tool for assessing systemic involvement of the disease.

PATIENTS AND METHODS

Two adult subjects with indolent SMCD had multiple clinical symptoms. Cutaneous lesions were the clue to the diagnosis but, subsequently, in the presence of disturbing symptoms, involvement of other organ systems was confirmed. In both cases, the authors used flow cytometry techniques, as described by Escribano et al. (1998) to define the immunophenotype of bone marrow mast cells.

RESULTS

Both patients were diagnosed with indolent SMCD with cutaneous and bone marrow involvement. Also, they presented visible clues to the presumptive bone, cardiovascular and nervous system involvement. Gastrointestinal manifestations were documented in one case.

CONCLUSIONS

The use of flow cytometry on bone marrow samples from patients with mastocytosis reveals immunophenotypic differences that can serve to allow classification of these subjects in the category of indolent SMCD even though involvement of another organ system may not be thoroughly confirmed.

Systemic mast cell disease without associated hematologic disorder: a combined retrospective and prospective study

OBJECTIVE

To study clinicopathologic correlations and identify prognostically important variables in patients with systemic mast cell disease (SMCD) who have no associated hematologic disorders.

PATIENTS AND METHODS

We identified 40 adult patients with SMCD without associated hematologic disorders. Clinical, laboratory, and bone marrow (BM) histologic findings at the time of referral were evaluated (November 1980-February 2001) for possible correlations with a history of aggressive systemic mastocytosis (retrospectively analyzed) as well as survival (prospectively analyzed).

RESULTS

The median follow-up time from diagnosis was 108 months and from BM examination was 24 months. A history of aggressive systemic mastocytosis correlated significantly with increased BM mast cell (MC) content, unfavorable MC infiltration pattern, BM eosinophilia, and elevated serum alkaline phosphatase (SAP) level, but not with BM angiogenesis, reticulin fibrosis, or levels of MC mediators. Of these factors, increased BM MC content and elevated SAP level were also associated with shortened survival from time of referral.

CONCLUSIONS

This study suggests that the BM MC burden, BM eosinophilia, and SAP level are prognostically important in SMCD without associated hematologic disorders. In contrast, BM angiogenesis, reticulin fibrosis, and levels of MC mediators showed no prognostic relevance.

Anaphylaxis: a review of causes and mechanisms

Anaphylaxis is a life-threatening syndrome resulting from the sudden release of mast cell- and basophil-derived mediators into the circulation. Foods and medications cause most anaphylaxis for which a cause can be identified, but virtually any agent capable of directly or indirectly activating mast cells or basophils can cause this syndrome. This review discusses the pathophysiologic mechanisms of anaphylaxis, its causes, and its treatment.

The crystal structure of human alpha1-tryptase reveals a blocked substrate-binding region

Human mast cell tryptases represent a subfamily of trypsin-like serine proteinases implicated in asthma. Unlike beta-tryptases, alpha-tryptases apparently are proteolytically inactive. We have solved the 2.2A crystal structure of mature human alpha1-tryptase. It reveals a frame-like tetrameric architecture that, surprisingly, does not require heparin-binding for stability. In marked contrast to beta2-tryptase, the Ser214-Gly219 segment, which normally provides the template for substrate binding, is kinked in alpha-tryptase, thereby blocking its non-primed subsites. This so far unobserved subsite distortion is incompatible with productive substrate binding and processing. alpha-Tryptase apparently is trapped in this off-conformation by repulsions and attractions of the Asp216 side-chain. However, proteolytic activity could be generated by an induced-fit mechanism.

Genetic deficiency of human mast cell alpha-tryptase

BACKGROUND

Human alpha- and beta-tryptases are proteases secreted by mast cells. Beta (but not alpha) tryptases are implicated in asthma. Genes encoding both types of tryptases cluster on chromosome 16p13.3.

OBJECTIVE

This study examines the hypothesis, generated from mapping data, that alpha-alleles compete with some beta-alleles at one locus and that an adjacent locus contains beta-alleles exclusively. This hypothesis predicts that beta-alleles outnumber alpha and that some genomes lack alpha genes altogether.

METHODS

To test this hypothesis, we developed PCR-based techniques to distinguish alpha from beta genes. We then genotyped genomic DNA from individuals and tryptase-expressing cell lines.

RESULTS

In support of our hypothesis, we find that alpha-tryptase deficiency affects 80/274 (29%) of individuals surveyed. The genotype of the alpha-deficient individuals is betabetabetabeta, due to inheritance of four beta genes. The percentage of the population with the mixed genotypes alphaalphabetabeta and alphabetabetabeta is 21% and 50%, respectively. Accounting for all alpha- and beta-alleles at the tandem loci on 16p13.3, overall alpha-allele frequency is only 0.23, with beta-alleles considerably outnumbering alpha as hypothesized. In samples of defined ethnicity, alpha deficiency affects 45% of Caucasians, but a much lower percentage of other backgrounds, including African-Americans and Asians. Examination of cell lines reveals that HMC-1 and U-937 lack alpha-genes; thus, lack of alpha transcripts in these cells is due to absence of alpha-genes rather than beta-selective transcription. By contrast, alpha-transcribing Mono Mac 6 and KU812 cells contain alpha- and beta-genes.

CONCLUSIONS

Genetic alpha-tryptase deficiency is common and varies strikingly between ethnic groups. Because beta-tryptases are implicated in allergic disorders, inherited differences in alpha/beta-genotype may affect disease susceptibility, severity and response to tryptase inhibitor therapy.

Elevated serum concentrations of beta-tryptase, but not alpha-tryptase, in Sudden Infant Death Syndrome (SIDS). An investigation of anaphylactic mechanisms

BACKGROUND

Sudden Infant Death Syndrome, (SIDS) or cot death, remains the most common category of post-perinatal death in the UK. By definition, the cause of death is unknown, but a long-standing theory is that some of these deaths could be the result of anaphylaxis.

OBJECTIVE

To investigate the potential contribution of anaphylactic mechanisms to deaths in infancy by determining relative levels of alpha- and beta-tryptases and both total and allergen-specific IgE in sera from groups of infants whose deaths were attributed to SIDS or to other causes.

METHODS

Serum samples were collected at the time of post-mortem examination from infants whose death was classed as SIDS (n = 40) and from a comparison group in which cause of death had been established (n = 32). Serum tryptase concentrations were measured with a radioimmunoassay with monoclonal antibody G5 which detects primarily beta-tryptase or an ELISA with antibody AA5 which has equal sensitivity for alpha- and beta-tryptases. Levels of total IgE and IgE specific for casein, beta-lactoglobulin, house dust mite and moulds were determined.

RESULTS

Analysis of the results of the two assays for tryptase indicated that levels of the beta-like tryptase (the form secreted on anaphylactic degranulation) were significantly higher in serum from infants with SIDS compared with those whose death was explained. There was no evidence for an increase in serum levels of alpha-tryptase (the variant secreted constitutively from mast cells). Total levels of serum IgE did not differ between the two groups and, reflecting the low circulating IgE concentrations in infancy, an elevation in IgE specific for the panel of allergens was not detected.

CONCLUSIONS

In a proportion of SIDS victims there may be increased serum levels of beta-like tryptase, a marker for anaphylaxis. The failure to detect an increase in alpha-tryptase would suggest that mast cell hyperplasia is not a feature of cot death. The nature of the inciting agents remains unclear, but anaphylaxis deserves serious consideration as a possible cause of sudden death in infancy.

Mastocytosis: review of clinical and experimental aspects

Mastcytosis is a rare disease characterized by an abnormal increase of mast cells in tissues. The skin is the organ most frequently involved, but mast cells also accumulate in the bone marrow, gastrointestinal tract, lymph nodes, spleen, and liver. Recent studies suggest that activating mutations of c-kit, a protooncogene encoding for the receptor (kit) of stem cell factor, are a possible cause of some forms of mastocytosis. In addition, an increased rate of chromosomal aberrations has been found. Despite significant advances in research on mastocytosis, curative treatment is not yet available. Current management is based on avoidance of mediator-releasing triggers and symptomatic treatment.

Mastocytosis

Mastocytosis represents a heterogeneous group of clinical disorders resulting from the infiltration of mast cells in the skin and other organs. Although mastocytosis was first described over 130 years ago, the pathophysiologic mechanisms responsible for this disease have been identified only recently. This article discusses the salient clinical features of the disease, the mechanisms responsible for its development, and provides treatment approaches that have proven useful for managing patients with this disorder.

Release of soluble tryptase but only minor amounts of chymase activity from cutaneous mast cells

Tryptase and chymase are the major serine proteinases of skin mast cells but their biologic significance depends on their activity. In this study, we demonstrate the release of soluble activity of tryptase, but not markedly that of chymase, into skin blister fluids induced by freezing with liquid nitrogen as well as into supernatant during incubation of 8 whole skin specimens with compound 48/80 for up to 2 days followed by sonication. Incubation of 3 other skin specimens in compound 48/80 for up to 2 days revealed that the number of mast cells displaying tryptase activity decreased significantly on day 2, and the number of mast cells showing chymase activity (but not those showing chymase immunoreactivity) decreased significantly on day 1 but not thereafter on day 2. The results of 3 skin organ cultures for up to 14 days showed steady decrease in the number of tryptase-positive cells but persistence of mast cells containing chymase activity. Chymase in solution was sensitively inhibited by 0.01 mg/ml alpha1-antichymotrypsin but higher concentrations (0.3-3.0 mg/ml) were needed for inhibiting chymase on skin sections. In conclusion, after mast cell degranulation tryptase activity is substantially solubilized and it may potentially affect both local and distant skin structures. Instead, chymase is partially inactivated and the remaining chymase activity persists at the site of degranulation having only local effects.

Diagnostic criteria and classification of mastocytosis: a consensus proposal

The term 'mastocytosis' denotes a heterogeneous group of disorders characterized by abnormal growth and accumulation of mast cells (MC) in one or more organ systems. Over the last 20 years, there has been an evolution in accepted classification systems for this disease. In light of such developments and novel useful markers, it seems appropriate now to re-evaluate and update the classification of mastocytosis. Here, we propose criteria to delineate categories of mastocytosis together with an updated consensus classification system. In this proposal, the diagnosis cutaneous mastocytosis (CM) is based on typical clinical and histological skin lesions and absence of definitive signs (criteria) of systemic involvement. Most patients with CM are children and present with maculopapular cutaneous mastocytosis (=urticaria pigmentosa, UP). Other less frequent forms of CM are diffuse cutaneous mastocytosis (DCM) and mastocytoma of skin. Systemic mastocytosis (SM) is commonly seen in adults and defined by multifocal histological lesions in the bone marrow (affected almost invariably) or other extracutaneous organs (major criteria) together with cytological and biochemical signs (minor criteria) of systemic disease (SM-criteria). SM is further divided into the following categories: indolent systemic mastocytosis (ISM), SM with an associated clonal hematologic non-mast cell lineage disease (AHNMD), aggressive systemic mastocytosis (ASM), and mast cell leukemia (MCL). Patients with ISM usually have maculopapular skin lesions and a good prognosis. In the group with associated hematologic disease, the AHNMD should be classified according to FAB/WHO criteria. ASM is characterized by impaired organ-function due to infiltration of the bone marrow, liver, spleen, GI-tract, or skeletal system, by pathologic MC. MCL is a 'high-grade' leukemic disease defined by increased numbers of MC in bone marrow smears (>or=20%) and peripheral blood, absence of skin lesions, multiorgan failure, and a short survival. In typical cases, circulating MC amount to >or=10% of leukocytes (classical form of MCL). Mast cell sarcoma is a unifocal tumor that consists of atypical MC and shows a destructive growth without (primary) systemic involvement. This high-grade malignant MC disease has to be distinguished from a localized benign mastocytoma in either extracutaneous organs (=extracutaneous mastocytoma) or skin. Depending on the clinical course of mastocytosis and development of an AHNMD, patients can shift from one category of MC disease into another. In all categories, mediator-related symptoms may occur and may represent a serious clinical problem. All categories of mastocytosis should be distinctively separated from reactive MC hyperplasia, MC activation syndromes, and a more or less pronounced increase in MC in myelogenous malignancies other than mastocytosis. Criteria proposed in this article should be helpful in this regard.

Diagnosis of mastocytosis: general histopathological aspects, morphological criteria, and immunohistochemical findings

An increase in mast cell (MC) numbers in hemopoietic tissues may be associated with (a) primary neoplastic MC disease (mastocytosis); (b) non-mast cell lineage myelogenous disorders (myelodysplastic or myeloproliferative syndromes and myeloid leukemias); or (c) reactive, i.e. non-clonal states (MC hyperplasia and reactive mastocytosis). However, the histologic discrimination between hyperplastic states and neoplastic MC proliferative disorders is sometimes very difficult. MC hyperplasia is characterized by a diffuse increase in mature, round or spindle-shaped, metachromatic MC that are loosely scattered throughout the tissue and do not form dense focal infiltrates, even in states of marked hyperplasia. However, loosely scattered MC are also a prominent feature of many cases of myelodysplastic syndromes and acute leukemia involving the MC lineage. In contrast, the demonstration of dense, focal and/or diffuse MC infiltrates can be regarded as indicative of primary MC disease/mastocytosis. In addition to the highly diagnostic focal MC infiltrates, mastocytosis may also present with a predominantly diffuse or a mixed (diffuse and focal) infiltration pattern. The relatively rare diffuse pattern is usually dominated by atypical, often hypogranulated or even non-metachromatic MC and is associated with the aggressive or frankly malignant subtypes of systemic mastocytosis and MC leukemia. Although the demonstration of MC infiltrates in Giemsa-stained tissue sections is still very important for the diagnosis of mastocytosis, immunohistochemical techniques using antibodies against MC-associated antigens such as tryptase or c-kit (CD117) are essential for the identification of highly atypical, hypogranulated MC, especially in MC leukemia, and for the detection of small and even minute MC infiltrates.

Utility of flow cytometric analysis of mast cells in the diagnosis and classification of adult mastocytosis

The diagnosis of bone marrow (BM) involvement in mastocytosis has mainly been based on conventional histology. Nevertheless, in recent years, three major methodological advances have been made: the measurement of serum tryptase levels, the immunohistochemical assessment of mast cell (MC) tryptase, and the immunophenotypical characterization of BMMC using flow cytometry (FCM). The most characteristic immunophenotypic feature in mastocytosis is the coexpression of CD2 and CD25 antigens, which are never present in normal BMMC and constitute a phenotypic hallmark of BMMC in adult mastocytosis. Such observations would support the need to include the immunophenotypic analysis of MC in the diagnosis of mastocytosis.

The many faces of systemic mastocytosis

OBJECTIVE

This short review article will augment the reader's knowledge of mast cell physiology and will offer an overview of current information on the pathophysiology, heterogeneity, and treatment of human mastocystosis.

DATA SOURCES AND STUDY SELECTION

Articles published since 1980, textbooks, information from computerized databases, references identified from bibliographies of relevant articles, and books published in the last 10 years.

RESULTS AND CONCLUSIONS

Mastocytosis is a complex disease with a multitude of clinical presentations, often misdiagnosed, which can embrace characteristics of other diseases and generate a chameleon-like picture. Mast cells possess many important physiologic functions in the human body, but as a consequence of poorly understood events, they can also start a cascade of pathologic reactions. Although a great deal is known about mechanisms involved in physiologic and pathologic processes of mast cells, many areas are waiting to be explored in this millennium.

Mastocytosis: recent advances in defining the disease

Mastocytosis is a rare disease characterized by a primary pathological increase in mast cells in different tissues, which may present in a variety of clinical patterns. Major advances have been made in recent years in the understanding of the pathogenesis of mastocytosis. This review is aimed at familiarizing dermatologists with these recent findings, and at exploring their possible implications for the diagnosis and treatment of the condition. The heterogeneous clinical presentation of mastocytosis is detailed with respect to the type of skin lesions, age at onset, family history, organ systems involved, associated haematological disorders and prognosis. Recent genetic findings also indicate different pathogenetic forms of mastocytosis, as adult patients and those with associated haematological diseases usually express activating mutations of the stem cell factor receptor c-kit, whereas most cases of childhood-onset and familial mastocytosis seem to lack these mutations. Despite the presence of c-kit mutations, patients with cutaneous lesions generally have a good prognosis, even when there is involvement of other organs. Some patients, particularly those with childhood-onset disease, experience spontaneous remission, mostly by puberty. c-kit mutations do not explain the initial cause of mastocytosis, and their prognostic significance is as yet unclarified, as is the pathogenesis in patients without the mutations. Furthermore, these novel findings have as yet not resulted in a more effective treatment of the cause of the disease, so that counselling, prevention of exposure to mast cell secretory stimuli, and symptomatic treatment remain the mainstays of current patient management.

Soluble stem cell factor receptor (CD117) and IL-2 receptor alpha chain (CD25) levels in the plasma of patients with mastocytosis: relationships to disease severity and bone marrow pathology

Systemic mastocytosis is a disease of mast cell proliferation that may be associated with hematologic disorders. There are no features on examination that allow the diagnosis of systemic disease, and mast cell–derived mediators, which may be elevated in urine or blood, may also be elevated in individuals with severe allergic disorders. Thus, the diagnosis usually depends on results of bone marrow biopsy. To facilitate evaluation, surrogate markers of the extent and severity of the disease are needed. Because of the association of mastocytosis with hematologic disease, plasma levels were measured for soluble KIT (sKIT) and soluble interleukin-2 receptor alpha chain (sCD25), which are known to be cleaved in part from the mast cell surface and are elevated in some hematologic malignancies. Results revealed that levels of both soluble receptors are increased in systemic mastocytosis. Median plasma sKIT concentrations as expressed by AU/mL (1 AU = 1.4 ng/mL) were as follows: controls, 176 (n = 60); urticaria pigmentosa without systemic involvement, 194 (n = 8); systemic indolent mastocytosis, 511 (n = 30); systemic mastocytosis with an associated hematologic disorder, 1320 (n = 7); aggressive mastocytosis, 3390 (n = 3). Plasma sCD25 levels were elevated in systemic mastocytosis; the highest levels were associated with extensive bone marrow involvement. Levels of sKIT correlated with total tryptase levels, sCD25 levels, and bone marrow pathology. These results demonstrate that sKIT and sCD25 are useful surrogate markers of disease severity in patients with mastocytosis and should aid in diagnosis, in the selection of those needing a bone marrow biopsy, and in the documentation of disease progression.

Soluble stem cell factor receptor (CD117) and IL-2 receptor alpha chain (CD25) levels in the plasma of patients with mastocytosis: relationships to disease severity and bone marrow pathology

Systemic mastocytosis is a disease of mast cell proliferation that may be associated with hematologic disorders. There are no features on examination that allow the diagnosis of systemic disease, and mast cell–derived mediators, which may be elevated in urine or blood, may also be elevated in individuals with severe allergic disorders. Thus, the diagnosis usually depends on results of bone marrow biopsy. To facilitate evaluation, surrogate markers of the extent and severity of the disease are needed. Because of the association of mastocytosis with hematologic disease, plasma levels were measured for soluble KIT (sKIT) and soluble interleukin-2 receptor alpha chain (sCD25), which are known to be cleaved in part from the mast cell surface and are elevated in some hematologic malignancies. Results revealed that levels of both soluble receptors are increased in systemic mastocytosis. Median plasma sKIT concentrations as expressed by AU/mL (1 AU = 1.4 ng/mL) were as follows: controls, 176 (n = 60); urticaria pigmentosa without systemic involvement, 194 (n = 8); systemic indolent mastocytosis, 511 (n = 30); systemic mastocytosis with an associated hematologic disorder, 1320 (n = 7); aggressive mastocytosis, 3390 (n = 3). Plasma sCD25 levels were elevated in systemic mastocytosis; the highest levels were associated with extensive bone marrow involvement. Levels of sKIT correlated with total tryptase levels, sCD25 levels, and bone marrow pathology. These results demonstrate that sKIT and sCD25 are useful surrogate markers of disease severity in patients with mastocytosis and should aid in diagnosis, in the selection of those needing a bone marrow biopsy, and in the documentation of disease progression.

Histamine and tryptase levels in patients with acute allergic reactions: An emergency department-based study

BACKGROUND

Emergency department visits for acute allergic reactions are common. Although the diagnosis and classification of these allergic reactions is primarily empiric, it is not always clear whether certain signs and symptoms constitute systemic mediator release syndromes, such as anaphylaxis, and thus may warrant more aggressive therapy or follow-up.

OBJECTIVE

We sought to determine associations between various clinical signs and symptoms with both plasma histamine levels and serum tryptase levels in adult patients presenting to an emergency department with acute allergic syndromes. The clinical correlates of raised beta-tryptase levels were also investigated.

METHODS

Ninety-seven adult emergency department patients were prospectively studied by using a questionnaire, physical examination, and serum-plasma sampling. Plasma histamine and serum total and beta-tryptase levels were determined. Clinical groupings were compared for mediator levels by using simple and multivariate analysis.

RESULTS

Elevated levels of plasma histamine (>10 nmol/L) and serum total tryptase (>15 ng/mL) were observed in 42 and 20 patients, respectively. Detectable beta-tryptase (>/=1 ng/mL) was observed in 23 patients, including 15 of the patients with elevated total tryptase levels. Suspected food allergy incidences and the duration of reaction were similar in patients with increased histamine levels and in patients with increased tryptase levels. Increased total tryptase levels, histamine levels, or both were observed in some patients who did not have airway, cardiovascular, or abdominal signs. Histamine levels correlated better with clinical signs than tryptase levels. Histamine elevations (>10 nmol/L) were observed more frequently in patients characterized by the following clinical signs in univariate analysis: the presence of urticaria, more extensive erythema, abnormal abdominal findings, and wheezing. Total tryptase increases were observed more frequently only in patients with urticaria. Histamine levels correlated with initial heart rates. In multivariate analysis the extent of urticaria was the best single predictor of plasma histamine levels and of either an elevated histamine or tryptase level. Detectable beta-tryptase levels were observed in some patients who had neither elevated total tryptase nor elevated histamine levels. Unlike patients without detectable beta-tryptase levels, patients who had detectable beta-tryptase levels had a significant correlation between total tryptase and histamine levels (P <.05).

CONCLUSIONS

Raised histamine and, less commonly, raised tryptase levels are observed in almost 50% of patients presenting to emergency departments with acute allergic reactions. Some cases associated with systemic mediator release do not have classical features of severe anaphylaxis, such as hypotension or tachycardia. The lack of total tryptase elevations in many patients with elevated plasma histamine levels suggests basophil involvement. The clinical utility of beta-tryptase determinations in the evaluation of acute allergic reactions needs further study.

Serum tryptase and the laboratory diagnosis of systemic mastocytosis

Total tryptase levels of 20 ng/mL or higher in a baseline serum sample when the ratio of total to beta-tryptase is 20 or greater strongly suggest underlying systemic mastocytosis. Whether these criteria prove to be more sensitive than a bone marrow biopsy will require further study. Although the absolute level of total tryptase does not predict disease severity, it may provide a practical method for assessing the efficacy of therapeutic interventions designed to reduce the mast cell burden.

Pediatric mastocytosis

Pediatric mastocytosis presents with heterogeneous cutaneous lesions and symptoms that are caused by increased numbers of tissue mast cells. In contrast with adult patients with mastocytosis, the course of pediatric patients is usually transient. Therefore, it has long been speculated that pediatric and adult mastocytosis may be based on different pathogenetic mechanisms. Indeed, new genetic findings now indicate differences in the pathogenesis. Adult patients usually express activating mutations of the growth factor receptor c-kit. Most children lack these mutations but sometimes carry other inactivating mutations of c-kit. Only children with progressive mastocytosis seem to express the activating mutations seen in adults. Causal treatment is not yet available, but H1 and H2 antihistamines may provide relief of symptoms. It is important to counsel patients and their parents carefully to avoid triggers that induce systemic mast cell degranulation.