Mastocytosis and Hymenoptera allergy

Alpha-Tryptase as a Risk-Modifying Factor for Mast Cell-Mediated Reactions

PURPOSE OF REVIEW

To provide an overview on the current understanding of genetic variability in human tryptases and summarize the literature demonstrating the differential impact of mature tryptases on mast cell-mediated reactions and associated clinical phenotypes.

RECENT FINDINGS

It is becoming increasingly recognized that tryptase gene composition, and in particular the common genetic trait hereditary alpha-tryptasemia (HαT), impacts clinical allergy. HαT has consistently been associated with clonal mast cell disorders (MCD) and has also been associated with more frequent anaphylaxis among these patients, and patients in whom no allergic trigger can be found, specifically idiopathic anaphylaxis. Additionally, more severe anaphylaxis among Hymenoptera venom allergy patients has been linked to HαT in both retrospective and prospective studies. An increased relative number of α-tryptase-encoding gene copies, even in the absence of HαT, has also been associated with systemic mastocytosis and has been shown to positively correlate with the severity of mast cell-mediated reactions to vibration and food. These findings may be due to increased generation of α/β-tryptase heterotetramers and differences in their enzymatic activity relative to β-tryptase homotetramers. HαT is a naturally occurring overexpression model of α-tryptase in humans. Increased relative α-tryptase expression modifies immediate hypersensitivity symptoms and is associated with more frequent and severe mast cell-mediated reactions, ostensibly due to increased α/β-tryptase heterotetramer production.

Bone Marrow Mastocytosis: A Diagnostic Challenge

Bone marrow mastocytosis (BMM) represents a provisional, indolent subvariant of systemic mastocytosis (SM). Utilizing WHO criteria, BMM requires bone marrow (BM) involvement and the absence of mastocytosis skin lesions. BMM is characterized by male sex prevalence, a slight increase of serum tryptase levels, low BM mast cells (MC) burden, and an indolent clinical course. BMM shows a strong correlation with severe anaphylaxis, mainly due to an IgE-mediated allergy to bee or wasp venom and, less frequently, to unexplained (idiopathic) anaphylaxis. Furthermore, BMM is often associated with osteoporosis which could be the only presenting symptom of the disease. BMM is an undervalued disease as serum tryptase levels are not routinely measured in the presence of unexplained osteoporosis or anaphylaxis. Moreover, BMM patients are often symptom-free except for severe allergic reactions. These factors, along with typical low BM MCs infiltration, may contribute to physicians overlooking BMM diagnosis, especially in medical centers that lack appropriately sensitive diagnostic techniques. This review highlights the need for a correct diagnostic pathway to diagnose BMM in patients with suspected symptoms but lacking typical skin lesions, even in the case of normal serum tryptase levels. Early diagnosis may prevent potential life-threatening anaphylaxis or severe skeletal complications.

Venom immunotherapy in patients with clonal mast cell disorders: IgG4 correlates with protection

BACKGROUND

Patients with clonal mast cell disorders (cMCD), systemic mastocytosis (SM) and monoclonal mast cell activation syndrome (MMAS), represent an increased risk for Hymenoptera venom anaphylaxis (HVA). Lifelong venom immunotherapy (VIT) is recommended; however, its efficacy and safety are controversial. Hence, we sought to evaluate the efficacy and safety of VIT in HVA patients with cMCD.

METHODS

A retrospective study was conducted among 46 patients with Vespula venom allergy who had experienced severe HVA, 32 cMCD (22 with SM and 10 with MMAS) and 14 controls. There were no differences between cMCD patients and controls in age (58 vs 66) and duration of VIT (47 vs 48 months), respectively.

RESULTS

During VIT, 11 (34%) cMCD patients experienced adverse reactions (ARs) (7% in controls), including 1 anaphylaxis. There were 23 re-stings in 17 (53%) patients during VIT. Of episodes, four (17%) presented with anaphylaxis, 14 (60%) presented with local reaction, and five (23%) were asymptomatic. In 11 episodes (48%), the patient did not take epinephrine, of these 8 (73%) presented with local reaction, and 3 (27%) were asymptomatic. Patient-based protection from anaphylaxis was 76% (4/17) in cMCD vs. 100% in controls during VIT. The venom-specific IgG4 concentrations increased during VIT (P < .001) although tryptase and IgE were unaltered.

CONCLUSION

Both safety and efficacy of VIT in cMCD patients were slightly reduced than controls. Severe ARs were rare. The elevated IgG4 levels may be a biomarker for efficacy of VIT in cMCD patients, as it correlates with protection from re-stings.

Venom immunotherapy in patients with allergic reactions to insect stings

INTRODUCTION

Allergy to Hymenoptera (Apis mellifera, Vespula species, Polistes species, Vespa crabro) venom can be safely and effectively treated by venom immunotherapy (VIT), which in the 40 years since its introduction has been able to prevent reactions to stings, and to treatment as well, though systemic reactions, occasionally severe, are possible. Areas covered: We reviewed the recent literature on VIT by searching in PubMed for the terms 'venom immunotherapy' and 'Hymenoptera venom immunotherapy' to highlight the current status of VIT and the likely development in the coming years. Expert commentary: VIT, provided the correct choice of the venom and adequate venom preparations and maintenance doses are used, is a treatment of great value in preventing systemic reactions to Hymenoptera stings. A 5-year duration ensures a prolonged tolerance to stings following VIT discontinuation, unless patients suffer from mastocytosis. In fact, due to reports of fatal reactions after stopping VIT, patients with mastocytosis, or with very severe reactions to stings, need an indefinite duration of treatment.

Advances in the understanding and clinical management of mastocytosis and clonal mast cell activation syndromes

Clonal mast cell activation syndromes and indolent systemic mastocytosis without skin involvement are two emerging entities that sometimes might be clinically difficult to distinguish, and they involve a great challenge for the physician from both a diagnostic and a therapeutic point of view. Furthermore, final diagnosis of both entities requires a bone marrow study; it is recommended that this be done in reference centers. In this article, we address the current consensus and guidelines for the suspicion, diagnosis, classification, treatment, and management of these two entities.

Self-medication of anaphylactic reactions due to Hymenoptera stings-an EAACI Task Force Consensus Statement

An anaphylactic reaction due to a Hymenoptera sting is a clinical emergency, and patients, their caregivers as well as all healthcare professionals should be familiar with its recognition and acute management. This consensus report has been prepared by a European expert panel of the EAACI Interest Group of Insect Venom Hypersensitivity. It is targeted at allergists, clinical immunologists, internal medicine specialists, pediatricians, general practitioners, emergency department doctors, and any other healthcare professional involved. The aim was to report the scientific evidence on self-medication of anaphylactic reactions due to Hymenoptera stings, to inform healthcare staff about appropriate patient self-management of sting reactions, to propose indications for the prescription of an adrenaline auto-injector (AAI), and to discuss other forms of medication. First-line treatment for Hymenoptera sting anaphylaxis is intramuscular adrenaline. Prescription of AAIs is mandatory in the case of venom-allergic patients who suffer from mast cell diseases or with an elevated baseline serum tryptase level and in untreated patients with a history of a systemic reaction involving at least two different organ systems. AAI prescription should also be considered in other specific situations before, during, and after stopping venom immunotherapy.

Added sensitivity of component-resolved diagnosis in hymenoptera venom-allergic patients with elevated serum tryptase and/or mastocytosis

BACKGROUND

Anaphylaxis caused by hymenoptera venom allergy is associated with elevation of baseline serum tryptase (sBT) and/or mastocytosis in about 5% of patients. Up to now, no information has become available on single venom allergen sIgE reactivity and the usefulness of component-resolved approaches to diagnose this high-risk patient group. To address the component-resolved sIgE sensitization pattern and diagnostic sensitivity in hymenoptera venom-allergic patients with elevated sBT levels and/or mastocytosis, a panel of yellow jacket and honeybee venom allergens was applied on a widely used IgE immunoassay platform.

METHODS

Fifty-three patients with mastocytosis and/or elevated sBT tryptase level and systemic reactions to hymenoptera venoms were analyzed for their IgE reactivity to recombinant yellow jacket and honeybee venom allergens by Immulite3 g.

RESULTS

sIgE reactivity to Ves v 1, Ves v 5, Api m 1 to Api m 4 and Api m 10 was found at a similar frequency in hymenoptera venom-allergic patients with and without elevated sBT levels and/or mastocytosis. However, the use of the recombinant allergens and a diagnostic cutoff of 0.1 kUA /L allowed the diagnosis of patients with otherwise undetectable IgE to venom extract. The diagnostic sensitivity of yellow jacket venom allergy using the combination of Ves v 1 and Ves v 5 was 100%.

CONCLUSIONS

In high-risk patients with elevated sBT levels and/or mastocytosis, the use of molecular components and decreasing the threshold sIgE level to 0.1 kUA /L may be needed to avoid otherwise undetectable IgE to hymenoptera venom extracts in about 8% of such patients.

Hymenoptera Allergy and Mast Cell Activation Syndromes

Mast cell activation syndrome (MCAS) can be diagnosed in patients with recurrent, severe symptoms from mast cell (MC)-derived mediators, which are transiently increased in serum and are attenuated by mediator-targeting drugs. When KIT-mutated, clonal MC are detected in these patients, a diagnosis of primary MCAS can be made. Severe systemic reactions to hymenoptera venom (HV) represent the most common form of anaphylaxis in patients with mastocytosis. Patients with primary MCAS and HV anaphylaxis are predominantly males and do not have skin lesions in the majority of cases, and anaphylaxis is characterized by hypotension and syncope in the absence of urticaria and angioedema. A normal value of tryptase (≤11.4 ng/ml) in these patients does not exclude a diagnosis of mastocytosis. Patients with primary MCAS and HV anaphylaxis have to undergo lifelong venom immunotherapy, in order to prevent further potentially fatal severe reactions.

Outcomes of allergy/immunology follow-up after an emergency department evaluation for anaphylaxis

BACKGROUND

Anaphylaxis guidelines currently recommend referring patients with anaphylaxis seen in the emergency department (ED) to an allergist for follow up.

OBJECTIVE

The objective of our study was to evaluate outcomes of allergy/immunology follow-up after an ED visit for anaphylaxis.

METHODS

A retrospective health records review was conducted from April 2008 to August 2012. Charts were reviewed independently by 2 allergists to determine outcomes. Descriptive statistics with corresponding 95% CIs were calculated.

RESULTS

Among 573 patients seen in the ED who met anaphylaxis diagnostic criteria, 217 (38%) had a documented allergy/immunology follow-up. After allergy/immunology evaluation, 16 patients (7% [95% CI, 5%-12%]) had anaphylaxis ruled out. Among those with an unknown ED trigger (n = 74), 24 (32% [95% CI, 23%-44%]) had a trigger identified; and, among those who had a specific suspected ED trigger (n = 143), 9 (6% [95% CI, 3%-12%]) had a trigger identified in a category other than the one suspected in the ED, and 28 (20% [95% CI, 14%-27%]) had an unknown trigger. Thus, there were a total of 77 patients (35% [95% CI, 29%-42%]) who had an alteration in the diagnosis of anaphylaxis or trigger after allergy/immunology evaluation. Four patients (2% [95% CI, 0.7%-4.6%]) were diagnosed with a mast cell activation disorder, and 13 patients (6% [95% CI, 4%-10%]) underwent immunotherapy or desensitization.

CONCLUSION

Overall, 35% of the patients with suspected anaphylaxis in the ED had an alteration in the diagnosis or suspected trigger after allergy/immunology evaluation. These results underscore the importance of allergy/immunology follow-up after an ED visit for anaphylaxis.

Anaphylaxis as a clinical manifestation of clonal mast cell disorders

Clonal mast cell disorders comprise a heterogeneous group of disorders characterized by the presence of gain of function KIT mutations and a constitutively altered activation-associated mast cell immunophenotype frequently associated with clinical manifestations related to the release of mast cells mediators. These disorders do not always fulfil the World Health Organization (WHO)-proposed criteria for mastocytosis, particularly when low-sensitive diagnostic approaches are performed. Anaphylaxis is a frequent presentation of clonal mast cell disorders, particularly in mastocytosis patients without typical skin lesions. The presence of cardiovascular symptoms, e.g., hypotension, occurring after a hymenoptera sting or spontaneously in the absence of cutaneous manifestations such as urticaria is characteristic and differs from the presentation of anaphylaxis in the general population without mastocytosis.

Nonaggressive systemic mastocytosis (SM) without skin lesions associated with insect-induced anaphylaxis shows unique features versus other indolent SM

BACKGROUND

Indolent systemic mastocytosis (ISM) without skin lesions (ISMs(-)) shows a higher prevalence in males, lower serum baseline tryptase levels, and KIT mutation more frequently restricted to bone marrow (BM) mast cells (MCs) than ISM with skin lesions (ISMs(+)). Interestingly, in almost one-half of ISMs(-) patients, MC-mediator release episodes are triggered exclusively by insects.

OBJECTIVE

We aimed to determine the clinical and laboratory features of ISMs(-) associated with insect-induced anaphylaxis (insectISMs(-)) versus other patients with ISM.

METHODS

A total of 335 patients presenting with MC activation syndrome, including 143 insectISMs(-), 72 ISMs(-) triggered by other factors (otherISMs(-)), 56 ISMs(+), and 64 nonclonal MC activation syndrome, were studied.

RESULTS

Compared with otherISMs(-) and ISMs(+) patients, insectISMs(-) cases showed marked male predominance (78% vs 53% and 46%; P < .001), a distinct pattern of MC-related symptoms, and significantly lower median serum baseline tryptase levels (22.4 vs 28.7 and 45.8 μg/L; P ≤ .009). Moreover, insectISMs(-) less frequently presented BM MC aggregates (46% vs 70% and 81%; P ≤ .001), and they systematically showed MC-restricted KIT mutation.

CONCLUSIONS

ISMs(-) patients with anaphylaxis triggered exclusively by insects display clinical and laboratory features that are significantly different from other ISM cases, including other ISMs(-) and ISMs(+) patients, suggesting that they represent a unique subgroup of ISM with a particularly low BM MC burden in the absence of adverse prognostic factors.

The significance of diagnosing associated clonal mast cell diseases in patients with venom-induced anaphylaxis and the role of bone marrow investigation

Hymenoptera venom allergy (HVA) represents a particular risk for exceptionally severe anaphylactic sting reactions in patients with clonal mast cell disorders (CMD). Nevertheless, conventional investigations are not sufficient to do accurate risk assessments. Increased levels of baseline serum tryptase (sBT) (>11.4 μg/L) is highly associated with severe anaphylactic reactions and with a possible underlying CMD. The measurement of baseline serum tryptase, thus, has opened the possibility to screen for CMD. In the present study, we sought to investigate whether bone marrow evaluation provides more accurate diagnosis in patients with HVA.Three patients of the same sex and similar age with HVA were enrolled in this clinical study. The patients underwent comprehensive allergy work-up including skin prick testing, measurements of serum total IgE concentrations and baseline serum tryptase. Bone-marrow biopsies were also performed in all three patients to assess underlying CMD.We evaluated characteristics of the bone marrow mast cells by pathology, flow cytometry and detection of D816V mutation by using current WHO-criteria, which led to changes in the final diagnosis compared to the assessments done by classical allergy work-up and measurements of sBT. Three distinct diagnostic outcomes including systemic mastocytosis, monoclonal mast cell activation syndrome and non-clonal HVA were revealed.We conclude that a bone marrow investigation is required for the correct diagnosis of hymenoptera venom-induced anaphylactic reactions in patients with elevated baseline tryptase levels (>11.4 μg/L), and this has important implications for management strategies.

Venom immunotherapy in patients with mastocytosis and hymenoptera venom anaphylaxis

Systemic mastocytosis (SM) is typically suspected in patients with cutaneous mastocytosis (CM). In recent years, the presence of clonal mast cells (MCs) in a subset of patients with systemic symptoms associated with MC activation in the absence of CM has been reported and termed monoclonal MC activation syndromes or clonal systemic MC activation syndromes. In these cases, bone marrow (BM) MC numbers are usually lower than in SM with CM, there are no detectable BM MC aggregates, and serum baseline tryptase is often <20 µg/l; thus, diagnosis of SM in these patients should be based on careful evaluation of other minor WHO criteria for SM in reference centers, where highly sensitive techniques for immunophenotypic analysis and investigation of KIT mutations on fluorescence-activated cell sorter-purified BM MCs are routinely performed. The prevalence of hymenoptera venom anaphylaxis (HVA) among SM patients is higher than among the normal population and it has been reported to be approximately 5%. In SM patients with IgE-mediated HVA, venom immunotherapy is safe and effective and it should be prescribed lifelong. Severe adverse reactions to hymenoptera stings or venom immunotherapy have been associated with increased serum baseline tryptase; however, presence of clonal MC has not been ruled out in most reports and thus both SM and clonal MC activation syndrome might be underdiagnosed in such patients. In fact, clonal BM MC appears to be a relevant risk factor for both HVA and severe reactions to venom immunotherapy, while the increase in serum baseline tryptase by itself should be considered as a powerful surrogate marker for anaphylaxis. The Spanish Network on Mastocytosis has developed a scoring system based on patient gender, the clinical symptoms observed during anaphylaxis and serum baseline tryptase to predict for the presence of both MC clonality and SM among individuals who suffer from anaphylaxis.

Hymenoptera venom immunotherapy

Subcutaneous venom immunotherapy is the only effective treatment for patients who experience severe hymenoptera sting-induced allergic reactions, and the treatment also improves health-related quality of life. This article examines advances in various areas of this treatment, which include the immunological mechanisms of early and long-term efficacy, indications and contraindications, selection of venom, treatment protocols, duration, risk factors for systemic reactions in untreated and treated patients as well as for relapse following cessation of treatment. Current and future strategies for improving safety and efficacy are also examined. However, although progress in the past few years has been fruitful, much remains to be accomplished.

In vitro Biphasic Effect of Honey Bee Venom on Basophils from Screened Healthy Blood Donors

Apis mellifera L. bee venom is the most studied hymenoptera allergen, but many aspects of its action on human basophils remain unclear. Allergologists seek evidence of the effectiveness of bee venom immunotherapy as this approach is the chosen treatment for systemic allergic reactions. The effect of bee venom on human basophils in vitro has not been studied in detail for many reasons, including the paucity of basophils in peripheral blood, inter-individual basophil response variability, and the reliability and predictability of basophil activation tests. We conducted a brief preliminary survey of the effect of Apis bee venom on healthy asymptomatic (non-allergic) subjects. A dose of an aqueous commercial extract of Apis bee venom as high as 10 µg/mL activated resting basophils (CD63=+80-90%, CD203c=+30%), while it inhibited the expression of CD63 (-50%) following basophil stimulation by the soluble agonists formyl-Met-Leu-Phe or anti-IgE. The activation of resting basophils appeared to be dose-related. Only when basophils were activated with an IgE-mediated agonist, did bee venom extract exhibit a possible priming mechanism at the lowest doses used only via CD63, while it was ineffective via CD203c. Autocrine interleukin-3 may play a role in the observed biphasic behavior.

How much specific is the association between hymenoptera venom allergy and mastocytosis?

BACKGROUND

The preferential association of mastocytosis with hymenoptera sting reactions is well known, but there is no data on the prevalence of clonal mast cell disorders in subjects with severe systemic reactions due to foods or drugs.

METHODS

Patients with food- or drug-induced severe systemic reactions, including anaphylaxis, and increased serum tryptase were studied for the presence of mastocytosis, and compared with a population of patients with hymenoptera allergy. The aetiological role of foods or drugs was assessed according to current recommendations. Systemic reactions were graded in severity according to the procedure described by Mueller. Serum tryptase was considered increased if the level was >11.4 ng/ml. Subjects with increased tryptase had dermatological evaluation and Bone marrow(BM) aspirate-biopsy, which included histology/cytology, flow cytometry and detection of KIT mutations.

RESULTS

A total of 137 subjects (57 male, mean age 42 years) were studied. Of them, 86 proved positive for drugs and 51 for foods. Overall, out of 137 patients, only nine (6.6%) had a basal tryptase >11.4 ng/ml, and only two (1.5%) were diagnosed with mastocytosis. This was clearly different from patients with hymenoptera allergy, where 13.9% had elevated tryptase and 11.1% had a clonal mast cell disorder.

CONCLUSION

The association of clonal mast cell disorders with hymenoptera allergy seems to be more specific than that with food- or drug-induced systemic reactions.

Mastocytosis and insect venom allergy: diagnosis, safety and efficacy of venom immunotherapy

The most important causative factor for anaphylaxis in mastocytosis are insect stings. The purpose of this review is to analyse the available data concerning prevalence, diagnosis, safety and effectiveness of venom immunotherapy (VIT) in mastocytosis patients. If data were unclear, authors were contacted personally for further information. Quality of evidence (A: high, B: moderate, C: low and D: very low) and strength of recommendation (strong 1 and weak 2) concerning VIT in mastocytosis patients are assessed according to the Grading of Recommendations Assessment, Development and Evaluation and are marked in square brackets. Results of VIT were described in 117 patients to date. The mean rate of side-effects during treatment in studies published so far is 23.9% (7.6% requiring adrenaline) with an overall protection rate of 72%. Based on the review we conclude that (1) mastocytosis patients have a high risk of severe sting reactions in particular to yellow jacket, (2) VIT could be suggested [2] in mastocytosis, (3) probably should be done life long [2], (4) VIT in mastocytosis is accompanied by a higher frequency of side-effects, so (5) special precautions should be taken into account notably during the built up phase of the therapy [2], (6) VIT is able to reduce systemic reactions, but to a lesser extent compared to the general insect venom allergic population [2], so (7) patients should be warned that the efficacy of VIT might be less than optimal and they should continue carrying two adrenaline auto injectors [2].

Practice of venom immunotherapy in the United Kingdom: a national audit and review of literature

BACKGROUND

Venom immunotherapy (VIT) is the only effective treatment for prevention of serious allergic reactions to bee and wasp stings in sensitized individuals. However, controversies exist relating to diagnosis, indications for treatment and treatment schedules. We audited current practice of VIT in the United Kingdom to evaluate adherence to international guidelines.

METHODS

An online questionnaire was sent to all clinicians practising immunotherapy identified on the British Society of Allergy and Clinical Immunology website. Eighty-six questionnaires were sent and 53 responses (61.6%) were received. Of these, 48 (85%) carried out VIT at their centre.

RESULTS

Skin prick tests (SPT) and serum venom-specific IgE (SSIgE) were equally preferred as first-line investigation. Fifty percent of the respondents perform intradermal tests if both SPT and SSIgE are negative. While 8% of respondents commence VIT in patients with negative SSIgE and a history of severe reaction, 57% prefer to repeat the tests in 6-12 months if serum tryptase is elevated. If the insect responsible is uncertain and SSIgE is detected against bee and wasp venoms, 22% of the respondents will desensitize to both while 32% initiate treatment against the venom with the higher SSIgE. A protocol of weekly up-dosing for 12 weeks is preferred for induction and only 25% of respondents have ever used rush or ultra-rush protocols. Three years is thought to be optimum duration of VIT by most (56%). Eleven percent perform sting challenges at the end of treatment. Although 47% measure SSIgE at the end of treatment, only 3% use these results as a basis for discontinuing VIT.

CONCLUSION

Currently there is considerable variation in the diagnosis and management of hymenoptera venom allergy in the United Kingdom. This audit has demonstrated that the current international guidelines for the diagnosis and management of hymenoptera venom allergy are not being followed by UK allergy practitioners.

Advances in hymenoptera venom immunotherapy

PURPOSE OF REVIEW

Venom immunotherapy is highly effective treatment, capable of improving health-related quality of life. This overview examines advances in various aspects of this treatment.

RECENT FINDINGS

New findings on the immunological mechanisms of the early and long-term efficacy of venom immunotherapy have been made. The decision to start and then to stop venom immunotherapy is best made on an individual case basis and should take into account medical and other factors, like the influence on patient quality of life. Venoms for use in immunotherapy should be selected according to the geographical distribution of each species and partial cross-reactivity between certain types of venom. Rapid protocols seem to be as safe as slower ones, though the major incidence of bee venom immunotherapy side-effects remains. Patients suffering from mast cell diseases seem to be at greater risk for an adverse reaction during treatment, without influencing its efficacy that much until the immunotherapy is actually ongoing. A number of new strategies for venom immunotherapy, mostly based on genetic engineering, have been described, and so far only a few have been used in humans.

SUMMARY

Although there has been progress in the past few years, much remains to be accomplished.

Animal models of anaphylaxis

PURPOSE OF REVIEW

In this review we will focus on recent advances in the role of mast cells in the pathophysiology of insect allergy and the possible mechanisms of mast cell activation in anaphylaxis.

RECENT FINDINGS

Anaphylactic reactions in the mouse can be induced by several independent pathways involving immunoglobulin E, immunoglobulin free light chains, or immunoglobulin G. There is considerable evidence that mast cells play a central role in anaphylactic reactions to insect stings. Mast cells can be directly activated by components of insect venom or after allergic sensitization. Of interest is the observation that mast cells are not only effector cells in insect allergy, but may also play a protective role in preventing the development of severe anaphylactic responses or by controlling inflammatory reactions by modulation of antigen-specific T-cell responses.

SUMMARY

The contribution of mast cells in anaphylactic responses to insect venom may be heterogeneous. On the one hand, activation of mast cells contributes to the pathology by the release of bioactive and tissue-damaging mediators. However, mast cell activation may neutralize constituents in insect venom and defend against the adverse effects of these toxins or they may modulate inflammation through downregulation of antigen-specific immune responses.

Mastocytosis and Hymenoptera venom allergy

PURPOSE OF REVIEW

Mastocytosis is a rare disease characterized by increased mast cells in skin and/or internal organs. We evaluate the impact of mastocytosis on diagnosis and treatment of Hymenoptera venom allergy.

RECENT FINDINGS

Patients with Hymenoptera venom allergy who suffer from mastocytosis develop life-threatening sting reactions more often than those who do not. When patients with Hymenoptera venom allergy were systematically examined for mastocytosis, it was found to be represented to an abnormally high extent. Most patients with mastocytosis tolerate venom immunotherapy with no or only minor systemic symptoms. Venom immunotherapy was found to be marginally less effective in patients with mastocytosis than in those without evidence of mast cell disease (defined as absent cutaneous mastocytosis combined with a serum tryptase concentration of <11.4 microg/l). Several deaths from sting reactions were reported in patients with mastocytosis after venom immunotherapy was stopped. These patients should have venom immunotherapy for the rest of their lives.

SUMMARY

Patients suffering from mastocytosis and Hymenoptera venom allergy are at risk from a particularly severe sting anaphylaxis. They need optimal diagnosis and treatment. In patients presenting with Hymenoptera venom allergy, screening tests by measurement of serum tryptase concentration, and a careful skin examination, are highly recommended.

Immunotherapy of hypersensitivity to hymenoptera venom

Insect sting allergy is a common condition with a risk of life-threatening anaphylaxis. After a severe reaction, the fear of being restung can significantly reduce quality of life. Venom immunotherapy (VIT) is a highly effective treatment of the underlying type I-sensitisation. This review addresses the mechanisms of immune modulation by VIT and outlines current clinical application. Although highly effective in the majority of patients, VIT fails in a few individuals. It can also cause systemic allergic side effects, restricting its application to physicians trained in the treatment of anaphylaxis. This review discusses several new strategies to overcome these problems, which are presently a promising focus of research. These include the use of new adjuvants, of recombinant and genetically engineered venom allergens, as well as vaccination with peptides.

Clinical reactivity to insect stings

PURPOSE OF REVIEW

Allergy to insect stings remains a hazard worldwide and is the object of updated guidelines on management. This paper reviews the various clinical responses that may occur following an insect sting.

RECENT FINDINGS

Although the general population is at slight risk, certain groups are more susceptible, including occasionally stung adult male agricultural workers, hobby honey beekeepers and family members of beekeepers. Individuals with systemic mastocytosis are especially reactive to stings. The body of evidence attesting to the marked beneficial effect that 3-5 years of venom immunotherapy has on the natural history of hymenoptera hypersensitivity is especially evident in children. Case reports indicate other consequences of hymenoptera sting, and these are discussed.

SUMMARY

Hypersensitivity to insect stings is common and may be life threatening. Although most occur away from medical facilities, their diagnosis and management are important to a wide spectrum of health care professionals. Most reactions to stings are nonallergic manifestations of the venom's toxic effects, and present as erythema, pain and swelling about the sting site. Fire ants bite with their mandibles and pivot their head, inflicting multiple stings that usually result in a sterile pseudopustule at the site. Hypersensitivity responses to venom range from large local reactions (a late-phase response) to life-threatening anaphylaxis. Venom-specific immunotherapy is highly effective in the modification of subsequent reactions to hymenoptera stings, as is whole body extract for fire ant stings.