Tryptase and histamine release due to a sting challenge in bee venom allergic patients treated successfully or unsuccessfully with hyposensitization

[Basophil activation test to follow-up of patients treated with hymenoptera venom immunotherapy: a review of current evidence]

Hymenoptera venom immunotherapy (HVI) is a long-term effective treatment to avoid new systemic reactions in patients with Hymenoptera allergy. The sting challenge test is considered the gold standard to confirm the tolerance. However, the use of this technique is not generalized in clinical practice, being the basophil activation test (BAT), which functionally explores allergen response, an alternative that does not entail any of the provocation risks associated with the sting challenge test. This study reviews the publications that used the BAT to follow up and evaluate the success of the HVI. Studies assessing the changes between a baseline BAT before the start and BATs performed between the starting and maintenance phases of the HVI were selected. Ten articles were found, comprising information from 167 patients, of which 29% used the sting challenge test. The studies concluded the importance of evaluating the responses with submaximal allergen concentrations, which reflect basophil sensitivity, to monitor the HVI using the BAT. It was also observed that changes in the maximum response (reactivity) could not reflect the clinical status of tolerance, particularly in the initial phases of HVI.

Mast Cell Desensitization in Allergen Immunotherapy

Allergen immunotherapy (AIT) is the only treatment with disease-transforming potential for allergic disorders. The immunological mechanisms associated with AIT can be divided along time in two phases: short-term, involving mast cell (MC) desensitization; and long-term, with a regulatory T cell (Treg) response with significant reduction of eosinophilia. This regulatory response is induced in about 70% of patients and lasts up to 3 years after AIT cessation. MC desensitization is characteristic of the initial phase of AIT and it is often related to its success. Yet, the molecular mechanisms involved in allergen-specific MC desensitization, or the connection between MC desensitization and the development of a Treg arm, are poorly understood. The major AIT challenges are its long duration, the development of allergic reactions during AIT, and the lack of efficacy in a considerable proportion of patients. Therefore, reaching a better understanding of the immunology of AIT will help to tackle these short-comings and, particularly, to predict responder-patients. In this regard, omics strategies are empowering the identification of predictive and follow-up biomarkers in AIT. Here, we review the immunological mechanisms underlying AIT with a focus on MC desensitization and AIT-induced adverse reactions. Also, we discuss the identification of novel biomarkers with predictive potential that could improve the rational use of AIT.

Safety, Efficacy, and Preventive Role of Subcutaneous and Sublingual Allergen Immunotherapy for the Treatment of Pediatric Asthma

Allergen-specific immunotherapy is currently the only treatment with the potential to modify and prevent progression of allergic asthma in children. In clinical practice, it is available in two forms: subcutaneous immunotherapy and sublingual immunotherapy. Trials and meta-analyses showed both the safety and the short- and long-term benefits of allergen-specific immunotherapy in asthmatic children. However, its use and role in asthma remains controversial, since studies are largely heterogeneous. This is mainly due to the lack of consensus on the optimal primary outcome to be considered for clinical trials evaluating the efficacy of allergen-specific immunotherapy in asthma. Therefore, well-conducted researchis needed using standardized and validated tools to evaluate key outcomes in asthmatic children.

Clinical Utility of Rush Venom Immunotherapy: Current Status

Hymenoptera venom allergy (HVA) is the leading cause of anaphylactic reactions in adults and the second most common cause in children. Venom immunotherapy (VIT) is used to elicit an immune tolerance against hymenoptera venom in allergic patients and is based on the administration of purified venom extracts regularly for defined periods. The protocols of administration include 2 phases: an up-dosing phase that incrementally reaches the final dose resulting in a protective effect, and a maintenance phase in order to obtain the sustained effect. The goal of this review is to detail the efficacy and the safety of the up-dosing phase also named rush. Pathophysiological mechanisms, indications of VIT and technical aspects of up-dosing protocol are also covered.

Hymenoptera Venom Allergy: How Does Venom Immunotherapy Prevent Anaphylaxis From Bee and Wasp Stings?

Hymenoptera stings may cause both local and systemic allergic reactions and even life threatening anaphylaxis. Along with pharmaceutical drugs and foods, hymenoptera venom is one of the most common causes of anaphylaxis in humans. To date, no parameter has been identified that may predict which sensitized people will have a future systemic sting reaction (SSR), however some risk factors, such as mastocytosis and age >40 years are known. Venom immunotherapy (VIT) is the most effective method of treatment for people who had SSR, which is shown to be effective even after discontinuation of the therapy. Development of peripheral tolerance is the main mechanism during immunotherapy. It is mediated by the production of blocking IgG/IgG4 antibodies that may inhibit IgE dependent reactions through both high affinity (FcεRI) and low affinity (FcεRII) IgE receptors on mast cells, basophils and B cells. The generation of antigen specific regulatory T cells produces IL-10 and suppresses Th2 immunity and the immune responses shift toward a Th1-type response. B regulatory cells are also involved in the production of IL-10 and the development of long term immune tolerance. During VIT the number of effector cells in target organs also decreases, such as mast cells, basophils, innate type 2 lymphocytes and eosinophils. Several meta-analyses and randomized controlled studies have proved that VIT is effective for preventing SSR to a sting and improves the quality of life. In this review, the risk of SSR in venom allergy and how VIT changed this risk are discussed.

Next generation immunotherapy for tree pollen allergies

Tree pollen induced allergies are one of the major medical and public health burdens in the industrialized world. Allergen-Specific Immunotherapy (AIT) through subcutaneous injection or sublingual delivery is the only approved therapy with curative potential to pollen induced allergies. AIT often is associated with severe side effects and requires long-term treatment. Safer, more effective and convenient allergen specific immunotherapies remain an unmet need. In this review article, we discuss the current progress in applying protein and peptide-based approaches and DNA vaccines to the clinical challenges posed by tree pollen allergies through the lens of preclinical animal models and clinical trials, with an emphasis on the birch and Japanese red cedar pollen induced allergies.

Impact of allergen immunotherapy in allergic asthma

Although traditional pharmacological approaches improve outcomes in disease management for allergic asthma, these fail to modify the underlying immune responses. Allergen immunotherapy remains the only etiological therapy for the treatment of respiratory allergies for which clinical efficacy has been demonstrated through several well-controlled studies. In this review, we examine evidence from the past 5 years regarding the impact of allergen immunotherapy on allergic asthma to inform practitioners and stimulate further discussion and research.

Follow-Up of Venom Immunotherapy on Flow Cytometry and Definition of a Protective Index

BACKGROUND

A major problem of venom-specific immunotherapy (VIT) is the absence of reliable parameters for deciding treatment discontinuation.

AIM OF THE STUDY

Intracutaneous tests (ICTs), the basophil activation test (BAT), specific IgEs (sIgEs) and blocking factor (BF) activity were measured during VIT. We made an evaluation by means of a protective index (PI) including ICT, BAT and BF values.

MATERIAL AND METHODS

A population of 45 patients who had experienced a systemic reaction after an insect sting were tested before VIT (T0), at 1 week (T1w), at 10 weeks (T10w) and at 21 weeks (T21w), and, for a subgroup of 17 patients, at 3-5 years (T3-5y). Basophil activation (expressed in % CD63 and in the area under the curve) and BF activity were measured by flow cytometry using the CCR3/CD63 protocol.

RESULTS

The first 21 weeks of follow-up showed no significant variation in the ICT, sIgE and BAT measurements, except for BAT, by eliminating weak negative anti-IgE responses. In these conditions, the decrease in basophil activation was significant at T10w (p = 0.009) and T21w (p = 0.009). Increased BF activity was also significant at T10w (p = 0.008) and T21w (p = 0.002). The PI threshold calculated from the mean ± 3 standard errors (SE) was 64.8 (14.7 ± 16.7, n = 25) at T0. PI increase was significant at T3-5y (3,430 ± 6,282; p < 0.001).

CONCLUSION

VIT induced a significant decrease in ICT values and basophil activation, along with an increase in serum BF activity, significant after 10 weeks of VIT. Evaluated in a larger population, the PI could represent a new tool for the clinico-biological follow-up of VIT efficacy.

Mechanisms of Aeroallergen Immunotherapy: Subcutaneous Immunotherapy and Sublingual Immunotherapy

Allergen immunotherapy (AIT) is an effective way to treat allergic disorders, targeting the underlying mechanisms and altering the disease course by inducing a long-lasting clinical and immune tolerance to allergens. Although sublingual and subcutaneous routes are used in daily practice, many novel ways to decrease side effects and duration and increase efficacy have been pursued. Further studies are needed to develop biomarkers for the identification of AIT responder patients and also to use the developed knowledge in allergy prevention studies. Future directions in AIT include treatments for autoimmune diseases, chronic infections, organ transplantation, and breaking immune tolerance to cancer cells.

Molecular and cellular mechanisms of food allergy and food tolerance

Ingestion of innocuous antigens, including food proteins, normally results in local and systemic immune nonresponsiveness in a process termed oral tolerance. Oral tolerance to food proteins is likely to be intimately linked to mechanisms that are responsible for gastrointestinal tolerance to large numbers of commensal microbes. Here we review our current understanding of the immune mechanisms responsible for oral tolerance and how perturbations in these mechanisms might promote the loss of oral tolerance and development of food allergies. Roles for the commensal microbiome in promoting oral tolerance and the association of intestinal dysbiosis with food allergy are discussed. Growing evidence supports cutaneous sensitization to food antigens as one possible mechanism leading to the failure to develop or loss of oral tolerance. A goal of immunotherapy for food allergies is to induce sustained desensitization or even true long-term oral tolerance to food allergens through mechanisms that might in part overlap with those associated with the development of natural oral tolerance.

Elevated and cross-responsive CD1a-reactive T cells in bee and wasp venom allergic individuals

The role of CD1a-reactive T cells in human allergic disease is unknown. We have previously shown that circulating CD1a-reactive T cells recognize neolipid antigens generated by bee and wasp venom phospholipase, and here tested the hypothesis that venom-responsive CD1a-reactive T cells associate with venom allergy. Circulating T cells from bee and wasp venom allergic individuals, before and during immunotherapy, were exposed to CD1a-transfected K562 cells in the presence of wasp or bee venom. T-cell response was evaluated based on IFNγ, GM-CSF, and IL-13 cytokine production. Venom allergic individuals showed significantly higher frequencies of IFN-γ, GM-CSF, and IL-13 producing CD1a-reactive T cells responsive to venom and venom-derived phospholipase than healthy individuals. Venom-responsive CD1a-reactive T cells were cross-responsive between wasp and bee suggesting shared pathways of allergenicity. Frequencies of CD1a-reactive T cells were initially induced during subcutaneous immunotherapy, peaking by weeks 5, but then reduced despite escalation of antigen dose. Our current understanding of venom allergy and immunotherapy is largely based on peptide and protein-specific T cell and antibody responses. Here, we show that lipid antigens and CD1a-reactive T cells associate with the allergic response. These data have implications for mechanisms of allergy and approaches to immunotherapy.

Mechanisms of allergen-specific immunotherapy and immune tolerance to allergens

Substantial progress in understanding mechanisms of immune regulation in allergy, asthma, autoimmune diseases, tumors, organ transplantation and chronic infections has led to a variety of targeted therapeutic approaches. Allergen-specific immunotherapy (AIT) has been used for 100 years as a desensitizing therapy for allergic diseases and represents the potentially curative and specific way of treatment. The mechanisms by which allergen-AIT has its mechanisms of action include the very early desensitization effects, modulation of T- and B-cell responses and related antibody isotypes as well as inhibition of migration of eosinophils, basophils and mast cells to tissues and release of their mediators. Regulatory T cells (Treg) have been identified as key regulators of immunological processes in peripheral tolerance to allergens. Skewing of allergen-specific effector T cells to a regulatory phenotype appears as a key event in the development of healthy immune response to allergens and successful outcome in AIT. Naturally occurring FoxP3⁺ CD4⁺CD25⁺ Treg cells and inducible type 1 Treg (Tr1) cells contribute to the control of allergen-specific immune responses in several major ways, which can be summarized as suppression of dendritic cells that support the generation of effector T cells; suppression of effector Th1, Th2 and Th17 cells; suppression of allergen-specific IgE, and induction of IgG4; suppression of mast cells, basophils and eosinophils and suppression of effector T cell migration to tissues. New strategies for immune intervention will likely include targeting of the molecular mechanisms of allergen tolerance and reciprocal regulation of effector and regulatory T cell subsets.

Mechanisms of allergen-specific immunotherapy: multiple suppressor factors at work in immune tolerance to allergens

Allergen-specific immunotherapy (AIT) has been used for more than 100 years as a desensitizing therapy for IgE-mediated allergic diseases and represents a potentially curative way of treatment. The mechanisms of action of AIT include the induction of very early desensitization of mast cells and basophils; generation of regulatory T and regulatory B (Breg) cell responses; regulation of IgE and IgG4; decreases in numbers and activity of eosinophils and mast cells in mucosal allergic tissues; and decreases in the activity of basophils in circulation. Skewing of allergen-specific effector T and effector B cells to a regulatory phenotype appears as a key event in the course of AIT and normal immune response to allergens. Recently, inducible IL-10-secreting Breg cells were also demonstrated to contribute to allergen tolerance through suppression of effector T cells and selective induction of IgG4 isotype antibodies. Allergen-specific regulatory T and Breg cells orchestrate a general immunoregulatory activity, which can be summarized as suppression of cytokines from inflammatory dendritic cells; suppression of effector TH1, TH2, and TH17 cells; suppression of allergen-specific IgE and induction of IgG4; and suppression of migration of mast cells, basophils, eosinophils, and effector T cells to tissues. A detailed knowledge of the mechanisms of AIT is not only important in designing the prevention and treatment of allergic diseases but might also find applications in the treatment of autoimmune diseases, organ transplantation, chronic infection, and cancer.

Mechanisms of allergen-specific immunotherapy and novel ways for vaccine development

Allergen-specific immunotherapy (SIT) is the only available curative treatment of allergic diseases. Recent evidence provided a plausible explanation to its multiple mechanisms inducing both rapid desensitization and long-term allergen-specific immune tolerance, and suppression of allergic inflammation in the affected tissues. During SIT, peripheral tolerance is induced by the generation of allergen-specific regulatory T cells, which suppress proliferative and cytokine responses against the allergen of interest. Regulatory T cells are characterized by IL-10 and TGF-beta secretion and expression of important cell surface suppressive molecules such as cytotoxic T lymphocyte antigen-4 and programmed death-1 that directly or indirectly influence effector cells of allergic inflammation, such as mast cells, basophils and eosinophils. Regulatory T cells and particularly IL-10 also have an influence on B cells, suppressing IgE production and inducing the production of blocking type IgG4 antibodies. In addition, development of allergen-specific B regulatory cells that produce IL-10 and develop into IgG4 producing plasma cells represent essential players in peripheral tolerance. These findings together with the new biotechnological approaches create a platform for development of the advanced vaccines. Moreover, reliable biomarkers could be selected and validated with the intention to select the patients who will benefit most from this immune-modifying treatment. Thus, allergen-SIT could provide a complete cure for a larger number of allergic patients and novel preventive approaches need to be elaborated.

Rapid desensitization induces internalization of antigen-specific IgE on mouse mast cells

BACKGROUND

Rapid desensitization transiently prevents severe allergic reactions, allowing administration of life-saving therapies in previously sensitized patients. However, the mechanisms underlying successful rapid desensitization are not fully understood.

OBJECTIVES

We sought to investigate whether the mast cell (MC) is an important target of rapid desensitization in mice sensitized to exhibit IgE-dependent passive systemic anaphylaxis in vivo and to investigate the antigen specificity and underlying mechanisms of rapid desensitization in our mouse model.

METHODS

C57BL/6 mice (in vivo) or primary isolated C57BL/6 mouse peritoneal mast cells (PMCs; in vitro) were passively sensitized with antigen-specific anti-2,4-dinitrophenyl IgE, anti-ovalbumin IgE, or both. MCs were exposed over a short period of time to increasing amounts of antigen (2,4-dinitrophenyl-human serum albumin or ovalbumin) in the presence of extracellular calcium in vitro or by means of intravenous administration to sensitized mice in vivo before challenging the mice with or exposing the PMCs to optimal amounts of specific or irrelevant antigen.

RESULTS

Rapidly exposing mice or PMCs to progressively increasing amounts of specific antigen inhibited the development of antigen-induced hypothermia in sensitized mice in vivo and inhibited antigen-induced PMC degranulation and prostaglandin D2 synthesis in vitro. Such MC hyporesponsiveness was induced antigen-specifically and was associated with a significant reduction in antigen-specific IgE levels on MC surfaces.

CONCLUSIONS

Rapidly exposing MCs to progressively increasing amounts of antigen can both enhance the internalization of antigen-specific IgE on the MC surface and also desensitize these cells in an antigen-specific manner in vivo and in vitro.

Novel developments in the mechanisms of immune tolerance to allergens

Allergy is the result of a disbalanced immune response to environmental innocuous antigens. Despite of accumulating data to define the pathomechanisms that take place in case of allergic diseases a detailed understanding of sequence of events that lead to the "normal" scenario of tolerance development are still under debate. Allergen-specific immunotherapy is the only causal treatment of allergic diseases. It modifies the immune response to a particular antigen to achieve tolerance against the symptom-causing allergen. This process is considered to mirror physiological peripheral tolerance induction. A number of immunological changes have been described to occur under allergen immunotherapy, including the generation of allergen-specific regulatory T cells, the induction of allergen-specific IgG4, an increase in the Th1/Th2 cytokine ratio and decreased activation and function of effector cells such as mast cells, basophils and eosinophils.

Immunological mechanisms for desensitization and tolerance in food allergy

Food allergy is a major public health concern in westernized countries, estimated to affect 5 % of children and 3-4 % of adults. Allergen-specific immunotherapy for food allergy is currently being actively evaluated, but is still experimental. The optimal protocol, in terms of the route of administration of the food, target maintenance dose, and duration of maintenance therapy, and the optimal patient for these procedures are still being worked out. The mechanisms underlying successful food desensitization are also unclear, in part, because there is no standard immunotherapy protocol. The mechanisms involved, however, may include mast cell and basophil suppression, development of food-specific IgG4 antibodies, reduction in the food-specific IgE/IgG4 ratio, up-regulation and expansion of natural or inducible regulatory T cells, a skewing from a Th2 to a Th1 profile, and the development of anergy and/or deletion in antigen-specific cells. Additional studies are required to elucidate and understand these mechanisms by which desensitization and tolerance are achieved, which may reveal valuable biomarkers for evaluating and following food allergic patients on immunotherapy.

Therapies for allergic inflammation: refining strategies to induce tolerance

Current therapies for asthma and allergy are relatively safe and effective at controlling symptoms but do not change the chronic course of disease. There is no established method to prevent asthma and allergy, and major unmet needs in this area include the better control of the severe forms of these diseases and the developments of curative therapies. Two major therapeutic strategies for asthma and allergy are currently being developed, and I here discuss the advances and challenges for future therapeutic development in these two areas. The first approach, allergen-specific immunotherapy, aims to induce specific immune tolerance and has a long-term disease-modifying effect. The second approach is the use of biological immune response modifiers to decrease pathological immune responses. Combination strategies using both of these approaches may also provide a route for addressing the unmet clinical needs in allergic diseases.

Immunology in the Clinic Review Series; focus on allergies: basophils as biomarkers for assessing immune modulation

Allergen-specific immunotherapy is an effective clinical treatment for hypersensitivity to many allergens. Studies of basophils during immunotherapy have provided insight into underlying immune mechanisms and support the potential use of basophil activation as a biomarker of clinical outcomes. This review examines the evidence for different pathways of basophil modulation associated with various forms of immunotherapy. Better understanding the molecular mechanisms of basophil activation and desensitization and the relationship between suppression of these effector cells to clinical outcomes holds promise for further development and improvement in potential therapies for allergic diseases.

Mechanisms of immunotherapy to wasp and bee venom

Hymenoptera venoms are important allergens that can elicit both local and systemic allergic reactions, including life-threatening anaphylaxis. Venom immunotherapy (VIT) remains the most effective treatment, reducing the risk of systemic reactions in individuals with Hymenoptera venom allergy. VIT can restore normal immunity against venom allergens and provide patients with a lifetime of tolerance to venoms. During VIT, peripheral tolerance is induced by the generation of allergen-specific regulatory T (Treg) cells, which suppress proliferative and cytokine responses against the venom allergens. Treg cells are characterized by IL-10 secretion that directly or indirectly influence effector cells of allergic inflammation, such as mast cells, basophils and eosinophils. Treg cells also have influence on B cells, suppressing IgE production and inducing the production of blocking type IgG4 antibodies against venom allergens. An accumulating body of evidence suggests that Treg cells may affect allergen sensitization and methods for enhancing this cell population may eventually improve the efficacy of VIT. In this article, immune mechanisms enrolled in bee and wasp VIT are reviewed.

Mechanisms of allergen-specific immunotherapy

Allergen-specific immunotherapy has been used for 100 years as a desensitizing therapy for allergic diseases and represents the potentially curative and specific method of treatment. The mechanisms of action of allergen-specific immunotherapy include the very early desensitization effects, modulation of T-and B-cell responses and related antibody isotypes, and migration of eosinophils, basophils, and mast cells to tissues, as well as release of their mediators. Regulatory T (Treg) cells have been identified as key regulators of immunologic processes in peripheral tolerance to allergens. Skewing of allergen-specific effector T cells to a regulatory phenotype appears as a key event in the development of healthy immune response to allergens and successful outcome in patients undergoing allergen-specific immunotherapy. Naturally occurring forkhead box protein 3-positive CD4(+)CD25(+) Treg cells and inducible T(R)1 cells contribute to the control of allergen-specific immune responses in several major ways, which can be summarized as suppression of dendritic cells that support the generation of effector T cells; suppression of effector T(H)1, T(H)2, and T(H)17 cells; suppression of allergen-specific IgE and induction of IgG4; suppression of mast cells, basophils, and eosinophils; and suppression of effector T-cell migration to tissues. New strategies for immune intervention will likely include targeting of the molecular mechanisms of allergen tolerance and reciprocal regulation of effector and Treg cell subsets.

An immunological overview of allergen specific immunotherapy -- subcutaneous and sublingual routes

Allergen-specific immunotherapy remains the most likely effective treatment modality for allergic disorders by targeting the underlying immune mechanisms and possibly causing modifications in the disease course, as well as treating the symptoms. Treatment and compliance experiences been gained over nearly a century in injection-type allergen-specific immunotherapy have motivated the development of newer, alternative routes. Adverse events and safety concerns, efficacy and ease of application seem to be the stimulating factors for the development of a sublingual form of this treatment modality, wherein the principal factor is the capture of the antigen (allergen) by dendritic cells, in the location where oral tolerance arises. Due to the presence of high numbers of tolerogenic dendritic cell subsets in this region, programming of the immune system towards a regulatory state with unresponsiveness to specific allergens occurs. Induction of peripheral tolerance through the generation of regulatory T cells is the key event, with several functional modulations in the allergic immune response. With an increase in understanding of the mechanism of regulatory pathways, promising progresses in the field of allergen-specific immunotherapy will ensue and may provide new options for the treatment of allergic disorders.

Nature of regulatory T cells in the context of allergic disease

Allergen-specific immunotherapy (SIT) is the cornerstone of the management of allergic diseases, which targets modification of the immunologic response, along with environmental allergen avoidance and pharmacotherapy. SIT is associated with improved tolerance to allergen challenge, with a decrease in immediate-phase and late-phase allergic inflammation. SIT has the potential to prevent development of new sensitizations and progression of allergic rhinitis to asthma. It has a role in cellular and humoral responses in a modified pattern. The ratio of T helper (Th)1 cytokines to Th2 cytokines is increased following SIT, and functional regulatory T cells are induced. Interleukin-10 production by monocytes, macrophages, and B and T cells is increased, as well as expression of transforming growth factor β. SIT is associated with increases in allergen-specific antibodies in IgA, IgG1, and IgG4 isotypes. These blocking-type immunoglobulins, particularly IgG4, may compete with IgE binding to allergen, decreasing the allergen presentation with the high- and low-affinity receptors for IgE (FcεRI and FcεRII, respectively). Additionally, SIT reduces the number of mast cells and eosinophils in the target tissues and release of mediators from these cells.

Changes in intracellular cyclic adenosine monophosphate levels in peripheral blood leukocytes during immunotherapy with vespid venom

BACKGROUND

The allergen-induced release of mediators from basophils is known to be decreased after rush venom immunotherapy (VIT) compared with pretreatment values. A rise in the intracellular cyclic adenosine monophosphate (cAMP) level is known to inhibit mediator release.

OBJECTIVES

To determine changes in cAMP levels in peripheral blood leukocytes (PBLs) during rush VIT and to evaluate their relation to allergen-specific reactivity of basophils.

METHODS

Ten patients allergic to vespid venom (VV) were investigated before rush VIT and after reaching the maintenance dose. Five VV-allergic patients not undergoing VIT served as controls. Patients' PBLs were incubated with VV, and allergen-induced histamine and leukotriene release from basophils was measured. Levels of cAMP were determined in PBLs and in plasma.

RESULTS

Immediately after rush VIT, VV-induced histamine release (P = .04) and VV-induced leukotriene release (P = .01) were significantly reduced. Intracellular cAMP levels increased significantly (P = .047). However, 6 months after VIT, mediator responses in basophils were comparable with pre-VIT values. No significant changes were found in the control group.

CONCLUSIONS

An increase in intracellular cAMP levels might account for the decreased reactivity of basophils to allergen after 1 week of VIT. However, similar to the decreased mediator release after 1 week of VIT, this is not a long-term effect as values returned to baseline after 6 months.

Mechanisms of allergen-specific immunotherapy

Allergen-specific immunotherapy (SIT) has been used for almost a century as a desensitizing therapy for allergic diseases and represents the only curative and specific method of treatment. Administration of appropriate concentrations of allergen extracts has been shown to be reproducibly effective when patients are carefully selected. The mechanisms by which allergen-SIT has its effects include the modulation of T-cell and B-cell responses and related antibody isotypes as well as effector cells of allergic inflammation, such as eosinophils, basophils, and mast cells. The balance between allergen-specific T-regulatory (Treg) and T(H)2 cells appears to be decisive in the development of allergic and healthy immune responses against allergens. Treg cells consistently represent the dominant subset specific for common environmental allergens in sensitized healthy individuals. In contrast, there is a high frequency of allergen-specific T(H)2 cells in patients with allergy. The induction of a tolerant state in peripheral T cells represents an essential step in allergen-SIT. Peripheral T-cell tolerance is characterized mainly by generation of allergen-specific Treg cells leading to suppressed T-cell proliferation and T(H)1 and T(H)2 cytokine responses against the allergen. This is accompanied by a significant increase in allergen-specific IgG(4), and also IgG(1) and IgA, and a decrease in IgE in the late stage of the disease. In addition, decreased tissue infiltration of mast cells and eosinophils and their mediator release including circulating basophils takes place. Current understanding of mechanisms of allergen-SIT, particularly the role of Treg cells in peripheral tolerance, may enable novel treatment strategies.

Prevention and treatment of hymenoptera venom allergy: guidelines for clinical practice

Based on the knowledge of the living conditions and habitat of social Aculeatae a series of recommendations have been formulated which can potentially greatly minimize the risk of field re-sting. After a systemic sting reaction, patients should be referred to an allergy specialist for evaluation of their allergy, and if necessary venom immunotherapy (VIT). An emergency medical kit should be supplied, its use clearly demonstrated and repeatedly practised until perfected. This should be done under the supervision of a doctor or a trained nurse. Epinephrine by intramuscular injection is regarded as the treatment of choice for acute anaphylaxis. H1-antihistamines alone or in combination with corticosteroids may be effective in mild to moderate reactions confined to the skin and may support the value of treatment with epinephrine in full-blown anaphylaxis. Up to 75% of the patients with a history of systemic anaphylactic sting reaction develop systemic symptoms once again when re-stung. Venom immunotherapy is a highly effective treatment for individuals with a history of systemic reaction and who have specific IgE to venom allergens. The efficacy of VIT in yellow jacket venom allergic patients has been demonstrated also by assessing health-related quality of life. If both skin tests and serum venom specific IgE turn negative, VIT may be stopped after 3 years. After VIT lasting 3-5 years, most patients with mild to moderate anaphylactic symptoms remain protected following discontinuation of VIT even with positive skin tests. Longer term or lifelong treatment should be considered in high-risk patients. Because of the small but relevant risk of re-sting reactions, in these patients, emergency kits, including epinephrine auto-injectors, should be discussed with every patient when stopping VIT.

Possible circadian variation of serum mast cell tryptase concentration

BACKGROUND

A temporarily elevated level of serum mast cell tryptase (ST) indicates mast cell activation and occurs in systemic anaphylactic reactions (SAR). We measured ST following a sting challenge in vespid venom-allergic patients treated with venom immunotherapy (VIT) and in healthy controls, respectively.

AIM OF THE STUDY

To assess changes of ST over time in vespid venom-allergic patients at the occasion of a re-sting and in healthy controls.

METHODS

A sting challenge was performed in 20 patients on vespid VIT to monitor efficacy of VIT. ST was measured between 9.00 and 10.00 a.m. (baseline). Sting challenge was performed at 2.00 p.m., and ST was determined again 20 min, 90 min and 18 h later. Measurements at corresponding times of the day were done in nine healthy controls.

RESULTS

One patient developed a mild SAR to the sting challenge which was associated with a temporary increase of ST. In the other 19 patients who tolerated the sting challenge without SAR ST decreased significantly by 18.0% (median, range 8.3-36.7%). Twenty minutes after the sting when compared with baseline levels (P < 0.001), a significant decrease of ST was still present after 90 min (median 13.7%) (P < 0.001), but not after 18 h (P = 0.57). A comparably significant temporary decline was found in controls.

CONCLUSIONS

The temporary decline of ST in patients and in controls suggests a circadian variation of ST concentration. A normal diurnal pattern of ST concentration after sting challenge is associated with successful treatment.

Can serum mast cell tryptase help diagnose anaphylaxis?

OBJECTIVE

We aimed to determine the utility of serum mast cell tryptase to diagnose anaphylaxis.

METHODS

As part of a venom immunotherapy trial, we performed 64 sting challenges. Blood samples were taken before the sting (baseline), and 15 min and 60 min after the sting. Tryptase was measured in baseline, 15 minute and 60 minute serum samples. Histamine was measured in baseline and 15 minute plasma samples. Eleven people had undisputed severe anaphylactic reactions; tryptase and histamine levels were assessed against this clinical gold standard diagnosis.

RESULTS

Excluding mild reactions from the analysis, peak tryptase readings had sensitivity of 0.36 and specificity of 0.93 using the recommended cut-off range (< 12.0 microg/L). Receiver-operator curve analysis found a cut-off of 9.0 microg/L would improve diagnostic performance (sensitivity 0.55, specificity 0.93). Serial tryptase measurement was significantly more discriminatory; an increase in tryptase of 2.0 microg/L or greater had a sensitivity of 0.73 and specificity of 0.98. The addition of histamine measurements, defining a positive result by either a rise in tryptase or a rise in histamine, appeared to further increase sensitivity (0.90).

CONCLUSIONS

Clinicians should use caution when using serum tryptase to refute or support a diagnosis of anaphylaxis. Serial tryptase measurement increases sensitivity and specificity. Further studies using serial tryptase determinations in general emergency department practice, perhaps supplemented by histamine determinations, are warranted.

Basophil activation during pollen season in patients monosensitized to grass pollens

BACKGROUND

Basotest is a new basophil-activation test based upon the expression of CD63 (gp53) in the presence of allergens. It is an effective diagnostic test for pollen-allergic patients. However, it is not known whether Basotest results differ during the pollen season.

METHODS

We examined the activation of basophils by Basotest in 13 patients sensitized only to grass pollen, before and during the pollen season, in order to assess whether Basotest could be used as a diagnostic test during the pollen season. Dose-response curves with 10-fold increasing concentrations of timothy grass pollen (10-4 to 100 AU) were carried out.

RESULTS

Basophils were not activated spontaneously during the pollen season since the CD63 expression was below detectable levels before in vitro cell activation. A decreased percentage of activated basophils at the peak of activation was found in comparing the pre- and in-season tests, but all patients had a positive test. When basophil activation was at its peak, the allergen concentration was similar during the two periods. Moreover, the median area under the curve was significantly (P < 0.02) reduced during the season as compared to before the season.

CONCLUSION

Basotest can therefore be used as a diagnostic test during the pollen season, but the allergen exposure needs to be characterized if quantitative studies are performed.

The frequency of phospholipase A2 binding of basophilic granulocytes does not decrease during bee-venom-specific immunotherapy

BACKGROUND

The major allergenic component of bee venom is phospholipase A2 (PLA2).

METHODS

In this study, PLA2 was used to analyze and enrich PLA2-binding cells from peripheral blood by high gradient magnetic cell sorting.

RESULTS

In normal donors, the frequency of allergen (PLA2)-binding cells among peripheral blood mononuclear cells (PBMC) as determined by flow cytometry is below 0.1%, whereas in bee-venom-allergic patients, PLA2-binding cells are readily detectable at frequencies of up to 2.3%. In severely bee-venom-allergic patients, many basophilic granulocytes are present, as defined by anti-CD9, CD25, and CD38 mAb, comprising up to 95% of the PLA2-binding cells. From blood of allergic and normal donors, about equal absolute numbers of allergen-binding CD19/21-positive B cells can be enriched. Severe anaphylactic reactions (Mueller grade IV) and failure of or adverse reactions during immunotherapy are associated with high numbers of circulating allergen-binding basophils. Interestingly, in the patients studied, the number of PLA2-binding basophilic granulocytes did not markedly change during rush immunotherapy and up to 6 months of maintenance immunotherapy.

CONCLUSIONS

The specific and reproducible enrichment of PLA2-binding cells provides a new tool for the analysis and monitoring of effector cells in bee-venom-allergic patients with immediate-type hypersensitivity.