Molecular characterization of human IgG monoclonal antibodies specific for the major birch pollen allergen Bet v 1. Anti-allergen IgG can enhance the anaphylactic reaction

Natural human Bet v 1-specific IgG antibodies recognize non-conformational epitopes whereas IgE reacts with conformational epitopes

BACKGROUND

The nature of epitopes on Bet v 1 recognized by natural IgG antibodies of birch pollen allergic patients and birch pollen-exposed but non-sensitized subjects has not been studied in detail.

OBJECTIVE

To investigate IgE and IgG recognition of Bet v 1 and to study the effects of natural Bet v 1-specific IgG antibodies on IgE recognition of Bet v 1 and Bet v 1-induced basophil activation.

METHODS

Sera from birch pollen allergic patients (BPA, n = 76), allergic patients without birch pollen allergy (NBPA, n = 40) and non-allergic individuals (NA, n = 48) were tested for IgE, IgG as well as IgG1 and IgG4 reactivity to folded recombinant Bet v 1, two unfolded recombinant Bet v 1 fragments comprising the N-terminal (F1) and C-terminal half of Bet v 1 (F2) and unfolded peptides spanning the corresponding sequences of Bet v 1 and the apple allergen Mal d 1 by ELISA or micro-array analysis. The ability of Bet v 1-specific serum antibodies from non-allergic subjects to inhibit allergic patients IgE or IgG binding to rBet v 1 or to unfolded Bet v 1-derivatives was assessed by competition ELISAs. Furthermore, the ability of serum antibodies from allergic and non-allergic subjects to modulate Bet v 1-induced basophil activation was investigated using rat basophilic leukaemia cells expressing the human FcεRI which had been loaded with IgE from BPA patients.

RESULTS

IgE antibodies from BPA patients react almost exclusively with conformational epitopes whereas IgG, IgG1 and IgG4 antibodies from BPA, NBPA and NA subjects recognize mainly unfolded and sequential epitopes. IgG competition studies show that IgG specific for unfolded/sequential Bet v 1 epitopes is not inhibited by folded Bet v 1 and hence the latter seem to represent cryptic epitopes. IgG reactivity to Bet v 1 peptides did not correlate with IgG reactivity to the corresponding Mal d 1 peptides and therefore does not seem to be a result of primary sensitization to PR10 allergen-containing food. Natural Bet v 1-specific IgG antibodies inhibited IgE binding to Bet v 1 only poorly and could even enhance Bet v 1-specific basophil activation.

CONCLUSION

IgE and IgG antibodies from BPA patients and birch pollen-exposed non-sensitized subjects recognize different epitopes. These findings explain why natural allergen-specific IgG do not protect against allergic symptoms and suggest that allergen-specific IgE and IgG have different clonal origin.

Human Monoclonal IgE Antibodies-a Major Milestone in Allergy

PURPOSE OF REVIEW

Bound to its high affinity receptor on mast cells and basophils, the IgE antibody molecule plays an integral role in the allergic reaction. Through interactions with the allergen, it provides the sensitivity and specificity parameters for cell activation and mediator release that produce allergic symptoms. Advancements in human hybridoma technologies allow for the generation and molecular definition of naturally occurring allergen-specific human IgE monoclonal antibodies.

RECENT FINDINGS

A high-resolution structure of dust mite allergen Der p 2 in complex with Fab of the human IgE mAb 2F10 was recently determined using X-ray crystallography. The structure reveals the fine molecular details of IgE 2F10 binding its 750 Å2 conformational epitope on Der p 2. This review provides an overview of this major milestone in allergy, the first atomic resolution structure of an authentic human IgE epitope. The molecular insights that IgE epitopes provide will allow for structure-based design approaches to the development of novel diagnostics, antibody therapeutics, and immunotherapies.

Versatile Application of Nanobodies for Food Allergen Detection and Allergy Immunotherapy

The unique characteristics of camelid heavy-chain only antibody (HCAb) derived nanobodies (Nbs) have facilitated their employment as tools for research and application in extensive fields including food safety inspection, diagnosis and therapy of diseases, etc., to develop immune detecting techniques or alternative candidates of conventional antibodies as diagnostic and therapeutic reagents. The wide application in the fields of food allergen inspection and immunotherapy has not been addressed as not much results published in the literature. The robust properties and straightforward selecting strategy of Nbs impel the advantageous employment compared with monoclonal antibodies (mAbs) to establish immunoassay and serve as blocking antibodies to compete immunoglobulin E (IgE) binding epitopes on food allergens. More and more efforts have been invested to develop specific Nbs against food allergen proteins, such as macadamia allergen of Mac i 1, peanut allergen of Ara h 3, and lupine allergen of Lup an 1, which demonstrated the potential of Nbs for research and application in food allergen surveillance. Meanwhile, the paratopes of Nbs preferably targeting the unique epitopes of food allergens can provide more possibilities to serve as blocking antibodies to shield IgE binding epitopes for food allergy immunotherapy. Regardless, the research and application of Nbs in the field of food allergen and allergic reactions are expected to attract dramatic focus and produce promising research outputs.

Nanobodies-Useful Tools for Allergy Treatment?

In the last decade single domain antibodies (nanobodies, VHH) qualified through their unique characteristics have emerged as accepted and even advantageous alternative to conventional antibodies and have shown great potential as diagnostic and therapeutic tools. Currently nanobodies find their main medical application area in the fields of oncology and neurodegenerative diseases. According to late-breaking information, nanobodies specific for coronavirus spikes have been generated these days to test their suitability as useful therapeutics for future outbreaks. Their superior properties such as chemical stability, high affinity to a broad spectrum of epitopes, low immunogenicity, ease of their generation, selection and production proved nanobodies also to be remarkable to investigate their efficacy for passive treatment of type I allergy, an exaggerated immune reaction to foreign antigens with increasing global prevalence.

Bee Venom Immunotherapy: Current Status and Future Directions

Bee venom immunotherapy is the main treatment option for bee sting allergy. Its major limitations are the high percentage of allergic side effects and long duration, which are driving the development of novel therapeutic modalities. Three general approaches have been evaluated including the use of hypoallergenic allergen derivatives, adjunctive therapy, and alternative delivery routes. This article reviews preclinical and clinical evidence on the therapeutic potential of these new therapies. Among hypoallergenic derivatives, hybrid allergens showed a markedly reduced IgE reactivity in mouse models. Whether they will offer therapeutic benefit over extract, it is still not known since clinical trials have not been carried out yet. T cell epitope peptides have proven effective in small clinical trials. Major histocompatibility complex class II restriction was circumvented by using long overlapping or promiscuous T cell epitope peptides. However, the T cell-mediated late-phase adverse events have been reported with both short and longer peptides. Application of mimotopes could potentially overcome both T cell- and IgE-mediated adverse events. During this evolution of vaccine, there has been a gain in safety. The efficacy was further improved with the use of Toll-like receptor-activating adjuvants and delivery systems. In murine models, the association of allergen Api m 1 with cytosine-guanosine rich oligonucleotides stimulated strong T-helper type-1 response, whereas its encapsulation into microbubbles protected mice against allergen challenge. An intralymphatic administration of low-dose vaccine has shown the potential to decrease treatment from 5 years to only 12 weeks. Bigger clinical trials are needed to follow up on these results.

Randomized controlled trial demonstrating the benefits of delta inulin adjuvanted immunotherapy in patients with bee venom allergy

Background

Allergic reactions to Hymenoptera insect stings remain a major global clinical problem. Although effective, parenteral desensitization regimens require use of costly venom extracts and require frequent visits over extended periods of time.

Objective

Adjuvants are commonly used to enhance the efficacy of infectious disease vaccines, and this study asked whether Advax (Vaxine Pty Ltd, Adelaide, Australia), a novel noninflammatory polysaccharide adjuvant, might provide similar benefits for allergy desensitization.

Methods

A randomized, controlled phase 1/2 trial was undertaken in 27 adults with a history of rapid-onset systemic allergic reactions to honeybee stings and positive specific IgE levels to evaluate the safety and efficacy of honeybee venom immunotherapy (HBVIT) combined with Advax adjuvant. Venom immunotherapy (VIT) was administered monthly for 30 months after achievement of maintenance doses.

Results

Advax-adjuvanted HBVIT was well tolerated. Around week 14 of VIT, specific IgG₄ responses peaked in both groups but increased earlier, peaked higher, and were better maintained through the end of the study in the Advax-adjuvanted arm. Several different patterns of serologic response to VIT were seen; some subjects had a dominant IgG₄ response, some had a combined IgG₄ and IgG₁ response, and some had an exclusively IgG₁ response. In some subjects specific IgE levels increased during the induction phase and then decreased, whereas in others specific IgE levels progressively decreased from the start of VIT.

Conclusion

Advax adjuvant favorably enhanced the immunogenicity of HBVIT, with an early and prolonged switch to specific IgG₄ production. The ability of Advax adjuvant to enhance VIT efficacy warrants further study.

Fusion proteins consisting of Bet v 1 and Phl p 5 form IgE-reactive aggregates with reduced allergenic activity

The cross-linking of effector cell-bound IgE antibodies by allergens induces the release of inflammatory mediators which are responsible for the symptoms of allergy. We demonstrate that a recombinant hybrid molecule consisting of the major birch (Bet v 1) and grass (Phl p 5) pollen allergen exhibited reduced allergenic activity as compared to equimolar mixes of the isolated allergens in basophil activation experiments. The reduced allergenic activity of the hybrid was not due to reduced IgE reactivity as demonstrated by IgE binding experiments using sera from allergic patients. Physicochemical characterization of the hybrid by size exclusion chromatography, dynamic light scattering, negative-stain electron microscopy and circular dichroism showed that the hybrid occurred as folded aggregate whereas the isolated allergens were folded monomeric proteins. IgG antibodies raised in rabbits against epitopes of Bet v 1 and Phl p 5 showed reduced reactivity with the hybrid compared to the monomeric allergens. Our results thus demonstrate that aggregation can induce changes in the conformation of allergens and lead to the reduction of allergenic activity. This is a new mechanism for reducing the allergenic activity of allergens which may be important for modifying allergens to exhibit reduced side effects when used for allergen-specific immunotherapy.

Allergen-Specific Antibodies Regulate Secondary Allergen-Specific Immune Responses

Immunoglobulin E (IgE)-associated allergy is the most common immunologically-mediated hypersensensitivity disease. It is based on the production of IgE antibodies and T cell responses against per se innocuous antigens (i.e., allergens) and subsequent allergen-induced inflammation in genetically pre-disposed individuals. While allergen exposure in sensitized subjects mainly boosts IgE production and T cell activation, successful allergen-specific immunotherapy (AIT) induces the production of allergen-specific IgG antibodies and reduces T cell activity. Under both circumstances, the resulting allergen-antibody complexes play a major role in modulating secondary allergen-specific immune responses: Allergen-IgE complexes induce mast cell and basophil activation and perpetuate allergen-specific T cell responses via presentation of allergen by allergen presenting cells to T cells, a process called IgE-facilitated antigen presentation (FAP). In addition, they may induce activation of IgE memory B cells. Allergen-induced production of specific IgGs usually exerts ameliorating effects but under certain circumstances may also contribute to exacerbation. Allergen-specific IgG antibodies induced by AIT which compete with IgE for allergen binding (i.e., blocking IgG) inhibit formation of IgE-allergen complexes and reduce activation of effector cells, B cells and indirectly T cells as FAP is prevented. Experimental data provide evidence that by binding of allergen-specific IgG to epitopes different from those recognized by IgE, allergen-specific IgG may enhance IgE-mediated activation of mast cells, basophils and allergen-specific IgE⁺ B cells. In this review we provide an overview about the role of allergen-specific antibodies in regulating secondary allergen-specific immune responses.

Allergen-specific immunotherapy: is it vaccination against toxins after all?

IgE-mediated allergies, in particular allergic rhinoconjunctivitis and asthma, have reached epidemic proportions, affecting about one-third of the population in developed countries. The most effective treatment for allergies is specific immunotherapy (SIT), which involves the injection of increasing doses of an allergen extract to allergic individuals. The current form of SIT was first introduced in 1911 and recently celebrated its 100th birthday for the treatment of hay fever. The concept of this therapy at the time was straightforward, as it was believed that pollen contained toxins against which the patient could be vaccinated. However, the understanding became blurred with the discovery that IgE antibodies were the effector molecules of the allergic response. Subsequent research focused on the idea that SIT should induce tolerance keeping the IgE antibodies at bay. In this review, we will discuss the various hypotheses for the mechanism of SIT and we will put forward the concept that allergens may be viewed as 'protoxins' which need to be activated by IgE antibodies. Within this framework, protoxin-neutralizing antibodies are the key effector molecules while a shift to Th1 or Treg cells mainly contributes to the efficacy of SIT by helping B cells to produce neutralizing IgG antibodies.

Antibodies and superantibodies in patients with chronic rhinosinusitis with nasal polyps

Background

Chronic rhinosinusitis with nasal polyps is associated with local immunoglobulin hyperproduction and the presence of IgE antibodies against Staphylococcus aureus enterotoxins (SAEs). Aspirin-exacerbated respiratory disease is a severe form of chronic rhinosinusitis with nasal polyps in which nearly all patients express anti-SAEs.

Objectives

We aimed to understand antibodies reactive to SAEs and determine whether they recognize SAEs through their complementarity-determining regions (CDRs) or framework regions.

Methods

Labeled staphylococcal enterotoxin (SE) A, SED, and SEE were used to isolate single SAE-specific B cells from the nasal polyps of 3 patients with aspirin-exacerbated respiratory disease by using fluorescence-activated cell sorting. Recombinant antibodies with “matched” heavy and light chains were cloned as IgG₁, and those of high affinity for specific SAEs, assayed by means of ELISA and surface plasmon resonance, were recloned as IgE and antigen-binding fragments. IgE activities were tested in basophil degranulation assays.

Results

Thirty-seven SAE-specific, IgG- or IgA-expressing B cells were isolated and yielded 6 anti-SAE clones, 2 each for SEA, SED, and SEE. Competition binding assays revealed that the anti-SEE antibodies recognize nonoverlapping epitopes in SEE. Unexpectedly, each anti-SEE mediated SEE-induced basophil degranulation, and IgG₁ or antigen-binding fragments of each anti-SEE enhanced degranulation by the other anti-SEE.

Conclusions

SEEs can activate basophils by simultaneously binding as antigens in the conventional manner to CDRs and as superantigens to framework regions of anti-SEE IgE in anti-SEE IgE-FcεRI complexes. Anti-SEE IgG₁s can enhance the activity of anti-SEE IgEs as conventional antibodies through CDRs or simultaneously as conventional antibodies and as “superantibodies” through CDRs and framework regions to SEEs in SEE–anti-SEE IgE-FcεRI complexes.

Food Allergy

Food allergy is receiving increased attention in recent years. Because there is currently no known cure for food allergy, avoiding the offending food is the best defense for sensitive individuals. Type I food allergy is mediated by food proteins, and thus, theoretically, any food protein is a potential allergen. Variability of an individual's immune system further complicates attempts to understand allergen-antibody interaction. In this article, we briefly review food allergy occurrence, prevalence, mechanisms, and detection. Efforts aimed at reducing/eliminating allergens through food processing are discussed. Future research needs are addressed.

An assay that may predict the development of IgG enhancing allergen-specific IgE binding during birch immunotherapy

BACKGROUND

It has been shown that birch pollen immunotherapy can induce IgG antibodies which enhance IgE binding to Bet v 1. We aimed to develop a serological assay to predict the development of antibodies which enhance IgE binding to Bet v 1 during immunotherapy.

METHODS

In 18 patients treated by Bet v 1-fragment-specific immunotherapy, the effects of IgG antibodies specific for the fragments on the binding of IgE antibodies to Bet v 1 were measured by ELISA. Blocking and possible enhancing effects on IgE binding were compared with skin sensitivity to Bet v 1 after treatment.

RESULTS

We found that fragment-specific IgG enhanced IgE binding to Bet v 1 in two patients who also showed an increase of skin sensitivity to Bet v 1.

CONCLUSION

Our results indicate that it may be possible to develop serological tests which predict the induction of unfavourable IgG antibodies enhancing the binding of IgE to Bet v 1 during immunotherapy.

A nonallergenic birch pollen allergy vaccine consisting of hepatitis PreS-fused Bet v 1 peptides focuses blocking IgG toward IgE epitopes and shifts immune responses to a tolerogenic and Th1 phenotype

Allergen-specific immunotherapy is the only allergen-specific and disease-modifying treatment for allergy. The construction and characterization of a vaccine for birch pollen allergy is reported. Two nonallergenic peptides, PA and PB, derived from the IgE-reactive areas of the major birch pollen allergen Bet v 1 were fused to the hepatitis B surface protein, PreS, in four recombinant fusion proteins containing different numbers and combinations of the peptides. Fusion proteins expressed in Escherichia coli and purified to homogeneity showed a lack of IgE reactivity and allergenic activity when tested with sera and basophils from patients allergic to birch pollen. Compared to Bet v 1 allergen, peptides PA and PB showed reduced T cell activation in PBMCs from allergic patients, whereas PreS fusion proteins induced less IL-5 and more IL-10 and IFN-γ. Immunization of rabbits with the fusion proteins, in particular with a PreS fusion protein 2PAPB-PreS, containing two copies of each peptide, induced high levels of IgG Abs against the major IgE-reactive site on Bet v 1 and related allergens. These IgG Abs inhibited allergic patients' IgE binding to Bet v 1 better than did IgG induced by immunization with complete Bet v 1. Furthermore, 2PAPB-PreS-induced IgG inhibited Bet v 1-induced basophil activation in allergic patients and CD23-facilitated allergen presentation. Our study exemplifies novel beneficial features for a PreS carrier-based peptide vaccine for birch pollen, which, in addition to the established reduction in allergenic activity, include the enhanced focusing of blocking Ab responses toward IgE epitopes, immunomodulatory activity, and reduction of CD23-facilitated allergen presentation.

Functional rather than immunoreactive levels of IgG4 correlate closely with clinical response to grass pollen immunotherapy

BACKGROUND

Induction of allergen-specific IgG(4) antibodies is the most consistent immunological finding in immunotherapy trials. However, quantitative assessments of IgG(4) antibodies have not proven beneficial in evaluating clinical changes during or after immunotherapy. In the current study, we investigated the relationship between clinical outcome and allergen-specific IgG(4) titres or functional antibody responses following immunotherapy. We hypothesized that functional assays of serum IgG-associated inhibitory activity such as inhibition of IgE-allergen interactions (IgE-blocking factor) and inhibition of CD23-dependent IgE-facilitated allergen binding (IgE-FAB) correlate more closely with clinical outcome and may be biomarkers of clinical response.

METHODS

In an 8-month dose-response randomized double-blind placebo-controlled study, 221 polysensitized subjects with severe seasonal rhinitis received Alutard SQ, Phleum pratense 100,000 SQ-U, 10,000 SQ-U or placebo injections. Serum specimens were collected before treatment, after up-dosing, during the peak season and at the end of the study. Allergen-specific IgG(4) titres and IgG-associated inhibitory activity were evaluated.

RESULTS

A time- and dose-dependent increase in serum inhibitory activity for both the IgE-blocking factor and IgE-FAB was observed, which paralleled increases in grass pollen-specific IgG(4) antibodies. A modest but significant inverse relationship was demonstrated between postimmunotherapy serum inhibitory activity and combined symptom-rescue medication scores (IgE-FAB: r = -0.25, P = 0.0002; IgE-blocking factor: r = -0.28, P < 0.0001), whereas this was not observed for immunoreactive IgG(4) levels (r = -0.11, P = 0.12).

CONCLUSIONS

Functional assays of inhibitory IgG(4) and IgE-blocking factor may be more useful surrogates of clinical response than IgG(4). Whether these antibody effects may serve as predictive biomarkers of clinical efficacy in individual patients requires further investigation.

Mechanisms of allergen-specific immunotherapy

Allergen-specific immunotherapy (allergen-SIT) is a potentially curative treatment approach in allergic diseases. It has been used for almost 100 years as a desensitizing therapy. The induction of peripheral T cell tolerance and promotion of the formation of regulatory T-cells are key mechanisms in allergen-SIT. Both FOXP3⁺CD4⁺CD25⁺ regulatory T (Treg) cells and inducible IL-10- and TGF-β-producing type 1 Treg (Tr1) cells may prevent the development of allergic diseases and play a role in successful allergen-SIT and healthy immune response via several mechanisms. The mechanisms of suppression of different pro-inflammatory cells, such as eosinophils, mast cells and basophils and the development of allergen tolerance also directly or indirectly involves Treg cells. Furthermore, the formation of non-inflammatory antibodies particularly IgG4 is induced by IL-10. Knowledge of these molecular basis is crucial in the understanding the regulation of immune responses and their possible therapeutic targets in allergic diseases.

Passive immunization with allergen-specific antibodies

The induction of allergen-specific IgG antibodies has been identified as a major mechanism responsible for the reduction of allergic inflammation in allergic patients treated by allergen-specific immunotherapy. Several studies suggest that allergen-specific IgG antibodies induced by vaccination with allergens block mast cell and basophil degranulation, IgE-facilitated allergen presentation to T cells and IgE production. The availability of recombinant allergens and technologies for the production of recombinant human antibodies allows engineering of allergen-specific antibodies which can be used for passive immunization (i.e., therapy) and eventually for the prevention of allergy (i.e., prophylaxis). This chapter summarizes data supporting the possible use of allergen-specific antibodies for treatment and prophylaxis. Finally, concrete approaches for the treatment and prevention of allergy based on blocking antibodies are envisioned.

An Allergen Portrait Gallery: Representative Structures and an Overview of IgE Binding Surfaces

Recent progress in the biochemical classification and structural determination of allergens and allergen-antibody complexes has enhanced our understanding of the molecular determinants of allergenicity. Databases of allergens and their epitopes have facilitated the clustering of allergens according to their sequences and, more recently, their structures. Groups of similar sequences are identified for allergenic proteins from diverse sources, and all allergens are classified into a limited number of protein structural families. A gallery of experimental structures selected from the protein classes with the largest number of allergens demonstrate the structural diversity of the allergen universe. Further comparison of these structures and identification of areas that are different from innocuous proteins within the same protein family can be used to identify features specific to known allergens. Experimental and computational results related to the determination of IgE binding surfaces and methods to define allergen-specific motifs are highlighted.

From allergen genes to allergy vaccines

IgE-mediated allergy is a hypersensitivity disease affecting more than 25% of the population. The structures of the most common allergens have been revealed through molecular cloning technology in the past two decades. On the basis of this knowledge of the sequences and three-dimensional structures of culprit allergens, investigators can now analyze the immune recognition of allergens and the mechanisms of allergic inflammation in allergic patients. Allergy vaccines have been constructed that are able to selectively target the aberrant immune responses in allergic patients via different pathways of the immune system. Here we review various types of allergy vaccines that have been developed based on allergen structures, results from their clinical application in allergic patients, and future strategies for allergen-specific immunotherapy and allergy prophylaxis.

A review of allergen-specific immunotherapy in human and veterinary medicine

This article reviews allergen-specific immunotherapy in human and veterinary medicine. Current hypotheses of possible mechanisms of actions are outlined. Indications, success rates, adverse effects and factors influencing outcome of therapy are discussed in humans, dogs, cats and horses.

Analysis of B-cell epitopes from the allergen Hev b 6.02 revealed by using blocking antibodies

Hev b 6.02 (hevein), identified as a major allergen from natural rubber latex (NRL), is involved in the latex-fruit syndrome and also acts as a pathogenesis defense-related protein. Its 3D structure has been solved at high resolution, and its linear epitopes have already been reported. However, information about conformational epitopes is still controversial, even though it is relevant for an accurate diagnosis and treatment, as well as for the study of allergen-antibody molecular interactions. We sought to analyze the B-cell epitopes of Hev b 6.02 at a molecular and structural level, using specific recombinant antibodies. We obtained a murine monoclonal antibody (mAb 6E7) and three human single chain fragments (scFvs A6, H8, and G7) anti-Hev b 6.02 that were able to compete for hevein binding with serum IgEs from latex allergic patients. In vitro assays showed that the mAb 6E7 and scFv H8 recognized the area of Hev b 6.02 where the aromatic residues are exposed; while the scFv G7 defined the amino and carboxy-terminal regions that lie close to each other, as a different epitope. The structural modeling of the Hev b 6.02-scFv H8 and Hev b 6.02-scFv G7 complexes revealed the putative regions of two conformational epitopes. In one of these, the aromatic residues, as well as polar side chains are important for the interaction, suggesting that they are part of a dominant conformational epitope also presented on the Hev b 6.02-IgE interactions. Antibodies recognizing this important allergen have potential to be used to diagnose and ultimately treat latex allergy.

[From the allergen-recognition by antibodies to new therapeutic concepts]

Cross-linking of IgE antibodies through allergens is a basic event in type I allergy and leads to the immediate release of mediators like histamine, responsible for allergic symptoms like rhino-conjunctivitis or asthma. Critical for the binding of allergens to IgE are the IgE-epitopes, which represent a congregation of several amino acid residues often derived from different regions of the allergen. By means of the mimotope-technology, we isolated peptides from phage libraries, which were able to structurally mimic IgE-epitopes of the plant allergens Bet v 1 (birch) and Phl p 5a (timothy grass). Hence, these are candidates for an epitope-specific immunotherapy. In this mode of immunotherapy, it is the aim to induce IgG antibodies directed exclusively against the IgE-epitopes of allergens without induction of anaphylactogenic IgG species, and without the risk of anaphylaxis through cross-linking of IgE. Immunizing mice, we applied the mimotopes displayed on bacteriophages as well as on alternative carrier systems to enhance their antigenicity. With these systems it was possible to elicit an allergen-specific immune response, which was also accompanied by the appropriate T-cell help. Mimotopes resemble a promising concept for an epitope-tailored immunotherapy of allergic patients.

Identification of a B-cell epitope of hyaluronidase, a major bee venom allergen, from its crystal structure in complex with a specific Fab

The major allergens of honeybee venom, hyaluronidase (Hyal) and phospholipase A2, can induce life-threatening IgE-mediated allergic reactions in humans. Although conventional immunotherapy is effective, up to 40% of patients develop allergic side effects including anaphylaxis and thus, there is a need for an improved immunotherapy. A murine monoclonal anti-Hyal IgG1 antibody (mAb 21E11), that competed for Hyal binding with IgEs from sera of bee venom allergic patients, was raised. The fragment of these IgG antibodies which bind to antigen (Fab) was produced and complexed (1:1) with Hyal. The crystal structure determination of Hyal/Fab 21E11 complex (2.6 A) enabled the identification of the Hyal-IgG interface which provides indirect information on the Hyal-IgE interaction (B-cell epitope). The epitope is composed of a linear array of nine residues (Arg138, His141-Arg148) located at the tip of a helix-turn-helix motive which protrudes away from the globular core and fits tightly into the deep surface pocket formed by the residues from the six complementarity determining regions (CDRs) of the Fab. The epitope is continuous and yet its conformation appears to be essential for Ab recognition, since the synthetic 15-mer peptide comprising the entire epitope (Arg138-Glu152) is neither recognized by mAb 21E11 nor by human IgEs. The structure of the complex provides the basis for the rational design of Hyal derivatives with reduced allergenic activity, which could be used in the development of safer allergen-specific immunotherapy.

The clinical significance of food specific IgE/IgG4 in food specific atopic dermatitis

Food is closely associated with the pathogenesis of atopic dermatitis. Food allergy is usually mediated by IgE antibody to specific food proteins and determination of specific IgE antibody is the basis of the common diagnostic test for food allergy. IgG4 have been reported as blocking antibody and the protective effects of blocking antibody may be clear in inhalant allergy. However, the role of IgG4 in food allergy is still a matter of debate. In this study, the clinical significance of food allergen-specific IgE/IgG4 in atopic dermatitis was investigated and compared with that of IgE. A total of 97 patients who fulfilled the diagnostic criteria for atopic dermatitis participated in this study. Skin prick test and allergy patch test were performed. Specific IgE and IgG4 concentration were measured using allergy protein chip, 'AllergyChip'. Double blinded placebo controlled food challenge test (DBPCFC) was performed for the diagnosis of allergy to milk, egg white, wheat, and soybean. DBPCFCs for milk, egg white, soybean, and wheat were performed. The positive rates were 31.7% (19/60) in milk, 36.7% (18/49) in egg white, 30.4% (7/23) in soybean, and 34.8% (8/23) in wheat. Mean IgE/IgG4 levels in DBPCFC (+) subjects is higher than those in DBPCFC (-) subjects in all food items studied. Of them, there were significantly different between two groups in egg white and wheat (Egg white in DBPCFC (+) vs. (-): 0.4 +/- 0.3 vs. 0.2 +/- 0.2, wheat in DBPCFC (+) vs. (-): 1.2 +/- 1.2 vs. 0.3 +/- 0.3, p < 0.05). Allergen-specific IgE/IgG4 may provide one of the clues to understand the mechanism of food allergy in atopic dermatitis. The present study suggests that protein microarray can be one of the useful methods to assess ongoing status of allergic diseases.

Immunological mechanisms of allergen-specific immunotherapy

Allergen-specific immunotherapy has been carried out for almost a century and remains one of the few antigen-specific treatments for inflammatory diseases. The mechanisms by which allergen-specific immunotherapy exerts its effects include the modulation of both T-cell and B-cell responses to allergen. There is a strong rationale for improving the efficacy of allergen-specific immunotherapy by reducing the incidence and severity of adverse reactions mediated by IgE. Approaches to address this problem include the use of modified allergens, novel adjuvants and alternative routes of administration. This article reviews the development of allergen-specific immunotherapy, our current understanding of its mechanisms of action and its future prospects.

Inhibition of rBet v 1-induced basophil histamine release with specific immunotherapy -induced serum immunoglobulin G: no evidence that FcgammaRIIB signalling is important

BACKGROUND

Human basophils and mast cells express the low-affinity immunoglobulin (Ig)G receptor FcgammaRIIB. It has previously been shown in artificial model systems that cross-linking of the high-affinity IgE receptor FcepsilonRI and FcgammaRIIB leads to inhibition of FcepsilonRI signalling.

OBJECTIVE

The aim of the present study was to investigate whether cross-linking of FcepsilonRI and FcgammaRIIB contributes to IgG-mediated inhibition of histamine release in human basophils in a system using the sera from specific immunotherapy (SIT) patients and the major allergen from birch pollen, Bet v 1. As IgG4 furthermore has been proposed to have special blocking properties, we investigated the significance of IgG subclass specificity for this inhibition.

METHODS

Binding of recombinant Bet v 1-IgG complexes to FcgammaRII and IgG-binding activities in the sera from 25 birch pollen-allergic patients treated with SIT were measured using (125)I-rBet v 1. Inhibition of basophil histamine release was assessed by incubating washed leucocytes with complexes of rBet v 1-IgG with or without blocking of FcgammaRII.

RESULTS

We observed low binding of rBet v 1-IgG complexes to FcgammaRII, which was negatively correlated with the relative IgG4-binding activities. Blocking of FcgammaRII did not reverse the SIT-IgG-induced inhibition of basophil histamine release. However, IgG-binding activities correlated significantly with the ability of the SIT sera to inhibit basophil histamine release.

CONCLUSION

We suggest that at least in birch pollen SIT, the contribution of FcgammaRIIB-mediated inhibitory signalling to SIT-IgG-induced inhibition of human basophil histamine release is of minor importance. The main contributor to the inhibitory effect of SIT-induced IgG seems to be blocking of the allergen-IgE interaction.

IgE-mediated allergen presentation and blocking antibodies: regulation of T-cell activation in allergy

It is well established that both the production of IgE by B lymphocytes and the maturation and recruitment of eosinophils in late-phase reactions are dependent on the activation of allergen-specific type-2 T-helper cells. What is less well known is the fact that efficient activation of allergen-specific T cells upon low-dose exposure to allergens is critically dependent on IgE-mediated or -facilitated allergen presentation. In fact, changes in the level of IgE-mediated allergen presentation may account for many of the immunological effects described for specific immunotherapy or anti-IgE treatment. This review aims to summarize the current knowledge, and will discuss the clinical relevance of blocking IgG antibodies induced by specific immunotherapy and anti-IgE monoclonal antibodies that both interfere with IgE-mediated allergen presentation.

Allergen-specific polyclonal antibodies reduce allergic disease in a mouse model of allergic asthma

BACKGROUND

Recombinant allergen-specific immunoglobulin G (IgG) antibody therapy can reduce allergic asthma symptoms by inhibiting the immunoglobulin E (IgE)-mediated allergic response. This study investigated the effect of intranasally administered allergen-specific monoclonal (mAb) and polyclonal (pAb) antibody on airway inflammation and hyperresponsiveness (AHR) in a mouse model of human asthma.

METHODS

Ovalbumin (OVA)-specific IgG2b antibodies were generated by phage display using spleens from OVA-immunized mice, and screening against OVA and finally expressed in CHO cells. Sensitized mice were treated intranasally with either a recombinant anti-OVA mAb (gc32) or a polyclonal preparation comprising seven selected antibodies (including gc32). Control mice received diluent only, OVA only, a control polymeric IgG or dexamethasone. Following challenge with nebulized OVA, investigators assessed airway inflammation by histology and cellular composition of the bronchoalveolar fluid, and methacholine-induced airway hyperresponsiveness (AHR). Serum levels of total and OVA-specific IgE were measured by ELISA.

RESULTS

Sensitized mice developed airway inflammation and AHR in response to OVA challenge. Intranasally administered OVA-specific murine polyclonal or monoclonal IgG2b antibodies both reduced OVA-induced lung inflammation. Polyclonal, but not anti-OVA mAb, also reduced AHR and eosinophil influx into the airway lumen. Both anti-OVA antibody preparations reduced levels of specific IgE with no effect on total IgE levels.

CONCLUSIONS

Intranasal treatment with allergen-specific pAb reduces pulmonary inflammation and AHR in a mouse model of allergic asthma, but allergen-specific mAb reduces inflammation only. Allergen-specific recombinant pAb offers a potentially valuable therapeutic approach to the management of allergic asthma.

Poor association between allergen-specific serum immunoglobulin E levels, skin sensitivity and basophil degranulation: a study with recombinant birch pollen allergen Bet v 1 and an immunoglobulin E detection system measuring immunoglobulin E capable of binding to Fc epsilon RI

BACKGROUND

Results from several studies indicate that the magnitude of immediate symptoms of type I allergy caused by allergen-induced cross-linking of high-affinity Fc epsilon receptors on effector cells (mast cells and basophils) is not always associated with allergen-specific IgE levels.

OBJECTIVE

To investigate the association of results from intradermal skin testing, basophil histamine release and allergen-specific IgE, IgG1-4, IgA and IgM antibody levels in a clinical study performed in birch pollen-allergic patients (n = 18).

METHODS

rBet v 1-specific IgEs were measured by quantitative CAP measurements and by using purified Fc epsilon RI-derived alpha-chain to quantify IgE capable of binding to effector cells. Bet v 1-specific IgG subclasses, IgA and IgM levels were measured by ELISA, and basophil histamine release was determined in whole blood samples. Intradermal skin testing was performed with the end-point titration method.

RESULTS

Our study demonstrates on the molecular level that the concentrations of allergen-specific IgE antibodies capable of binding to Fc epsilon RI and biological sensitivities are not necessarily associated. A moderate association was found between cutaneous and basophil sensitivity.

CONCLUSION

Our results highlight the quantitative discrepancies and limitations of the present diagnostic tools in allergy, even when using a single allergenic molecule. The quantity of allergen-specific serum IgE is only one component of far more complex cellular systems (i.e. basophil-based tests, skin tests) used as indirect diagnostic tests for IgE-mediated allergic sensitivity.

Development of an in vitro system for the study of allergens and allergen-specific immunoglobulin E and immunoglobulin G: Fce receptor I supercross-linking is a possible new mechanism of immunoglobulin G-dependent enhancement of type I allergic reactions

BACKGROUND

IgE-dependent activation of mast cells (MCs) is a key pathomechanism of type I allergies. In contrast, allergen-specific IgG Abs are thought to attenuate immediate allergic reactions by blocking IgE binding and by cross-linking the inhibitory Fcgamma receptor IIB on MCs.

OBJECTIVES

To establish a defined in vitro system using human MCs to study the biological activity of allergens and to investigate the role of allergen-specific IgE and IgG.

METHODS

Purified human intestinal MCs sensitized with different forms of specific IgE Abs were triggered by monomeric and oligomeric forms of recombinant Bet v 1, the major birch pollen allergen, in the presence or absence of allergen-specific IgG Abs. Results MCs sensitized with an anti-Bet v 1 IgE mAb or sera obtained from birch pollen allergic patients released histamine and sulphidoleukotrienes after exposure to oligomeric Bet v 1. Monomeric Bet v 1 provoked mediator release only in MCs sensitized with patients sera but not in MCs sensitized with anti-Bet v 1 IgE mAb. Interestingly, MC activation could be induced by supercross-linking of monomeric Bet v 1 bound to monovalent IgE on MCs with a secondary allergen-specific IgG pAb. By using IgG F(ab')2 fragments we provide evidence that this effect is not a result of IgG binding to Fcgamma receptors.

CONCLUSION

This assay represents a new tool for the in vitro study of MC activation in response to natural and genetically modified allergens. Fcepsilon receptor I supercross-linking by allergen-specific IgG Abs provides a possible new mechanism of IgG-dependent enhancement of type I allergic reactions.

Mechanisms of immunotherapy: IgG revisited

PURPOSE OF REVIEW

This paper will review historical and recent evidence for the induction of 'blocking' IgG antibodies during successful specific immunotherapy.

RECENT FINDINGS

Specific immunotherapy is frequently associated with a rise in allergen-specific IgG4 antibodies and a modest reduction in specific IgE titres, although this does not always correlate with clinical efficacy. There is accumulating evidence that specific immunotherapy also influences the blocking activity on IgE-mediated responses by IgG4, and cellular assays are commonly used to investigate these changes. Recently, a novel assay, which detects allergen-IgE binding using flow cytometry, has been used to detect 'functional' specific immunotherapy-induced changes in IgG antibody activity. Results suggest that successful specific immunotherapy is associated with an increase in IgG blocking activity that is not solely dependent on the quantity of IgG antibodies.

SUMMARY

Successful immunotherapy is associated with quantitative and qualitative changes in the allergen-specific IgG antibody response. The induction of IgG antibodies with blocking activity may have a protective role not only through the inhibition of allergen-induced, IgE-mediated release of inflammatory mediators from mast cells and basophils, but also through the inhibition of IgE-facilitated antigen presentation to T cells. Qualitative changes in the allergen-specific IgG antibody response may possibly be an important mechanism underlying the clinical efficacy of specific immunotherapy. Monitoring changes in blocking activity using cellular assays may give an early indication of the potential success of treatment.

Non-anaphylactic surface-exposed peptides of the major birch pollen allergen, Bet v 1, for preventive vaccination

BACKGROUND

Almost 100 million allergic patients are sensitized to the major birch pollen allergen, Bet v 1, a 17 kDa protein containing most of the IgE epitopes present in pollens of trees belonging to the Fagales order and plant-derived food.

OBJECTIVE

Our aim was to develop an approach for the rational design of B cell epitope-derived, non-allergenic peptide allergy vaccines.

METHODS

According to the three-dimensional (3-D) structure of birch pollen allergen, Bet v 1, six peptides comprising 25-32 preferably solvent-exposed amino acids were synthesized.

RESULTS

Because of lack of secondary structure, the peptides showed no allergenic activity in allergic patients. In a mouse model of birch pollen allergy, peptide vaccination induced Bet v 1-specific IgG and prevented IgE-mediated allergic sensitization to Bet v 1. The protective role of peptide-induced blocking antibodies is demonstrated by inhibition of allergic patients IgE binding to the allergen and by blocking of allergen-induced basophil degranulation.

CONCLUSION

Our results indicate the mechanistic importance of blocking antibodies for allergy vaccination and present a B cell epitope-based approach for the rational design of safe peptide allergy vaccines whenever the structure of the disease-eliciting allergen is known.

Evaluation of recombinant and native timothy pollen (rPhl p 1, 2, 5, 6, 7, 11, 12 and nPhl p 4)- specific IgG4 antibodies induced by subcutaneous immunotherapy with timothy pollen extract in allergic patients

BACKGROUND

Allergen immunotherapy is a widely accepted treatment for IgE-mediated allergies. The evaluation of immunotherapy-induced IgG4 antibodies based on allergen extract is questionable because the amount of allergen-extract-specific IgG4 to individual disease-eliciting allergens cannot be determined using crude allergen extracts. In this study, we examined the specific IgE and IgG4 serum binding profiles to individual Phleum pratense allergens in grass-pollen-sensitive patients who had received grass-pollen-specific immunotherapy (SIT).

METHODS

The study included 33 patients from North-West Italy. All suffered from seasonal rhinoconjunctivitis and/or asthma. A modified "cluster" regimen of injections of a standardized aluminium-adsorbed P.pratense extract, with once-weekly visits and 10 injections for 5 weeks followed by 3 weeks of maintenance injections was instituted. Patients' sera were analyzed for specific IgE and IgG4 reactivity to individual P. pratense allergens (recombinant Phl p 1, Phl p 2, Phl p 5, Phl p 6, Phl p 7, Phl p 11, Phl p12 and native Phl p 4) and natural P. pratense extract using the Pharmacia CAP system.

RESULTS

IgE reactivities to new allergen components were not detected by CAP in treated patients after 15 weeks and a cumulative dose of approximately 65 microg of the major allergen Phl p 5. Patients lacking specific IgE reactivity towards individual allergens at the start of SIT did not produce significant levels of specific serum IgG4 to serum IgE-negative allergens. On the other hand, an increase in specific IgG4 only to allergens to which patients were previously sensitized was observed. Significant increases in specific IgG4 levels to rPhl p 1 (p < 0.05), 2 (p < (0.01), 5 (p < 0.0001), 6 (p < 0.0001), 7 (p < 0.05), 11 (p < 0.05) and nPhl p 4 (p < 0.01) were observed after P. pratense extract immunotherapy. No significant rPhl p 12-specific IgG4 antibody increase was documented after treatment.

CONCLUSION

These findings suggest that Phl p 12 was underrepresented in the extract used, as indicated by the low specific IgG4 response induced by this grass-pollen-specific vaccine. Thus, the simple detection of specific serum IgG4 antibodies a few weeks after the start of SIT could represent a valuable tool to estimate the presence of relevant allergens in a given immunotherapeutic allergen extract.

The blocking activity of birch pollen-specific immunotherapy-induced IgG4 is not qualitatively superior to that of other IgG subclasses

Allergen-specific IgG antibodies induced by specific immunotherapy (SIT) interfere with the allergen-IgE interaction, and act as blocking antibodies in vitro. It has been hypothesised that IgG4, as opposed to other IgG subclasses, is particularly important in this function, which may play a role for the clinical efficacy of SIT. In this study, fractionated serum samples from 14 SIT-treated birch pollen allergic individuals enabled determination of the inhibitory capacity of IgG4 alone versus non-IgG4 IgG. Allergen-binding activities of IgG and the IgG-mediated inhibition of allergen binding to autologous IgE were detected using 125I-labelled rBet v 1.2801, a recombinant variant of the major allergen of Betula verrucosa pollen. Results show that IgG4-depletion resulted in equivalent reductions in binding and blocking activities. In contrast, a significant but less than two-fold higher relative blocking activity was found in the purified IgG4 fraction. There was no significant difference in the binding avidities (1/K(d)) measured in the two IgG fractions. Thus, it appears that SIT-induced specific IgG4 contributes to the IgG blocking of allergen binding to IgE in a simple quantitative manner and not by a particular intrinsic blocking activity.

Renaissance of the blocking antibody concept in type I allergy

Formation of IgE antibodies against per se harmless antigens (i.e. allergens) is the hallmark and key pathomechanism of type I allergy, a hypersensitivity disease affecting more than 25% of the population. Classical experiments performed more than 65 years ago demonstrated that allergen-specific IgG antibodies, termed blocking antibodies, can antagonize the cascade of allergic inflammation resulting from allergen recognition by IgE antibodies. However, controversial results have questioned the protective role of IgG antibodies in allergic diseases. Here, we review recent data demonstrating that blocking antibodies inhibit allergen-induced release of inflammatory mediators from basophils and mast cells as well as IgE-facilitated allergen presentation to T cells, thus leading to suppression of T cell activation. Furthermore, it has been reported that the development of blocking antibodies is associated with reduced boosts of allergen-specific IgE production in patients receiving allergen-specific immunotherapy. These findings suggest that blocking antibodies have protective activity by inhibiting immediate as well as late inflammatory responses and long-term ameliorating activity on the allergic immune response by antagonizing the underlying IgE production. Induction of blocking antibodies is thus an important mechanism underlying allergen-specific immunotherapy. In addition, passive administration of blocking antibodies may be considered as a potential therapeutic strategy for allergic diseases.

Allergen-specific immunotherapy with a monophosphoryl lipid A-adjuvanted vaccine: reduced seasonally boosted immunoglobulin E production and inhibition of basophil histamine release by therapy-induced blocking antibodies

BACKGROUND

Allergen-specific immunotherapy represents a causal form of treatment for IgE-mediated allergies. The allergen extract-based analyses of immunotherapy-induced effects yielded highly controversial results regarding a beneficial role of therapy-induced IgG antibodies.

OBJECTIVE

We analysed allergen-specific IgE, IgG subclass, and IgM responses in patients treated with a grass pollen allergy vaccine adjuvanted with monophosphoryl lipid A (MPL), a Th1-inducing agent, and in a placebo group using recombinant timothy grass pollen allergen molecules (rPhl p 1, rPhl p 2, rPhl p 5).

RESULTS

The strong induction of allergen-specific IgG1 and IgG4 antibodies observed only in the actively treated group was associated with significant clinical improvement. Therapy-induced allergen-specific IgM and IgG2 responses were also noted in several actively treated patients. An inhibition of allergen-dependent basophil histamine release was only obtained with sera containing therapy-induced allergen-specific IgG, but not with sera obtained before therapy or from placebo-treated patients. Moreover, patients with therapy-induced allergen-specific IgG antibodies showed a reduced induction of allergen-specific IgE responses during seasonal grass pollen exposure.

CONCLUSION

Successful immunotherapy with the MPL-adjuvanted grass pollen allergy vaccine is associated with the production of allergen-specific IgG antibodies. These blocking antibodies may have protective effects by inhibiting immediate-type reactions and systemic increases of IgE responses caused by seasonal allergen exposure.

Phage-displayed Bet mim 1, a mimotope of the major birch pollen allergen Bet v 1, induces B cell responses to the natural antigen using bystander T cell help

BACKGROUND AND OBJECTIVE

In previous studies we have generated mimotopes of Bet v 1, the major birch pollen allergen, by biopannings of phage-display random peptide libraries. In the present study, we analysed the humoral and cellular immune response to Bet v 1-mimotopes.

METHODS

The mimotope CFPYCYPSESA, designated Bet mim 1, was used for intraperitoneal immunizations of BALB/c mice in phage-displayed form. For examination of the humoral immune response, enzyme-linked immunosorbent assay (ELISA) experiments were applied. Stimulation capacities were investigated in cultured mouse splenocytes and in humoral Bet v 1-specific T cell clones.

RESULTS

We demonstrated that the Bet mim 1-induced murine antibody response against Bet v 1 was predominated by the IgG1 isotype. In these mice only the phage-displayed mimotopes, but neither the allergen nor the synthetic Bet mim 1-mimotopes were able to stimulate proliferation of cultured splenocytes. Using Bet v 1-specific T cell clones of allergic patients, phage-displayed and synthetic mimotopes were unable to stimulate T cell proliferation. Moreover, tolerance induction to Bet v 1 in mice by intranasal administration of Bet mim 1-phages or Bet mim 1-peptide failed.

CONCLUSION

Taking these results together, our data indicate that Bet mim 1 mimics a Bet v 1-epitope on the B cell but not on the T cell level. We suggest that the phage itself is responsible for the recruitment of T cells providing bystander help in the formation of a mimotope-specific humoral response.

Evolution of IgM, IgE and IgG(1-4 )antibody responses in early childhood monitored with recombinant allergen components: implications for class switch mechanisms

The formation of IgE antibodies against environmental allergens represents the hallmark of type I allergy. Data from in vitro cultured cells and experimental animal models provide controversial evidence for isotype switching from IgM to IgE production via sequential as well as non-sequential (i.e. direct) class switch. We analyzed the evolution of IgE responses in 11 children developing birch pollen and/or grass pollen allergy during the first 7 years of life using purified recombinant allergen molecules (major birch pollen allergen, Bet v 1; major timothy grass pollen allergens, Phl p 1, Phl p 2, Phl p 5). Demographic, clinical and serological data indicated a postnatal sensitization to pollen allergens. A parallel development of IgG(1-4) and IgE responses to recombinant allergen molecules compatible with a strictly sequential class switch to IgE was observed only in one child. The only partly synchronized and dissociated development of allergen-specific antibody responses found in all other cases can be best explained by a partly sequential class switch involving few switch stations or, more likely, by direct class switching. Kinetics and courses of allergen-specific antibody responses (IgM, IgG(1-4), IgE) during the first years of life suggest that, once established, allergen-specific IgE responses are driven by antigen contact rather than by cytokines controlling class switch to IgE.

Monovalent fusion proteins of IgE mimotopes are safe for therapy of type I allergy

By screening phage display random peptide libraries with purified immunoglobulin E (IgE) from birch pollen-allergic patients, we previously defined peptides mimicking natural IgE epitopes (mimotopes) of the major birch pollen allergen Bet v 1. The present study aimed to define a monovalent carrier for the IgE mimotopes to induce protective antibodies directed to the IgE epitopes, suitable for mimotope-specific therapy. We expressed the selected mimotopes as fusion proteins together with streptococcal albumin binding protein (ABP). The fusion proteins were recognized specifically by anti-Bet v 1 human IgE, which demonstrated that the mimotopes fused to ABP resemble the natural IgE epitope. Bet v 1-specific IgG was induced by immunization of BALB/c mice with fusion proteins. These IgG antibodies could inhibit IgE binding to Bet v 1. Skin testing of Bet v 1 allergic mice showed that the ABP mimotope constructs did not elicit type I skin reactions, although they possess IgE binding structures. Our data suggest that IgE mimotopes are safe for epitope-specific immunotherapy of sensitized individuals, when presented in a monovalent form. Therefore, ABP-fused mimotopes are promising candidates for a new type of immunotherapy based on the precise induction of blocking antibodies.

The ACVD task force on canine atopic dermatitis (IV): environmental allergens

Numerous environmental allergens have been incriminated in the pathogenesis of canine atopic dermatitis (AD). These include dust and storage mite antigens, house dust, pollens from grasses, trees and weeds, mould spores, epidermal antigens, insect antigens, and miscellaneous antigens such as kapok. In this paper, we review the literature concerning the allergens that have been reported to contribute to canine AD. We conclude that attempts to identify the relevant canine antigens in the past have been plagued by a lack of standardisation of extracts and techniques, and the presence of false-positive and -negative reactions in allergy tests. Until these problems are rectified, it is unlikely that we will be able to provide a list of major and minor antigens for dogs. Hence, we recommend that future studies should be aimed at determining the major patterns of reactivity and cross-reactivity to specific protein allergens within antigenic extracts using electrophoresis and immunoblotting techniques. Once this information becomes available, it may be possible to use a selection of genetically engineered, highly pure antigens for both diagnostic and therapeutic purposes in canine allergy investigations. The use of such antigens will allow standardisation of canine allergy testing and immunotherapy so that the reliability and efficacy of these procedures can be objectively assessed.

Nonanaphylactic synthetic peptides derived from B cell epitopes of the major grass pollen allergen, Phl p 1, for allergy vaccination

Worldwide more than 200 million individuals are allergic to group 1 grass pollen allergens. We have used the major timothy grass pollen allergen Phl p 1, which cross-reacts with most grass-, corn-, and monocot-derived group 1 allergens to develop a generally applicable strategy for the production of hypoallergenic allergy vaccines. On the basis of the experimentally determined B cell epitopes of Phl p 1, we have synthesized five synthetic peptides. These peptides are derived from the major Phl p 1 IgE epitopes and were between 28-32 amino acids long. We demonstrate by nuclear magnetic resonance that the peptides exhibit no secondary and tertiary structure and accordingly failed to bind IgE antibodies from grass pollen allergic patients. The five peptides, as well as an equimolar mixture thereof, lacked allergenic activity as demonstrated by basophil histamine release and skin test experiments in grass pollen allergic patients. When used as immunogens in mice and rabbits, the peptides induced protective IgG antibodies, which recognized the complete Phl p 1 wild-type allergen and group 1 allergens from other grass species. Moreover, peptide-induced antibodies inhibited the binding of grass pollen allergic patients IgE antibodies to the wild-type allergen. We thus demonstrate that synthetic hypoallergenic peptides derived from B cell epitopes of major allergens represent safe vaccine candidates for the treatment of IgE- mediated allergies.

Immunoglobulin E antibodies of atopic individuals exhibit a broad usage of VH-gene families

The term 'atopy' describes the genetically determined tendency to mount immunoglobulin E (IgE) antibody responses against per se harmless antigens (allergens). In this study we investigated the usage of VH families in the formation of IgE antibodies in 10 patients suffering from mucosal and/or skin manifestations of atopy. IgE antibody reactivities to exogenous allergen sources as well as to autoallergens were determined and, by immunoabsorption, it was demonstrated that allergen-specific IgE accounted for most of the total serum IgE levels in these patients. Using primers with specificity for the VH1-6 gene families and a primer specific for the first constant region of human IgE, cDNAs coding for IgE heavy chain fragments were amplified using the reverse transcription-polymerase chain reaction (RT-PCR) from peripheral blood lymphocytes of the 10 atopic individuals. Hybridization of the heavy chain-encoding cDNAs with an IgE-specific internal oligonucleotide probe revealed a broad usage of all VH-gene families in the atopic individuals. The spectrum of VH families used in a given atopic individual was neither associated with the type or severity of clinical symptoms nor with the number of allergens recognized. The fact that allergen-specific IgE antibodies in atopic individuals originate from a broad variety of B cells thus reflects the activation of multiple B-cell clones during allergen sensitization. This finding should be borne in mind if therapeutic strategies for Type I allergy are considered that aim at a clonal elimination of allergen-specific B cells.