Hev b 9, an enolase and a new cross-reactive allergen from hevea latex and molds. Purification, characterization, cloning and expression

Natural rubber latex allergy is an IgE-mediated disease that is caused by proteins that elute from commercial latex products. A complementary DNA (cDNA) coding for Hev b 9, an enolase (2-phospho-D-glycerate hydrolyase) and allergen from latex of the rubber tree Hevea brasiliensis, was amplified by PCR. The PCR primers were designed according to conserved regions of enolases from plants. The obtained cDNA amplification product consisted of 1651 bp and encoded a protein of 445 amino-acid residues with a calculated molecular mass of 47.6 kDa. Sequence comparisons revealed high similarities of the Hevea latex enolase to mold enolases that have been identified as important allergens. In addition, the crucial amino-acid residues that participate in the formation of the catalytic site and the Mg2+ binding site of enolases were also conserved. Hevea latex enolase was produced as a recombinant protein in Escherichia coli with an N-terminal hexahistidyl tag, and purified by affinity chromatography. The yield amounted to 110 mg of purified Hev b 9 per litre of bacterial culture. The recombinant allergen bound IgE from latex, as well as mold-allergic patients, in immunoblot and ELISA experiments. The natural enolase was isolated from Hevea latex by (NH4)2SO4 precipitation and ion exchange chromatography. The natural and the recombinant (r)Hev b 9 showed equivalent enzymatic activity. Patients' IgE-antibodies preincubated with rHev b 9 lost their ability to bind to natural (n) Hev b 9, indicating the identity of the B-cell epitopes on both molecules. Cross-reactivity with two enolases from Cladosporium herbarum and Alternaria alternata was determined by inhibition of IgE-binding to these enolases by rHev b 9. Therefore, enolases may represent another class of highly conserved enzymes with allergenic potentials.

Allergen mimotopes for 3-dimensional epitope search and induction of antibodies inhibiting human IgE

There is no definite information available on the structural characteristics of IgE binding epitopes on allergenic molecules, although it is widely accepted that most of them are conformational. In the current study we aimed to characterize the IgE epitope of Bet v 1, the major birch pollen allergen, by the application of phage display peptide libraries. We purified IgE specific for Bet v 1 from allergic patients' sera to select mimotopes representing artificial IgE epitopes by biopanning of phage libraries. By linear alignment, it was not possible to attribute mimotope sequences to the primary structure of Bet v 1. We developed a computer-aided, 3-dimensional coarse-grained epitope search. The 3-dimensional search, followed by statistical analysis, revealed an exposed area on the Bet v 1 molecule (located between residues 9-22 and 104-123) as the IgE binding structure. The IgE epitope was located at a 30 A distance from a previously described IgG epitope and the respective mimotope, designated Bet mim E. Such mimotopes could potentially be used for the induction of IgG capable of interfering with the IgE/allergen interaction. To test this hypothesis, we immunized BALB/c mice with the phage-displayed Bet mim E. Immunizations resulted in the induction of Bet v 1-specific IgG, which was able to block the IgE binding to Bet v 1 in vitro. Based on these observations, we propose that immunotherapy with IgE mimotopes generated by biopannings result in formation of blocking IgG. We conclude that mimotope immunotherapy may represent a new and promising concept for treatment of type I allergic disease.

Rapid production of the major birch pollen allergen Bet v 1 in Nicotiana benthamiana plants and its immunological in vitro and in vivo characterization

Type I allergies are immunological disorders that afflict a quarter of the world's population. Improved diagnosis of allergic diseases and the formulation of new therapeutic approaches are based on the use of recombinant allergens. We describe here for the first time the application of a rapid plant-based expression system for a plant-derived allergen and its immunological characterization. We expressed our model allergen Bet v 1, the major birch pollen allergen, in the tobacco-related species Nicotiana benthamiana using a tobacco mosaic virus vector. Two weeks postinoculation, plants infected with recombinant viral RNA containing the Bet v 1 coding sequence accumulated the allergen to levels of 200 microg/g leaf material. Total nonpurified protein extracts from plants were used for immunological characterizations. IgE immunoblots and ELISA (enzyme-linked immunoassay) inhibition assays showed comparable IgE binding properties for tobacco recombinant (r) Bet v 1 and natural (n) Bet v 1, suggesting that the B cell epitopes were preserved when the allergen was expressed in N. benthamiana plants. Using a murine model of type I allergy, mice immunized with crude leaf extracts containing Bet v 1 with purified rBet v 1 produced in E. coli or with birch pollen extract generated comparable allergen-specific IgE and IgG1 antibody responses and positive type I skin test reactions. These results demonstrate that nonpurified Bet v 1 overexpressed in N. benthamina has the same immunogenicity as purified Bet v 1 produced in E. coli or nBet v 1. We therefore conclude that this plant expression system offers a viable alternative to fermentation-based production of allergens in bacteria or yeasts. In addition, there may be a broad utility of this system for the development of new and low-cost vaccination strategies against allergy.

Molecular and biochemical classification of plant-derived food allergens

Molecular biology and biochemical techniques have significantly advanced the knowledge of allergens derived from plant foods. Surprisingly, many of the known plant food allergens are homologous to pathogenesis-related proteins (PRs), proteins that are induced by pathogens, wounding, or certain environmental stresses. PRs have been classified into 14 families. Examples of allergens homologous to PRs include chitinases (PR-3 family) from avocado, banana, and chestnut; antifungal proteins such as the thaumatin-like proteins (PR-5) from cherry and apple; proteins homologous to the major birch pollen allergen Bet v 1 (PR-10) from vegetables and fruits; and lipid transfer proteins (PR-14) from fruits and cereals. Allergens other than PR homologs can be allotted to other well-known protein families such as inhibitors of alpha-amylases and trypsin from cereal seeds, profilins from fruits and vegetables, seed storage proteins from nuts and mustard seeds, and proteases from fruits. As more clinical data and structural information on allergenic molecules becomes available, we may finally be able to answer what characteristics of a molecule are responsible for its allergenicity.

Characterization of api g 1.0201, a new member of the Api g 1 family of celery allergens

BACKGROUND

The association of pollinosis with allergy to plant foods occurs in up to 70% of tree pollen-allergic patients. In recent years, some of the relevant cross-reacting proteins have been characterized at the molecular and immunological level. Api g 1 has been identified as the celery homologue of the major birch pollen allergen, Bet v 1. Although a number of Bet v 1 isoforms have been characterized from birch pollen, little is known about isoforms of food allergens and their allergenic features.

METHODS

Api g 1.0201, an isoform of Api g 1, was isolated from a cDNA library, cloned and sequenced. The cDNA was expressed in Escherichia coli and the purified recombinant protein was tested in immunoblots.

RESULTS

Api g 1.0201 displays 72% sequence similarity to the previously identified Api g 1.0101 and consists of 159 amino acid residues. The sequence of Api g 1.0201 has five additional amino acid residues at the carboxy-terminus as compared to Api g 1.0101. Purified recombinant Api g 1.0201 is recognized by IgE from the sera of celery-allergic patients, as well as by the murine monoclonal anti-Bet v 1 antibody. In general, this isoform displays a weaker IgE-binding capacity than Api g 1.0101, as concluded from immunoblotting experiments. Results from inhibition assays revealed that IgE-binding to Api g 1.0201 is only slightly reduced by preincubation with either purified recombinant Api g 1.0101 or purified recombinant Bet v 1a. Total inhibition was only achieved when using purified natural Bet v 1.

CONCLUSIONS

At present, little is known about the IgE-binding capacity of isoforms of Bet v 1 homologues of food allergens. Identification and characterization of such isoforms may help to contribute to a better understanding of food allergy and the observed cross-reactivity to pollen allergy.

Characterization of T cell responses to Hev b 3, an allergen associated with latex allergy in spina bifida patients

The prevalence of type I allergy to Hevea brasiliensis latex is particularly high among individuals with frequent exposure such as health care workers and patients with spina bifida (SB). Due to a birth defect of the spinal canal and the resulting neurological and orthopedic defects, these patients require multiple surgeries during childhood. SB patients display a unique pattern of sensitization: IgE-reactivity is preferentially directed against Hev b 3 and Hev b 1, two latex allergens with high sequence similarity. In this study, we analyzed the T cell response to Hev b 3 in latex-allergic SB patients using poly-, oligo-, and monoclonal T lymphocyte cultures. All T cell clones (TCC) were CD3/CD4-positive and expressed the alphabeta TCR. According to their cytokine production pattern (IL-4 vs IFN-gamma), 12 of 21 TCC were classified as Th2-like, 2 of 21 were Th1-like, and 7 of 21 belonged to a Th0-like subset. Using 11 T cell lines and 21 TCC, nine T cell stimulating fragments were determined out of 52 overlapping 12-mer peptides representing the complete amino acid sequence of Hev b 3. Ag presentation of one dominant T cell epitope could be associated with a four-amino acid binding motif (YSTS, position 11-13) in the beta 1 chain of HLA-DR molecules expressed by the respective patients. No reactivity was observed when Hev b 3-reactive T cell lines or TCC were incubated with peptides representing homologous parts of the Hev b 1 molecule, i.e., no cross-reactivity between Hev b 3 and Hev b 1 at the T cell level was evident.

N-terminal sequences of high molecular weight allergens from celery tuber

BACKGROUND

Celery tuber is an important source of food allergens. Low molecular weight celery allergens were identified as homologues of Bet v 1 and profilin. Little is known about the relevant allergens with molecular weights between 45 and 60 kDa, which cross-react with other plant food and pollen allergens.

OBJECTIVE

The aim of this study was to isolate cross-reactive, high molecular weight allergens from celery and to characterize them by N-terminal sequencing.

METHODS

High molecular weight allergens of celery were identified by immunoglobulin (Ig) E immunoblotting with patients' sera, and the IgE-binding patterns were compared with those of the monoclonal antibirch pollen antibody BIP3, as well as of a polyclonal rabbit anti-Art v 1 antiserum. Two independent methods, elution from preparative SDS-PAGE or anion exchange chromatography, were used to purify the IgE-binding celery proteins of interest. The isolated proteins were examined by N-terminal sequencing and IgE-immunoblots.

RESULTS

Celery allergens with molecular masses of 55, 58 and 63 kDa, which were also recognized by the monoclonal BIP3 antibody and a polyclonal anti-Art v 1 antiserum, were isolated. The 63-kDa allergen was N-terminally blocked. The 55- and 58-kDa compounds yielded the same N-terminus, which showed no homology to known proteins in the databases.

CONCLUSION

The combination of two independent protein separation techniques, immunoblotting and N-terminal sequencing, identified an N-terminus of two allergens in the 60-kDa molecular weight region. Our data will be helpful for the definite molecular characterization of these important cross-reactive molecules.

Skin prick test reactivity to recombinant latex allergens

BACKGROUND

Allergy to latex has become a serious and increasingly common health problem, particularly for healthcare workers and patients who undergo frequent surgical procedures. Testing for latex allergy currently involves in vitro tests and skin prick testing using crude preparations of natural rubber latex (NRL). To date, 10 latex proteins have received designation as allergens (Hev b 1 to Hev b 10) and, except for Hev b 4, have been cloned as recombinant proteins. Our aim was to compare the skin prick test (SPT) reactivity of six recombinant latex allergens with SPT reactivity to natural rubber latex proteins in known latex-allergic individuals.

METHODS

Six recombinant proteins were expressed in Escherichia coli, and tested as the intact fusion proteins (Hev b 2, 5, 6, 8) or as purified proteins (Hev b 3 and 7). SPT with the six recombinant latex allergens was performed using 10-fold serial dilutions on 31 latex-allergic subjects to determine the level of reactivity to each recombinant allergen. Latex-specific IgE was determined using the AlaSTAT assay.

RESULTS

All six recombinant allergens were reactive by SPT in at least 1 latex-allergic patient but not in any of the control patients. The frequency of sensitization to the various recombinant allergens was similar to previous studies using the native proteins isolated from NRL. The minimal level of protein for a positive skin test was 70 pg/ml for NRL and 1 ng/ml for one recombinant allergen (Hev b 7). In our patients, the use of a combination of recombinant latex allergens Hev b 5, 6 and 7 diagnosed latex allergy with 93% sensitivity and 100% specificity.

CONCLUSION

Recombinant latex allergens are clinically reactive, can be produced in a standardized manner, and could potentially provide safe, sensitive and specific reagents for the diagnosis of latex allergy.

Latex allergy in children

Natural rubber is a component of the latex of the tropical Hevea brasiliensis tree which is widely used in the manufacturing of medical devices and a large variety of articles for everyday use. Over a dozen allergens have been identified in the latex of H. brasiliensis. The allergens Hev b 1, Hev b 3, Hev b 6, and Hev b 7 are proteins that are involved in the biosynthesis of rubber or the coagulation of latex. Allergens that are part of the plant's defense system are represented by Hev b 2 and class I endochitinases. The allergens Hev b 4, Hev b 5, and Hev b 8-10 were classified as either structural or housekeeping proteins. Immediate-type hypersensitivity reactions to proteins present in Hevea latex were first described in 1927. Since then, natural rubber latex (NRL) allergy has become an important medical problem for an increasing number of individuals. Sensitization mainly occurs by wound or mucosal contact with NRL devices during surgery or by inhalation of airborne allergens released from powdered latex gloves. The number of surgical interventions and an atopic disposition are the most important risk factors for developing latex allergy, especially in children with spina bifida. Exposure to NRL products should be carefully avoided for individuals who belong to high-risk groups. Initial studies on establishing a latex-free environment for surgery in all spina bifida patients have reported on a decrease in sensitization and allergy to NRL.

Quantitative IgE inhibition experiments with purified recombinant allergens indicate pollen-derived allergens as the sensitizing agents responsible for many forms of plant food allergy

BACKGROUND

Type I allergic symptoms in the oropharyngeal mucosa upon contact with plant-derived food in patients with pollen allergies have been termed oral allergy syndrome (OAS). IgE cross-reactivity between pollen and food allergens represents the molecular basis for this phenomenon. The sensitizing allergen source (pollen or plant food) in OAS is a controversial issue.

OBJECTIVE

We sought to determine the primary sensitizing molecules in patients with OAS.

METHODS

We used recombinant birch pollen (rBet v 1 and rBet v 2) and plant food allergens (apple, rMal d 1; celery, rApi g 1; and carrot, rDau c 1), as well as natural pollen (birch and timothy grass) and plant food (apple, peach, kiwi, hazelnut, celery, and carrot) allergens, to identify cross-reactive allergens by using qualitative immunoblot inhibitions. In addition, we determined the percentage of plant food-specific IgE that can be preadsorbed with recombinant and natural pollen allergens by quantitative RAST inhibitions by using sera from 71 patients with OAS.

RESULTS

Preincubation of sera with recombinant and natural pollen allergens led to an almost complete inhibition of IgE binding to plant food allergens in Western blots, as well as in RAST inhibition experiments. In contrast, recombinant plant food allergens poorly inhibited IgE binding to Bet v 1.

CONCLUSION

Most IgE epitopes in plant food recognized by patients with OAS are resembled by pollen allergens. Thus pollen allergens may be responsible for the elicitation and maintenance of OAS.

Molecular and immunologic characterization of new isoforms of the Hevea brasiliensis latex allergen hev b 7: evidence of no cross-reactivity between hev b 7 isoforms and potato patatin and proteins from avocado and banana

BACKGROUND

Hev b 7 is a Hevea brasiliensis latex allergen with sequence identities of 39% to 42% to patatins recently identified as potato allergens. The complementary DNAs encoding 2 different Hev b 7 isoforms were previously reported.

OBJECTIVE

The aim of this study was to determine the sequence variation of Hev b 7 and to compare the IgE reactivity of individual isoforms in vitro and in vivo. A further objective was to evaluate possible cross-reactivities between Hev b 7 and patatins and proteins from banana and avocado.

METHODS

An H brasiliensis lambda ZAP complementary DNA (cDNA) library was screened with use of a Hev b 7 cDNA probe. Four Hev b 7 isoforms were produced in recombinant form and their IgE-binding capacities were compared. IgE immunoblot inhibitions and ELISA inhibition assays were used to investigate the possible cross-reactivity between Hev b 7 and recombinant potato patatin and proteins from avocado and banana.

RESULTS

Two new isoforms, S2 and D2, were identified by sequencing 32 cDNA clones with full-length coding regions. All 4 recombinant isoforms displayed esterase activity and identical IgE-binding capacities. The new isoforms S2 and D2 were evaluated in skin prick tests and provoked responses equivalent to natural Hev b 7. No cross-reactivity was observed between Hev b 7 isoforms and potato patatin and proteins from avocado and banana.

CONCLUSIONS

All 4 recombinant Hev b 7 isoforms have equivalent IgE-binding capacity and therefore represent suitable reagents for the development of in vitro and in vivo diagnostic tests. Hev b 7, patatins, and their homologs appear not to contribute to cross-reactivity in the latex-fruit syndrome.

Cloning, expression, and characterization of recombinant Hev b 3, a Hevea brasiliensis protein associated with latex allergy in patients with spina bifida

BACKGROUND

Two natural rubber latex proteins, Hev b 1 and Hev b 3, have been described in spina bifida (SB)-associated latex allergy.

OBJECTIVE

The aim of this study was to clone and express Hev b 3 and to obtain the immunologic active and soluble recombinant allergen for diagnosis of SB-associated latex allergy.

METHODS

A complementary DNA (cDNA) coding for Hev b 3 was amplified from RNA of fresh latex collected from Malaysian rubber trees (Hevea brasiliensis). PCR primers were designed according to sequences of internal peptide fragments of natural (n) Hev b 3. The 5'-end sequence was obtained by specific amplification of cDNA ends. The recombinant (r) Hev b 3 was produced in Escherichia coli as a 6xHis tagged protein. Immunoblotting and inhibition assays were performed to characterize the recombinant allergen.

RESULTS

An Hev b 3 cDNA clone of 922 bp encoding a protein of 204 amino acid residues corresponding to a molecular weight of 22.3 kd was obtained. In immunoblots 29/35, latex-allergic patients with SB revealed IgE binding to rHev b 3, as did 4 of 15 of the latex-sensitized group. The presence of all IgE epitopes on rHev b 3 was shown by its ability to abolish all IgE binding to nHev b 3. Hev b 3 is related to Hev b 1 by a sequence identity of 47%. Cross-reactivity between these 2 latex allergens was illustrated by the large extent of inhibition of IgE binding to nHev b 1 by rHev b 3.

CONCLUSION

rHev b 3 constitutes a suitable in vitro reagent for the diagnosis of latex allergy in patients with SB. The determination of the full sequence of Hev b 3 and the production of the recombinant allergen will allow the epitope mapping and improve diagnostic reagents for latex allergy.

Allergen mimotopes in food enhance type I allergic reactions in mice

BIP1is a murine IgG antibody capable of enhancing the IgE binding to Bet v 1, the major birch pollen allergen. We have previously generated a mimotope of BIP1, designated Bet mim 1, from a constrained phage display peptide library. We demonstrated that oral immunization of BALB/c mice with the Bet mim 1 mimotope resulted in the induction of Bet v 1-specific IgG. The aim of this study was to test the influence of such an oral immunization with Bet mim 1 on a subsequent type I allergic response to Bet v 1. Phages displaying Bet mim 1 or control mimotopes, or PBS alone, were delivered to BALB/c mice by intragastric gavages prior to systemic sensitization with recombinant Bet v 1 and Al(OH)(3), an adjuvant inducing preferentially IgE antibody responses. Only mice fed with Bet mim 1-phages displayed substantially enhanced type I allergic skin reactivity to Bet v 1, as compared to mice pretreated with control mimotopes or PBS. A gastric digestion assay indicated that Bet v 1 and its homologue from apple, Mal d 1, were degraded within seconds under physiological conditions. In contrast, phage-displayed mimotopes were resistant to digestion. Our data indicate that allergen mimics in the diet that resist digestion, can induce allergen specific IgG able to enhance an allergic response. We therefore conclude that sensitization via the oral route may represent a mechanism for aggravating type I allergic reactions, probably leading to an earlier onset of symptoms even at lower allergen dosage.

IgE reactivity to Api g 1, a major celery allergen, in a Central European population is based on primary sensitization by Bet v 1

BACKGROUND

Up to 70% of patients with tree pollen allergy display allergic symptoms when eating certain fruits and vegetables. Homologous proteins with allergenic features are present in a wide range of plant species and can cause allergic reactions.

OBJECTIVE

The aim of this study was to evaluate recombinant Api g 1, a major celery allergen, for in vivo and in vitro diagnosis of celery allergy in populations from Davos, Switzerland, and Montpellier, France.

METHODS

A group of patients with celery and birch pollen allergy from Davos was tested, and the results from those tests were compared with results from a group of patients allergic to celery from Montpellier. Skin prick tests were performed with a commercial celery extract, crude celery, and purified recombinant Api g 1. Quantitative and qualitative serology was done with natural and recombinant allergens by means of RASTs and immunoblotting.

RESULTS

Recombinant Api g 1 allowed accurate in vivo diagnosis of celery allergy in all patients from the Swiss group. RAST results with celery extract were negative in 8 of 24 patients; results of immunoblotting with celery extract were negative in 4 of 24 patients, and results of immunoblotting with recombinant (r)Api g 1 were negative in 8 of 24 patients. In the French group 11 of 12 patients had a positive skin reaction with crude celery extract, but only 2 patients reacted with rApi g 1. RAST results for celery were positive in 8 of 12 patients. In immunoblotting experiments 8 patient sera displayed IgE directed against various celery allergens, whereas no patients sera had rApi g 1-specific IgE.

CONCLUSION

Our results document that rApi g 1 allows accurate in vivo diagnosis only in areas where birch trees are common. In areas where no birch trees grow, primary sensitization takes place through different pollen allergens (eg, mugwort pollen). Moreover, it became evident that birch pollen and celery allergy are highly related in Central Europe, whereas in Southern Europe the mugwort-celery type is predominant.

New Bet v 1 isoforms including a naturally occurring truncated form of the protein derived from Austrian birch pollen

Bet v 1, the major pollen allergen from white birch, displays a considerable degree of heterogeneity. Until now, all molecular and immunological characterization studies of Bet v 1 isoforms have been performed with commercially available pollen of Swedish origin. In regard to clinical studies with Austrian birch pollen allergic individuals, knowledge about the isoform repertoire in Austrian birch pollen was necessary. cDNAs coding for Bet v 1 isoforms from Austrian birch pollen were cloned by PCR amplification and sequenced. Besides the Austrian variants of the Swedish isoforms Bet v 1a (62% of the clones), ALK167 (4%), and Bet v 1d/h, Bet v 1g, and Bet v 11 (24%), three sequences with a significantly lower homology to known isoforms and two Bet v 1a-homologous sequences with a 7 bp insertion coding for a truncated protein were detected. No Austrian variants of the majority of the Swedish isoforms were found. The isoforms coding for truncated proteins were expressed in Escherichia coli and tested by immunoblotting. They bound a polyclonal anti-Bet v 1 antibody but did not recognize birch pollen allergic patients' serum IgE and two Bet v 1-specific monoclonal antibodies. The similarity of the Bet v 1 isoform patterns of Swedish and Austrian birch pollen justifies the use of Bet v 1 derived from Swedish pollen for clinical studies with birch pollen allergic individuals from outside Northern Europe.

Isolation, characterization, and functional analysis of a novel cDNA clone encoding a small rubber particle protein from Hevea brasiliensis

Biochemical evidence reported so far suggests that rubber synthesis takes place on the surface of rubber particles suspended in the latex of Hevea brasiliensis. We have isolated and characterized a cDNA clone that encodes a protein tightly bound on a small rubber particle. We named this protein small rubber particle protein (SRPP). Prior to this study, this protein was known as a latex allergen, and only its partial amino acid sequence was reported. Sequence analysis revealed that this protein is highly homologous to the rubber elongation factor and the Phaseolus vulgaris stress-related protein. Southern and Northern analyses indicate that the protein is encoded by a single gene and highly expressed in latex. An allergenicity test using the recombinant protein confirmed that the cloned cDNA encodes the known 24-kDa latex allergen. Neither ethylene stimulation nor wounding changed the transcript level of the SRPP gene in H. brasiliensis. An in vitro rubber assay showed that the protein plays a positive role in rubber biosynthesis. Therefore, it is likely that SRPP is a part of the rubber biosynthesis machinery, if not the rubber polymerase, along with the rubber elongation factor.

Molecular characterization of Dau c 1, the Bet v 1 homologous protein from carrot and its cross-reactivity with Bet v 1 and Api g 1

BACKGROUND

Up to 70% of patients with birch pollen allergy exhibit the so-called oral allergy syndrome, an IgE-mediated food allergy. The most frequent and therefore best characterized pollen-fruit syndrome is apple allergy in patients suffering from tree pollen-induced pollinosis. The occurrence of adverse reactions to proteins present in vegetables such as celery and carrots in patients suffering from pollen allergy has also been reported. cDNAs for Bet v 1 homologous proteins have been cloned from celery, apple and cherry. Objective The aim of the study was to identify Bet v 1 homologues from carrot (Daucus carota), to isolate the respective cDNA, to compare the IgE-binding capacity of the natural protein to the recombinant allergen and determine the cross-reactivity to Api g 1 and Bet v 1.

METHODS

Molecular characterization of the carrot allergen was performed using IgE-immunoblotting, cross-inhibition assays, N-terminal sequencing, PCR-based cDNA cloning and expression of the recombinant protein in Escherichia coli.

RESULTS

A 16-kDa protein from carrot was identified as a major IgE-binding component and designated Dau c 1. Sequencing corresponding cDNAs revealed three extremely similar sequences (Dau c 1.1, 1.2 and 1.3) with an open reading frame of 462 bp coding for 154 amino acid residues.

CONCLUSIONS

Purified recombinant Dau c 1.2 was tested in immunoblots displaying IgE-binding capacity comparable to its natural counterpart. Cross-inhibition assays verified the existence of common B-cell epitopes present on Dau c 1, Api g 1 as well as on Bet v 1.

Identification of a highly promiscuous and an HLA allele-specific T-cell epitope in the birch major allergen Bet v 1: HLA restriction, epitope mapping and TCR sequence comparisons

BACKGROUND

Allergen-specific CD4+ T cells play an important regulatory role in atopic allergy.

OBJECTIVE

To investigate the human leucocyte antigen (HLA) restriction and T-cell receptor (TCR) usage of allergen-specific T-cell clones (TCCs) that react with defined epitopes of Bet v 1, the major birch pollen allergen.

METHODS

Five Bet v 1-specific TCCs derived from two birch pollen-allergic individuals and specific for Bet v 1, were epitope-mapped with overlapping synthetic peptides. In addition, HLA-restriction and TCR CDR3 sequences were determined.

RESULTS

Three TCCs reacted with a Bet v 1 peptide containing amino acid residues 21-33 (BP21), the other two TCCs reacted with a minimal peptide comprising residues 37-45 (BP37). Studies using neutralizing anti-HLA-monoclonal antibodies and HLA-typed APCs showed that the BP37-specific TCCs were restricted by a HLA-DQA1*0301/DQB1*0603 heterodimer. In contrast, BP21 was recognized in a highly promiscuous manner. TCCs recognizing this sequence were restricted by HLA-DPB1*0201, a HLA-DQA1*0201/DQB1*0201 heterodimer, or HLA-DRB3*0101. Reverse transcription-polymerase chain reaction with primers for all known TCRAV and TCRBV gene segments, followed by CDR3 region sequencing, revealed the usage of five different TCRAV and four different TCRBV gene segments by the TCCs, as well as diversity in the joining region. All BP21-specific TCCs contained a negatively charged residue in their CDR3alpha regions, the CDR3beta regions showed a high concentration of polar and OH-group bearing residues. BP37-specific TCCs shared the amino acid combination LY in the middle of their CDR3alpha regions, the CDR3beta regions showed high concentration of OH-group bearing or charged residues.

CONCLUSIONS

This study shows the existence of a highly promiscuous T-cell epitope in Bet v 1. The presence of additional T-cell epitopes in Bet v 1 may, however, hamper the clinical applicability of the epitope. Likewise, the diversity in TCR usage by T cells recognizing the epitope does not support the development of TCR-directed immunotherapy for birch pollen allergy.

Cloning of the patatin-like latex allergen Hev b 7, its expression in the yeast Pichia pastoris and its immunological characterization

The 43-kD latex allergen Hev b 7 was purified from the latex of Hevea brasiliensis and identified by N-terminal and internal peptide sequences as highly homologous to patatins. Patatins are storage proteins encoded by a multigene family found in plants such as potato and tomato. We have obtained a cDNA clone coding for a cytoplasmic form of Hev b 7. The recombinant protein was expressed in the methylotrophic yeast Pichia pastoris at 10 mg/l culture supernatant. Both natural Hev b 7 and rHev b 7 were recognized by IgE in 11% of the latex-allergic patients. rHev b 7 inhibited binding to its counterpart in natural rubber latex extracts. Purified rHev b 7 used at concentrations of 10 micrograms/ml in skin prick tests produced wheal-and-flare reactions of sizes equal to those produced by nHev b 7. Furthermore, we were able to show that rHev b 7 possessed esterase activity. A plant expression system for the production of larger quantities of recombinant latex allergens as an alternative to the preparation from H. brasiliensis sap is discussed.

The importance of recombinant allergens for diagnosis and therapy of IgE-mediated allergies

In the past 10 years, a considerable number of cDNAs coding for allergens have been isolated and expressed. Intensive investigations showed that recombinant allergens and their respective natural counterparts possess comparable properties with respect to structure, function and interaction with the immune system. Recent studies documented that in vitro as well as in vivo diagnosis of IgE-mediated allergic diseases can be successfully improved by the application of recombinant allergens. In addition, new strategies for a safer specific immunotherapy (SIT) have been developed based on the knowledge of the primary structures of allergens. Naturally occurring isoforms of allergens as well as recombinant allergens with modified amino acid sequences show very low IgE binding capacity but strong T cell-stimulatory activity and represent possible candidates. In case of Bet v 1, the major birch pollen allergen, isoforms d, g and l and a Bet v 1a mutant, produced by site-directed mutagenesis resulting in 6 amino acid exchanges, fulfilled the above mentioned criteria. In a third approach, two adjacent peptides covering the entire Bet v 1a sequence were produced in an Escherichia coli expression system. These peptides contained most of the relevant T cell epitopes, but lost their IgE binding capacity and, thus, their ability to activate mast cells and basophils of sensitized patients. Our results suggest that allergen variants (isoforms, mutants, T cell epitope-containing peptides) may be used as 'hypoallergenic agents' in SIT.

Peptide mimotopes displayed by phage inhibit antibody binding to bet v 1, the major birch pollen allergen, and induce specific IgG response in mice

The major birch pollen allergen Bet v 1 is one of the most extensively characterized allergens both on the molecular and the immunological level. To define conformational B cell epitopes on Bet v 1, we screened filamentous phage libraries expressing circular or linear nonapeptides to select ligands specific for anti-Bet v 1 murine monoclonal antibodies BIP1 and BIP4. The deduced amino acid sequence of the BIP1 ligand was CFPYCYPSESA, and of the BIP4-ligand, CRQTRTMPGC. Both sequences derived from the circular phage library. Alignments to the sequence of Bet v 1 showed no similarities, indicating that the antibodies most likely recognize discontinuous epitopes. Phages displaying these mimotopes were capable of inhibiting interactions of the anti-Bet v 1 monoclonals with Bet v 1 in a dose-dependent manner in ELISA. In contrast, sequence-identical synthetic peptides were ineffective in blocking the antibody-allergen interactions. This is in agreement with the conformational inhomogeneity of the peptides in solution as observed by nuclear magnetic resonance spectroscopy. Intragastric administration of phages expressing the BIP1 mimotope induced a Bet v 1-specific IgG response in Balb/c mice. We conclude that peptide mimotopes, when displayed on phages, may induce a protective IgG response preventing IgE-mediated allergic reactions, suggesting a possible clinical application.