Cloning, sequencing and expression in Escherichia coli of Pha a 1 and four isoforms of Pha a 5, the major allergens of canary grass pollen

EAACI Molecular Allergology User's Guide 2.0

Since the discovery of immunoglobulin E (IgE) as a mediator of allergic diseases in 1967, our knowledge about the immunological mechanisms of IgE-mediated allergies has remarkably increased. In addition to understanding the immune response and clinical symptoms, allergy diagnosis and management depend strongly on the precise identification of the elicitors of the IgE-mediated allergic reaction. In the past four decades, innovations in bioscience and technology have facilitated the identification and production of well-defined, highly pure molecules for component-resolved diagnosis (CRD), allowing a personalized diagnosis and management of the allergic disease for individual patients. The first edition of the "EAACI Molecular Allergology User's Guide" (MAUG) in 2016 rapidly became a key reference for clinicians, scientists, and interested readers with a background in allergology, immunology, biology, and medicine. Nevertheless, the field of molecular allergology is moving fast, and after 6 years, a new EAACI Taskforce was established to provide an updated document. The Molecular Allergology User's Guide 2.0 summarizes state-of-the-art information on allergen molecules, their clinical relevance, and their application in diagnostic algorithms for clinical practice. It is designed for both, clinicians and scientists, guiding health care professionals through the overwhelming list of different allergen molecules available for testing. Further, it provides diagnostic algorithms on the clinical relevance of allergenic molecules and gives an overview of their biology, the basic mechanisms of test formats, and the application of tests to measure allergen exposure.

Sensitization Profiles of Timothy Grass Pollen in Northern China

Purpose

Grass pollen is an important cause of IgE-mediated allergy in countries worldwide, especially within Europe. However, there has been no research on grass pollen allergy in northern China. We aimed to determine the status of grass pollen allergy and the sensitization patterns to Phleum pratense (P. pratense) in northern China.

Patients and Methods

Pollen data were collected for three geographic areas (Beijing, Shenmu, Shizuishan) in northern China. The study enrolled 101 patients (62 men; age range, 1–64 years; median age, 10 years) who had allergic rhinoconjunctivitis and/or asthma during the grass pollen season and positive skin prick test results positive to P. pratense. Serum-specific IgE (sIgE) against Phl p 1, Phl p 2, Phl p 5, Phl p 6, Phl p 7, Phl p 12 was measured by ImmunoCAP.

Results

The pollen season of P. pratense was from June to September in Beijing, May to September in Shenmu and July to August in Shizuishan. P. pratense pollen accounted for 2–3% of the annual pollen index of total pollen counts. Among 101 patients with positive skin prick test results to P. pratense, 72% had detectable sIgE to P. pratense. Phl p 12 was the most frequently recognized component (45%), followed by Phl p 1 (22%), Phl p 5 (14%), Phl p 6 (8%) and Phl p 7 (3%). No patients had sIgE to Phl p 2. Ten sensitization patterns to the six components were observed. High rate of sIgE to Phl p 12 was positively correlated with co-sensitization to weed or tree pollen.

Conclusion

Considering the pollen concentration, P. pratense was a minor pollen allergen in northern China and its pollen season overlapped with that of weed pollen. IgE sensitization to P. pratense was likely to be induced by cross-reactivity between grass pollen allergy and weed/tree pollen allergy.

EAACI Molecular Allergology User's Guide

The availability of allergen molecules ('components') from several protein families has advanced our understanding of immunoglobulin E (IgE)-mediated responses and enabled 'component-resolved diagnosis' (CRD). The European Academy of Allergy and Clinical Immunology (EAACI) Molecular Allergology User's Guide (MAUG) provides comprehensive information on important allergens and describes the diagnostic options using CRD. Part A of the EAACI MAUG introduces allergen molecules, families, composition of extracts, databases, and diagnostic IgE, skin, and basophil tests. Singleplex and multiplex IgE assays with components improve both sensitivity for low-abundance allergens and analytical specificity; IgE to individual allergens can yield information on clinical risks and distinguish cross-reactivity from true primary sensitization. Part B discusses the clinical and molecular aspects of IgE-mediated allergies to foods (including nuts, seeds, legumes, fruits, vegetables, cereal grains, milk, egg, meat, fish, and shellfish), inhalants (pollen, mold spores, mites, and animal dander), and Hymenoptera venom. Diagnostic algorithms and short case histories provide useful information for the clinical workup of allergic individuals targeted for CRD. Part C covers protein families containing ubiquitous, highly cross-reactive panallergens from plant (lipid transfer proteins, polcalcins, PR-10, profilins) and animal sources (lipocalins, parvalbumins, serum albumins, tropomyosins) and explains their diagnostic and clinical utility. Part D lists 100 important allergen molecules. In conclusion, IgE-mediated reactions and allergic diseases, including allergic rhinoconjunctivitis, asthma, food reactions, and insect sting reactions, are discussed from a novel molecular perspective. The EAACI MAUG documents the rapid progression of molecular allergology from basic research to its integration into clinical practice, a quantum leap in the management of allergic patients.

Characterization of allergens isolated from the freshwater fish blunt snout bream (Megalobrama amblycephala)

Fish are an important source of dietary protein for humans throughout the world. However, they are recognized as one of the most common food allergens and pose a serious health problem in countries where fish consumption is high. Many marine fish allergens have been extensively studied, but relatively little is known about freshwater fish allergens. This study identified two main allergens from blunt snout bream (Megalobrama amblycephala), a freshwater fish widely consumed in China. Sera from 11 patients with convincing clinical history of blunt snout bream allergy were utilized in IgE immunoblot analysis to identify prominent allergens. Several blunt snout bream proteins revealed specific binding to serum IgE, with the 47 and 41 kDa proteins being the most immunodominant among them. Two-dimensional gel electrophoresis (2D SDS-PAGE) enabled resolution of the 47 and 41 kDa proteins into several protein spots with distinct isoelectric points. 2D SDS-PAGE along with IgE immunoblot analysis further confirmed the strong reactivity of these protein spots with the pooled sera from blunt snout bream-sensitive patients. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of the peptides generated by trypsin digestion of the different spots corresponding to the 47 and 41 kDa proteins indicated that these spots were isoforms of enolase and muscle creatine kinase, respectively. The potential allergenicity of these proteins was further verified by an bioinformatics approach using the full-length and 80 amino acid sliding window FASTA searches, which revealed a significant amino acid sequence homology between blunt snout bream allergens and several known inhaled and crustacean allergens.

Mapping of IgE-binding regions on recombinant Cyn d 1, a major allergen from Bermuda Grass Pollen (BGP)

Background

Bermuda grass (Cynodon dactylon; subfamily Chloridoideae) is an important source of seasonal aeroallergens in warm tropical and sub-tropical areas worldwide. Improved approaches to diagnosis and therapy of allergic diseases require a thorough understanding of the structure and epitopes on the allergen molecule that are crucial for the antigen-antibody interaction. This study describes the localization of the human IgE-binding regions of the major group 1 pollen allergen Cyn d 1 from Bermuda grass.

Methods

A cDNA library was constructed from Bermuda grass pollen (BGP) using a Lambda gt11 expression vector. The gene encoding the Cyn d 1 allergen was isolated by screening the library with a mouse monoclonal antibody raised against grass group 1 allergen. In order to characterize the IgE epitopes on Cyn d 1, seven overlapping fragments and three deletion mutants were cloned and over-expressed in E. coli. The recombinant fragments and deletion mutants were evaluated for their comparative IgE reactivity with sera of non atopic individuals and grass pollen allergic patients by ELISA and a dot-blot assay.

Results

Analysis of IgE binding regions by overlapping fragments and deletion mutants identified two major allergenic regions corresponding to amino acids 120–170 and 224–244. Deletion of either or both regions led to a significant reduction in IgE binding, emphasizing the importance of the C-terminal region on Cyn d 1 in epitope-IgE interaction.

Conclusion

Anti-Cyn d 1 IgE antibodies from allergic human sera recognize two epitopes located at the C-terminal end of the molecule. These data will enable the design of improved diagnostic and therapeutic approaches for BGP hypersensitivity.

Immunology

The concept of forbidden foods that should not be eaten goes back to the Garden of Eden and apart from its religious meanings it may also have foreshadowed the concept of foods that can provoke adverse reactions. Thus we could say that allergic diseases have plagued mankind since the beginning of life on earth. The prophet Job was affected by a condition that following the rare symptoms described by the Holy Bible might be identified as a severe form of atopic dermatitis (AD). The earliest record of an apparently allergic reaction is 2621 B.C., when death from stinging insects was first described by hieroglyphics carved into the walls of the tomb of Pharaoh Menes depicting his death following the sting of a wasp. In 79 A.D., the death of the Roman admiral Pliny the Elder was ascribed to the SO₂-rich gases emanating from the eruption of Mount Vesuvius. Hippocrates (460–377 B.C.) was probably the first to describe how cow’s milk (CM) could cause gastric upset and hives, proposing dietetic measures including both treatment and prevention for CM allergy.

The Major Grass Pollen Group 5 Allergen from Dactylis glomerata and Its C-Terminal Split Product Both Behave as Dimers: Implications for Allergen Standardization

BACKGROUND

On SDS-PAGE grass pollen group-5 allergens migrate as a doublet with an apparent molecular mass (M(r)) of 25 kDa. Immunoblot analysis revealed additional group 5 reactivity at double and half this M(r). The aim of this study was to investigate these group 5 molecular entities and to compare their allergenicity and behavior in quantitative immunoassays.

METHODS

Group-5-specific monoclonal antibodies were produced and used for the development of a group-5-specific sandwich ELISA. Affinity-purified Dac g 5 was separated by SDS-PAGE/Western blotting; individual bands were analyzed by N-terminal sequencing. Size exclusion chromatography (SEC) in conjunction with group-5-specific ELISA, competitive RIA and RAST inhibition were used to analyze the size distribution of Dac g 5. Basophil histamine release assays were used to assess biological activity.

RESULTS

The lower band of the typical group 5 doublet was identified as a truncated form lacking the typical group 5 N-terminus AD(L)/(A)GY, observed in the upper band. The 12-kDa peptide was shown to be the C-terminal half of Dac g 5 (amino acid 127 onwards). SEC in conjunction with competitive RIA revealed that around 45% of Dac g 5 is represented by the 12-kDa peptide. Both the C-terminal half and the whole allergen dimerize under nondenaturing conditions. In competitive RIA and RAST inhibition both forms are equally well detected. In contrast, the half molecule is poorly recognized in sandwich ELISA and displays negligible biological activity in basophil histamine release tests with purified IgE.

CONCLUSIONS

These observations stress the need to evaluate the performance of allergen standardization protocols in detail, with special attention to allergen size distribution.

Gain of structure and IgE epitopes by eukaryotic expression of the major Timothy grass pollen allergen, Phl p 1

Approximately 400 million allergic patients are sensitized against group 1 grass pollen allergens, a family of highly cross-reactive allergens present in all grass species. We report the eukaryotic expression of the group 1 allergen from Timothy grass, Phl p 1, in baculovirus-infected insect cells. Domain elucidation by limited proteolysis and mass spectrometry of the purified recombinant glycoprotein indicates that the C-terminal 40% of Phl p 1, a major IgE-reactive segment, represents a stable domain. This domain also exhibits a significant sequence identity of 43% with the family of immunoglobulin domain-like group 2/3 grass pollen allergens. Circular dichroism analysis demonstrates that insect cell-expressed rPhl p 1 is a folded species with significant secondary structure. This material is well behaved and is adequate for the growth of crystals that diffract to 2.9 A resolution. The importance of conformational epitopes for IgE recognition of Phl p 1 is demonstrated by the superior IgE recognition of insect-cell expressed Phl p 1 compared to Escherichia coli-expressed Phl p 1. Moreover, insect cell-expressed Phl p 1 induces potent histamine release and leads to strong up-regulation of CD203c in basophils from grass pollen allergic patients. Deglycosylated Phl p 1 frequently exhibits higher IgE binding capacity than the recombinant glycoprotein suggesting that rather the intact protein structure than carbohydrate moieties themselves are important for IgE recognition of Phl p 1. This study emphasizes the important contribution of conformational epitopes for the IgE recognition of respiratory allergens and provides a paradigmatic tool for the structural analysis of the IgE allergen interaction.

Recombinant allergens for analysing T-cell responses

T-cell responses constitute a central element of allergic disease and a model for studying Th1 and Th2 cytokine pathways. Most studies to date have used extracts of allergens which contain variable quantities of different allergens and non-allergenic antigens. Recombinant allergens provide the tools for studying the responses to allergens in a reproducible and dose-dependent manner and the different T-cell responses of allergic and non-allergic subjects provide a method for verifying the responses and their relationship to allergic sensitisation. Most allergies show dominant responses to one or a few major allergens. These allergens have been described for the common allergies and have been produced as recombinant allergens. A particular problem for allergens is that many are mixtures of proteins from multi-gene families or are highly polymorphic. Information now exists so the sequence variation can be represented. Purified recombinant allergens produced by standard expression systems stimulate the expected T-cell responses from the peripheral blood of allergic and non-allergics to allergen extracts. Although stimulation with recombinant allergens which are not produced with a natural IgE binding activity can provide a measure of allergenicity, the altered tertiary structure can reduce Th2 responses. The sequence information now available provides the means to use PCR to produce cDNA for the production of recombinant allergens from readily available sources. The production of the highly reactive recombinant Der p 2 allergen of house dust mite from natural sources is described.

Genetic variation of Der p 2 allergens: effects on T cell responses and immunoglobulin E binding

BACKGROUND

Der p 2 is a highly polymorphic allergen that shows a distinct pattern of sequence divergence. The effect of the variations on T cell and antibody responses has not been compared.

OBJECTIVES

To compare IgE antibody binding and T cell proliferation and cytokine release induced by variants of Der p 2.

METHODS

Peripheral blood mononuclear cells (PBMC) from 19 allergic and 15 non-allergic people were stimulated with recombinant variants of Der p 2. IL-5, IL-10, IL-13 and IFN-gamma were measured by a time resolved fluorescence (TRF) assay. Serum IgE antibody was measured using a solid-phase TRF assay.

RESULTS

Overall the most prevalent variant of Der p 2 (Der p 2. 0101) was the highest or approximately equal highest inducer of T cell proliferation and IL-5, IL-10, IL-13 and IFN-gamma release. The most divergent variant 0104 induced the next highest responses. The variants 0107 and 0108 showed interesting changes especially when the allergic status was considered. Responses to 0107 showed poor Th1/Th2 polarization and, except for IL-10 release, cytokine responses to 0108 were low for non-allergic subjects. The variant 0101 showed similar monoclonal antibody binding but moderately less IgE binding than the other variants.

CONCLUSIONS

The most prevalent variant, Der p 2. 0101, was the most active for T cell stimulation and although its IgE binding was slightly less than other variants that was highly correlated. The variant Der p 2. 0104 which contains the known common polymorphic changes had a response which was similar to Der p 2. 0101 and thus these two variants were the most stimulatory representations of Der p 2. The T cell responses to the less common variants 0107 and 0108 however, showed consistent differences demonstrating that changes in the sequence could change the cytokine response.

Molecular cloning and sequence analysis of full-length cDNAs encoding new group of Cyn d 1 isoallergens

BACKGROUND

Cyn d 1, the major allergen of Bermuda grass pollen, contains some acidic/basic isoforms. The N-terminal amino acid sequences of some acidic Cyn d 1 isoforms were found to be different from those of Cyn d 1 cDNA clones identified previously.

METHODS

A predicted 17-meric oligonucleotide probe was designed to fish the unidentified isoallergen cDNAs out of BGP cDNA library. The reactive clones were isolated and verified by sequencing. Two of them were expressed in the yeast Pichia pastoris to obtain recombinant Cyn d 1 proteins.

RESULTS

All four cDNA clones encode the full-length Cyn d 1 with mature proteins of 244 amino acid residues. A 97-99% identity was found among the deduced amino acids of these four clones while an 86% identity was elicited between the four clones and the ones previously identified. The predicted isoelectric focusing (pI) values of the newly identified Cyn d 1s are acidic while pIs of the previously identified Cyn d 1s are basic. The two recombinant acidic Cyn d 1 proteins possess the epitopes recognized by mouse and rabbit polyclonal anti-Cyn d 1 antibodies, and have human IgE-binding capacity as revealed by immunodot assay.

CONCLUSIONS

The present study identified full-length cDNAs encoding new isoallergens of Cyn d 1, and separated Cyn d 1 gene into an acidic group and a basic group.

Allergens of wild house dust mites: environmental Der p 1 and Der p 2 sequence polymorphisms

BACKGROUND

Sequence diversity is a common feature of mite allergens. Previous studies, using predominantly commercial mite clones, have described several polymorphic residues for Der p 1 and Der p 2.

OBJECTIVE

This study aimed at determining the occurrence of sequence diversity in environmental mite isolates.

METHODS

Mites were isolated from houses in Perth and Sydney, Australia. Total RNA was extracted from 1 to 30 Perth mites, and cDNA was synthesized by reverse transcriptase PCR. Der p 1 and Der p 2 cDNAs were PCR amplified and sequenced. Genomic Der p 1 DNA was amplified from whole Sydney mites directly by PCR and then sequenced.

RESULTS

Twelve Der p 1 and 9 Der p 2 cDNA clones and 3 Der p 1 genomic DNA were analyzed and showed a high frequency of amino acid polymorphisms. Der p 2 displayed a clear pattern of divergence toward 2 alleles that differed by 4 amino acids and had characteristic silent nucleotide changes. The pattern for Der p 1 was different and unusual, with almost no silent nucleotide substitutions but frequent sporadic missense changes. Proliferative responses of peripheral blood mononuclear cells to peptides containing polymorphic residues of Der p 1 were detected in 8 of 19 subjects, with stimulation being found only for either one of the variant forms of the peptides. However, the responses to variants of whole recombinant allergens were similar, as shown for 4 variants of Der p 2.

CONCLUSION

Two clones for each of the allergens were identified as containing sequences that were largely representative of environmental isolates. A small-scale reverse transcriptase PCR used to produce cDNA from individual mites isolated from house dust will have wide application for studies on mite genetics and the production of recombinant mite allergens. Differences in T-cell responses to peptides representing variant epitopes were found, but responses to variants of whole recombinant allergens were similar. The GenBank and Swiss Prot database entries for Der p 1 (U11695) and Der p 2 (P49278) have been updated with the inclusion of the sequence polymorphisms described in this study.

Isolation of total RNA from pollens

Isolation of total RNA from plant materials has been difficult, due to the presence of complex organic substances and the associated pigmentation. In fact, there is a dearth of standardized protocols for isolating total RNA from pollens. To find a simple and reliable method for isolating total RNA from pollen, four methods, viz. phenol/SDS (PS), guanidine HCl (GH), tri-reagent (TR), and modified SDS-betaME (SB) were tested with fresh pollen of Ricinus communis (procured at -70 degrees C) and pollen dried at 30-37 degrees C. The quality and quantity of RNA was superior for the material processed at -70 degrees C. SB gave the highest RNA yield (2.35 mg/g, OD260/280 >2.0), compared to other methods. The results obtained by the SB method were found to be comparable with the widely used tri-reagent method. This was validated with other pollens of Imperata cylindrica and Xanthium strumarium. The yield obtained from graded amounts of pollen was consistent with SB, compared to the TR method. The RNA isolated by SB gave good quality mRNA for synthesizing cDNA. The SDS-betaME method is simple, efficient, and uses less expensive reagents. Hence, we recommend the modified SDS-betaME method for isolating total RNA from pollens.

Molecular cloning, expression and immunological characterisation of Lol p 5C, a novel allergen isoform of rye grass pollen demonstrating high IgE reactivity

A novel isoform of a major rye grass pollen allergen Lol p 5 was isolated from a cDNA expression library. The new isoform, Lol p 5C, shares 95% amino acid sequence identity with Lol p 5A. Both isoforms demonstrated shared antigenic activity but different allergenic activities. Recombinant Lol p 5C demonstrated 100% IgE reactivity in 22 rye grass pollen sensitive patients. In comparison, recombinant Lol p 5A showed IgE reactivity in less than 64% of the patients. Therefore, Lol p 5C represents a novel and highly IgE-reactive isoform allergen of rye grass pollen.

B cell epitopes of the major timothy grass pollen allergen, phl p 1, revealed by gene fragmentation as candidates for immunotherapy

Group 1 grass pollen allergens are recognized by IgE antibodies of almost 40% of allergic individuals and therefore belong to the most important elicitors of Type I allergy worldwide. We have previously isolated the cDNA coding for the group 1 allergen from timothy grass, Phl p 1, and demonstrated that recombinant Phl p 1 contains most of the B cell as well as T cell epitopes of group 1 allergens from a variety of grass and corn species. Here we determine continuous B cell epitopes of Phl p 1 by gene fragmentation. IgE antibodies of grass pollen allergic patients identified five continuous epitope-containing areas that on an average bound 40% of Phl p 1-specific IgE antibodies and were stably recognized in the course of disease. In contrast to untreated patients, patients undergoing grass pollen immunotherapy started to mount IgG(4) antibodies to the recombinant IgE-defined fragments in the course of immunotherapy. The protective role of these IgG(4) antibodies is demonstrated by observations that 1) increases in rPhl p 1 fragment-specific IgG(4) were in parallel with decreases in Phl p 1-specific IgE, and 2) preincubation of rPhl p 1 with patients sera containing rPhl p 1 fragment-specific IgG(4) blocked histamine release from basophils of an untreated grass pollen allergic patient. We propose to use recombinant Phl p 1 fragments for active immunotherapy in order to induce protective IgG responses against IgE epitopes in grass pollen allergic patients. This concept may be applied for the development of allergy vaccines whenever the primary sequence or structure of an allergen is available.

Subtribe-specific monoclonal antibodies to Lolium perenne

BACKGROUND AND OBJECTIVES

The ability to measure personal exposure to airborne grass pollen is important in the understanding of allergic diseases. Visual identification is time consuming and it is difficult to distinguish between many grass pollens morphologically. Although grass pollens share common allergenic determinants, we attempted to produce monoclonal antibodies that would distinguish between species, tribes and subfamilies of grasses which would allow immunodetection of pollens.

METHODS

Monoclonal antibodies raised against Lolium perenne were screened for specificity against an extended panel of grass pollen extracts using standard ELISA techniques and a novel particle blotting assay using whole pollen grains.

RESULTS

Antibodies showing specificity ranging from subfamily to part-tribe specificity were raised. The most specific monoclonal antibodies (numbers 4, 13 and 17) had reactivity to Lolium perenne and Festuca elatior but displayed little cross-reactivity to Phalaris arundinaceae and the rest of the Poeae tribe when tested by ELISA and no detectable cross-reaction when tested with particle blotting.

CONCLUSION

Monoclonal antibodies that are functionally specific to only two grasses can be produced and used to discriminate between related grass species.

Sequence polymorphism of the group 1 allergen of Bermuda grass pollen

BACKGROUND

Cyn d 1, the major allergen of Bermuda grass pollen, consists of a number of isoforms.

OBJECTIVE

To examine the extent of sequence variation of Cyn d 1 isoforms at the molecular level.

METHODS

A Bermuda grass pollen lambdaZAP II cDNA expression library was immunoscreened with anti-Cyn d 1 monoclonal antibodies. The reactive clones were isolated, subcloned into Escherichia coli, and sequenced. Some of them were expressed in the yeast Pichia pastoris to obtain recombinant Cyn d 1 proteins.

RESULTS

Ten cDNA clones were obtained, all these clones encode the full length of Cyn d 1 protein. Their deduced mature proteins can be grouped into: the long ones with 246 amino acids, and the short ones with 244 amino acids. The last two amino acids (AG) of the long Cyn d 1 are deleted in the short Cyn d 1. The remaining amino acid sequences share more than 98% identity; a total of nine amino acid variations were observed. Two recombinant Cyn d 1 proteins (rCyn d 3-2 and rCyn d 5-4) with three amino acid substitutions showed differential IgE-binding profiles.

CONCLUSION

The present study extended our understanding of the primary structure of isoforms of Cyn d 1.

Expression of two isoforms of Lep d 2, the major allergen of Lepidoglyphus destructor, in both prokaryotic and eukaryotic systems

BACKGROUND

The dust mite Lepidoglyphus destructor is a major cause of allergic diseases among farmers. We have previously cloned and sequenced two isoforms of the major allergen Lep d 2 (formerly designated Lep d 1) and found significant homology to group 2 allergens of the house dust mite species Dermatophagoides. We now report on the production and characterization of recombinant Lep d 2.

OBJECTIVE

We have expressed both isoforms in two different expression systems; a eukaryotic system, baculovirus in insect cells and a prokaryotic system, E. coli. We have compared the two systems in regard to production yields and immunoreactivity of the recombinant allergens.

METHODS

The complete cDNA including the natural leader sequence was cloned into the pBlueBacIII transfer vector, and the rLep d 2 was produced as a secreted protein in baculovirus. For the expression in E. coli, the cDNA was cloned into the pET vector, and the rLep d 2 was produced with six C-terminal histidine residues. The purified recombinant allergens were tested for immunoreactivity with 10 sera from subjects allergic to Lepidoglyphus destructor and were compared with native Lep d 2 using inhibition immunoblotting. The ability of the recombinant allergens to release histamine from basophils was evaluated using a histamine release assay.

RESULTS

Both expression systems produced immunoreactive recombinant allergens. They inhibited the binding of human sera to native Lep d 2 confirming their retained IgE binding properties. The yield of pure recombinant protein from the prokaryotic system was approximately 1 mg/L compared to the eukaryotic system which produced up to 4 mg/L in an adherent cell culture system.

CONCLUSIONS

We have produced recombinant Lep d 2 in prokaryotic and eukaryotic expression systems which are comparable to the native allergen. Recombinant Lep d 2 might now be included in more extensive clinical studies to confirm its usefulness in the in vitro and the in vivo diagnosis of Lepidoglyphus destructor.

Post-translational modifications influence IgE reactivity to the major allergen Phl p 1 of timothy grass pollen

BACKGROUND

Grass group I consists of very potent allergenic components which are found in the pollen of all temperate grasses. Several post-translational modifications are predicted from the cDNA data.

OBJECTIVE

The aim of this study was to identify sequential IgE-binding sites on the allergen Phl p 1 and to determine their influence on IgE reactivity.

METHODS

Based on cDNA data and microsequencing results we synthesized overlapping decapeptides covering the complete Phl p 1 molecule and tested them for immunological reactivity by means of the PEPSCAN technique. In a dot test we determined the frequency of IgE reactivities to post-translationally modified structures (hydroxylated proline residues, carbohydrate structure, and disulphide formations).

RESULTS

Screening by overlapping peptides demonstrated an IgE binding site on the 10 N-terminal amino acids. Comprehensive studies showed that the two hydroxyproline residues of the native Phl p 1 allergen (at positions 5 and 8) and the N-glycan (at position 9) can result in an increased IgE reactivity; 3.3% of the sera exclusively bound to the hydroxyproline bearing peptide, while only 0.4% bound to the proline containing peptide. With regard to glycosylation, we estimated that 20% of sera recognized protein and carbohydrate epitopes, while one serum exclusively bound to the glycan. The formation of disulphide bonds has no detectable effect on the IgE reactivity to Phl p 1.

CONCLUSION

Our results indicate that the post-translational modifications, the carbohydrate structure and the hydroxylation of proline residues, can enhance the IgE reactivity of Phl p 1.

Modulation of IgE reactivity of allergens by site-directed mutagenesis: potential use of hypoallergenic variants for immunotherapy

Specific immunotherapy is an efficient treatment for patients suffering from type I allergy. The mechanisms underlying successful immunotherapy are assumed to operate at the level of T helper cells, leading to a modulation of the immune response to allergens. During immunotherapy, increasing doses of allergens are given on a regular basis, and the beneficial effects for the patient depend on the concentration of allergen used. On the other hand, the risk of IgE-mediated anaphylactic side effects also increase with the amount of allergen applied per injection. Therefore, we have proposed the use of hypoallergenic (low IgE binding activity) forms of allergens for immunotherapy. We evaluated by site-directed mutagenesis the contributions of individual amino acid residues/positions for IgE binding to Bet v 1, the major allergen of birch pollen. We found that IgE binding to Bet v 1 depended on at least six amino acid residues/positions. Immunoblot analyses and inhibition experiments showed that the multiple-point Bet v 1 mutant exhibited extremely low reactivity with serum IgE from birch pollen-allergic patients. In vivo (skin prick) tests showed that the potency of the multiple-point mutant to induce typical urticarial type I reactions in pollen-allergic patients was significantly lower than for wild-type Bet v 1. Proliferation assays of allergen-specific T cell clones demonstrated that these six amino acid exchanges in the Bet v 1 sequence did not influence T cell recognition. Thus, the Bet v 1 six-point mutant displayed significantly reduced IgE binding activity, but conserved T cell activating capacity, which is necessary for immunomodulation. The approach described here may be generally applied to produce allergen variants to be used in a safe therapy form of immediate-type allergies.

Group 5 determination in Pooideae grass pollen extracts by monoclonal antibody-based ELISA. Correlation with biologic activity

A solid-phase, monoclonal antibody-based ELISA was set up to quantitate group 5 allergens in pollen extracts of wild and cultivated Pooideae grasses. The method was able to evaluate group 5 concentration in mass units with a sensitivity in the ng/ml range and a practical working range of 1-100 ng/ml. The group 5 ELISA was compared with rocket immunoelectrophoresis for determination of allergen levels in several Phleum pratense extracts, and a very good quantitative correlation was found (r = 0.98; P < 0.0001). A highly significant correlation (r > 0.8) was also obtained in comparing allergenic potency determined by RAST inhibition to group 5 content in several wild and cultivated grass species. The results proved the usefulness of the method in the standardization of Pooideae pollen extracts employed in diagnosis and treatment.

Sequencing and immunochemical characterization of the American cockroach per a 3 (Cr-PI) isoallergenic variants

Two additional members of the American cockroach (Periplaneta americana) Per a 3 (Cr-PI) allergen, C13 and C28, were isolated and sequenced. They encoded proteins of 470 and 393 amino acids with two and no potential N-glycosylation sites, respectively. The molecular weights for C13 and C28 cloned proteins are 56,200 and 46,7000, with PI values of 7.06 and 6.54. C13 and C28 display 95.4% identity with several overlapping predicted central antigenic determinants. Both allergens were also found to have a 95% sequence homology with previously cloned C20 and share similar antigenic determinants, as defined by the structural prediction and ELISA analysis. However, the recombinant C13 and C28 allergens showed 26.3 and 94.7% skin reactivities on asthmatic patients while C20 elicited 47.4%. While no sequence similarity was found to other known allergens, these two aromatic amino acid-rich allergens were highly related to insect hemolymph proteins (28.7-36.5%), as with C20 cloned protein. Results suggest that these two are isoallergenic variants of C20. Sequence variations among isoforms, resulting a significant difference in skin reactivities, will be useful in elucidating the allergenic determinants.

Cloning and expression pattern of Hor v 9, the group 9 pollen isoallergen from barley

In this study we report the cloning, sequence, and characterization of Hor v 9 allergen cDNAs from barley (Hordeum vulgare) pollen. Structural homologues of Kentucky bluegrass (Poa pratensis) group 9 pollen allergens were identified in a cDNA library of barley pollen expressed mRNAs. The Hor v 9 cDNA clone (hvp9742) contained an open reading frame encoding 313 amino acids which included a putative 27-residue signal peptide and one asparagine sequon for glycosylation. The mRNA corresponding to clone hvp9742 was produced abundantly in pollen during the late stages of anther development. The protein encoded by clone hvp974 was synthesized as a fusion protein in the E. coli expression vector pMAL. Immunoblots using antibodies to this recombinant allergen, rHor v 9, showed that Hor v 9 protein accumulated during pollen development and was produced maximally at pollen maturity. Using these antibodies, we also provide evidence that Hor v 9 protein localized to the extracellular matrix of mature pollen. Southern blots suggested that Hor v 9 allergens exist as multiple isoforms in barley. Sequence comparisons showed that the Hor v 9 cDNA clones were also homologous to group 5 allergens of Timothy grass (Phleum pratense) pollen and canary grass (Phalaris aquatica) pollen, and the group 9 allergen of ryegrass (Lolium perenne) pollen.