Expression and secondary structure determination by NMR methods of the major house dust mite allergen Der p 2

Force Field Effects in Simulations of Flexible Peptides with Varying Polyproline II Propensity

Five peptides previously suggested to possess polyproline II (PPII) structure have here been investigated by using atomistic molecular dynamics simulations to compare how well four different force fields known for simulating intrinsically disordered proteins relatively well (Amber ff99SB-disp, Amber ff99SB-ILDN, CHARM36IDPSFF, and CHARMM36m) can capture this secondary structure element. The results revealed that all force fields sample PPII structures but to different extents and with different propensities toward other secondary structure elements, in particular, the β-sheet and "random coils". A cluster analysis of the simulations of histatin 5 also revealed that the conformational ensembles of the force fields are quite different. We compared the simulations to circular dichroism and nuclear magnetic resonance spectroscopy experiments and conclude that further experiments and methods for interpreting them are needed to assess the accuracy of force fields in determining PPII structure.

Mapping Human Monoclonal IgE Epitopes on the Major Dust Mite Allergen Der p 2

IgE Abs drive the symptoms of allergic disease upon cross-linking allergens on mast cells or basophils. If the IgE binding sites on the allergens could be identified, it may be useful for creating new forms of immunotherapy. However, direct knowledge of the human IgE (hIgE) epitopes is limited because of the very low frequency of IgE-producing B cells in blood. A new hybridoma technology using human B cells from house dust mite-allergic patients was used to identify four Der p 2-specific hIgE mAbs. Their relative binding sites were assessed and compared by immunoassays with three previously studied murine IgG mAbs. Immunoassays showed that the recognition of Der p 2 by the first three hIgE was inhibited by a single murine IgG, but the fourth hIgE recognized a different epitope from all the other mAbs. The functional ability of the hIgE that bind different epitopes to cross-link Der p 2 was demonstrated in a mouse model of passive systemic anaphylaxis. Nuclear magnetic resonance analyses of Der p 2 in complex with IgG and IgE Abs were used to identify specific residues in the epitopes. To our knowledge, the combination of immunoassays to distinguish overlapping epitopes and nuclear magnetic resonance analyses to identify specific residues involved in Ab binding provided the first epitope mapping of hIgE mAbs to an allergen. The technologies developed in this study will be useful in high-resolution mapping of human epitopes on other Ags and the design of improved therapeutics.

A Human IgE Antibody Binding Site on Der p 2 for the Design of a Recombinant Allergen for Immunotherapy

Der p 2 is one of the most important allergens from the house dust mite Dermatophagoides pteronyssinus Identification of human IgE Ab binding epitopes can be used for rational design of allergens with reduced IgE reactivity for therapy. Antigenic analysis of Der p 2 was performed by site-directed mutagenesis based on the x-ray crystal structure of the allergen in complex with a Fab from the murine IgG mAb 7A1 that binds an epitope overlapping with human IgE binding sites. Conformational changes upon Ab binding were confirmed by nuclear magnetic resonance using a 7A1-single-chain variable fragment. In addition, a human IgE Ab construct that interferes with mAb 7A1 binding was isolated from a combinatorial phage-display library constructed from a mite-allergic patient and expressed as two recombinant forms (single-chain Fab in Pichia pastoris and Fab in Escherichia coli). These two IgE Ab constructs and the mAb 7A1 failed to recognize two Der p 2 epitope double mutants designed to abolish the allergen-Ab interaction while preserving the fold necessary to bind Abs at other sites of the allergen surface. A 10-100-fold reduction in binding of IgE from allergic subjects to the mutants additionally showed that the residues mutated were involved in IgE Ab binding. In summary, mutagenesis of a Der p 2 epitope defined by x-ray crystallography revealed an IgE Ab binding site that will be considered for the design of hypoallergens for immunotherapy.

Contributions and Future Directions for Structural Biology in the Study of Allergens

Allergy is defined as an inappropriate immune response to something normally considered harmless. The symptomatic immune response is driven by IgE antibodies directed against allergens. The study of allergens has contributed significantly to our understanding of allergic disease in 3 main areas. First, identifying allergens as the cause of symptoms and developing allergen standards has led to many advances in exposure assessment and patient diagnostics. Second, a biochemical understanding of allergens has suggested a number of hypotheses related to the mechanisms of allergic sensitization. And finally, studies of allergen-antibody interactions have contributed to understanding the cross-reactivity of allergens, mapping patient epitopes, and the development of hypoallergens. In this review, a few select cases are highlighted where structural biology, in particular, has contributed significantly to allergen research and provided new avenues for investigation.

High-level expression and purification of the major house dust mite allergen Der p 2 in Escherichia coli

Der p 2, a major allergen derived from the house dust mite Dermatophagoides pteronyssinus, is one of the most clinically relevant allergens worldwide. Recombinant Der p 2 (rDer p 2) is useful in clinical diagnosis and disease-specific immunotherapy. However, previous studies showed that Der p 2 can only be expressed in Escherichia coli (E. coli) cells as inclusion bodies, thus protein refolding is required to obtain functional products. Here we report a new method to produce biologically active Der p 2 protein in E. coli. N-terminal hexahistidine- and trigger factor (TF)-tagged Der p 2 was expressed in soluble form in E. coli and purified using a combination of chromatography processes. This procedure produced milligram-level high purity Der p 2 per liter of bacterial culture. Moreover, far-UV region circular dichroism (CD) analysis and serum specific IgE reactivity test demonstrated that the secondary structure and IgE reactivity properties of rDer p 2 produced in our study were almost identical to those of natural Der p 2 (nDer p 2). In conclusion, the method developed in this work provides a useful tool for the production of immunologically active recombinant Der p 2 for clinical applications.

Relationship between the magnitude of IgE production in mice and conformational stability of the house dust mite allergen, Der p 2

BACKGROUND

Protein antigens are degraded by endosomal protease in antigen presentation cell. T cells recognize peptides derived from antigen proteins bound to class II major histocompatibility complex molecules. We previously reported that an increase in the conformational stability of an antigen depressed its immunogenicity. However, there is little information on antigens with differences in molecular properties such as net charges and molecular weight.

METHODS

Denaturation experiments against guanidine hydrochloride. The serum IgE levels to protein antigens at 35days after the first immunization analyzed using ELISA.

RESULTS

The Der p 2 mutations in which Ile13 is mutated to Ala (I13A) and Ala122 is mutated to Ile (A122I) were shown to have lower and higher conformational stability than the wild-type, respectively, by denaturation experiments. The amount of IgE production by the less stable I13A mutant was higher and that of the stable A122I mutant was lower than that of the wild-type.

CONCLUSION

Our results suggest that the increased conformational stability of Der p 2 depressed the IgE production in mice.

GENERAL SIGNIFICANCE

These findings should provide a milestone for the engineering of allergen vaccines.

Effect of Amino Acid Polymorphisms of House Dust Mite Der p 2 Variants on Allergic Sensitization

Purpose

The sequence variations of the Der p 2 allergen of Dermatophagoides pteronyssinus diverge along 2 pathways with particular amino acid substitutions at positions 40,47,111, and 114. The environmental prevalence and IgE binding to Der p 2 variants differ among regions. To compare IgE binding to Der p 2 variants between sera from Bangkok, Thailand and Perth, Western Australia with different variants and to determine the variant-specificity of antibodies induced by vaccination with recombinant variants.

Methods

The structures of recombinant variants produced in yeast were compared by circular dichroism and 1-anilinonaphthalene 8-sulfonic acid staining of their lipid-binding cavity. Sera from subjects in Bangkok and Perth where different variants are found were compared by the affinity (IC₅₀) of IgE cross-reactivity to different variants and by direct IgE binding. Mice were immunized with the variants Der p 2.0101 and Der p 2.0110, and their IgG binding to Der p 2.0103, 2.0104, and 2.0109 was measured.

Results

The secondary structures of the recombinant variants resembled the natural allergen but with differences in ANS binding. The IC₅₀ of Der p 2.0101 required 7-fold higher concentrations to inhibit IgE binding to the high-IgE-binding Der p 2.0104 than for homologous inhibition in sera from Bangkok where it is absent, while in sera from Perth that have both variants the IC₅₀ was the same and low. Reciprocal results were obtained for Der p 2.0110 not found in Perth. Direct binding revealed that Der p 2.0104 was best for detecting IgE in both regions, followed by Der p 2.0101 with binding to other variants showing larger differences. Mouse anti-Der p 2.0101 antibodies had a high affinity of cross-reactivity but bound poorly to other variants.

Conclusions

The affinity of IgE antibody cross-reactivity, the direct IgE binding, and the specificities of antibodies induced by vaccination show that measures of allergic sensitization and therapeutic strategies could be optimized with knowledge of Der p 2 variants.

Expression and characterization of natural-like recombinant Der p 2 for sublingual immunotherapy

BACKGROUND

Recombinant allergens with a native conformation represent an alternative to natural extracts for immunotherapy and diagnostic purposes.

METHODS

We produced the Der p 2 mite allergen in Pichia pastoris and Escherichia coli. After purification by cation exchange chromatography, recombinant molecules were compared to their natural counterpart based upon structural (disulfide bonds, secondary structure, thermal stability) and immunological properties (antibody reactivity, basophil and T cell activation, tolerance induction in a murine sublingual immunotherapy model).

RESULTS

The Der p 2.0101 isoform was confirmed to be prevalent in Dermatophagoides pteronyssinus extracts. It was then produced as a secreted molecule in P. pastoris or refolded from E. coli inclusion bodies. The yeast-expressed rDer p 2 molecule exhibits a natural-like disulfide bridge distribution and secondary structure, whereas the E. coli-derived rDer p 2 presents some heterogeneity in cysteine bonds and a lower stability following thermal stress. The two recombinant as well as natural Der p 2 molecules exhibit comparable IgE recognition and activate basophil and CD4+ T cells. Sublingual immunotherapy of nDer p 2- sensitized mice using either one of the rDer p 2 molecules efficiently decreases airway hyperresponsiveness as well as Th2 responses.

CONCLUSIONS

Natural and recombinant Der p 2 molecules produced in P. pastoris and E. coli exhibit comparable immunological properties despite distinct structural features. Natural-like cysteine pairing is a critical parameter to identify stable, well-folded and homogenous proteins appropriate for immunotherapy and diagnostic purposes.

House dust mite allergens in asthma and allergy

IgE antibodies in house dust mite (HDM) allergy follow a predictable pattern. Half are directed against two dominant allergens and the remainder largely against four midpotency allergens. This hierarchical pattern is not changed by the titre of the IgE response or severity of disease. The structures of these allergens are known and they can be produced as authentic recombinant allergens. There is also evidence that the allergenicity is augmented by the biological activity of the key allergens, validating them as targets for vaccination. Collectively, these developments should facilitate the development of new diagnostics, improve immunotherapy and allow vaccination with defined reagents. Highly purified recombinant polypeptides representing the important mite allergens are now available so that informative and reproducible experiments can be performed with mite allergens in place of poorly defined and variable extracts.

Reduction of the in vivo allergenicity of Der p 2, the major house-dust mite allergen, by genetic engineering

The major allergen of the house-dust mite Dermatophagoides pteronyssinus, Der p 2, is recognized by approximately 90% of mite-allergic patients. We have produced two recombinant fragments of Der p 2 comprising aa 1-53 and aa 54-129 and a hybrid molecule (aa 54-129+1-53), combining the two fragments in inverse order, by genetic engineering. The recombinant Der p 2 derivatives were expressed in E. coli and purified to homogeneity. rDer p 2 derivatives (fragments and hybrid) showed a considerably reduced beta sheet structure and IgE reactivity compared to the Der p 2 wild-type allergen. The allergenic activity of the Der p 2 derivatives was reduced more than tenfold as evaluated in vitro in basophil activation assays and in vivo by skin prick testing of mite-allergic patients. Immunization of mice and rabbits with rDer p 2 derivatives induced Der p 2-specific IgG antibodies, which inhibited the binding of allergic patients' IgE to Der p 2. Immunization of mice with rDer p 2 derivatives induced less allergenic IgE responses than immunization with rDer p 2. Thus the rDer p 2 derivatives exhibited less in vivo allergenic activity and allergenicity than the Der p 2 allergen but preserved immunogenicity and may hence represent candidates for specific immunotherapy of house-dust mite allergy.

Dilution method to refold bacterially expressed recombinant Der f 2 and Der p 2 to exhibit the secondary structure and histamine-releasing activity of natural allergens

BACKGROUND

Structurally refolded recombinant forms of major house dust mite group 2 allergens, Der f 2 and Der p 2, expressed in Escherichia coli, were prepared by solubilizing the insoluble products with urea and subsequently dialyzing against buffer. In this study, we determined conditions for refolding the urea-denatured recombinant Der f 2 and Der p 2 by one-step dilution as an alternative to dialysis, which requires several steps of handling and much time and cost.

METHODS

The insoluble bacterial product containing recombinant Der f 2 was solubilized with a buffer containing 8 M urea, and the solution was diluted to various urea concentrations. The refolding efficiency in each dilution was estimated from the height of the peak corresponding to the folded recombinant Der f 2 and that containing the aggregated form on anion exchange chromatography. The structure and allergenicity of the purified recombinant Der f 2 and Der p 2 refolded using the dilution method were analyzed based on circular dichroism and a basophil histamine-releasing assay, respectively.

RESULTS

Although the refolding efficiency decreased as the urea concentration in the dilution increased, experimental conditions whereby the protein and urea concentrations in the dilution were less than 0.5 mg/ml and 0.8 M, respectively, achieved maximum refolding efficiency. The recombinant allergens prepared by the dilution method exhibited the secondary structure and histamine-releasing activity of natural allergens purified from mite culture.

CONCLUSIONS

The dilution method established in this study is more convenient in terms of handling, time, and cost than the dialysis method and will be useful for large-scale production and for the preparation of numbers of mutants to analyze IgE epitopes.

Isoforms of the Major Peanut Allergen Ara h 2: IgE Binding in Children with Peanut Allergy

BACKGROUND

The major peanut allergen Ara h 2 consists of two isoforms, namely Ara h 2.0101 and Ara h 2.0201. The recently identified Ara h 2.0201 isoform contains an extra 12 amino acids including an extra copy of the reported immunodominant epitope DPYSPS. This study aimed to evaluate the IgE binding of the two Ara h 2 isoforms.

METHODS

Ten clones of Ara h 2 were sequenced to assess the relative frequency of the Ara h 2 isoforms and to identify whether there was further variation in the Ara h 2 sequence. IgE binding to Ara h 2.0101 and Ara h 2.0201 was measured for 70 peanut-allergic children using an IgE DELFIA assay to quantitate specific IgE binding. A competition assay was used to measure whether Ara h 2.0201 contained IgE epitopes other than those found for Ara h 2.0101.

RESULTS

The original Ara h 2.0101 sequence was found for 6/10 clones and Ara h 2.0201 was found for 2/10 clones. Ara h 2.0201 had the expected insertion of 12 amino acids as well as substitutions at positions 40 (40G) and 142 (142E). Two new isoforms were identified as different polymorphisms of position 142. One Ara h 2.01 clone (Ara h 2.0102) contained 142E and one Ara h 2.02 clone (Ara h 2.0202) contained 142D. A polymorphism that was previously identified by other investigators at position 77 (77Q or 77R) was not found for any of the 10 sequences. Although the level of IgE binding to Ara h 2.0201 of individual patients was frequently higher than the binding to Ara h 2.0101 (p < 0.01), there was a strong correlation in binding to both isoforms (r = 0.987, p < 0.0001) and when analyzed as a group the means were similar. Ara h 2.0101 was not as efficient at blocking reactivity to Ara h 2.0201 indicating there is an additional IgE specificity for the Ara h 2.0201 isoform.

CONCLUSIONS

Ara h 2.0201 has similar but higher IgE binding than the originally sequenced Ara h 2.0101 isoform and contains other IgE specificities.

A rapid test for detection of mite allergens in homes

BACKGROUND

International guidelines recommend allergen avoidance for asthma management, but do not include making assessments of allergen exposure. Mite allergen exposure cannot be assumed, especially in geographical regions where climatic conditions vary.

OBJECTIVE

To develop a rapid test that would enable consumers to detect mite allergen in the home.

METHODS

A lateral flow test using gold labelled antibody for mite group 2 allergen was developed as part of a detection kit incorporating the MITEST dust sampling device. Dust samples were assayed by ELISA for group 1 and group 2 allergens and by using the rapid test. The tests were compared as indices of mite allergen exposure.

RESULTS

There was a good correlation between group 1 and group 2 levels by ELISA (n = 349, r = 0.60, P < 0.001). In a multi-centre study of 65 homes (263 dust samples) in five countries, there was a strong correlation between ELISA and the rapid test. Most samples with high scores in the test (43/48, 90%) contained > 1 microg/m2 group 2 allergen, whereas most low samples contained < 1 microg/m2 (50/64, 78%). Differences between mean group 2 levels of samples that scored low (0.28 microg/m2), medium (1.68 microg/m2) or high (3.18 microg/m2) on the test were highly significant (P 0.007 to < 0.001).

CONCLUSIONS

A simple rapid test has been developed that detects mite allergen in the home within 10 min. The mite screening test should educate consumers about allergen exposure and encourage compliance with allergen-avoidance procedures. This technology has applications for the detection of other common environmental allergens.

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.

Characterization and immunobiology of house dust mite allergens

The examination of house dust mite extracts has indicated that over 30 different proteins can induce IgE antibody in patients allergic to the house dust mite. There are however dominant specificities especially the group 1 and 2 allergens which can account for much of the allergenicity of extracts. Of the 19 denominated allergens, the major IgE binding has been reported for the group 1, 2, 3, 9, 11, 14 and 15 allergens. The high-molecular-weight group 11, 14 and 15 allergens have only recently been described and although high IgE binding has been anticipated from immunoblotting, there is a need for considerable corroboration. Similarly, the study of the group 3 and 9 serine protease allergens has been incomplete. The group 4, 5, 7 and 8 allergens have shown intermediate IgE binding and the group 10 tropomyosins are of interest because of their potential cross-reactivity with allergen from disparate species. Although the progress with the production of recombinant group 1 allergens has been recent, many of the allergens can be produced as high IgE-binding polypeptides. The tertiary structure of the group 2 allergens has been determined from recombinant proteins and they are an excellent model for the investigation of modified allergens. An unexpected property of the group 1, 2 and 3 allergens has been the high degree of polymorphism found by cDNA analysis. It has however been possible to identify sequences to represent the variation in the natural allergens. The group 7 and 14 allergens show secondary modifications which vary in different extracts creating batch variation. While some estimate of the importance of allergens can be obtained from IgE binding, few analyses of T-cell responses have been made and these regulate both the development of, and the protection from sensitization.

Non-allergenic antigen in allergic sensitization: responses to the mite ferritin heavy chain antigen by allergic and non-allergic subjects

BACKGROUND

The majority of house dust mite proteins are non-allergenic. There is, however, no information on the type of immune responses produced to these proteins and if the responses are affected by allergic sensitization.

OBJECTIVE

To identify and produce a non-allergenic antigen of the house dust mite and compare antibody and T cell responses with the responses to allergens in sensitized and non-sensitized individuals.

RESULTS

Ferritin heavy chain was cloned from a cDNA library as a candidate non-allergen of the house dust mite. It bound IgG but not IgE in the sera of allergic and non-allergic subjects and induced high T cell proliferative responses that correlated highly with the responses to the major allergen Der p 2. The cytokine response to the non-allergen was characterized by the release of high levels of both Th1 and Th2 cytokines from the PBMC of both allergic and non-allergic subjects. In contrast, the response to Der p 2 showed the expected high level of Th2 cytokine release from the PBMC of allergic subjects, while the Th2 cytokine production from PBMC of non-allergic subjects was low and even lower than that induced by ferritin heavy chain. The levels of IFN-gamma release were similar for all groups. Der p 2 induced significantly more IL-10 than ferritin in the non-allergic group.

CONCLUSION

The T cell responses to a non-allergenic protein of the house dust mite were high and strongly correlated with the response to the major allergen. The non-allergenic protein induced high levels of Th1 and Th2 cytokine in both allergic and non-allergic subjects, while the allergen induced high levels of Th2 cytokine in allergic subjects and low levels in non-allergic subjects. The responses to the allergen were thus independently up- and down-regulated with no evidence of bystander regulation.

Der p 2 isoallergens have different allergenicity, and quantification with 2-site ELISA using monoclonal antibodies is influenced by the isoallergens

BACKGROUND

Der p 2 isoallergens have been reported and the possibility of different allergenicity has also been suggested. In addition, the quantification with 2-site ELISA may be affected by the isoallergens.

OBJECTIVES

Two different recombinant Der p 2 (rDer p 2) isoallergens were compared in terms of human IgE responses and the reliability of quantification of them with two-site ELISA kits which use monoclonal antibodies (mAbs) as capture and detection of Der p 2.

METHODS

Seven different Der p 2 cDNA from the cultured Dermatophagoides pteronyssinus (DP) were cloned and polymorphism in nine amino acid residues was found. Two different recombinant isoallergens (rDer p 2A and rDer p 2B) were expressed and compared to their human IgE immune responses by ELISA and the ELISA inhibition test with 23 sera of DP-allergic patients. The reliability of quantification of two different available 2-site ELISA kits, which used mAbs for capture and detection of Der p 2, was evaluated.

RESULTS

The ELISA optical density of rDer p 2B-specific IgE (sIgE) was higher than that of rDer p 2A (P < 0.001). The ELISA inhibition curve of rDer p 2B sIgE in pool I sera (n = 5; high sIgE both to rDer p 2A and rDer p 2B) did not show any differences in the 50% inhibition concentration and maximum inhibitory percentage of rDer p 2A and rDer p 2B sIgE. However, with pool II sera (n = 5; markedly higher sIgE to rDer p 2B than rDer p 2A), the 50% inhibitory concentrations (10 microg/mL vs. 40 ng/mL) and maximum inhibitory percentage (61% vs. 99%) of rDer p 2B sIgE with the two recombinant isoallergens were quite different. rDer p 2B could be quantified with two different 2-site ELISA kits, but rDer p 2A was detected by only one kit.

CONCLUSION

We conclude that isoallergens of Der p 2 may have different IgE immune responses. Quantification of Der p 2 with 2-site ELISA kits that adopted mAbs, might be affected by the prevalent form of the isoallergens in reservoir dust.

The crystal structure of a major dust mite allergen Der p 2, and its biological implications

The crystal structure of the common house mite (Dermatophagoides sp.) Der p 2 allergen was solved at 2.15 A resolution using the MAD phasing technique, and refined to an R-factor of 0.209. The refined atomic model, which reveals an immunoglobulin-like tertiary fold, differs in important ways from the previously described NMR structure, because the two beta-sheets are significantly further apart and create an internal cavity, which is occupied by a hydrophobic ligand. This interaction is structurally reminiscent of the binding of a prenyl group by a regulatory protein, the Rho guanine nucleotide exchange inhibitor. The crystal structure suggests that binding of non-polar molecules may be essential to the physiological function of the Der p 2 protein.

Cloning and sequence analysis of a cDNA encoding Pso o II, a mite group II allergen of the sheep scab mite (Acari: Psoroptidae)

Psoroptes ovis (Hering), the sheep scab mite, is responsible for psoroptic scabies of cattle and sheep. Reverse translation of 30 N-terminal amino acids of the major P. ovis allergen, previously chosen as a candidate immunogen and identified as a 16 kDa protein yielded a degenerate sequence used to design oligodeoxynucleotide polymerase chain reaction (PCR) primers. Use of the PCR primers with a P. ovis cDNA library succeeded in amplification of a 90 bp cDNA gene fragment that was cloned, sequenced, and used to select unique sequencing/PCR primers. Primer walking generated overlapping subclones which yielded the 588 nucleotide consensus sequence of the cDNA encoding the 143 amino acid P. ovis allergen precursor. Nucleotide and translated sequences of the cDNA were compared with sequences in GenBank and found to be homologous to mite group II allergens Lep d II (formerly Lep d I) of Lepidoglyphus destructor Schrank, DerfII of Dermatophagoides farinae Hughes, Der p II of Derrmatophagoides pteronyssinus (Trouessart), Tyr p II of Tyrophagus putrescentiae (Schrank), Eur m II of Euroglyphus maynei (Cooreman) and Gly d II of Glycophagus domesticus (De Geer). The mature P. ovis allergen is composed of 126 amino acids with a calculated molecular mass of 13,468 Da, three disulfide bonds, and pI of 6.06 with one potential o-glycosylation site at Thr116. We designate the P. ovis 16 kDa protein as Pso o II in conformity with nomenclature for mite group II allergens.

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.

Characterization and identification of allergen epitopes: recombinant peptide libraries and synthetic, overlapping peptides

For the understanding of the relationship between protein structure and allergenicity, it is important to identify allergenic epitopes. Two methods to characterize primarily linear epitopes are compared using the major allergen from brown shrimp (Penaeus aztecus), Pen a 1, as an example. A recombinant peptide library was constructed and synthetic, overlapping peptides, spanning the entire Pen a 1 molecule, were synthesized and tested for specific IgE reactivity. Both methods identified IgE-binding of Pen a 1, however, the SPOTs procedure resulted in the identification of more epitopes of the major shrimp allergen Pen a 1 than the usage of the recombinant peptide library. For detection of specific IgE antibodies, the usage of 125I-labeled detection antibody seems to be superior over enzyme-labeled anti IgE antibodies. The regeneration of SPOTs membranes is possible, but it is prudent to test regenerated membranes for residual activity. If a given food allergen contains significant linear epitopes, which seems to be true for stable major allergens such as those of peanut and shrimp the SPOTs system may be more advantageous than the use of recombinant peptides libraries. However, if allergens are studied that contain more conformational epitopes, recombinant peptide libraries may help to identify the relevant epitopes. It has to be emphasized that no system for epitope identification will detect all epitopes and that the relevance of identified epitopes has to be confirmed with other methods such as inhibition studies, crystallographic analysis or the immunological evaluation of modified whole allergens.

A sensitive reverse ELISA for the measurement of specific IgE to Der p 2, a major Dermatophagoides pteronyssinus allergen

BACKGROUND

Epidemiologic studies have shown that the presence of IgE antibodies to house dust mite and other indoor allergens is an important risk factor for asthma.

OBJECTIVE

The aim of this study was to develop a reverse ELISA (rELISA) for measuring specific IgE to Der p 2, a major Dermatophagoides pteronyssinus (Dpt) allergen, as a potential tool for followup of allergen immunotherapy.

METHODS

Recombinant Der p 2 allergen or a monoclonal antibody to Der p 2 was used to coat plates in conventional ELISA (cELISA) and rELISA, respectively. Sera from 48 asthmatic patients with positive skin prick test (SPT+) to D. pteronyssinus extract were analyzed for total IgE and specific IgE to Der p 2, and the results were compared with a group of 41 SPT asthmatic and 30 SPT- control subjects.

RESULTS

The sensitivity of the two assays for Der p 2-specific IgE was 3.9 EU/mL and their specificities were confirmed by inhibition tests, in a dose-dependent manner. There was a significant positive correlation between cELISA and rELISA (r = 0.74; P < 0.0001). However, rELISA was more sensitive than was cELISA, regarding both the positive sera percentage (70.8% vs 52.1%) and the Der p 2-specific IgE levels (28.4 vs 4.5 EU/mL) in SPT+ asthmatic patients.

CONCLUSIONS

rELISA has shown to be a sensitive and alternative method for measuring Der p 2-specific IgE without using radioactive techniques. Detection of specific IgE to major allergens and relevant peptides, and identification of B cell epitopes in allergens will provide valuable information for the design of allergen analogs and peptides for immunotherapy.

Hydrogen exchange nuclear magnetic resonance spectroscopy mapping of antibody epitopes on the house dust mite allergen Der p 2

New strategies for allergen-specific immunotherapy have focused on reducing IgE reactivity of purified recombinant allergens while maintaining T-cell epitopes. Previously, we showed that disrupting the disulfide bonds of the major house dust mite allergen Der p 2 resulted in 10-100-fold less skin test reactivity in mite-allergic subjects but did not change in vitro T-cell proliferative responses. To provide a more complete picture of the antigenic surface of Der p 2, we report here the identification of three epitopes using hydrogen protection nuclear magnetic resonance spectroscopy. The epitopes are defined by monoclonal antibodies that are able to inhibit IgE antibody binding to the allergen. Each monoclonal antibody affected the amide exchange rate of 2-3 continuous residues in different regions of Der p 2. Based on these data, a number of other residues were predicted to belong to each epitope, and this prediction was tested for monoclonal antibody 7A1 by generating alanine point mutants. The results indicate that only a small number of residues within the predicted epitope are functionally important for antibody binding. The molecular definition of these three epitopes will enable us to target limited positions for mutagenesis and to expand our studies of hypoallergenic variants for immunotherapy.

Cross-reactivity studies of a new group 2 allergen from the dust mite Glycyphagus domesticus, Gly d 2, and group 2 allergens from Dermatophagoides pteronyssinus, Lepidoglyphus destructor, and Tyrophagus putrescentiae with recombinant allergens

BACKGROUND

Dust mites are important inducers of allergic disease. Group 2 allergens are recognized as major allergens in several mite species, including Dermatophagoides pteronyssinus, Lepidoglyphus destructor, and Tyrophagus putrescentiae. No allergens have thus far been characterized on the molecular level from the dust mite Glycyphagus domesticus.

OBJECTIVE

We sought to examine the cross-reactivity among group 2 allergens of G domesticus, L destructor, T putrescentiae, and D pteronyssinus.

METHODS

A group 2 allergen from G domesticus, Gly d 2, was cloned and expressed as a recombinant protein. Cross-reactivity between Gly d 2 and 3 other group 2 allergens, Lep d 2, Tyr p 2, and Der p 2, was studied by using individual sera and a serum pool RAST-positive to G domesticus, L destructor, T putrescentiae, and D pteronyssinus. Recombinant allergens were used as inhibitors of IgE binding in immunoblotting experiments. Molecular modeling on the basis of the Der p 2 structure was carried out for Gly d 2, Lep d 2, and Tyr p 2.

RESULTS

Two cDNAs encoding isoforms of Gly d 2 were isolated, but only the Gly d 2.02 isoform was used in this study. Sixteen of 17 subjects had IgE to Gly d 2. The protein sequence of Gly d 2 revealed 79% identity to Lep d 2 and 46% and 41% identity to Tyr p 2 and Der p 2, respectively. Extensive cross-reactivity was demonstrated among Gly d 2, Lep d 2, and Tyr p 2, but little cross-reactivity was found between these allergens and Der p 2. According to the tertiary structure of Der p 2 and 3-dimensional models of Gly d 2, Lep d 2, and Tyr p 2, differences reside mainly in surface-exposed residues.

CONCLUSION

Gly d 2 showed high sequence homology to Lep d 2. Cross-reactivity was observed between Gly d 2, Lep d 2, and Tyr p 2, but only limited cross-reactivity was demonstrated between these 3 allergens and Der p 2.

Sequence polymorphisms and antibody binding to the group 2 dust mite allergens

BACKGROUND

The group 2 allergens Der p 2, Der f 2 and Eur m 2 are 14-kD proteins with > 80% sequence identity. Isoforms within each genus have been identified which differ by 3-4 amino acids. The aim of this study was to investigate the importance of these substitutions to antibody binding.

METHODS

Recombinant allergens were expressed and purified from Escherichia coli. ELISA and skin testing were used to evaluate antibody binding. Molecular modeling of the tertiary structure was preformed to examine the location of substitutions.

RESULTS

The three Der f 2 isoforms and two of three of the Der p 2 isoforms reacted with all monoclonal antibodies (mAb). Der p 2.0101, the isoform with aspartate at position 114, bound all mAb except 1D8. Substitution of asparagine for aspartate restored binding of rDer p 2.0101 to mAb 1D8 and increased the correlation coefficient for IgE binding from 0.72 to 0.77. The three Der p 2 isoforms showed comparable skin test reactivity to nDer p 2 and commercial extract. rEur m 2.0101 bound to all mAb except 7A1 and when compared with rDer p 2 for IgE binding, r(2) = of 0.58 (n = 72). Lep d 2 did not react with mAb or with Dermatophagoides spp. allergic sera. Modeling revealed that Eur m 2, Lep d 2 and Tyr p 2 retain the tertiary fold of Der p 2 and the substitutions are on the surface.

CONCLUSIONS

mAb could distinguish isoform substitutions. IgE binding showed a good correlation among all isoforms, thus the recombinant allergens are useful for diagnosis.

Localization of a major allergen, Der p 2, in the gut and faecal pellets of Dermatophagoides pteronyssinus

BACKGROUND

The house dust mite Dermatophagoides ptronyssinus is one of the most significant indoor sensitizing agents of allergy. Allergen localization may indicate the importance of secreted materials, faeces, and nonexcreted mite body components as allergen sources.

OBJECTIVE

This study attempted to localize the sites and concentrations of Der p 2 in the cryostat sections of D. pteronyssinus using antirecombinant Der p 2 monoclonal antibody.

METHODS

Male and female mites and mite faeces collected separately from both sexes were used. Live mites were embedded and serial cryostat sections for light microscopy were performed. Anti-recombinant Der p 2 monoclonal antibody previously produced by the authors was used. For immunoprobing, mite cryostat sections were incubated in the following antibody-containing solutions: monoclonal antibody against Der p 2 was initially applied to the sections and fluorescent isothiocyanate conjugated antimouse immunoglobulin G was reacted as the secondary antibody. The faecal pellets were treated the same as described above.

RESULTS

Immunofluorescent probing of cryostat sections with the monoclonal antibody showed labelling of the gut lining, gut contents and defecated faecal pellets. No other internal organs were identified as positively labelled.

CONCLUSION

This study suggested that a major allergen, Der p 2, found in the house dust mite D. pteronyssinus is derived from the digestive tract and concentrated in the faeces.

High-molecular-weight allergens of the house dust mite: an apolipophorin-like cDNA has sequence identity with the major M-177 allergen and the IgE-binding peptide fragments Mag1 and Mag3

BACKGROUND

A 349-residue recombinant polypeptide of Dermatophagoides farinae, Mag 3, has been shown to represent part of a larger 177-kD (M-177) allergen with very high IgE-binding activity.

METHODS

Cloning and sequencing of cDNA from the house dust mites Dermatophagoides pteronyssinus and Euroglyphus maynei was used to characterise the polypeptide containing the Mag 3 sequence.

RESULTS

cDNA clones containing the complete sequence of the E. maynei homologue of the M-177 allergen were isolated and analysed. The translation contained not only an amino acid sequence with 90% identity to the 349-residue Mag-3 fragment but also a further sequence with 90% identity to another IgE-binding recombinant D. farinae polypeptide designated Mag 1. The complete sequence encoded a mature polypeptide of 1,650 residues and a molecular mass of 189.5 kD. cDNA clones from D. pteronyssinus also encoded sequences equivalent to the Mag 1 and 3 polypeptides. The M-177 sequence showed strong similarity to the lipid transport apolipophorins found in insect lipophorins.

CONCLUSIONS

cDNA sequence data show that the D. pteronyssinus and E. maynei homologues of the M-177 high-molecular-weight D. farinae allergen contain sequences equivalent to both the Mag 1 and Mag 3 recombinant IgE-binding fragments. The N-terminal sequence of the full-length 1,650 amino-acid allergen showed strong similarity to the insect apolipophorins which are poorly soluble in aqueous extracts and exist in the lipid transport particles in haemolymph. It is proposed that presentation in lipid particles could be a factor which enhances the immunogenicity of this group of allergens.

Molecular characterization of the group 4 house dust mite allergen from Dermatophagoides pteronyssinus and its amylase homologue from Euroglyphus maynei

BACKGROUND

Of the ten recognised groups of Dermatophagoides pteronyssinus allergens, the group 4 is the only group that has not been characterised at the molecular level.

METHODS

Primers were designed to PCR amplify Der p 4 (D. pteronyssinus) and Eur m 4 (Euroglyphus maynei) cDNA. These fragments were used to screen the corresponding cDNA libraries and the cDNA clones obtained were subsequently sequenced. The coding regions of Der p 4 and Eur m 4 were cloned into the pET expression vector and recombinant histidine-tagged proteins expressed in Escherichia coli.

RESULTS

cDNA clones which included the mature protein coding sequence for Der p 4 and Eur m 4 were sequenced. The Der p 4 and Eur m 4 genes were found to code for 496 amino acid mature proteins with residues important for the function of alpha-amylase highly conserved. Der p 4 and Eur m 4 were calculated to be 90% identical and a BLAST search of the GenBank database found these sequences to be approximately 50% identical to insect and mammalian alpha-amylases. The calculated molecular weights of Der p 4 and Eur m 4 were approximately 57,000, although recombinant Der p 4 and Eur m 4 migrate on SDS-PAGE at about 60,000. Der p 4 recombinant protein was found to bind specific IgE in 3 of the 10 house dust mite allergic patients tested.

CONCLUSIONS

This paper describes the first cDNA sequence of Der p 4 and Eur m 4 confirming that this allergen is house dust mite alpha-amylase.

Normal human immunoglobulin G4 is bispecific: it has two different antigen-combining sites

Unlike other immunoglobulin G (IgG) subclasses, IgG4 antibodies in plasma have been reported to be functionally monovalent. In this paper we show that the apparent monovalency of circulating IgG4 is caused by asymmetry of plasma IgG4. A large fraction of plasma IgG4 molecules have two different antigen-binding sites, resulting in bispecificity. Sera from patients with IgG4 antibodies to both house dust mite and grass pollen induced cross-linking of Sepharose-bound grass pollen antigen to radiolabelled house dust mite allergen Der p I. This bispecific binding activity was not observed in sera with IgG4 antibodies to either grass pollen or house dust mite exclusively. Depletion of IgG4 antibodies resulted in disappearance of the bispecific activity. By size exclusion chromatography we excluded the possibility that bispecific activity was caused by aggregation of IgG4 antibodies. These results indicate that circulating (polyclonal) IgG4 antibodies have two different antigen-binding sites and therefore are functionally monovalent antibodies.

Efficient presentation of house dust mite allergen Der p 2 by monocyte-derived dendritic cells and the role of beta 2 integrins

Monocyte-derived dendritic cells (MDDC) are potent antigen-presenting cells (APC). The APC functions of MDDC in allergy were examined. MDDC presentation of the major house dust mite allergen Der p 2 resulted in 4-12-fold higher T-cell proliferation and markedly higher IFN-gamma and IL-5 production than PBMC cultures. Comparable T-cell proliferation was obtained with 10-fold fewer MDDC than purified monocytes. MDDC cultured from adherent cells, or CD14+, CD11b+ or Percoll-purified monocytes were comparable in presenting soluble Ag, and in stimulating allogeneic MLR. Importantly, MDDC presentation of Der p 2 resulted in both Th1 and Th2 stimulation, although MDDC are known to produce high levels of IL-12 and stimulate biased Th1 responses. The basis for the potent APC function of MDDC was further examined. MDDC were found to be highly phagocytic. Immunoprecipitation studies showed markedly elevated ICAM-1 expression but > 10-fold reduction in LFA-1 expression on MDDC compared with monocytes. Monoclonal antibody (MoAb)-blocking experiments showed that ICAM-LFA-1 interaction was essential for MDDC stimulation of Der p 2-specific T-cell proliferative responses. These results show that the use of MDDC as APC provides a simple, sensitive and versatile method for detecting T-cell responses to allergens and that the strong phagocytic capability and the increased ICAM-1 expression of MDDC contribute significantly to their Ag presentation potency.

IgE binding capacity of synthetic and recombinant peptides of the major storage mite (Lepidoglyphus destructor) allergen, Lep d 2

BACKGROUND

Lepidoglyphus destructor is an important non-pyroglyphid mite species in Europe and a dominant allergen in farming environments. The major allergen of L. destructor, Lep d 2, is a protein of 13.2 kD that is recognised by about 90% of sera RAST positive to this mite species.

METHODS

The cDNA of two isoallergens of the Lep d 2 has previously been sequenced and the protein expressed in different protein expression systems. In order to map the B-cell epitopes, the full length protein and the truncated forms of the protein have been expressed in Escherichia coli as glutathione-S-transferase (GST) fusion proteins. Recombinant Lep d 2 fragments and synthetic overlapping 15 mer peptides spanning Lep d 2 were probed with sera from patients allergic to storage mite.

RESULTS

The full-length (125 amino acids) GST fusion protein reacted strongly with patient IgE in Western blots and dot blots. Synthetic peptides failed to react with IgE antibodies from mite-allergic patients and the truncated fusion proteins displayed weak IgE-binding capacity.

CONCLUSION

We conclude that there are no dominant linear IgE-binding epitopes in Lep d 2. Recombinant or synthetic Lep d 2 fragments may, however, be further evaluated as hypoallergenic candidate molecules for specific immunotherapy.

Future directions for allergen immunotherapy

Over the last 30 years several approaches to modify immunotherapy have been tested, including allergoids, alum precipitation, and most recently peptides. However, none of these have replaced the traditional regimens. Over the same period our scientific understanding of allergic disease has been transformed. Today it is possible to identify and monitor changes occurring during treatment and to target many different aspects of the immune system. Recombinant technology provides a powerful technique both for sequencing proteins and producing allergens in commercial quantities. The recombinant proteins can be modified by site-directed mutagenesis so as to decrease their reactivity with IgE antibodies while maintaining reactivity with T cells. Knowledge of the tertiary structure of allergens will make it simpler to identify and change surface epitopes. A completely different approach is to use plasmids to introduce the genes for an allergen. The strength of this technique is that the plasmid can be designed to control expression and also to influence the cytokine profile of the response or the isotype of antibodies produced. Finally, different adjuvants can be used with proteins to alter the response. These include IL-12, immunostimulatory sequences of DNA, and bacterial proteins such as those used in HibVax. It is now possible to identify the cells that control the immune response to allergens and to design treatments that will either downregulate or change the response of T cells. The challenge is to transform this information into an effective treatment for allergic disease.

Prevalence of IgG anti-Der p 2 antibodies in children from high and low antigen exposure groups: relationship of IgG and subclass antibody responses to exposure and allergic symptoms

Serum IgG PAN, IgG1-4, and IgE antibodies (Ab) specific for the house dust mite Dermatophagoides antigen (Ag) Der p 2 were measured by enzyme-linked immunosorbent assay (ELISA) in two groups of school children, age 12-14, exposed to high (Charlottesville, VA) and low (Los Alamos, NM) mite Ag levels in their environment. More than 90% of the children were found to have Der p 2-specific IgG antibodies, although the levels of both IgG PAN and IgG 1-4 Ab were substantially higher in the high exposure group (P = 0.001). In addition, there was considerable overlap between these two groups in all Ab measurements. The presence of IgG anti-Der p 2 Ab in the Los Alamos children was unexpected and suggests continuing Ag exposure, although the source of such exposure is not apparent. There is no correlation between RAST (+) and RAST (-) subjects with respect to the level of IgG Ab measured by ELISA. These results suggest that the IgG Ab response to house dust mite has been underestimated in the RAST negative population. Two twin pairs were included in this study and the divergent and varied Ab responses in these individuals indicate that factors in addition to environmental exposure and genetic susceptibility require further investigation and provide evidence for the complexity of the pathogenesis of the allergic response.