An experimental and modeling-based approach to locate IgE epitopes of plant profilin allergens

Comparative analysis of tropomyosin allergenicity in three different species of molluscs: insights into the role of amino acid composition in IgE epitopes

Limited research has been conducted on the differences in allergenicity among Alectryonella plicatula tropomyosin (ATM), Haliotis discus hannai tropomyosin (HTM), and Mimachlamys nobilis tropomyosin (MTM) in molluscs. Our study aimed to comprehensively analyze and compare their immunoreactivity, sensitization, and allergenicity while simultaneously elucidating the underlying molecular mechanisms involved. We assessed the immune binding activity of TM utilizing 86 sera from allergic patients and evaluated sensitization and allergenicity through two different types of mouse models. The dot-blot and basophil activation test assays revealed strong immunoreactivity for HTM, ATM, and MTM, with HTM exhibiting significantly lower levels compared to ATM. In the BALB/c mouse sensitization model, all TM groups stimulated the production of specific antibodies, elicited IgE-mediated immediate hypersensitivity responses, and caused an imbalance in the IL-4/IFN-γ ratio. Similarly, in the BALB/c mouse model of food allergy, all TM variants induced IgE-mediated type I hypersensitivity responses, leading to the development of food allergies characterized by clinical symptoms and an imbalance in the IL-4/IFN-γ ratio. The stimulation ability of sensitization and the severity of food allergies consistently ranked as ATM > MTM > HTM. Through an in-depth analysis of non-polar amino acid frequency and polar hydrogen bonds, HTM exhibited higher frequencies of non-polar amino acids in its amino acid sequence and IgE epitopes, in comparison with ATM and MTM. Furthermore, HTM demonstrated a lower number of polar hydrogen bonds in IgE epitopes. Overall, HTM exhibited the lowest allergenic potential in both allergic patients and mouse models, likely due to its lower polarity in the amino acid sequence and IgE epitopes.

Molecular Basis of Plant Profilins' Cross-Reactivity

Profilins are ubiquitous allergens with conserved structural elements. Exposure to profilins from different sources leads to IgE-cross-reactivity and the pollen-latex-food syndrome. Monoclonal antibodies (mAbs) that cross-react with plant profilins and block IgE-profilin interactions are relevant for diagnosis, epitope mapping, and specific immunotherapy. We generated IgGs mAbs, 1B4, and 2D10, against latex profilin (anti-rHev b 8) that inhibit the interaction of IgE and IgG4 antibodies from sera of latex- and maize-allergic patients by 90% and 40%, respectively. In this study, we evaluated 1B4 and 2D10 recognition towards different plant profilins, and mAbs recognition of rZea m 12 mutants by ELISAs. Interestingly, 2D10 highly recognized rArt v 4.0101 and rAmb a 8.0101, and to a lesser extent rBet v 2.0101, and rFra e 2.2, while 1B4 showed recognition for rPhl p 12.0101 and rAmb a 8.0101. We demonstrated that residue D130 at the α-helix 3 in profilins, which is part of the Hev b 8 IgE epitope, is essential for the 2D10 recognition. The structural analysis suggests that the profilins containing E130 (rPhl p 12.0101, rFra e 2.2, and rZea m 12.0105) show less binding with 2D10. The distribution of negative charges on the profilins' surfaces at the α-helices 1 and 3 is relevant for the 2D10 recognition, and that may be relevant to explain profilins' IgE cross-reactivity.

Identification of linear epitopes and their major role in the immunoglobulin E-binding capacity of tropomyosin from Alectryonella plicatula

Tropomyosin (TM) is an important allergen in molluscans. However, there was a lack of information about TM as an allergen in oysters. TM was purified and identified from Alectryonella plicatula (ATM), and its primary sequence was cloned and encoded with 284 amino acids (AAs). Chemical denaturants were used to destroy the structure to confirm that linear epitopes played a major role in the immunoglobulin E-binding capacity of ATM. Subsequently, nine linear epitopes were identified using a serological test. The peptide with AA_27-41 was regarded as the key epitope because it could be recognized strongly by most sera of oyster-sensitive individuals in comparison to other epitope peptides. Finally, the epitopes and the primary sequence of TM among shellfish were aligned to find the two conserved epitopes (AA_117-132 and AA_164-178) in oyster, octopus, abalone, scallop, clam, shrimp, and crab. Overall, these data provide a foundation for the allergenicity and cross-reactivity of TM.

A native IgE in complex with profilin provides insights into allergen recognition and cross-reactivity

Allergies have become a rising health problem, where plentiful substances can trigger IgE-mediated allergies in humans. While profilins are considered minor allergens, these ubiquitous proteins are primary molecules involved in cross-reactivity and pollen-food allergy syndrome. Here we report the first crystal structures of murine Fab/IgE, with its chains naturally paired, in complex with the allergen profilin from Hevea brasiliensis (Hev b 8). The crystallographic models revealed that the IgE's six complementarity-determining regions (CDRs) interact with the allergen, comprising a rigid paratope-epitope surface of 926 Å2, which includes an extensive network of interactions. Interestingly, we also observed previously unreported flexibility at Fab/IgE's elbow angle, which did not influence the shape of the paratope. The Fab/IgE exhibits a high affinity for Hev b 8, even when using 1 M NaCl in BLI experiments. Finally, based on the encouraging cross-reactivity assays using two mutants of the maize profilin (Zea m 12), this antibody could be a promising tool in IgE engineering for diagnosis and research applications.

Two hypo-allergenic derivatives lacking the dominant linear epitope of Scy p 1 and Scy p 3

Scylla paramamosain frequently elicits IgE-mediated type-I hypersensitivity reactions. Molecular candidates for crab allergen-specific immunotherapy have not been studied previously. In this study, reduced and alkylated (red/alk) derivatives with destroyed conformational epitopes and mutant derivatives (mtALLERGEN) with deleted heat/digestion-stable linear epitopes were produced of tropomyosin and myosin light chain. Structural changes and the allergenicity of derivatives was analyzed. Compared with wild-type allergens, red/alk derivatives had dramatically altered protein structures, whereas mtALLERGEN showed slightly structural effects. Enzyme linked immunosorbent assay revealed the heterogeneous epitope-recognition patterns with derivatives among 29 crab-sensitised patients, of whom 13% and 62% recognised conformational and linear epitopes, respectively, whereas 25% recognised both epitope types to the same extent. Furthermore, mtALLERGEN could not bind to IgE or induce basophil activation in some patients. These results imply that hypo-allergenic derivatives of crab myofibril allergens that specifically lacked linear epitopes may serve as viable candidates for immunotherapy.

Identification and Amino Acid Analysis of Allergenic Epitopes of a Novel Allergen Paramyosin (Rap v 2) from Rapana venosa

Besides tropomyosin (TM) that is widely recognized as a major allergen in molluscs, a 99-kDa novel allergen (Rap v 2) was recently found in the sea snail Rapana venosa and identified as paramyosin (PM). However, the allergenic epitopes of PM in any molluscs have not been identified yet. In the present study, seven allergenic epitopes of Rap v 2 were identified by immunoinformatics tools, dot-blot inhibition assay, and basophil degranulation assay. Based on the analysis of PM and allergenic epitope amino acids, it was found that highly hydrophobic and positively charged amino acid residues play an important role in the formation of Rap v 2 epitopes. In addition, three potential critical amino acids that may account for TM and PM cross-reactivity in molluscs were found by sequence- and structure-based methods. These findings could be of major importance for improving the understanding of relevant paramyosin epitopes and the prevention and therapy of mollusc allergy.

Novel murine mAbs define specific and cross-reactive epitopes on the latex profilin panallergen Hev b 8

The production of specific antibodies able to recognize allergens from different sources or block interactions between allergens and antibodies mediating allergic reactions is crucial for developing successful tools for diagnostics and therapeutics. Panallergens are highly conserved proteins present in widely different species, implicated in relevant cross-reactions. The panallergen latex profilin (Hev b 8) has been associated with the latex-food-pollen syndrome. We generated five monoclonal IgGs and one IgE from murine hybridomas against recombinant Hev b 8 and evaluated their interaction with this allergen using ELISA and biolayer interferometry (BLI). Affinity purified mAbs exhibited high binding affinities towards rHev b 8, with K_D1 values ranging from 10^-10 M to 10^-11 M. Some of these antibodies also recognized the recombinant profilins from maize and tomato (Zea m 12 and Sola l 1), and the ash tree pollen (Fra e 2). Competition ELISA demonstrated that some mAb pairs could bind simultaneously to rHev b 8. Using BLI, we detected competitive, non-competitive, and partial-competition interactions between pairs of mAbs with rHev b 8, suggesting the existence of at least two non-overlapping epitopes on the surface of this allergen. Three-dimensional models of the Fv of 1B4 and 2D10 IgGs and docking simulations of these Fvs with rHev b 8 revealed these epitopes. Furthermore, these two mAbs inhibited the interaction of polyclonal IgE and IgG4 antibodies from profilin-allergic patients with rHev b 8, indicating that the mAbs and the antibodies present in sera from allergic patients bind to overlapping epitopes on the allergen. These mAbs can be useful tools for immune-localization studies, immunoassay development, or standardization of allergenic products.

Profilin is a marker of severity in allergic respiratory diseases

BACKGROUND

The capacity of profilin to induce allergic symptoms in patients with respiratory allergy has been questioned. In this sense, the aim of this study was to investigate the correlation between profilin exposure and induction of symptoms in a prospective case-control study.

METHODS

The concentration of profilin as well as pollen levels in the air was measured. A diary score of symptoms was collected from allergic patients. Seventy-nine individuals were included in the study; fifty cases and 28 controls were positive or negative to profilin, respectively. Conjunctival and bronchial provocation tests were performed with purified profilin (Pho d 2) in a subgroup of cases and controls.

RESULTS

Profilin was detected in the environment on 133 days (maximum peak of 0.56 ng/m³ ). A positive correlation between profilin and pollen count of Olea and Poaceae was observed (ρ = 0.24; P < .001). Intensity of total, nasal and ocular symptoms was statistically higher in cases than in controls (P < .001). The risk of suffering symptoms, measured by the percentage of patients who presented any of the symptoms each day, was also higher in cases than in controls. The provocation test was positive in 95% of bronchial and 90% of conjunctival challenges in cases, and negative in all controls.

CONCLUSIONS

Profilin was detected in the environment and had the ability to induce a specific allergen response. Patients sensitized to this panallergen showed more symptoms and were more likely to have symptoms. Therefore, sensitization to profilin seems to be a marker of severity in patients with rhinoconjunctivitis and asthma mediated by pollen.

Comparative structural and thermal stability studies of Cuc m 2.0101, Art v 4.0101 and other allergenic profilins

Worldwide, more than one-third of the population suffers from allergies. A significant fraction of officially registered allergens originate from the profilin family of proteins. Profilins are small ubiquitous proteins which are found in plants, viruses and various eukaryotes including mammals. Although they are primarily regarded as minor allergens, profilins are important players in immunoglobulin E (IgE) cross-reactivity. However, in some populations profilins are recognized by IgE from at least 50% of patients allergic to a given allergen source. Cuc m 2.0101 is recognized by IgE in more than 80% of muskmelon-allergic patients. The recombinant isoallergen Cuc m 2.0101 was produced in significant quantities and its X-ray crystal structure was determined. In addition, a new Art v 4.0101 (mugwort profilin) structure was determined. The profilins Cuc m 2.0101 and Art v 4.0101 were compared in terms of their structure and thermal stability. Furthermore, structural similarities and IgE cross-reactivity between profilins from different sources are discussed to explain the molecular basis of various clinical syndromes involving this group of allergens. Special emphasis is placed on discussion of profilins' quaternary structures and their relation to biological function, as well as to protein allergenicity. Moreover, a potential impact of protein purification protocols on the structure of profilins is highlighted.

Peptide Mapping, In Silico and In Vivo Analysis of Allergenic Sorghum Profilin Peptides

Background and objectives: Nearly 20–30% of the world’s population suffers from allergic rhinitis, among them 15% are progressing to asthma conditions. Sorghum bicolor profilin (Sorb PF), one of the panallergens, was identified, but the allergen specificity is not yet characterized. Materials and Methods: To map the antigenic determinants responsible for IgE binding, the present study is focused on in silico modeling, simulation of Sorb PF and docking of the Sorb PF peptides (PF1-6) against IgG and IgE, followed by in vivo evaluation of the peptides for its allergenicity in mice. Results: Peptide PF3 and PF4 displayed high docking G-scores (−9.05) against IgE only. The mice sensitized with PF3 peptide showed increased levels of IL5, IL12, TNF-alpha, and GMCSF when compared to other peptides and controls, signifying a strong, Th2-based response. Concurrently, the Th1 pathway was inhibited by low levels of cytokine IL2, IFN-γ, and IL-10 justifying the role of PF3 in allergenic IgE response. Conclusions: Based on the results of overlapping peptides PF3 and PF4, the N-terminal part of the PF3 peptide (TGQALVI) plays a crucial role in allergenic response of Sorghum profilin.

A robust method for the estimation and visualization of IgE cross-reactivity likelihood between allergens belonging to the same protein family

Among the vast number of identified protein families, allergens emanate from relatively few families which translates to only a small fraction of identified protein families. In allergy diagnostics and immunotherapy, interactions between immunoglobulin E and allergens are crucial because the formation of an allergen-antibody complex is necessary for triggering an allergic reaction. In allergic diseases, there is a phenomenon known as cross-reactivity. Cross-reactivity describes a situation where an individual has produced antibodies against a particular allergenic protein, but said antibodies fail to discriminate between the original sensitizer and other similar proteins that usually belong to the same family. To expound the concept of cross-reactivity, this study examines ten protein families that include allergens selected specifically for the analysis of cross-reactivity. The selected allergen families had at least 13 representative proteins, overall folds that differ significantly between families, and include relevant allergens with various potencies. The selected allergens were analyzed using information on sequence similarities and identities between members of the families as well as reports on clinically relevant cross-reactivities. Based on our analysis, we propose to introduce a new A-RISC index (Allergens’–Relative Identity, Similarity and Cross-reactivity) which describes homology between two allergens belonging to the same protein family and is used to predict the likelihood of cross-reactivity between them. Information on sequence similarities and identities, as well as on the values of the proposed A-RISC index is used to introduce four categories describing a risk of a cross-reactive reaction, namely: high, medium-high, medium-low and low. The proposed approach can facilitate analysis in component-resolved allergy diagnostics, generation of avoidance guidelines for allergic individuals, and help with the design of immunotherapy.

Gene encoding vesicle-associated membrane protein-associated protein from Triticum aestivum (TaVAP) confers tolerance to drought stress

Abiotic stresses like drought, salinity, high and low temperature, and submergence are major factors that limit the crop productivity. Hence, identification of genes associated with stress response in crops is a prerequisite for improving their tolerance to adverse environmental conditions. In an earlier study, we had identified a drought-inducible gene, vesicle-associated membrane protein-associated protein (TaVAP), in developing grains of wheat. In this study, we demonstrate that TaVAP is able to complement yeast and Arabidopsis mutants, which are impaired in their respective orthologs, signifying functional conservation. Constitutive expression of TaVAP in Arabidopsis imparted tolerance to water stress conditions without any apparent yield penalty. Enhanced tolerance to water stress was associated with maintenance of higher relative water content, photosynthetic efficiency, and antioxidant activities. Compared to wild type, the TaVAP-overexpressing plants showed enhanced lateral root proliferation that was attributed to higher endogenous levels of IAA. These studies are the first to demonstrate that TaVAP plays a critical role in growth and development in plants, and is a potential candidate for improving the abiotic stress tolerance in crop plants.

Structural insights into the IgE mediated responses induced by the allergens Hev b 8 and Zea m 12 in their dimeric forms

Oligomerization of allergens plays an important role in IgE-mediated reactions, as effective crosslinking of IgE- FcεRI complexes on the cell membrane is dependent on the number of exposed B-cell epitopes in a single allergen molecule or on the occurrence of identical epitopes in a symmetrical arrangement. Few studies have attempted to experimentally demonstrate the connection between allergen dimerization and the ability to trigger allergic reactions. Here we studied plant allergenic profilins rHev b 8 (rubber tree) and rZea m 12 (maize) because they represent an important example of cross-reactivity in the latex-pollen-food syndrome. Both allergens in their monomeric and dimeric states were isolated and characterized by exclusion chromatography and mass spectrometry and were used in immunological in vitro experiments. Their crystal structures were solved, and for Hev b 8 a disulfide-linked homodimer was found. Comparing the structures we established that the longest loop is relevant for recognition by IgE antibodies, whereas the conserved regions are important for cross-reactivity. We produced a novel monoclonal murine IgE (mAb 2F5), specific for rHev b 8, which was useful to provide evidence that profilin dimerization considerably increases the IgE-mediated degranulation in rat basophilic leukemia cells.

Component-Resolved Diagnosis of Peanut Allergy and Its Possible Origins of Sensitization in China

BACKGROUND

Clinical and immunological characteristics of food allergies vary depending on geographic regions. Little is known about peanut allergy in China. The aim of this study was to investigate the peanut sensitization profile in China.

METHODS

Thirty-eight participants with immunoglobulin E (IgE)-positive responses to peanuts (peanut-sensitized) were included in our study, and clinical characteristics were evaluated. Total and specific IgE reactivity against peanuts, other plant-derived foods, pollens, and related allergen components were determined.

RESULTS

Eighteen patients were symptomatic when exposed to peanuts. The majority of them presented with systemic reactions. More than half of the peanut-sensitized subjects also suffered from mugwort pollinosis and peach allergy. In patients with both peanut and peach allergies, reactions to peanuts were the same as or severer than those to peaches. Positivity rates of IgE response to rAra h 1-3, 8, and 9 in the peanut allergy group were 5.6, 11.1, 5.6, 22.2, and 83.3%, respectively. 66.7% (12/18) of the peanut-allergic patients were monosensitized to rAra h 9. Anti-nArt v 3 [mugwort nonspecific lipid transfer protein (nsLTP)] IgE positivity in the peanut allergy group was significantly higher than that in the asymptomatic peanut-sensitized group. In Ara h 9 (peanut nsLTP)-sensitized patients with mugwort pollinosis, anti-nArt v 3 IgE levels were remarkably higher than anti-rAra h 9 (peanut nsLTP) IgE levels as well as anti-Pru p 3 (peach nsLTP) IgE levels.

CONCLUSIONS

Ara h 9 was the major allergen of peanut, and Ara h 9 monosensitization was the most common peanut sensitization pattern in our population. Furthermore, there was a strong correlation between peanut sensitization and mugwort pollinosis, as well as peach allergy, in our country.

Structural, Functional, and Immunological Characterization of Profilin Panallergens Amb a 8, Art v 4, and Bet v 2

Ragweed allergens affect several million people in the United States and Canada. To date, only two ragweed allergens, Amb t 5 and Amb a 11, have their structures determined and deposited to the Protein Data Bank. Here, we present structures of methylated ragweed allergen Amb a 8, Amb a 8 in the presence of poly(l-proline), and Art v 4 (mugwort allergen). Amb a 8 and Art v 4 are panallergens belonging to the profilin family of proteins. They share significant sequence and structural similarities, which results in cross-recognition by IgE antibodies. Molecular and immunological properties of Amb a 8 and Art v 4 are compared with those of Bet v 2 (birch pollen allergen) as well as with other allergenic profilins. We purified recombinant allergens that are recognized by patient IgE and are highly cross-reactive. It was determined that the analyzed allergens are relatively unstable. Structures of Amb a 8 in complex with poly(l-proline)10 or poly(l-proline)14 are the first structures of the plant profilin in complex with proline-rich peptides. Amb a 8 binds the poly(l-proline) in a mode similar to that observed in human, mouse, and P. falciparum profilin·peptide complexes. However, only some of the residues that form the peptide binding site are conserved.

Inhibition of weak-affinity epitope-IgE interactions prevents mast cell degranulation

Development of specific inhibitors of allergy has had limited success, in part, owing to a lack of experimental models that reflect the complexity of allergen-IgE interactions. We designed a heterotetravalent allergen (HtTA) system, which reflects epitope heterogeneity, polyclonal response and number of immunodominant epitopes observed in natural allergens, thereby providing a physiologically relevant experimental model to study mast cell degranulation. The HtTA design revealed the importance of weak-affinity epitopes in allergy, particularly when presented with high-affinity epitopes. The effect of selective inhibition of weak-affinity epitope-IgE interactions was investigated with heterobivalent inhibitors (HBIs) designed to simultaneously target the antigen- and nucleotide-binding sites on the IgE Fab. HBI demonstrated enhanced avidity for the target IgE and was a potent inhibitor of degranulation in vitro and in vivo. These results demonstrate that partial inhibition of allergen-IgE interactions was sufficient to prevent mast cell degranulation, thus establishing the therapeutic potential of the HBI design.

Design of a heterotetravalent synthetic allergen that reflects epitope heterogeneity and IgE antibody variability to study mast cell degranulation

The present paper describes the design of a HtTA (heterotetravalent allergen) as a multi-component experimental system that enables an integrative approach to study mast cell degranulation. The HtTA design allows presentation of two distinct haptens, each with a valency of 2, thereby better reflecting the complexity of natural allergens by displaying epitope heterogeneity and IgE antibody variability. Using the HtTA design, synthetic allergens HtTA-1 and HtTA-2 were synthesized to model a combination of epitope/IgE affinities. HtTA-1 presented DNP (2,4-dinitrophenyl) and dansyl haptens (Kd=22 and 54 nM for IgEDNP and IgEdansyl respectively) and HtTA-2 presented dansyl and the weak-affinity DNP-Pro (DNP-proline) haptens (Kd=550 nM for IgEDNP). Both HtTAs effectively induced degranulation when mast cells were primed with both IgEDNP and IgEdansyl antibodies. Interestingly tetravalent DNP-Pro or bivalent dansyl were insufficient in stimulating a degranulation response, illustrating the significance of valency, affinity and synergy in allergen-IgE interactions. Importantly, maximum degranulation with both HtTA-1 and HtTA-2 was observed when only 50% of the mast cell-bound IgEs were hapten-specific (25% IgEdansyl and 25% IgEDNP). Taken together, results of the present study establish the HtTA system as a physiologically relevant experimental model and demonstrates its utility in elucidating critical mechanisms of mast cell degranulation.

Assessment of 3D models for allergen research

Allergenic proteins must crosslink specific IgE molecules, bound to the surface of mast cells and basophils, to stimulate an immune response. A structural understanding of the allergen-IgE interface is needed to predict cross-reactivities between allergens and to design hypoallergenic proteins. However, there are less than 90 experimentally determined structures available for the approximately 1500 sequences of allergens and isoallergens cataloged in the Structural Database of Allergenic Proteins. To provide reliable structural data for the remaining proteins, we previously produced more than 500 3D models using an automated procedure, with strict controls on template choice and model quality evaluation. Here, we assessed how well the fold and residue surface exposure of 10 of these models correlated with recently published experimental 3D structures determined by X-ray crystallography or NMR. We also discuss the impact of intrinsically disordered regions on the structural comparison and epitope prediction. Overall, for seven allergens with sequence identities to the original templates higher than 27%, the backbone root-mean square deviations were less than 2 Å between the models and the subsequently determined experimental structures for the ordered regions. Further, the surface exposure of the known IgE epitopes on the models of three major allergens, from peanut (Ara h 1), latex (Hev b 2), and soy (Gly m 4), was very similar to the experimentally determined structures. For the three remaining allergens with lower sequence identities to the modeling templates, the 3D folds were correctly identified. However, the accuracy of those models is not sufficient for a reliable epitope mapping.

A mutant of the major melon allergen, Cuc m 2, with reduced IgE binding capacity is a good candidate for specific immunotherapy

Hypoallergenic mutants with reduced IgE-binding capacity but which show a similar T-cell response to the corresponding natural allergen are ideal tools for immunotherapy, for preventing a possible anaphylactic shock. An IgE conformational epitope has been identified in Cuc m 2, the major allergen and profilin from melon. Since this epitope is highly conserved in most pollen profilins, it may contribute to an explanation of cross-reactivity between pollen and food profilins. Mutants (Mut 1 and Mut 2) were generated by changing specific residues of the Cuc m 2 epitope to alanine, produced in Escherichia coli, and purified by chromatographic methods. Mut 1 showed a slight reduction in IgE binding but an allergenic activity that was similar to recombinant Cuc m 2, as measured by basophil activation test (BAT) and skin prick test (SPT). By contrast, Mut 2 displayed a substantial reduction in IgE-binding capacity (57%) and positive responses, as determined by BAT (33%) and SPT (50%), when compared to those of rCuc m 2. However, the T-cell proliferation and cytokine production induced by Mut 2 and rCuc m 2 were similar. Thus, this mutant represent potential candidate for immunotherapy of profilin allergies.

Molecular cloning and expression of Cucumisin (Cuc m 1), a subtilisin-like protease of Cucumis melo in Escherichia coli

BACKGROUND

Oral allergy syndrome resulted from plant-derived foods is frequent among adults. Allergy to melon (cucumis melo) is one of the most frequent fruit allergies in Iran. Three different major allergens have been found in Cucumis melo that Cuc m 1 (cucumisin) has been identified as the major allergen of melon. Cucumisin is an alkaline serine protease that it is found as a 78kDa protein in precursor form. The aim of this study was production of recombinant Cuc m 1 in Escherichia coli (E. coli) cells and characterization of its allergenicity property.

METHODS

Production of recombinant Cuc m 1 was carried out by cDNA cloning technique into the pET32b(+) vector using specific primers designed based on cucumisin nucleotide sequence available in Genebank database, cucumisin encoding gene and directional cloning method. Cloned plasmid into E. coli TOP10 was transformed into E. coli BL21 and expression of the protein was induced by IPTG. The recombinant protein was purified via Ni-NTA affinity chromatography using histidine tag in recombinant protein. IgE binding of this protein was assessed by IgE-immunoblotting, ELISA and inhibition ELISA.

RESULTS

The directional cloning was resulted in expression of a fusion Cuc m 1. Immunoblotting with sera of patients allergic to melon showed strong reactivity with purified protein band. Inhibition assays demonstrated that purified rCuc m 1 could be the same with natural form of Cuc m 1 in total extract.

CONCLUSIONS

In the present study, we have provided a functional recombinant cucumisin allergen, rCuc m 1 with 86kDa, which may be used as a standard allergen for clinical diagnosis and study of allergy to melon.

Pollen and plant food profilin allergens show equivalent IgE reactivity

BACKGROUND

Profilins are commonly involved in polysensitization of allergic patients; therefore, appropriate markers should be used in component-resolved diagnosis.

OBJECTIVE

To evaluate the immunological equivalence between profilins from pollens and plant-derived foods, to be used in component-resolved diagnosis.

METHODS

Specific immunoglobulin (Ig) G antibodies against pollen and fruit profilins, as well as sera from patients allergic to mustard, melon, or olive pollen, were used. Purified profilins from mustard seeds, fruit melon, and chenopod and birch pollen were assayed in immunoblotting, enzyme-linked immunosorbent assay (ELISA), and ELISA inhibition assays.

RESULTS

Significant correlation was found in the response of purified profilins by ELISA and immunoblotting for both specific IgG and IgE. The highest levels of IgE binding were obtained for olive pollen-allergic patients, which could be related to the route of sensitization. The responses of individual patients to profilins were also similar and independent of the sensitizing source. The inhibition between pairs of allergens was generally higher than 70%, indicating that profilins share most of the IgE epitopes. Modeling of mimotopes in the conformational structure of the implicated profilins supports their strong cross-reactivity obtained experimentally.

CONCLUSIONS

No correlation exists between the level of IgE response of individual patients to specific profilins and the corresponding theoretical sensitizing source, suggesting that the sensitization could be attributable to any profilin present in the environment of the patients. This would bear out the use of most profilins as a common marker for polysensitization in component-resolved diagnosis and for therapeutic approaches.

Profilins: mimickers of allergy or relevant allergens?

Profilins are ubiquitous proteins, present in all eukaryotic cells and identified as allergens in pollen, latex and plant foods. The highly conserved structure justifies the cross-reactive nature of IgE antibodies against plant profilins and their designation as pan-allergens. Primary sensitization to profilin seems to arise from pollen sensitization with later development of cross-reactive IgE antibodies against plant food (and possibly latex) profilins. The role of profilin in inducing allergic symptoms needs to be evaluated and raises important issues in allergy diagnosis due to cross-reactivity. IgE cross-reactivity among profilins is associated with multiple pollen sensitization and with various pollen-food syndromes. In respiratory allergy, sensitization to pollen to which the patient has virtually no environmental exposure has been identified as a manifestation of profilin sensitization. As a food allergen, profilin usually elicits mild reactions, such as oral allergy syndrome, is not modified by processing and is especially important in allergy to some fruits, such as melon, watermelon, banana, tomato, citrus fruit and persimmon. Purified natural and recombinant profilins for in vitro and in vivo allergy tests are helpful in the diagnostic work-up. Herein we review the current state of knowledge about the allergen profilin and its implications in the diagnosis and treatment of allergic diseases. We conclude that, although its role in triggering allergic symptoms is still controversial, profilin is undoubtedly a relevant allergen. As a pan-allergen, profilin is associated with multiple pollen sensitization and pollen-food-latex syndromes that the allergist has to be aware of in order to accomplish an accurate diagnosis and successful treatment of allergic diseases.

A generic approach to evaluate how B-cell epitopes are surface-exposed on protein structures

Methods that predict antibody epitopes could help to promote the development of diagnostic tools, vaccines or immunotherapies by affecting the epitope binding of antibodies during an immunological response to antigens.

It is generally assumed that there is a direct relationship between antibody accessibility to antigens and accessible surface of proteins. Based on this assumption, prediction systems often includes solvent accessibility values calculated from the primary sequence of proteins or from their three dimensional structures as a predictive criterion. However, the current prediction systems seem weakly efficient in view of benchmark tests.

We were interested in evaluating how amino acids that have been experimentally identified as epitopic elements could differ from the rest of the antigenic molecule at the level of surface exposure, hence we assessed the average accessibility of epitopes. The approach used here utilises published epitopes deduced from numerous identification techniques, including sequence scanning and structure visualisation after crystallography, and it involves many types of antigens from toxins to allergens. Our results show that epitopic residues are not distributed among any specific Relative Surface Accessibility and Protrusion Index values and that, in some cases, epitopes cover the entire antigenic sequence.

These results led to the conclusion that the classification of known epitopes with respect to the experimental conditions used to identify them should be introduced before attempting to characterise epitopic areas in a generic way.

nsLTP and profilin are allergens in mustard seeds: cloning, sequencing and recombinant production of Sin a 3 and Sin a 4

BACKGROUND

Patients allergic to mustard are frequently sensitized to peach.

OBJECTIVE

To identify and analyse new yellow mustard allergens that could be involved in IgE cross-reactivity.

METHODS

Sera from mustard-allergic patients with symptoms to peach were studied. Mass spectrometry analyses provided sequences of IgE-reactive proteins. cDNAs encoding Sin a 3 and Sin a 4 were amplified by polymerase chain reaction, cloned and sequenced. The recombinant allergens were obtained in Pichia pastoris and Escherichia coli, respectively, and used for ELISA, immunoblotting and inhibition experiments. Sequence alignment was used to identify common IgE epitopes.

RESULTS

Sin a 3- and Sin a 4-specific cDNAs encode for mature proteins of 92 and 131 amino acids that belong to nsLTP and profilin protein families, respectively. Sin a 3 and Sin a 4 showed 54% and 80% identity with allergenic nsLTP from peach and profilin from melon, respectively. Both recombinant allergens were IgE-reactive in ELISA and immunoblotting. Peach pulp and peel, and melon extracts nearly abolished the IgE binding to recombinant Sin a 3 or recombinant Sin a 4 in immunoblotting.

CONCLUSION

Sin a 3 (nsLTP) and Sin a 4 (profilin) were identified as new mustard allergens and showed IgE cross-reactivity with fruits such as peach or melon, respectively. The knowledge of these two allergens will contribute towards better understand with cross-reactivity between mustard and other plant food allergens, and their availability will provide physicians with useful tools for molecular diagnosis.

The identification of allergen proteins in sugar beet (Beta vulgaris) pollen causing occupational allergy in greenhouses

Background

During production of sugar beet (Beta vulgaris) seeds in greenhouses, workers frequently develop allergic symptoms. The aim of this study was to identify and characterize possible allergens in sugar beet pollen.

Methods

Sera from individuals at a local sugar beet seed producing company, having positive SPT and specific IgE to sugar beet pollen extract, were used for immunoblotting. Proteins in sugar beet pollen extracts were separated by 1- and 2-dimensional electrophoresis, and IgE-reactive proteins analyzed by liquid chromatography tandem mass spectrometry.

Results

A 14 kDa protein was identified as an allergen, since IgE-binding was inhibited by the well-characterized allergen Che a 2, profilin, from the related species Chenopodium album. The presence of 17 kDa and 14 kDa protein homologues to both the allergens Che a 1 and Che a 2 were detected in an extract from sugar beet pollen, and partial amino acid sequences were determined, using inclusion lists for tandem mass spectrometry based on homologous sequences.

Conclusion

Two occupational allergens were identified in sugar beet pollen showing sequence similarity with Chenopodium allergens. Sequence data were obtained by mass spectrometry (70 and 25%, respectively for Beta v 1 and Beta v 2), and can be used for cloning and recombinant expression of the allergens. As for treatment of Chenopodium pollinosis, immunotherapy with sugar beet pollen extracts may be feasible.