Recombinant expression, purification and cross-reactivity of chenopod profilin: rChe a 2 as a good marker for profilin sensitization

Structural insights into the amino acid usage variations in the profilin gene family

Profilin protein is present ubiquitously in all forms of life and is allied with allergic responses among atopic individuals. In addition to this, profilins from various food sources are also associated with IgE cross-reactivity and are thus classified as pan-allergens. The present study unravels the physicochemical basis of differential amino acid usage patterns observed in the profilin gene family. Correspondence analysis based on amino acid usage of allergen and non-allergen profilins revealed discrete clusters among them, signifying differential patterns of amino acid usage. The amino acids, namely methionine, proline, histidine, glutamine, glutamic acid, tryptophan and glycine were found to be more frequently utilised by the allergen profilins compared to the non-allergens. Correlation analysis revealed that physicochemical features like protein disorder, trypsin digestion and solubility differed significantly among the allergen and non-allergen profilins, thus supporting the observations from correspondence analysis. In addition, comprehensive sequence analysis revealed that the allergen profilins possess conserved motifs which may correlate with their distinct physicochemical features. An in-depth structural analysis revealed that the over-represented amino acids in allergen profilins have a propensity of being exposed on the surface, which may be attributed to their distinct allergenic characteristics. The distinguished physicochemical features observed among allergens and non-allergens can be employed as descriptors to develop machine learning-based allergenicity prediction models.

Environmental behaviour of airborne Amaranthaceae pollen in the southern part of the Iberian Peninsula, and its role in future climate scenarios

The Amaranthaceae family includes a number of species which, through a series of specific adaptations, thrive in salty soils, arid environments and altered human settlements. Their ability to tolerate high temperatures favours summer flowering, giving rise to the widespread involvement of Amaranthaceae pollen grains in summer allergies, both in Mediterranean Europe and in areas with arid climates. This study analysed a 21-year set of historical airborne Amaranthaceae pollen records for an area located in the southern part of the Iberian Peninsula, in order to chart species' environmental reaction to changing climate conditions which occurred in the last decades. Airborne pollen data were collected from January 1991 to December 2011 using a Hirst-type volumetric impact sampler. Results showed that Amaranthaceae pollen remained in the atmosphere for over 6 months along the year, from early spring until early autumn. The annual Pollen Index ranged from barely 200 grains to almost 2000 grains, and was strongly influenced by rainfall during the flowering period, which prompted the development of new individuals and thus an increase in pollen production. A trend was noted towards increasingly early pollen peak dates; peaks were recorded in August-September in years with summer rainfall, but as early as May-June in years when over 50% of annual rainfall was recorded in the months prior to flowering. The gradual decline in the annual Pollen Index over later years is attributable not only to growing urbanisation of the area but also to a change in rainfall distribution pattern. High maximum temperatures in spring were also directly related to the peak date and the Pollen Index. This ability to adapt to changeable and occasionally stressful and restrictive, environmental conditions places Amaranthaceae at a competitive advantage with respect to other species sharing the same ecological niche. An increased presence of Amaranthaceae is likely to have a greater impact on future scenarios for pollen allergy diseases associated with climate change.

The spectrum of olive pollen allergens. From structures to diagnosis and treatment

Olive tree is one of the main allergy sources in Mediterranean countries. The identification of the allergenic repertoire from olive pollen has been essential for the development of rational strategies of standardization, diagnosis, and immunotherapy, all of them focused to increase the life quality of the patients. From its complex allergogram, twelve allergens - Ole e 1 to Ole e 12 - have been identified and characterized to date. Most of them have been cloned and produced as recombinant forms, whose availability have allowed analyzing their three-dimensional structures, mapping their T-cell and B-cell epitopes, and determining the precise allergenic profile of patients for a subsequent patient-tailored immunotherapy. Protein mutant, hypoallergenic derivatives, or recombinant fragments have been also useful experimental tools to analyze the immune recognition of allergens. To test these molecules before using them for clinic purposes, a mouse model of allergic sensitizations has been used. This model has been helpful for assaying different prophylactic approaches based on tolerance induction by intranasal administration of allergens or hypoallergens, used as free or integrated in different delivery systems, and their findings suggest a promising utilization as nasal vaccines. Exosomes - nanovesicles isolated from bronchoalveolar lavage fluid of tolerogenic mice - have shown immunomodulatory properties, being able to protect mice against sensitization to Ole e 1.

Allergens of weed pollen: an overview on recombinant and natural molecules

Weeds represent a botanically unrelated group of plants that usually lack commercial or aesthetical value. Pollen of allergenic weeds are able to trigger type I reactions in allergic patients and can be found in the plant families of Asteraceae, Amaranthaceae, Plantaginaceae, Urticaceae, and Euphorbiaceae. To date, 34 weed pollen allergens are listed in the IUIS allergen nomenclature database, which were physicochemically and immunologically characterized to varying degrees. Relevant allergens of weeds belong to the pectate lyase family, defensin-like family, Ole e 1-like family, non-specific lipid transfer protein 1 family and the pan-allergens profilin and polcalcins. This review provides an overview on weed pollen allergens primarily focusing on the molecular level. In particular, the characteristics and properties of purified recombinant allergens and hypoallergenic derivatives are described and their potential use in diagnosis and therapy of weed pollen allergy is discussed.

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.

Chenopodium album pollen profilin (Che a 2): homology modeling and evaluation of cross-reactivity with allergenic profilins based on predicted potential IgE epitopes and IgE reactivity analysis

The inhalation of Chenopodium album (C. album) pollen has been reported as an important cause of allergic respiratory symptoms. The aim of this study was to produce the recombinant profilin of C. album (rChe a 2) pollen and to investigate its cross-reactivity with other plant-derived profilins based on potential conformational epitopes and IgE reactivity analysis. Che a 2-coding sequence was cloned, expressed, and purified using one step metal affinity chromatography to recover high-purity target protein. We assessed cross-reactivity and predicted IgE potential epitopes among rChe a 2 and other plant-derived profilins. Immunodetection and inhibition assays using sixteen individual sera from C. album allergic patients demonstrated that purified rChe a 2 could be the same as that in the crude extract. The results of inhibition assays among rChe a 2 and other plant-derived profilins were in accordance with those of the homology of predicted conserved conformational regions. In this study, amino acid sequence homology analysis showed that a high degree of IgE cross-reactivity among plant-derived profilins may depend on predicted potential IgE epitopes.

Component-resolved diagnosis of pollen allergy based on skin testing with profilin, polcalcin and lipid transfer protein pan-allergens

BACKGROUND

Allergy diagnosis needs to be improved in patients suffering from pollen polysensitization due to the existence of possible confounding factors in this type of patients.

OBJECTIVE

To evaluate new diagnostic strategies by comparing skin responses to pan-allergens and conventional allergenic extracts with specific IgE (sIgE) to purified allergen molecules.

METHODS

One thousand three hundred and twenty-nine pollen-allergic patients were diagnosed by a combination of an in vitro method with a panel of 13 purified allergens, including major allergens and pan-allergens, using a high-capacity screening technology (ADVIA-Centaur) and skin prick test (SPT) to pan-allergens and conventional extracts.

RESULTS

There was a high concordance (kappa index) between in vitro (sIgE to major allergens) and in vivo (SPT to conventional extracts) methods in patients who were not sensitized to pan-allergens, but SPT with conventional extracts failed to diagnose patients with sensitization to pan-allergens. In patients who were simultaneously sensitized to polcalcins and profilins, there was a duplication both in the number of sensitizations to major allergens and in the years of disease evolution. There was a statistical association between sensitization to profilins and/or lipid transfer proteins and food allergy (P<0.0001).

CONCLUSION

The novel diagnostic strategy has proven to be a valuable tool in daily clinical practice. Introduction of routine SPT to pan-allergens is a simple and feasible way of improving diagnostic efficacy. Patients sensitized to pan-allergens should be tested by an adequate panel of allergenic molecules in order to identify the allergens that are responsible for the allergic disease.

Cloning and expression of the allergen Cro s 2 profilin from saffron (Crocus sativus)

BACKGROUND

Profilin is a panallergen that is recognized by IgE in allergic patients. Allergy to saffron (Crocus sativus) pollen has been described in people exposed to its pollen. Saffron contains a profilin that may cause allergic reactions in atopic subjects. The aim of this study was to describe the cloning, expression and purification of saffron profilin from pollen.

METHODS

Cloning of saffron profilin was performed by polymerase chain reaction using specific primers from saffron pollen RNA. Expression was carried out in Escherichia coli BL21 (DE3) using a vector pET-102- TOPO. A recombinant fusion protein was expressed and the recombinant profilin was purified by metal precipitation. Immunological characterization was performed by immunoblotting experiments.

RESULTS

The 34kDa- recombinant saffron profilin, Cro s 2, as a fusion protein was purified. Immunoblotting tested with the sera of allergic patients showed a specific reaction with the recombinant Cro s 2 band.

CONCLUSIONS

The sequence of Cro s 2 showed a high degree of identity and similarity to other plant profilins and the recombinant saffron profilin, Cro s 2, may be used for target-specific diagnosis and structural analyses and investigation of cross reactivity of Cro s 2 with other plant profilins.

Understanding patient sensitization profiles in complex pollen areas: a molecular epidemiological study

BACKGROUND

Allergy diagnosis in patients exposed to multiple pollen species is complex and misdiagnosis is often a cause for unsuccessful specific immunotherapy.

OBJECTIVE

We studied the sensitization profile of individual allergens (major, minor and pan-allergens) in pollen-sensitized patients in a region with high exposure to olive pollen by investigating the influence of minor allergens on allergic disease and the association between pan- and minor allergen sensitizations.

METHODS

A panel of 13 purified allergens, which included the most relevant allergens in the area, as well as minor olive allergens and pan-allergens, were screened using a high-capacity technology (ADVIA-Centaur) in 891 patients.

RESULTS

Olive allergy as measured by specific IgE to Ole e 1 was the leading pollinosis in the area. The minor olive allergens Ole e 7 and Ole e 9 were markers of more severe allergic illness. Profilin sensitization was associated mainly with grass allergy, the second most prevalent pollinosis. Salsola kali pollen allergy was the third most common cause of pollinosis in the area. The prevalence of sensitization to the peach allergen Pru p 3, a nonspecific lipid-transfer protein, was notable.

CONCLUSION

Epidemiological analysis by component-resolved diagnosis is a new method, which elucidates the interaction between allergen exposure gradient and patient sensitization. High exposure leads to differential sensitization profiles some of which are associated with more severe allergic conditions. Profilin sensitization, related mainly to grass pollinosis, was a marker of more severe grass pollen sensitization.

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.

A pectin methylesterase as an allergenic marker for the sensitization to Russian thistle (Salsola kali) pollen

BACKGROUND

Chenopodiaceae pollen is considered the main cause of pollen allergy in desert countries and its incidence is world-wide increasing by the desertization of extensive zones. Although the correlation between the sensitization to Chenopodium album and Salsola kali pollens of patients suffering from allergy to Chenopodiaceae pollens is high, a significant number of patients exhibited IgE sensitivity exclusively towards S. kali.

OBJECTIVE

To analyse this differential reactivity and to purify, clone and characterize the putative responsible allergen.

METHODS

Immunoblotting was used to analyse the IgE binding to pollen extract for S. kali and C. album. The protein was isolated by two chromatographic steps and characterized by Edman degradation, mass spectrometry, finger print analysis and Concanavalin A lectin staining. Specific cDNA was amplified by polymerase chain reaction, cloned in Escherichia coli and sequenced. Immunologic characterization was performed by immunoblotting, enzyme-linked immunoassay detection and inhibition experiments using sera from 11 patients allergic to S. kali pollen.

RESULTS

cDNA codifies for a mature protein of 339 amino acids plus a putative signal peptide of 23 residues and it belongs to the plant pectin methylesterase (PME) family. It is a mildly basic and polymorphic protein and was recognized by the IgE from all the patients allergic to S. kali included in the study, and was called Sal k 1. The protein was not recognized in the C. album pollen extract using the sera of these patients.

CONCLUSION

Sal k 1 is a protein from the PME family with a high allergenic relevance. Considering this allergen as responsible for the different sensitization between S. kali and C. album pollen, it may be a useful marker to classify patients allergic to Chenopodiaceae allowing a safer and more specific immunotherapy.

Emerging pollen allergens

Numerous pollen allergens have been reported over the last few years. Most of them belong to well-known families of proteins but some others constitute the first member of new allergenic families. Some of the factors that can contribute to the detection and identification of new pollen allergens are: a) advances in the technology tools for molecular analysis; and b) the deep knowledge of many allergenic sources. The combination of these factors has provided vast information on the olive pollen allergogram and the identification of minor allergens that become major ones for a significant population. The close taxonomical relationship between olive tree and ash -both Oleaceae- has permitted to identify Fra e 1 (the Ole e 1-like allergen) in ash pollen and to detect the presence of protein homologues of Ole e 3 and Ole e 6. In the other hand, extensive areas of south Europe are suffering an increasing desertification. As a consequence of this, new botanical species are spontaneously growing in these areas or being used in greening ground programs: Chenopodium album and Salsola kali are some examples recently recognized as allergenic woods. The identification of the complete panel of allergens from the hypersensitizing sources might help to develop more accurate diagnosis, and efficient and safer therapy tools for Type-I allergic diseases.

Hypersensitivity to black locust (Robinia pseudoacacia) pollen: "allergy mirages"

BACKGROUND

The allergenicity of the ornamental tree Robinia pseudoacacia, or black locust, is unknown.

OBJECTIVE

To evaluate the prevalence of sensitization to R. pseudoacacia pollen, its possible allergenic cross-reactivity with other common pollens, and the potential implication of pollen panallergens (profilin, polcalcin, and 1,3-beta-glucanase) as a cause of sensitization to R. pseudoacacia pollen.

METHODS

Skin prick testing with R. pseudoacacia pollen was performed in 149 patients with pollinosis. Nasal challenge with R. pseudoacacia pollen was performed in 10 patients. The prevalence of sensitization to the recombinant forms of profilin (rChe a 2), polcalcin (rChe a 3), and the N-terminal of the 1,3-beta-glucanase (rNtD of Ole e 9) was investigated. Immunoblotting, enzyme-linked immunosorbent assay, and competitive inhibition assays were performed with R. pseudoacacia pollen and recombinant pollen allergens.

RESULTS

Sixty-four patients (43%) had positive skin prick test reactions to R. pseudoacacia pollen. Nasal challenge results were positive in 5 sensitized patients and negative in 4 controls and 1 sensitized patient. The allergenic profile of R. pseudoacacia pollen comprises at least the panallergen profilin, a calcium-binding protein, and a 1,3-beta-glucanase. The prevalence of sensitization to rChe a 2, rChe a 3, and rNtD of Ole e 9 was 60%, 33%, and 87%, respectively, among patients sensitized to R. pseudoacacia pollen. Binding of IgE to R. pseudoacacia extract was completely inhibited by Robinia, Chenopodium, Olea, Cupressus, and Lolium extracts.

CONCLUSIONS

The high prevalence of R. pseudoacacia pollen sensitization in patients with pollinosis is likely to be due to cross-sensitization to panallergens (profilin, polcalcin, and 1,3-beta-glucanase) from other common pollens. This phenomenon may lead to a diagnosis of "allergy mirages."

Cross-reactivity of pollen allergens: recommendations for immunotherapy vaccines

PURPOSE OF REVIEW

This review will summarize recent research on pollen allergen and epitope cross-reactivity. Knowledge of these relationships aids in the rational formulation of allergen immunotherapy vaccines.

RECENT FINDINGS

There has been further clarification of panallergens and their roles as both major and minor allergens. Recent studies have targeted non-specific lipid transfer proteins and calcium-binding proteins (polcalcins), as well as pathogenesis-related protein families and profilins. Polcalcins and non-specific lipid transfer proteins are responsible for pollen-fruit interactions as well as pollen cross-reactivity, in some cases, but not all, accounting for major allergenicity. Delineation of the enzymatic activity of certain allergens explains the ubiquitous nature of these pollen proteins.

SUMMARY

Characterization of specific pollen allergens and their protein families has provided insight into the grounds for cross-reactivity. Continuing clarification of these relationships will allow the substitution and consolidation of inhalant extracts as described in the conclusion.