Diagnosis of Parietaria judaica pollen allergy using natural and recombinant Par j 1 and Par j 2 allergens

Allergenicity at component level of sub-pollen particles from different sources obtained by osmolar shock: A molecular approach to thunderstorm-related asthma outbreaks

BACKGROUND

The so-called "thunderstorm asthma" (TA) is an uncommon but dramatic outbreak of asthma attacks occurring during a thunderstorm in the pollen and moulds season. Mechanisms which make the pollen able to enter the deeper airways and provoke severe asthma symptoms are still unclear.

OBJECTIVE

To test the hypothesis that sub-pollen particles (SPPs) originated from the rupture by an osmotic shock of pollen associated with TA contain allergens.

METHODS

After hydration, SPPs released from pollen grains of grass, pellitory, olive, cypress, ragweed and birch were isolated and determined by microscopy. Allergens were determined by in vitro ELISA inhibition tests indirectly using the sera from 10 polyreactive patients. An inhibition <50% was considered as negative, 50%-75% moderate and > 75% complete.

RESULTS

The inhibition experiments showed that the SPPs from birch and cypress were unable to inhibit serum IgE reactivity to Bet v 1 and Cup a 1, respectively. Ragweed SPPs inhibited ragweed pollen extract and Amb a 1 by 75.8 ± 0.11% and 81.2 ± 0.15%, respectively. Olive and pellitory SPPs retained almost the whole IgE-binding capability in all cases tested. Grass SPPs inhibited 32 ± 0.06% of Lolium perenne Lol p 1 and 65% of Phleum pratense extracts, but results were highly variable for individual allergens (97.5%-0.03% for Phl p 2, 45.3 ± 0.12% for Phl p 5, 24.7 ± 0.22% for Phl p 6, and 38.3 ± 0.2% for Phl p 1).

CONCLUSIONS

Inhibition experiments confirm the hypothesis that SSPs obtained after the osmotic shock of pollen involved in TA, namely grass, pellitory and olive tree pollen, contain allergens and therefore they can induce severe asthma attacks during thunderstorms.

Recombinant allergens for immunotherapy: state of the art

PURPOSE OF REVIEW

More than 30 years ago, the first molecular structures of allergens were elucidated and defined recombinant allergens became available. We review the state of the art regarding molecular AIT with the goal to understand why progress in this field has been slow, although there is huge potential for treatment and allergen-specific prevention.

RECENT FINDINGS

On the basis of allergen structures, several AIT strategies have been developed and were advanced into clinical evaluation. In clinical AIT trials, promising results were obtained with recombinant and synthetic allergen derivatives inducing allergen-specific IgG antibodies, which interfered with allergen recognition by IgE whereas clinical efficacy could not yet be demonstrated for approaches targeting only allergen-specific T-cell responses. Available data suggest that molecular AIT strategies have many advantages over allergen extract-based AIT.

SUMMARY

Clinical studies indicate that recombinant allergen-based AIT vaccines, which are superior to existing allergen extract-based AIT can be developed for respiratory, food and venom allergy. Allergen-specific preventive strategies based on recombinant allergen-based vaccine approaches and induction of T-cell tolerance are on the horizon and hold promise that allergy can be prevented. However, progress is limited by lack of resources needed for clinical studies, which are necessary for the development of these innovative strategies.

Expression and characterization of recombinant Par j 1 and Par j 2 resembling the allergenic epitopes of Parietaria judaica pollen

The weed wall pellitory, Parietaria judaica, is one the most important pollen allergen sources in the Mediterranean area causing severe symptoms of hay fever and asthma in allergic patients. We report the expression of the major Parietaria allergens, Par j 1 and Par j 2 which belong to the family of lipid transfer proteins, in insect cells. According to circular dichroism analysis and gel filtration, the purified allergens represented folded and monomeric proteins. Insect cell-expressed, folded Par j 2 exhibited higher IgE binding capacity and more than 100-fold higher allergenic activity than unfolded Escherichia coli-expressed Par j 2 as demonstrated by IgE ELISA and basophil activation testing. IgE ELISA inhibition assays showed that Par j 1 and Par j 2, contain genuine and cross-reactive IgE epitopes. IgG antibodies induced by immunization with Par j 2 inhibited binding of allergic patients IgE to Par j 1 only partially. IgE inhibition experiments demonstrated that insect cell-expressed Par j 1 and Par j 2 together resembled the majority of allergenic epitopes of the Parietaria allergome and therefore both should be used for molecular diagnosis and the design of vaccines for allergen-specific immunotherapy of Parietaria allergy.

Pollen Allergens for Molecular Diagnosis

Pollen allergens are one of the main causes of type I allergies affecting up to 30% of the population in industrialized countries. Climatic changes affect the duration and intensity of pollen seasons and may together with pollution contribute to increased incidences of respiratory allergy and asthma. Allergenic grasses, trees, and weeds often present similar habitats and flowering periods compromising clinical anamnesis. Molecule-based approaches enable distinction between genuine sensitization and clinically mostly irrelevant IgE cross-reactivity due to, e. g., panallergens or carbohydrate determinants. In addition, sensitivity as well as specificity can be improved and lead to identification of the primary sensitizing source which is particularly beneficial regarding polysensitized patients. This review gives an overview on relevant pollen allergens and their usefulness in daily practice. Appropriate allergy diagnosis is directly influencing decisions for therapeutic interventions, and thus, reliable biomarkers are pivotal when considering allergen immunotherapy in the context of precision medicine.

Recombinant allergen-based provocation testing

Over the last 25 years, recombinant allergens from all important allergen sources have been cloned and are now available as recombinant proteins. These molecules can be produced in practically unlimited amounts without biological or batch-to-batch variability. It has been shown in provocation tests that recombinant allergens have similar clinical effects as their natural counterparts. With the help of these tools it is possible to reveal the precise reactivity profiles of patients and to uncover and differentiate cross-reactivity from genuine sensitization to an allergen source. Although it has been shown some time ago that it would be possible to replace crude allergen extracts with recombinant allergens for skin prick testing, and even though the use of allergen components can improve routine diagnosis, these tools are still not available for clinical routine applications. The use of provocation tests is a crucial step in the development of new, hypoallergenic vaccines for therapy of allergic disease. Here we describe important provocation methods (skin prick test, intradermal test, atopy patch test, nasal provocation, colonoscopic provocation test) and give an overview of the clinical provocation studies which have been performed with recombinant allergens so far.

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.

Diagnosis of Chenopodium album allergy with a cocktail of recombinant allergens as a tool for component-resolved diagnosis

Chenopodium album pollen is one of the main sources of pollen allergy in desert and semi-desert areas and contains three identified allergens, so the aim of this study is comparison of the diagnostic potential of C. album recombinant allergens in an allergenic cocktail and C. album pollen extract. Diagnostic potential of the allergenic cocktail was investigated in 32 individuals using skin prick test and obtained results were compared with the acquired results from C. album pollen extract. Specific IgE reactivity against the pollen extract and allergenic cocktail was determined by ELISA and western blotting tests. Inhibition assays were performed for the allergenic cocktail characterization. The exact sensitization profile of all patients was identified which showed that 72, 81 and 46% of allergic patients had IgE reactivity to rChe a 1, rChe a 2 and rChe a 3, respectively. Almost all of C. album allergic patients (30/32) had specific IgE against the allergenic cocktail. In addition, there was a high correlation between IgE levels against the allergenic cocktail and IgE levels against the pollen extract. The allergenic cocktail was able to completely inhibit IgE binding to natural Che a 1, Che a 2 and Che a 3 in C. album extract. In addition, positive skin test reactions were seen in allergic patients that tested by the allergenic cocktail. The reliable results obtained from this study confirmed that the allergenic cocktail with high diagnostic potential could be replaced with natural C. album allergen extracts in skin prick test and serologic tests.

Par j 1 and Par j 2, the two major allergens in Parietaria judaica, bind preferentially to monoacylated negative lipids

Par j 1 and Par j 2 proteins are the two major allergens in Parietaria judaica pollen, one of the main causes of allergic diseases in the Mediterranean area. Each of them contains eight cysteine residues organized in a pattern identical to that found in plant nonspecific lipid transfer proteins. The 139- and 102-residue recombinant allergens, corresponding respectively to Par j 1 and Par j 2, refold properly to fully functional forms, whose immunological properties resemble those of the molecules purified from the natural source. Molecular modeling shows that, despite the lack of extensive primary structure homology with nonspecific lipid transfer proteins, both allergens contain a hydrophobic cavity suited to accommodate a lipid ligand. In the present study, we present novel evidence for the formation of complexes of these natural and recombinant proteins from Parietaria pollen with lipidic molecules. The dissociation constant of oleyl-lyso-phosphatidylcholine is 9.1 +/- 1.2 microm for recombinant Par j 1, whereas pyrenedodecanoic acid shows a much higher affinity, with a dissociation constant of approximately 1 microm for both recombinant proteins, as well as for the natural mixture. Lipid binding does not alter the secondary structure content of the protein but is very efficient in protecting disulfide bonds from reduction by dithiothreitol. We show that Par j 1 and Par j 2 not only bind lipids from micellar dispersions, but also are able to extract and transfer negative phospholipids from bilayers.

Quantification of Art v 1 and Act c 1 being major allergens of mugwort pollen and kiwi fruit extracts in mass-units by ion-exchange HPLC-UV method

A simple ion-exchange HPLC-UV method was developed for determination of major allergens from mugwort pollen and kiwi fruit extracts in mass-units. The separation of Art v 1 and Act c 1 from other components in the extracts was achieved in one step. The extinction coefficients used in the study were theoretically determined and compared to the extinction coefficients determined by gravimetry. We also reported a close correlation of the major allergen contents with the overall allergenic potency of the extracts determined by inhibition ELISA. This method could be a useful tool for standardization of allergenic extracts for clinical use.

Genetically engineered hybrid proteins from Parietaria judaica pollen for allergen-specific immunotherapy

BACKGROUND

Despite the use of conventional allergen-specific immunotherapy in clinical practice, more defined, efficient, and safer allergy vaccines are required.

OBJECTIVE

The aim of the study was to obtain hypoallergenic molecules by deleting B-cell epitopes, which could potentially be applied to Parietaria judaica pollen allergy treatment.

METHODS

Three hybrid molecules (Q1, Q2, and Q3) derived from fragments of the 2 major P judaica pollen allergens, Par j 1 and Par j 2, were engineered by means of PCR. Hybrid structures were compared with their natural components by means of circular dichroism, and their biologic activities were compared by using T-cell proliferation assays. Their IgE-binding activity was determined with Western blotting, skin prick tests, and enzyme allergosorbent and ELISA inhibition tests.

RESULTS

The hybrid proteins, especially Q2 and Q3, revealed significantly reduced IgE reactivity compared with the natural allergens, as well as with the whole P judaica extract. Furthermore, in vivo skin prick tests showed that the hybrid proteins had a significantly lower potency to induce cutaneous reactions than the whole P judaica extract. Two (Q1 and Q2) of the 3 hybrid proteins induced a comparable T-cell proliferation response as that produced by the whole extract and natural allergens.

CONCLUSION

Considering its reduced anaphylactogenic potential, together with its conserved T-cell reactivity, the engineered Q2 protein could be used in safe and shortened schedules of allergen-specific immunotherapy against P judaica pollen allergy.

CLINICAL IMPLICATIONS

Recombinant hybrid Q2 is able to induce T-cell proliferation, thus evidencing a potential therapeutic effect. Its reduced IgE-binding capacity envisages an excellent safety profile.