Biochemical and immunological characterization of a recombinant precursor form of the house dust mite allergen Der p 1 produced by Drosophila cells

[Evaluation of sensitization to Der p 1 and Der p 2 in a pediatric population of the North of Portugal]

INTRODUCTION

In Portugal, data on the role of Der p 1 and Der p 2 in patients with house dust mite (HDM) allergy are scarce. Allergen-specific immunotherapy (sIT) is the only treatment that improves symptoms, reduces the need for pharmacological therapy and modifies the natural history of the disease. With this study, the authors aim to understand the local epidemiology and to clarify if the molecular assay of major allergens is advantageous in deciding and/or modifying the decision to initiate sIT in children with clinical indication which are sensitized to Dermatophagoides pteronyssinus.

METHODS

Retrospective study with analysis of patients with asthma and/or rhinitis.

STUDY PERIOD

January/2013-December/2016.

INCLUSION CRITERIA

1) positive prick-test to Dermatophagoides pteronyssinus; and 2) clinically relevant disease under treatment. Assay Der p 1 and Der p 2 values ≥0.35 kUA/L were considered positive. Statistical significance was set at P<.05.

RESULTS

The clinical files of 279 patients. Mean ages 9.55 years (min.4-max.17). Asthma was present in 199 children (71.3%) and rhinitis in 245 (87.8%). Der p 1 and Der p 2 was <0.35kUA/L in 29 (10,4%) patients. The value of Der p 1/Der p 2 correlated with the size of the prick-test papule, the value of the eosinophils and the total IgE.

CONCLUSIONS

Der p 1 and Der p 2 are dominant allergens in our population and there may be benefits in determining these molecular allergen levels in patients with a positive prick-test and a clinical indication for sIT prior to a decision of initiating sIT or not.

Papain Degrades Tight Junction Proteins of Human Keratinocytes In Vitro and Sensitizes C57BL/6 Mice via the Skin Independent of its Enzymatic Activity or TLR4 Activation

Papain is commonly used in food, pharmaceutical, textile, and cosmetic industries and is known to induce occupational allergic asthma. We have previously shown that the papain-like cysteine protease Dermatophagoides pteronyssinus 1 from house dust mite exhibits percutaneous sensitization potential. We aimed here to investigate the potential of papain itself in epicutaneous sensitization. The effects of papain on tight junction (TJ) proteins were tested in vitro in human primary keratinocytes. Using C57BL/6 wild-type and Toll-like receptor 4 (TLR4)-deficient mice, we analyzed the sensitization potential of papain, its effects on the skin barrier, and immune cell recruitment. Our results show that papain affects the skin barrier by increasing transepidermal water loss, degrading TJ proteins and inducing vasodilation. When topically applied, papain exhibited a high epicutaneous inflammatory potential by recruiting neutrophils, mast cells, and CD3-positive cells and by induction of a TH2-biased antibody response. However, its high potency for specific sensitization via the skin was TLR4 independent and, in spite of its capacity to degrade epidermal TJ proteins, does not rely on its enzymatic function. From our data, we conclude that papain has all features to act as a strong allergen via the skin.

Orchestration of an uncommon maturation cascade of the house dust mite protease allergen quartet

In more than 20% of the world population, sensitization to house dust mite allergens triggers typical allergic diseases such as allergic rhinitis and asthma. Amongst the 23 mite allergen groups hitherto identified, group 1 is cysteine proteases belonging to the papain-like family whereas groups 3, 6, and 9 are serine proteases displaying trypsin, chymotrypsin, and collagenolytic activities, respectively. While these proteases are more likely to be involved in the mite digestive system, they also play critical roles in the initiation and in the chronicity of the allergic response notably through the activation of innate immune pathways. All these allergenic proteases are expressed in mite as inactive precursor form. Until recently, the exact mechanisms of their maturation into active proteases remained to be fully elucidated. Recent breakthroughs in the understanding of the activation mechanisms of mite allergenic protease precursors have highlighted an uncommon and unique maturation pathway orchestrated by group 1 proteases that tightly regulates the proteolytic activities of groups 1, 3, 6, and 9 through complex intra- or inter-molecular mechanisms. This review presents and discusses the currently available knowledge of the activation mechanisms of group 1, 3, 6, and 9 allergens of Dermatophagoides pteronyssinus laying special emphasis on their localization, regulation, and interconnection.

In planta expression of a mature Der p 1 allergen isolated from an Italian strain of Dermatophagoides pteronyssinus

European (Dermatophagoides pteronyssinus) and American (Dermatophagoides farinae) house dust mite species are considered the most common causes of asthma and allergic symptoms worldwide. Der p 1 protein, one of the main allergens of D. pteronyssinus, is found in high concentration in mites faecal pellets, which can became easily airborne and, when inhaled, can cause perennial rhinitis and bronchial asthma. Here we report the isolation of the Der p 1 gene from an Italian strain of D. pteronyssinus and the PVX-mediated expression of its mature form (I-rDer p 1) in Nicotiana benthamiana plants. Human sera from characterized allergic patients were used for IgE binding inhibition assays to test the immunological reactivity of I-rDer p 1 produced in N. benthamiana plants. The binding properties of in planta produced I-rDer p 1 versus the IgE of patients sera were comparable to those obtained on Der p 1 preparation immobilized on a microarray. In this paper we provide a proof of concept for the production of an immunologically active form of Der p 1 using a plant viral vector. These results pave the way for the development of diagnostic allergy tests based on in planta produced allergens.

Serum and salivary IgE, IgA, and IgG4 antibodies to Dermatophagoides pteronyssinus and its major allergens, Der p1 and Der p2, in allergic and nonallergic children

Allergic rhinitis (AR) is a public health problem with high prevalence worldwide. We evaluated levels of specific IgE, IgA, and IgG4 antibodies to the Dermatophagoides pteronyssinus (Dpt) house dust mite and to its major allergens (Der p1 and Der p2) in serum and saliva samples from allergic and nonallergic children. A total of 86 children were analyzed, from which 72 had AR and 14 were nonallergic healthy children. Serum IgE and serum/salivary IgG4 levels to Dpt, Der p1, and Der p2 were higher in allergic children whereas serum/salivary IgA levels to all allergens were higher in nonallergic children. IgE levels positively correlated with IgG4 and IgA to all allergens in allergic children, while IgA levels negatively correlated with IgG4 to Dpt and Der p1 in nonallergic children. In conclusion, mite-specific IgA antibodies predominate in the serum and saliva of nonallergic children whereas mite-specific IgE and IgG4 are prevalent in allergic children. The presence of specific IgA appears to have a key role for the healthy immune response to mucosal allergens. Also, specific IgA measurements in serum and/or saliva may be useful for monitoring activation of tolerance-inducing mechanisms during allergen specific immunotherapeutic procedures, especially sublingual immunotherapy.

Production of native and modified recombinant Der p 1 molecules in tobacco plants

BACKGROUND

As a complex molecule requiring post-translational processing, it has been difficult to produce the Der p 1 major allergen from the Dermatophagoides pteronyssinus house dust mite in a recombinant form.

OBJECTIVE

Here, we tested whether transgenic tobacco plants are suitable to express Der p 1, either as a wild-type molecule or as variants lacking N-glycosylation sites (Gly(-)) and/or cysteine protease activity (Enz(-)). Methods Using Agrobacterium tumefaciens-based transformation, pro Der p 1 molecules bearing mutations within either the N-glycosylation sites (N34Q, N150Q) and/or the cysteine protease-active site (C132V) were expressed in tobacco plants. After purification by ion exchange chromatography, allergens were characterized using immunoblotting, circular dichroism (CD), as well as basophil and T lymphocyte stimulation assays.

RESULTS

Four forms of recombinant Der p 1 (i.e. wild-type Gly(+)/Enz(+), as well as Gly(-)/Enz(+), Gly(+)/Enz(-) or Gly(-)/Enz(-) variants) were successfully expressed in tobacco leaves as pro Der p 1 molecules. Spontaneous cleavage of the pro-peptide was observed in tobacco leaf extracts for all forms of recombinant Der p 1 (r Der p 1). CD confirmed that all r Der p 1 molecules, with the exception of the Gly(-)/Enz(-) variant, exhibited secondary structures comparable to the natural protein. A cysteine protease activity was associated only with the Gly(+)/Enz(+) form. All these molecules exhibit a profile similar to natural Der p 1 with respect to IgE immunoreactivity, basophil activation and T cell recognition.

CONCLUSION

A tobacco plant expression system allows the production of various forms of mature Der p 1, which could be used for diagnostic or immunotherapeutic purposes.

Comparative enzymology of native and recombinant house dust mite allergen Der p 1

BACKGROUND

The cysteine peptidase activity of group 1 house dust mite allergens is important for their allergenicity and may offer new therapeutic targets for allergy treatment. Hitherto, the design of specific inhibitors has been impeded because the availability of pure, fully active allergens has limited the implementation of drug screening campaigns. Similarly, investigation of the mechanisms by which peptidase allergens promote sensitization has also been restricted. Our aim was to compare the enzymology of recombinant and native forms of Der p 1 to establish if an easily expressed recombinant form of Der p 1 could be used as a drug discovery tool.

METHODS

Enzymatic activity of natural and recombinant Der p 1 was compared fluorimetrically using a novel specific substrate (ADZ 50,059) and a novel specific active site titrant (ADZ 50,000). The effect of recombinant Der p 1 prodomain on the catalytic activity of both Der p 1 preparations was also examined.

RESULTS

Although differing substantially in molecular weight, the enzymological properties of recombinant and native Der p 1 were indistinguishable. Our data show clearly by experiment that, in contrast to some suggestions, Der p 1 is not an enzyme of bifunctional mechanism.

CONCLUSION

The catalytic activity of Der p 1 is tolerant of glycosylation differences that occur at N150 when the protein is expressed in Pichia pastoris. This suggests that this recombinant protein may be suitable for drug design studies and in the elucidation of how peptidase activity promotes sensitization to peptidase and nonpeptidase bystander allergens.

A hypoallergenic variant of Der p 1 as a candidate for mite allergy vaccines

BACKGROUND

Recombinant hypoallergens that display reduced allergenicity but retain T-cell reactivity represent promising candidates to improve the safety and efficacy of allergen-specific vaccines or immunotherapy.

OBJECTIVE

The current study reports the immunologic characterization of a hypoallergenic variant of the major mite allergen Der p 1.

METHODS

The recombinant proform of Der p 1 (ProDer p 1) was expressed in Escherichia coli (ProDer p 1 coli), purified and characterized at the level of its secondary structure, and IgE and T-cell reactivities. Moreover, the prophylactic potential of ProDer p 1 coli vaccinations was evaluated in a murine Der p 1 sensitization model.

RESULTS

After purification and refolding, ProDer p 1 coli remained aggregated with a higher beta-sheet content and altered Der p 1 conformational epitopes compared with the correctly folded monomeric ProDer p 1 produced in Chinese hamster ovary cells. Both ProDer p 1 forms were able to retain the Der p 1-specific T-cell reactivity but direct ELISA, competitive inhibition, and rat basophil leukemia assays clearly showed that ProDer p 1 coli displays a very weak IgE reactivity. Mice vaccinations with aggregated ProDer p 1 adjuvanted with alum induced a T(H)1-biased immune response that prevented the subsequent allergic response after Der p 1 sensitization and airway challenge with aerosolized mite extracts. Furthermore, ProDer p 1 coli treatment inhibited the development of airway eosinophilia and airway hyperresponsiveness to inhaled methacholine.

CONCLUSION

Aggregated forms of Der p 1 could represent hypoallergens suitable for the prevention of mite allergy.

Suspension-cultured BY-2 tobacco cells produce and mature immunologically active house dust mite allergens

The replacement of crude allergen extracts by selected allergens currently represents a major goal for the improvement of allergy diagnosis and immunotherapy. Indeed, the development of molecularly defined vaccines would facilitate both standardization and enhance batch-to-batch reproducibility as well as treatment specificity. In this study, we have investigated the potential of tobacco plant cells to produce biologically active forms of the two major allergens from the house dust mite. A detailed characterization of these plant-made allergens has shown similar proteolytic maturation and folding as well as comparable immunoreactivity to their natural counterparts. Altogether, our results exemplify that suspension-cultured BY-2 tobacco cells represent a low cost and environmentally safe expression system suitable to produce recombinant allergens from Dermatophagoides pteronyssinus under a form appropriate for diagnostic and therapeutic purposes.

Mite immunotherapy

Dermatophagoides pteronyssinus and D. farinae are the most common house dust mites and are among the most common sources of indoor allergens worldwide. These species are very common in humid regions, where most allergic individuals are sensitized to house dust mites. Specific immunotherapy with mite extracts has demonstrated clinical benefits in several double-blind, placebo-controlled trials that are included in recent reviews of subcutaneous immunotherapy, including pediatric and adult patients with rhinoconjunctivitis and or asthma. Most successful studies of mite immunotherapy have used native allergen extracts adsorbed onto aluminum hydroxide, or chemically modified mite-allergen extracts. Several studies have also shown efficacy using sublingual immunotherapy in pediatric and adult patients with asthma and/or rhinitis. Additionally, the efficacy of subcutaneous immunotherapy has been demonstrated in patients with atopic dermatitis, although more double-blind, placebo-controlled studies are needed. Based on several studies, it cannot be concluded that mite immunotherapy is more dangerous or safer than immunotherapy with grasses, epithelia, or animal epithelia. Because the delivery of high doses of allergen carries with it the risk for immunoglobulin E (IgE)-mediated events, several methods have been developed to reduce specific IgE binding to mite-allergen extracts. An important challenge for future mite immunotherapy modalities is the delivery of relatively high doses without a significant risk for severe reactions.

Eukaryotic expression of recombinant Pso o 1, an allergen fromPsoroptes ovis, and its localization in the mite

A cDNA encoding the immunogen Pso o 1 fromPsoroptes oviswas obtained by polymerase chain reaction (PCR) amplification. The amplicon contained the entire coding sequence for the prepro-enzyme in an open reading frame (ORF) of 966 bp. This gene encoded a predicted protein of 322 amino acids (aa) with 64% aa identity (80% similarity) to the major house dust mite faecal allergen Der f 1. The pro-enzyme form of Pso o 1 was expressed as a recombinant protein in thePichia pastoris-eukaryotic expression system. Maturation of the recombinant pro-enzyme by autocatalytic activation was not observed, and such maturation could not be achieved using a number of techniques known to activate recombinant Der p 1 and Der f 1 expressed in the same system. Serum raised against recombinant Pso o 1 cross-reacted with mature Der p 1 and allowed Pso o 1 to be immunolocalized to the gut ofP. ovis.

Glycosylation of Recombinant Proforms of Major House Dust Mite Allergens Der p 1 and Der f 1 Decelerates the Speed of Maturation

BACKGROUND

The efficient manufacture of recombinant Der p 1 and Der f 1 has been an important bottleneck in the study of house dust mite allergies and the development of applications for allergen engineering. While Der f 1 has only one N-glycosylation motif in the mature sequence, Der p 1 has two motifs, one in the prosequence and the other in the mature sequence. To test whether inefficient maturation of a recombinant Pro-Der p 1 versus Pro-Der f 1 is due to N-glycosylation, the maturation speed of N-glycosylation motif mutants was compared.

METHODS

Expression vectors for the mutants, in which the motif in the Der p 1 prodomain was disrupted or a motif was created within the Der f 1 prodomain, were constructed by site-directed mutagenesis of preproforms with or without the motif within the mature portion. Culture supernatants of yeast Pichia pastoris transfectant cells containing proforms were buffer exchanged by gel filtration and incubated for maturation. Samples from the reactions were collected every 20 min and subjected to electrophoresis. The maturation speed was compared based on the band densities of the pro- and mature forms.

RESULTS

Disruption of the motif in the mature portion decreased the productivity and accelerated the maturation. Maturation was also accelerated by disruption of the other motif in the Der p 1 prodomain and slowed down by introduction of the motif into the Der f 1 prodomain.

CONCLUSIONS

Maturation systems using Pro-Der p 1 without the prodomain glycosylation are useful for the efficient preparation of a recombinant mature allergen. In addition, these results demonstrated that the maturation of cysteine protease could be controlled through glycosylation of the prodomain.

Vaccination with the recombinant allergen ProDer p 1 complexed with the cationic lipid DiC14-amidine prevents allergic responses to house dust mite

The present study evaluated the prophylactic potential of ProDer p 1, the recombinant precursor form of the major mite allergen Der p 1, combined with the cationic lipid diC14-amidine in a murine model of house dust mite allergy. Naive mice vaccinated with the amidine/allergen complex developed a Th1-biased immune response characterized by the absence of specific IgE, the production of specific IgG2a, and the presence of IFN-gamma in splenocyte cultures. In contrast, ProDer p 1 adjuvanted with alum induced typical strictly Th2-biased allergic responses with strong IgG1 and IgE titers and IL-5 secretion. Removal of negatively charged sialic acids in ProDer p 1 or increasing the ionic strength reduced the binding of ProDer p 1 to the cationic liposomes and resulted in a decrease of the allergen immunogenicity, suggesting that complexation is required for triggering an optimal immune response. Finally, prophylactic vaccination with ProDer p 1-diC14-amidine reduced drastically the production of specific IgE and airway eosinophilia following subsequent immunization with Der p 1-alum and challenge with aerosolized house dust mite extracts. In conclusion, recombinant ProDer p 1 complexed with diC14-amidine could represent an efficient prophylactic vaccine against house dust mite allergy.

Substitution of Pichia pastoris-derived recombinant proteins with mannose containing O- and N-linked glycans decreases specificity of diagnostic tests

BACKGROUND

Recombinant proteins from Pichia pastoris need to be fully evaluated before used as diagnostic tools.

OBJECTIVE

The objective of this study was to investigate whether glycosylation by P. pastoris interferes with the specificity of diagnostic tests.

METHODS

An autoantigen involved in Wegener's disease (protease 3) and 2 major inhalant allergens from grass pollen (Dac g 5) and house dust mite (Der p 1) were produced as recombinant molecules in P. pastoris. O-linked glycans on Dac g 5 were characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The immune reactivity of the recombinant proteins was compared to that of their natural counterparts by ELISA and a radio-allergosorbent test (RAST) as well as by ELISA and RAST inhibition.

RESULTS

In contrast to the non-glycosylated natural allergen, recombinant Dac g 5 was shown to carry at least 2 small mannose-containing O-glycans. We showed that both these O-glycans and the N-linked glycans on recombinant protease 3 and recombinant Der p 1 were recognized in ELISA by IgG antibodies in sera of healthy individuals. These IgG responses were closely correlated. The natural autoantigen and allergens were not recognized by IgG antibodies from healthy subjects. The carbohydrate nature of the epitopes recognized by IgG on the recombinant proteins was confirmed by inhibition studies with mannose and yeast mannan. IgE recognition of yeast glycans was observed in 2 out of 9 positive sera from patients with allergic bronchopulmonary aspergillosis.

CONCLUSION

Production of recombinant molecules in yeast (or moulds) can introduce IgG-binding glycans that negatively affect the specificity of diagnostic tests.

Posttranslational modification of therapeutic proteins in plants

Plants have emerged as an alternative to current systems for the production of therapeutic proteins. The advantages of plants for the low-cost and large-scale production of safe and biologically active mammalian proteins have been documented recently. A major advantage of transgenic plants over production systems that are based on yeast or Escherichia coli is their ability to perform most of the posttranslational modifications (PTMs) that are required for the bioactivity and pharmacokinetics of recombinant therapeutic proteins. Furthermore, recent advances in the control of PTMs in transgenic plants have made it possible for plants to perform, at least to some extent, human-like modifications of recombinant proteins. Hence, plants have become a suitable alternative to animal cell factories for the production of therapeutic proteins.

Expression and immunogenicity of the major house dust mite allergen Der p 1 following DNA immunization

The mite protein Der p 1 is a major trigger of allergy and atopic asthma world-wide, and thus, a good vaccine candidate for allergy prevention. Since it is a cysteine protease, the catalytic effects of Der p 1 vaccination may be unpredictable. One approach to reduce this risk is to vaccinate with DNA encoding enzymatically inactive forms of Der p 1. Here we show that Der p 1 DNA without its native pre-pro sequences potently induced Der p 1-specific antibodies, as long as its pre-sequence was substituted by another leader sequence. Without any pre-pro sequence, the same DNA fragment was well expressed but failed to induce significant level of anti-Der p 1 antibodies, without further boosting by protein.

Maturation of the activities of recombinant mite allergens Der p 1 and Der f 1, and its implication in the blockade of proteolytic activity

Recombinant pro-Der p 1 expressed in yeast Pichia pastoris was convertible into the prosequence-removed mature Der p 1 with full activities of cysteine protease and IgE-binding with or without N-glycosylation of the mature sequence as well as pro-Der f 1. The active recombinant variants will be the basis for various future studies. The major N-terminus of pro-Der p 1 with low proteolytic activity was the putative signal-cleavage site, while that of pro-Der f 1 contained not only the equivalent site but also 21 residues downstream, and pro-Der f 1 retained significant activity. Contribution of the N-terminal region of the Der p 1 prosequence including an N-glycosylation motif on effective inhibition of proteolytic activity of pro-Der p 1 was suggested.

Identification of an antigen from the sheep scab mite, Psoroptes ovis, homologous with house dust mite group I allergens

Infestation of sheep with the ectoparasitic mite Psoroptes ovis, results in a severe allergic dermatitis. Currently, little is known about the allergens/antigens that stimulate the allergic response. We have isolated an 836-bp cDNA from a P. ovis cDNA library which displays strong homology to cysteine proteases and, in particular, to the group I house dust mite allergens Der p 1, Der f 1 and Eur m 1. The cDNA was expressed in Escherchia coli, fused to a hexahistidine tag and the recombinant protein (Pso o 1) purified using a nickel-affinity column. The recombinant Pso o 1 was tested for recognition by immunoglobulin (Ig)G and IgE in serum from P. ovis naïve and P. ovis infested sheep. Using Western blots, both classes of antibody to Pso o 1 were detected in postinfestation serum. In enzyme-linked immunosorbent assays, a pronounced IgG-antibody response to Pso o 1 was detected in five of five sheep 3 weeks postinfestation. The IgE-antibody response to whole mite extract was poor in four of five animals. However, a marked IgE response occurred in the fifth animal, and IgE anti Pso o 1 was detected in the serum.

High-level expression of recombinant house dust mite allergen Der p 1 in Pichia pastoris

BACKGROUND

The major house dust mite Der p 1 allergen is associated with allergic disease. Heterologous over-expression of biologically active Der p 1 was previously attempted but with limited success.

OBJECTIVE

The aim of this study was to establish an efficient system for the production of recombinant Der p 1.

METHODS

The proform of Der p 1 was expressed in Pichia pastoris as a fusion with the alpha mating factor signal sequence. The recombinant product was purified from culture medium and compared to Der p 1 isolated from mite culture, in terms of enzymatic activity as well as IgE binding capacity.

RESULTS

ProDer p 1 was efficiently secreted into culture medium as a hyperglycosylated protein of 40-60 kDa. Postpurification dialysis in acidic buffer was required for the autocatalytic processing of Der p 1. During this treatment, the prosequence was efficiently removed to give highly glycosylated recombinant mature Der p 1. Competition ELISA experiments as well as cysteine proteinase activity assays indicated that recombinant processed Der p 1 was similar to natural Der p 1 isolated from mite cultures in terms of IgE binding and enzymatic activities. However, the histamine releasing activity of recombinant Der p 1 was slightly weaker than that of natural Der p 1.

CONCLUSION

This efficient system for recombinant Der p 1 expression leads the way for the design of new diagnostics for house dust mite allergy, epitope mapping, allergen engineering, structural and immunological studies and new immunotherapeutic treatments.

Recombinant pronapin precursor produced in Pichia pastoris displays structural and immunologic equivalent properties to its mature product isolated from rapeseed

2S albumin storage proteins from rapeseed (Brassica napus), called napins, consist of two different polypeptide chains linked by disulphide bridges, which are derived by proteolytic cleavage from a single precursor. The precursor form of the napin BnIb (proBnIb) has been cloned using a PCR strategy and sequenced. The amino-acid sequence deduced from the clone includes 31 residues of the small chain and 75 of the large chain, which are connected by the peptide Ser-Glu-Asn. Expression of the cDNA encoding proBnIb has been carried out in the methylotrophic yeast Pichia pastoris. The induced protein was secreted to the extracellular medium at a yield of 80 mg.L(-1) of culture and was purified by means of size-exclusion chromatography and reverse phase-HPLC. Recombinant proBnIb appeared properly folded as its molecular and spectroscopic properties were equivalent to those of the mature heterodimeric protein. As 2S albumin storage proteins from Brassicaceae have been shown to be type I allergy inducers, the immunological activity of the recombinant proBnIb was analysed as a measure of its structural integrity. The immunological properties of the recombinant precursor and the natural napin were indistinguishable by immunoblotting and ELISA inhibition using polyclonal antisera and sera of patients allergic to mustard and rapeseed. In conclusion, the recombinant expression of napin precursors in P. pastoris has been shown to be a successful method for high yield production of homogeneous and properly folded proteins whose polymorphism and complex maturation process limited hitherto their availability.

Maturation of Pichia pastoris-derived recombinant pro-Der p 1 induced by deglycosylation and by the natural cysteine protease Der p 1 from house dust mite

The mature cysteine protease from Dermatophgoides pteronyssinus, Der p 1, is a major house dust mite allergen. Its enzymatic activity has been shown to have pro-inflammatory effects that could also negatively influence efficacy of allergen-specific immunotherapy. The aim of this study was to express recombinant pro-Der p 1 (rpro-Der p 1) in the yeast Pichia pastoris and to study its maturation. Expression was achieved at a concentration ranging from 45 mg.L-1 (methanol-induced expression) to 168 mg.L-1 (constitutive expression). No significant spontaneous maturation of the secreted proenzyme was observed. rpro-Der p 1 with a sequence-based molecular mass of 34 kDa was hyperglycosylated by the yeast, migrating at 50-60 kDa on SDS/PAGE. Compared with its natural counterpart (nDer p 1), the recombinant proenzyme demonstrated decreased IgE reactivity, resulting in a 30-fold lower capacity to induce histamine release from human basophils. Decreased immunoreactivity was also shown by competitive RIA and sandwich ELISA with Der p 1-specific antibody reagents. CD spectra of rpro-Der p 1 and nDer p 1 revealed significant structural differences. Deglycosylation of rpro-Der p 1 with endoglycosidase H resulted in a decrease in apparent molecular mass from 50 kDa to 34 kDa, but did not affect nDer p 1. On removal of N-glycans from rpro-Der p 1, which harbours two putative N-glycosylation sites in both propeptide and mature sequence, the mature rDer p 1 appeared. This suggests that hyperglycosylation hampers spontaneous maturation. Maturation of the recombinant pro-enzyme was also achieved by addition of the active natural cysteine protease, nDer p 1. In conclusion, high-level expression of rpro-Der p 1 in P. pastoris results in a stable hypoallergenic proenzyme with potential for use in allergen-specific immunotherapy.

Th2 polarization by Der p 1--pulsed monocyte-derived dendritic cells is due to the allergic status of the donors

The polarization of the immune response toward a Th2 or a Th1 profile can be mediated by dendritic cells (DCs) following antigen presentation and interaction with T cells. Costimulatory molecules such as CD80 and CD86 expressed by DCs, the polarizing cytokine environment during DC--T-cell interaction, and also the nature of the antigen are critical in the orientation of the immune response. In this study, the effect of the cysteine protease Der p 1, one of the major allergens of the house dust mite Dermatophagoides pteronyssinus, on these different parameters was evaluated comparatively on monocyte-derived DCs obtained from healthy donors, from pollen-sensitive patients, or from patients sensitive to Dermatophagoides pteronyssinus. Results showed that Der p 1 induced an increase in CD86 expression only on DCs from house dust mite--sensitive patients. This was also associated with a higher capacity to induce T-cell proliferation, a rapid increase in the production of proinflammatory cytokines, tumor necrosis factor--alpha and interleukin (IL)-1 beta, and the type 2 cytokine IL-10. No changes in the release of IL-12 p70 were induced by Der p 1. Finally, purified T cells from house dust mite-sensitive patients stimulated by autologous Der p 1--pulsed DCs preferentially produced IL-4 rather than interferon-gamma. These effects were abolished in the presence of the inactive precursor of Der p 1 (ProDer p 1). Taken together, these data suggest that DCs from house dust mite--sensitive patients, in contrast to DCs from healthy donors and from pollen-sensitive patients, exposed to Der p 1 play a pivotal role in the enhancement of the Th2 response associated with the allergic reaction developed in response to house dust mite exposure. (Blood. 2001;98:1135-1141)

Recombinant allergens for diagnosis and therapy of allergic disease

Many of the problems associated with using natural allergenic products for allergy diagnosis and treatment can be overcome with use of genetically engineered recombinant allergens. Over the past 10 years, the most important allergens from mites, pollens, animal dander, insects, and foods have been cloned, sequenced, and expressed. In many cases the three-dimensional allergen structure has been determined and B-cell and T-cell epitopes have been mapped. These studies show that allergens have diverse biologic functions (they may be enzymes, enzyme inhibitors, lipocalins, or structural proteins) and that as a rule the allergen function is unrelated to its ability to cause IgE antibody responses. High-level expression systems have been developed to produce recombinant allergens in bacteria, yeast, or insect cells. Recombinant allergens show comparable IgE antibody binding to their natural counterparts (where available) and show excellent reactivity on skin testing and in in vitro diagnostic tests. Cocktails of recombinant allergens can be formulated with predetermined and uniform allergen levels, which could replace natural allergens and result in the development of innovative, patient-based tests for allergy diagnosis. Recombinant allergens also offer the exciting possibility of developing new forms of allergen immunotherapy, including the use of hypoallergens, allergens coupled to IgE suppressive adjuvants, and peptide-based therapies. The production of recombinant allergens as defined molecular entities makes it feasible to consider the possibility of developing prophylactic allergen vaccines. The introduction of recombinant allergens in research and in clinical trials should lead to significant improvements in allergy diagnosis and treatment.