The effect of the food matrix on in vivo immune responses to purified peanut allergens

There is little knowledge about the factors that determine the allergenicity of food proteins. One aspect that remains to be elucidated is the effect of the food matrix on immune responses to food proteins. To study the intrinsic immunogenicity of allergens and the influence of the food matrix, purified peanut allergens (Ara h 1, Ara h 2, Ara h 3, or Ara h 6) and a whole peanut extract (PE) were tested in the popliteal lymph node assay (PLNA) and in an oral model of peanut hypersensitivity. In the PLNA, peanut proteins were injected into the hind footpad of BALB/c mice; in the oral exposure experiments C3H/HeOuJ mice were gavaged weekly with PE or allergens in the presence of cholera toxin (CT). Upon footpad injection, none of the allergens induced significant immune activation. In contrast, PE induced an increase in cell number, cytokine production, and activation of antigen-presenting cells. Furthermore, the presence of a food matrix enhanced the immune response to the individual allergens. Oral exposure to the purified allergens in the presence of CT induced specific IgE responses, irrespective of the presence of a food matrix. These results suggest that purified peanut allergens possess little intrinsic immune-stimulating capacity in contrast to a whole PE. Moreover, the data indicate that the food matrix can influence responses to individual proteins and, therefore, the food matrix must be taken into account when developing models for allergenic potential assessment.

Large scale purification of rapeseed proteins (Brassica napus L.)

Rapeseed (Brassica napus L.) cruciferin (12S globulin), napin (2S albumin) and lipid transfer proteins (LTP) were purified at a multi-g scale. The procedure developed was simple, rather fast and resolutive; it permitted the recovery of these proteins with a good yield, such as 40% for cruciferin and 18% for napin. Nanofiltration eliminated the major phenolic compounds. The remaining protein fraction was fractionated by cation exchange chromatography (CEC) on a streamline SP-XL column in alkaline conditions. The unbound neutral cruciferin was polished by size exclusion chromatography. The alkaline napin isoforms and LTP, adsorbed on the beads, were eluted as a whole fraction and further separated by an other CEC step at acidic pH. Napins were polished by hydrophobic interaction chromatography (HIC). The fractions were characterized by reverse phase HPLC, electrophoresis, N-terminal sequencing and mass spectrometry. All the fractions contained less than 5% of impurities.

Influence of the maillard reaction on the allergenicity of rAra h 2, a recombinant major allergen from peanut (Arachis hypogaea), its major epitopes, and peanut agglutinin

The influence of thermal processing and nonenzymatic browning reactions on the IgE-binding activity of rAra h 2 was studied and compared to findings recently reported for the allergen's natural counterpart. ELISA experiments as well as inhibition assays revealed that thermal treatment of rAra h 2 in the presence of reactive carbohydrates and carbohydrate breakdown products induces a strong increase of the IgE-binding activity, thus collaborating with the data reported for the natural protein isolated from peanuts. To localize the Ara h 2 sequences responsible for the formation of highly IgE-affine glycation sites, model peptides have been synthesized mimicking sequences which contain possible targets for glycation as well as the immunodominant epitopes. Immunological evaluation of these peptides heated in the absence or presence of reducing sugars and carbonyls, respectively, revealed that neither the two lysine residues of Ara h 2 nor its N-terminus are involved in the formation of IgE-affine structures by Maillard reaction. Also, the cysteine-containing major epitope 3 (aa 27-36) was found to lose its IgE-binding capacity upon heating. By contrast, the overlapping major epitopes 6 and 7, which do not contain any lysine or arginine moieties, showed a distinct higher level of IgE binding when subjected to Maillard reaction, thus giving the first evidence that nonbasic amino acids might be accessible for nonenzymatic glycation reactions and that these posttranslational modifications might induce increased IgE binding of the glycated Ara h 2. Analogous experiments were performed with peanut agglutinin, considered in the literature as a minor allergen. ELISA experiments revealed that the majority of tested sera samples from peanut-sensitive patients showed a high level of IgE binding to the lectin even after heat treatment. In contradiction to published data, nonenzymatic browning reactions seem to deteriorate the IgE affinity of the lectin.

Emulsion properties of sunflower (Helianthus annuus) proteins

Emulsions were made with sunflower protein isolate (SI), helianthinin, and sunflower albumins (SFAs). Emulsion formation and stabilization were studied as a function of pH and ionic strength and after heat treatment of the proteins. The emulsions were characterized with respect to average droplet size, surface excess, and the occurrence of coalescence and/or droplet aggregation. Sunflower proteins were shown to form stable emulsions, with the exception of SFAs at neutral and alkaline pH values. Droplet aggregation occurred in emulsions made with SI, helianthinin, and SFAs. Droplet aggregation and subsequent coalescence of emulsions made with SFAs could be prevented at pH 3. Calcium was found to cause droplet aggregation of emulsions made with helianthinin, at neutral and alkaline pH values. Treatments that increase conformational flexibility of the protein molecule improved the emulsion properties of sunflower proteins.

Isolation and characterization of natural Ara h 6: evidence for a further peanut allergen with putative clinical relevance based on resistance to pepsin digestion and heat

Peanut allergy is a significant health problem because of its prevalence and the potential severity of the allergic reaction. The characterization of peanut allergens is crucial to the understanding of the mechanism of peanut allergy. Recently, we described cloning of the peanut allergen Ara h 6. The aim of this study was isolation and further characterization of nAra h 6. We purified nAra h 6 from crude peanut extract using gel filtration and anion exchange chromatography. The preparation was further characterized by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) with subsequent immunoblotting. Stability of nAra h 6 was studied by an in vitro digestibility assay as well as by resistance against thermal processing. Sequencing of nAra h 6 identified the N-terminal amino acid sequence as MRRERGRQGDSSS. Further results clearly demonstrated stability of nAra h 6 against pepsin digestion and heating. Immunoglobulin G (IgE) binding analysis and its biological activity shown by RBL 25/30-test of natural Ara h 6 supported the importance of this peanut allergen. Investigation of nAra h 6 revealed evidence for a further peanut allergen with putative clinical relevance based on resistance to pepsin digestion and heat.

Stability of the major allergen Brazil nut 2S albumin (Ber e 1) to physiologically relevant in vitro gastrointestinal digestion

The major 2S albumin allergen from Brazil nuts, Ber e 1, was subjected to gastrointestinal digestion using a physiologically relevant in vitro model system either before or after heating (100 degrees C for 20 min). Whilst the albumin was cleaved into peptides, these were held together in a much larger structure even when digested by using a simulated phase 1 (gastric) followed by a phase 2 (duodenal) digestion system. Neither prior heating of Ber e 1 nor the presence of the physiological surfactant phosphatidylcholine affected the pattern of proteolysis. After 2 h of gastric digestion, approximately 25% of the allergen remained intact, approximately 50% corresponded to a large fragment of M(r) 6400, and the remainder comprised smaller peptides. During duodenal digestion, residual intact 2S albumin disappeared quickly, but a modified form of the 'large fragment' remained, even after 2 h of digestion, with a mass of approximately 5000 Da. The 'large fragment' comprised several smaller peptides that were identified, by using different MS techniques, as deriving from the large subunit. In particular, sequences corresponding to the hypervariable region (Q37-M47) and to another peptide (P42-P69), spanning the main immunoglobulin E epitope region of 2S albumin allergens, were found to be largely intact following phase 1 (gastric) digestion. They also contained previously identified putative T-cell epitopes. These findings indicate that the characteristic conserved skeleton of cysteine residues of 2S albumin family and, particularly, the intrachain disulphide bond pattern of the large subunit, play a critical role in holding the core protein structure together even after extensive proteolysis, and the resulting structures still contain potentially active B- and T-cell epitopes.

Extensive in vitro cross-reactivity to seed storage proteins is present among walnut (Juglans) cultivars and species

BACKGROUND

Tree nuts, including English walnuts (Juglans regia), are sources of food allergens often associated with life-threatening allergic reactions. It is unknown if seed storage proteins from other Juglans species have IgE epitopes similar to those of the important English walnut allergens, Jug r 1 (2S albumin) and Jug r 2 (vicilin-like).

OBJECTIVE

To screen for potential germplasm sources of hypoallergenic seed storage proteins of relevance in walnut food allergy. We sought to identify English walnut cultivars (cvs) or other Juglans species that showed decreased IgE binding to major seed storage proteins or an inability to cross-react with Jug r 1 or Jug r 2.

METHODS

We determined if IgE in sera of patients who have had life-threatening systemic reactions to English walnut bound protein extracts from all tested walnut cvs (57 cvs total) or species (six) by Western immunoblot. Further, we used immunoblot inhibition to determine the in vitro cross-reactivity of Jug r 1 and Jug r 2, native and recombinant, with several walnut species.

RESULTS

All walnut cvs and species contain allergenic proteins. Furthermore, as shown by in vitro immunoblot inhibition, the major walnut allergens in the species tested cross-reacted with those in J. regia cv. Chandler and J. nigra cv. Thomas extracts.

CONCLUSIONS

Based on our findings, it is unlikely that a composite hypoallergenic walnut could be bred from available germplasm. In addition, patients with severe allergy to English walnut are likely to be clinically allergic to all commercial English walnut cvs and other closely related Juglans species.

Solution structure and stability against digestion of rproBnIb, a recombinant 2S albumin from rapeseed: relationship to its allergenic properties

NMR spectroscopy has been used to determine the solution structure of the precursor form of the recombinant napin BnIb, rproBnIb, a 2S albumin, 109-residue protein from the seeds of Brassica napus. More than 90% of the side-chain proton resonances were unambiguously assigned from the analysis of two-dimensional correlation (COSY), total correlation (TOCSY), and nuclear Overhauser effect (NOESY) spectra. The final structures were computed by using restrained molecular dynamics on the basis of 1316 upper-limit distance constraints derived from NOE cross-correlation intensities. The computed structures exhibited a root-mean-square deviation (RMSD) radius of 0.66 A for the backbone and 1.16 A for the side-chain heavy atoms of the structural core. The resulting structure consists of five amphipathic helices arranged in a right-handed super helix, a folding motif found in other proteins of the prolamin superfamily. As in the case of the mature protein, the recombinant precursor behaves as a plant food allergen. To trace out the origin and characteristics of its allergenic properties, rproBnIb was assayed against simulated gastric fluid and found to be very resistant to proteolysis. Also, heat treatment of the protein followed up to 85 degrees C by circular dichroism showed a very limited unfolding, which was recovered after cooling to 20 degrees C, indicating a high thermal stability. These results suggest that rproBnIb, as other 2S albumins, may be able to reach the gut immune system intact. A comparison of the putative epitopes against IgE antibodies of the three members of the prolamine family [2S albumins, nonspecific lipid transfer proteins (nsLTPs), and alpha-amylase/trypsin inhibitors] indicates that there are not common surfaces of interaction with IgE. Though the epitopes appear to be located in different regions of the proteins, they do comply with the requirements of being solvent-exposed and flexible.

Reversible denaturation of Brazil nut 2S albumin (Ber e1) and implication of structural destabilization on digestion by pepsin

The high resistance of Brazil nut 2S albumin, previously identified as an allergen, against proteolysis by pepsin was examined in this work. Although the denaturation temperature of this protein exceeds the 110 degrees C at neutral pH, at low pH a fully reversible thermal denaturation was observed at approximately 82 degrees C. The poor digestibility of the protein by pepsin illustrates the tight globular packing. Chemical processing (i.e., subsequent reduction and alkylation of the protein) was used to destabilize the globular fold. Far-UV circular dichroism and infrared spectroscopy showed that the reduced and alkylated form had lost its beta-structures, whereas the alpha-helix content was conserved. The free energy of stabilization of the globular fold of the processed protein as assessed by a guanidine titration study was only 30-40% of that of the native form. Size exclusion chromatography indicated that the heavy chain lost its globular character once separated from the native 2S albumin. The consequences of these changes in structural stability for degradation by pepsin were analyzed using gel electrophoresis and mass spectrometry. Whereas native 2S albumin was digested slowly in 1 h, the reduced and alkylated protein was digested completely within 30 s. These results are discussed in view of the potential allergenicity of Brazil nut 2S albumin.

Characterization of the T-cell epitopes of a major peanut allergen, Ara h 2

BACKGROUND

The development of safe and effective immunotherapy for peanut allergy has been complicated by the high anaphylactic potential of native peanut extracts. We sought to map the T-cell epitopes of the major peanut allergen, Ara h 2 in order to develop T-cell targeted vaccines.

METHODS

A panel of eight peanut-specific CD4+ T-cell lines (TCL) was derived from eight peanut-allergic subjects and proliferative and cytokine responses to stimulation with a set of overlapping 20-mer peptides representing the entire sequence of Ara h 2 determined. Proliferation was assessed in 72 h assays via tritiated thymidine incorporation, while interleukin (IL)-5 and interferon (IFN)-gamma production were assessed via sandwich enzyme-linked immunosorbent assay (ELISA) of cell culture supernatants.

RESULTS

Eight of the 17 Ara h 2 peptides were recognized by one or more subjects, with the two peptides showing highest reactivity [Ara h 2 (19-38) and Ara h 2 (73-92)] being recognized by three subjects each. Adjoining peptides Ara h 2 (28-47) and Ara h 2 (100-119) induced proliferative responses in two subjects. Each of these peptides was associated with a Th2-type cytokine response.

CONCLUSION

Two highly immunogenic T-cell reactive regions of Ara h 2 have been identified, Ara h 2 (19-47) and Ara h 2 (73-119), providing scope for the development of safe forms of immunotherapy for peanut allergy.

The major human structural IgE epitope of the Brazil nut allergen Ber e 1: a chimaeric and protein microarray approach

A protein microarray system containing different dilutions of 77 related and non-related proteins was used to show that IgE from subjects allergic to Brazil nut specifically recognise the seed 2S albumin protein (Ber e 1). Further, correctly folded chimaeric 2S albumin proteins containing structural epitope replacement were constructed and directed to the secretion pathway of the methylotropic yeast Pichia pastoris. Through the use of a chimaeric protein microarray system together with sera from a panel of 18 well-characterised Brazil nut allergic subjects, a structural IgE epitope of Ber e 1 was mapped to a helix-loop-helix region. The same structural region has been previously reported as the immunodominant region in related food allergens by different techniques. In conclusion, the combination of chimaeric proteins and protein microarrays will greatly facilitate the screening of a large number of individuals for a particular structural epitope and help to further our understanding of how proteins are recognised by the adaptive immune system.

Conformational states of sunflower (Helianthus annuus) Helianthinin: effect of heat and pH

The structure and solubility of helianthinin, the most abundant protein of sunflower seeds, was investigated as a function of pH and temperature. Dissociation of the 11S form (hexamer) into the 7S form (trimer) gradually increased with increasing pH from 5.8 to 9.0. High ionic strength (I = 250 mM) stabilizes the 11S form at pH > 7.0. Heating and low pH resulted in dissociation into the monomeric constituents (2-3S). Next, the 7S and 11S forms of helianthinin were isolated and shown to differ in their secondary and tertiary structure, and to have denaturation temperatures (T(d)) of 65 and 90 degrees C, respectively. Furthermore, the existence of two populations of the monomeric form of helianthinin with denaturation temperatures of 65 and 90 degrees C was described. This leads to the hypothesis that helianthinin can adopt two different conformational states: one with T(d) = 65 degrees C and a second with T(d) = 90 degrees C.

Competitive inhibition ELISA for quantification of Ara h 1 and Ara h 2, the major allergens of peanuts

Allergies to peanuts are becoming an increasingly important health problem as a result of the persistence and severity of the reaction in allergic individuals. Because no treatment currently is available, avoidance is the only option for peanut-allergic individuals. Avoidance of an abundant and often disguised food such as peanuts, however, is very difficult; therefore, competitive inhibition ELISAs were developed to detect and quantitate each of the major peanut allergens, Ara h 1 and Ara h 2. Under optimal conditions for each assay, the sensitivity of the Ara h 1 and Ara h 2 detection assays were 12 and 0.5 ng/mL, respectively. These assays were primarily devised to effectively compare the levels of Ara h 1 and Ara h 2 in a wide variety of peanuts or peanut products but can also be used to identify cross-reactive antigens. The method is simple and rapid, requiring only one allergen-specific antibody and, therefore, could be adapted specifically to detect the presence of these individual allergens in different foods.

Can commercial peanut assay kits detect peanut allergens?

Peanut is the food group mostly associated with severe and fatal allergic reactions. In the United States, more than 90% of peanut-allergic individuals' serum IgE recognized peanut proteins Ara h 1 and Ara h 2, thus establishing these proteins as major peanut allergens. The amount of Ara h 1 and Ara h 2 in 3 varieties of peanut cultivars that are commonly processed in the industrialized countries was determined to be 12-16 and 6-9%, respectively. Current commercial peanut test kits use polyclonal peanut-specific antibodies to detect soluble or buffer extractable peanut proteins. Because the 2 major peanut allergens Ara h 1 and Ara h 2 are isolated from soluble peanut proteins, it is generally assumed that these commercial kits can detect peanut allergens, although none of these kits claims to detect peanut allergen. This study showed for the first time that the peanut test kits could, in fact, detect major peanut allergens Ara h 1 and Ara h 2 in both native or heat-denatured structures; therefore, these kits qualified to be classified as peanut allergen enzyme-linked immunosorbent assays.

Development of an epitope-specific analytical tool for the major peanut allergen Ara h 2 using a high-density multiple-antigenic peptide strategy

Using the major peanut allergen Ara h 2 as an example, an analytical tool enabling the determination of immunoglobulin E (IgE)-epitopes in processed food allergens was developed. We synthesized a multiple-antigenic peptide (MAP) of the IgE-reactive linear epitope 3 (amino acid positions 27-36) of Ara h 2 and raised a monospecific antiserum against this epitope to obtain a positive control for future epitope resolved diagnostics. First, a MAP of epitope 3, having a molecular mass of 7770 Da, was synthesized, purified, and its structure confirmed by liquid chromatography-mass spectrometry (electrospray ionization) (LC-MS(ESI)), matrix assisted laser desorption/ionization-time of flight (MALDI-TOF), and Edman sequencing. The MAP was then used to raise high titer antibodies in rabbits using the adjuvant Titermax and to characterize the specificity of IgE from allergenic patients sensitized to Ara h 2. The antiserum exclusively detects Ara h 2 in crude peanut extract with a titer of 10(7) by Western blot and reacts specifically with epitope 3 shown by epitope mapping for a library of solid-phase-bound synthetic 15-mer peptides covering the entire sequence of Ara h 2. Such IgE-reactive epitopes are of high analytical relevance as they could constitute the basis for epitope-specific detection systems for use in quality control in the food industry or for forensic purposes in cases of fatal reactions to otherwise undetected peanut proteins.

A napin-like polypeptide with translation-inhibitory, trypsin-inhibitory, antiproliferative and antibacterial activities from kale seeds

A heterodimeric napin-like polypeptide with translation-inhibiting and antibacterial activities has been isolated from kale seeds. The purification procedure entailed ion-exchange chromatography on dielthylaminoethyl (DEAE)-cellulose, affinity chromatography on Affi-gel blue gel, ion-exchange chromatography by fast protein liquid chromatography (FPLC) on Mono S, and gel filtration by FPLC on Superdex 75. The napin-like polypeptide was unadsorbed on DEAE-cellulose but adsorbed on Affi-gel blue gel and Mono S. Its 7-kDa large subunit differs in N-terminal amino acid sequence from the 4-kDa small subunit. The polypeptide inhibited translation in the rabbit reticulocyte lysate system with an IC50 of 37.5 nM. This activity was preserved between pH 5 and pH 11, and between 10 and 40 degrees C. It fell to a low level at pH 3 and pH 13 and at 70 degrees C. Antibacterial activity against Bacillus, Megabacterium, and Pseudomonas species and antiproliferative activity against leukemia L1210 cells were observed. However, the polypeptide did not exert antifungal, ribonuclease, or protease activity.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Effect of pH and ionic strength modifications on thermal denaturation of the 11S globulin of sunflower (Helianthus annuus)

Helianthinin, the main storage protein of sunflowers, has low water solubility and does not form a gel when heated; this behavior is different from other 11S globulins and limits its food applications. To understand this particular behavior, changes on helianthinin association-dissociation state induced by modifications in pH and ionic strength were analyzed. The influence of these different medium conditions on its thermal stability and tendency to form aggregates was also studied. Helianthinin behavior at different pH values and ionic strengths is similar to other 11S globulins except that it remains in a trimeric form at pH 11. Helianthinin thermal stability is higher than other 11S globulins but is lower than oat 11S globulin. Alkaline pH produces a 10 degrees C decrease of its denaturation temperature and also of the cooperativity of denaturation process, but it does not affect the denaturation activation energy. The decrease in thermal stability with the pH increase is also manifested by its tendency to form aggregates by SH/SS interchange reactions. When thermal treatments at alkaline pH are performed, all helianthinin subunits form aggregates, characterized by a higher proportion of beta-polypeptides than alpha-polypeptides, which is an indication that aggregation is accompanied by dissociation. Treatments at 80 degrees C are sufficient to induce aggregation but not to produce denaturation, and in these conditions hexameric forms remain after the treatment.

Detailed physicochemical characterization of the 2S storage protein from rape (Brassica napus L.)

Chromatographic, chemical, and spectroscopic techniques were used to characterize the physicochemical properties of napin purified by preparative chromatography. The molar extinction coefficient was determined (epsilon = 0.56), and static and dynamic light scattering measurements enabled the average molecular weight (M(w) = 13919), the second virial coefficient (A(2) = 23.95 x 10(-)(5) mol cm(3) g(-)(2)), and the hydrodynamic radius (R(H) = 1.98 nm) to be determined. No conformational changes were observed by fluorescence and circular dichroism measurements in different buffers at pH 3, 4.6, 7, and 12, confirming the high pH stability of this protein. From MALDI-TOF analysis and after enzymatic digestion, it was found that this purified sample, extracted from the rapeseed variety Express, contained mainly isoform 2SS3_BRANA.

[Polymorphism and inheritance of seed storage protein in sunflower]

The data on polymorphism and inheritance of the seed storage protein helianthinin are presented. The results of hybrid analysis indicate that in the annual sunflower Helianthus annuus, helianthinin synthesis is controlled by at least three loci: HelA, HelB, HelB, and HelC. Codominant alleles controlling different electrophoretic variants of polypeptides were identified at each of the loci. The HelA locus was inherited independently of HelB and HelC in a series of dihybrid crosses. The frequencies of recombination between loci HelB and HelC estimated in F2 and BC of two crossing combinations were respectively 21.8 and 19.0%. Segregation of the Hel-C-controlled variants in the progenies from the crosses of cultured sunflower with annual wild species and forms corresponded to that theoretically expected for Mendelian inheritance. The maternal type of helianthinin inheritance was observed in the progenies from the crosses of inbred H. annuus lines with perennial diploid and polyploid Helianthus species. Altered expression of the HelC locus was detected in some hybrid combinations. These alterations appeared in early (F1, F2) hybrid generations and were similar in different hybrid combinations. They did not depend on the perennial paternal species being more influenced by the maternal genotype and by the mode of obtaining hybrids (in an embryo culture or in the field). These results are explained by "genomic shock" generated by hybridization of genetically incompatible species.

Mixed antibody and T cell responses to peanut and the peanut allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6 in an oral sensitization model

BACKGROUND

Peanut allergy is known for its severity and persistence through life. Several peanut proteins have been identified as allergenic and are indicated as Ara h 1-7. Very little is known about the mechanisms that underlie sensitization to peanut proteins.

OBJECTIVE

The purpose of the present study was to reveal the immune responses that are induced against peanut and the peanut allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6 during sensitization, including the very early responses.

METHODS

Humoral and T cell responses against peanut and the peanut allergens were examined in an early and later stage of sensitization in an established murine model of peanut anaphylaxis. Therefore C3H/HeJ mice were orally exposed to two different doses of peanut extract plus cholera toxin.

RESULTS

Oral sensitization to peanut was characterized by an antigen-induced mixed cytokine response in the spleen (IL-4, IL-5, IL-10 and IFN-gamma), which could already be observed 7 days after the onset of exposure. Additionally, polyisotypic humoral responses (IgE, IgG1 and IgG2a) against peanut were found in the serum. Moreover, we demonstrated that these T helper (Th)1/Th2 cytokine and antibody responses were also directed specifically against the major peanut allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6.

CONCLUSIONS

This study implicates that both Th1 and Th2 phenomena are involved in the development of peanut allergy in the C3H/HeJ murine model. Furthermore, we show that the present oral model is suitable to examine immune responses to food allergens during different stages of sensitization upon treatment with a whole food extract.

Transport of ricin and 2S albumin precursors to the storage vacuoles of Ricinus communis endosperm involves the Golgi and VSR-like receptors

We have studied the transport of proricin and pro2S albumin to the protein storage vacuoles of developing castor bean (Ricinus communis L.) endosperm. Immunoelectron microscopy and cell fractionation reveal that both proteins travel through the Golgi apparatus and co-localize throughout their route to the storage vacuole. En route to the PSV, the proteins co-localize in large (>200 nm) vesicles, which are likely to represent developing storage vacuoles. We further show that the sequence-specific vacuolar sorting signals of both proricin and pro2SA bind in vitro to proteins that have high sequence similarity to members of the VSR/AtELP/BP-80 vacuolar sorting receptor family, generally associated with clathrin-mediated traffic to the lytic vacuole. The implications of these findings in relation to the current model for protein sorting to storage vacuoles are discussed.

Solution structure of a methionine-rich 2S albumin from sunflower seeds: relationship to its allergenic and emulsifying properties

The three-dimensional structure in aqueous solution of SFA-8, a 2S albumin 103-residue protein from seeds of sunflower (Helianthus anuus L.), has been determined by NMR methods. An almost complete (1)H resonance assignment was accomplished from analysis of two-dimensional (2D) COSY and 2D TOCSY spectra, and the structure was computed by using restrained molecular dynamics on the basis of 1393 upper limit distance constraints derived from NOE cross-correlation intensities measured in 2D NOESY spectra. In contrast with most other 2S albumins, SFA-8 consists of a single polypeptide chain without any cleavage in the segment of residues 30-46. The computed structures exhibited an rmsd radius of 0.52 A for the backbone structural core (residues 11-30 and 46-101) and 1.01 A for the side chain heavy atoms. The resulting structure consists of five amphipathic helices arranged in a right-handed superhelix, a folding motif first observed in nonspecific lipid transfer (nsLTP) proteins, and common to other 2S albumins. In contrast to nsLTP proteins, neither SFA-8 nor RicC3 (a 2S albumin from castor bean) has an internal cavity that is able to host a lipid molecule, which results from an exchange in the pairing of disulfide bridges in the CXC segment. Both 2S albumins and nonspecific lipid transfer proteins belong to the prolamin superfamily, which includes a number of important food allergens. Differences in the extension and solvent exposition of the so-called "hypervariable loop" (which connects helices III and IV) in SFA-8 and RicC3 may be responsible for the different allergenic properties of the two proteins. SFA-8 has been shown to form highly stable emulsions with oil/water mixtures. We propose that these properties may be determined partly by a hydrophobic patch at the surface of the protein which consists of five methionines that partially hide the Trp76 residue. The flexibility of the loop which contains Trp76 and the hydrophobicity of the whole environment may favor a conformational change, by which the Trp76 side chain may become inserted into the oil phase.

Relevance of Ara h1, Ara h2 and Ara h3 in peanut-allergic patients, as determined by immunoglobulin E Western blotting, basophil-histamine release and intracutaneous testing: Ara h2 is the most important peanut allergen

BACKGROUND

A number of allergenic proteins in peanut has been described and the relative importance of these allergens is yet to be determined.

OBJECTIVES

We have investigated the relevance of previously identified peanut allergens in well-characterized peanut-allergic patients by in vitro, ex vivo and in vivo assays.

METHODS

Thirty-two adult peanut-allergic patients were included based on careful and standardized patient history and the presence of peanut-specific IgE. The diagnosis peanut allergy was confirmed using double-blind placebo-controlled food challenges in 23 patients. Major peanut allergens Ara h1, Ara h2 and Ara h3 were purified from peanuts using ion-exchange chromatography. IgE immunoblotting was performed and IgE-cross-linking capacity was examined by measuring histamine release (HR) after incubating patient basophils as well as passively sensitized basophils with several dilutions of the allergens. Intracutaneous tests (ICTs) using 10-fold dilution steps of the purified allergens and crude peanut extract were performed.

RESULTS

Ara h2 was recognized most frequently (26 out of 32) in all tests and induced both positive skin tests and basophil degranulation at low concentrations, whereas Ara h1 and Ara h3 were recognized less frequently and reacted only at 100-fold higher concentrations as analysed with HR and intracutaneous testing (ICT). Next to the three tested allergens, proteins with molecular weights of somewhat smaller than 15 kDa were identified as a IgE-binding proteins on immunoblot in the majority of the patients (20 out of 32).

CONCLUSION

We conclude that Ara h2 is, for our patient group, the most important peanut allergen, and that previously unidentified peanut proteins with molecular weights of somewhat smaller than 15 kDa may be important allergens as well. ICT in combination with basophil-HR and IgE immunoblotting provides insight in the patient specificity towards the individual peanut allergens.

High-yield expression in Escherichia coli, purification, and characterization of properly folded major peanut allergen Ara h 2

Allergic reactions to peanuts are a serious health problem because of their high prevalence, associated with potential severity, and chronicity. One of the three major allergens in peanut, Ara h 2, is a member of the conglutin family of seed storage proteins. Ara h 2 shows high sequence homology to proteins of the 2S albumin family. Presently, only very few structural data from allergenic proteins of this family exist. For a detailed understanding of the molecular mechanisms of food-induced allergies and for the development of therapeutic strategies knowledge of the high-resolution three-dimensional structure of allergenic proteins is essential. We report a method for the efficient large-scale preparation of properly folded Ara h 2 for structural studies and report CD-spectroscopic data. In contrast to other allergenic 2S albumins, Ara h 2 exists as a single continuous polypeptide chain in peanut seeds, and thus heterologous expression in Escherichia coli was possible. Ara h 2 was expressed as Trx-His-tag fusion protein in E. coli Origami (DE3), a modified E. coli strain with oxidizing cytoplasm which allows the formation of disulfide bridges. It could be shown that recombinant Ara h 2, thus overexpressed and purified, and the allergen isolated from peanuts are identical as judged from immunoblotting, analytical HPLC, and circular dichroism spectra.