Engineering, characterization and in vitro efficacy of the major peanut allergens for use in immunotherapy

BACKGROUND

Numerous strategies have been proposed for the treatment of peanut allergies, but despite the steady advancement in our understanding of atopic immune responses and the increasing number of deaths each year from peanut anaphylaxis, there is still no safe, effective, specific therapy for the peanut-sensitive individual. Immunotherapy would be safer and more effective if the allergens could be altered to reduce their ability to initiate an allergic reaction without altering their ability to desensitize the allergic patient.

METHODS

The cDNA clones for three major peanut allergens, Ara h 1, Ara h 2, and Ara h 3, have been cloned and characterized. The IgE-binding epitopes of each of these allergens have been determined and amino acids critical to each epitope identified. Site-directed mutagenesis of the allergen cDNA clones, followed by recombinant production of the modified allergen, provided the reagents necessary to test our hypothesis that hypoallergenic proteins are effective immunotherapeutic reagents for treating peanut-sensitive patients. Modified peanut allergens were subjected to immunoblot analysis using peanut-positive patient sera IgE, T cell proliferation assays, and tested in a murine model of peanut anaphylaxis.

RESULTS

In general, the modified allergens were poor competitors for binding of peanut-specific IgE when compared to their wild-type counterpart. The modified allergens demonstrated a greatly reduced IgE-binding capacity when individual patient serum IgE was compared to the binding capacity of the wild-type allergens. In addition, while there was considerable variability between patients, the modified allergens retained the ability to stimulate T cell proliferation.

CONCLUSIONS

These modified allergen genes and proteins should provide a safe immunotherapeutic agent for the treatment of peanut allergy.

A soybean G2 glycinin allergen. 2. Epitope mapping and three-dimensional modeling

BACKGROUND

Multiple allergens have been documented in soybean extracts. IgE from individuals allergic to soybeans, but not to peanut, has been shown by immunoblot analysis to bind to proteins with a molecular weight of approximately 22 kD. These findings suggested that this unique protein fraction from soybean might be responsible, in part, for soybean allergic reactivity. The objective of the present study was to characterize specific B cell epitopes, to determine if any amino acid was critical to IgE binding and to model the 22-kD G2 soybean allergen to the three-dimensional (3-D) phaseolin molecule.

METHODS

B cell epitopes were identified using SPOTs peptide analysis. Structural orientation of the IgE-binding regions was mapped to the 3-D phaseolin molecule using molecular modeling of the protein tertiary structure.

RESULTS

Eleven linear epitopes, representing 15 amino acid peptide sequences, bound to IgE in the glycinin molecule. These epitopes were predicted to be distributed asymmetrically on the surface of G2 trimers.

CONCLUSIONS

Only 1 epitope could be rendered non-IgE binding by alanine substitutions in the peptide. The nonrandom distribution of the IgE binding sites provides new insight into their organization in trimers in 11S complexes of the G2 glycinin allergen.

A soybean G2 glycinin allergen. 1. Identification and characterization

BACKGROUND

Multiple allergens have been documented in soybean extracts. IgE from individuals allergic to soybeans, but not to peanut, was shown by immunoblot analysis to bind to proteins with a molecular weight of approximately 21 kD. These findings suggested that unique proteins in soybeans might be responsible for soybean allergic reactivity. The objective of the present study was to identify unique proteins in soybean extracts that bind to specific IgE from soybean-sensitive individuals, and to characterize the allergen using physicochemical methods and IgE binding.

METHODS

Two-dimensional and preparative SDS-PAGE/IgE immunoblot analysis was used to identify a 22-kD soybean-specific allergen from crude soybean extracts. N-terminal sequence analysis was used to determine the identification of the protein binding IgE from soybean-sensitive individuals.

RESULTS

IgE immunoblot and amino acid sequence analysis identified the 22-kD protein as a member of the G2 glycinin soybean protein family. Further investigation revealed that the IgEs reacted with basic chains from each member of the glycinin family of soybean storage proteins.

CONCLUSIONS

Each of the subunits from glycinin, the storage protein that is the most prevalent component of soybean, are major allergens.

Mutational analysis of the IgE-binding epitopes of P34/Gly m Bd 30K

BACKGROUND

Peanuts and soybeans are 2 foods that have been shown to be responsible for many atopic disorders. Because of their nutritional benefit, soybean proteins are now being used increasingly in a number of food products. Previous studies have documented multiple allergens in soybean extracts, including glycinin, beta-conglycinin, and the P34/Gly m Bd 30K protein.

OBJECTIVE

Our overall goal was to identify soybean-specific allergens to begin to understand molecular and immunochemical characteristics of legume proteins. The specific aim of the current investigation was to identify the essential amino acid residues necessary for IgE binding in the 5 distinct immunodominant epitopes of P34/Gly m Bd 30K.

METHODS

Serum IgE from 6 clinically sensitive soybean-allergic individuals was used to identify P34/Gly m Bd 30K in the native and single amino acid substituted peptides with use of the SPOTS peptide synthesis technique to determine critical amino acids required for IgE binding.

RESULTS

The intensity of IgE binding and epitope recognition by serum IgE from the individuals varied substantially. With use of serum from 6 clinically soybean-sensitive individuals, 2 of the 5 immunodominant epitopes could be mutagenized to non-IgE binding peptides.

CONCLUSIONS

Single-site amino acid substitution of the 5 immunodominant epitopes of Gly m Bd 30K with alanine revealed that IgE binding could be reduced or eliminated in epitopes 6 and 16 in the serum obtained from 6 soybean-sensitive patients.

Cellular and molecular characterization of a major soybean allergen

Soybean proteins share a large number of cross-reacting allergens with other members of the legume family; however, soy-allergic patients rarely react clinically to other members of the legume family. Gly m Bd 30K, an IgE-binding protein with a molecular weight of 30 kD, was identified in soybean extracts by Western IgE-immunoblot analysis. This monomeric allergen was shown to have an N-terminal amino acid sequence and amino acid composition identical to that of the seed 34-kD protein, P34, a thiol protease of the papain family. Electron-microscopic immunolocalization of P34 monoclonal antibodies and IgE binding to sections of soybean seeds showed dense staining throughout the vacuolar bodies, localizing the allergens in protein storage vacuoles of seed cotyledons. We used pooled serum from soybean-sensitive patients to determine the linear IgE-specific epitopes in the 34-kD allergen amino acid sequence. B-cell epitope mapping revealed 10 regions of IgE-binding activity using an overlapping peptide strategy of 15-mers offset by 8 amino acids throughout the P34 sequence. Smaller overlapping peptides, 10-mers offset by 2 amino acids, revealed 16 distinct linear epitopes, 9 of which were mapped to the mature protein. No obvious amino acid sequence motifs could be identified by the smaller IgE-binding epitopes. Using individual patient serum, 5 immunodominant epitopes were identified in this allergen.

Identification and mutational analysis of the immunodominant IgE binding epitopes of the major peanut allergen Ara h 2

A major peanut allergen, Ara h 2, is recognized by serum IgE from > 90% of patients with peanut hypersensitivity. Biochemical characterization of this allergen indicates that it is a glycoprotein of approximately 17.5 kDa. Using N-terminal amino acid sequence data from purified Ara h 2, oligonucleotide primers were synthesized and used to identify a clone (741 bp) from a peanut cDNA library. This clone was capable of encoding a 17.5-kDa protein with homology to the conglutin family of seed storage proteins. The major linear immunoglobulin E (IgE)-binding epitopes of this allergen were mapped using overlapping peptides synthesized on an activated cellulose membrane and pooled serum IgE from 15 peanut-sensitive patients. Ten IgE-binding epitopes were identified, distributed throughout the length of the Ara h 2 protein. Sixty-three percent of the amino acids represented in the epitopes were either polar uncharged or apolar residues. In an effort to determine which, if any, of the 10 epitopes were recognized by the majority of patients with peanut hypersensitivity, each set of 10 peptides was probed individually with serum IgE from 10 different patients. All of the patient sera tested recognized multiple epitopes. Three epitopes (aa27-36, aa57-66, and aa65-74) were recognized by all patients tested. In addition, these three peptides bound more IgE than all the other epitopes combined, indicating that they are the immunodominant epitopes of the Ara h 2 protein. Mutational analysis of the Ara h 2 epitopes indicate that single amino acid changes result in loss of IgE binding. Two epitopes in region aa57-74 contained the amino acid sequence DPYSP that appears to be necessary for IgE binding. These results may allow for the design of improved diagnostic and therapeutic approaches to peanut hypersensitivity.

Mapping and mutational analysis of the IgE-binding epitopes on Ara h 1, a legume vicilin protein and a major allergen in peanut hypersensitivity

Peanut allergy is a significant health problem because of the prevelance and potential severity of the allergic reaction. Serum IgE from patients with documented peanut hypersensitivity reactions and overlapping peptides were used to identify the IgE-binding epitopes on the major peanut allergen, Ara h 1. At least twenty-three different linear IgE-binding epitopes, located throughout the length of the Ara h 1 protein, were identified. All of the epitopes were 6-10 amino acids in length, but there was no obvious sequence motif shared by all peptides. Four of the peptides appeared to be immunodominant IgE-binding epitopes in that they were recognized by serum from more than 80% of the patients tested and bound more IgE than any of the other Ara h 1 epitopes. Mutational analysis of the immunodominant epitopes revealed that single amino acid changes within these peptides had dramatic effects on IgE-binding characteristics. The identification and determination of the IgE-binding capabilities of core amino acids in epitopes on the Ara h 1 protein will make it possible to address the pathophysiologic and immunologic mechanisms regarding peanut hypersensitivity reactions specifically and food hypersensitivity in general.

Isolation and characterization of a clone encoding a major allergen (Bla g Bd90K) involved in IgE-mediated cockroach hypersensitivity

Previous studies have established that atopic individuals living in cockroach-infested housing become sensitized to cockroach aeroallergens and produce IgE antibodies to a variety of proteins. We describe the isolation of a complementary DNA clone from an expression library, constructed with messenger RNA from German (Blattella germanica) cockroaches, which encodes a major allergen involved in mediating cockroach hypersensitivity. Approximately 0.2% of the clones from a lambda ZAP XR cDNA library bound IgE from a patient with cockroach sensitivity. A randomly selected subset of these clones revealed that they were either different isolates of the same gene or members of a closely related gene family. One of the largest clones (a 4 kb insert) from this subset, Bla g Bd90K hybridized to a single mRNA of approximately the same size. DNA sequence analysis showed that this gene consisted of seven 576 bp tandem repeats with a short unique region at either end. No significant sequence homologies were found between the cockroach clone and any other gene reported in the GenBank database. Serum from 17 of 22 (77%) patients with cockroach hypersensitivity identified IgE-binding recombinant protein expressed from clone Bla g Bd90K in Escherichia coli XL-Blue cells as determined by sodium dodecylsulfate-polyacrylamide gel electrophoresis/immunoblot analysis. This recombinant protein migrates with a molecular weight (90 kd) apparently similar to one identified in whole body extracts. We have identified and isolated a cDNA that encodes a major cockroach allergen (Bla g Bd90K) present in German cockroaches.

Recombinant peanut allergen Ara h I expression and IgE binding in patients with peanut hypersensitivity

Peanut allergy is a significant health problem because of the frequency, the potential severity, and the chronicity of the allergic sensitivity. Serum IgE from patients with documented peanut hypersensitivity reactions and a peanut cDNA expression library were used to identify clones that encode peanut allergens. One of the major peanut allergens, Ara h I, was selected from these clones using Ara h I specific oligonucleotides and polymerase chain reaction technology. The Ara h I clone identified a 2.3-kb mRNA species on a Northern blot containing peanut poly (A)+ RNA. DNA sequence analysis of the cloned inserts revealed that the Ara h I allergen has significant homology with the vicilin seed storage protein family found in most higher plants. The isolation of the Ara h I clones allowed the synthesis of this protein in E. coli cells and subsequent recognition of this recombinant protein in immunoblot analysis using serum IgE from patients with peanut hypersensitivity. With the production of the recombinant peanut protein it will now be possible to address the pathophysiologic and immunologic mechanisms regarding peanut hypersensitivity reactions specifically and food hypersensitivity in general

Isolation, identification, and characterization of clones encoding antigens responsible for peanut hypersensitivity

Peanut allergy is a significant health problem because of the frequency, the potential severity, and the chronicity of the allergic sensitivity. Serum IgE from patients with documented peanut hypersensitivity reactions and a peanut cDNA expression library were used to identify clones that encode peanut allergens. One of the major peanut allergens, Ara h I, was selected from these clones using Ara h I-specific oligonucleotides and polymerase chain reaction technology. The Ara h I clone identified a 2.3-kb mRNA species on a Northern blot containing peanut poly A+RNA. DNA sequence analysis of the cloned inserts revealed that the Ara h I allergen has significant homology with the vicilin seed storage protein family found in most higher plants. The isolation of the Ara h I clones allowed the synthesis of this protein in Escherichia coli cells and subsequent recognition of this recombinant protein in immunoblot analysis using serum IgE from patients with peanut hypersensitivity. With the production of the recombinant peanut protein it will now be possible to address the pathophysiologic and immunologic mechanisms regarding peanut hypersensitivity reactions specifically and food hypersensitivity in general.

Epitope specificity of the major peanut allergen, Ara h II

The antigenic and allergenic structure of Ara h II, a major allergen of peanuts, was investigated with the use of four monoclonal antibodies obtained from BALB/c mice immunized with purified Ara h II. Our previous studies with monoclonal antibodies generated to peanut allergens showed this method to be useful for epitope mapping. When used as a solid phase in an ELISA, these monoclonal antibodies captured peanut antigen, which bound human IgE from patients with positive peanut challenge responses. The Ara h II monoclonal antibodies were found to be specific for peanut antigens when binding for other legumes was examined. In ELISA inhibition studies with the monoclonal antibodies, we identified two different antigenic sites on Ara h II. In similar studies with pooled human IgE serum from patients with positive challenge responses to peanuts, we identified two closely related IgE-binding epitopes. These characterized monoclonal antibodies to Ara h II will be useful for future studies to immunoaffinity purify the Ara h II allergen and to use in conjunction with recombinant technology for determining structure-function relationships.

Identification of peanut agglutinin and soybean trypsin inhibitor as minor legume allergens

Peanuts and soybeans are frequent causes of food hypersensitivity reactions in children. Sera from 12 patients with atopic dermatitis and a positive double-blind placebo-controlled food challenge to peanut and sera from 5 patients with atopic dermatitis and a positive double-blind placebo-controlled food challenge to soybean were used to identify and characterize specific legume allergens. Identification of a minor allergen from peanut and a minor allergen from soybean was accomplished using various physicochemical techniques. The peanut fraction, peanut agglutinin, isolated by anion-exchange chromatography and electrolution and confirmed by amino acid sequencing, bound IgE in only 50% of the peanut challenge positive patients. The soybean fraction, soybean trypsin inhibitor, identified by gel filtration and electroelution and confirmed by amino acid sequencing, bound IgE in only 20% of the soy challenge positive patients. The identification of these two known legume proteins as minor allergens should allow further immunologic and structural investigations to compare the major and minor legume allergens.

Epitope specificity and immunoaffinity purification of the major peanut allergen, Ara h I

The antigenic and allergenic structure of Ara h I, a major allergen of peanuts, was investigated with the use of seven monoclonal antibodies obtained from BALB/c mice immunized with purified Ara h I. Previous work with monoclonal antibodies produced to allergens has primarily been done with inhalant allergens. Only recently have the major allergens of various foods been determined so that investigations with monoclonal antibodies into the allergenic epitopes could begin. When used as a solid phase in an ELISA, these monoclonal antibodies captured peanut antigen, which bound human IgE from patients with positive results to challenges to peanuts. The Ara h I monoclonal antibodies were found to be specific for peanut antigens when binding for other legumes was examined. In ELISA inhibition studies with the monoclonal antibodies, we identified four different antigenic sites on Ara h I. In related studies with pooled human IgE serum from patients with positive results to challenges to peanuts, we identified three similar IgE-binding epitopes. As a means of purifying the Ara h I allergen, we prepared an immunoaffinity column with monoclonal antibody 8D9. We eluted from this column the allergen Ara h I, which had a mean molecular weight of 63.5 kd and which bound human IgE from individual and pooled serum of patients with peanut sensitivity.

In vitro translation of RNA from the German cockroach Blattella germanica

The translation of mRNA within total RNA of German (Blattella germanica) cockroaches was performed using a rabbit reticulocyte lysate system. Analysis of the translation products by SDS-PAGE and combined autoradiography revealed several synthesized proteins with apparent molecular weights ranging from 20 kD to 110 kD. SDS-PAGE/Western blotting of non-radiolabeled translation products and incubation with human serum with IgE to cockroach allergens showed the presence of a 36 kD and 50 kD allergen. The confirmation of the translation of the cockroach allergens from total RNA is an important first step in the cloning of cockroach allergens.

Allergenicity of peanut and soybean extracts altered by chemical or thermal denaturation in patients with atopic dermatitis and positive food challenges

Peanuts and soybeans are two of the six most common foods to cause food hypersensitivity reactions in children. We used the serum of 10 patients with atopic dermatitis and positive double-blind, placebo-controlled, food challenges to peanut and two patients with atopic dermatitis and positive double-blind, placebo-controlled, food challenges to soybean to investigate the change in IgE-specific and IgG-specific binding to these proteins altered by either chemical or thermal denaturation. We used IgE- and IgG-specific ELISA-inhibition analyses to compare these effects on the crude peanut and crude soy extracts, as well as on the major allergenic fractions of both proteins. Heating the soy proteins at various temperatures and time intervals did not significantly change the IgE- or IgG-specific binding of the soy positive pooled serum. When the peanut proteins were subjected to similar heating experiments, the IgE- and IgG-specific binding did not change. When these same proteins were treated with enzymes in the immobilized digestive enzyme assay system used to mimic human digestion, the binding of IgE to the crude peanut and crude soy extracts was reduced; 100-fold for peanut and 10-fold for soybean. Therefore it appears that thermal denaturation of peanut and soybean protein extracts does not enhance or reduce IgE- and IgG-specific binding activity. Chemical denaturation appears to minimally reduce the binding of these proteins.

Identification and characterization of a second major peanut allergen, Ara h II, with use of the sera of patients with atopic dermatitis and positive peanut challenge

Peanuts are frequently a cause of food hypersensitivity reactions in children. Serum from nine patients with atopic dermatitis and a positive double-blind, placebo-controlled, food challenge to peanut were used in the process of identification and purification of the peanut allergens. Identification of a second major peanut allergen was accomplished with use of various biochemical and molecular techniques. Anion exchange chromatography of the crude peanut extract produced several fractions that bound IgE from the serum of the patient pool with positive challenges. By measuring antipeanut specific IgE and by IgE-specific immunoblotting we have identified an allergic component that has two closely migrating bands with a mean molecular weight of 17 kd. Two-dimensional gel electrophoresis of this fraction revealed it to have a mean isoelectric point of 5.2. According to allergen nomenclature of the IUIS Subcommittee for Allergen Nomenclature this allergen is designated, Ara h II (Arachis hypogaea).

Effect of soy protein ingestion on total and specific immunoglobulin G concentrations in neonatal porcine serum measured by enzyme-linked immunosorbent assay

Crossbred neonatal pigs from spring and summer farrowings were used to evaluate the systemic humoral immune response in porcine serum after ingestion of soy protein. At 10 to 12 d of age (average BW 3.8 kg), pigs were randomly allotted to three treatment groups according to litter, weight, and sex. Treatments were intermittent gavage feedings two or three times daily for six consecutive days with nonfat dry milk (NFDM) or textured vegetable protein (TVP) and a nongavaged control group. Pigs were weaned at 20 to 22 d of age (average BW 5.7 kg) and fed a corn-soybean meal-based starter diet. Total serum immunoglobulin G (IgG) and IgG concentrations specific for soy protein were measured by ELISA. Blood samples were taken at 1 d of age after colostrum intake and at 4-d intervals from the beginning of treatment to 31 d of age. When averaged from d 1 to 31, spring-farrowed pigs had greater (P less than .005) total IgG and soy-protein-specific IgG concentrations than did summer-farrowed pigs (8.70 vs 6.51 mg/mL and 1.59 vs .55 micrograms/mL, respectively). Total serum IgG concentrations changed with time (P = .005); they initially decreased, then recovered after weaning. These changes were independent of treatment, sex, or farrowing season. Soy-protein-specific IgG concentrations also changed with time (P = .003); however, this trend was dependent on season (P = .014). Summer-farrowed pigs exhibited a more rapid and severe decrease in serum IgG concentrations specific for soy protein than did spring-farrowed pigs.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a major peanut allergen, Ara h I, in patients with atopic dermatitis and positive peanut challenges

Peanuts are among the most common causes of immediate hypersensitivity reactions to foods. Serum from nine patients with atopic dermatitis and a positive double-blind, placebo-controlled, food challenge to peanut were used to begin the process of identification and purification of the major peanut allergens. Identification of a major peanut allergen was accomplished by use of anion-exchange column chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, ELISA, thin-layer isoelectric focusing, and IgE-specific immunoblotting. Anion-exchange chromatography revealed several fractions that bound IgE from the serum of the challenge-positive patient pool. By measuring antipeanut-specific IgE in the ELISA and in IgE-specific immunoblotting, we identified an allergenic component with two Coomassie brilliant blue staining bands by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a mean molecular weight of 63.5 kd. Examination of this fraction by the IgE antipeanut ELISA with individual serum and by the ELISA-inhibition assay with pooled serum, we identified this fraction as a major allergen. Thin-layer isoelectric focusing and immunoblotting of this 63.5 kd fraction revealed it to have an isoelectric point of 4.55. Based on allergen nomenclature of the IUIS Subcommittee for Allergen Nomenclature, this allergen is designated, Ara h I (Arachis hypogaea).