Human IgE-binding synthetic peptides of bovine beta-lactoglobulin and alpha-lactalbumin. In vitro cross-reactivity of the allergens

Effect of lactic acid bacteria fermentation on cow milk allergenicity and antigenicity: A review

Cow milk is a major allergenic food. The potential prevention and treatment effects of lactic acid bacteria (LAB)-fermented dairy products on allergic symptoms have garnered considerable attention. Cow milk allergy (CMA) is mainly attributed to extracellular and/or cell envelope proteolytic enzymes with hydrolysis specificity. Numerous studies have demonstrated that LAB prevents the risk of allergies by modulating the development and regulation of the host immune system. Specifically, LAB and its effectors can enhance intestinal barrier function and affect immune cells by interfering with humoral and cellular immunity. Fermentation hydrolysis of allergenic epitopes is considered the main mechanism of reducing CMA. This article reviews the linear epitopes of allergens in cow milk and the effect of LAB on these allergens and provides insight into the means of predicting allergenic epitopes by conventional laboratory analysis methods combined with molecular simulation. Although LAB can reduce CMA in several ways, the mechanism of action remains partially clarified. Therefore, this review additionally attempts to summarize the main mechanism of LAB fermentation to provide guidance for establishing an effective preventive and treatment method for CMA and serve as a reference for the screening, research, and application of LAB-based intervention.

Development of a Two-Step Hydrolysis Hypoallergenic Cow's Milk Formula and Evaluation of Residue Allergenicity by Peptidomics and Immunoreactivity Analysis

Cow's milk allergy (CMA) is an abnormal immune response that severely affects the nutritional supplementation of allergic infants. Currently, only a limited number of hypoallergenic formulas are available on the market, and these are only categorized according to their degree of hydrolysis, which still poses an allergy risk and cannot be consumed by CMA patients, especially infants. To address this issue, we developed a two-step hydrolysis hypoallergenic formula targeting destruction of allergen epitope from whey protein. Then, a comprehensive evaluation system was constructed, including peptidomics analysis, in vivo and in vitro allergenicity assessments, revealing allergic changes in the product from the epitope structure level to the immunological level. The results showed that 97.14% of hydrolyzed peptides from α-lactalbumin and β-lactoglobulin did not contain allergenic epitopes after treatment with trypsin and flavourzyme. In vitro and in vivo allergenicity assessment results confirmed that the two-step hydrolysis method effectively reduced the allergenicity of whey protein. Compared with the common milk powder, the hypoallergenic formula induced lower levels of basophil degranulation and relieved the body's anaphylactic symptoms caused by cow milk. This study provides a promising solution to the limited hypoallergenic formula problem and may benefit allergic infants who require nutritional supplements.

Isolation and allergenicity evaluation of glycated α-lactalbumin digestive products and identification of allergenic peptides

This study aimed to isolate and evaluate the allergenicity of glycated α-lactalbumin (ALA) digestive products and identify its allergenic peptides. The digestive products of native-, alone glycated- and ultrasound-assisted glycated ALA (ALA-D, ALA-gal-D, 100ALA-gal-D) were isolated into three fractions (F1, F2 and F3). High-resolution mass spectrometry showed that the digestion-resistant peptides of F2 and F3 mainly distributed in amino acid sequence (AA) 25-31, AA32-53, AA40-53, AA54-60, AA80-90, AA94-104. The allergenicity of the three fractions of glycated ALA was lower than that in ALA-D, indicating glycation of ALA could indeed reduce its allergenicity after digestion. Furthermore, most fractions isolated from high glycation-degree ALA had the lowest allergenicity. The IgG/IgE binding abilities of synthesized peptides indicated that AA94-104 firstly identified by us embodied the strongest allergenicity and might be the potential allergenic peptide. This will provide a theory for preparing hypoallergenic products based on the identified allergenic peptides.

Mechanism on the Allergenicity Changes of α-Lactalbumin Treated by Sonication-Assisted Glycation during In Vitro Gastroduodenal Digestion

Physical-assisted chemical modification is effective to reduce the allergenicity of α-lactalbumin (ALA). However, there are few in-depth studies on the allergenicity changes of physical-assisted chemical-modified ALA during digestion. The effect of gastroduodenal digestion on the allergenicity changes of ALA treated by sonication-assisted glycation was assessed. Digestion of both ALA and its glycated forms generated peptide fractions, and intact undigested glycated ALA in the hydrolysates still covalently bound to d-galactose. High-resolution mass spectrometry revealed that a higher glycation degree was discovered in sonication-preprocessed ALA compared to native ALA. Enzyme-linked immunosorbent assay and basophil degranulation showed that sonication-assisted glycation could significantly reduce ALA allergenicity. The allergenicity of both gastric and gastroduodenal hydrolysates was further increased, and the hydrolysates of sonication-assisted glycated ALA showed the lowest allergenicity. The reason could be the shielding effect of the linear epitope found to be caused by a higher glycation degree; although linear epitopes were exposed, d-galactose covalently bound to intact undigested glycated ALA in the hydrolysates retained its masking role. These results indicated that sonication-assisted glycation could be a promising method to prepare immunotherapeutic agents for allergen immunotherapy to achieve the purpose of allergy desensitization.

Identification of IgE and IgG epitopes on native Bos d 4 allergen specific to allergic children

Alpha-lactalbumin (ALA) is one of the major allergens in cow's milk. However, research on its conformational epitopes has been relatively limited. In our study, specific antibodies against cow's milk ALA were purified from eight children by two-step affinity chromatography. Subsequently, mimotopes against IgG and IgE were biopanned from Ph.D.-12 and Ph.D.-C7C, respectively. Based on the mimotopes, linear epitopes were defined with the UniProt alignment tool. Conformational epitopes were computed using the Pepitope Server. Six IgE and seven IgG linear epitopes were identified. Meanwhile, five IgE and three IgG conformational epitopes were revealed with PyMOL. The results showed that common residues were identified in both IgE and IgG epitopes and some residues of the conformational epitopes were composed of linear epitopes on bovine α-lactalbumin. The results indicated that the data could be used for developing hypoallergenic dairy products on the basis of epitopes and providing a diagnostic tool for the assessment of patients who are allergic to cow's milk.

Single recombinant and purified major allergens and peptides: How they are made and how they change allergy diagnosis and treatment

Objective

To review the current knowledge regarding recombinant and purified allergens and allergen-derived peptides.

Data Sources

PubMed, homepages relevant to the topic, and the National Institutes of Health clinical trial database were searched.

Study Selections

The literature was screened for studies describing purified and recombinant allergens and allergen-derived peptides. Studies relevant to the topic were included in this review.

Results

Advantages and drawbacks of pure and defined recombinant allergens and peptides over allergen extracts in the context of allergy research, diagnosis, and allergen immunotherapy are discussed. We describe how these molecules are manufactured, which products are currently available on the market, and what the regulative issues are. We furthermore provide an overview of clinical studies with vaccines based on recombinant allergens and synthetic peptides. The possibility of prophylactic vaccination based on recombinant fusion proteins consisting of viral carrier proteins and allergen-derived peptides without allergenic activity are also discussed.

Conclusion

During the last 25 years more than several hundred allergen sequences were determined, which led to a production of recombinant allergens that mimic biochemically and immunologically their natural counterparts. Especially in Europe, recombinant allergens are increasingly replacing allergen extracts in diagnosis of allergy. Despite many challenges, such as high cost of clinical trials and regulative issues, allergy vaccines based on recombinant allergens and peptides are being developed and will likely soon be available on the market.

Thymic Stromal Lymphopoietin Induction Is Mediated by the Major Whey Proteins α-Lactalbumin and β-Lactoglobulin through the NF-κB Pathway in Immune Cells

α-Lactalbumin and β-lactoglobulin are two major whey proteins that specifically bind immunoglobulin E and are suspected as major allergens causing cow's milk allergy (CMA). Recent studies have shown that thymic stromal lymphopoietin is a critical factor linking at the interface of the body and environment to the T-helper 2 response. However, it is not known whether thymic stromal lymphopoietin expression is changed by α-lactalbumin and β-lactoglobulin in immune cells. Using RT-PCR and ELISA, the present study was conducted to examine if intravenous injection of α-lactalbumin and β-lactoglobulin increased pro-inflammatory cytokines, T-helper 2 cytokines, and thymic stromal lymphopoietin expression in several immune cells, including macrophages, mast cells, and keratinocytes. Results showed that α-lactalbumin and β-lactoglobulin induced thymic stromal lymphopoietin, interleukin-6, and tumor necrosis factor-α expression. It was concluded that the allergenicity of α-lactalbumin and β-lactoglobulin may be attributed to thymic stromal lymphopoietin induction, T-helper 2 cytokines, and pro-inflammatory cytokines.

The high molecular weight glutenin subunit Bx7 allergen from wheat contains repetitive IgE epitopes

BACKGROUND

Wheat is one of the most common food allergen sources for children and adults. The aim of this study was to characterize new wheat allergens using an IgE discovery approach and to investigate their IgE epitopes.

METHODS

A cDNA expression library representing the wheat transcriptome was constructed in phage lambda gt11 and screened with IgE antibodies from wheat food allergic patients. IgE-reactive cDNA clones coding for portions of high molecular weight (HMW) glutenin subunits were identified by sequence analysis of positive clones. IgE epitopes were characterized using recombinant fragments from the HMW Bx7 and synthetic peptides thereof for testing of allergic patients' sera and in basophil degranulation assays.

RESULTS

We found that the major IgE-reactive areas of HMW glutenins are located in the repetitive regions of the protein and could show that two independent IgE-reactive fragments from HMW Bx7 contained repetitive IgE epitopes.

CONCLUSIONS

Our results demonstrate that IgE antibodies from wheat food allergic patients can recognize repetitive epitopes in one of the important wheat food allergens. Recombinant HMW Bx7 may be included into the panel of allergens for component-resolved diagnosis of wheat food allergy.

Fluorescent immunosorbent assay for the detection of alpha lactalbumin in dairy products with monoclonal antibody bioconjugated with CdSe/ZnS quantum dots

In this work, a new method termed competitive fluorescence-linked immunosorbent assay (FLISA) was developed for specifically quantification of bovine α-lactalbumin (α-La) in dairy products. The monoclonal antibodies (mAbs) against α-La were produced through hybridoma technology, and the mAbs were covalently conjugated with the CdSe/ZnS quantum dots (QDs) using the crossing-linking reagents. Moreover, a competitive FLISA based on QD-mAb conjugates was established to detect α-La in dairy products. It was shown that there was a good linear relationship between inhibition efficiency, and logarithm of α-La concentration after the detection parameters were optimised in which the concentration of α-La varied from 0.1 to 1000ng/mL. The value of IC50 was 0.03μg/mL, and the FLISA method exhibited high sensitivity with the LOD at 0.1ng/mL. The developed FLISA has been successfully applied to determine α-La in commercial dairy products, providing more sensitive analysis compared with the ELISA method.

Assessment of the potential allergenicity of a Milk Basic Protein fraction

BACKGROUND

A specific basic fraction of bovine milk, termed Milk Basic Protein (MBP), has the potential to provide nutritionally important benefits if used as a food ingredient. Although derived from milk, MBP is intended for use as an ingredient in other foods. Cows' milk is a well studied, commonly allergenic food. Although the proteins in MBP are not identified as milk allergens, food products containing MBP will be labelled as containing milk as a caution to milk allergic consumers under food labelling guidelines in the US and the European Union as MBP has not been demonstrated to be free of milk allergens. However, as part of an overall safety evaluation of MBP, the developers sought to evaluate the potential allergenicity of the primary protein components for characteristics of allergenic food proteins and to assess whether intake of these proteins at intended use levels could present a significant new allergenic risk for consumers.

OBJECTIVE

To evaluate the potential allergenicity of the five identified proteins in MBP. While extensive studies have not demonstrated allergenicity of lactoferrin, the four other proteins are less studied. The four were tested here by sequence identity comparison to known allergens, and for stability of these proteins in acidic pepsin as a characteristic common to many food allergens.

METHODS

Sequences of the proteins were compared to those listed in AllergenOnline.com, by methods recommended for the evaluation of proteins introduced in crops through genetic engineering. Pepsin stability was assessed by incubating the various proteins in simulated gastric fluid at pH 1.2 with porcine pepsin for up to 60 min at 37 degrees C, with samples withdrawn and analyzed at specific times.

RESULTS

No significant sequence similarities were identified for the MBP proteins compared to known allergens. All but one of the protein components of MBP were digested relatively quickly by pepsin. The more stable protein will be of low abundance as consumed in contrast to most pepsin-stable food allergens.

CONCLUSIONS

Based on molecular characteristics and expected exposure, the protein components in MBP are unlikely to present any increased risk of allergy for milk allergic subjects or of cross-reactivity for other allergic subjects. However, since the proteins are derived from milk, products containing MBP will need to be labelled as containing milk proteins to warn milk allergic subjects of the potential risk of allergic reactions.

IgE-Mediated Rat Mast Cell Triggering with Tryptic and Synthetic Peptides of Bovine β-Lactoglobulin

BACKGROUND

Immunoglobulin E (IgE) epitopes of beta-lactoglubulin (betaLG) have been identified by ELISA inhibition methods using sera from allergic patients. However, the functional capacity of these epitopes to stimulate mast cells is unknown. It is the goal of the present study to identify bivalent IgE epitopes of betaLG able to trigger target mast cells.

METHODS

Peptides were obtained either by purification from tryptic hydrolysates of betaLG or by synthesis. They were examined for their triggering activity in vitro on peritoneal 3H-serotonin-labeled rat mast cells passively sensitized with IgE anti-betaLG antibodies. In vivo, rats immunized with betaLG were administered peptides by gavage for intestinal rat mast cell protease II release.

RESULTS

Compared with intact betaLG, purified or synthetic tryptic-like betaLG peptides have a sharply decreased allergenicity. Peptide 149-162 retains the highest bivalent IgE epitope-mediated triggering capacity.

CONCLUSION

A functional bivalent IgE epitope was identified at the C terminal end of betaLG.

Screening of transgenic proteins expressed in transgenic food crops for the presence of short amino acid sequences identical to potential, IgE - binding linear epitopes of allergens

BACKGROUND

Transgenic proteins expressed by genetically modified food crops are evaluated for their potential allergenic properties prior to marketing, among others by identification of short identical amino acid sequences that occur both in the transgenic protein and allergenic proteins. A strategy is proposed, in which the positive outcomes of the sequence comparison with a minimal length of six amino acids are further screened for the presence of potential linear IgE-epitopes. This double track approach involves the use of literature data on IgE-epitopes and an antigenicity prediction algorithm.

RESULTS

Thirty-three transgenic proteins have been screened for identities of at least six contiguous amino acids shared with allergenic proteins. Twenty-two transgenic proteins showed positive results of six- or seven-contiguous amino acids length. Only a limited number of identical stretches shared by transgenic proteins (papaya ringspot virus coat protein, acetolactate synthase GH50, and glyphosate oxidoreductase) and allergenic proteins could be identified as (part of) potential linear epitopes.

CONCLUSION

Many transgenic proteins have identical stretches of six or seven amino acids in common with allergenic proteins. Most identical stretches are likely to be false positives. As shown in this study, identical stretches can be further screened for relevance by comparison with linear IgE-binding epitopes described in literature. In the absence of literature data on epitopes, antigenicity prediction by computer aids to select potential antibody binding sites that will need verification of IgE binding by sera binding tests. Finally, the positive outcomes of this approach warrant further clinical testing for potential allergenicity.

Allergy to bovine beta-lactoglobulin: specificity of human IgE to tryptic peptides

BACKGROUND

Bovine beta-lactoglobulin (Blg) is a major cow's milk allergen. It is the main whey protein, without any counterpart in human milk. Blg chemical hydrolysates appeared to retain most of the immunoreactivity of the native protein. Allergenicity of Blg has already been shown to be associated with the four peptides derived from cyanogen bromide cleavage of Blg.

OBJECTIVES

To map the major allergenic epitopes (e.g. regions of the molecule able to bind IgE) on Blg using specific IgE from sera of 46 milk-allergic patients as a probe.

METHODS

Direct and competitive inhibition enzyme immunoassays involving immobilized native protein or purified peptides derived from Blg tryptic cleavage.

RESULTS

Several peptides capable of specifically binding human IgEs were identified and were classified according to the intensity and frequency of the responses. The major epitopes appeared to be fragments (41-60), (102-124) and (149-162) recognized by 92, 97 and 89% of sera, respectively, whilst a second group which contained the fragments (1-8) and (25-40) was recognized by 58 and 72% of the population. A third group, comprising peptides (9-14), (84-91) and (92-100), was still detected by more than 40% of sera.

CONCLUSION

Three peptides were identified as major epitopes, recognized by a large majority of human IgE antibodies. Numerous other epitopes are scattered all along the Blg sequence.

Structure, genomic localization and recombinant expression of the mouse 6-pyruvoyl-tetrahydropterin synthase gene

The 6-pyruvoyl-tetrahydropterin synthase (PTPS) is the second enzyme in the biosynthetic pathway from GTP to tetrahydrobiopterin (BH4). BH4 is an essential cofactor of NO synthases and aromatic amino acid hydroxylases, the latter being responsible for hepatic phenylalanine degradation and monoamine neurotransmitter biosynthesis. BH4 deficiency due to autosomal recessive mutations in the human gene for PTPS leads to a broad range of phenotypes ranging from mild hyperphenylalaninemia to high phenylalanine levels concomitant with neurotransmitter depletion. An animal model to study PTPS deficiency is thus desired to investigate the molecular basis of the disease and its variability. Here, we report on the isolation and recombinant expression of the mouse PTPS gene, Pts. It is located on chromosome 9C-D and contains six exons with an open reading frame of 144 codons. The derived protein monomer has a molecular mass of 16187 Da and shows 82% and 93% identity to its human and rat counterparts, respectively. The mouse PTPS was expressed in bacterial cells and purified to homogeneity. The kinetic properties of the recombinant protein, apparent Km of approximately 10 microM and k(cat) of 0.27 s(-1), were similar to the native mouse enzyme in liver and brain extracts, and to the corresponding human and rat PTPS.

Identification of epitopes within beta lactoglobulin recognised by polyclonal antibodies using phage display and PEPSCAN

Two different epitope mapping techniques were used to identify linear epitopes recognised by polyclonal IgG antibodies from rabbits immunised with bovine beta lactoglobulin (BLG), which is generally regarded as a major allergen in milk. The first, PEPSCAN, was used to investigate the binding of several rabbit polyclonal antisera to sequential overlapping peptides (12-mers) across the sequence of BLG. Each peptide was synthesized on a different polypropylene PIN, and a standard ELISA procedure was used to locate which of these peptides bound the antibodies under investigation. Comparisons of PEPSCANs for antisera from six different rabbits showed that each rabbit recognized a similar set of epitopes within BLG. PEPSCAN analysis also showed that polyclonal antibodies from the mouse recognize a set of epitopes similar to those recognized by the rabbit. The second epitope mapping technique is known as phage display and utilizes libraries of randomized short peptides fused to the coat proteins of filamentous phage as a source of epitopes for analysis. A gene VIII phage display library was used in this study with constrained nonapeptides, which were screened for epitopes recognized by affinity purified rabbit anti-BLG IgG. Immobilised rabbit anti-BLG IgG was screened in two separate experiments, each consisting of three rounds of panning. For each separate experiment, a sensitive phage ELISA was used to screen several hundred single phage clones for binding to anti-BLG IgG immobilised on microtiter plates. As a result, a number of positive phage were identified from the two separate screens of the library (19 different peptides were isolated, which resembled four different regions of BLG). The identified sequences were found to constitute a subset of the linear epitopes recognized by the PEPSCAN technique. The coordinates of the crystal structure of BLG were used to display mapped epitopes on its structure. This study has permitted detailed mapping of the major linear antigenic regions within BLG recognised by IgG antibodies from immunised rabbits and mice.

A major continuous allergenic epitope of bovine beta-lactoglobulin recognized by human IgE binding

Hexapeptides of sequential overlapping sequences of beta-lactoglobulin (BLG) were used to probe serum from children with immediate-type cow milk allergy for IgE binding to continuous epitopes of BLG in an enhanced enzyme-linked immunosorbent assay (ELISA). Six regions of IgE binding were identified on the BLG molecule and these were synthesized as dodecapeptides. Inhibition of IgE binding to whole BLG was used to confirm the BLG-specific binding of IgE to each of the synthesized peptides. One of the peptides, peptide 4, showed inhibition in an IgE anti-BLG radioimmunoassay to all 16 sera tested. The patterns of inhibition with the native BLG molecule and peptide 4 were significantly correlated (P = 0.005), suggesting that this peptide contains a major continuous IgE binding epitope of BLG.

Localization of T-cell determinants on bovine beta-lactoglobulin

T-cell determinants of bovine beta-lactoglobulin (beta-LG) in BALB/c(H-2d), C57BL/6(H-2b) and C3H/He(H-2k) mice were identified using a set of overlapping synthetic peptides encompassing the entire primary structure of the protein. Lymph node cells from mice immunized with beta-LG were subjected to cell proliferation assay in the presence of these peptides and uptake of 3H-labeled thymidine was measured. Determinant regions were indicated to lie in residues 42-56, 62-76 and 139-153 in BALB/c mice, residues 11-26, 72-86, 100-113 and 119-133 in C57BL/6 mice, residues 72-86, 91-104, 129-143 and 139-153 in C3H/He mice. Some of these fragments included the antigenic motifs predicted by hypotheses according to amphipathicity and sequential patterns of peptides. We reported elsewhere that residues 42-56 and 72-86 represent one of the B-cell antigenic determinants in BALB/c and C3H/He, respectively. These peptides serve as good models of colinear T- and B-cell determinants as they contain both of T- and B-cell determinants.