Antigenic and allergenic determinants of ovalbumin--III. MHC Ia-binding peptide (OA 323-339) interacts with human and rabbit specific antibodies

Deciphering the interactions of phytochemicals with ovalbumin, the major food allergen from egg white: spectroscopic and computational studies

Ovalbumin (OVA), the major component of egg white, has been used as a model carrier protein to study the interaction of four bioactive phytochemicals 6-hydroxyflavone, chrysin, naringin, and naringenin. A static quenching mechanism was primarily associated with the complexation of the flavonoids with OVA. Hydrophobic forces play a major part in the stability of the complexes. The structural changes within the protein in response to flavonoid binding revealed a decrease in OVA's α-helical content. The hypothesized binding site for flavonoids in OVA overlaps with one or more immunoglobulin E-binding epitopes that may have some effect in the immunoglobulin E response pathway. The flavonoids remain in the same binding site throughout the simulation time and impart protein stability by forming different noncovalent interactions. This study presents comprehensive information about the interaction of the flavonoids with OVA and the associated structural variations after the binding, which might help researchers better comprehend similar medication pharmacodynamics and provide critical information for future therapeutic development.

Antigen- and Epitope-Delivering Nanoparticles Targeting Liver Induce Comparable Immunotolerance in Allergic Airway Disease and Anaphylaxis as Nanoparticle-Delivering Pharmaceuticals

The targeting of natural tolerogenic liver sinusoidal endothelial cells (LSEC) by nanoparticles (NPs), decorated with a stabilin receptor ligand, is capable of generating regulatory T-cells (Tregs), which can suppress antigen-specific immune responses, including to ovalbumin (OVA), a possible food allergen. In this regard, we have previously demonstrated that OVA-encapsulating poly(lactic-co-glycolic acid) (PLGA) nanoparticles eliminate allergic airway inflammation in OVA-sensitized mice, prophylactically and therapeutically. A competing approach is a nanocarrier platform that incorporates pharmaceutical agents interfering in mTOR (rapamycin) or NF-κB (curcumin) pathways, with the ability to induce a tolerogenic state in nontargeted antigen-presenting cells system-wide. First, we compared OVA-encapsulating, LSEC-targeting tolerogenic nanoparticles (TNPs) with nontargeted NPs incorporating curcumin and rapamycin (Rapa) in a murine eosinophilic airway inflammation model, which is Treg-sensitive. This demonstrated roughly similar tolerogenic effects on allergic airway inflammation by stabilin-targeting NP^OVAversus nontargeted NPs delivering OVA plus Rapa. Reduction in eosinophilic inflammation and TH2-mediated immune responses in the lung was accompanied by increased Foxp3⁺ Treg recruitment and TGF-β production in both platforms. As OVA incorporates IgE-binding as well as non-IgE-binding epitopes, the next experiment explored the possibility of obtaining immune tolerance by non-anaphylactic T-cell epitopes. This was accomplished by incorporating OVA^323-339 and OVA^257-264 epitopes in liver-targeting NPs to assess the prophylactic and therapeutic impact on allergic inflammation in transgenic OT-II mice. Importantly, we demonstrated that the major histocompatibility complex (MHC)-II binding (former) but not the MHC-I binding (latter) epitope interfered in allergic airway inflammation, improving TNP^OVA efficacy. The epitope-specific effect was transduced by TGF-β-producing Tregs. In the final phase of experimentation, we used an OVA-induced anaphylaxis model to demonstrate that targeted delivery of OVA and its MHC-II epitope could significantly suppress the anaphylaxis symptom score, mast cell release, and the late-phase inflammatory response. In summary, these results demonstrate comparable efficacy of LSEC-targeting versus pharmaceutical PLGA nanoparticles, as well as the ability of T-cell epitopes to achieve response outcomes similar to those of the intact allergens.

A liposome-based cancer vaccine for a rapid and high-titre anti-ErbB-2 antibody response

Vaccines are arguably the most important medical technology developed to date. However, effective treatment of diseases such as breast cancer have so far evaded standard vaccination strategies. One popular target for cancer treatment is the cell surface membrane protein, ErbB-2, also known as Her-2 or neu. It is localised to the cell surface and has raised expression in 15-30% of all breast cancers, as well as in ovarian, colon and lung cancer. Here, a liposomal system comprised of spatially separated ErbB-2 peptide, to activate B cells, and ovalbumin peptide OVA323-339, to provide non-cognate T cell support, was used to generate antibodies against the epitope of the ErbB-2 protein targeted by Pertuzumab, a monoclonal antibody licensed for the treatment of ErbB-2 expressing cancers. After just 7 days a raised (7.3-fold, p<0.01), isotype-switched, humoral immune response specific for the ErbB-2 peptide was achieved in mice with pre-existing immunity to OVA which were exposed to liposomes with external ErbB-2 and internal OVA323-339. The absence of pre-existing OVA immunity in the mice or OVA323-339 peptide in the liposomes removed the effect. The effect of this anti-ErbB-2 antibody response was characterised against an ErbB-2 overexpressing tumour cell line both in vitro and in vivo. Notably, antibody responses were demonstrated to induce cell death in vitro, resulting in 96% reduction in viable cells. This study, therefore, demonstrates the feasibility of this approach to generate a rapid, high-titre, isotype-switched, antibody response that specifically targets ErbB-2 overexpression on tumour cells and is capable of inducing cell death in vitro in the absence of complement or immune cells.

Optimization of secretion and surface localization of heterologous OVA protein in mycobacteria by using LipY as a carrier

BACKGROUND

Mycobacterium bovis Bacille Calmette-Guérin (BCG) is not only used as a vaccine against tuberculosis but also protects against leprosy and is used as part of bladder cancer treatment to induce a protective immune response. However, protection by BCG vaccination is not optimal. To improve vaccine efficacy, recombinant BCG expressing heterologous antigens has been put forward to elicit antigen-specific cellular and humoral responses. Cell surface localized or secreted antigens induce better immune responses than their cytosolic counterparts. Optimizing secretion of heterologous proteins or protein fragments holds therefore unexplored potential for improving the efficacy of recombinant BCG vaccine candidates. Secretion of heterologous antigens requires crossing the mycobacterial inner and outer membrane. Mycobacteria have specialized ESX or type VII secretion systems that enable translocation of proteins across both membranes. Probing this secretion system could therefore be a valid approach to surface localize heterologous antigens.

RESULTS

We show that ESX-5 substrate LipY, a lipase, can be used as a carrier for heterologous secretion of an ovalbumin fragment (OVA). LipY contains a PE domain and a lipase domain, separated by a linker region. This linker domain is processed upon secretion. Fusion of the PE and linker domains of LipY to OVA enabled ESX-5-dependent secretion of the fusion construct LipY-OVA in M. marinum, albeit with low efficiency. Subsequent random mutagenesis of LipY-OVA and screening for increased secretion resulted in mutants with improved heterologous secretion. Detailed analysis identified two mutations in OVA that improved secretion, i.e. an L280P mutation and a protein-extending frameshift mutation. Finally, deletion of the linker domain of LipY enhanced secretion of LipY-OVA, although this mutation also reduced surface association. Further analysis in wild type LipY showed that the linker domain is required for surface association.

CONCLUSION

We show that the ESX-5 system can be used for heterologous secretion. Furthermore, minor mutations in the substrate can enhance secretion. Especially the C-terminal region seems to be important for this. The linker domain of LipY is involved in surface association. These findings show that non-biased screening approaches aid in optimization of heterologous secretion, which can contribute to heterologous vaccine development.

Oral Administration of Recombinant Saccharomyces boulardii Expressing Ovalbumin-CPE Fusion Protein Induces Antibody Response in Mice

Saccharomyces boulardii, a subspecies of Saccharomyces cerevisiae, is a well-known eukaryotic probiotic with many benefits for human health. In the present study, a recombinant strain of S. boulardii was prepared to use as a potential oral vaccine delivery vehicle. In this sense, a ura3 auxotroph strain of S. boulardii CNCM I-745 (known as S. cerevisiae HANSEN CBS 5926, Yomogi^®) was generated using CRISPR/Cas9 methodology. Then a gene construct encoding a highly immunogenic protein, ovalbumin (OVA), was prepared and transformed into the ura3^- S. boulardii. To facilitate the transport of the recombinant immunogen across the intestinal barrier, a claudin-targeting sequence from Clostridium perfringens enterotoxin (CPE) was added to the C-terminus of the expression cassette. The recombinant S. boulardii strain expressing the OVA-CPE fusion protein was then administered orally to a group of mice, and serum IgG and fecal IgA levels were evaluated by ELISA. Our results demonstrated that anti-OVA IgG in serum significantly increased in test group (P < 0.001) compared to control groups (receiving wild type S. boulardii or PBS), and the fecal IgA titer was significantly higher in test group (P < 0.05) than control groups. In parallel, a recombinant S. boulardii strain expressing the similar construct lacking C-terminal CPE was also administered orally. The result showed an increased level of serum IgG in group receiving yeasts expressing the CPE negative construct compared to control groups; however, the fecal IgA levels did not increase significantly. In conclusion, our findings indicated that the yeast S. boulardii, as a delivery vehicle with possible immunomodulatory effects, and c-CPE, as a targeting tag, synergistically assist to stimulate systemic and local immunity. This proposed recombinant S. boulardii system might be useful in the expression of other antigenic peptides, making it as a promising tool for oral delivery of vaccines or therapeutic proteins.

PilVax - a novel peptide delivery platform for the development of mucosal vaccines

Peptide vaccines are an attractive strategy to engineer the induction of highly targeted immune responses and avoid potentially allergenic and/or reactogenic protein regions. However, peptides by themselves are often unstable and poorly immunogenic, necessitating the need for an adjuvant and a specialised delivery system. We have developed a novel peptide delivery platform (PilVax) that allows the presentation of a stabilised and highly amplified peptide as part of the group A streptococcus serotype M1 pilus structure (PilM1) on the surface of the non-pathogenic bacterium Lactococcus lactis. To show proof of concept, we have successfully inserted the model peptide Ova_324–339 into 3 different loop regions of the backbone protein Spy0128, which resulted in the assembly of the pilus containing large numbers of peptide on the surface of L. lactis. Intranasal immunisation of mice with L. lactis PilM1-Ova generated measurable Ova-specific systemic and mucosal responses (IgA and IgG). Furthermore, we show that multiple peptides can be inserted into the PilVax platform and that peptides can also be incorporated into structurally similar, but antigenically different pilus structures. PilVax may be useful as a cost-effective platform for the development of peptide vaccines against a variety of important human pathogens.

Intranasal exposure to monoclonal antibody Fab fragments to Japanese cedar pollen Cry j1 suppresses Japanese cedar pollen-induced allergic rhinitis

BACKGROUND AND PURPOSE

Fab fragments (Fabs) of antibodies have the ability to bind to specific allergens but lack the Fc portion that exerts effector functions via binding to receptors including FcεR1 on mast cells. In the present study, we investigated whether intranasal administration of the effector function-lacking Fabs of a monoclonal antibody IgG1 (mAb, P1-8) to the major allergen Cry j1 of Japanese cedar pollen (JCP) suppressed JCP-induced allergic rhinitis in mice.

EXPERIMENTAL APPROACH

Balb/c mice sensitized with JCP on days 0 and 14 were challenged intranasally with the pollen on days 28, 29, 30 and 35. Fabs prepared by the digestion of P1-8 with papain were also administered intranasally 15 min before each JCP challenge.

KEY RESULTS

Intranasal administration of P1-8 Fabs was followed by marked suppression of sneezing and nasal rubbing in mice with JCP-induced allergic rhinitis. The suppression of these allergic symptoms by P1-8 Fabs was associated with decreases in mast cells and eosinophils and decreased hyperplasia of goblet cells in the nasal mucosa.

CONCLUSIONS AND IMPLICATIONS

These results demonstrated that intranasal exposure to P1-8 Fabs was effective in suppressing JCP-induced allergic rhinitis in mice, suggesting that allergen-specific mAb Fabs might be used as a tool to regulate allergic pollinosis.

Interactions of epigallo-catechin 3-gallate and ovalbumin, the major allergen of egg white

Polyphenols, the potent plant secondary metabolites, have beneficial effects on human health, but the mechanism(s) by which these effects are exerted is not well understood. Here, we present the detailed analysis of the interactions between the major green tea catechin, epigallo-catechin 3-gallate (EGCG), and the major dietary protein and allergen, ovalbumin (OVA). We show that EGCG binds to the pocket that partly overlaps with the previously identified IgE-binding region in OVA, and that this interaction induces structural changes in the allergen. Moreover, our ex vivo studies reveal that OVA binds IgE and stimulates degranulation of basophils, and that its uptake by monocytes proceeds at a slower rate in the presence of EGCG. This study provides further evidence in support of the proposed mechanism by which EGCG interactions with the food allergens contribute to its diverse biological activities and may impair antigen uptake by antigen-presenting cells.

Intratracheal exposure to Fab fragments of an allergen-specific monoclonal antibody regulates asthmatic responses in mice

Fab fragments (Fabs) maintain the ability to bind to specific antigens but lack effector functions due to the absence of the Fc portion. In the present study, we tested whether Fabs of an allergen-specific monoclonal antibody (mAb) were able to regulate asthmatic responses in mice. Asthmatic responses were induced in BALB/c mice by passive sensitization with anti-ovalbumin (OVA) polyclonal antibodies (pAbs) (day 0) and by active sensitization with OVA (days 0 and 14), followed by intratracheal (i.t.) challenge with OVA on day 1 and days 28, 29, 30 and 35. Fabs prepared by the digestion of an anti-OVA IgG1 (O1-10) mAb with papain were i.t. administered only once 30 min before antigenic challenge on day 1 or day 35. The results showed that i.t. administration of O1-10 Fabs with OVA markedly suppressed the early and/or late phases of asthmatic responses caused by passive and active sensitization. Similar results were obtained when Fabs of anti-OVA IgG2b mAb (O2B-3) were i.t. administered. In contrast, neither i.t. injection of intact 01-10/O2B-3 nor systemic injection of O1-10 Fabs suppressed the asthmatic responses. In vitro studies revealed that the capture of OVA by O1-10 Fabs prevented the subsequent binding of intact anti-OVA pAbs to the captured OVA. These results suggest that asthmatic responses may be down-regulated by the i.t. exposure to Fabs of an allergen-specific mAb via a mechanism involving the capture of allergen by Fabs in the respiratory tract before the interaction of intact antibody and allergen essential for the induction of asthmatic responses.

Comparison of polystyrene nanoparticles and UV-inactivated antigen-displaying adenovirus for vaccine delivery in mice

Background

Inert nanoparticles are attracting attention as carriers for protein-based vaccines. Here we evaluate the immunogenicity of the model antigen ovalbumin delivered on polystyrene particles and directly compare particulate delivery with adenovirus-based immunization.

Findings

Mice were vaccinated with soluble ovalbumin, ovalbumin-coated polystyrene particles of different sizes, or an adenovirus-based expression-display vector that encodes and displays a pIX-ovalbumin fusion protein. Antibody responses were clearly higher when ovalbumin was administered on polystyrene particles compared to soluble protein administration, regardless of the particle size. Compared to adenovirus-based immunization, antibody levels were lower if an equivalent amount of protein was delivered, and no cellular immune response was detectable.

Conclusions

We demonstrate in a side-by-side comparison that inert nanoparticles allow for the reduction of the administered antigen amount compared to immunization with soluble protein and induce strongly enhanced antibody responses, but responses are lower compared to adenovirus-based immunization.

Airway inflammation and bronchial remodelling in toluene diisocyanate-exposed BALB/c mouse model

Toluene diisocyanate (TDI), a highly reactive industrial chemical, is one of the leading causes of occupation-related asthma in industrialized countries. The pathogenesis of TDI-induced asthma, however, remains not fully understood, in part due to lack of appropriate animal models. Twenty five female BALB/c mice (age: 8 weeks) were randomly divided into 5 groups: Ovabumin (OVA); OVA peptide amino acid residues No. 323-339 (Pep); TDI; alum and physiological saline. Mice were intraperitoneally injected with 25 microg OVA or pep absorbed on 300 microg alum, 300 microg alum or saline on days 0, 7 and 14. For the TDI group, mice were sensitized subcutaneously with 20 microl neat TDI on day 0; 20 microl of TDI in olive oil (1:10) on days 7 and 14; on days 21-23. Then each group was challenged intranasally with 20 microl of 1% OVA, 1% Pep, 1% TDI, 10% alum and saline respectively. On day 28, mice were killed under pentothal anesthesia. The results demonstrated that neutrophil-dominant inflammation with a few eosinophil infiltration occurred in the peri-bronchial and peri-vascular regions of the lungs. This was accompanied by hyperplasia/hypertrophy of cells lining the airways and mucus production as shown by HE staining. Positive immunohistochemical MBP staining in parenchyma was also shown. Th2 cytokine IL-4 and IgE production were significant increased 5 days after last challenge while IFN-gamma level was below the detection limit.

CONCLUSION

the clear elevation of IL-4 and IgE could allow to conclude a possible Th2-like dominated allergic response in TDI-exposed BALB/c mouse model.

Deglycosylation of ovalbumin prohibits formation of a heat-stable conformer

To study the influence of the carbohydrate-moiety of ovalbumin on the formation of the heat-stable conformer S-ovalbumin, ovalbumin is deglycosylated with PNGase-F under native conditions. Although the enzymatic deglycosylation procedure resulted in a complete loss of the ability to bind to Concavalin A column-material, only in about 50% the proteins lost their complete carbohydrate moiety, as demonstrated by mass spectrometry and size exclusion chromatography. Thermal stability and conformational changes were determined using circular dichroism and differential scanning calorimetry and demonstrated at ambient temperature no conformational changes due to the deglycosylation. Also the denaturation temperature of the processed proteins remained the same (77.4 +/- 0.4 degrees C). After heat treatment of the processed protein at 55 degrees C and pH 9.9 for 72 h, the condition that converts native ovalbumin into the heat-stable conformer (S-ovalbumin), only the material with the intact carbohydrate moiety forms this heat-stable conformer. The material that effectively lost its carbohydrate moiety appeared fully denatured and aggregated due to these processing conditions. These results indicate that the PNGase-F treatment of ovalbumin prohibits the formation and stabilization of the heat-stable conformer S-ovalbumin. Since S-ovalbumin in egg protein samples is known to affect functional properties, this work illustrates a potential route to control the quality of egg protein ingredients.

T-cell epitopes of food allergens

During recent years, a great deal of research has focused on the identification of food allergens, their characterization at the molecular level, and the investigation of immunological mechanisms responsible for food hypersensitivity. Allergen-reactive T-helper 2 cells play a central role in the pathophysiology of allergic diseases. After activation with allergens, this subset of CD4(+) T-lymphocytes produces a spectrum of cytokines that induce high serum levels of immunoglobulin E and eosinophilia, which, in turn, mediate the clinical symptoms. Furthermore, T-helper 2 cells are present in target organs during the late response to allergen exposure. The analysis of the allergic T-cell response, including cytokine production and the identification of T-cell epitopes, provides important information on the characteristics of food allergens. Therefore, in vitro cultures of allergen-specific T-cells derived from peripheral blood or different target organs have been of indispensable help. Results obtained from such studies may not only contribute to the understanding of cellular mechanisms underlying different types of food allergy but also to the development of novel strategies for immunotherapy of food allergy.

The [173–196] fragment of ovalbumin suppresses ovalbumin-specific rat IgE responses

Peptides and protein hydrolysates are attractive tools for the induction of tolerance or regulation of targeted B and/or T cell responses. In vivo, peptides are mainly produced by the action of digestive enzymes or following the processing of exogenous antigens by antigen-presenting cells (APCs). In vitro, these molecules are generally produced by enzymatic digestion and chemical hydrolysis of proteins. We investigated the T and B cell determinants of the major food allergen ovalbumin (nOVA) in rat by analyzing (1) the stimulatory effect of nOVA peptides generated by cyanogen bromide (CNBr) cleavage on nOVA-specific T cells, and (2) the potential of CNBr-derived OVA fractions to induce oral tolerance to nOVA. Peptide fractions of the CNBr-hydrolysated OVA were isolated by high-pressure liquid chromatography and tested for their ability to stimulate nOVA-specific T cells isolated from rats parenterally immunized with nOVA. The nOVA fractions containing the stimulatory determinants were then intragastrically administered to rat to test their potential to induce oral tolerance. The hole CNBr hydolysate stimulated proliferation of nOVA-specific T cells. Three out of the five HPLC-purified peptidic fractions were also able to stimulate proliferation and cytokine production by nOVA-specific T cells. A peptide fraction exhibiting a single peak by HPLC contained the 173-196 nOVA segment and stimulated nOVA-specific T cells. This segment also promoted oral tolerance to nOVA and reduced IgE responses. CNBr hydrolysis releases several peptides with stimulatory effect on nOVA-specific T cells including a new nOVA [173-196] T cell determinant which induces oral tolerance to nOVA.

Chemical processing as a tool to generate ovalbumin variants with changed stability

Processing of ovalbumin may result in proteins that differ more than 23 degrees C in denaturation temperature while the structural fold is not significantly affected. This is achieved by 1) conversion of positive residues into negative ones (succinylation); 2) elimination of negative charges (methylation); 3) reducing the proteins hydrophobic exposure (glycosylation); 4) increasing the hydrophobic exposure (lipophilization); or by 5) processing under alkaline conditions and elevated temperature (S-ovalbumin). The effect on the structural fold was investigated using a variety of biochemical and spectroscopic tools. The consequences of the modification on the thermodynamics of the protein was studied using differential scanning calorimetry and by monitoring the tryptophan fluorescence or ellipticity at 222 nm of protein samples dissolved in different concentrations of guanidine-HCl. The impact of the modification on the denaturation temperature scales for all types of modifications with a free energy change of about 1 kJ per mol ovalbumin per Kelvin (or 0.0026 kJ per mol residue per K). The nature of the covalently coupled moiety determines the impact of the modification on the protein thermodynamics. It is suggested that especially for lipophilized protein the water-binding properties are substantially lowered. Processing of globular proteins in a controlled manner offers great opportunities to control a desired functionality, for example, as texturizer in food or medical applications.

Characterization of high-pressure-treated egg albumen

Addition of NaCl or sucrose to egg albumen prior to high-pressure treatment (up to 10 min at 800 MPa) prevented insolubilization or gel formation after pressure treatment. As a consequence of protein unfolding, the treated albumen had increased viscosity but retained its foaming and heat-gelling properties. Susceptibility of egg albumen proteins to hydrolysis by trypsin increased dramatically after pressure treatment. The S-form of ovalbumin, the presence of which is an index of egg aging, was not found in any of the pressure-treated samples, which also did not display evidence for covalent protein aggregation. However, recognition of ovalbumin by an anti-ovalbumin antiserum was reduced to 40% of that of untreated sample.

Ovalbumin peptide encapsulated in poly(d,l lactic-co-glycolic acid) microspheres is capable of inducing a T helper type 1 immune response

An ovalbumin (OVA) peptide, consisting of residues 323-339, was incorporated into poly(d,l lactic-co-glycolic acid) (PLGA) microspheres and administered to mice. It was hypothesized that microencapsulation of the peptide in PLGA microspheres would avoid the need for traditional adjuvants and bias the immune response towards a type 1 T helper (Th1) response. An immunomodulator, monophosphoryl lipid A (MPLA), was incorporated into the microspheres to determine its efficacy in enhancing a Th1 response. The specificity of the immune response was determined using a T cell proliferation assay. The type of T helper response was determined by analysis of the cytokine secretion profiles of the proliferating T cells. Following s.c. immunization, the results revealed a T cell-specific immune response for the encapsulated OVA peptide both with and without MPLA. The cytokine profiles revealed high levels of IFN-gamma with very low levels of IL-4 and IL-10, suggesting a Th1 response. Furthermore, incorporation of MPLA in the peptide loaded PLGA microspheres resulted in an increase in the production of IFN-gamma. Hence, peptide-loaded PLGA microspheres are capable of eliciting a specific Th1 immune response, which may be further enhanced in the presence MPLA.

A non-denaturing enzyme linked immunosorbent assay with protein preadsorbed onto aluminum hydroxide

A method has been developed which prevents denaturation of proteins used for coating of plastic surfaces in enzyme linked immunosorbent assays (ELISA). The system takes advantage of the use of aluminum hydroxide (Al(OH)3) as an adsorbent for proteins. A model protein has been analyzed. and monoclonal antibodies specific for either the native form or the denatured form of the protein were used to monitor the extent of denaturation. Adsorption of the proteins to Al(OH)3 in carbonate buffer, pH 9.3, before coating the ELISA plate abolished the denaturation otherwise observed after direct adsorption of protein to plastic surfaces. The protection against denaturation was dependent on the buffer system and was not observed when phosphate buffers were used, due to elution of protein from Al(OH)3 or lack of binding to Al(OH)3 in the presence of phosphate. There is evidence that protein adsorbed onto the Al(OH)3 is required for binding of Al(OH)3 onto the plastic surface. This system may be useful in assay systems where discrimination between the native and denatured forms of proteins is important.

Assessment of the allergenic potential of foods derived from genetically engineered crop plants

This article provides a science-based, decision tree approach to assess the allergenic concerns associated with the introduction of gene products into new plant varieties. The assessment focuses on the source from which the transferred gene was derived. Sources fall into three general categories: common allergenic food proteins; less common allergenic foods or other known allergen sources; and sources with no history of allergenicity. Information concerning the amino acid sequence identity to known allergenic proteins, in vitro and/or in vivo immunologic assays, and assessment of key physiochemical properties are included in reaching a recommendation on whether food derived from the genetically modified plant variety should be labeled as to the source of the transferred gene. In the end, a balanced judgement of all the available data generated during allergenicity assessment will assure the safety of foods derived from genetically engineered crops. Using the approaches described here, new plant varieties generated by genetic modification should be introduced into the marketplace with the same confidence that new plant varieties developed by traditional breeding have been introduced for decades.

Allergenic epitopes of ovalbumin (OVA) in patients with hen's egg allergy: inhibition of basophil histamine release by haptenic ovalbumin peptide

We studied allergenic determinants that induce hypersensitivity to OVA, the major allergen in egg allergy, using immunoblot and histamine release assays. Immunoblot analysis demonstrated a part of the OVA epitope was in the C-terminal region comprising residues 347-385 (OVA347-385). Histamine was released from basophils of a patient with egg allergy upon stimulation with the OVA fragment corresponding to OVA347-385. Furthermore, detailed epitope mapping using overlapping peptides (residues 347-366, OVA-A; residues 357-376, OVA-B; and residues 367-385, OVA-C) in the OVA 347-385 region was carried out using the histamine release assay. In order for histamine release from basophils to occur, the allergen must possess two or more allergenic determinants located on the protein molecule at distances that would be equivalent to the distances between IgE molecules on the membrane surface. these results suggest that there are at least two epitopes that bind IgE antibodies on each OVA peptide. In addition, one epitope that binds IgE antibodies in two patients appears to reside in the haptenic peptide OVA357-366 (OVA-B1). The histamine release from basophils stimulated by OVA-B was completely inhibited by OVA-B1 in one of these patients. Similarly, OVA-B1 inhibited the histamine release produced by OVA-A in the other by more than 40%. These results suggest that haptenic synthetic peptides could regulate the allergic reaction in the effector phase if common epitope(s) recognized by IgE antibodies in the patients with egg allergy can be found. These are the first studies that provide an antigen-specific approach to inhibiting histamine release from basophils by a haptenic peptide recognized by IgE antibodies in an allergic disorder.

A comparison of the immunogenicity of the native and denatured forms of a protein

The effect of heat denaturation on the physicochemical and immunological properties of a model protein, ovalbumin, and its formaldehyde/lysine-treated form was investigated. Polyacrylamide gel electrophoresis and gel filtration showed that heat denaturation converted ovalbumin to high Mr polymers, whereas formaldehyde/lysine-treated ovalbumin remained monomeric with only a small proportion forming oligomers. NMR analysis demonstrated that non-denatured structures could easily be differentiated from the denatured structures. Intraperitoneal immunization of rabbits and mice showed that both native and denatured forms of ovalbumin induced an immune response, but denatured forms of ovalbumin were found to be less immunogenic and to have a lower epitope density than native ovalbumin. Analysis of the antisera in crossed immunoelectrophoresis showed that they were specific for either native or denatured forms of ovalbumin. These findings were further investigated by ELISA and immunoaffinity chromatography, and the high specificity and low cross-reactivity was confirmed. We conclude that the immunogenic epitopes on denatured ovalbumin are different from those on ovalbumin, and that these epitopes reflect a continuum of denatured conformations.

Epitope analysis of the allergen ovalbumin (Gal d II) with monoclonal antibodies and patients' IgE

Ovalbumin (OVA) is a major allergen (Gal d II) of hen egg white and is often the cause of hypersensitivity reactions to food. Further knowledge of the antigenic and allergenic epitopes of allergens will provide better treatment of this disease. To analyse these epitopes we produced a panel of monoclonal antibodies (mAbs) against native OVA. The initial information about the epitopes was obtained with the binding patterns of these mAbs in IEF-immunoprints and western blots of OVA under reducing and non-reducing conditions. It was possible to demonstrate that the different conformations of OVA exhibit different epitopes, and that there are other epitopes which are shared by each conformation. Seven different, although sometimes overlapping epitopes, could be determined on native OVA; four different epitopes on denaturated non-reduced OVA by means of immunoblots of the intact molecule. The number of epitopes which could be differentiated by the mAbs was increased by the use of peptide blots after CNBr fragmentation of the molecule. IgE binding to different OVA conformations and to CNBr-fragments of OVA was also detectable and appears in the same regions as the reactivity of some mAbs. Western blots of OVA and CNBr-peptides demonstrate that some antigenic/allergenic binding sites seem at least partly to be continuous epitopes. The identification of the CNBr-fragments was performed by a microsequence analysis of blotted CNBr-fragments after a 2-dimensional electrophoresis. IgE was found to bind the two largest CNBr-fragments (residues 41-172 and 301-385), but not the fragment corresponding to residues 173-196. A number of monoclonal antibodies also reacted with the two large fragments, especially with fragment 301-385, and some bind also to shorter peptides, such as fragment 173-196, which were not reactive to patients' IgE. Most of the monoclonal antibodies and patients' IgE bind to the fragments 41-172 and 301-385 in 2D-PAGE blots suggesting that these fragments are involved in an immunogenic structure.

Oxidized low-density lipoprotein reduces plasma coagulation in vitro

Oxidation of low-density lipoprotein (LDL) was shown to occur in vivo and involved lipid peroxidation and apolipoprotein modification. We studied the effect of oxidized-LDL (Ox-LDL) on plasma coagulation by measuring prothrombin time (PT) and partial thromboplastin time (PTT) following the addition of Ox-LDL to normal plasma. Ox-LDL, but not native LDL, caused prolongation of PT and PTT by 30% in a dose- and time-dependent pattern. This effect was also shown to be present following lipoprotein delipidation, suggesting that it was the apolipoprotein fraction of Ox-LDL, but not its lipid fraction, that was responsible for the prolongation of PT and PTT. This was further substantiated since similar effect could be obtained by adding LDL treated with trinitrobenzenesulphonic acid to block the lysine groups, as occurs in oxidized LDL. Ox-LDL, unlike LDL, was found to reduce plasma ionized calcium by 33%. Moreover, adding calcium ions to Ox-LDL negated its effect on PT and PTT, suggesting that Ox-LDL apolipoprotein may influence coagulation by binding calcium ions.