Mapping of the IgE and IgG4 sequential epitopes of milk allergens with a peptide microarray–based immunoassay

Mapping of the IgE and IgG4 sequential epitopes of ovomucoid with a peptide microarray immunoassay

BACKGROUND

Ovomucoid (Gal d 1) has been demonstrated to be the most important allergen in IgE-mediated egg allergy. Peptide microarray analysis is a novel method that can provide useful information on the nature of specific allergens.

METHODS

A peptide microarray immunoassay was performed using a 15- and 20-amino acid (aa) library of overlapping peptides (3-offset) of the primary sequence of ovomucoid. Sera from 50 patients with IgE-mediated egg allergy and reactivity to ovomucoid, with more than 1 year of follow-up, and sera from 10 controls were tested. Peptides were considered major epitopes when the average weighted Z-score was greater than 3 and recognized by at least 20% of the patient's sera. Specific IgE epitopes were established on the basis of the IgE/IgG4 Z-score ratio.

RESULTS

The IgE and IgG4 recognition pattern was similar in both sets of peptides, but the signal intensity was generally higher in the 20-aa set. Thirty-four percent of the patients did not recognize any IgE sequential peptide and 20% of the patients recognized more than 10 sequential peptides. We identified 3 major IgE B-cell epitopes in domains I and II of ovomucoid. IgE/IgG4 ratio analysis showed that peptides 1-2 (aa 4-20) and peptides 29-31 (aa 91-104) were specific IgE epitopes.

CONCLUSION

By using peptide microarray immunoassay in egg-allergic patients, we established that 34% of the patients do not have any linear epitope recognized by IgE. Further studies are needed to determine the clinical relevance of this finding.

Peanut oral immunotherapy modifies IgE and IgG4 responses to major peanut allergens

BACKGROUND

Patients with peanut allergy have highly stable pathologic antibody repertoires to the immunodominant B-cell epitopes of the major peanut allergens Ara h 1 to 3.

OBJECTIVE

We used a peptide microarray technique to analyze the effect of treatment with peanut oral immunotherapy (OIT) on such repertoires.

METHODS

Measurements of total peanut-specific IgE (psIgE) and peanut-specific IgG(4) (psIgG(4)) were made with CAP-FEIA. We analyzed sera from 22 patients with OIT and 6 control subjects and measured serum specific IgE and IgG(4) binding to epitopes of Ara h 1 to 3 using a high-throughput peptide microarray technique. Antibody affinity was measured by using a competitive peptide microarray, as previously described.

RESULTS

At baseline, psIgE and psIgG(4) diversity was similar between patients and control subjects, and there was broad variation in epitope recognition. After a median of 41 months of OIT, polyclonal psIgG(4) levels increased from a median of 0.3 μg/mL (interquartile range [25% to 75%], 0.1-0.43 μg/mL) at baseline to 10.5 μg/mL (interquartile range [25% to 75%], 3.95-45.48 μg/mL; P < .0001) and included de novo specificities. psIgE levels were reduced from a median baseline of 85.45 kU(A)/L (23.05-101.0 kU(A)/L) to 7.75 kU(A)/L (2.58-30.55 kU(A)/L, P < .0001). Affinity was unaffected. Although the psIgE repertoire contracted in most OIT-treated patients, several subjects generated new IgE specificities, even as the total psIgE level decreased. Global epitope-specific shifts from IgE to IgG(4) binding occurred, including at an informative epitope of Ara h 2.

CONCLUSION

OIT differentially alters Ara h 1 to 3 binding patterns. These changes are variable between patients, are not observed in control subjects, and include a progressive polyclonal increase in IgG(4) levels, with concurrent reduction in IgE amount and diversity.

Synthetic allergen design reveals the significance of moderate affinity epitopes in mast cell degranulation

This study describes the design of a well-defined homotetravalent synthetic allergen (HTA) system to investigate the effect of hapten-IgE interactions on mast cell degranulation. A library of DNP variants with varying affinities for IgE(DNP) was generated (K(d) from 8.1 nM to 9.2 μM), and 8 HTAs spanning this range were synthesized via conjugation of each DNP variant to the tetravalent scaffold. HTAs with hapten K(d) < 235 nM stimulated degranulation following a bell-shaped dose response curve with maximum response occurring near the hapten K(d). HTAs with hapten K(d) ≥ 235 nM failed to stimulate degranulation. To mimic physiological conditions, the percent of allergen specific IgE on cell surface was varied, and maximum degranulation occurred at 25% IgE(DNP). These results demonstrated that moderate hapten-IgE affinities are sufficient to trigger mast cell degranulation. Moreover, this study established the HTA design as a well-defined, controllable, and physiologically relevant experimental system to elucidate the mast cell degranulation mechanism.

Tolerability of a fully maturated cheese in cow's milk allergic children: biochemical, immunochemical, and clinical aspects

BACKGROUND

From patients' reports and our preliminary observations, a fully maturated cheese (Parmigiano-Reggiano; PR) seems to be well tolerated by a subset of cow's milk (CM) allergic patients.

OBJECTIVE AND METHODS

To biochemically and immunologically characterize PR samples at different maturation stage and to verify PR tolerability in CM allergic children. Seventy patients, with suspected CM allergy, were enrolled. IgE to CM, α-lactalbumin (ALA), β-lactoglobulin (BLG) and caseins (CAS) were tested using ImmunoCAP, ISAC103 and skin prick test. Patients underwent a double-blind, placebo-controlled food challenge with CM, and an open food challenge with 36 months-maturated PR. Extracts obtained from PR samples were biochemically analyzed in order to determine protein and peptide contents. Pepsin and trypsin-chymotrypsin-pepsin simulated digestions were applied to PR extracts. Each PR extract was investigated by IgE Single Point Highest Inhibition Achievable assay (SPHIAa). The efficiency analysis was carried out using CM and PR oral challenges as gold standards.

RESULTS

The IgE binding to milk allergens was 100% inhibited by almost all PR preparations; the only difference was for CAS, mainly α(S1)-CAS. Sixteen patients sensitized to CM tolerated both CM and PR; 29 patients tolerated PR only; 21 patients, reacted to both CM and PR, whereas 4 patients reactive to CM refused to ingest PR. ROC analysis showed that the absence of IgE to BLG measured by ISAC could be a good marker of PR tolerance. The SPHIAa using digested PR preparations showed a marked effect on IgE binding to CAS and almost none on ALA and BLG.

CONCLUSIONS

58% of patients clinically reactive to CM tolerated fully maturated PR. The preliminary digestion of CAS induced by PR maturation process, facilitating a further loss of allergenic reactivity during gut digestion, might explain the tolerance. This hypothesis seems to work when no IgE sensitization to ISAC BLG is detected.

A bioinformatics approach to identify patients with symptomatic peanut allergy using peptide microarray immunoassay

BACKGROUND

Peanut allergy is relatively common, typically permanent, and often severe. Double-blind, placebo-controlled food challenge is considered the gold standard for the diagnosis of food allergy-related disorders. However, the complexity and potential of double-blind, placebo-controlled food challenge to cause life-threatening allergic reactions affects its clinical application. A laboratory test that could accurately diagnose symptomatic peanut allergy would greatly facilitate clinical practice.

OBJECTIVE

We sought to develop an allergy diagnostic method that could correctly predict symptomatic peanut allergy by using peptide microarray immunoassays and bioinformatic methods.

METHODS

Microarray immunoassays were performed by using the sera from 62 patients (31 with symptomatic peanut allergy and 31 who had outgrown their peanut allergy or were sensitized but were clinically tolerant to peanut). Specific IgE and IgG(4) binding to 419 overlapping peptides (15 mers, 3 offset) covering the amino acid sequences of Ara h 1, Ara h 2, and Ara h 3 were measured by using a peptide microarray immunoassay. Bioinformatic methods were applied for data analysis.

RESULTS

Individuals with peanut allergy showed significantly greater IgE binding and broader epitope diversity than did peanut-tolerant individuals. No significant difference in IgG(4) binding was found between groups. By using machine learning methods, 4 peptide biomarkers were identified and prediction models that can predict the outcome of double-blind, placebo-controlled food challenges with high accuracy were developed by using a combination of the biomarkers.

CONCLUSIONS

In this study, we developed a novel diagnostic approach that can predict peanut allergy with high accuracy by combining the results of a peptide microarray immunoassay and bioinformatic methods. Further studies are needed to validate the efficacy of this assay in clinical practice.

Design of a heterobivalent ligand to inhibit IgE clustering on mast cells

We describe the design, synthesis, and characterization of a heterobivalent ligand (HBL) system that competitively inhibits allergen binding to mast cell bound IgE antibody, thereby inhibiting mast cell degranulation. HBLs are composed of a hapten conjugated to a nucleotide analog allowing simultaneous targeting of the antigen-binding site as well the "unconventional nucleotide binding site" on IgE Fab domains. Simultaneous bivalent binding to both sites provides HBLs with over 100-fold enhancement both in avidity for IgE(DNP) (K(d) = 0.33 μM) and in inhibition of allergen binding to IgE(DNP) (IC(50) = 0.45 μM) than the monovalent hapten (K(d)(mono) = 41 μM; IC(50)(mono) = 55.4 μM, respectively). In cellular assays, HBL2 effectively inhibits mast cell degranulation (IC(50) = 15 μM), whereas no inhibition is detected by the monovalent hapten. In conclusion, this study establishes the use of multivalency in a novel HBL design to inhibit mast cell degranulation.

Food allergy: recent advances in pathophysiology and diagnosis

Approximately 5% of young children and 3-4% of adults exhibit adverse immune responses to foods in westernized countries, with a tendency to increase. The pathophysiology of food allergy (FA) relies on immune reactions triggered by epitopes, i.e. small amino-acid sequences able to bind to antibodies or cells. Some food allergens share specific physicochemical characteristics that allow them to resist digestion, thus enhancing allergenicity. These allergens encounter specialized dendritic cell populations in the gut, which leads to T-cell priming. In case of IgE-mediated allergy, this process triggers the production of allergen-specific IgE by B cells. Tissue-resident reactive cells, including mast cells, then bind IgE, and allergic reactions are elicited when these cells, with adjacent IgE molecules bound to their surface, are re-exposed to allergen. Allergic reactions occurring in the absence of detectable IgE are labeled non-IgE mediated. The abrogation of oral tolerance which leads to FA is likely favored by genetic disposition and environmental factors (e.g. increased hygiene or enhanced allergenicity of some foods). For an accurate diagnosis, complete medical history, laboratory tests and, in most cases, an oral food challenge are needed. Noticeably, the detection of food-specific IgE (sensitization) does not necessarily indicate clinical allergy. Novel diagnostic methods currently under study focus on the immune responses to specific food proteins or epitopes of specific proteins. Food-induced allergic reactions represent a large array of symptoms involving the skin and gastrointestinal and respiratory systems. They can be attributed to IgE-mediated and non-IgE-mediated (cellular) mechanisms and thus differ in their nature, severity and outcome. Outcome also differs according to allergens.

Epitope mapping of Atlantic salmon major allergen by peptide microarray immunoassay

BACKGROUND

IgE epitope mapping of allergens reveals important information about antigen elicitors involved in allergic reactions. The peptide-based microarray immunoassay offers an advantage of scale and parallel design over previous methods of epitope mapping. It has been used to map epitopes of some food allergens but has never been used with fish allergens.

OBJECTIVE

We sought to develop a peptide microarray immunoassay to map allergenic fish epitopes of two isoforms of Atlantic salmon (Salmo salar) parvalbumin, Sal s 1 beta 1 and Sal s 1 beta 2.

METHODS

Sera from 16 fish-allergic patients with specific IgE to salmon parvalbumin were used. Twelve healthy volunteers were used as negative controls. A library of overlapping peptides was synthesized commercially, representing the primary sequence of Sal s 1 beta 1 and Sal s 1 beta 2. Peptides were used to analyze allergen-specific IgE antibodies by immunolabeling with patient sera.

RESULTS

Three antigenic regions, not previously described, were identified in Sal s 1 beta 1. Two of them correlated with those previously reported in Gad c 1, parvalbumin from Baltic cod (Gadus callarias). No allergenic regions were found in Sal s 1 beta 2. This could be explained by crucial amino acid substitutions between isoforms.

CONCLUSIONS

We have identified three antigenic regions in Sal s 1 beta 1 using a peptide microarray immunoassay. These three sequential epitopes formed a unique antigenic determinant in the three-dimensional model of the protein. In addition, we proved that isoforms from the same protein might have a different allergenic behavior.

Molecular diagnosis of cow's milk allergy

PURPOSE OF REVIEW

To identify and discuss studies on the molecular diagnosis of cow's milk allergy (CMA) with a view to update allergists since a general review of the methodology in 2006.

RECENT FINDINGS

Seven basic research studies reporting the use of component-resolved diagnostics in CMA were found. All studies were on children positively reacting to a formal challenge with cow's milk. Six studies used natural allergens and three used recombinant milk proteins. Microarray platforms were customized and, thus, differed across studies. Three studies assessed the association between molecular-scale patterns and different presentations of the condition, that is the association between anaphylaxis, gastrointestinal symptoms and other severe phenotypes and the pattern of protein sensitization. Two studies assessed the association between positive oral food challenge and the persistence of milk allergy over time. Protein profiling could be useful to indicate appropriate specific immunotherapy.

SUMMARY

Accurate diagnosis of CMA is challenging and essential. The determination of the immunoglobulin E (IgE)-mediated response to sequenced and characterized allergens may be more useful in predicting the presence and severity of clinical allergy than the currently used skin or blood tests performed with whole extracts. However, as component recognition pattern heterogeneity is observed in different areas, further clinical studies are essential to correlate useful molecular diagnostics and biological markers with disease and patient profiles. Until such markers are found and validated in different age groups, oral food challenge remains the reference standard for the diagnosis of CMA.

Immunoglobulin-E-binding epitopes of wheat allergens in patients with food allergy to wheat and in mice experimentally sensitized to wheat proteins

BACKGROUND

At present, B cell epitopes involved in food allergy to wheat are known only for a few allergens and a few categories of patients.

OBJECTIVE

To characterize the epitopes of different wheat kernel allergens: α-, γ, ω2, and ω5-gliadin, a low-molecular-weight (LMW) glutenin subunit, and a lipid transfer protein (LTP1) recognized by allergic patients and by sensitized mice and provide further understanding of the role of structure in determining allergic response.

METHODS

Sera were obtained from 39 patients suffering from food allergy to wheat. BALB/c mice were sensitized to gliadins or LTP1 by intraperitoneal immunizations. Continuous epitopes bound by IgE were delineated by the Pepscan technique. The response to reduced, alkylated LTP1 was compared with that of the native form to evaluate the importance of protein folding on IgE reactivity.

RESULTS

Few continuous epitopes of LTP1 reacted with IgE from allergic patients and mice, but one of them was common to several patients and sensitized mice. The unfolded protein was not recognized by either patient or mouse IgE, emphasizing the major role of LTP1 folding and discontinuous epitopes in IgE-binding. In contrast, many continuous epitopes were detected by patient and mouse IgE especially for an ω5-gliadin, which is an unstructured protein, and to a lesser extent, for the other gliadins and a LMW-glutenin subunit.

CONCLUSION AND CLINICAL RELEVANCE

The conformation of LTP1 appeared to have a strong impact on the type of IgE-binding epitopes elicited by this protein in both man and mouse. The responses in mice sensitized to gliadins or LTP1 were sufficiently comparable with the human response in terms of IgE-binding epitopes to provide support for the use of the mouse model in further investigations.

Microarrayed recombinant allergens for diagnostic testing

The development of protein microarray-based immunoassays and the availability of recombinant allergens have, to a significant extent, emerged together over the past decade. Their long-anticipated wider application to allergy diagnosis has recently begun to accelerate. This review discusses some of the strengths and weaknesses of molecularly defined allergy testing and the microarray platform. Several recent applications of microarray assays to allergy testing are also summarized. Promising findings, particularly in the context of food and latex allergy, point to the potential for greater resolution between clinical reactivity and asymptomatic sensitization with this platform.

Milk and soy allergy

Cow's milk allergy (CMA) affects 2% to 3% of young children and presents with a wide range of IgE and non-IgE-mediated clinical syndromes, which have a significant economic and lifestyle effect. It is logical that a review of CMA would be linked to a review of soy allergy because soy formula is often an alternative source of nutrition for infants who do not tolerate cow's milk. This review examines the epidemiology, pathogenesis, clinical features, natural history, and diagnosis of cow's milk and soy allergy. Cross-reactivity and management of milk allergy are also discussed.

The diagnosis of food allergy

BACKGROUND

Food allergy is increasingly common; however, there is a discrepancy between the large number of people who believe they or their children are affected and the actual number with true food allergies. It is therefore imperative that physicians evaluating patients with possible adverse reactions to foods understand the current modalities used to diagnose food allergies.

METHODS

Simple tests including skin-prick testing (SPT) and serum food-specific IgE testing are the most commonly used diagnostic tests to evaluate for IgE-mediated food reactions. However, these tests have pitfalls and their usefulness must be appreciated to avoid over- and underdiagnosis.

RESULTS

A firm diagnosis is imperative because a misdiagnosis could lead to life-threatening reactions and overdiagnosis will lead to unnecessary elimination diets with nutritional and social implications. Physician-supervised oral food challenges (OFC) remain the gold standard for food allergy diagnosis; however, a careful medical history and simple tests can often provide a reliable diagnosis.

CONCLUSION

In this review, we examine the usefulness and pitfalls of SPT used by allergists and serum food-specific IgE levels that are available to all practitioners. We also review the OFC as a diagnostic modality in food allergy. Finally, we describe emerging tests, such as the basophil activation test, atopy patch testing, and component-resolved diagnostics, that may be of benefit in the future.

Proteolysis by Lactobacillus fermentum IFO3956 isolated from Egyptian milk products decreases immuno-reactivity of αS1-casein

Proteinase activity of Lactobacillus fermentum IFO3956 cells was higher when they were grown on milk-based media than on 10% reconstituted skim milk. The lowest protease activity was observed when cells were grown on milk-free media. The extraction of milk-induced cell-bound proteases from Lb. fermentum IFO3956 was most efficient using 1% Tween 80 while the use of 1% SDS inhibited all proteolytic activity. Two bands of ∼35 and >100 kDa were observed by zymogram, indicating that proteolytic activity corresponded to the presence of at least two types of enzymes or two molecular forms of one enzyme. Mass spectrometry analyses of αS1-casein hydrolysates detected 24 peptides with sizes ranging from 5 to 36 amino acids, including 9 phosphorylated peptides, resulting from the fermentation of Lb. fermentum IFO3956 of αS1-casein. Most of the identified peptides originated from the N-terminal portion of αS1-casein. The studied bacterial strain could hydrolyze αS1-casein in many sites including the epitopes triggering the allergic reactions against αS1-casein e.g. at the positions 23, 30, 41, 71, 91, 98, 126, 179. After hydrolysis of αS1-casein with Lb. fermentum IFO3956 the recognition and the binding of this casein to IgE from the pooled sera of 18 patients with cow's milk allergy was significantly reduced.

Future therapies for food allergies

Food allergy is an increasingly prevalent problem in westernized countries, and there is an unmet medical need for an effective form of therapy. A number of therapeutic strategies are under investigation targeting foods that most frequently provoke severe IgE-mediated anaphylactic reactions (peanut, tree nuts, and shellfish) or are most common in children, such as cow's milk and hen's egg. Approaches being pursued are both food allergen specific and nonspecific. Allergen-specific approaches include oral, sublingual, and epicutaneous immunotherapy (desensitization) with native food allergens and mutated recombinant proteins, which have decreased IgE-binding activity, coadministered within heat-killed Escherichia coli to generate maximum immune response. Diets containing extensively heated (baked) milk and egg represent an alternative approach to food oral immunotherapy and are already changing the paradigm of strict dietary avoidance for patients with food allergy. Nonspecific approaches include monoclonal anti-IgE antibodies, which might increase the threshold dose for food allergen in patients with food allergy, and a Chinese herbal formulation, which prevented peanut-induced anaphylaxis in a murine model and is currently being investigated in clinical trials. The variety of strategies for treating food allergy increases the likelihood of success and gives hope that accomplishing an effective therapy for food allergy is within reach.

Dietary antigens, epitope recognition, and immune complex formation in recent onset psychosis and long-term schizophrenia

Peptides derived from dietary antigens such as bovine milk caseins are opioid receptor ligands and contribute to schizophrenia-associated hyperpeptidemia and hyperpeptiduria. The IgG antibody response to bovine caseins is increased in schizophrenia and recent onset psychosis. To identify specific casein peptide sequences that are antigenic in patients vs controls, we measured serum IgG binding to 10-26 amino acid long linear epitopes of casein with immunoassays for the entire group (n=95 recent onset psychosis; n=103 long-term schizophrenia; n=65 control), and with peptide microarray libraries in a casein-sensitive subset (n=14 recent onset; n=10 control). In the entire group, we compared anti-casein peptide IgG vs anti-whole casein IgG and evaluated whether peptide immune complexes contributed to IgG binding results. Anti-whole casein IgG levels correlated with anti-casein peptide IgG in controls only (R2=0.17-0.25, p≤0.002-0.03). In recent onset psychosis, IgG binding to linear peptide sequences was significantly decreased 3.8-5.7-fold compared to controls in immunoassays (OR 0.18-0.26, p≤0.0001-0.001). In peptide microarrays, recent onset patients again showed significantly reduced IgG binding and fewer epitopes than controls (p≤0.00001-0.05). Anti-peptide IgG levels did not differ between patients with long-term schizophrenia and controls. Finally, significantly more recent onset individuals had casein peptide-IgG immune complexes than controls (OR 4.96, p≤0.001). These findings suggest an immunological specificity that differs in early vs later stages of neuropsychiatric diseases and an IgG saturation by casein-derived peptides that may in part explain the reduced IgG binding to small linear epitopes observed in these patients.

Food allergy

Food allergies affect up to 6% of young children and 3%-4% of adults. They encompass a range of disorders that may be IgE and/or non-IgE mediated, including anaphylaxis, pollen food syndrome, food-protein-induced enterocolitis syndrome, food-induced proctocolitis, eosinophilic gastroenteropathies, and atopic dermatitis. Many complex host factors and properties of foods are involved in the development of food allergy. With recent advances in the understanding of how these factors interact, the development of several novel diagnostic and therapeutic strategies is underway and showing promise.

Electrochemical immunosensor for casein based on gold nanoparticles and poly(L-Arginine)/multi-walled carbon nanotubes composite film functionalized interface

In this paper, a novel electrochemical immunosensor for the determination of casein based on gold nanoparticles and poly(L-Arginine)/multi-walled carbon nanotubes (P-L-Arg/MWCNTs) composite film was proposed. The P-L-Arg/MWCNTs composite film was used to modify glassy carbon electrode (GCE) to fabricate P-L-Arg/MWCNTs/GCE through electropolymerization of L-Arginine on MWCNTs/GCE. Gold nanoparticles were adsorbed on the modified electrode to immobilize the casein antibody and to construct the immunosensor. The stepwise assembly process of the immunosensor was characterized by cyclic voltammetry and differential pulse voltammetry. Results demonstrated that the peak currents of [Fe(CN)(6)](3-/4-) redox pair decreased due to the formation of antibody-antigen complex on the modified electrode. The optimization of the adsorption time of gold nanoparticles, the pH of supporting electrolyte and the incubation time were investigated in details. Under optimal conditions, the peak currents obtained by DPV decreased linearly with the increasing casein concentrations in the range from 1 × 10(-7) to 1 × 10(-5) g mL(-1) with a linear coefficiency of 0.993. This electrochemical immunoassay has a low detection limit of 5 × 10(-8) g mL(-1) and was successfully applied to the determination of casein in cheese samples.

Microarrayed allergen molecules for the diagnosis of allergic diseases

IgE-mediated allergic diseases are among the most prevalent diseases worldwide. The use of extracts in the skin test and the additional use of IgE testing still represent the current basis for the diagnostic work-up. During the past 30 years, knowledge of the molecular structure of allergens has increased dramatically, and the characterization and production of allergenic molecules, as natural purified compounds or recombinant products, is allowing us to approach the allergy diagnostic work-up differently. Much of this is based on the adoption of microtechnology since the first release of a biochip for IgE detection. Its use has prompted the development of new concepts linked to the diagnosis of allergic diseases. This review describes the background of allergy diagnosis and the tools currently used for specific IgE detection. It gives insight into the most recent advancement in the field of biotechnology leading to allergenic molecule availability, microtechnology leading to the routine use of protein biochips for IgE detection, and how they should be combined with information technology.

Management of the patient with multiple food allergies

Food allergies affect 6% of children and 3% to 4% of adults in the United States. Although several studies have examined the prevalence of food allergy, little information is available regarding the prevalence of multiple food allergies. Estimates of prevalence of people allergic to multiple foods is difficult to ascertain because those with allergy to one food may avoid additional foods for concerns related to cross-reactivity, positive tests, or prior reactions, or they may be reluctant to introduce foods known to be common allergens. Diagnosis relies on an accurate history and selective IgE testing. It is important to understand the limitations of the available tests and the role of cross-reactivity between allergens. Allergen avoidance and readily accessible emergency medications are the cornerstones of management. In addition, a multidisciplinary approach to management of individuals with multiple food allergies may be needed, as avoidance of several food groups can have nutritional, developmental, and psychosocial consequences.

An Allergen Portrait Gallery: Representative Structures and an Overview of IgE Binding Surfaces

Recent progress in the biochemical classification and structural determination of allergens and allergen-antibody complexes has enhanced our understanding of the molecular determinants of allergenicity. Databases of allergens and their epitopes have facilitated the clustering of allergens according to their sequences and, more recently, their structures. Groups of similar sequences are identified for allergenic proteins from diverse sources, and all allergens are classified into a limited number of protein structural families. A gallery of experimental structures selected from the protein classes with the largest number of allergens demonstrate the structural diversity of the allergen universe. Further comparison of these structures and identification of areas that are different from innocuous proteins within the same protein family can be used to identify features specific to known allergens. Experimental and computational results related to the determination of IgE binding surfaces and methods to define allergen-specific motifs are highlighted.

Peanut allergy

PURPOSE OF REVIEW

To highlight recent advances in management of peanut allergy.

RECENT FINDINGS

Peanut allergy presents during early childhood. The prevalence of peanut allergy in children in developed countries appears to be increasing. Several factors, such as peanut-specific or environmental, are hypothesized as contributing to increased prevalence. However, there is no consensus on this matter. Component-related diagnostic tests are being explored to characterize clinical sensitivity. Currently, the primary treatment includes avoidance of peanut and immediate treatment of anaphylaxis. Recent peanut oral immunotherapy (OIT) trials achieved successful desensitization to peanuts in study participants, which may benefit many patients. Newer prospective studies are exploring effects of early high-dose peanut protein introduction versus avoidance in high-risk infants and development of peanut tolerance [Learning Early About Peanut Allergy (LEAP) study]. Several other immunotherapeutic approaches are being investigated in animal models.

SUMMARY

There is no cure for peanut allergy. Peanut oral immunotherapy offers a potential treatment for desensitization.

Identification of IgE sequential epitopes of lentil (Len c 1) by means of peptide microarray immunoassay

BACKGROUND

Lentils are often responsible for allergic reactions to legumes in Mediterranean children. Although the primary sequence of the major allergen Len c 1 is known, the location of the IgE-binding epitopes remains undefined.

OBJECTIVE

We sought to identify IgE-binding epitopes of Len c 1 and relate epitope binding to clinical characteristics.

METHODS

One hundred thirty-five peptides corresponding to the primary sequence of Len c 1 were probed with sera from 33 patients with lentil allergy and 15 nonatopic control subjects by means of microarray immunoassay. Lentil-specific IgE levels, skin prick test responses, and clinical reactions to lentil were determined. Epitopes were defined as overlapping signal above interslide and intraslide cutoffs and confirmed by using inhibition assays with a peptide from the respective region. Hierarchic clustering of microarray data was used to correlate binding patterns with clinical findings.

RESULTS

The patients with lentil allergy specifically recognized IgE-binding epitopes located in the C-terminal region between peptides 107 and 135. Inhibition experiments confirmed the specificity of IgE binding in this region, identifying different epitopes. Linkage of cluster results with clinical data and lentil-specific IgE levels displayed a positive correlation between lentil-specific IgE levels, epitope recognition, and respiratory symptoms. Modeling based on the 3-dimensional structure of a homologous soy vicilin suggests that the Len c 1 epitopes identified are exposed on the surface of the molecule.

CONCLUSION

Several IgE-binding sequential epitopes of Len c 1 have been identified. Epitopes are located in the C-terminal region and are predicted to be exposed on the surface of the protein. Epitope diversity is positively correlated with IgE levels, pointing to a more polyclonal IgE response.

Microarray and allergenic activity assessment of milk allergens

BACKGROUND

Cow's milk is one of the most common causes of food allergy affecting approximately 2.5% of infants in the first years of their life. However, only limited information regarding the allergenic activity of individual cow's milk allergens is available.

OBJECTIVE

To analyse the frequency of IgE reactivity and to determine the allergenic activity of individual cow's milk allergens.

METHODS

A nitrocellulose-based microarray, based on purified natural and recombinant cow's milk allergens was used to determine IgE reactivity profiles using sera from 78 cow's milk-sensitized individuals of varying ages. The allergenic activity of the individual allergens was tested using patients' sera for loading rat basophil leukaemia cells (RBL) expressing the α-chain of the human receptor FcεRI.

RESULTS

Using the microarray and the RBL assay, cow's milk allergens were assessed for frequency of IgE recognition and allergenic activity. Moreover, the RBL assay allowed distinguishing individuals without or with mild clinical reactions from those with severe systemic or gastrointestinal symptoms as well as persons who grew out cow's milk allergy from those who did not.

CONCLUSIONS

Component-resolved testing using milk allergen microarrays and RBL assays seems to provide useful additional diagnostic information and may represent a basis for future forms of prophylactic and therapeutic strategies for cow's milk allergy.

Microarrays: Molecular allergology and nanotechnology for personalised medicine (II)

Progress in nanotechnology and DNA recombination techniques have produced tools for the diagnosis and investigation of allergy at molecular level. The most advanced examples of such progress are the microarray techniques, which have been expanded not only in research in the field of proteomics but also in application to the clinical setting. Microarrays of allergic components offer results relating to hundreds of allergenic components in a single test, and using a small amount of serum which can be obtained from capillary blood. The availability of new molecules will allow the development of panels including new allergenic components and sources, which will require evaluation for clinical use. Their application opens the door to component-based diagnosis, to the holistic perception of sensitisation as represented by molecular allergy, and to patient-centred medical practice by allowing great diagnostic accuracy and the definition of individualised immunotherapy for each patient. The present article reviews the application of allergenic component microarrays to allergology for diagnosis, management in the form of specific immunotherapy, and epidemiological studies. A review is also made of the use of protein and gene microarray techniques in basic research and in allergological diseases. Lastly, an evaluation is made of the challenges we face in introducing such techniques to clinical practice, and of the future perspectives of this new technology.

Greater epitope recognition of shrimp allergens by children than by adults suggests that shrimp sensitization decreases with age

BACKGROUND

Shellfish allergy is a long-lasting disorder typically affecting adults. Despite its high prevalence, there is limited information about allergenic shrimp proteins and the epitopes implicated in such allergic reactions.

OBJECTIVE

We sought to identify the IgE-binding epitopes of the 4 shrimp allergens and to characterize epitope recognition profiles of children and adults with shrimp allergy.

METHODS

Fifty-three subjects, 34 children and 19 adults, were selected with immediate allergic reactions to shrimp, increased shrimp-specific serum IgE levels, and positive immunoblot binding to shrimp. Study subjects and 7 nonatopic control subjects were tested by means of peptide microarray for IgE binding with synthetic overlapping peptides spanning the sequences of Litopenaeus vannamei shrimp tropomyosin, arginine kinase (AK), myosin light chain (MLC), and sarcoplasmic calcium-binding protein (SCP). The Wilcoxon test was used to determine significant differences in z scores between patients and control subjects.

RESULTS

The median shrimp IgE level was 4-fold higher in children than in adults (47 vs 12.5 kU(A)/L). The frequency of allergen recognition was higher in children (tropomyosin, 81% [94% for children and 61% for adults]; MLC, 57% [70% for children and 31% for adults]; AK, 51% [67% for children and 21% for adults]; and SCP, 45% [59% for children and 21% for adults]), whereas control subjects showed negligible binding. Seven IgE-binding regions were identified in tropomyosin by means of peptide microarray, confirming previously identified shrimp epitopes. In addition, 3 new epitopes were identified in tropomyosin (epitopes 1, 3, and 5b-c), 5 epitopes were identified in MLC, 3 epitopes were identified in SCP, and 7 epitopes were identified in AK. Interestingly, frequency of individual epitope recognition, as well as intensity of IgE binding, was significantly greater in children than in adults for all 4 proteins.

CONCLUSIONS

Children with shrimp allergy have greater shrimp-specific IgE antibody levels and show more intense binding to shrimp peptides and greater epitope diversity than adults.

Early recovery from cow's milk allergy is associated with decreasing IgE and increasing IgG4 binding to cow's milk epitopes

BACKGROUND

The dynamics and balance of allergen-specific IgE, IgG4, and IgA binding might contribute to the development of tolerance in patients with cow's milk allergy (CMA). Profiling of antibody binding to cow's milk (CM) protein epitopes might help in predicting the natural history of allergy.

OBJECTIVE

We sought to investigate differences in IgE, IgG4, and IgA binding to CM epitopes over time between patients with early recovery or with persisting CMA.

METHODS

We studied serum samples at the time of diagnosis (mean age, 7 months), 1 year later, and at follow-up (mean age, 8.6 years) from 11 patients with persisting IgE-mediated CMA at age 8 to 9 years and 12 patients who recovered by age 3 years. We measured the binding of IgE, IgG4, and IgA antibodies to sequential epitopes derived from 5 major CM proteins with a peptide microarray-based immunoassay. We analyzed the data with a novel image-processing method together with machine learning prediction.

RESULTS

IgE epitope-binding patterns were stable over time in patients with persisting CMA, whereas binding decreased in patients who recovered early. Binding patterns of IgE and IgG4 overlapped. Among patients who recovered early, the signal of IgG4 binding increased and that of IgE decreased over time. IgE and IgG4 binding to a panel of alpha(s1)-, alpha(s2)-, beta-, and kappa-casein regions predicted outcome with significant accuracy.

CONCLUSIONS

Attaining tolerance to CM is associated with decreased epitope binding by IgE and a concurrent increase in corresponding epitope binding by IgG4.

Correlation of IgE/IgG4 milk epitopes and affinity of milk-specific IgE antibodies with different phenotypes of clinical milk allergy

BACKGROUND

Results from large-scale epitope mapping with a peptide microarray have been shown to correlate with clinical features of milk allergy.

OBJECTIVES

We sought to assess IgE and IgG4 epitope diversity and IgE affinity in different clinical phenotypes of milk allergy and identify informative epitopes that might be predictive of clinical outcomes of milk allergy.

METHODS

Forty-one subjects were recruited from a larger study on the effects of ingesting heat-denatured milk proteins in subjects with milk allergy. Using food challenges, subjects were characterized as being clinically reactive to all forms of milk (n = 17), being tolerant to heated milk (HM) products (n = 16), or having outgrown their milk allergy (n = 8). Eleven healthy volunteers without milk allergy served as control subjects. A peptide microarray was performed by using the previously published protocol.

RESULTS

Subjects with milk allergy had increased epitope diversity compared with those who outgrew their allergy. HM-tolerant subjects had IgE-binding patterns similar to those who had outgrown their allergy, but IgG4-binding patterns that were more similar to those of the allergic group. Binding to higher numbers of IgE peptides was associated with more severe allergic reactions during challenge. There was no association between IgG4 peptides and clinical features of milk allergy. Using a competitive peptide microarray assay, allergic patients demonstrated a combination of high- and low-affinity IgE binding, whereas HM-tolerant subjects and those who had outgrown their milk allergy had primarily low-affinity binding.

CONCLUSIONS

Greater IgE epitope diversity and higher affinity, as determined by using the peptide microarray, were associated with clinical phenotypes and severity of milk allergy.

The role of immunoglobulin E-binding epitopes in the characterization of food allergy

PURPOSE OF REVIEW

Allergen-specific immunoglobulin E (IgE) antibodies play a central role in food allergic reactions. IgE epitope mapping of food allergens may provide information regarding patient's clinical history and contribute to food allergy diagnosis/prognosis. The goal of this article is to review recent developments in the methods for IgE epitope mapping and the role of IgE-binding epitopes in the characterization of food allergy.

RECENT FINDINGS

Recent studies have suggested a potential role for sequential IgE-binding epitopes as biomarkers for characterizing various phenotypes of food allergy. Studies of allergens in milk, peanut, egg and wheat have shown a correlation between IgE sequential epitope diversity and patients' allergy severity or persistence. Several informative epitopes in milk allergens have been identified as candidate biomarkers to predict the development of tolerance to milk. However, limitations with current methods of IgE-binding epitope identification need to be addressed before they can be applied in the diagnosis/prognosis of food allergy.

SUMMARY

IgE epitope mapping has the potential to become an additional tool for the diagnosis/prognosis of food allergy and lead to a better understanding of the pathogenesis and tolerance induction of food allergy.

Exploring and profiling protein function with peptide arrays

Development of array technologies started in the late 1980s and was first extensively applied to DNA arrays especially in the genomic field. Today this technique has become a powerful tool for high-throughput approaches in biology and chemistry. Progresses were mainly driven by the human genome project and were associated with the development of several new technologies, which led to the onset of additional "omic" topics like proteomics, glycomics, antibodyomics or lipidomics. The main characteristics of the array technology are (i) spatially addressable immobilization of a huge number of different capture molecules; (ii) probing the array in a simultaneous and highly parallel manner with a biological sample; (iii) tendency towards miniaturization of the arrays; and (iv) software-supported read-out and data analysis. We review some general concepts about peptide arrays on planar supports and point out technical aspects concerning the generation of peptide microarrays. Finally, we discuss recent applications by describing relevant literature.

Antibody signatures defined by high-content peptide microarray analysis

Circulating antibodies are highly selective binding reagents directed to a vast repertoire of antigens. Candidate antigens displayed as overlapping peptides on microarrays can be used to screen for recognition by serum antibodies from clinically well-defined patient populations. The methodology is robust and enables unbiased visualization of antigen-specific B-cell responses. Additionally, autoantibody signatures of diagnostic value could be detected using microarrays displaying thousands of human peptides.

Food allergy

Adverse immune responses to foods affect approximately 5% of young children and 3% to 4% of adults in westernized countries and appear to have increased in prevalence. Food-induced allergic reactions are responsible for a variety of symptoms and disorders involving the skin and gastrointestinal and respiratory tracts and can be attributed to IgE-mediated and non-IgE-mediated (cellular) mechanisms. Genetic disposition and environmental factors might abrogate oral tolerance, leading to food allergy. Disease outcomes are influenced by the characteristics of the immune response and of the triggering allergen. Diagnosis is complicated by the observation that detection of food-specific IgE (sensitization) does not necessarily indicate clinical allergy. Therefore diagnosis requires a careful medical history, laboratory studies, and, in many cases, an oral food challenge to confirm a diagnosis. Novel diagnostic methods, including ones that focus on immune responses to specific food proteins or epitopes of specific proteins, are under study. Currently, management of food allergies consists of educating the patient to avoid ingesting the responsible allergen and to initiate therapy (eg, with injected epinephrine for anaphylaxis) in case of an unintended ingestion. Improved therapeutic strategies under study include oral and sublingual immunotherapy, Chinese herbal medicine, anti-IgE antibodies, and modified vaccines.

Anaphylaxis: Recent advances in assessment and treatment

The incidence rate of anaphylaxis is increasing, particularly during the first 2 decades of life. Common triggers include foods, medications, and insect stings. Clinical diagnosis is based on a meticulous history of an exposure or event preceding characteristic symptoms and signs, sometimes but not always supported by a laboratory test such as an elevated serum total tryptase level. Physician-initiated investigation of patients with anaphylaxis whose symptoms and signs are atypical sometimes leads to important insights into previously unrecognized triggers and mechanisms. In idiopathic anaphylaxis, in which no trigger can be confirmed by means of skin testing or measurement of specific IgE, the possibility of mastocytosis or a clonal mast cell disorder must be considered in addition to the possibility of a previously unrecognized trigger. Long-term risk reduction in patients with anaphylaxis focuses on optimal management of relevant comorbidities such as asthma and other respiratory diseases, cardiovascular disease, and mastocytosis or a clonal mast cell disorder; avoidance of the relevant confirmed allergen trigger; and relevant immunomodulation such as medication desensitization, venom immunotherapy, and possibly in the future, immunotherapy with food. Emergency preparedness for recurrence of anaphylaxis in community settings includes having epinephrine (adrenaline) autoinjectors available, knowing when and how to use them, and having a written, personalized anaphylaxis emergency action plan and up-to-date medical identification. Randomized controlled trials of the pharmacologic interventions used in an acute anaphylaxis episode are needed.

Peptide array-based analysis of the specific IgE and IgG4 in cow's milk allergens and its use in allergy evaluation

Cow's milk (CM) is one of the major causes of food allergies in children. We constructed a peptide array consisting of a linear 16-mer peptide library with an offset of 3-mer, which corresponds to the primary sequences of six major CM allergens. The immune reactivity to cow's milk proteins diminishes with age and clinical tolerance commonly occurs. Although the central role of IgE in allergy is well established, the role of other specific antibody classes in obtaining immunotolerance is not well known. The hypothesis that patients become tolerant when they develop immunological changes particularly with the IgG4 isotype has been proposed. In this study, the binding pattern of the CM protein-specific IgE and IgG4 epitopes was measured using the peptide array with sera of 12 patients with persistent CM allergy (CMA), sera of 5 children who outgrew CMA, and sera of 7 CM-sensitized children without allergy symptoms. In CMA patients the IgG4/IgE fluorescence intensity ratios varied greatly from peptide to peptide, and the scatter plots of IgE versus IgG4 signals using significant IgE-binding peptides showed different distribution patterns. When setting the boundary line based on the IgG4/IgE ratio (IgG4/IgE=2), patients with persistent CMA and CM-sensitized children can be distinguished by the plot pattern of peptides. Furthermore, the number of peptide plots in these regions was less in children who outgrew CMA. The approach employed in this study will allow for the distinction between CMA and CM-sensitization, and will enable the estimation of CMA outgrow by monitoring the time elapsed data.

Food allergy: recent advances in pathophysiology and treatment

Food allergies are adverse immune reactions to food proteins that affect up to 6% of children and 3-4% of adults. A wide range of symptoms can occur depending on whether IgE or non-IgE mediated mechanism are involved. Many factors influence the development of oral tolerance, including route of exposure, genetics, age of the host, and allergen factors. Advances have been made in the understanding of how these factors interact in the pathophysiology of food allergy. Currently, the mainstay of treatment for food allergies is avoidance and ready access to emergency medications. However, with the improved understanding of tolerance and advances in characterization of food allergens, several therapeutic strategies have been developed and are currently being investigated as potential treatments and/or cures for food allergy.

Development of a novel peptide microarray for large-scale epitope mapping of food allergens

BACKGROUND

The peptide microarray is a novel assay that facilitates high-throughput screening of peptides with a small quantity of sample.

OBJECTIVE

We sought to use overlapping peptides of milk allergenic proteins as a model system to establish a reliable and sensitive peptide microarray-based immunoassay for large-scale epitope mapping of food allergens.

METHODS

A milk peptide microarray was developed by using commercially synthesized peptides (20-mers, 3 offset) covering the primary sequences of alpha(s1)-casein, alpha(s2)-casein, beta-casein, kappa-casein, and beta-lactoglobulin. Conditions for printing and immunolabeling were optimized using a serum pool of 5 patients with milk allergy. Reproducibility of the milk peptide microarray was evaluated using replicate arrays immunolabeled with the serum pool, whereas specificity and sensitivity were assessed by using serial dilution of the serum pool and a peptide inhibition assay.

RESULTS

Our results show that epitopes identified by the peptide microarray were mostly consistent with those identified previously by SPOT membrane technology, but with specific binding to a few newly identified epitopes of milk allergens. Data from replicate arrays were reproducible (r > or = 0.92) regardless of printing lots, immunolabeling, and serum pool batches. Using the serially diluted serum pool, we confirmed that IgE antibody binding detected in the array was specific. Peptide inhibition of IgE binding to the same peptide and overlapping peptides further confirmed the specificity of the array.

CONCLUSION

A reliable peptide microarray was established for large-scale IgE epitope mapping of milk allergens, and this robust technology could be applied for epitope mapping of other food allergens.

Advances in allergic skin disease, anaphylaxis, and hypersensitivity reactions to foods, drugs, and insects in 2008

This review highlights some of the research advances in anaphylaxis, and hypersensitivity reactions to foods, drugs, and insects and in allergic skin disease that were reported in the Journal in 2008. Key epidemiologic observations include a rise in anaphylaxis in a population-based study and lower rates of peanut allergy in Israel, where infants consume peanut early compared with the United Kingdom, where dietary introduction is generally delayed. Advances in food allergy diagnosis include IgE epitope mapping that discloses the likelihood and severity of allergy; studies correlating likelihood of clinical reactivity on the basis of food-specific IgE to sesame, peanut, milk, and tree nuts; and an observation that a low baseline angiotensin-converting enzyme level may be associated with having pharyngeal edema during a reaction. Molecular, immunologic, and genetic studies are discerning pathways that are key in development of food allergy, identifying new modalities to interrupt mast cell degranulation, and elucidating risks associated with penicillin allergy. Regarding treatment, clinical studies show a majority of children with milk and egg allergy tolerate these proteins in modest amounts when they are extensively heated in baked goods, and studies show promise for oral immunotherapy to treat milk allergy and sublingual immunotherapy for honey bee venom hypersensitivity. The importance of skin barrier dysfunction has continued to be highlighted in the pathophysiology of atopic dermatitis (AD). Research has also continued to identify immunologic defects that contribute to the propensity of patients with AD to develop viral and bacterial infection. New therapeutic approaches to AD, urticaria, and angioedema have been reported including use of probiotics, biologics, vitamin D, and skin barrier creams.