Allergen Profile, Wheat, IgE With Components Reflex

Serum

1 mL

0.8 mL (Note: This volume does not allow for repeat testing.)

Red-top tube or gel-barrier tube

This test is used to support the diagnosis of wheat allergy by detection of sIgE antibodies to whole wheat extract and individual allergenic components.

Wheat sensitization (as determined by wheat extract based sIgE testing) is much more common that true clinical allergy.¹ sIgE is necessary but not sufficient for elicit an allergic response and thus generating a definitive diagnosis of allergic disease. The presence of specific sIgE to wheat without a clear history of symptoms after wheat exposure is not diagnostic as many people can be sensitized to wheat but tolerate wheat exposure, especially in grass pollen sensitized individuals.¹

Wheat sensitization caused by cross-reactivity but also by sensitization to wheat-specific allergens is common in the grass-allergic children.²

No single allergen can be used for molecular allergy diagnostics in wheat allergy, since the IgE response is heterogeneous and directed against multiple allergens.¹ Reactions to Tri a 19 (omega-5-gliadin) do not necessarily require exercise as a cofactor although it can lower the antigen threshold dose necessary to trigger the anaphylaxis.^3-5

Tri a 19 sensitization is not WDEIA specific since sIgE can be detected in a substantial portion of patients who have classical wheat allergy.^6,7

Measurement of sIgE to wheat extract can be negative in patients that are positive for IgE to either Tri a 14 or Tri a 19. Thus, when wheat allergy is suspected, sIgE assessment for these markers can improve diagnostic performance.⁸

Thermo Fisher ImmunoCAP(R) Allergen-specific IgE

Wheat (Triticum aestivum) is an important source of food globally.^1,9 IgE mediated allergy to wheat can occur after exposure to wheat proteins via ingestion, inhalation or through cutaneous exposure.^1,9,10 Wheat allergy can produce a variety of symptoms that can include urticaria/angioedema, atopic dermatitis, abdominal pain, vomiting, allergic rhinitis, asthma,anaphylaxis or a severe form of exercise-related wheat allergy.^1,9,11,12 Wheat allergy is more prevalent in children compared to adults, especially if wheat is introduced after six months of age.¹³ Children tend to outgrow wheat allergies with two thirds of children becoming tolerant by 12 years of age.¹⁴ Allergic reactions to wheat in adults are often characterized by a prolonged time between food intake and the onset of symptoms.^15,16 In many cases, wheat allergic reactions in adults involves a cofactor, such as exercise.¹⁶ A history of wheat ingestion without allergic reaction (in the absence of cofactor) can conceal the role of wheat in cofactor-dependent allergy, delaying diagnosis.¹⁶

The diagnostic assessment of allergy starts with the patient's clinical history and examination and is followed by allergen-specific testing to establish a diagnosis.¹ Traditional testing for suspected wheat allergy has historically relied on assessment of sensitization to whole wheat extract either by skin prick testing (SPT) or measurement specific IgE (sIgE) levels in serum. If required, an oral food challenge test, which is considered to be the diagnostic “gold standard” for diagnosis of wheat allergy, may be performed. While up to three percent of patients test positive by other wheat extract-based tests (SPT and sIgE), oral food challenge studies estimate the prevalence of true wheat food allergy to be more in the range between 0.2% to 1%.^10,13,17-23 The use of wheat extract-based SPT and sIgE tests for clinical diagnosis is suboptimal due to low specificity. Wheat is a cereal grain, and cross-reactions with other cereals like rye and barley are common.^2,6,24,25 Wheat is also a grass originating from the Poaceae family, widespread members of which contain grass pollen allergens that have been reported to cross-react with wheat.^{1,2,9,14,18,19,24,26-32} Also, some cases of wheat extract positivity can occur due to cross-reactivity with lipid transfer proteins from foods such as peach, peanut, walnut, hazelnut and almond.^8,33-36

Sensitivity, specificity, positive predictive value and negative predictive value of wheat extract-based tests vary tremendously depending on the population tested.^{6,18,32,37-42} Pediatric patients with high titers of wheat-specific IgE tend to have more severe clinical manifestations of wheat allergy and have shown less favorable outcomes and more delayed development of wheat tolerance.^{14,18,39,43,44} Nonetheless, some children outgrow their wheat allergy with even the highest levels of wheat IgE.^14,26

Whole allergen extracts contain most of the extractable allergenic components from the suspected sensitizer. Testing with assays utilizing these extracts does not lend itself to the differentiation of primary sensitization from a cross-reactivity-driven response because of the complexity of the extracts and their inclusion of proteins that are homologous to proteins from other potential sensitizers.¹ Another weakness of testing exclusively with extractable allergen extracts is that these extracts may not contain clinically important (non-extractable) proteins that are relevant to allergy. Component Resolved Diagnostics (CRD) refers to the use of individual purified or recombinant allergenic proteins in the serologic assessment of individuals who suffer reproducible hypersensitivity reactions with exposures to an allergen at a dose tolerated by non-allergic individuals.¹ This approach offers advantages over the use of a complete extract alone, especially in polysensitized individuals, given its usefulness for distinguishing between sensitizations specific to singular species and sensitizations due to cross-reactivity.¹

The protein composition of wheat is complex and can be broadly divided into three major fractions based on extraction method: 1) water soluble albumins; 2) salt-soluble globulins; and 3) insoluble prolamins (gliadins and the glutenins).⁴¹ Each of these fractions contains allergenic proteins that have been associated with clinical symptoms.¹ The material used in the wheat extract ImmunoCAP™ test is predominantly composed of the water soluble albumins and salt-soluble globulins and is relatively devoid of insoluble prolamins. In addition to the wheat extract sIgE test, ImmunoCAP™ tests are now available for a number of wheat-specific and wheat extract cross-reactive components that can aid in the diagnostic workup of potential wheat allergy.

• Gliadin-specific IgE

n-Gliadin is a natural, non-recombinant mix of alpha, beta, gamma and omega gliadins (fast omega-gliadin and slow omega-gliadin) soluble in alcohols. Whole wheat extract-based testing is compromised by under representation of proteins of the gliadin sub-fraction due to their relative insolubility in aqueous extraction buffer.^45,46 Pure omega 5-gliadin (Tri a 19) (fast omega-gliadin) is also available as a recombinant allergen.

• Tri a 14: Nonspecific Lipid Transfer Protein (nsLTP)

This wheat component is a pathogenesis-related (PR) protein that serves in plant defense mechanisms against phytopathogens (bacteria and fungi).³⁶ Wheat Tri a 14 shows a high thermal stability and resistance to gastrointestinal digestion.³⁶ Wheat extract-based tests sometimes do not detect Tri a 14 sensitization due to its low abundance in extracts.⁸ Sensitization to Tri a 14 has been found to be directly related to sensitization to many other LTP related foods including peach, peanut, walnut, hazelnut and almond.^33-35,47 Studies suggest that Tri a 14 has little cross-reactivity with grass pollen¹ and that measurement of sIgE to this component may help in differentiating wheat sensitization from pollen allergy in patients with high levels of grass pollen-specific IgE.¹ Wheat allergy due to Tri a 14 is frequently related with systemic reactions, and because allergic reactions to wheat often require cofactors, wheat allergy may not be suspected.⁸

• Tri a 19: Omega-5-gliadin

The best characterized single component of wheat is omega-5 gliadin.^6,40,48-51 Due to its poor solubility in aqueous conditions, this component is under-represented in wheat extract.⁴⁵ Relevant to cofactor dependency of food allergic reactions to wheat, concomitant ingestion of alcohol or aspirin has been demonstrated to increase plasma gliadin levels.^5,51

• Phl p 12: Timothy Grass Profilin

Profilins have highly conserved sequences and structures and are found in all plants.^52,53 Pollens are often the primary sensitizer in patients sensitized to profilin.⁵⁴ It is often unclear whether the wheat extract sensitization reflects an sIgE response to wheat or a potential cross-reactivity with grass pollen allergens. Due to the high structural similarity of profilins from all species, testing for sIgE to the grass pollen profilin, Phl p 12, serves as a proxy for assessing sIgE sensitization to all profilins. Grass-sensitized patients who are positive for sIgE to wheat but tolerate wheat are often Phl p 12 sIgE positive.² Since profilins are labile to gastric enzymes and heat denaturation, sensitized patients exposed to profilins in foods usually develop Oral Allergy Syndrome reactions.

• Cross-reactive Carbohydrate Determinants (CCDs)

One of the main obstacles to determining species specificity of allergen sensitization is the occurrence of specific N-linked glycosylation of allergens.⁵⁵ Many allergen proteins are post-translationally glycosylated with unique alpha 1,3-linked fucose residues. While many mammalian proteins are glycosylated, only plants and insect proteins contain this specifically can residue. Since this specific glycosylation does not occur in humans, exposure to proteins that are glycosylated with alpha 1,3-linked fucose residues often induces allergic sensitization and IgE production. This glycan sIgE does not reflect exposure to any specific allergen but represents a pan-sensitization to “Cross-reactive Carbohydrate Determinants” or “CCD” sensitization.⁵⁵ IgE antibodies directed against CCD confound diagnostic tests using whole allergen extracts.⁵⁵ CCD-IgE produces a positive wheat-extract based test results that doesn't reflect specific wheat exposure.⁵⁵ As a consequence, tests using component proteins can be used to differentiate true wheat sensitization from CCD sensitization in wheat-extract positive patients.²

The clinical expression of wheat allergy can be quite diverse due to different routes and amounts of exposure and the diversity of populations affected. Consequently, four distinct patterns of wheat allergy are encountered in clinical practice: classic IgE-mediated food allergy, occupational asthma (or baker's asthma and rhinitis), wheat-dependent exercise-induced anaphylaxis (WDEIA) and contact urticaria (often associated with exposure cosmetics).^10,56,57

Classic IgE-mediated Food Allergy: This clinical syndrome of wheat-induced food allergy is similar to that of other early childhood food allergies. In this condition, gastrointestinal (or cutaneous) uptake of wheat-containing foods can lead to IgE sensitization to stable wheat proteins.¹ Many wheat allergic individuals develop symptoms within minutes to one to two hours after ingestion of a wheat.^{1,10,11,45,58} More delayed symptoms including the worsening of atopic dermatitis and gastrointestinal symptoms such as stomach pain and diarrhea or loose stools can also occur.¹ Sensitization to wheat allergens in often atopic infants is the basis of most typical IgE-mediated wheat allergy, extending often until school age and in rare cases, up to adulthood.¹ The prognosis of IgE-mediated wheat allergy in children is generally favorable, with the majority becoming tolerant by school age.^{14,18,44,59,60} Peak levels of wheat extract IgE levels correlate with the age at which wheat allergic children become tolerant,^59,61 and patients with lifetime peak wheat IgE levels greater than 50 kUA/L are likely to retain wheat allergy until adolescence or adulthood.¹⁴

Tri a 14 has also been implicated as an allergic sensitizer in IgE mediated food allergies in children^34,62-67 and in adult-onset IgE-mediated wheat allergy.⁶⁷ Tri a 14 sIgE positivity is often associated with cross-reactivity with other foods, making a food challenge necessary to avoid unjustified food avoidance.³³ In a case series of subjects with classical wheat allergy verified by food challenge, Scibilia et al reported that sensitization to Tri a 14 a was associated with a favorable prognosis and reduction of clinical manifestations due to wheat a few years after diagnosis.⁶⁸

Several studies have indicated that gliadins can be important sensitizers for wheat allergy.^{6,7,18,41,63,69,70} In studies of Japanese children, Tri a 19 was been shown to correctly predict challenge-proven IgE-mediated allergy to wheat^40,49,71 and to predict the persistent of wheat allergy.⁷² In a Swedish population, Tri a 19 specific IgE correlated better with food challenge-proven wheat allergy than the wheat extract-based ImmunoCAP® test or tests for other component allergens.¹⁸ However, these results for Tri a 19 have not been reproduced in American or German populations.⁷³ Overall, sensitization to Tri a 19 implies a higher probability of severe reactions.^18,33,61,74 Tri a 19 sIgE levels have been used to predict how much wheat can be tolerated and the intensity of the reactions in patients treated with wheat immunotherapy.⁷⁴ Tri a 19 has also been implicated as an allergic sensitizer in adult-onset IgE-mediated wheat allergy in a number of studies.^{6,18,40,41,49,61,67,72,75-78}

A recent study compared Tri a 14 and Tri a 19 sIgE positivity in wheat allergic subjects and found that the two sensitizations were independent, with a significant inverse relation in their levels.³³ This study further found that sIgE sensitization to Tri a 19 or Tri a 14 determine different clinical pictures. In particular, sensitization to Tri a 19 implies a higher probability of severe reactions while Tri a 14 sensitization implies a higher cross-reactivity with other foods, but it is more frequently asymptomatic with respect to wheat, making a food challenge necessary to prevent unneeded food avoidance.³³

Baker's Allergy or Asthma: Baker's asthma is an IgE-mediated wheat allergy that develops after allergen inhalation, especially cereal flour dust present in the work environment, and affects pastry factory workers, cereal handlers, confectioners and bakery workers.^45,46,79,80 It is one of the most common types of occupational asthma.^45,46,79,80 Although wheat is the most commonly involved cereal, others (rye, barley, rice, maize and oats) also play a role in baker’s asthma. This condition tends to be more common in atopic subjects who are exposed to high levels of wheat allergens for several hours per day. Consuming cooked wheat or products containing it does not manifest symptoms in these patients, but they may react after eating products contaminated with raw wheat flour.⁸¹ The majority of affected individuals did not suffer from asthma before developing the occupational disease.⁴⁶ The diagnosis of baker's asthma or allergic rhinitis is based on clinical history, the presence of specific IgE to wheat and, in selected individuals, a positive nasal or bronchial response to provocation.⁴⁶

Wheat component sensitization profiles of bakers have revealed great inter-individual variability, and no wheat allergen could be classified as the major allergen.⁷⁹ However, individual wheat component testing might help to discriminate between wheat-induced food allergy, grass pollen allergy and baker's asthma.⁷⁹ Twelve percent of patients with baker’s asthma had IgE reactive αβ-gliadin and 33 percent showed sensitization to natural total gliadin.⁸² Tri a 14^34,56,83,84 and Tri a 19^69,70 have been reported to be positive in some patients with baker's asthma/allergy. While individual components can be positive in these patients, the first choice for in vitro diagnosis of baker's asthma is still the determination of allergen sIgE antibodies against the whole wheat flour extracts because of superior diagnostic sensitivity.^69,79,85,86 Ultimately, for the establishment of a definite diagnosis of baker's asthma, specific challenge testing with occupational allergens may need to be performed.⁸⁰

Wheat-dependent, Exercise-induced Anaphylaxis (WDEIA): Exercise-induced anaphylaxis (EIA) may occur independently of food ingestion and is thought to be associated with five to 15 percent of all cases of anaphylaxis.⁸⁷ The epidemiology and clinical presentation of this condition implies pathogenic mechanisms potentially distinct from those of childhood-onset food allergy.¹² This relatively uncommon form of IgE mediated wheat allergy can occur at any age but most commonly affects adolescents and adults.^1,12 EIA should be suspected when a patient experiences severe allergic episodes a few (one to six) hours after exercise.^{1,12,15,16,58,88-90} Sometimes the level of exercise can be relatively light such as brisk walking. Symptoms vary from generalized urticaria to severe anaphylactic reaction.^1,12

EIA is considered to be wheat-dependent (WDEIA) if the patient experiences the symptoms only if they ingested wheat prior to the exercise and wheat is well-tolerated in the absence of exercise.^12,15,58 Patients with WDEIA have a relatively low prevalence of other atopic diseases (atopic dermatitis, allergic rhino conjunctivitis and asthma).^15,16 A number of cofactors (i.e., the intensity of exercise, pollen exposure, concomitant ingestions of non-steroidal anti-inflammatory drugs or alcohol and the presence of menses in females) can affect the incidence of WDEIA.^3,4.5,12,16 Cofactors augment clinical reactions by lowering the threshold for and increasing the severity of the allergic reaction in patients with WDEIA.^4,91 The combination of multiple cofactors can increase the risk of more severe reactions.⁴ Some cases of WDEIA are mild, with only cutaneous signs such as urticaria, erythema and angioedema, while more severe cases can include anaphylactic features, such as bronchospasm, gastrointestinal involvement and hypotension.⁹² Some patients with WDEIA tolerate wheat ingestion on the majority of occasions without reaction, and then can have severe reactions for no apparent reason.⁹² The intermittent nature of the condition, its relative rarity and the lack of recognition by physicians often frequently results in a prolonged time lag to diagnosis of this condition.^12,15,91

Tri a 19 has been shown to be the major sensitizer for WDEIA.^{3-7,12,15,16,40,48-50,73,76,88,89,91-98} A recent study of Japanese patients with WDEIA found that the majority (>85%) of patients with Tri a19 sIgE-associated WDEIA maintained elevated Tri a 19 sIgE over time during several years of observation.⁸⁸ Tri a 14 sensitization has also been implicated as allergic sensitizers in some cases of WDEIA.^{12,34,63,66,99-101} In one study, α/β/γ-gliadin was positive in 82 percent for patients with WDEIA including some patients lacking IgE to Tri a 19.⁹⁹

Contact urticaria: Hydrolysis of wheat is carried out to overcome its insolubility in cosmetics, and exposure to hydrolyzed wheat protein (HWP) can cause either contact urticaria or even anaphylaxis when consuming gluten-containing food.^1,102 Contact urticaria with use of cosmetics is relatively common, and hydrolyzed wheat should always be thought as one possible inducer.^1,103 Patients with wheat related urticaria have been reported to frequently have low to moderate levels of sIgE to wheat extract and/or gluten.¹⁰⁴ Some patients develop WDEIA after using HWP-containing soap.¹⁰⁴