Bread wheat, also known as Triticum aestivum, is one of the commonly grown crops worldwide. It can be grown worldwide because it grows easily in different climates, and has a high nutritional value, high palatability, and can be processed into many foods and drinks. However, despite these benefits, common wheat is recognized as an immune-mediated food allergen because it activates immunoglobulin E (IgE) and non-IgE immune responses. IgE-mediated reactions to wheat are well-known and can be due to either ingestion (food allergy) or inhalation (respiratory allergy).

Etiology

• IgE-mediated allergic reaction: This type of reaction to wheat proteins is characterized by the presence of wheat-specific IgE antibodies and can be lethal. It includes food allergies and respiratory allergies, such as baker's asthma.
• Non-IgE-mediated allergic reaction: This involves chronic eosinophilic and lymphocytic infiltration of the gastrointestinal tract. Conditions such as eosinophilic esophagitis and eosinophilic gastritis fall under this category.

Pathophysiology

• Mediator release: Wheat allergy manifests through the release of mediators like histamine, platelet activator factor, and leukotrienes from mast cells and basophils.
• IgE production: The production of IgE is due to a breach of oral tolerance, resulting from type 2 helper T cell-biased immune dysregulation that causes sensitization and B-cell IgE production.
• Common allergens in wheat: These include alpha-purothionin, alpha-amylase/trypsin inhibitor, peroxidase, thioredoxin, lipid-protein transfer, serine proteinase inhibitor, thaumatin-like protein (TLP), gliadin, thiol reductase, 1-cys-peroxiredoxin, and serine protease-like inhibitor.

Celiac Disease

• Autoantibodies: Specific autoantibodies against tissue transglutaminase 2 (anti-tTG2), endomysium, and deamidated gliadin peptide are characteristic of celiac disease.
• Immune response: Gliadin peptides activate CD4 T-lymphocytes, producing high levels of pro-inflammatory cytokines which activate T-helper 1 and T-helper 2 patterns, leading to an expansion of B-lymphocytes that secrete anti-gliadin and anti-tissue-transglutaminase antibodies.
• Histological changes: Expected changes in the small intestines include an increased number of intraepithelial lymphocytes, crypt elongation, and partial to total villous atrophy.

History and Physical Examination

• Comprehensive history: Providers should obtain a detailed history, including prior food allergic reactions to wheat or respiratory allergies to wheat flour.
• Symptom onset: Symptoms appearing one to three hours after wheat exposure should prompt confirmation of the allergy via skin prick test (SPT) or serum IgE measurement.
• Occupational history: It is important to include the patient's occupational history, including current and past employment.

Symptoms

• Wheat allergy: Symptoms include urticaria, angioedema, asthma, allergic rhinitis, abdominal pain, vomiting, acute exacerbation of atopic dermatitis, or exercise-induced anaphylaxis.
• Wheat-dependent exercise-induced anaphylaxis (WDEIA): Symptoms include pruritus, urticaria, angioedema, flushing, shortness of breath, dysphagia, chest tightness, profuse sweating, syncope, headache, diarrhea, nausea, throat closing, abdominal pain, and hoarseness occurring during intense physical exercise following wheat intake within the prior four hours.
• Celiac disease: Symptoms include diarrhea, constipation, bloating, abdominal pain, anorexia, flatulence, weight loss, poor growth in childhood, anemia, dermatitis herpetiformis, fatigue, and osteoporosis.