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In Taiwan, the most common allergic diseases include six major types: allergic rhinitis, asthma, allergic conjunctivitis, ectopic dermatitis, urticaria and food allergies. Symptoms of these allergic diseases are listed below (Table 1)(4):
| Name of allergic diseases | Clinical symptoms |
| Asthma | Short breath, wheezing, tight chest, chronic cough, night cough |
| Allergic rhinitis | Sneezing, runny nose, nasal itching, nasal congestion |
| Allergic conjunctivitis | Blinking, red eyes, swollen and itching eyes, black eyes |
| Gastrointestinal allergy | Gastrointestinal discomfort after eating some food, along with diarrhea, abdominal pain, intestinal colic, nausea and vomiting |
| Ectopic dermatitis | Severe itching, dry, desquamative eczema, erythema |
| Urticaria | Sudden red lumps on the skin, prurigo |
| Table 1. Common allergic diseases and their symptoms | |
Symptoms of allergy generally result from the immune system recognizing normally harmless substances as plant pollen or food proteins as dangerous by mistake and then leading to a chain of events causing an immune system overreaction. Atopic allergies are one type of allergy and are triggered by immunoglobulin E (IgE) binding to the allergen. Type 2 helper T-cells (Th2) mainly regulates allergic immune responses in the body, while type 1 helper T-cells (Th1) mainly defends against infection by viruses, bacteria and other pathogens.
Cytokines and other molecules secreted by the two types of T cells regulate each other along with other immune cells, generally reaching a healthy balance of immunoregulation. Healthy individuals have strong type 1 responses as the principal reaction helping to prevent diseases caused by invading pathogens.
Fig. 1. When the immune system comes into contact with allergens, a series of immune interactions occur, resulting in an allergic response.
When the immune system encounters allergens, a large number of Th2 cells in the body will be activated causing the secretion of Th2 associated cytokines, such as interleukin-4, 5, 13 (IL-4, 5, 13), etc. IL-4 and IL-13 can promote immunoglobulin class switching by B cells to the IgE class resulting in secretion of allergen-specific IgE into the bloodstream(5).
IL-13 also has the ability to stimulate the airway epithelial cells, causing physiological reactions such as smooth muscle contraction, resulting in conditions such as airway hyperresponsiveness (AHR). Consequently, AHR increases airway resistance resulting in difficulty breathing(6), which is the most common symptom of asthma patients. IL-5 is known to activate and attract eosinophils (EOS), which accumulate, causing serious local inflammation. In addition, inhaled allergens can also combine with the IgE antibodies on the surface of mast cells, activating them and resulting in the secretion of inflammatory substances such as histamine, leukotriene B4 (LTB4), etc. causing respiratory tract inflammation(7, 8) (Fig. 1).
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