Allergic reactions (both harmless and detrimental for health) are hypersensitivity of immune system lacking organism protection in response to external exposure. Development of allergic reactions is provoked by specific Ag called allergens. Acute manifestation of hypersensitivity with magnitude is anaphylaxis. Allergic reactions comprise pathogenic basis of allergic diseases.
ALLERGENS
Though there are contexts using the terms "allergen" and "antigen" as synonyms, it should be noted that not each Ag is able to provoke allergic reaction. Allergens differ by some physical and chemical properties as well as by specific ways to penetrate an organism. Several allergenic properties are listed below:
• Relatively small molecular mass.
• Capacity of sorption and aggregation in small particles thus defusing mucous secrets and integumentary tissues without evident defects of the latter.
• High solubility and easy elution in liquid media of organism.
• In vivo chemical stability (allergens do not metabolize easily at least).
• Among proteins the most frequent allergens are enzymes, proteases. Non-protein allergens are distinguished by their capacity to join protein compounds of own organism.
• Allergens are able to produce a small dosing effect. For instance, significant pathogenic total dosing of ambrosia allergen is 1 mcg per year. Classification. Allergens may be classified by various principles. For
practical application they may be easily grouped either by origin (allergens of pollen, insect poisons, animal epidermis and excretions, foodstuffs, drugs, etc.) or by "entrance gate" to organism (domestic, professional) and so on. The substances of different chemical groups that very often provoke allergic reactions are listed below.