Physical and biochemical characteristics of allergens

ABSTRACT

What makes a certain molecule to elicit allergic responses? It has been a long-running question in allergology and immunology. Molecular properties of allergens have been characterized for last 30 years. However, it has become evident that allergen alone cannot induce allergic reactions. The way of introduction to the immune system and adjuvant-like activity of concomitantly administered molecules are thought to be important. Physical properties which facilitate delivery may characterize inhalant allergens. Buoyant and sticky antigens with small molecular weight (10-50 kDa) may be carried by particles and remain airborne. Most allergens could be grouped into allergen families according to biochemical properties. Protease, lipid-binding/transfer protein, actin-binding protein, Ca-binding protein, α-amylase/trypsin inhibitor, and pectate lyase account for a significant number of allergens. Biochemical properties which enhance the activation of Th2-immune responses could be another characteristic of allergens. The protease activity of allergens can help break the skin barrier or mucus membrane and its penetration into the body. The capacity of allergen to carry immunologically active substances could increase the allergenicity. Lipid-binding ability is believed to play a role in this aspect. Danger signals, such as endotoxin, β-glucan, and chitin derived from the pathogens, commensals and from the environment can enhance the immune response to allergens. The known characteristics of food allergens are resistance to heat, acid, and digestive enzymes. However, food processing makes it more complex. Understanding the intrinsic properties of allergens may shed light on the mechanisms on the pathogenesis of allergic disorders and improve the diagnostic and therapeutic approaches.