Allergy to mammalian proteins: at the borderline between foreign and self?

Atopic individuals are characterized by their genetically determined tendency to mount IgE antibody responses against otherwise harmless antigens. Many of the environmental allergens (e. g., plant-, insect-, mould-derived allergens) are recognized as foreign intruders by the immune system. However, a substantial proportion of atopic individuals mount IgE responses to allergens of mammalian origin and, as recently reported, certain of them even react with human proteins (i. e., autoallergens). Through the application of molecular biological techniques for allergen characterization, the molecular nature and biological function of an increasing number of mammalian allergens have been revealed. This review provides a summary of well characterized mammalian allergens derived from hair/dander, saliva, serum and urine of animals (cat, dog, rodents, cow, horse) as well as of some recently characterized autoallergens. In addition, mammalian allergens were grouped in protein families with similar sequences and/or biological functions. The importance of cross-reactivities is exemplified for albumins which represent abundant mammalian serum proteins and highly cross-reactive allergens. Finally, possible advantages of using recombinant animal allergens for novel forms of component-resolved diagnosis and treatment of allergies to mammalian proteins are described.