The major cat allergen, Fel d 1, in diagnosis and therapy.

Sensitization to cat is a common cause of allergic disease all over the world. Symptoms range from mild rhinoconjunctivitis to potentially life-threatening asthmatic exacerbations. In vivo and in vitro diagnostics of cat allergy is currently based on cat dander extract. As allergen extracts from natural sources are heterogeneous in composition, the allergen content may vary. With the introduction of allergens produced by recombinant techniques, a large panel of recombinant allergenic molecules including the major cat allergen, recombinant Fel d 1, has become available for immunological investigations, diagnosis and treatment. Studies have shown that this single allergen, which belongs to the uteroglobin protein family, is at least as good as cat dander extract in identifying cat-allergic patients. The introduction of recombinant Fel d 1-based tests into clinical practice will increase our knowledge of this single allergen molecule as a diagnostic tool and improve the selection for therapy of cat allergy. Several different modes for allergen-specific immunotherapy of cat allergy based on Fel d 1 have been developed. These include Fel d 1 hypoallergens and allergen constructs where Fel d 1 is coupled to immunomodulatory proteins or carriers. The approaches have been evaluated in experimental in vitro and in vivo model systems with promising results. In addition, immunotherapy with Fel d 1 peptides containing T-cell epitopes has been tested in clinical trials. After initial problems with adverse reactions, more recent data show that peptide immunotherapy modulates the immune response to Fel d 1 and reduces early- and late-phase effector reactions in cat-allergic patients.