Most patients who are allergic to cats are aware of symptoms on entering a house with a cat or if they touch their face after contact with an animal.
Purification of the main cat allergen Fel d 1 from cat washings or pelt extract is difficult, partly because it is expensive to keep a large number of cats. The details of the structure of this allergen were not known until mAbs made it possible to obtain the N-terminal sequence and then to clone and sequence the molecule. At one point it seemed likely that Fel d1 was a salivary protein, and that it accumulated on the fur in part because cats licked themselves. However, when cats were restrained from licking themselves, Fel d 1 still accumulated on shaved skin, and it became clear that the primary site of synthesis of this allergen was in the skin.
On crossed radioimmunoelectrophoresis (CRIE) or on Western blotting, other proteins produced by cats can be shown to be allergens for some patients. However, only two of these have been purified and characterized, cat albumin (Fel d 2) and a cystatin (Fel d 3), and both are less important than Fel d 1. Thus, sensitization to the other allergens is only found in a minority of cat-allergic patients.
Cat extracts are manufactured either from washings or from pelt. Pelt extracts are thought to be less representative of natural exposure because they contain a large relative concentration of serum proteins (e.g., albumin). Because washing cats is used as a method of making commercial cat extracts, this procedure can remove allergens from the cat. When cats are washed repeatedly, the allergen recovered decreases progressively. This observation lead to the investigation of washing as a method of controlling exposure. Additional studies showed that cat allergen can be removed from a cat by washing, and that the animal will subsequently release less allergen. 10 However, this effect does not last for long, less than 1 week. Washing of cats or dogs needs to be repeated frequently to be effective. 11
References:
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Woodfolk JA, Luczynska CM, de Blay F, et al: Cat allergy, Ann Allergy 69:273, 1992.
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Avner DB, Perzanowski MS, Platts-Mills TA, et al: Evaluation of different techniques for washing cats: quantitation of allergen removed from the cat and the effect on airborne Fel d 1, J Allergy Clin Immunol 100:307, 1997.
Klucka CV, Ownby DR, Green J, et al: Cat shedding of Fel d 1 is not reduced by washings, Allerpet-C spray, or acepromazine, J Allergy Clin Immunol 95:1164, 1995.
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