Fel d1
The majority of cat allergies are caused by a small stable protein called Fel d1. As allergens are discovered, they are identified by species and also given a number, so we the first cat allergen discovered was Feline domesticus allergen 1, (Fel d 1).
Fel d1 is produced by glands primarily in the skin and saliva. Additionally, it is produced in perianal glands and excreted onto the feces. During grooming, Fel-d1 from saliva becomes airborne. Allergen from the skin glands is greasy, and easily transferred to soft surfaces such as clothing, carpet, and upholstery. Litter boxes contain large amounts of Fel d1, as the highest concentration is found in the perianal glands.
In 2006, we measured Fel d1 allergen in 240 un-neutered adult Siberians. Half of the Siberians tested were substantially lower than other domestic breeds. Roughly 15% of the cats had very low levels of Fel d1, suitable for homes with moderate to severe cat allergies. Both males and females were found in the lowest group.
We studied over 200 Siberian matings in an effort to understand allergen genetics. The lowest allergen kittens were produced from low allergen matings, but even these litters tended to produce mixed allergen levels. When two cats with normal allergen levels are mated, all kittens have normal (high) levels of allergen. A few very high-allergen cats only produce high allergen offspring.
Gender, Color, and Fur Length
Multiple studies have shown neutering male cats reduces Fel-d 1. Allergen levels are hormonally controlled, with intact (non-neutered) males producing the highest amount. In genetically low allergen cats, there is little difference between intact males and females.
Fur length does not change the amount of allergen produced, but dense fur can retain a higher levels of allergen. The fine downy crimped undercoat of Siberians can also cause itching of the face – but this is an irritant not an allergen. Shedding occurs throughout the year, but is highest in early spring.
Most Silver/Smoke Siberians have very high Fel d1 allergen. Our early studies (2005) found no low allergen Silver Siberians, but we do see some low Silver/Smoke now (15 years later). Silver is a fairly recent introduction in Siberians, and is likely in linkage equilibrium with Fel d1.
Other Cat Allergens
There are no simple answers to cat allergies, as most people are allergic to more than one allergen. To date, eight cat allergens have been isolated, and are found in cat saliva, fur, urine, and feces. These allergens may cause a reaction in one person but not another.
Most cat allergies are caused by four allergens: Fel d1 (feline secretoglobin), Fel d2 (feline albumin), Fel d4 (feline lipocalin), or Fel d7 (another lipocalin).
Some people with horse allergies also react to Fel d4, as the allergens have similar shapes and share epitopes (binding sites). These individuals are considered to be horse/cat cross-reactive.
Asthma and other airway reactions to animals are usually caused by Fel d1 or Fel d4. Eczema tends to caused by lipocalin, and as these reactions are slower onset, they can be more difficult to identify.
Several studies show intact male mice produce more lipocalin than intact females, and that neuter/spay reduces lipocalins in both male and female mice. These studies have not been performed on cats, but it is reasonable to assume that individuals with severe horse or rabbit allergies will have less reaction to altered cats.
Anyone with cat induced asthma should spend time with a tested low Fel d1 allergen Siberian before purchasing a kitten. Testing with fur samples is a great starting point, but may not be identify all allergies to lipocalin or albumin.
The following chart lists the commonest cat allergens, and the rough percentage of cat-allergic people who react to each allergen.
| Allergen | Class | Percent of Individuals Reacting |
|---|---|---|
| Fel d1 | Secretoglobin | 60-90% (always causes asthma) |
| Fel d2 | Serum Albumin | 17% (asthma, rhinitis, eczema) cross reacts w/ horse, rabbit, pig |
| Fel d3 | Cystatin | |
| Fel d4 | Lipocalin | 70% (asthma & eczema) cross reacts with rabbit & horse |
| Fel d5 | Feline Immunoglobulin A (F IgA) | |
| Fel d6 | Feline Immunoglobulin M (F IgM) | |
| Fel d7 | Lipocalin: von Ebner gland protein | 31% (asthma, eczema, rhinitis) cross reacts with dog allergen 1 |
Suggested reference reading.
Allergen Nomenclature Database
The Allergen Nomenclature Sub-committee operates under the auspices of the International Union of Immunological Societies (I.U.I.S.) and the World Health Organization (W.H.O.). They have an excellent allergen databases.
Cat Dander
Thermo Fisher Scientific publishes great technical articles on feline allergens and cross reactions with other animals.
The Major Cat Allergen, Fel d 1, in Diagnosis and Therapy
Some of the best work in indoor feline allergens has been performed by the Clinical Immunology and Allergy Unit, Department of Medicine, Karolinska Institutet and University Hospital, Stockholm, Sweden.
Fel d 4, A Cat Lipocalin Allergen
Lipocalin may be a major cause of initial sensitization to cat. This technical study on feline lipocalins is available on PubMed.gov
© 2005 KittenTesting