e94 Fel d 1 | Thermo Fisher Scientific (2024)

e94 Fel d 1 Scientific Information




Fel d 1

Route of Exposure:

Airway (Inhalation)

Allergen code:


Source Material:

Epidermis, fur

Other Names:

Cat I, Ag4, Fel d 1-related protein

Whole Allergen: Cat dander

Related Allergens: e220 rFel d 2, Cat serum albumin, e228 rFel d 4, Cat


Fel d 1 is the most important and major cat allergen as it has been observed in up to 95% of individuals with cat allergy. Sixty to 90% of all IgE reactivity to cat dander is against the Fel d 1. The primary production of Fel d 1 takes place in sebaceous, anal, and salivary glands and its highest concentration can be found in the fur and epidermis of a cat. Fel d 1 becomes airborne very easily and then is carried by small particles, which in turn transfers it to environments that have not had any exposure to a cat.

Fel d 1 is a uteroglobin, but the biological role remains a mystery. The allergenicity of inhaled Fel d 1 increases after it manages to bind the mannose receptors present on dendritic cells. This binding initiates the production of IgE and IgG1 specific to Fel d 1.

Higher levels of IgE specific to Fel d 1 have been seen in cat allergic children with allergic asthma as compared to those only with rhinitis. This indicates that an increased asthma risk could be predicted by high levels of IgE antibodies to Fel d 1. (1)


Worldwide distribution

Fel d 1 is the major feline allergen, it is mainly a component in cat dander and dominates the IgE response in patients with cat allergy. Cat allergic patients with IgE to Fel d 1 have also reacted to different species of the Felidae family, such as puma, Siberian tiger, lion, jaguar, and snow leopard. (2)

Environmental Characteristics

Source and tissue

It has been documented that Fel d 1 becomes airborne very easily and then is carried by small particles, which in turn transfers it to environments that have not had any exposure to a cat. The concentration in such environments has been at levels that exceed the proposed sensitization threshold of 8 µg/gm. (3-6)

Risk factors

A study by Bjerg and colleagues on 696 Swedish children reported that current asthma and symptoms of asthma after contact with cats were linked to co-sensitization to Fel d 1 and Fel d 4. (7)

Clinical Relevance

Allergic rhinitis and Asthma

The increment of Fel d 1 IgE levels could be a significant risk factor for allergic asthma in children. A study demonstrated Fel d 1 strong association with the prevalence, severity, and persistence of asthma in a 19-year-old population. Furthermore, in a study where patients were sensitized to cat extract and components, the ones sensitized to components were more likely to develop asthma and rhinitis. (3).

Gronlund and colleagues did a case-control study on 140 cat allergic patients from Austria and Sweden, in which all subjects were suffering from asthma and/or rhinoconjunctivitis. They observed that 95.6% of children and 94.4% of adults had IgE against Fel d 1. The IgE levels were found in asthmatic children were significantly higher than the ones of children suffering from rhinoconjunctivitis. (3)

Prevention and Therapy

Allergen immunotherapy

Fel d 1 IgE have shown to have a similar or slightly lower sensitivity for positive diagnosis and it is correlated with the severity and risk of asthma occurrence and could be a good prospect for immunotherapy in years to come. (3)

Molecular Aspects


The molecular weight of Fel d 1 is 36 kDa (9). It is a dimer of a polypeptide comprised of two chains 1 and 2 (also known as α and β), chain 1 consists of 70 and chain 2 is made up of 92 amino acid residues. They have conformational IgE binding epitopes independent of carbohydrate residues even though N- terminal oligosaccharides are present on chain 2. It is an uteroglobulin , previously called secretoglobulin.

Studies conducted on recombinantly synthesized chain 1 and 2 have shown that IgE binding epitopes are present on both chains and both the chains contribute to the allergenicity of Fel d 1.

Isoforms, epitopes, antibodies

Two mammalian allergens have been characterized as members of uteroglobin(part of secretoglobulin superfamily) protein family, namely Fel d 1 from cat and Ory c 3 from rabbit. (8) Ory c 3, the major rabbit allergen is a lipophilin and found to be a Fel d 1-like molecule. However, the sequence identity between the two allergens is very low and no IgE cross-reactivity has been observed between them. (9)


No major cross-reactivity to Fel d 1 has been reported. (1)

Diagnostic Relevance

Disease Severity

It has been observed that individuals sensitized to cat components have a higher risk of developing asthma than the individuals sensitized only to cat extract, this risk becomes even higher in children. (3)

A review by Bonnet and colleagues in 2018 suggests that measuring IgE antibodies to Fel d 1 makes it possible to better estimate the prognosis of cat allergy and evaluate the severity of cat allergy. (3)


As the major cat protein Fel d 1 is a “sticky” allergen, it can take several months after the removal of the cat to alleviate the allergic symptoms particularly in carpeted households. (10, 11). It has been observed that Fel d 1 levels are reduced after up to 20 weeks after the removal of the cat. (11)

Compiled By

Reviewer: Dr. Christian Fischer

Last reviewed: November 2020

e94 Fel d 1 | Thermo Fisher Scientific (2024)


What is E094 IgE FEL D-1? ›

Fel d 1 is the major feline allergen, it is mainly a component in cat dander and dominates the IgE response in patients with cat allergy. Cat allergic patients with IgE to Fel d 1 have also reacted to different species of the Felidae family, such as puma, Siberian tiger, lion, jaguar, and snow leopard. ( 2)

What is fel d 1 allergen? ›

Fel d1 is the major cat allergen, causing IgE reactions in up to 90% of cat-allergic adults.

Can I develop an allergy to cats? ›

Pet allergies are common. However, you're more likely to develop a pet allergy if allergies or asthma runs in your family. Being exposed to pets at an early age may help you avoid pet allergies.

How to reduce Fel d 1 in cats? ›

A diet with an egg product ingredient containing anti-Fel d 1 IgY was fed to cats, resulting in significant decreases in active Fel d 1 (Fel d 1 that is capable of binding to IgE and triggering an allergic response in sensitized individuals) in the cats' saliva and on their hair.

Which cat has the lowest Fel d 1 protein? ›

The Siberian may not seem like the best fit for those allergic to cats due to its long coat. However, Siberian cats produce less Fel d 1 protein and dander than other cat breeds, making them safer for allergy sufferers.

What cat food neutralizes Fel d 1? ›

There is a cat chow that was developed to help reduce the amount of major cat allergen (Fel d 1) in the environment where a cat lives. This is most likely the thing you may have heard about. Pro Plan LiveClear is a cat food made by Purina. It reduces the major allergen after a cat eats it for several weeks.

Do chicken eggs reduce cat allergies? ›

Chickens raised near cats can develop antibodies against the protein Fel d 1, which is found in cat saliva and is responsible for 90% of the reactivity in people who are allergic to cats. The chickens can pass these antibodies onto their egg yolks. If a cat is fed these eggs, it could potentially be less allergenic.

What neutralizes cat allergies? ›

Purina's research

Purina scientists discovered that an egg product ingredient containing antibodies to Fel d 1, the major cat allergen, can bind to Fel d 1 in the cat's saliva, preventing its ability to trigger an allergic response in a cat allergen-sensitized individual.

Can I live with a cat if I'm allergic? ›

Living with cat allergies is possible for many people as long as you take the right precautions. Keep allergies in mind while choosing a cat, reduce allergens in your house, and groom and clean up after your pet, and you and your cat will be set up for many sneeze-free years together.

Why am I all of a sudden allergic to my cat? ›

In most cases, people may only experience a cat allergy as they grow older because they have repeatedly been in contact with the same allergen, and their immune system may have triggered some reaction.

What foods are cats most allergic to? ›

The foods typically associated with food allergies in cats include beef, fish, chicken, and dairy. A cat must have been exposed to a food ingredient before developing an allergy to it. An ingredient a cat has consumed for a long time can still cause an allergy at some point in the cat's life.

Can cats be allergic to litter? ›

Cat litter may contain chemicals, bentonite, silica dust, clay and/or fragrances that can cause your cat to exhibit allergies and begin avoiding the litter box. Cats that have already been diagnosed with other allergies will be more prone to developing a litter allergy.

What is the best medicine for cat allergies? ›

Zyrtec, Benadryl, and Claritin are some of the most common antihistamines for cat allergies. These medications can improve cat allergy symptoms like sneezing and itching. You may be unaware of having a cat allergy until you get your first pet. Cat and pet allergies can cause symptoms such as sneezing and itching.

How to get rid of cat allergies permanently? ›

One way to reduce cat allergies is limiting exposure to cat allergens. This includes cleaning more often and limiting the rooms your cat is allowed in. The best way to get long-term relief is through allergy immunotherapy which retrains your immune system to stop being allergic.

What is a high IgE level for allergies? ›

An elevated IgE level (100 ≥ IgE < 1000 kU/L) indicates allergy, eczema, or chronic skin infection.

What are the IgE levels for anaphylaxis? ›

IgE antibodies undeniably can play an important role in conferring immunological specificity to effector cell activation in anaphylaxis and other allergic diseases. IgE is by far the isotype found at the lowest concentrations in the circulation (50-200 ng/ml total circulating IgE in healthy individuals vs.

What is the severity scale for cat allergy? ›

Class 1: Low level of allergy (0.35 KUA/L – 0.69 KUA/L) indicative of ongoing sensitization. Class 2: Moderate level of allergy (0.70 KUA/L – 3.49 KUA/L) indicative of stronger ongoing sensitization. Class 3: High level of allergy (3.5 KUA/L – 17.4 KUA/L) indicative of high level sensitization.

What is the IgE test for dog allergies? ›

The Labcorp OnDemand Dog and Cat Allergy Test measures immunoglobulin E (IgE) antibodies to assess your sensitivity to certain allergens (substances that can cause an allergic reaction) found in the dander, saliva and urine of cats and dogs.


Top Articles
Latest Posts
Article information

Author: Jonah Leffler

Last Updated:

Views: 5992

Rating: 4.4 / 5 (45 voted)

Reviews: 84% of readers found this page helpful

Author information

Name: Jonah Leffler

Birthday: 1997-10-27

Address: 8987 Kieth Ports, Luettgenland, CT 54657-9808

Phone: +2611128251586

Job: Mining Supervisor

Hobby: Worldbuilding, Electronics, Amateur radio, Skiing, Cycling, Jogging, Taxidermy

Introduction: My name is Jonah Leffler, I am a determined, faithful, outstanding, inexpensive, cheerful, determined, smiling person who loves writing and wants to share my knowledge and understanding with you.