The Basics Behind
Cat Allergies

Many of us often find ourselves with a runny nose, puffy, watery eyes, and constant sneezing every time we encounter a cat. Unfortunately, the allergy doesn’t spare even the cat lovers among us, who sometimes have to choose between the companionship of their beloved feline and maintaining their own health and quality of life. But relief may already be on its way to them - researchers are currently working on developing a vaccine against the allergy-causing proteins in cat saliva. 

The allergy is actually not a reaction to the cats’ fur but rather to the proteins secreted in the cats’ saliva that remain on their fur when they groom themselves. A sleeping cat and the fur it sheds | Shutterstock, Doucefleur

?What is an allergy

An allergy is a misidentification by our immune system. The body mistakenly regards certain substances that are harmless to us, such as flower pollen or proteins produced by cats, as dangerous disease agents, producing antibodies against them in order to attack. The antibodies allow cells of the immune system to recognize these substances and to secrete a molecule called histamine, which generates an inflammatory response and causes allergic symptoms. These symptoms can range from itching and hives, nasal congestion, and watery eyes to severe symptoms of asthma and life-threatening anaphylaxis. 

When we inhale small particles, we often experience respiratory symptoms, such as coughing or sneezing. If larger particles come into contact with the skin, we will typically experience skin allergies. We may also experience several symptoms at the same time. The bottom line is that we feel sick not due to the allergen -  the substance that initiates the allergic reaction, but due to the response of our immune system to its presence.

Cat allergies are a common phenomenon: According to estimates, 10-30 percent of the world’s population suffer from them. When we are allergic to mammals, we usually react to their fur, but contrary to popular belief the allergy isn’t to the cat’s fur itself but to the proteins secreted in the cats’ saliva that remain on their fur when they groom themselves. The main protein causing the allergic reaction is called Fel d 1. 

The same allergens can also be found in sweat, urine, and dry skin cells. The latter are particularly problematic since they are very small, can remain suspended in the air for a long time, and tend to cling to surfaces, carpets, curtains, and clothes. The allergenic protein can remain on the surfaces even 6-9 months after a cat has come into contact with them, thus it is possible to get exposed to the allergen even without the presence of a cat.

While it is difficult to completely avoid exposure to an allergen, there are several ways of dealing with it. In the short term, the home in which the cat resides can be thoroughly cleaned. This method can indeed alleviate allergy symptoms, but only for a short time and requires significant effort. Another solution is to take antihistamines to treat the symptoms of the allergy. These constitute a large class of drugs that block the histamine receptors in our body’s cells, thus preventing the inflammatory response generated by them. The medications help to prevent the allergic reaction, if taken before contact with the allergy causing agent and help reduce the symptoms of a reaction that has already developed. However, these drugs can have side effects, especially if taken regularly and over a long period of time. 

It may also be possible to get in front of the situation: studies show that exposure to animals at a young age reduces the tendency to develop allergies and diseases of the upper respiratory tract. People who do not show a tendency to develop a strong allergic reaction respond to the allergen by producing antibodies that are similar to the antibodies often produced in response to a viral infection, which are different from those that cause allergy symptoms. Those who were exposed to cats at a young age are more likely to belong to this group.

Even hairless cats can produce and secrete the allergens. A Sphynx cat | Shutterstock, Peterpancake

Immunotherapy

Traditional immunotherapy against allergies encourages the body to produce the type of antibodies that do not cause an allergic reaction. The goal is for these antibodies to recognize and neutralize the allergen before it is recognized by the antibodies that generate the immune response that causes the allergy symptoms. Conventional immunotherapies usually involve weekly injections of purified allergens, such as, for example, a mixture of the allergy-causing cat proteins, over a certain period of time. Immunotherapy is effective in some cases but does not always provide a perfect solution and some patients continue to suffer from symptoms and are forced to rely on antihistamines. In addition, some respond to the treatment with the same allergy symptoms that the treatment aims to prevent. 

One attempt to improve immunotherapy includes injection of antibodies against the 'allergy-stimulating' protein TSLP, which is involved in the immune response to allergens. The hope is that following neutralization of this protein, patients will experience the allergy with lessened severity and the effect of the immunotherapy will be prolonged. The treatments are currently found in advanced research stages in humans, and the researchers reported promising findings in an interview with the scientific journal Nature, but the data itself has not been published yet.  It appears that the treatment itself is likely to be expensive and is therefore likely to be recommended at this stage only for patients with severe allergy and asthma symptoms. In future, the researchers hope that the treatment can also be used to treat other allergies. 

In a long-term study that started in England a few years ago, the researchers tried to use a vaccine that does not contain the allergenic protein Fel d 1, but instead contains a smaller synthetic protein, which is based on the structure of the original protein. The synthetic protein has a lower chance of provoking an allergic reaction and therefore the treatment can be given in higher doses. In this manner, the scientists hope to enable allergy resistance in as little as four treatments. The treatment has shown promising results in animal trials and is currently being tested in human trials.

The treatments mentioned above rely on the person exposed to the allergen to develop a very specific immune response that will create immunity by generating the type of antibodies similar to antiviral antibodies instead of antibodies that encourage the secretion of histamine. But what about those people who do not develop the desired immune response? For them, researchers from New York are developing additional treatment options.

The treatment is based on external administration of two types of engineered antibodies, which are also able to bind to the allergen and thus compete for the binding with the body’s own antibodies, involved in inducing allergy symptoms. Instead of stimulating the immune system and hoping that the patient will develop the “desired” antibodies against the allergen, as in conventional treatments, the engineered antibodies would prevent the “stimulation” of the immune system and the generation of an inflammatory response that results in those disturbing allergy symptoms. The disadvantage of this treatment is that since it is not a true immune response of the body itself but rather external administration of the antibodies, the patients will have to receive regular injections of the engineered antibodies to prevent the allergic reaction from forming. 

Traditional immunotherapy approaches against allergies encourage the body to produce the type of antibodies that do not cause an allergic response. A cat is looking anxiously at a syringe. Shutterstock | SakSa

From man to cat

All cats, even hairless cats such as Sphynx cats, produce allergenic proteins, including Fel d 1. Admittedly, there are differences in the protein levels between cats: unneutered males produce more of the protein than females, and in the case of the  Siberian cat, for example, a mutation has been discovered that likely impairs production of the allergenic protein, causing lower protein levels. However, even low levels of the protein may still cause an allergy. 

The levels of the secreted protein in cat dander can be reduced by bathing the cat twice a week. However, the protein levels will return back to normal within two days, and given that most cats dislike water, it’s probably not a good idea anyway. Good luck! It is recommended to groom the cat frequently to keep its skin healthy and reduce the amount of shedding around the house. 

Some cats shed less fur and thus spread fewer allergens, but a real “hypoallergenic cat” is a myth. However, in the future it may become possible: researchers are investigating the possibility of using genetic editing to create cats that will not produce the allergy-causing protein. While dogs have many proteins that cause allergies in humans, in cats it is enough to remove the main protein, Fel d 1, to significantly reduce the allergy. The problem is that researchers have not yet deciphered the precise role of the protein that causes the allergy, and therefore they do not know what will happen to a cat lacking this protein. According to some hypotheses, the protein helps with sexual hormonal activity, and some researchers also believe that it protects the skin. 

Another experimental treatment is targeted gene therapy, designed to remove the gene that codes for the problematic protein in “regular” cats, in other words -  another way to create a truly hypoallergenic cat. This is a solution that is available to cats that are not genetically modified from birth and does not require to establish a new breed of cats. 

The levels of the secreted protein in cat dandruff can be reduced by bathing the cat twice a week - but we don’t recommend doing so. A grumpy cat in the bathtub | Shutterstock, Olleg 

Vaccines for cats

A relatively new study performed in Switzerland examines the possibility of vaccinating the cats themselves with an engineered version of the allergenic protein disguised as a virus, so that the cats produce antibodies against it and these will attack the allergen that the cats themselves produce. The goal is for the cat’s antibodies to block the production of the protein before it reaches our nose via the cat’s skin cells. The researchers developed a vaccine consisting of a genetically engineered Fel d 1 protein and a virus-like particle containing a tetanus-toxin derived protein engulfed in the envelope of a plant-infecting virus. The cat’s immune system should respond to the vaccine as if it were a virus and produce antibodies against it. 

After administering the vaccine during the trial, a significant reduction in the levels of the protein was detected in the cats’ tears. Thirteen cats belonging to cat-allergic owners participated in the study, with the owners reporting a decrease in symptoms and an increase in the amount of time they were able to spend with their cats before an allergic reaction occurred. No serious adverse effects were reported in the cats. However, this is currently a very small study, and it is not yet known how long the effect of the vaccine will last. It is likely that at some point it will be necessary to boost the vaccine with additional booster doses.

If and when the vaccine is submitted for approval to the health authorities, the question of whether it is morally right to perform a medical procedure that contributes nothing to the animal's health will also be raised. Such vaccines were previously approved in the United States but not in Europe. The leading researcher, Bachmann, who himself suffers from an allergy to his pet cat, believes that the vaccine will also be effective for humans and will cause their immune system to change its behavior and not produce histamines in response to the allergen. He even told Nature journal that he went so far as to test an initial version of the vaccine on himself. 

Another product already on the market represents an attempt to mitigate the allergy by feeding cats antibodies-coated cat food. The researchers exposed chickens to the allergenic cat protein for them to create antibodies against the protein, which then become naturally concentrated in their egg yolks. The egg powder was then coated onto fry cat food. In the experiment, the researchers let the cats eat the food for six months with no adverse effects detected. Another study reported a decrease of 47 percent in the concentration of the allergenic protein in the fur of 105 cats, after they consumed the antibody-coated food.

Pets contribute to us in many varied ways. They contribute both to our physical health, for example, when the dog calls us to go for a walk with him, and to our mental health, by giving us unconditional love and teaching us compassion. The new research in the field will hopefully enable more people to curl up on the sofa with their cat on a cold winter day without suffering from allergies.