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Scientists figure out how cats cause allergies, could pave way for treatment

Do your eyes water at the sight of a furball? Can you only enjoy a feline friend without sneezing through a YouTube video?

Scientists say they have figured out why cats are making your allergies crazy -- and their research might also help those allergic to dogs as well.

An allergic reaction is really just the body overreacting to what it thinks is a bacteria or virus. The body confuses the allergen (like pollen or peanuts) as a substance that will harm it, so it mounts an unnecessary full-blown immune system defense to get it out. This results in sneezing, wheezing, scratching and all kinds of unpleasant symptoms we associate with allergies.

Cat protein Fel D1 -- also known as cat dander -- has been known to trigger severe allergic reactions. Since cat hair gets everywhere, it's hard to avoid. Before the study, scientists didn't know why it triggered responses in people.

The scientists found that when Fel D1 comes in contact with a common bacteria toxin called lipopolysaccharide (LPS), it activates a receptor that recognizes the pathogen called Toll-like receptor 4 (TLR4). TLR4 is also the receptor that causes the allergic response to dust mites and the metal nickel. When TLR4 is turned on, it beefs up the body's immune system response to Fel D1. The response continues to grow, and the person's allergic symptoms become worse.

"How cat dander causes such a severe allergic reaction in some people has long been a mystery," lead author Dr. Clare Bryant, from the University of Cambridge's Department of Veterinary Medicine, said in a press release. "Not only did we find out that LPS exacerbates the immune response's reaction to cat dander, we identified the part of immune system that recognizes it, the receptor TLR4."

Researchers then exposed human cells to a drug that stops the TLR4 response. It was able to block out the cells' reaction to dander protein.

The researchers also discovered that a different protein, Can F6 -- dog dander, which causes allergic reactions to dogs -- also was enhanced by the presence of LPS. Together, they triggered TLR4.

"As drugs have already been developed to inhibit the receptor TLR4, we are hopeful that our research will lead to new and improved treatments for cat and possibly dog allergy sufferers," Bryant added.

Allergy UK director of clinical services Maureen Jenkins, told the BBC that this research was important in order to figure out a way to get rid of cat and dog allergies in humans -- which would be the cat's meow.

"Cat allergen is particularly difficult to avoid as it is a 'sticky' molecule that is carried into every building on people's shoes and clothes," Jenkins explained. "It can also still be found in a home, on the walls and ceiling or fittings, even a few years after a cat has ceased to live there. Therefore, this new information identifying the specific receptor interaction in the immune system could pave the way for treatments for those with persistent disease triggered by cat allergen and, in the future, potentially dog and house dust mite allergen."

The study was published in the The Journal of Immunology on July 22.

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