Allergic reactions happen when the immune system overreacts to a perceived danger. Normally, the immune system identifies and responds to harmful viruses and bacteria. But with an allergy, the immune system wrongly identifies an allergen as dangerous, such as pet dander, and starts an immune response.
The most common cause of severe allergic reactions to cats is a protein called Fel d 1, which is found in microscopic pieces of animal skin (often accompanied by dried saliva) from grooming.
The Cambridge team discovered how this protein can trigger an inflammatory response when in the presence of a common bacterial toxin found in the environment called lipopolysaccharide, or LPS.
"How cat dander causes such a severe allergic reaction in some people has long been a mystery," said Clare Bryant, who led the research at the University of Cambridge’s Department of Veterinary Medicine. "Not only did we find out that LPS [intensifies] the immune response’s reaction to cat dander, we identified the part of immune system that recognizes it, the receptor TLR4."
The scientists then used medication that curbs the TLR4 response and found it blocks the effects of the cat dander protein on human cells, thereby preventing an inflammatory response.
Bryant says she's hopeful that the research will lead to new treatments for people with cat allergies, and possibly those with dog allergies.
The study is published in The Journal of Immunology.
Maureen Jenkins, director of clinical services at Allergy UK, describes the findings as "a big step forward in understanding how cat allergen causes such severe allergic reactions."
"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," she says in an e-mail. "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."
The new findings 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," she says.