New therapy for treating cat allergies looks promising

Mar 28 2005

Andrew Saxon, M.D., and a team of researchers at University of California, Los Angeles (UCLA) have found that a molecule designed to block cat allergies can prevent allergic reactions in laboratory mice and was also successful when tested on human cells in a test tube.

In the future, these promising results could lead to a new therapy not only for human cat allergies, but also possibly for severe food allergies such as those to peanuts; the research was funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health. Millions of people who are affected by cat allergies will be encouraged by the news of this novel approach says NIAID Director Anthony S. Fauci, M.D.

The injectable treatment puts stops the release of a key chemical, histamine, from cells involved in cat allergy reactions which brings on symptoms such as sneezing, wheezing, itching, watery eyes and sometimes asthma. When a cat-allergic person touches or inhales a protein found in cat saliva or dander (small scales from skin or hair), key immune system cells react by sending out histamine.

It is estimated that 14 percent of children 6 to 19 years old are allergic to cats. The molecule ties a feline and a human protein together, the feline part is the notorious protein (called Fel d1) found in cat dander and saliva, the other part consists of piece of human antibody (called IgG Fcƒ×1) that docks to a cell receptor that can be recruited to stop allergic reactions. They have named the molecule GFD, or gamma Feline domesticus, for its human and feline parts. The cat allergen end of GFD binds to antibodies on the surface of the cell. The human end of GFD links to a different cell surface protein (called Fcƒ×RIIB) that interrupts the allergic response.

GFD was first tested in blood donated by people allergic to cats; blood cells were cultured with either GFD or with a purified human antibody as a control. Then they added the cat protein that triggers allergic reactions to all the blood cell cultures; more than 90 percent less histamine was measured in the cultures with GFD, and the results suggest that GFD successfully prevents the immune cells from reacting to cat allergen. The next step was to tested GFD in mice made allergic to the allergenic protein found in cat saliva and dander.

The researchers tested GFD in two different types of allergic mice. One set was genetically engineered to have human cat-allergy cell receptors. These mice were "passively allergic" to cats: they would react to cat protein only after the scientists first injected them with human allergic antibodies to cats. When these mice were then injected with cat allergen, GFD blocked the allergic reaction involving the human cell receptors, an indication that it might also work in people. Another set of mice were made allergic to cats by injecting them with cat protein and an immune system booster. These mice became "actively allergic" to cats: their reactions to cat allergen would be comparable to reactions in a cat-allergic person. Scientists injected some of these mice with GFD, and then injected cat allergen into the windpipes of all the mice, including a control group that was not allergic to cats. GFD damped asthma-like and other allergic reactions in the cat-allergic mice: reactions in the mice that received GFD were similar to the control group mice that were not allergic to cats.

Dr. Saxon says the molecule has the potential to prevent allergic reactions long after injections cease, further research and clinical testing is needed before it could be used in humans and he is interested in applying this approach to develop a preventive treatment for serious food allergies.

NIAID is a component of the National Institutes of Health, an agency of the U.S. Department of Health and Human Services. NIAID supports basic and applied research to prevent, diagnose and treat infectious diseases such as HIV/AIDS and other sexually transmitted infections, influenza, tuberculosis, malaria and illness from potential agents of bioterrorism. NIAID also supports research on transplantation and immune-related illnesses, including autoimmune disorders, asthma and allergies.