Gesundheit: a cat allergy is nothing to sneeze at. Find out what some scientists are doing to stop kitty-caused sniffles in their tracks.

Meow. To many people, that's the sound made by a cute, cuddly animal. But to the 10 percent of Americans with a cat allergy, it's the sound of an oncoming sneezing attack. That's because certain particles in a cat's hair, skin, saliva, and urine start a chain reaction inside an allergic person's body that eventually leads to a loud, wet ahh-choo!

"A lot of people presume they're allergic to cat hair, but in reality they're allergic to a protein (chemical made by instructions from a cell's DNA) that the cats emit," says Simon Brodie, president of Allerca, Inc., a California-based company. This sneeze-causing kitty protein is known as Fel (for feline) d1.

But soon, cat-allergic noses may get a sniff of relief. Scientists at Allerca are working to produce the world's first hypoallergenic, or nonallergy triggering, kittens.

Read on to find out how tiny particles can cause an allergy and how Allerca plans to help allergy-prone cat lovers keep a furry pal.

SNEEZY SOURCE

People can be allergic to all sorts of things. Pollen, bees, nuts, and milk all contain common allergy-causing particles called allergens. And allergens are everywhere--even if their source is nowhere nearby. "You probably have cat allergens in your home even if you don't have a cat," says Kevin Parks, an allergist (allergy doctor) at Creighton University in Nebraska. How's that possible? When people are in public places where cat owners have been, they can come into contact with the tiny allergens. Then, according to a recent study by the National Institute of Environmental Health Sciences, the Fel d1 proteins can hitch a ride home.

HAVE THE SNIFFLES?

You come into contact with these microscopic particles every day. And once they're on your skin or inside your airway, the allergens run into a group of specialized cells and organs, called the immune system. The cells in this system search out and destroy any microbe that could be dangerous to the body. A nonallergic person's immune system recognizes that allergens are harm less--they do not cause disease--and ignores them.

But when an allergic person comes into contact with an allergen, such as Fel d1, their immune system has a different response. They may sneeze, get a rash, or even have breathing difficulties. "An allergic person's body is attempting to protect them from something it really doesn't need to," says Steven Kernerman, an allergist at the Spokane Allergy and Asthma Clinic in Washington. But having allergies isn't a sign of a faulty immune system. If anything, it means the body's immune system works too well, like an over-protective bodyguard.

ON GUARD

If everyone encounters allergens, why do only about one out of every four people in the United States have these overreactive immune systems? "Some people will inherit from their mother and father certain genes (units of hereditary material) that help establish whether they can become allergic or not," says Kernerman. A person with those genes has the ability to develop an allergic reaction to many types of allergens, but they must first be exposed to that allergen. In other words, you won't be allergic to cats if you never come into contact with its allergens.

When an allergy-prone person is first exposed to an allergen, such as a cat's, their immune system produces millions of IgE anti-bodies. These Y-shaped molecules are trained to recognize a specific allergen and alert the body's defenses. A person who is allergic to cats has a stockpile of anti-bodies specific to cat allergens (see Nuts & Bolts, p. 10). Someone who isn't allergic to furry felines does not make as many IgE antibodies. "If someone is allergic to cats you can measure the antibodies against cats in their blood with a skin test," says Kernerman. "The more allergic antibodies in the person's blood, the greater is the likelihood that the person will have an allergic reaction when they meet a cat."

THE PURRFECT CAT

Doctors treat most allergies with medicine. But the best way to avoid a reaction is to simply steer clear of tHe animal or object that causes a sneeze storm. That's bad news for cat lovers who are allergic. For them, the perfect cat would not produce allergens at all.

By 2007, Allerca plans to start selling a genetically engineered cat that doesn't make people sneeze. "We aim to use a technology known as gene silencing to

stop the gene from producing the [Fel d1] protein," says Brodie.

Before the kittens are born, the scientists will inject them with a virus that interferes with the cat's ability to produce the protein. After birth, the cats will go through a series of tests to make sure they are healthy.

If all goes well, cat fans will be able to purchase a hypoallergenic cat from Allerca for $3,500. "It's a luxury item," says Brodie. "Just as if someone points to your purse and says that's a Gucci. We want people to say they own an Allerca cat."

If Allerca succeeds, they will produce the first brand-name animal, known as a "lifestyle pet." What are some of the pros and cons to a future world in which a person can customize pets?

Nuts & Bolts

STEPS TO A SNEEZE

An allergic person cuddles with a velvety-soft cat. In a flash, expect a sneeze.

1 Flakes of a cat's skin contain the protein Fel d 1. The flakes can enter a person's airways through the nostrils.

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2 First-time contact with the cat allergen causes special cells, called mast cells, to produce the IgE antibody. IgE molecules now coat the surface of mast cells.

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3. Fel d1 proteins bind to the mast cells' IgE molecules. This is known as cross-linking.

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4 Cross-linking causes the inflammatory substance histamine to burst from granules inside the mast cells.

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5 Histamine causes the lining of the nose to swell and produce excess mucus.

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6 Nerves in the nose become irritated by the mucus and fire a message to the brain. The brain relays the message to the nose and ...

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Did You Know?

* Scientists think that cats may use their Fel d1 proteins as a scent marker--male cats produce more of the protein than female cats.

* Why would the immune system attack a harmless particle? Scientists hypothesize that the part of the immune system that responds to allergens originally evolved to protect people against deadly parasitic worms. "Nowadays we don't have a lot of these parasites around," says allergist Steven Kernerman. But the proteins on parasites recognized by the immune system look similar to what's recognized on the allergen.

Resources

* This fun quiz, called the Ahh-Choo IQ, was developed by a psychologist to determine what your sneeze says about your personality: http://66.33.52.33/index.cfm?s=2

* For an easy refresher on all of the components and workings of the immune system, visit the National Institute of Allergy and Infectious Diseases: www.niaid.nih.gov/publications/immune/the_immune_system.pdf