From Science News July 7, 2007 issue:

"Bad News for Cats: Cat allergen hits all allergic people by Carolyn Barry
For people who have asthma or respiratory problems that are triggered by
cats, living with Fluffy is obviously a bad idea. Now, researchers have
found evidence suggesting that people who know that they have other
allergies may also want to avoid the furry felines. " ....

"The unexpected result emerged from a broad study of allergy and lung
function. The researchers went into the homes of 1,884 randomly selected
volunteers and tested mattress-dust samples for allergens from cats and dust
mites. Volunteers were also tested to determine whether they were allergic
to common triggers such as dust mites, cats, Cladosporium mold, and timber
grass, a relative of Kentucky bluegrass. " ....

"Surprisingly, Chinn says, people living around cats performed worse on the
lung function test even if they weren't specifically allergic to cats. By
contrast, exposure to dust mites made no difference to the test results of
people not allergic to the bugs. "

References:

Chinn, S., et al. 2007. Bronchial responsiveness in atopic adults increases
with exposure to cat allergen. American Journal of Respiratory and Critical
Care Medicine 176(July):20-26. Abstract available at
http://ajrccm.atsjournals.org/cgi/content/abstract/176/1/20.