Asthma occurs when the body's natural system of defense against bacteria, viruses, and other harmful microbes becomes overprotective. It misidentifies relatively harmless pollens, dust, and dander, setting up a reaction that narrows and inflames small airways in the lungs. From that comes breathlessness, wheezing, tissue damage, and, in the worst cases, death.
In the standard textbook version of what happens, so-called T helper cells respond to ragweed, dust, and other irritants by secreting proteins that attack the irritants as if they are bits of disease-causing bacteria or viruses. Umetsu and his colleagues decided to take a look at this process from a new perspective. They checked the lung cells of 25 patients, 14 of whom were nonsmokers with moderate to severe asthma. To their surprise, they found that most of the trouble-raising cells in the lungs of asthmatics aren't helper cells but a little-known group of natural killer cells. In general, killer cells enjoy the reputation of destroying disease-causing invaders, but this special group wages war on otherwise normal lungs.
The finding means that physicians may not be treating asthma sufferers with the right kinds of drugs. For example, natural killer T cells seem to be resistant to the corticosteroids in widely used inhalers.
..."We are working on ways to get at the natural killer T cells without knocking out helper T cells, which are involved in many different kinds of protective responses," Umetsu explains. Such responses include defenses against microbes like the AIDS and bird flu viruses, and bacteria that cause tuberculosis. Drugs that knock out the killer cells without hindering the work of helper cells would have fewer side effects, and should be more effective than the steroids in inhalers. The steroids were designed to cripple helper T cells only.
http://www.hno.harvard.edu/gazette/2006/03.16/01-asthma.html