Asthma--An Epidemic in the Absence of Infection?

In a report in this issue of Science , Shirakawa et al . ( p. 77 ) show an inverse relation between exposure to the bacterium that causes tuberculosis and the incidence of asthma, leading to the proposition that childhood infections can protect against later development of asthma and similar allergic reactions. In their Perspective, Cookson and Moffatt explain the immunological basis of this proposition and discuss its implications.