Researchers have homed in an explanation for an intriguing observation: Children who grow up on dairy farms are much less likely than the average child to develop asthma. A European team reports that bits of bacteria found in farm dust trigger an inflammatory response in the animals' lungs that later protects them from this respiratory disease. An enzyme involved in this defense is sometimes disabled in people with asthma, suggesting that treatments inspired by this molecule could ward off the condition in people. The study, published on page 1106, offers new support for the so-called hygiene hypothesis, a 26-year-old idea that posits that our modern zeal for cleanliness and widespread use of antibiotics have purged the environment of microorganisms that once taught a child's developing immune system not to overreact to foreign substances.  www.glorybios.com