The recent sharp rise in asthma in developed countries may be caused in part by a decline in other childhood maladies, new findings suggest. An article published in tomorrow's issue of Science describes epidemiological findings implying that respiratory infections can, ironically, protect kids against allergies and the asthma they trigger. If so, vaccines--which mimic the effects of an actual pathogen to create immunity--might help the body ward off asthma, too.
The researchers, from Britain and Japan, were seeking clues to the mysterious doubling in asthma cases in developed countries over the past 20 years, an increase not seen in less developed countries. Air pollution is one suspect, but the fact that people in some polluted Eastern Europe cities have less asthma than those in the cleaner West suggests it's not the whole story.
The scientists glimpsed another part of the story when they studied medical records for 867 Japanese children who had been immunized for tuberculosis and later tested for their response to TB. They found that positive TB responses, a sign that the children had either responded strongly to the vaccine or been exposed to the infectious agent itself, correlated with asthma rates that were two or three times lower than in children with a negative response. The children with high TB responses were also making more TH1 cells, a kind of immune cell that suppresses other cells producing the antibodies involved in allergic responses. "As the body develops immunity to TB, it could be switching off molecular messengers that promote allergies" that result in asthma, explains pulmonologist Julian M. Hopkin of Churchill Hospital in Oxford, U.K., the lead author. Once the mechanism by which TB and other infectious diseases boost TH1 cell counts is better understood, note researchers William Cookson and Miriam Moffatt of the University of Oxford in an accompanying commentary, it may be possible to vaccinate children to increase their TH1 response and thus protect them against asthma.
"It's an interesting paper," agrees asthma researcher Richard Locksley of the University of California, San Francisco. However, he notes that the picture may be more complicated--for example, some scientists have suggested that exposure to intestinal worms might also protect children against allergies by altering their immune system. A TB vaccine alone, he says, "may not be the most effective way" to reduce asthma.