Mayo Clinic researchers have used a comparative genomic strategy to demonstrate a causative link between eosinophils, a rare type of white blood cell, and asthma. Their research shows that the presence of these unique blood cells is absolutely required for the development of asthma. The details of this animal-based study appear in the Sept. 17, 2004, issue of Science, the journal of the American Association for the Advancement of Science (AAAS).