Dr. Lester Kobzik and colleagues at the Harvard School of Public Health used a mouse model of asthma to evaluate how inhaling pollutants affects the airways. The mice were sensitized to the allergen ovalbumin, which induces a lung condition in the mice similar to that found in people with asthma. The investigators hypothesized that exposure to concentrated ambient particles (CAPs) plus ozone would cause a synergistic (or greater-than-additive) response in the mice. Kobzik and colleagues evaluated two endpoints associated with the asthmatic response: airway responsiveness using whole-body plethysmography and airway inflammation by assessing numbers of inflammatory cells in bronchoalveolar lavage fluid. In addition, the investigators evaluated in vitro how concentrated particles might induce the synthesis of cellular mediators associated with inflammation.