July 24 (HealthDay News) -- In experiments with mice, U.S. researchers have discovered why viral infections have more severe consequences in smokers than in nonsmokers. For example, smokers with influenza are more likely to die than nonsmokers with influenza.

The Yale University School of Medicine team found that a combination of cigarette smoke and compounds that mimic viral components caused more severe airway damage in a mouse model of chronic obstructive pulmonary disease (COPD) than the compounds that mimic viral components alone.

In addition, cigarette smoke further enhanced the effects of influenza in mice, the study found.

Jack Elias and his colleagues said the effects of the combination of cigarette smoke and the compounds that mimic viral components were associated with increased immune response in the lungs. A detailed analysis revealed the molecular pathways involved in this response.

The study was published in the current issue of the Journal of Clinical Investigation.

The importance of defining the signaling pathways involved in the cigarette smoke-enhanced effects of viral infection for human disease are outlined in an accompanying editorial by Rubin Tuder and Jeong Yun of the University of Colorado School of Medicine.

SOURCE: Journal of Clinical Investigation, news release, July 24, 2008