Sensitive airways prone to infection.

• Position: Respiratory Tract

Viral infections can exacerbate asthma and, in turn, make people with the condition more sensitive to environmental exposures such as endotoxin. Yet, how viral infections contribute to this sensitivity in airway cells has not been clear--until now. A study by the University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, shows that these infections may increase sensitivity in lung epithelial (surface) cells by changing expression of receptors on those cells.

Using models, scientists specifically demonstrated that respiratory syncytial virus (RSV) infection increases the number of a type of receptor called Toll-4 on the airway cells. This Toll-4 receptor can provide a foothold for inhaled endotoxin, a naturally occurring environmental contaminant that comes from bacteria and is found in household dust, grain dust, and objects such as pillows. The presence of receptors for endotoxin would lead to interaction between the epithelial cell and the endotoxin and potentially cause inflammation.

"The big picture here is that viral infections may upregulate, or increase, one or more receptors on the airway cells and make them more sensitive to environmental exposures. This could explain the viral-induced ... exacerbations seen in people with asthma," suggests Martha Monick, senior research assistant in the Division of Pulmonary, Critical Care and Occupational Medicine.

Monick says the inspiration for the study came when...