Role of respiratory infection in onset of asthma and chronic obstructive pulmonary disease.

There is renewed interest in the possible role of events occurring during early life in determining predisposition to asthma and allergies. Among these events, respiratory illnesses associated with viral infections have been the matter of considerable research interest. There is now evidence suggesting that an immune response to viral infection in early life that is skewed toward an IgE- or an eosinophil-mediated slant is predictive of persistent wheezing symptoms up to the age of 6 years. Genetic and environmental factors (specifically bacterial infection burden) may be important determinants of the maturation of immune responses from a default 'Th-2-like' at birth to mature, non-Th-2-like responses. Homing of Th-2-like responses to the lung may be determined in part by inheritance of bronchial hyperresponsiveness, and in part by the progressive nature of chronic, uncontrolled airway inflammation. The main risk factor for the development of wheezing episodes in children who are not predisposed to allergic asthma is diminished airway function, which can also be detected shortly after birth. These children may stop wheezing later during childhood, but their levels of lung function track with age. It is tempting to speculate that chronic obstructive pulmonary disease may occur more frequently in these children.